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Lee S, Li G, Liu T, Tse G. COVID-19: Electrophysiological mechanisms underlying sudden cardiac death during exercise with facemasks. Med Hypotheses 2020; 144:110177. [PMID: 33254499 PMCID: PMC7417258 DOI: 10.1016/j.mehy.2020.110177] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2020] [Accepted: 08/09/2020] [Indexed: 02/06/2023]
Abstract
The mandatory use of facemasks is a public health measure implemented by various countries in response to the novel coronavirus disease 19 (COVID-19) pandemic. However, there have been case reports of sudden cardiac death (SCD) with the wearing of facemasks during exercise. In this paper, we hypothesize that exercise with facemasks may increase the risk of ventricular tachycardia/ventricular fibrillation (VT/VF) leading to SCD via the development of acute and/or intermittent hypoxia and hypercapnia. We discuss the potential underlying mechanisms including increases in adrenergic stimulation and oxidative stress leading to electrophysiological abnormalities that promote arrhythmias via non-reentrant and reentrant mechanisms. Given the interplay of multiple variables contributing to the increased arrhythmic risk, we advise avoidance of a facemask during high intensity exercise, or if wearing of a mask is mandatory, exercise intensity should remain low to avoid precipitation of lethal arrhythmias. However, we cannot exclude the possibility of an arrhythmic substrate even with low intensity exercise especially in those with established chronic cardiovascular disease in whom baseline electrophysiological abnormalities may be found.
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Affiliation(s)
- Sharen Lee
- Laboratory of Cardiovascular Physiology, Li Ka Shing Institute of Health Sciences, Hong Kong, China
| | - Guoliang Li
- Department of Cardiovascular Medicine, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta West Road, Xi'an 710061, China
| | - Tong Liu
- Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular Disease, Department of Cardiology, Tianjin Institute of Cardiology, Second Hospital of Tianjin Medical University, Tianjin 300211, China
| | - Gary Tse
- Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular Disease, Department of Cardiology, Tianjin Institute of Cardiology, Second Hospital of Tianjin Medical University, Tianjin 300211, China.
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Gussak G, Marszalec W, Yoo S, Modi R, O’Callaghan C, Aistrup GL, Cordeiro JM, Goodrow R, Kanaporis G, Blatter LA, Shiferaw Y, Arora R, Zhou J, Burrell AR, Wasserstrom JA. Triggered Ca 2+ Waves Induce Depolarization of Maximum Diastolic Potential and Action Potential Prolongation in Dog Atrial Myocytes. Circ Arrhythm Electrophysiol 2020; 13:e008179. [PMID: 32433891 PMCID: PMC7340345 DOI: 10.1161/circep.119.008179] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
BACKGROUND We have identified a novel form of abnormal Ca2+ wave activity in normal and failing dog atrial myocytes which occurs during the action potential (AP) and is absent during diastole. The goal of this study was to determine if triggered Ca2+ waves affect cellular electrophysiological properties. METHODS Simultaneous recordings of intracellular Ca2+ and APs allowed measurements of maximum diastolic potential and AP duration during triggered calcium waves (TCWs) in isolated dog atrial myocytes. Computer simulations then explored electrophysiological behavior arising from TCWs at the tissue scale. RESULTS At 3.3 to 5 Hz, TCWs occurred during the AP and often outlasted several AP cycles. Maximum diastolic potential was reduced, and AP duration was significantly prolonged during TCWs. All electrophysiological responses to TCWs were abolished by SEA0400 and ORM10103, indicating that Na-Ca exchange current caused depolarization. The time constant of recovery from inactivation of Ca2+ current was 40 to 70 ms in atrial myocytes (depending on holding potential) so this current could be responsible for AP activation during depolarization induced by TCWs. Modeling studies demonstrated that the characteristic properties of TCWs are potentially arrhythmogenic by promoting both conduction block and reentry arising from the depolarization induced by TCWs. CONCLUSIONS Triggered Ca2+ waves activate inward NCX and dramatically reduce atrial maximum diastolic potential and prolong AP duration, establishing the substrate for reentry which could contribute to the initiation and maintenance of atrial arrhythmias.
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Affiliation(s)
- Georg Gussak
- The Feinberg Cardiovascular and Renal Research Institute and Department of Medicine (Cardiology), Northwestern Feinberg School of Medicine, Chicago, IL
| | - William Marszalec
- The Feinberg Cardiovascular and Renal Research Institute and Department of Medicine (Cardiology), Northwestern Feinberg School of Medicine, Chicago, IL
| | - Shin Yoo
- The Feinberg Cardiovascular and Renal Research Institute and Department of Medicine (Cardiology), Northwestern Feinberg School of Medicine, Chicago, IL
| | - Rishi Modi
- The Feinberg Cardiovascular and Renal Research Institute and Department of Medicine (Cardiology), Northwestern Feinberg School of Medicine, Chicago, IL
| | - Caitlin O’Callaghan
- The Feinberg Cardiovascular and Renal Research Institute and Department of Medicine (Cardiology), Northwestern Feinberg School of Medicine, Chicago, IL
| | | | | | | | - Giedrius Kanaporis
- Department of Physiology and Biophysics, Rush University Medical School, Chicago, IL
| | - Lothar A. Blatter
- Department of Physiology and Biophysics, Rush University Medical School, Chicago, IL
| | | | - Rishi Arora
- The Feinberg Cardiovascular and Renal Research Institute and Department of Medicine (Cardiology), Northwestern Feinberg School of Medicine, Chicago, IL
| | - Junlan Zhou
- The Feinberg Cardiovascular and Renal Research Institute and Department of Medicine (Cardiology), Northwestern Feinberg School of Medicine, Chicago, IL
| | - Amy R. Burrell
- The Feinberg Cardiovascular and Renal Research Institute and Department of Medicine (Cardiology), Northwestern Feinberg School of Medicine, Chicago, IL
| | - J. Andrew Wasserstrom
- The Feinberg Cardiovascular and Renal Research Institute and Department of Medicine (Cardiology), Northwestern Feinberg School of Medicine, Chicago, IL
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53
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Chu Z, Yang D, Huang X. Conditions for the genesis of early afterdepolarization in a model of a ventricular myocyte. CHAOS (WOODBURY, N.Y.) 2020; 30:043105. [PMID: 32357650 DOI: 10.1063/1.5133086] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2019] [Accepted: 03/17/2020] [Indexed: 06/11/2023]
Abstract
Early afterdepolarization (EAD) is a major arrhythmogenic factor in the long QT syndrome (LQTS), whose conditions for genesis have puzzled people for several decades. Here, we employ the phase I Luo-Rudy ventricular myocyte model to investigate EAD using methods from nonlinear dynamics and provide valuable insights into EAD genesis from a physical perspective. Two major results are obtained: (i) Sufficient parametric conditions for EAD are analytically determined and then used to analyze in detail the effects of the physiological parameters. (ii) The normal form of the Hopf bifurcation that leads to EAD is derived and then used to determine whether the Hopf bifurcation is subcritical or supercritical for EAD genesis and the corresponding amplitude and period of the EAD oscillation. Our work here paves the way for further studies of more complicated multi-scale dynamics of EAD and may lead to effective treatments for LQTS arrhythmias.
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Affiliation(s)
- Zhikun Chu
- Department of Physics, South China University of Technology, Guangzhou 510640, China
| | - Dongping Yang
- Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China
| | - Xiaodong Huang
- Department of Physics, South China University of Technology, Guangzhou 510640, China
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54
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Sahli-Costabal F, Seo K, Ashley E, Kuhl E. Classifying Drugs by their Arrhythmogenic Risk Using Machine Learning. Biophys J 2020; 118:1165-1176. [PMID: 32023435 DOI: 10.1101/545863] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Revised: 11/27/2019] [Accepted: 01/13/2020] [Indexed: 05/25/2023] Open
Abstract
All medications have adverse effects. Among the most serious of these are cardiac arrhythmias. Current paradigms for drug safety evaluation are costly, lengthy, conservative, and impede efficient drug development. Here, we combine multiscale experiment and simulation, high-performance computing, and machine learning to create a risk estimator to stratify new and existing drugs according to their proarrhythmic potential. We capitalize on recent developments in machine learning and integrate information across 10 orders of magnitude in space and time to provide a holistic picture of the effects of drugs, either individually or in combination with other drugs. We show, both experimentally and computationally, that drug-induced arrhythmias are dominated by the interplay between two currents with opposing effects: the rapid delayed rectifier potassium current and the L-type calcium current. Using Gaussian process classification, we create a classifier that stratifies drugs into safe and arrhythmic domains for any combinations of these two currents. We demonstrate that our classifier correctly identifies the risk categories of 22 common drugs exclusively on the basis of their concentrations at 50% current block. Our new risk assessment tool explains under which conditions blocking the L-type calcium current can delay or even entirely suppress arrhythmogenic events. Using machine learning in drug safety evaluation can provide a more accurate and comprehensive mechanistic assessment of the proarrhythmic potential of new drugs. Our study paves the way toward establishing science-based criteria to accelerate drug development, design safer drugs, and reduce heart rhythm disorders.
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Affiliation(s)
| | - Kinya Seo
- Department of Medicine, Stanford University, Stanford, California
| | - Euan Ashley
- Department of Medicine, Stanford University, Stanford, California; Department of Pathology, Stanford University, Stanford, California
| | - Ellen Kuhl
- Department of Mechanical Engineering, Stanford University, Stanford, California; Department of Bioengineering, Stanford University, Stanford, California.
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55
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Sahli-Costabal F, Seo K, Ashley E, Kuhl E. Classifying Drugs by their Arrhythmogenic Risk Using Machine Learning. Biophys J 2020; 118:1165-1176. [PMID: 32023435 PMCID: PMC7063479 DOI: 10.1016/j.bpj.2020.01.012] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Revised: 11/27/2019] [Accepted: 01/13/2020] [Indexed: 12/17/2022] Open
Abstract
All medications have adverse effects. Among the most serious of these are cardiac arrhythmias. Current paradigms for drug safety evaluation are costly, lengthy, conservative, and impede efficient drug development. Here, we combine multiscale experiment and simulation, high-performance computing, and machine learning to create a risk estimator to stratify new and existing drugs according to their proarrhythmic potential. We capitalize on recent developments in machine learning and integrate information across 10 orders of magnitude in space and time to provide a holistic picture of the effects of drugs, either individually or in combination with other drugs. We show, both experimentally and computationally, that drug-induced arrhythmias are dominated by the interplay between two currents with opposing effects: the rapid delayed rectifier potassium current and the L-type calcium current. Using Gaussian process classification, we create a classifier that stratifies drugs into safe and arrhythmic domains for any combinations of these two currents. We demonstrate that our classifier correctly identifies the risk categories of 22 common drugs exclusively on the basis of their concentrations at 50% current block. Our new risk assessment tool explains under which conditions blocking the L-type calcium current can delay or even entirely suppress arrhythmogenic events. Using machine learning in drug safety evaluation can provide a more accurate and comprehensive mechanistic assessment of the proarrhythmic potential of new drugs. Our study paves the way toward establishing science-based criteria to accelerate drug development, design safer drugs, and reduce heart rhythm disorders.
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Affiliation(s)
| | - Kinya Seo
- Department of Medicine, Stanford University, Stanford, California
| | - Euan Ashley
- Department of Medicine, Stanford University, Stanford, California; Department of Pathology, Stanford University, Stanford, California
| | - Ellen Kuhl
- Department of Mechanical Engineering, Stanford University, Stanford, California; Department of Bioengineering, Stanford University, Stanford, California.
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56
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Thioridazine Induces Cardiotoxicity via Reactive Oxygen Species-Mediated hERG Channel Deficiency and L-Type Calcium Channel Activation. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2020; 2020:3690123. [PMID: 32064022 PMCID: PMC6998749 DOI: 10.1155/2020/3690123] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/07/2019] [Revised: 11/01/2019] [Accepted: 11/25/2019] [Indexed: 02/06/2023]
Abstract
Thioridazine (THIO) is a phenothiazine derivative that is mainly used for the treatment of psychotic disorders. However, cardiac arrhythmias especially QT interval prolongation associated with the application of this compound have received serious attention after its introduction into clinical practice, and the mechanisms underlying the cardiotoxicity induced by THIO have not been well defined. The present study was aimed at exploring the long-term effects of THIO on the hERG and L-type calcium channels, both of which are relevant to the development of QT prolongation. The hERG current (I hERG) and the calcium current (I Ca-L) were measured by patch clamp techniques. Protein levels were analyzed by Western blot, and channel-chaperone interactions were determined by coimmunoprecipitation. Reactive oxygen species (ROS) were determined by flow cytometry and laser scanning confocal microscopy. Our results demonstrated that THIO induced hERG channel deficiency but did not alter channel kinetics. THIO promoted ROS production and stimulated endoplasmic reticulum (ER) stress and the related proteins. The ROS scavenger N-acetyl cysteine (NAC) significantly attenuated hERG reduction induced by THIO and abolished the upregulation of ER stress marker proteins. Meanwhile, THIO increased the degradation of hERG channels via disrupting hERG-Hsp70 interactions. The disordered hERG proteins were degraded in proteasomes after ubiquitin modification. On the other hand, THIO increased I Ca-L density and intracellular Ca2+ ([Ca2+]i) in neonatal rat ventricular cardiomyocytes (NRVMs). The specific CaMKII inhibitor KN-93 attenuated the intracellular Ca2+ overload, indicating that ROS-mediated CaMKII activation promoted calcium channel activation induced by THIO. Optical mapping analysis demonstrated the slowing effects of THIO on cardiac repolarization in mouse hearts. THIO significantly prolonged APD50 and APD90 and increased the incidence of early afterdepolarizations (EADs). In human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), THIO also resulted in APD prolongation. In conclusion, dysfunction of hERG channel proteins and activation of L-type calcium channels via ROS production might be the ionic mechanisms for QT prolongation induced by THIO.
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Kurata Y, Tsumoto K, Hayashi K, Hisatome I, Kuda Y, Tanida M. Multiple Dynamical Mechanisms of Phase-2 Early Afterdepolarizations in a Human Ventricular Myocyte Model: Involvement of Spontaneous SR Ca 2+ Release. Front Physiol 2020; 10:1545. [PMID: 31998140 PMCID: PMC6965073 DOI: 10.3389/fphys.2019.01545] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2019] [Accepted: 12/05/2019] [Indexed: 12/19/2022] Open
Abstract
Early afterdepolarization (EAD) is known to cause lethal ventricular arrhythmias in long QT syndrome (LQTS). In this study, dynamical mechanisms of EAD formation in human ventricular myocytes (HVMs) were investigated using the mathematical model developed by ten Tusscher and Panfilov (Am J Physiol Heart Circ Physiol 291, 2006). We explored how the rapid (IKr) and slow (IKs) components of delayed-rectifier K+ channel currents, L-type Ca2+ channel current (ICa L), Na+/Ca2+ exchanger current (INCX), and intracellular Ca2+ handling via the sarcoplasmic reticulum (SR) contribute to initiation, termination and modulation of phase-2 EADs during pacing in relation to bifurcation phenomena in non-paced model cells. Parameter-dependent dynamical behaviors of the non-paced model cell were determined by calculating stabilities of equilibrium points (EPs) and limit cycles, and bifurcation points to construct bifurcation diagrams. Action potentials (APs) and EADs during pacing were reproduced by numerical simulations for constructing phase diagrams of the paced model cell dynamics. Results are summarized as follows: (1) A modified version of the ten Tusscher-Panfilov model with accelerated ICaL inactivation could reproduce bradycardia-related EADs in LQTS type 2 and β-adrenergic stimulation-induced EADs in LQTS type 1. (2) Two types of EADs with different initiation mechanisms, ICaL reactivation-dependent and spontaneous SR Ca2+ release-mediated EADs, were detected. (3) Termination of EADs (AP repolarization) during pacing depended on the slow activation of IKs. (4) Spontaneous SR Ca2+ releases occurred at higher Ca2+ uptake rates, attributable to the instability of steady-state intracellular Ca2+ concentrations. Dynamical mechanisms of EAD formation and termination in the paced model cell are closely related to stability changes (bifurcations) in dynamical behaviors of the non-paced model cell, but they are model-dependent. Nevertheless, the modified ten Tusscher-Panfilov model would be useful for systematically investigating possible dynamical mechanisms of EAD-related arrhythmias in LQTS.
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Affiliation(s)
- Yasutaka Kurata
- Department of Physiology II, Kanazawa Medical University, Uchinada, Japan
| | - Kunichika Tsumoto
- Department of Physiology II, Kanazawa Medical University, Uchinada, Japan
| | - Kenshi Hayashi
- Department of Cardiovascular and Internal Medicine, Graduate School of Medical Sciences, Kanazawa University, Kanazawa, Japan
| | - Ichiro Hisatome
- Department of Genetic Medicine and Regenerative Therapeutics, Graduate School of Medical Sciences, Tottori University, Yonago, Japan
| | - Yuhichi Kuda
- Department of Physiology II, Kanazawa Medical University, Uchinada, Japan
| | - Mamoru Tanida
- Department of Physiology II, Kanazawa Medical University, Uchinada, Japan
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58
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Ginsenoside Rb1 exerts antiarrhythmic effects by inhibiting I Na and I CaL in rabbit ventricular myocytes. Sci Rep 2019; 9:20425. [PMID: 31892729 PMCID: PMC6938504 DOI: 10.1038/s41598-019-57010-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2019] [Accepted: 12/19/2019] [Indexed: 12/18/2022] Open
Abstract
Ginsenoside Rb1 exerts its pharmacological action by regulating sodium, potassium and calcium ion channels in the membranes of nerve cells. These ion channels are also present in cardiomyocytes, but no studies have been reported to date regarding the effects of Rb1 on cardiac sodium currents (INa), L-type calcium currents (ICaL) and action potentials (APs). Additionally, the antiarrhythmic potential of Rb1 has not been assessed. In this study, we used a whole-cell patch clamp technique to assess the effect of Rb1 on these ion channels. The results showed that Rb1 inhibited INa and ICaL, reduced the action potential amplitude (APA) and maximum upstroke velocity (Vmax), and shortened the action potential duration (APD) in a concentration-dependent manner but had no effect on the inward rectifier potassium current (IK1), delayed rectifier potassium current (IK) or resting membrane potential (RMP). We also designed a pathological model at the cellular and organ level to verify the role of Rb1. The results showed that Rb1 abolished high calcium-induced delayed afterdepolarizations (DADs), depressed the increase in intracellular calcium ([Ca2+]i), relieved calcium overload and protected cardiomyocytes. Rb1 can also reduce the occurrence of ventricular premature beats (VPBs) and ventricular tachycardia (VT) in ischemia-reperfusion (I-R) injury.
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59
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Han D, Xu L, Liu P, Liu Y, Sun C, Yin Y. Allicin disrupts cardiac Cav1.2 channels via trafficking. PHARMACEUTICAL BIOLOGY 2019; 57:245-249. [PMID: 30929547 PMCID: PMC6450490 DOI: 10.1080/13880209.2019.1577469] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/19/2018] [Revised: 10/06/2018] [Accepted: 01/25/2019] [Indexed: 06/09/2023]
Abstract
CONTEXT Allicin is a potential antiarrhythmic agent. The antiarrhythmic properties of allicin rely on its blockade of various cardiac ion channels. The l-type calcium (Cav1.2) channel provides a pivotal substrate for cardiac electrophysiologic activities. The mechanism of allicin on Cav1.2 remains unclear. OBJECTIVE This study evaluated the potential of allicin on the synthesis and trafficking of Cav1.2 channels. MATERIALS AND METHODS Primary cardiomyocytes (CMs) from neonatal Sprague-Dawley (SD) rats were exposed to allicin (0, 0.0001, 0.001, 0.01, 0.1, 1, 10, 100 μg/mL) for 24 and 48 h. The CellTiter-Glo assay was performed to measure CM viability. Western blot with grayscale analysis and confocal laser scanning microscopy were used to evaluate the effects of allicin on the synthesis and trafficking of Cav1.2 channel proteins in primary CMs. RESULTS There was no significant difference in apoptotic toxicity from the actual cell viability (p > 0.05) in any group (0, 0.0001, 0.001, 0.01, 0.1, 1, 10, 100 μg/mL allicin), except that viability in the 0.001 and 0.01 μg/mL groups at 24 h were significantly greater (137.37 and 135.96%) (p < 0.05). Western blot with grayscale analysis revealed no substantial inhibition by allicin of the synthesis of Cav1.2 proteins. Confocal laser scanning microscopy revealed trafficking dysfunction of Cav1.2 channels caused by allicin in primary CMs. CONCLUSION This study is the first to demonstrate that allicin inhibits cardiac Cav1.2 channels by disrupting trafficking, possibly mediating its antiarrhythmic benefits. Therefore, allicin might serve as a new antiarrhythmic agent in the future.
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Affiliation(s)
- Dan Han
- Arrhythmia Unit, Department of Cardiology, The First Affiliated Hospital of Xi’an Jiaotong University, Xi’an, China
| | - Lingping Xu
- Arrhythmia Unit, Department of Cardiology, The First Affiliated Hospital of Xi’an Jiaotong University, Xi’an, China
- Xianyang Central Hospital, Xianyang, China
| | - Peng Liu
- Arrhythmia Unit, Department of Cardiology, The First Affiliated Hospital of Xi’an Jiaotong University, Xi’an, China
| | - Yingying Liu
- Arrhythmia Unit, Department of Cardiology, The First Affiliated Hospital of Xi’an Jiaotong University, Xi’an, China
| | - Chaofeng Sun
- Arrhythmia Unit, Department of Cardiology, The First Affiliated Hospital of Xi’an Jiaotong University, Xi’an, China
| | - Yanrong Yin
- Arrhythmia Unit, Department of Cardiology, The First Affiliated Hospital of Xi’an Jiaotong University, Xi’an, China
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Liu MB, Vandersickel N, Panfilov AV, Qu Z. R-From-T as a Common Mechanism of Arrhythmia Initiation in Long QT Syndromes. Circ Arrhythm Electrophysiol 2019; 12:e007571. [PMID: 31838916 PMCID: PMC6924944 DOI: 10.1161/circep.119.007571] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Accepted: 09/24/2019] [Indexed: 02/07/2023]
Abstract
BACKGROUND Long QT syndromes (LQTS) arise from many genetic and nongenetic causes with certain characteristic ECG features preceding polymorphic ventricular tachyarrhythmias (PVTs). However, how the many molecular causes result in these characteristic ECG patterns and how these patterns are mechanistically linked to the spontaneous initiation of PVT remain poorly understood. METHODS Anatomic human ventricle and simplified tissue models were used to investigate the mechanisms of spontaneous initiation of PVT in LQTS. RESULTS Spontaneous initiation of PVT was elicited by gradually ramping up ICa,L to simulate the initial phase of a sympathetic surge or by changing the heart rate, reproducing the different genotype-dependent clinical ECG features. In LQTS type 2 (LQT2) and LQTS type 3 (LQT3), T-wave alternans was observed followed by premature ventricular complexes (PVCs). Compensatory pauses occurred resulting in short-long-short sequences. As ICa,L increased further, PVT episodes occurred, always preceded by a short-long-short sequence. However, in LQTS type 1 (LQT1), once a PVC occurred, it always immediately led to an episode of PVT. Arrhythmias in LQT2 and LQT3 were bradycardia dependent, whereas those in LQT1 were not. In all 3 genotypes, PVCs always originated spontaneously from the steep repolarization gradient region and manifested on ECG as R-on-T. We call this mechanism R-from-T, to distinguish it from the classic explanation of R-on-T arrhythmogenesis in which an exogenous PVC coincidentally encounters a repolarizing region. In R-from-T, the PVC and the T wave are causally related, where steep repolarization gradients combined with enhanced ICa,L lead to PVCs emerging from the T wave. Since enhanced ICa,L was required for R-from-T to occur, suppressing window ICa,L effectively prevented arrhythmias in all 3 genotypes. CONCLUSIONS Despite the complex molecular causes, these results suggest that R-from-T is likely a common mechanism for PVT initiation in LQTS. Targeting ICa,L properties, such as suppressing window ICa,L or preventing excessive ICa,L increase, could be an effective unified therapy for arrhythmia prevention in LQTS.
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Affiliation(s)
- Michael B. Liu
- Department of Medicine (M.B.L., Z.Q.), University of California, Los Angeles
| | - Nele Vandersickel
- Department of Physics and Astronomy, Ghent University, Belgium (N.V., A.V.P.)
| | - Alexander V. Panfilov
- Department of Physics and Astronomy, Ghent University, Belgium (N.V., A.V.P.)
- Laboratory of Computational Biology and Medicine, Ural Federal University, Ekaterinburg, Russia (A.V.P.)
| | - Zhilin Qu
- Department of Medicine (M.B.L., Z.Q.), University of California, Los Angeles
- Department of Biomathematics (Z.Q.), University of California, Los Angeles
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61
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Landaw J, Qu Z. Bifurcations Caused by Feedback between Voltage and Intracellular Ion Concentrations in Ventricular Myocytes. PHYSICAL REVIEW LETTERS 2019; 123:218101. [PMID: 31809131 PMCID: PMC7042026 DOI: 10.1103/physrevlett.123.218101] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2019] [Indexed: 05/04/2023]
Abstract
We develop an iterated map model to describe the bifurcations and complex dynamics caused by the feedback between voltage and intracellular Ca^{2+} and Na^{+} concentrations in paced ventricular myocytes. Voltage and Ca^{2+} can form either a positive or a negative feedback loop, while voltage and Na^{+} form a negative feedback loop. Under certain diseased conditions, when the feedback between voltage and Ca^{2+} is positive, Hopf bifurcations occur, leading to periodic oscillatory behaviors. When this feedback is negative, period-doubling bifurcation routes to alternans and chaos occur.
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62
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Aguilar-Sanchez Y, Rodriguez de Yurre A, Argenziano M, Escobar AL, Ramos-Franco J. Transmural Autonomic Regulation of Cardiac Contractility at the Intact Heart Level. Front Physiol 2019; 10:773. [PMID: 31333477 PMCID: PMC6616252 DOI: 10.3389/fphys.2019.00773] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2019] [Accepted: 06/03/2019] [Indexed: 01/14/2023] Open
Abstract
The relationship between cardiac excitability and contractility depends on when Ca2+ influx occurs during the ventricular action potential (AP). In mammals, it is accepted that Ca2+ influx through the L-type Ca2+ channels occurs during AP phase 2. However, in murine models, experimental evidence shows Ca2+ influx takes place during phase 1. Interestingly, Ca2+ influx that activates contraction is highly regulated by the autonomic nervous system. Indeed, autonomic regulation exerts multiple effects on Ca2+ handling and cardiac electrophysiology. In this paper, we explore autonomic regulation in endocardial and epicardial layers of intact beating mice hearts to evaluate their role on cardiac excitability and contractility. We hypothesize that in mouse cardiac ventricles the influx of Ca2+ that triggers excitation–contraction coupling (ECC) does not occur during phase 2. Using pulsed local field fluorescence microscopy and loose patch photolysis, we show sympathetic stimulation by isoproterenol increased the amplitude of Ca2+ transients in both layers. This increase in contractility was driven by an increase in amplitude and duration of the L-type Ca2+ current during phase 1. Interestingly, the β-adrenergic increase of Ca2+ influx slowed the repolarization of phase 1, suggesting a competition between Ca2+ and K+ currents during this phase. In addition, cAMP activated L-type Ca2+ currents before SR Ca2+ release activated the Na+-Ca2+ exchanger currents, indicating Cav1.2 channels are the initial target of PKA phosphorylation. In contrast, parasympathetic stimulation by carbachol did not have a substantial effect on amplitude and kinetics of endocardial and epicardial Ca2+ transients. However, carbachol transiently decreased the duration of the AP late phase 2 repolarization. The carbachol-induced shortening of phase 2 did not have a considerable effect on ventricular pressure and systolic Ca2+ dynamics. Interestingly, blockade of muscarinic receptors by atropine prolonged the duration of phase 2 indicating that, in isolated hearts, there is an intrinsic release of acetylcholine. In addition, the acceleration of repolarization induced by carbachol was blocked by the acetylcholine-mediated K+ current inhibition. Our results reveal the transmural ramifications of autonomic regulation in intact mice hearts and support our hypothesis that Ca2+ influx that triggers ECC occurs in AP phase 1 and not in phase 2.
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Affiliation(s)
- Yuriana Aguilar-Sanchez
- Department of Physiology and Biophysics, School of Medicine, Rush University Medical Center, Chicago, IL, United States
| | - Ainhoa Rodriguez de Yurre
- Laboratorio de Cardio Inmunologia, Instituto de Biofisica Carlos Chagas Filho, Rio de Janeiro, Brazil
| | - Mariana Argenziano
- Division of Human Genetics, Children's Hospital of Philadelphia, Philadelphia, PA, United States
| | - Ariel L Escobar
- Department of Bioengineering, School of Engineering, University of California, Merced, Merced, CA, United States
| | - Josefina Ramos-Franco
- Department of Physiology and Biophysics, School of Medicine, Rush University Medical Center, Chicago, IL, United States
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Sahli Costabal F, Yao J, Sher A, Kuhl E. Predicting critical drug concentrations and torsadogenic risk using a multiscale exposure-response simulator. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2019; 144:61-76. [PMID: 30482568 PMCID: PMC6483901 DOI: 10.1016/j.pbiomolbio.2018.10.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2018] [Revised: 09/21/2018] [Accepted: 10/11/2018] [Indexed: 12/12/2022]
Abstract
Torsades de pointes is a serious side effect of many drugs that can trigger sudden cardiac death, even in patients with structurally normal hearts. Torsadogenic risk has traditionally been correlated with the blockage of a specific potassium channel and a prolonged recovery period in the electrocardiogram. However, the precise mechanisms by which single channel block translates into heart rhythm disorders remain incompletely understood. Here we establish a multiscale exposure-response simulator that converts block-concentration characteristics from single cell recordings into three-dimensional excitation profiles and electrocardiograms to rapidly assess torsadogenic risk. For the drug dofetilide, we characterize the QT interval and heart rate at different drug concentrations and identify the critical concentration at the onset of torsades de pointes: For dofetilide concentrations of 2x, 3x, and 4x, as multiples of the free plasma concentration Cmax = 2.1 nM, the QT interval increased by +62.0%, +71.2%, and +82.3% compared to baseline, and the heart rate changed by -21.7%, -23.3%, and +88.3%. The last number indicates that, at the critical concentration of 4x, the heart spontaneously developed an episode of a torsades-like arrhythmia. Strikingly, this critical drug concentration is higher than the concentration estimated from early afterdepolarizations in single cells and lower than in one-dimensional cable models. Our results highlight the importance of whole heart modeling and explain, at least in part, why current regulatory paradigms often fail to accurately quantify the pro-arrhythmic potential of a drug. Our exposure-response simulator could provide a more mechanistic assessment of pro-arrhythmic risk and help establish science-based guidelines to reduce rhythm disorders, design safer drugs, and accelerate drug development.
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Affiliation(s)
| | - Jiang Yao
- Dassault Systèmes Simulia Corporation, Johnston, RI, 02919, United States
| | - Anna Sher
- Internal Medicine Research Unit, Pfizer Inc, Cambridge, MA, 02139, United States
| | - Ellen Kuhl
- Department of Mechanical Engineering, Stanford University, Stanford, CA, 94305, United States.
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64
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Kettlewell S, Saxena P, Dempster J, Colman MA, Myles RC, Smith GL, Workman AJ. Dynamic clamping human and rabbit atrial calcium current: narrowing I CaL window abolishes early afterdepolarizations. J Physiol 2019; 597:3619-3638. [PMID: 31093979 PMCID: PMC6767690 DOI: 10.1113/jp277827] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2019] [Accepted: 05/13/2019] [Indexed: 11/08/2022] Open
Abstract
Key points Early‐afterdepolarizations (EADs) are abnormal action potential oscillations and a known cause of cardiac arrhythmias. Ventricular EADs involve reactivation of a Ca2+ current (ICaL) in its ‘window region’ voltage range. However, electrical mechanisms of atrial EADs, a potential cause of atrial fibrillation, are poorly understood. Atrial cells were obtained from consenting patients undergoing heart surgery, as well as from rabbits. ICaL was blocked with nifedipine and then a hybrid patch clamp/mathematical‐modelling technique, ‘dynamic clamping’, was used to record action potentials at the same time as injecting an artificial, modifiable, ICaL (ICaL,D‐C). Progressively widening the ICaL,D‐C window region produced EADs of various types, dependent on window width. EAD production was strongest upon moving the activation (vs. inactivation) side of the window. EADs were then induced by a different method: increasing ICaL,D‐C amplitude and/or K+ channel‐blockade (4‐aminopyridine). Narrowing of the ICaL,D‐C window by ∼10 mV abolished these EADs. Atrial ICaL window narrowing is worthy of further testing as a potential anti‐atrial fibrillation drug mechanism.
Abstract Atrial early‐afterdepolarizations (EADs) may contribute to atrial fibrillation (AF), perhaps involving reactivation of L‐type Ca2+ current (ICaL) in its window region voltage range. The present study aimed (i) to validate the dynamic clamp technique for modifying the ICaL contribution to atrial action potential (AP) waveform; (ii) to investigate the effects of widening the window ICaL on EAD‐propensity; and (iii) to test whether EADs from increased ICaL and AP duration are supressed by narrowing the window ICaL. ICaL and APs were recorded from rabbit and human atrial myocytes by whole‐cell‐patch clamp. During AP recording, ICaL was inhibited (3 µm nifedipine) and replaced by a dynamic clamp model current, ICaL,D‐C (tuned to native ICaL characteristics), computed in real‐time (every 50 µs) based on myocyte membrane potential. ICaL,D‐C‐injection restored the nifedipine‐suppressed AP plateau. Widening the window ICaL,D‐C, symmetrically by stepwise simultaneous equal shifts of half‐voltages (V0.5) of ICaL,D‐C activation (negatively) and inactivation (positively), generated EADs (single, multiple or preceding repolarization failure) in a window width‐dependent manner, as well as AP alternans. A stronger EAD‐generating effect resulted from independently shifting activation V0.5 (asymmetrical widening) than inactivation V0.5; for example, a 15 mV activation shift produced EADs in nine of 17 (53%) human atrial myocytes vs. 0 of 18 from inactivation shift (P < 0.05). In 11 rabbit atrial myocytes in which EADs were generated either by increasing the conductance of normal window width ICaL,D‐C or subsequent 4‐aminopyridine (2 mm), window ICaL,D‐C narrowing (10 mV) abolished EADs of all types (P < 0.05). The present study validated the dynamic clamp for ICaL, which is novel in atrial cardiomyocytes, and showed that EADs of various types are generated by widening (particularly asymmetrically) the window ICaL, as well as abolished by narrowing it. Window ICaL narrowing is a potential therapeutic mechanism worth pursuing in the search for improved anti‐AF drugs. Early‐afterdepolarizations (EADs) are abnormal action potential oscillations and a known cause of cardiac arrhythmias. Ventricular EADs involve reactivation of a Ca2+ current (ICaL) in its ‘window region’ voltage range. However, electrical mechanisms of atrial EADs, a potential cause of atrial fibrillation, are poorly understood. Atrial cells were obtained from consenting patients undergoing heart surgery, as well as from rabbits. ICaL was blocked with nifedipine and then a hybrid patch clamp/mathematical‐modelling technique, ‘dynamic clamping’, was used to record action potentials at the same time as injecting an artificial, modifiable, ICaL (ICaL,D‐C). Progressively widening the ICaL,D‐C window region produced EADs of various types, dependent on window width. EAD production was strongest upon moving the activation (vs. inactivation) side of the window. EADs were then induced by a different method: increasing ICaL,D‐C amplitude and/or K+ channel‐blockade (4‐aminopyridine). Narrowing of the ICaL,D‐C window by ∼10 mV abolished these EADs. Atrial ICaL window narrowing is worthy of further testing as a potential anti‐atrial fibrillation drug mechanism.
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Affiliation(s)
- Sarah Kettlewell
- Institute of Cardiovascular & Medical Sciences, University of Glasgow, Glasgow, UK
| | - Priyanka Saxena
- Institute of Cardiovascular & Medical Sciences, University of Glasgow, Glasgow, UK
| | - John Dempster
- Strathclyde Institute of Pharmacy & Biomedical Sciences, University of Strathclyde, Glasgow, UK
| | | | - Rachel C Myles
- Institute of Cardiovascular & Medical Sciences, University of Glasgow, Glasgow, UK
| | - Godfrey L Smith
- Institute of Cardiovascular & Medical Sciences, University of Glasgow, Glasgow, UK
| | - Antony J Workman
- Institute of Cardiovascular & Medical Sciences, University of Glasgow, Glasgow, UK
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Oshita K, Kozasa Y, Nakagawa Y, Kuwabara Y, Kuwahara K, Nakagawa T, Nakashima N, Hiraki T, Takano M. Overexpression of the HCN2 channel increases the arrhythmogenicity induced by hypokalemia. J Physiol Sci 2019; 69:653-660. [PMID: 31087220 PMCID: PMC6583697 DOI: 10.1007/s12576-019-00684-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2019] [Accepted: 04/30/2019] [Indexed: 12/19/2022]
Abstract
Hypokalemia, an abnormally low level of potassium (K+), is a electrolyte imbalance that commonly occurs in heart failure patients. Hypokalemia is well known to induce lethal ventricular arrhythmia. However, the effects of hypokalemia in failing hearts that have undergone electrophysiological remodeling, i.e., the reactivation of fetal-type ion channels, remain unexplored. We have examined the effect of hypokalemia in the myocytes of transgenic mice overexpressing the hyperpolarization-activated, cyclic nucleotide-sensitive (HCN) channel in the heart (HCN2-Tg mice). Perfusion with a mild hypokalemic solution containing 3 mM K+ induced ectopic ventricular automaticity in 55.0% of HCN2-Tg mouse myocytes. In the remaining HCN2-Tg mouse myocytes, the resting membrane potential (RMP) was more depolarized than that of wild-type myocytes subjected to the same treatment and could also be hyperpolarized by an HCN channel blocker. We conclude that in hypokalemia in our mice model, the HCN2 channel was constitutively activated at the hyperpolarized RMP, thereby destabilizing the electrophysiological activity of ventricular myocytes.
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Affiliation(s)
- Kensuke Oshita
- Department of Physiology, Kurume University School of Medicine, 67 Asahi-Machi, Kurume, 830-0011, Japan.,Department of Anesthesiology, Kurume University School of Medicine, Kurume, Japan
| | - Yuko Kozasa
- Department of Physiology, Kurume University School of Medicine, 67 Asahi-Machi, Kurume, 830-0011, Japan.,Department of Anesthesiology, Kurume University School of Medicine, Kurume, Japan
| | - Yasuaki Nakagawa
- Department of Cardiovascular Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Yoshihiro Kuwabara
- Department of Cardiovascular Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Koichiro Kuwahara
- Department of Cardiovascular Medicine, Shinshu University School of Medicine, Matsumoto, Japan
| | - Taku Nakagawa
- Department of Physiology, Kurume University School of Medicine, 67 Asahi-Machi, Kurume, 830-0011, Japan
| | - Noriyuki Nakashima
- Department of Physiology, Kurume University School of Medicine, 67 Asahi-Machi, Kurume, 830-0011, Japan
| | - Teruyuki Hiraki
- Department of Anesthesiology, Kurume University School of Medicine, Kurume, Japan
| | - Makoto Takano
- Department of Physiology, Kurume University School of Medicine, 67 Asahi-Machi, Kurume, 830-0011, Japan.
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66
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Uchida S, Asai Y, Kariya Y, Tsumoto K, Hibino H, Honma M, Abe T, Nin F, Kurata Y, Furutani K, Suzuki H, Kitano H, Inoue R, Kurachi Y. Integrative and theoretical research on the architecture of a biological system and its disorder. J Physiol Sci 2019; 69:433-451. [PMID: 30868372 PMCID: PMC6456489 DOI: 10.1007/s12576-019-00667-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2018] [Accepted: 02/08/2019] [Indexed: 11/28/2022]
Abstract
An organism stems from assemblies of a variety of cells and proteins. This complex system serves as a unit, and it exhibits highly sophisticated functions in response to exogenous stimuli that change over time. The complete sequencing of the entire human genome has allowed researchers to address the enigmas of life and disease at the gene- or molecular-based level. The consequence of such studies is the rapid accumulation of a multitude of data at multiple levels, ranging from molecules to the whole body, that has necessitated the development of entirely new concepts, tools, and methodologies to analyze and integrate these data. This necessity has given birth to systems biology, an advanced theoretical and practical research framework that has totally changed the directions of not only basic life science but also medicine. During the symposium of the 95th Annual Meeting of The Physiological Society of Japan 2018, five researchers reported on their respective studies on systems biology. The topics included reactions of drugs, ion-transport architecture in an epithelial system, multi-omics in renal disease, cardiac electrophysiological systems, and a software platform for computer simulation. In this review article these authors have summarized recent achievements in the field and discuss next-generation studies on health and disease.
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Affiliation(s)
- Shinichi Uchida
- Department of Nephrology, Graduate Schools of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo, Tokyo, 113-8519, Japan
| | - Yoshiyuki Asai
- Department of Systems Bioinformatics, Yamaguchi University Graduate School of Medicine, Ube, Yamaguchi, 755-8505, Japan
| | - Yoshiaki Kariya
- Department of Pharmacy, The University of Tokyo Hospital, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-8655, Japan
| | - Kunichika Tsumoto
- Division of Molecular and Cellular Pharmacology, Department of Pharmacology, Osaka University, Suita, Japan.,Center for Advanced Medical Engineering and Informatics, Osaka University, Suita, Japan.,Department of Physiology II, Kanazawa Medical University, Ishikawa, 920-0293, Japan
| | - Hiroshi Hibino
- Department of Molecular Physiology, Niigata University School of Medicine, 1-757 Asahimachi-dori, Chuo-ku, Niigata, Niigata, 951-8510, Japan. .,AMED-CREST, AMED, Niigata, Japan.
| | - Masashi Honma
- Department of Pharmacy, The University of Tokyo Hospital, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-8655, Japan
| | - Takeshi Abe
- Department of Systems Bioinformatics, Yamaguchi University Graduate School of Medicine, Ube, Yamaguchi, 755-8505, Japan
| | - Fumiaki Nin
- Department of Molecular Physiology, Niigata University School of Medicine, 1-757 Asahimachi-dori, Chuo-ku, Niigata, Niigata, 951-8510, Japan.,AMED-CREST, AMED, Niigata, Japan
| | - Yasutaka Kurata
- Department of Physiology II, Kanazawa Medical University, Ishikawa, 920-0293, Japan
| | - Kazuharu Furutani
- Department of Physiology and Membrane Biology, University of California Davis, Davis, 95616, USA
| | - Hiroshi Suzuki
- Department of Pharmacy, The University of Tokyo Hospital, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-8655, Japan
| | - Hiroaki Kitano
- The Systems Biology Institute, Shinagawa-ku, Tokyo, 108-0071, Japan
| | - Ryuji Inoue
- Department of Physiology, Fukuoka University School of Medicine, 7-45-1 Nanakuma, Jonan-ku, Fukuoka, 814-0180, Japan.
| | - Yoshihisa Kurachi
- Division of Molecular and Cellular Pharmacology, Department of Pharmacology, Osaka University, Suita, Japan. .,Center for Advanced Medical Engineering and Informatics, Osaka University, Suita, Japan.
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67
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Kügler P, Erhardt AH, Bulelzai MAK. Early afterdepolarizations in cardiac action potentials as mixed mode oscillations due to a folded node singularity. PLoS One 2018; 13:e0209498. [PMID: 30596698 PMCID: PMC6312222 DOI: 10.1371/journal.pone.0209498] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2018] [Accepted: 12/06/2018] [Indexed: 12/27/2022] Open
Abstract
Early afterdepolarizations (EADs) are pathological voltage oscillations during the repolarization phase of cardiac action potentials. They are considered as potential precursors to cardiac arrhythmias and have recently gained much attention in the context of preclinical drug safety testing under the Comprehensive in vitro Proarrhythmia Assay (CiPA) paradigm. From the viewpoint of multiple time scales theory, the onset of EADs has previously been studied by means of mathematical action potential models with one slow ion channel gating variable. In this article, we for the first time associate EADs with mixed mode oscillations in dynamical systems with two slow gating variables and present a folded node singularity of the slow flow as a novel mechanism for EADs genesis. We derive regions of the pharmacology parameter space in which EADs occur using both the folded node analysis and a full system bifurcation analysis, and we suggest the normal distance to the boundary of the EADs region as a mechanism-based risk metric to computationally estimate a drug’s proarrhythmic liability.
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Affiliation(s)
- Philipp Kügler
- Institute of Applied Mathematics and Statistics, University of Hohenheim, Stuttgart, Germany
- * E-mail:
| | | | - M. A. K. Bulelzai
- Departmeny of Basic Sciences and Related Studies, Quaid-e-Awam University of Engineering, Science and Technology, Nawabshah, Pakistan
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68
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Christophe B, Crumb WJ. Impact of disease state on arrhythmic event detection by action potential modelling in cardiac safety pharmacology. J Pharmacol Toxicol Methods 2018; 96:15-26. [PMID: 30580044 DOI: 10.1016/j.vascn.2018.12.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2018] [Revised: 12/11/2018] [Accepted: 12/17/2018] [Indexed: 11/15/2022]
Abstract
INTRODUCTION The use of in silico cardiac action potential simulations is one of the pillars of the CiPA initiative (Comprehensive in vitro Proarrhythmia Assay) currently under evaluation designed to detect more accurately proarrhythmic liabilities of new drug candidate. In order to take into account the variability of clinical situations, we propose to improve this method by studying the impact of various disease states on arrhythmic events induced by 30 torsadogenic or non-torsadogenic compounds. METHOD In silico modelling was done on the human myocytes using the Dutta revised O'Hara-Rudy algorithm. Results were analysed using a new metric based on the compound IC50s against the seven cardiac ionic currents considered to be the most important by the CiPA initiative (IKr, IKs, INa, INaL, IK1, Ito, ICaL) and the minimal rate of action potential voltage decrease calculated at the early-afterdepolarization (EAD) take-off membrane voltage (Vmin). RESULTS The specific threshold at which each torsadogenic compounds induced EAD, was exacerbated by the presence of cardiac risk factors ranked as follows: congestive heart failure > hypertrophic cardiomyopathy > cardiac pause > no risk factor. Non-torsadogenic compounds induced no EAD even in the presence of cardiac risk factors. DISCUSSION The present study highlighted the impact of pre-existing cardiovascular disease on arrhythmic event detection suggesting that disease state modelling may need to be incorporated in order to fully realize the goal of the CiPA paradigm in a more accurate predictability of proarrhythmic liabilities of new drug candidate.
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Affiliation(s)
| | - William J Crumb
- Nova Research Laboratories LLC, 1441 Canal Street, New Orleans, LA 70112, USA.
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69
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Huang X, Song Z, Qu Z. Determinants of early afterdepolarization properties in ventricular myocyte models. PLoS Comput Biol 2018; 14:e1006382. [PMID: 30475801 PMCID: PMC6283611 DOI: 10.1371/journal.pcbi.1006382] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2018] [Revised: 12/06/2018] [Accepted: 09/17/2018] [Indexed: 12/20/2022] Open
Abstract
Early afterdepolarizations (EADs) are spontaneous depolarizations during the repolarization phase of an action potential in cardiac myocytes. It is widely known that EADs are promoted by increasing inward currents and/or decreasing outward currents, a condition called reduced repolarization reserve. Recent studies based on bifurcation theories show that EADs are caused by a dual Hopf-homoclinic bifurcation, bringing in further mechanistic insights into the genesis and dynamics of EADs. In this study, we investigated the EAD properties, such as the EAD amplitude, the inter-EAD interval, and the latency of the first EAD, and their major determinants. We first made predictions based on the bifurcation theory and then validated them in physiologically more detailed action potential models. These properties were investigated by varying one parameter at a time or using parameter sets randomly drawn from assigned intervals. The theoretical and simulation results were compared with experimental data from the literature. Our major findings are that the EAD amplitude and takeoff potential exhibit a negative linear correlation; the inter-EAD interval is insensitive to the maximum ionic current conductance but mainly determined by the kinetics of ICa,L and the dual Hopf-homoclinic bifurcation; and both inter-EAD interval and latency vary largely from model to model. Most of the model results generally agree with experimental observations in isolated ventricular myocytes. However, a major discrepancy between modeling results and experimental observations is that the inter-EAD intervals observed in experiments are mainly between 200 and 500 ms, irrespective of species, while those of the mathematical models exhibit a much wider range with some models exhibiting inter-EAD intervals less than 100 ms. Our simulations show that the cause of this discrepancy is likely due to the difference in ICa,L recovery properties in different mathematical models, which needs to be addressed in future action potential model development. Early afterdepolarizations (EADs) are abnormal depolarizations during the plateau phase of action potential in cardiac myocytes, arising from a dual Hopf-homoclinic bifurcation. The same bifurcations are also responsible for certain types of bursting behaviors in other cell types, such as beta cells and neuronal cells. EADs are known to play important role in the genesis of lethal arrhythmias and have been widely studied in both experiments and computer models. However, a detailed comparison between the properties of EADs observed in experiments and those from mathematical models have not been carried out. In this study, we performed theoretical analyses and computer simulations of different ventricular action potential models as well as different species to investigate the properties of EADs and compared these properties to those observed in experiments. While the EAD properties in the action potential models capture many of the EAD properties seen in experiments, the inter-EAD intervals in the computer models differ a lot from model to model, and some of them show very large discrepancy with those observed in experiments. This discrepancy needs to be addressed in future cardiac action potential model development.
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Affiliation(s)
- Xiaodong Huang
- Department of Physics, South China University of Technology, Guangzhou, China
| | - Zhen Song
- Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
| | - Zhilin Qu
- Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
- Department of Biomathematics, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
- * E-mail:
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70
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Zhong M, Rees CM, Terentyev D, Choi BR, Koren G, Karma A. NCX-Mediated Subcellular Ca 2+ Dynamics Underlying Early Afterdepolarizations in LQT2 Cardiomyocytes. Biophys J 2018; 115:1019-1032. [PMID: 30173888 DOI: 10.1016/j.bpj.2018.08.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2018] [Revised: 07/18/2018] [Accepted: 08/02/2018] [Indexed: 12/12/2022] Open
Abstract
Long QT syndrome type 2 (LQT2) is a congenital disease characterized by loss of function mutations in hERG potassium channels (IKr). LQT2 is associated with fatal ventricular arrhythmias promoted by triggered activity in the form of early afterdepolarizations (EADs). We previously demonstrated that intracellular Ca2+ handling is remodeled in LQT2 myocytes. Remodeling leads to aberrant late RyR-mediated Ca2+ releases that drive forward-mode Na+-Ca2+ exchanger (NCX) current and slow repolarization to promote reopening of L-type calcium channels and EADs. Forward-mode NCX was found to be enhanced despite the fact that these late releases do not significantly alter the whole-cell cytosolic calcium concentration during a vulnerable period of phase 2 of the action potential corresponding to the onset of EADs. Here, we use a multiscale ventricular myocyte model to explain this finding. We show that because the local NCX current is a saturating nonlinear function of the local submembrane calcium concentration, a larger number of smaller-amplitude discrete Ca2+ release events can produce a large increase in whole-cell forward-mode NCX current without increasing significantly the whole-cell cytosolic calcium concentration. Furthermore, we develop novel insights, to our knowledge, into how alterations of stochastic RyR activity at the single-channel level cause late aberrant Ca2+ release events. Experimental measurements in transgenic LTQ2 rabbits confirm the critical arrhythmogenic role of NCX and identify this current as a potential target for antiarrhythmic therapies in LQT2.
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Affiliation(s)
- Mingwang Zhong
- Physics Department and Center for Interdisciplinary Research in Complex Systems, Northeastern University, Boston, Massachusetts
| | - Colin M Rees
- Physics Department and Center for Interdisciplinary Research in Complex Systems, Northeastern University, Boston, Massachusetts
| | - Dmitry Terentyev
- Cardiovascular Research Centre, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, Rhode Island
| | - Bum-Rak Choi
- Cardiovascular Research Centre, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, Rhode Island
| | - Gideon Koren
- Cardiovascular Research Centre, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, Rhode Island
| | - Alain Karma
- Physics Department and Center for Interdisciplinary Research in Complex Systems, Northeastern University, Boston, Massachusetts.
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71
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Choi BR, Li W, Terentyev D, Kabakov AY, Zhong M, Rees CM, Terentyeva R, Kim TY, Qu Z, Peng X, Karma A, Koren G. Transient Outward K + Current (I to) Underlies the Right Ventricular Initiation of Polymorphic Ventricular Tachycardia in a Transgenic Rabbit Model of Long-QT Syndrome Type 1. Circ Arrhythm Electrophysiol 2018; 11:e005414. [PMID: 29769222 PMCID: PMC6081959 DOI: 10.1161/circep.117.005414] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/08/2017] [Accepted: 03/21/2018] [Indexed: 12/29/2022]
Abstract
BACKGROUND Sudden death in long-QT syndrome type 1 (LQT1), an inherited disease caused by loss-of-function mutations in KCNQ1, is triggered by early afterdepolarizations (EADs) that initiate polymorphic ventricular tachycardia (pVT). We investigated ionic mechanisms that underlie pVT in LQT1 using a transgenic rabbit model of LQT1. METHODS Optical mapping, cellular patch clamping, and computer modeling were used to elucidate the mechanisms of EADs in transgenic LQT1 rabbits. RESULTS The results showed that shorter action potential duration in the right ventricle (RV) was associated with focal activity during pVT initiation. RV cardiomyocytes demonstrated higher incidence of EADs under 50 nmol/L isoproterenol. Voltage-clamp studies revealed that the transient outward potassium current (Ito) magnitude was 28% greater in RV associated with KChiP2 but with no differences in terms of calcium-cycling kinetics and other sarcolemmal currents. Perfusing with the Ito blocker 4-aminopyridine changed the initial focal sites of pVT from the RV to the left ventricle, corroborating the role of Ito in pVT initiation. Computer modeling showed that EADs occur preferentially in the RV because of the larger conductance of the slow-inactivating component of Ito, which repolarizes the membrane potential sufficiently rapidly to allow reactivation of ICa,L before IKr has had sufficient time to activate. CONCLUSIONS Ito heterogeneity creates both triggers and an arrhythmogenic substrate in LQT1. In the absence of IKs, Ito interactions with ICa,L and IKr promote EADs in the RV while prolonging action potential duration in the left ventricle. This heterogeneity of action potential enhances dispersion of refractoriness and facilitates conduction blocks that initiate pVTs.
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Affiliation(s)
- Bum-Rak Choi
- Cardiovascular Research Center, Division of Cardiology, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence (B.-R.C., W.L., D.T., A.Y.K., R.T., T.Y.K., G.K.).
| | - Weiyan Li
- Cardiovascular Research Center, Division of Cardiology, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence (B.-R.C., W.L., D.T., A.Y.K., R.T., T.Y.K., G.K.)
| | - Dmitry Terentyev
- Cardiovascular Research Center, Division of Cardiology, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence (B.-R.C., W.L., D.T., A.Y.K., R.T., T.Y.K., G.K.)
| | - Anatoli Y Kabakov
- Cardiovascular Research Center, Division of Cardiology, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence (B.-R.C., W.L., D.T., A.Y.K., R.T., T.Y.K., G.K.)
| | - Mingwang Zhong
- Department of Physics, Northeastern University, Boston MA (M.Z., C.M.R., A.K.)
| | - Colin M Rees
- Department of Physics, Northeastern University, Boston MA (M.Z., C.M.R., A.K.)
| | - Radmila Terentyeva
- Cardiovascular Research Center, Division of Cardiology, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence (B.-R.C., W.L., D.T., A.Y.K., R.T., T.Y.K., G.K.)
| | - Tae Yun Kim
- Cardiovascular Research Center, Division of Cardiology, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence (B.-R.C., W.L., D.T., A.Y.K., R.T., T.Y.K., G.K.)
| | - Zhilin Qu
- Department of Medicine (Cardiology), University of California, Los Angeles (Z.Q.)
| | - Xuwen Peng
- Department of Comparative Medicine, Pennsylvania State University College of Medicine, Hershey (X.P.)
| | - Alain Karma
- Department of Physics, Northeastern University, Boston MA (M.Z., C.M.R., A.K.)
| | - Gideon Koren
- Cardiovascular Research Center, Division of Cardiology, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence (B.-R.C., W.L., D.T., A.Y.K., R.T., T.Y.K., G.K.).
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72
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Xie A, Song Z, Liu H, Zhou A, Shi G, Wang Q, Gu L, Liu M, Xie LH, Qu Z, Dudley SC. Mitochondrial Ca 2+ Influx Contributes to Arrhythmic Risk in Nonischemic Cardiomyopathy. J Am Heart Assoc 2018; 7:JAHA.117.007805. [PMID: 29627768 PMCID: PMC6015427 DOI: 10.1161/jaha.117.007805] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Background Heart failure (HF) is associated with increased arrhythmia risk and triggered activity. Abnormal Ca2+ handling is thought to underlie triggered activity, and mitochondria participate in Ca2+ homeostasis. Methods and Results A model of nonischemic HF was induced in C57BL/6 mice by hypertension. Computer simulations were performed using a mouse ventricular myocyte model of HF. Isoproterenol‐induced premature ventricular contractions and ventricular fibrillation were more prevalent in nonischemic HF mice than sham controls. Isolated myopathic myocytes showed decreased cytoplasmic Ca2+ transients, increased mitochondrial Ca2+ transients, and increased action potential duration at 90% repolarization. The alteration of action potential duration at 90% repolarization was consistent with in vivo corrected QT prolongation and could be explained by augmented L‐type Ca2+ currents, increased Na+‐Ca2+ exchange currents, and decreased total K+ currents. Of myopathic ventricular myocytes, 66% showed early afterdepolarizations (EADs) compared with 17% of sham myocytes (P<0.05). Intracellular application of 1 μmol/L Ru360, a mitochondrial Ca2+ uniporter–specific antagonist, could reduce mitochondrial Ca2+ transients, decrease action potential duration at 90% repolarization, and ameliorate EADs. Furthermore, genetic knockdown of mitochondrial Ca2+ uniporters inhibited mitochondrial Ca2+ uptake, reduced Na+‐Ca2+ exchange currents, decreased action potential duration at 90% repolarization, suppressed EADs, and reduced ventricular fibrillation in nonischemic HF mice. Computer simulations showed that EADs promoted by HF remodeling could be abolished by blocking either the mitochondrial Ca2+ uniporter or the L‐type Ca2+ current, consistent with the experimental observations. Conclusions Mitochondrial Ca2+ handling plays an important role in EADs seen with nonischemic cardiomyopathy and may represent a therapeutic target to reduce arrhythmic risk in this condition.
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Affiliation(s)
- An Xie
- Department of Medicine, Lillehei Heart Institute, University of Minnesota, Minneapolis, MN
| | - Zhen Song
- Department of Medicine, David Geffen School of Medicine at University of California, Los Angeles, CA
| | - Hong Liu
- Department of Medicine, Lillehei Heart Institute, University of Minnesota, Minneapolis, MN
| | - Anyu Zhou
- Department of Medicine, Lillehei Heart Institute, University of Minnesota, Minneapolis, MN
| | - Guangbin Shi
- Department of Medicine, Lillehei Heart Institute, University of Minnesota, Minneapolis, MN
| | - Qiongying Wang
- Department of Medicine, Lillehei Heart Institute, University of Minnesota, Minneapolis, MN
| | - Lianzhi Gu
- Department of Medicine, Lillehei Heart Institute, University of Minnesota, Minneapolis, MN
| | - Man Liu
- Department of Medicine, Lillehei Heart Institute, University of Minnesota, Minneapolis, MN
| | - Lai-Hua Xie
- Department of Cell Biology and Molecular Medicine, New Jersey Medical School Rutgers, The State University of New Jersey, Newark, NJ
| | - Zhilin Qu
- Department of Medicine, David Geffen School of Medicine at University of California, Los Angeles, CA
| | - Samuel C Dudley
- Department of Medicine, Lillehei Heart Institute, University of Minnesota, Minneapolis, MN
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73
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Landaw J, Qu Z. Memory-induced nonlinear dynamics of excitation in cardiac diseases. Phys Rev E 2018; 97:042414. [PMID: 29758700 PMCID: PMC6542282 DOI: 10.1103/physreve.97.042414] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2017] [Indexed: 11/07/2022]
Abstract
Excitable cells, such as cardiac myocytes, exhibit short-term memory, i.e., the state of the cell depends on its history of excitation. Memory can originate from slow recovery of membrane ion channels or from accumulation of intracellular ion concentrations, such as calcium ion or sodium ion concentration accumulation. Here we examine the effects of memory on excitation dynamics in cardiac myocytes under two diseased conditions, early repolarization and reduced repolarization reserve, each with memory from two different sources: slow recovery of a potassium ion channel and slow accumulation of the intracellular calcium ion concentration. We first carry out computer simulations of action potential models described by differential equations to demonstrate complex excitation dynamics, such as chaos. We then develop iterated map models that incorporate memory, which accurately capture the complex excitation dynamics and bifurcations of the action potential models. Finally, we carry out theoretical analyses of the iterated map models to reveal the underlying mechanisms of memory-induced nonlinear dynamics. Our study demonstrates that the memory effect can be unmasked or greatly exacerbated under certain diseased conditions, which promotes complex excitation dynamics, such as chaos. The iterated map models reveal that memory converts a monotonic iterated map function into a nonmonotonic one to promote the bifurcations leading to high periodicity and chaos.
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Affiliation(s)
- Julian Landaw
- Department of Medicine (Cardiology), University of California, Los Angeles, California 90095, USA and Department of Biomathematics, University of California, Los Angeles, California 90095, USA
| | - Zhilin Qu
- Department of Medicine (Cardiology), University of California, Los Angeles, California 90095, USA and Department of Biomathematics, University of California, Los Angeles, California 90095, USA
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74
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Van Nieuwenhuyse E, Seemann G, Panfilov AV, Vandersickel N. Effects of early afterdepolarizations on excitation patterns in an accurate model of the human ventricles. PLoS One 2017; 12:e0188867. [PMID: 29216239 PMCID: PMC5720514 DOI: 10.1371/journal.pone.0188867] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2017] [Accepted: 11/14/2017] [Indexed: 12/17/2022] Open
Abstract
Early Afterdepolarizations, EADs, are defined as the reversal of the action potential before completion of the repolarization phase, which can result in ectopic beats. However, the series of mechanisms of EADs leading to these ectopic beats and related cardiac arrhythmias are not well understood. Therefore, we aimed to investigate the influence of this single cell behavior on the whole heart level. For this study we used a modified version of the Ten Tusscher-Panfilov model of human ventricular cells (TP06) which we implemented in a 3D ventricle model including realistic fiber orientations. To increase the likelihood of EAD formation at the single cell level, we reduced the repolarization reserve (RR) by reducing the rapid delayed rectifier Potassium current and raising the L-type Calcium current. Varying these parameters defined a 2D parametric space where different excitation patterns could be classified. Depending on the initial conditions, by either exciting the ventricles with a spiral formation or burst pacing protocol, we found multiple different spatio-temporal excitation patterns. The spiral formation protocol resulted in the categorization of a stable spiral (S), a meandering spiral (MS), a spiral break-up regime (SB), spiral fibrillation type B (B), spiral fibrillation type A (A) and an oscillatory excitation type (O). The last three patterns are a 3D generalization of previously found patterns in 2D. First, the spiral fibrillation type B showed waves determined by a chaotic bi-excitable regime, i.e. mediated by both Sodium and Calcium waves at the same time and in same tissue settings. In the parameter region governed by the B pattern, single cells were able to repolarize completely and different (spiral) waves chaotically burst into each other without finishing a 360 degree rotation. Second, spiral fibrillation type A patterns consisted of multiple small rotating spirals. Single cells failed to repolarize to the resting membrane potential hence prohibiting the Sodium channel gates to recover. Accordingly, we found that Calcium waves mediated these patterns. Third, a further reduction of the RR resulted in a more exotic parameter regime whereby the individual cells behaved independently as oscillators. The patterns arose due to a phase-shift of different oscillators as disconnection of the cells resulted in continuation of the patterns. For all patterns, we computed realistic 9 lead ECGs by including a torso model. The B and A type pattern exposed the behavior of Ventricular Tachycardia (VT). We conclude that EADs at the single cell level can result in different types of cardiac fibrillation at the tissue and 3D ventricle level.
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Affiliation(s)
| | - Gunnar Seemann
- Institute for Experimental Cardiovascular Medicine, University Heart Center Freiburg, Bad Krozingen, Germany
- Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | | | - Nele Vandersickel
- Department of Physics and Astronomy, Ghent University, Ghent, Belgium
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75
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Trenor B, Cardona K, Saiz J, Noble D, Giles W. Cardiac action potential repolarization revisited: early repolarization shows all-or-none behaviour. J Physiol 2017; 595:6599-6612. [PMID: 28815597 PMCID: PMC5663823 DOI: 10.1113/jp273651] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Accepted: 08/09/2017] [Indexed: 12/15/2022] Open
Abstract
In healthy mammalian hearts the action potential (AP) waveform initiates and modulates each contraction, or heartbeat. As a result, AP height and duration are key physiological variables. In addition, rate-dependent changes in ventricular AP duration (APD), and variations in APD at a fixed heart rate are both reliable biomarkers of electrophysiological stability. Present guidelines for the likelihood that candidate drugs will increase arrhythmias rely on small changes in APD and Q-T intervals as criteria for safety pharmacology decisions. However, both of these measurements correspond to the final repolarization of the AP. Emerging clinical evidence draws attention to the early repolarization phase of the action potential (and the J-wave of the ECG) as an additional important biomarker for arrhythmogenesis. Here we provide a mechanistic background to this early repolarization syndrome by summarizing the evidence that both the initial depolarization and repolarization phases of the cardiac action potential can exhibit distinct time- and voltage-dependent thresholds, and also demonstrating that both can show regenerative all-or-none behaviour. An important consequence of this is that not all of the dynamics of action potential repolarization in human ventricle can be captured by data from single myocytes when these results are expressed as 'repolarization reserve'. For example, the complex pattern of cell-to-cell current flow that is responsible for AP conduction (propagation) within the mammalian myocardium can change APD and the Q-T interval of the electrocardiogram alter APD stability, and modulate responsiveness to pharmacological agents (such as Class III anti-arrhythmic drugs).
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Affiliation(s)
- Beatriz Trenor
- Centro de Investigación e BioingenieríaUniversitat Politècnica de ValènciaValenciaSpain
| | - Karen Cardona
- Centro de Investigación e BioingenieríaUniversitat Politècnica de ValènciaValenciaSpain
| | - Javier Saiz
- Centro de Investigación e BioingenieríaUniversitat Politècnica de ValènciaValenciaSpain
| | - Denis Noble
- University Laboratory of PhysiologyUniversity of OxfordOxfordOX1 3PTUK
| | - Wayne Giles
- Faculties of Kinesiology and MedicineUniversity of CalgaryCalgaryAlbertaCanadaT2N 1N4
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76
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Hysteretic Dynamics of Multi-Stable Early Afterdepolarisations with Repolarisation Reserve Attenuation: A Potential Dynamical Mechanism for Cardiac Arrhythmias. Sci Rep 2017; 7:10771. [PMID: 28883639 PMCID: PMC5589958 DOI: 10.1038/s41598-017-11355-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2017] [Accepted: 08/23/2017] [Indexed: 02/08/2023] Open
Abstract
Some cardiovascular and non-cardiovascular drugs frequently cause excessive prolongation of the cardiac action potential (AP) and lead to the development of early afterdepolarisations (EADs), which trigger lethal ventricular arrhythmias. Combining computer simulations in APs with numerical calculations based on dynamical system theory, we investigated stability changes of APs observed in a paced human ventricular myocyte model by decreasing and/or increasing the rapid (IKr) and slow (IKs) components of delayed rectifying K+ current. Upon reducing IKr, the APs without EADs (no-EAD response) showed gradual prolongation of AP duration (APD), and were annihilated without AP configuration changes due to the occurrence of saddle-node bifurcations. This annihilation caused a transition to an AP with EADs as a new stable steady state. Furthermore, reducing repolarisation currents (repolarisation reserve attenuation) evoked multi-stable states consisting of APs with different APDs, and caused multiple hysteretic dynamics. Depending on initial ion circumstances within ventricular myocytes, these multi-stable AP states might increase the local/global heterogeneity of AP repolarisations in the ventricle. Thus, the EAD-induced arrhythmias with repolarisation reserve attenuation might be attributed to the APD variability caused by multi-stability in cardiac AP dynamics.
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77
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Dutta S, Chang KC, Beattie KA, Sheng J, Tran PN, Wu WW, Wu M, Strauss DG, Colatsky T, Li Z. Optimization of an In silico Cardiac Cell Model for Proarrhythmia Risk Assessment. Front Physiol 2017; 8:616. [PMID: 28878692 PMCID: PMC5572155 DOI: 10.3389/fphys.2017.00616] [Citation(s) in RCA: 100] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2017] [Accepted: 08/09/2017] [Indexed: 12/19/2022] Open
Abstract
Drug-induced Torsade-de-Pointes (TdP) has been responsible for the withdrawal of many drugs from the market and is therefore of major concern to global regulatory agencies and the pharmaceutical industry. The Comprehensive in vitro Proarrhythmia Assay (CiPA) was proposed to improve prediction of TdP risk, using in silico models and in vitro multi-channel pharmacology data as integral parts of this initiative. Previously, we reported that combining dynamic interactions between drugs and the rapid delayed rectifier potassium current (IKr) with multi-channel pharmacology is important for TdP risk classification, and we modified the original O'Hara Rudy ventricular cell mathematical model to include a Markov model of IKr to represent dynamic drug-IKr interactions (IKr-dynamic ORd model). We also developed a novel metric that could separate drugs with different TdP liabilities at high concentrations based on total electronic charge carried by the major inward ionic currents during the action potential. In this study, we further optimized the IKr-dynamic ORd model by refining model parameters using published human cardiomyocyte experimental data under control and drug block conditions. Using this optimized model and manual patch clamp data, we developed an updated version of the metric that quantifies the net electronic charge carried by major inward and outward ionic currents during the steady state action potential, which could classify the level of drug-induced TdP risk across a wide range of concentrations and pacing rates. We also established a framework to quantitatively evaluate a system's robustness against the induction of early afterdepolarizations (EADs), and demonstrated that the new metric is correlated with the cell's robustness to the pro-EAD perturbation of IKr conductance reduction. In summary, in this work we present an optimized model that is more consistent with experimental data, an improved metric that can classify drugs at concentrations both near and higher than clinical exposure, and a physiological framework to check the relationship between a metric and EAD. These findings provide a solid foundation for using in silico models for the regulatory assessment of TdP risk under the CiPA paradigm.
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Affiliation(s)
- Sara Dutta
- Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, U.S. Food and Drug AdministrationSilver Spring, MD, United States
| | - Kelly C Chang
- Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, U.S. Food and Drug AdministrationSilver Spring, MD, United States
| | - Kylie A Beattie
- Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, U.S. Food and Drug AdministrationSilver Spring, MD, United States
| | - Jiansong Sheng
- Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, U.S. Food and Drug AdministrationSilver Spring, MD, United States
| | - Phu N Tran
- Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, U.S. Food and Drug AdministrationSilver Spring, MD, United States
| | - Wendy W Wu
- Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, U.S. Food and Drug AdministrationSilver Spring, MD, United States
| | - Min Wu
- Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, U.S. Food and Drug AdministrationSilver Spring, MD, United States
| | - David G Strauss
- Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, U.S. Food and Drug AdministrationSilver Spring, MD, United States
| | - Thomas Colatsky
- Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, U.S. Food and Drug AdministrationSilver Spring, MD, United States
| | - Zhihua Li
- Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, U.S. Food and Drug AdministrationSilver Spring, MD, United States
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78
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Britton OJ, Abi-Gerges N, Page G, Ghetti A, Miller PE, Rodriguez B. Quantitative Comparison of Effects of Dofetilide, Sotalol, Quinidine, and Verapamil between Human Ex vivo Trabeculae and In silico Ventricular Models Incorporating Inter-Individual Action Potential Variability. Front Physiol 2017; 8:597. [PMID: 28868038 PMCID: PMC5563361 DOI: 10.3389/fphys.2017.00597] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2017] [Accepted: 08/02/2017] [Indexed: 01/20/2023] Open
Abstract
Background:In silico modeling could soon become a mainstream method of pro-arrhythmic risk assessment in drug development. However, a lack of human-specific data and appropriate modeling techniques has previously prevented quantitative comparison of drug effects between in silico models and recordings from human cardiac preparations. Here, we directly compare changes in repolarization biomarkers caused by dofetilide, dl-sotalol, quinidine, and verapamil, between in silico populations of human ventricular cell models and ex vivo human ventricular trabeculae. Methods and Results:Ex vivo recordings from human ventricular trabeculae in control conditions were used to develop populations of in silico human ventricular cell models that integrated intra- and inter-individual variability in action potential (AP) biomarker values. Models were based on the O'Hara-Rudy ventricular cardiomyocyte model, but integrated experimental AP variability through variation in underlying ionic conductances. Changes to AP duration, triangulation and early after-depolarization occurrence from application of the four drugs at multiple concentrations and pacing frequencies were compared between simulations and experiments. To assess the impact of variability in IC50 measurements, and the effects of including state-dependent drug binding dynamics, each drug simulation was repeated with two different IC50 datasets, and with both the original O'Hara-Rudy hERG model and a recently published state-dependent model of hERG and hERG block. For the selective hERG blockers dofetilide and sotalol, simulation predictions of AP prolongation and repolarization abnormality occurrence showed overall good agreement with experiments. However, for multichannel blockers quinidine and verapamil, simulations were not in agreement with experiments across all IC50 datasets and IKr block models tested. Quinidine simulations resulted in overprolonged APs and high incidence of repolarization abnormalities, which were not observed in experiments. Verapamil simulations showed substantial AP prolongation while experiments showed mild AP shortening. Conclusions: Results for dofetilide and sotalol show good agreement between experiments and simulations for selective compounds, however lack of agreement from simulations of quinidine and verapamil suggest further work is needed to understand the more complex electrophysiological effects of these multichannel blocking drugs.
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Affiliation(s)
- Oliver J. Britton
- Department of Computer Science, University of OxfordOxford, United Kingdom
| | | | - Guy Page
- AnaBios CorporationSan Diego, CA, United States
| | | | | | - Blanca Rodriguez
- Department of Computer Science, University of OxfordOxford, United Kingdom
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Abstract
Our sense of hearing boasts exquisite sensitivity, precise frequency discrimination, and a broad dynamic range. Experiments and modeling imply, however, that the auditory system achieves this performance for only a narrow range of parameter values. Small changes in these values could compromise hair cells' ability to detect stimuli. We propose that, rather than exerting tight control over parameters, the auditory system uses a homeostatic mechanism that increases the robustness of its operation to variation in parameter values. To slowly adjust the response to sinusoidal stimulation, the homeostatic mechanism feeds back a rectified version of the hair bundle's displacement to its adaptation process. When homeostasis is enforced, the range of parameter values for which the sensitivity, tuning sharpness, and dynamic range exceed specified thresholds can increase by more than an order of magnitude. Signatures in the hair cell's behavior provide a means to determine through experiment whether such a mechanism operates in the auditory system. Robustness of function through homeostasis may be ensured in any system through mechanisms similar to those that we describe here.
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80
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Osadchii OE. Role of abnormal repolarization in the mechanism of cardiac arrhythmia. Acta Physiol (Oxf) 2017; 220 Suppl 712:1-71. [PMID: 28707396 DOI: 10.1111/apha.12902] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
In cardiac patients, life-threatening tachyarrhythmia is often precipitated by abnormal changes in ventricular repolarization and refractoriness. Repolarization abnormalities typically evolve as a consequence of impaired function of outward K+ currents in cardiac myocytes, which may be caused by genetic defects or result from various acquired pathophysiological conditions, including electrical remodelling in cardiac disease, ion channel modulation by clinically used pharmacological agents, and systemic electrolyte disorders seen in heart failure, such as hypokalaemia. Cardiac electrical instability attributed to abnormal repolarization relies on the complex interplay between a provocative arrhythmic trigger and vulnerable arrhythmic substrate, with a central role played by the excessive prolongation of ventricular action potential duration, impaired intracellular Ca2+ handling, and slowed impulse conduction. This review outlines the electrical activity of ventricular myocytes in normal conditions and cardiac disease, describes classical electrophysiological mechanisms of cardiac arrhythmia, and provides an update on repolarization-related surrogates currently used to assess arrhythmic propensity, including spatial dispersion of repolarization, activation-repolarization coupling, electrical restitution, TRIaD (triangulation, reverse use dependence, instability, and dispersion), and the electromechanical window. This is followed by a discussion of the mechanisms that account for the dependence of arrhythmic vulnerability on the location of the ventricular pacing site. Finally, the review clarifies the electrophysiological basis for cardiac arrhythmia produced by hypokalaemia, and gives insight into the clinical importance and pathophysiology of drug-induced arrhythmia, with particular focus on class Ia (quinidine, procainamide) and Ic (flecainide) Na+ channel blockers, and class III antiarrhythmic agents that block the delayed rectifier K+ channel (dofetilide).
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Affiliation(s)
- O. E. Osadchii
- Department of Health Science and Technology; University of Aalborg; Aalborg Denmark
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81
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Hegyi B, Horváth B, Váczi K, Gönczi M, Kistamás K, Ruzsnavszky F, Veress R, Izu LT, Chen-Izu Y, Bányász T, Magyar J, Csernoch L, Nánási PP, Szentandrássy N. Ca 2+-activated Cl - current is antiarrhythmic by reducing both spatial and temporal heterogeneity of cardiac repolarization. J Mol Cell Cardiol 2017; 109:27-37. [PMID: 28668303 DOI: 10.1016/j.yjmcc.2017.06.014] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/12/2017] [Revised: 06/26/2017] [Accepted: 06/28/2017] [Indexed: 01/26/2023]
Abstract
The role of Ca2+-activated Cl- current (ICl(Ca)) in cardiac arrhythmias is still controversial. It can generate delayed afterdepolarizations in Ca2+-overloaded cells while in other studies incidence of early afterdepolarization (EAD) was reduced by ICl(Ca). Therefore our goal was to examine the role of ICl(Ca) in spatial and temporal heterogeneity of cardiac repolarization and EAD formation. Experiments were performed on isolated canine cardiomyocytes originating from various regions of the left ventricle; subepicardial, midmyocardial and subendocardial cells, as well as apical and basal cells of the midmyocardium. ICl(Ca) was blocked by 0.5mmol/L 9-anthracene carboxylic acid (9-AC). Action potential (AP) changes were tested with sharp microelectrode recording. Whole-cell 9-AC-sensitive current was measured with either square pulse voltage-clamp or AP voltage-clamp (APVC). Protein expression of TMEM16A and Bestrophin-3, ion channel proteins mediating ICl(Ca), was detected by Western blot. 9-AC reduced phase-1 repolarization in every tested cell. 9-AC also increased AP duration in a reverse rate-dependent manner in all cell types except for subepicardial cells. Neither ICl(Ca) density recorded with square pulses nor the normalized expressions of TMEM16A and Bestrophin-3 proteins differed significantly among the examined groups of cells. The early outward component of ICl(Ca) was significantly larger in subepicardial than in subendocardial cells in APVC setting. Applying a typical subepicardial AP as a command pulse resulted in a significantly larger early outward component in both subepicardial and subendocardial cells, compared to experiments when a typical subendocardial AP was applied. Inhibiting ICl(Ca) by 9-AC generated EADs at low stimulation rates and their incidence increased upon beta-adrenergic stimulation. 9-AC increased the short-term variability of repolarization also. We suggest a protective role for ICl(Ca) against risk of arrhythmias by reducing spatial and temporal heterogeneity of cardiac repolarization and EAD formation.
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Affiliation(s)
- Bence Hegyi
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary; Department of Pharmacology, Genome and Biomedical Science Facility, University of California, Davis, 451 Health Sciences Drive, Rm 3503, Davis, CA 95616, USA
| | - Balázs Horváth
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary; Faculty of Pharmacy, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
| | - Krisztina Váczi
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
| | - Mónika Gönczi
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary; MTA-DE Momentum, Laboratory of Protein Dynamics, Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
| | - Kornél Kistamás
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
| | - Ferenc Ruzsnavszky
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
| | - Roland Veress
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
| | - Leighton T Izu
- Faculty of Pharmacy, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
| | - Ye Chen-Izu
- Faculty of Pharmacy, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary; Department of Biomedical Engineering, Genome and Biomedical Science Facility, University of California, Davis, 451 Health Sciences Drive, Rm 2303, Davis, CA 95616, USA; Department of Internal Medicine, Division of Cardiology, Genome and Biomedical Science Facility, University of California, Davis, 451 Health Sciences Drive, Rm 6315, Davis, CA 95616, USA
| | - Tamás Bányász
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
| | - János Magyar
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary; Division of Sport Physiology, Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
| | - László Csernoch
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
| | - Péter P Nánási
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary; Department of Dental Physiology and Pharmacology, Faculty of Dentistry, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary.
| | - Norbert Szentandrássy
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary; Department of Dental Physiology and Pharmacology, Faculty of Dentistry, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
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82
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Vandersickel N, Van Nieuwenhuyse E, Seemann G, Panfilov AV. Spatial Patterns of Excitation at Tissue and Whole Organ Level Due to Early Afterdepolarizations. Front Physiol 2017; 8:404. [PMID: 28690545 PMCID: PMC5479889 DOI: 10.3389/fphys.2017.00404] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2017] [Accepted: 05/29/2017] [Indexed: 01/08/2023] Open
Abstract
Early after depolarizations (EAD) occur in many pathological conditions, such as congenital or acquired channelopathies, drug induced arrhythmias, and several other situations that are associated with increased arrhythmogenicity. In this paper we present an overview of the relevant computational studies on spatial EAD dynamics in 1D, 2D, and in 3D anatomical models and discuss the relation of EADs to cardiac arrhythmias. We also discuss unsolved problems and highlight new lines of research in this area.
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Affiliation(s)
| | | | - Gunnar Seemann
- Institute for Experimental Cardiovascular Medicine, University Heart Center Freiburg · Bad Krozingen, Medical Center, University of FreiburgFreiburg, Germany.,Faculty of Medicine, University of FreiburgFreiburg, Germany
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83
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Colman MA, Ni H, Liang B, Schmitt N, Zhang H. In silico assessment of genetic variation in KCNA5 reveals multiple mechanisms of human atrial arrhythmogenesis. PLoS Comput Biol 2017. [PMID: 28622331 PMCID: PMC5493429 DOI: 10.1371/journal.pcbi.1005587] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
A recent experimental study investigating patients with lone atrial fibrillation identified six novel mutations in the KCNA5 gene. The mutants exhibited both gain- and loss-of-function of the atrial specific ultra-rapid delayed rectifier K+ current, IKur. The aim of this study is to elucidate and quantify the functional impact of these KCNA5 mutations on atrial electrical activity. A multi-scale model of the human atria was updated to incorporate detailed experimental data on IKur from both wild-type and mutants. The effects of the mutations on human atrial action potential and rate dependence were investigated at the cellular level. In tissue, we assessed the effects of the mutations on the vulnerability to unidirectional conduction patterns and dynamics of re-entrant excitation waves. Gain-of-function mutations shortened the action potential duration in single cells, and stabilised and accelerated re-entrant excitation in tissue. Loss-of-function mutations had heterogeneous effects on action potential duration and promoted early-after-depolarisations following beta-adrenergic stimulation. In the tissue model, loss-of-function mutations facilitated breakdown of excitation waves at more physiological excitation rates than the wild-type, and the generation of early-after-depolarisations promoted unidirectional patterns of excitation. Gain- and loss-of-function IKur mutations produced multiple mechanisms of atrial arrhythmogenesis, with significant differences between the two groups of mutations. This study provides new insights into understanding the mechanisms by which mutant IKur contributes to atrial arrhythmias. In addition, as IKur is an atrial-specific channel and a number of IKur-selective blockers have been developed as anti-AF agents, this study also helps to understand some contradictory results on both pro- and anti-arrhythmic effects of blocking IKur. In a recent study, six mutations resulting in either gain-of-function or loss-of-function in the ultra-rapid delayed rectifier potassium current IKur, were identified to be associated with atrial fibrillation (AF). However, the causative link between the mutant IKur (either gain- or loss-of-function) and AF genesis, especially the difference and similarity between the two mutant groups, has not been elucidated. In our study, we used multiscale computational models to investigate the mechanism of arrhythmogenesis mediated by the two groups of mutations. The results suggest that the gain-of-function mutations shortened atrial action potential duration, stabilised and accelerated re-entrant excitation waves in tissue; the loss-of-function mutation promoted early-after-depolarisations following beta-adrenergic stimulation and thus wave breaks in tissue. We show these two groups of mutants carrying IKur produced multiple mechanisms of atrial arrhythmogenesis, with significant differences between the two groups. Our study provides new insights into understanding the mechanisms by which mutant IKur contributes to atrial arrhythmias. In addition, as IKur is an atrial-specific channel and a number of IKur-selective blockers have been developed as anti-AF agents, this study also helps to understand some contradictory results on both pro- and anti-arrhythmic effects of blocking IKur.
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Affiliation(s)
- Michael A. Colman
- Biological Physics Group, School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom
- School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
| | - Haibo Ni
- Biological Physics Group, School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom
| | - Bo Liang
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Nicole Schmitt
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Henggui Zhang
- Biological Physics Group, School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom
- School of Computer Science and Technology, Harbin Institute of Technology, Harbin, China
- * E-mail:
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84
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Li Z, Dutta S, Sheng J, Tran PN, Wu W, Chang K, Mdluli T, Strauss DG, Colatsky T. Improving the In Silico Assessment of Proarrhythmia Risk by Combining hERG (Human Ether-à-go-go-Related Gene) Channel-Drug Binding Kinetics and Multichannel Pharmacology. Circ Arrhythm Electrophysiol 2017; 10:e004628. [PMID: 28202629 DOI: 10.1161/circep.116.004628] [Citation(s) in RCA: 114] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/01/2016] [Accepted: 01/19/2017] [Indexed: 11/16/2022]
Abstract
BACKGROUND The current proarrhythmia safety testing paradigm, although highly efficient in preventing new torsadogenic drugs from entering the market, has important limitations that can restrict the development and use of valuable new therapeutics. The CiPA (Comprehensive in vitro Proarrhythmia Assay) proposes to overcome these limitations by evaluating drug effects on multiple cardiac ion channels in vitro and using these data in a predictive in silico model of the adult human ventricular myocyte. A set of drugs with known clinical torsade de pointes risk was selected to develop and calibrate the in silico model. METHODS AND RESULTS Manual patch-clamp data assessing drug effects on expressed cardiac ion channels were integrated into the O'Hara-Rudy myocyte model modified to include dynamic drug-hERG channel (human Ether-à-go-go-Related Gene) interactions. Together with multichannel pharmacology data, this model predicts that compounds with high torsadogenic risk are more likely to be trapped within the hERG channel and show stronger reverse use dependency of action potential prolongation. Furthermore, drug-induced changes in the amount of electronic charge carried by the late sodium and L-type calcium currents was evaluated as a potential metric for assigning torsadogenic risk. CONCLUSIONS Modeling dynamic drug-hERG channel interactions and multi-ion channel pharmacology improves the prediction of torsadogenic risk. With further development, these methods have the potential to improve the regulatory assessment of drug safety models under the CiPA paradigm.
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Affiliation(s)
- Zhihua Li
- From the Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, US Food and Drug Administration, Silver Spring, MD.
| | - Sara Dutta
- From the Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, US Food and Drug Administration, Silver Spring, MD
| | - Jiansong Sheng
- From the Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, US Food and Drug Administration, Silver Spring, MD
| | - Phu N Tran
- From the Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, US Food and Drug Administration, Silver Spring, MD
| | - Wendy Wu
- From the Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, US Food and Drug Administration, Silver Spring, MD
| | - Kelly Chang
- From the Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, US Food and Drug Administration, Silver Spring, MD
| | - Thembi Mdluli
- From the Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, US Food and Drug Administration, Silver Spring, MD
| | - David G Strauss
- From the Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, US Food and Drug Administration, Silver Spring, MD
| | - Thomas Colatsky
- From the Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, US Food and Drug Administration, Silver Spring, MD
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85
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Ocorr K, Zambon A, Nudell Y, Pineda S, Diop S, Tang M, Akasaka T, Taylor E. Age-dependent electrical and morphological remodeling of the Drosophila heart caused by hERG/seizure mutations. PLoS Genet 2017; 13:e1006786. [PMID: 28542428 PMCID: PMC5459509 DOI: 10.1371/journal.pgen.1006786] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2016] [Revised: 06/05/2017] [Accepted: 04/30/2017] [Indexed: 12/03/2022] Open
Abstract
Understanding the cellular-molecular substrates of heart disease is key to the development of cardiac specific therapies and to the prevention of off-target effects by non-cardiac targeted drugs. One of the primary targets for therapeutic intervention has been the human ether a go-go (hERG) K+ channel that, together with the KCNQ channel, controls the rate and efficiency of repolarization in human myocardial cells. Neither of these channels plays a major role in adult mouse heart function; however, we show here that the hERG homolog seizure (sei), along with KCNQ, both contribute significantly to adult heart function as they do in humans. In Drosophila, mutations in or cardiac knockdown of sei channels cause arrhythmias that become progressively more severe with age. Intracellular recordings of semi-intact heart preparations revealed that these perturbations also cause electrical remodeling that is reminiscent of the early afterdepolarizations seen in human myocardial cells defective in these channels. In contrast to KCNQ, however, mutations in sei also cause extensive structural remodeling of the myofibrillar organization, which suggests that hERG channel function has a novel link to sarcomeric and myofibrillar integrity. We conclude that deficiency of ion channels with similar electrical functions in cardiomyocytes can lead to different types or extents of electrical and/or structural remodeling impacting cardiac output. We have used the fruit fly cardiac model to show that seizure, the fly homolog of the human ether a go-go K+ channel hERG, is functional in the fly heart. This channel plays a major role in cardiac repolarization in humans but not in adult rodent hearts. Loss of channel function in the fly causes bradycardia, electrical arrhythmia and altered myofibrillar structure. Gene expression analysis indicates that Wnt signaling is affected and we show a genetic interaction between sei and pygopus, a Wnt pathway component, on heart function.
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Affiliation(s)
- Karen Ocorr
- Development, Aging and Regeneration Program, Sanford-Burnham-Prebys Medical Discovery Institute, La Jolla, California, United States of America
- * E-mail:
| | - Alexander Zambon
- Development, Aging and Regeneration Program, Sanford-Burnham-Prebys Medical Discovery Institute, La Jolla, California, United States of America
| | - Yoav Nudell
- Development, Aging and Regeneration Program, Sanford-Burnham-Prebys Medical Discovery Institute, La Jolla, California, United States of America
| | - Santiago Pineda
- Development, Aging and Regeneration Program, Sanford-Burnham-Prebys Medical Discovery Institute, La Jolla, California, United States of America
| | - Soda Diop
- Development, Aging and Regeneration Program, Sanford-Burnham-Prebys Medical Discovery Institute, La Jolla, California, United States of America
| | - Min Tang
- Development, Aging and Regeneration Program, Sanford-Burnham-Prebys Medical Discovery Institute, La Jolla, California, United States of America
| | - Takeshi Akasaka
- Development, Aging and Regeneration Program, Sanford-Burnham-Prebys Medical Discovery Institute, La Jolla, California, United States of America
| | - Erika Taylor
- Development, Aging and Regeneration Program, Sanford-Burnham-Prebys Medical Discovery Institute, La Jolla, California, United States of America
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86
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Period doubling cascades of limit cycles in cardiac action potential models as precursors to chaotic early Afterdepolarizations. BMC SYSTEMS BIOLOGY 2017; 11:42. [PMID: 28376924 PMCID: PMC5379775 DOI: 10.1186/s12918-017-0422-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/06/2016] [Accepted: 03/24/2017] [Indexed: 12/02/2022]
Abstract
Background Early afterdepolarizations (EADs) are pathological voltage oscillations during the repolarization phase of cardiac action potentials (APs). EADs are caused by drugs, oxidative stress or ion channel disease, and they are considered as potential precursors to cardiac arrhythmias in recent attempts to redefine the cardiac drug safety paradigm. The irregular behaviour of EADs observed in experiments has been previously attributed to chaotic EAD dynamics under periodic pacing, made possible by a homoclinic bifurcation in the fast subsystem of the deterministic AP system of differential equations. Results In this article we demonstrate that a homoclinic bifurcation in the fast subsystem of the action potential model is neither a necessary nor a sufficient condition for the genesis of chaotic EADs. We rather argue that a cascade of period doubling (PD) bifurcations of limit cycles in the full AP system paves the way to chaotic EAD dynamics across a variety of models including a) periodically paced and spontaneously active cardiomyocytes, b) periodically paced and non-active cardiomyocytes as well as c) unpaced and spontaneously active cardiomyocytes. Furthermore, our bifurcation analysis reveals that chaotic EAD dynamics may coexist in a stable manner with fully regular AP dynamics, where only the initial conditions decide which type of dynamics is displayed. Conclusions EADs are a potential source of cardiac arrhythmias and hence are of relevance both from the viewpoint of drug cardiotoxicity testing and the treatment of cardiomyopathies. The model-independent association of chaotic EADs with period doubling cascades of limit cycles introduced in this article opens novel opportunities to study chaotic EADs by means of bifurcation control theory and inverse bifurcation analysis. Furthermore, our results may shed new light on the synchronization and propagation of chaotic EADs in homogeneous and heterogeneous multicellular and cardiac tissue preparations. Electronic supplementary material The online version of this article (doi:10.1186/s12918-017-0422-4) contains supplementary material, which is available to authorized users.
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87
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Karagueuzian HS, Pezhouman A, Angelini M, Olcese R. Enhanced Late Na and Ca Currents as Effective Antiarrhythmic Drug Targets. Front Pharmacol 2017; 8:36. [PMID: 28220073 PMCID: PMC5292429 DOI: 10.3389/fphar.2017.00036] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Accepted: 01/18/2017] [Indexed: 11/30/2022] Open
Abstract
While recent advances clarified the molecular and cellular modes of action of antiarrhythmic drugs (AADs), their link to suppression of dynamical arrhythmia mechanisms remains only partially understood. The current classifications of AADs (Classes I, III, and IV) rely on blocking peak Na, K and L-type calcium currents (ICa,L), with Class II with dominant beta receptor blocking activity and Class V including drugs with diverse classes of actions. The discovery that the calcium and redox sensor, cardiac Ca/calmodulin-dependent protein kinase II (CaMKII) enhances both the late Na (INa-L) and the late ICa,L in patients at high risk of VT/VF provided a new and a rational AAD target. Pathological rise of either or both of INa-L and late ICa,L are demonstrated to promote cellular early afterdepolarizations (EADs) and EAD-mediated triggered activity that can initiate VT/VF in remodeled hearts. Selective inhibition of the INa-L without affecting their peak transients with the highly specific prototype drug, GS-967 suppresses these EAD-mediated VT/VFs. As in the case of INa-L, selective inhibition of the late ICa,L without affecting its peak with the prototype drug, roscovitine suppressed oxidative EAD-mediated VT/VF. These findings indicate that specific blockers of the late inward currents without affecting their peaks (gating modifiers), offer a new and effective AAD class action i.e., “Class VI.” The development of safe drugs with selective Class VI actions provides a rational and effective approach to treat VT/VF particularly in cardiac conditions associated with enhanced CaMKII activity such as heart failure.
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Affiliation(s)
- Hrayr S Karagueuzian
- Translational Arrhythmia Section, David Geffen School of Medicine, University of California, Los AngelesLos Angeles, CA, USA; Cardiovascular Research Laboratory, Departments of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los AngelesLos Angeles, CA, USA
| | - Arash Pezhouman
- Translational Arrhythmia Section, David Geffen School of Medicine, University of California, Los AngelesLos Angeles, CA, USA; Cardiovascular Research Laboratory, Departments of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los AngelesLos Angeles, CA, USA
| | - Marina Angelini
- Department of Anesthesiology and Perioperative Medicine, David Geffen School of Medicine, University of California, Los Angeles Los Angeles, CA, USA
| | - Riccardo Olcese
- Cardiovascular Research Laboratory, Departments of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los AngelesLos Angeles, CA, USA; Department of Anesthesiology and Perioperative Medicine, David Geffen School of Medicine, University of California, Los AngelesLos Angeles, CA, USA; Department of Physiology, David Geffen School of Medicine, University of California, Los AngelesLos Angeles, CA, USA
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88
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Devenyi RA, Ortega FA, Groenendaal W, Krogh-Madsen T, Christini DJ, Sobie EA. Differential roles of two delayed rectifier potassium currents in regulation of ventricular action potential duration and arrhythmia susceptibility. J Physiol 2016; 595:2301-2317. [PMID: 27779762 DOI: 10.1113/jp273191] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Accepted: 10/18/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Arrhythmias result from disruptions to cardiac electrical activity, although the factors that control cellular action potentials are incompletely understood. We combined mathematical modelling with experiments in heart cells from guinea pigs to determine how cellular electrical activity is regulated. A mismatch between modelling predictions and the experimental results allowed us to construct an improved, more predictive mathematical model. The balance between two particular potassium currents dictates how heart cells respond to perturbations and their susceptibility to arrhythmias. ABSTRACT Imbalances of ionic currents can destabilize the cardiac action potential and potentially trigger lethal cardiac arrhythmias. In the present study, we combined mathematical modelling with information-rich dynamic clamp experiments to determine the regulation of action potential morphology in guinea pig ventricular myocytes. Parameter sensitivity analysis was used to predict how changes in ionic currents alter action potential duration, and these were tested experimentally using dynamic clamp, a technique that allows for multiple perturbations to be tested in each cell. Surprisingly, we found that a leading mathematical model, developed with traditional approaches, systematically underestimated experimental responses to dynamic clamp perturbations. We then re-parameterized the model using a genetic algorithm, which allowed us to estimate ionic current levels in each of the cells studied. This unbiased model adjustment consistently predicted an increase in the rapid delayed rectifier K+ current and a drastic decrease in the slow delayed rectifier K+ current, and this prediction was validated experimentally. Subsequent simulations with the adjusted model generated the clinically relevant prediction that the slow delayed rectifier is better able to stabilize the action potential and suppress pro-arrhythmic events than the rapid delayed rectifier. In summary, iterative coupling of simulations and experiments enabled novel insight into how the balance between cardiac K+ currents influences ventricular arrhythmia susceptibility.
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Affiliation(s)
- Ryan A Devenyi
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Francis A Ortega
- Physiology, Biophysics, and Systems Biology Graduate Program, Weill Cornell Graduate School, New York, NY, USA
| | - Willemijn Groenendaal
- Greenberg Division of Cardiology, Weill Cornell Medical College, New York, NY, USA.,IMEC, Holst Centre, Eindhoven, The Netherlands
| | - Trine Krogh-Madsen
- Greenberg Division of Cardiology, Weill Cornell Medical College, New York, NY, USA
| | - David J Christini
- Physiology, Biophysics, and Systems Biology Graduate Program, Weill Cornell Graduate School, New York, NY, USA.,Greenberg Division of Cardiology, Weill Cornell Medical College, New York, NY, USA
| | - Eric A Sobie
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, USA
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89
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Kurata Y, Tsumoto K, Hayashi K, Hisatome I, Tanida M, Kuda Y, Shibamoto T. Dynamical mechanisms of phase-2 early afterdepolarizations in human ventricular myocytes: insights from bifurcation analyses of two mathematical models. Am J Physiol Heart Circ Physiol 2016; 312:H106-H127. [PMID: 27836893 DOI: 10.1152/ajpheart.00115.2016] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/02/2016] [Revised: 11/08/2016] [Accepted: 11/08/2016] [Indexed: 01/16/2023]
Abstract
Early afterdepolarization (EAD) is known as a cause of ventricular arrhythmias in long QT syndromes. We theoretically investigated how the rapid (IKr) and slow (IKs) components of delayed-rectifier K+ channel currents, L-type Ca2+ channel current (ICaL), Na+/Ca2+ exchanger current (INCX), Na+-K+ pump current (INaK), intracellular Ca2+ (Cai) handling via sarcoplasmic reticulum (SR), and intracellular Na+ concentration (Nai) contribute to initiation, termination, and modulation of phase-2 EADs, using two human ventricular myocyte models. Bifurcation structures of dynamical behaviors in model cells were explored by calculating equilibrium points, limit cycles (LCs), and bifurcation points as functions of parameters. EADs were reproduced by numerical simulations. The results are summarized as follows: 1) decreasing IKs and/or IKr or increasing ICaL led to EAD generation, to which mid-myocardial cell models were especially susceptible; the parameter regions of EADs overlapped the regions of stable LCs. 2) Two types of EADs (termination mechanisms), IKs activation-dependent and ICaL inactivation-dependent EADs, were detected; IKs was not necessarily required for EAD formation. 3) Inhibiting INCX suppressed EADs via facilitating Ca2+-dependent ICaL inactivation. 4) Cai dynamics (SR Ca2+ handling) and Nai strongly affected bifurcations and EAD generation in model cells via modulating ICaL, INCX, and INaK Parameter regions of EADs, often overlapping those of stable LCs, shifted depending on Cai and Nai in stationary and dynamic states. 5) Bradycardia-related induction of EADs was mainly due to decreases in Nai at lower pacing rates. This study demonstrates that bifurcation analysis allows us to understand the dynamical mechanisms of EAD formation more profoundly. NEW & NOTEWORTHY We investigated mechanisms of phase-2 early afterdepolarization (EAD) by bifurcation analyses of human ventricular myocyte (HVM) models. EAD formation in paced HVMs basically depended on bifurcation phenomena in non-paced HVMs, but was strongly affected by intracellular ion concentrations in stationary and dynamic states. EAD generation did not necessarily require IKs.
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Affiliation(s)
- Yasutaka Kurata
- Department of Physiology, Kanazawa Medical University, Ishikawa, Japan;
| | - Kunichika Tsumoto
- Department of Pharmacology, Graduate School of Medicine, Osaka University, Osaka, Japan
| | - Kenshi Hayashi
- Division of Cardiovascular Medicine, Kanazawa University Graduate School of Medicine, Kanazawa, Japan; and
| | - Ichiro Hisatome
- Department of Genetic Medicine and Regenerative Therapeutics, Tottori University Graduate School of Medical Science, Yonago, Japan
| | - Mamoru Tanida
- Department of Physiology, Kanazawa Medical University, Ishikawa, Japan
| | - Yuhichi Kuda
- Department of Physiology, Kanazawa Medical University, Ishikawa, Japan
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90
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Le Page S, Niro M, Fauconnier J, Cellier L, Tamareille S, Gharib A, Chevrollier A, Loufrani L, Grenier C, Kamel R, Sarzi E, Lacampagne A, Ovize M, Henrion D, Reynier P, Lenaers G, Mirebeau-Prunier D, Prunier F. Increase in Cardiac Ischemia-Reperfusion Injuries in Opa1+/- Mouse Model. PLoS One 2016; 11:e0164066. [PMID: 27723783 PMCID: PMC5056696 DOI: 10.1371/journal.pone.0164066] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2016] [Accepted: 09/19/2016] [Indexed: 11/21/2022] Open
Abstract
Background Recent data suggests the involvement of mitochondrial dynamics in cardiac ischemia/reperfusion (I/R) injuries. Whilst excessive mitochondrial fission has been described as detrimental, the role of fusion proteins in this context remains uncertain. Objectives To investigate whether Opa1 (protein involved in mitochondrial inner-membrane fusion) deficiency affects I/R injuries. Methods and Results We examined mice exhibiting Opa1delTTAG mutations (Opa1+/-), showing 70% Opa1 protein expression in the myocardium as compared to their wild-type (WT) littermates. Cardiac left-ventricular systolic function assessed by means of echocardiography was observed to be similar in 3-month-old WT and Opa1+/- mice. After subjection to I/R, infarct size was significantly greater in Opa1+/- than in WTs both in vivo (43.2±4.1% vs. 28.4±3.5%, respectively; p<0.01) and ex vivo (71.1±3.2% vs. 59.6±8.5%, respectively; p<0.05). No difference was observed in the expression of other main fission/fusion protein, oxidative phosphorylation, apoptotic markers, or mitochondrial permeability transition pore (mPTP) function. Analysis of calcium transients in isolated ventricular cardiomyocytes demonstrated a lower sarcoplasmic reticulum Ca2+ uptake, whereas cytosolic Ca2+ removal from the Na+/Ca2+ exchanger (NCX) was increased, whilst SERCA2a, phospholamban, and NCX protein expression levels were unaffected in Opa1+/- compared to WT mice. Simultaneous whole-cell patch-clamp recordings of mitochondrial Ca2+ movements and ventricular action potential (AP) showed impairment of dynamic mitochondrial Ca2+ uptake and a marked increase in the AP late repolarization phase in conjunction with greater occurrence of arrhythmia in Opa1+/- mice. Conclusion Opa1 deficiency was associated with increased sensitivity to I/R, imbalance in dynamic mitochondrial Ca2+ uptake, and subsequent increase in NCX activity.
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Affiliation(s)
- Sophie Le Page
- Institut MITOVASC, Université Angers, CHU Angers, Angers, France
- Laboratoire Cardioprotection Remodelage et Thrombose, Angers, France
- Service de Cardiologie, CHU Angers, Angers, France
| | - Marjorie Niro
- Institut MITOVASC, Université Angers, CHU Angers, Angers, France
- Laboratoire Cardioprotection Remodelage et Thrombose, Angers, France
- Service de Cardiologie, CHU Angers, Angers, France
| | | | - Laura Cellier
- Institut MITOVASC, Université Angers, CHU Angers, Angers, France
- Laboratoire Cardioprotection Remodelage et Thrombose, Angers, France
| | - Sophie Tamareille
- Institut MITOVASC, Université Angers, CHU Angers, Angers, France
- Laboratoire Cardioprotection Remodelage et Thrombose, Angers, France
| | | | - Arnaud Chevrollier
- Institut MITOVASC, Université Angers, CHU Angers, Angers, France
- INSERM UMR_S1083, CNRS UMR_C6214, BNMI, Angers, France
| | - Laurent Loufrani
- Institut MITOVASC, Université Angers, CHU Angers, Angers, France
- INSERM UMR_S1083, CNRS UMR_C6214, BNMI, Angers, France
| | - Céline Grenier
- Institut MITOVASC, Université Angers, CHU Angers, Angers, France
- INSERM UMR_S1083, CNRS UMR_C6214, BNMI, Angers, France
| | - Rima Kamel
- Institut MITOVASC, Université Angers, CHU Angers, Angers, France
- Laboratoire Cardioprotection Remodelage et Thrombose, Angers, France
| | - Emmanuelle Sarzi
- Institut des Neurosciences de Montpellier, INSERM U1051, Université Montpellier I et II, Montpellier, France
| | - Alain Lacampagne
- INSERM U1046, Université Montpellier I et II, Montpellier, France
| | | | - Daniel Henrion
- Institut MITOVASC, Université Angers, CHU Angers, Angers, France
- INSERM UMR_S1083, CNRS UMR_C6214, BNMI, Angers, France
| | - Pascal Reynier
- Institut MITOVASC, Université Angers, CHU Angers, Angers, France
- INSERM UMR_S1083, CNRS UMR_C6214, BNMI, Angers, France
| | - Guy Lenaers
- Institut MITOVASC, Université Angers, CHU Angers, Angers, France
- INSERM UMR_S1083, CNRS UMR_C6214, BNMI, Angers, France
| | - Delphine Mirebeau-Prunier
- Institut MITOVASC, Université Angers, CHU Angers, Angers, France
- INSERM UMR_S1083, CNRS UMR_C6214, BNMI, Angers, France
| | - Fabrice Prunier
- Institut MITOVASC, Université Angers, CHU Angers, Angers, France
- Laboratoire Cardioprotection Remodelage et Thrombose, Angers, France
- Service de Cardiologie, CHU Angers, Angers, France
- * E-mail:
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91
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Huang X, Kim TY, Koren G, Choi BR, Qu Z. Spontaneous initiation of premature ventricular complexes and arrhythmias in type 2 long QT syndrome. Am J Physiol Heart Circ Physiol 2016; 311:H1470-H1484. [PMID: 27765749 DOI: 10.1152/ajpheart.00500.2016] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2016] [Accepted: 10/03/2016] [Indexed: 02/07/2023]
Abstract
The occurrence of early afterdepolarizations (EADs) and increased dispersion of repolarization are two known factors for arrhythmogenesis in long QT syndrome. However, increased dispersion of repolarization tends to suppress EADs due to the source-sink effect, and thus how the two competing factors cause initiation of arrhythmias remains incompletely understood. Here we used optical mapping and computer simulation to investigate the mechanisms underlying spontaneous initiation of arrhythmias in type 2 long QT (LQT2) syndrome. In optical mapping experiments of transgenic LQT2 rabbit hearts under isoproterenol, premature ventricular complexes (PVCs) were observed to originate from the steep spatial repolarization gradient (RG) regions and propagated unidirectionally. The same PVC behaviors were demonstrated in computer simulations of tissue models of rabbits. Depending on the heterogeneities, these PVCs could lead to either repetitive focal excitations or reentry without requiring an additional vulnerable substrate. Systematic simulations showed that cellular phase 2 EADs were either suppressed or confined to the long action potential region due to the source-sink effect. Tissue-scale phase 3 EADs and PVCs occurred due to tissue-scale dynamical instabilities caused by RG and enhanced L-type calcium current (ICa,L), occurring under both large and small RG. Presence of cellular EADs was not required but potentiated PVCs when RG was small. We also investigated how other factors affect the dynamical instabilities causing PVCs. Our main conclusion is that tissue-scale dynamical instabilities caused by RG and enhanced ICa,L give rise to both the trigger and the vulnerable substrate simultaneously for spontaneous initiation of arrhythmias in LQT2 syndrome.
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Affiliation(s)
- Xiaodong Huang
- Department of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los Angeles, California.,Department of Physics, South China University of Technology, Guangzhou, China; and
| | - Tae Yun Kim
- Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, Rhode Island
| | - Gideon Koren
- Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, Rhode Island
| | - Bum-Rak Choi
- Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, Rhode Island
| | - Zhilin Qu
- Department of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los Angeles, California; .,Department of Biomathematics, David Geffen School of Medicine, University of California, Los Angeles, California
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92
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Sheehan ET, Frizzell JD, Gabaldon J, West MB. Quinine and the ABCs of Long QT: A Patient's Misfortune with Arthritis, (Alcoholic) Beverages, and Cramps. J Gen Intern Med 2016; 31:1254-7. [PMID: 27173501 PMCID: PMC5023602 DOI: 10.1007/s11606-016-3738-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Revised: 09/15/2015] [Accepted: 05/02/2016] [Indexed: 01/08/2023]
Abstract
A 91-year-old woman presented to the emergency department by ambulance after her family found her minimally responsive. Telemetry monitoring demonstrated episodes of non-sustained polymorphic ventricular tachycardia (PMVT) associated with significantly prolonged repolarization. Her medical history revealed that she was taking quinine or a derivative in three different forms: hydroxychloroquine, quinine sulfate (for leg cramps), and her gin mixed with tonic water (containing quinine). The present case is illustrative of classic etiologies and findings of acquired long QT syndrome, and serves as an important reminder for providers to take a complete medication history, including use of duplicative and alternative medicines and type of alcohol consumption.
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Affiliation(s)
- Elyce T Sheehan
- Department of Internal Medicine, University of New Mexico, Albuquerque, NM, USA.
| | - Jarrod D Frizzell
- Department of Internal Medicine, University of New Mexico, Albuquerque, NM, USA
| | - Jude Gabaldon
- San Juan Regional Medical Center, Farmington, NM, USA
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93
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Chen Y, Zhu D, Yuan J, Han Z, Wang Y, Qian Z, Hou X, Wu T, Zou J. CLOCK-BMAL1 regulate the cardiac L-type calcium channel subunit CACNA1C through PI3K-Akt signaling pathway. Can J Physiol Pharmacol 2016; 94:1023-32. [PMID: 27376484 DOI: 10.1139/cjpp-2015-0398] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The heterodimerized transcription factors CLOCK-BMAL1 regulate the cardiomyocyte circadian rhythms. The L-type calcium currents play important role in the cardiac electrogenesis and arrhythmogenesis. Whether and how the CLOCK-BMAL1 regulate the cardiac L-type calcium channels are yet to be determined. The functions of the L-type calcium channels were evaluated with patch clamping techniques. Recombinant adenoviruses of CLOCK and BMAL1 were used in the expression experiments. We reported that the expressions and functions of CACNA1C (the α-subunit of the L-type calcium channels) showed circadian rhythms, with the peak at zeitgeber time 3 (ZT3). The endocardial action potential durations 90 (APD90) were correspondingly longer at ZT3. The protein levels of the phosphorylated Akt at threonine 308 (pAkt T308) also showed circadian rhythms. Overexpressions of CLOCK-BMAL1 significantly reduced the levels of CACNA1C while increasing the levels of pAkt T308 and pik3r1. Furthermore, the inhibitory effects of CLOCK-BMAL1 on CACNA1C could be abolished by the Akt inhibitor MK2206 or the PDK1 inhibitor GSK2334470. Collectively, our findings suggested that the expressions of the cardiac CACNA1C were under the CLOCK-BMAL1 regulation, probably through the PI3K-Akt signal pathway.
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Affiliation(s)
- Yanhong Chen
- Department of Cardiology, the First Affiliated Hospital, Nanjing Medical University, Nanjing, China
- Department of Cardiology, Wuhan Asia Heart Hospital, Hubei, China
| | - Didi Zhu
- Department of Cardiology, the First Affiliated Hospital, Nanjing Medical University, Nanjing, China
| | - Jiamin Yuan
- Department of Cardiology, the First Affiliated Hospital, Nanjing Medical University, Nanjing, China
| | - Zhonglin Han
- Department of Cardiology, the First Affiliated Hospital, Nanjing Medical University, Nanjing, China
| | - Yao Wang
- Department of Cardiology, the First Affiliated Hospital, Nanjing Medical University, Nanjing, China
| | - Zhiyong Qian
- Department of Cardiology, the First Affiliated Hospital, Nanjing Medical University, Nanjing, China
| | - Xiaofeng Hou
- Department of Cardiology, the First Affiliated Hospital, Nanjing Medical University, Nanjing, China
| | - Tingting Wu
- Department of Cardiology, the First Affiliated Hospital, Nanjing Medical University, Nanjing, China
| | - Jiangang Zou
- Department of Cardiology, the First Affiliated Hospital, Nanjing Medical University, Nanjing, China
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94
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Effects of allocryptopine on outward potassium current and slow delayed rectifier potassium current in rabbit myocardium. JOURNAL OF GERIATRIC CARDIOLOGY : JGC 2016; 13:316-25. [PMID: 27403141 PMCID: PMC4921544 DOI: 10.11909/j.issn.1671-5411.2016.04.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Objective Allocryptopine (ALL) is an effective alkaloid of Corydalis decumbens (Thunb.) Pers. Papaveraceae and has proved to be anti-arrhythmic. The purpose of our study is to investigate the effects of ALL on transmural repolarizing ionic ingredients of outward potassium current (Ito) and slow delayed rectifier potassium current (IKs). Methods The monophasic action potential (MAP) technique was used to record the MAP duration of the epicardium (Epi), myocardium (M) and endocardium (Endo) of the rabbit heart and the whole cell patch clamp was used to record Ito and IKs in cardiomyocytes of Epi, M and Endo layers that were isolated from rabbit ventricles. Results The effects of ALL on MAP of Epi, M and Endo layers were disequilibrium. ALL could effectively reduce the transmural dispersion of repolarization (TDR) in rabbit transmural ventricular wall. ALL decreased the current densities of Ito and IKs in a voltage and concentration dependent way and narrowed the repolarizing differences among three layers. The analysis of gating kinetics showed ALL accelerated the channel activation of Ito in M layers and partly inhibit the channel openings of Ito in Epi, M and Endo cells. On the other hand, ALL mainly slowed channel deactivation of IKs channel in Epi and Endo layers without affecting its activation. Conclusions Our study gives partially explanation about the mechanisms of transmural inhibition of Ito and IKs channels by ALL in rabbit myocardium. These findings provide novel perspective regarding the anti-arrhythmogenesis application of ALL in clinical settings.
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95
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Tan AY, Ellenbogen K. Ventricular Arrhythmias in Apparently Normal Hearts: Who Needs an Implantable Cardiac Defibrillator? Card Electrophysiol Clin 2016; 8:613-21. [PMID: 27521094 DOI: 10.1016/j.ccep.2016.04.010] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Idiopathic ventricular tachycardia is often considered a benign form of ventricular arrhythmia in patients without apparent structural heart disease. However, a subset of patients may develop malignant ventricular arrhythmias and present with syncope and sudden cardiac arrest. Survivors of cardiac arrest are candidates for implantable cardiac defibrillators (ICDs). The indications for ICDs in patients with less than a full-blown cardiac arrest presentation but with electrocardiographically high-risk ectopy features remain uncertain. This article addresses some of the uncertainties and pitfalls in ICD risk stratification in this patient group and explores potential mechanisms for malignant conversion of benign premature ventricular complexes to sustained arrhythmia.
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Affiliation(s)
- Alex Y Tan
- Electrophysiology Section, Division of Cardiology, Hunter Holmes McGuire VA Medical Center, 1201 Broad Rock Boulevard, Richmond, VA 23249, USA; VCU Pauley Heart Center, Medical College of Virginia, Virginia Commonwealth University School of Medicine, 1250 E Marshall Street, Richmond, VA 23298, USA.
| | - Kenneth Ellenbogen
- VCU Pauley Heart Center, Medical College of Virginia, Virginia Commonwealth University School of Medicine, 1250 E Marshall Street, Richmond, VA 23298, USA
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96
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Zeng H, Roman MI, Lis E, Lagrutta A, Sannajust F. Use of FDSS/μCell imaging platform for preclinical cardiac electrophysiology safety screening of compounds in human induced pluripotent stem cell-derived cardiomyocytes. J Pharmacol Toxicol Methods 2016; 81:217-22. [PMID: 27222351 DOI: 10.1016/j.vascn.2016.05.009] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Revised: 05/06/2016] [Accepted: 05/18/2016] [Indexed: 11/28/2022]
Abstract
FDSS/μCell is a high-speed acquisition imaging platform (Hamamatsu Ltd., Hamamatsu, Japan) that allows for simultaneous high-throughput reading under controlled conditions. We evaluated the Ca(2+) transients or optical membrane potential changes of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) (iCells) in the presence or absence of 44 pharmacological agents known to interfere with cardiac ion channels (e.g., hERG, IKs, NaV1.5, CaV1.2). We tested two Ca(2+)-sensitive fluorescence dyes (Codex ACTOne® and EarlyTox®) and a membrane potential dye (FLIPR® membrane potential dye). We were able to quantify and report drug-induced early-after depolarizations (EAD)-like waveforms, cardiomyocyte ectopic beats and changes in beating rate from a subgroup of pharmacological agents acting acutely (within a 1-hour period). Cardiovascular drugs, such as dofetilide and d,l-sotalol, exhibited EAD-like signals at 3nM and 10μM, respectively. CNS drugs, such as haloperidol and sertindole, exhibited EAD-like signals and ectopic beats at 30nM and 1μM, respectively. Other drugs, such as astemizole, solifenacin, and moxifloxacin, exhibited similar arrhythmias at 30nM, 3μM and 300μM, respectively. Our data suggest that the membrane potential and intracellular Ca(2+) signal are tightly coupled, supporting the idea that the EAD-like signals reported are the accurate representation of an EAD signal of the cardiac action potential. Finally, the EAD-like Ca(2+) signal was well correlated to clinically-relevant concentrations where Torsade de Pointes (TdPs) arrhythmias were noted in healthy volunteers treated orally with some of the compounds we tested, as reported in PharmaPendium®.
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Affiliation(s)
- Haoyu Zeng
- SALAR, Safety & Exploratory Pharmacology Department, Merck Research Laboratories, West Point, PA 19486, USA.
| | - Maria I Roman
- SALAR, Safety & Exploratory Pharmacology Department, Merck Research Laboratories, West Point, PA 19486, USA
| | - Edward Lis
- SALAR, Safety & Exploratory Pharmacology Department, Merck Research Laboratories, West Point, PA 19486, USA
| | - Armando Lagrutta
- SALAR, Safety & Exploratory Pharmacology Department, Merck Research Laboratories, West Point, PA 19486, USA
| | - Frederick Sannajust
- SALAR, Safety & Exploratory Pharmacology Department, Merck Research Laboratories, West Point, PA 19486, USA
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97
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Stams TR, Oosterhoff P, Heijdel A, Dunnink A, Beekman JD, van der Nagel R, van Rijen HV, van der Heyden MA, Vos MA. Beat-to-Beat Variability in Preload Unmasks Latent Risk of Torsade de Pointes in Anesthetized Chronic Atrioventricular Block Dogs. Circ J 2016; 80:1336-45. [PMID: 27151565 DOI: 10.1253/circj.cj-15-1335] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
BACKGROUND Beat-to-beat variability in ventricular repolarization (BVR) associates with increased arrhythmic risk. Proarrhythmic remodeling in the dog with chronic AV-block (CAVB) compromises repolarization reserve and associates with increased BVR, which further increases upon dofetilide infusion and correlates with Torsade de Pointes (TdP) arrhythmias. It was hypothesized that these pro-arrhythmia-associated increases in BVR are induced by beat-to-beat variability in preload. METHODS AND RESULTS Left ventricular monophasic action potential duration (LVMAPD) was recorded in acute (AAVB) and CAVB dogs, before and after dofetilide infusion. BVR was quantified as short-term variability of LVMAPD. The PQ-interval was controlled by pacing: either a constant or an alternating preload pattern was established, verified by PV-loop. The effect of the stretch-activated channel blocker, streptomycin, on BVR was evaluated in a second CAVB group. At alternating preload only, BVR was increased after proarrhythmic remodeling (0.45±0.14 ms AAVB vs. 2.2±1.1 ms CAVB, P<0.01). At CAVB, but not at AAVB, dofetilide induced significant proarrhythmia. Preload variability augmented the dofetilide-induced BVR increase at CAVB (+1.5±0.8 ms vs. +0.9±0.9 ms, P=0.058). In the second group, the increase in baseline BVR by alternating preload (0.3±0.03 ms to 1.0±0.8 ms, P<0.01) was abolished by streptomycin (0.5±0.2 ms, P<0.05). CONCLUSIONS In CAVB dogs, the inverse relation between BVR and repolarization reserve originates from an augmented sensitivity of ventricular repolarization to beat-to-beat preload changes. Stretch-activated channels appear to be involved in the mechanism of BVR. (Circ J 2016; 80: 1336-1345).
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Affiliation(s)
- Thom Rg Stams
- Department of Medical Physiology, Division of Heart and Lungs, University Medical Center
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98
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Abstract
Atrial fibrillation (AF) is associated with increased morbidity and mortality. Atrial-selective potassium (K(+)) channel blockers may represent a novel therapeutic target. The best validated atrial-specific ion currents are the acetylcholine-activated inward-rectifier K(+) current IK,ACh and ultrarapidly activating delayed-rectifier K(+) current IKur. Two-pore domain and small-conductance Ca(2+)-activated K(+) channels and Kv1.1 channels may also contribute to the atrial repolarization. We review the molecular and electrophysiologic characteristics of atrial-selective K(+) channels and their potential pathophysiologic role in AF. We summarize currently available K(+) channel blockers focusing on the most important compounds.
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Affiliation(s)
- Niels Voigt
- Institute of Pharmacology, West German Heart and Vascular Center, University Duisburg-Essen, Hufelandstr. 55, Essen 45122, Germany
| | - Dobromir Dobrev
- Institute of Pharmacology, West German Heart and Vascular Center, University Duisburg-Essen, Hufelandstr. 55, Essen 45122, Germany.
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99
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Kügler P. Early Afterdepolarizations with Growing Amplitudes via Delayed Subcritical Hopf Bifurcations and Unstable Manifolds of Saddle Foci in Cardiac Action Potential Dynamics. PLoS One 2016; 11:e0151178. [PMID: 26977805 PMCID: PMC4792449 DOI: 10.1371/journal.pone.0151178] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2016] [Accepted: 02/24/2016] [Indexed: 01/01/2023] Open
Abstract
Early afterdepolarizations (EADs) are pathological oscillations in cardiac action potentials during the repolarization phase and may be caused by drug side effects, ion channel disease or oxidative stress. The most widely observed EAD pattern is characterized by oscillations with growing amplitudes. So far, its occurence has been explained in terms of a supercritical Hopf bifurcation in the fast subsystem of the action potential dynamics from which stable limit cycles with growing amplitudes emerge. The novel contribution of this article is the introduction of two alternative explanations of EAD genesis with growing amplitudes that do not involve stable limit cycles in fast subsystems. In particular, we demonstrate that EAD patterns with growing amplitudes may alternatively arise due to a delayed subcritical Hopf bifurcation or an unstable manifold of a saddle focus fixed point in the full fast-slow system modelling the action potential. Our work extends the list of possible dynamical EAD mechanisms and may contribute to a classification of drug effects in preclinical cardiotoxicity testing.
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Affiliation(s)
- Philipp Kügler
- Institute of Applied Mathematics and Statistics, University of Hohenheim, Schloss 1, 70599 Stuttgart, Germany
- Research Group Mathematical Methods in Molecular and Systems Biology, Radon Institute for Computational and Applied Mathematics, Altenbergerstrasse 69, 4040 Linz, Austria
- * E-mail:
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100
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Teka W, Stockton D, Santamaria F. Power-Law Dynamics of Membrane Conductances Increase Spiking Diversity in a Hodgkin-Huxley Model. PLoS Comput Biol 2016; 12:e1004776. [PMID: 26937967 PMCID: PMC4777484 DOI: 10.1371/journal.pcbi.1004776] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2015] [Accepted: 01/27/2016] [Indexed: 12/19/2022] Open
Abstract
We studied the effects of non-Markovian power-law voltage dependent conductances on the generation of action potentials and spiking patterns in a Hodgkin-Huxley model. To implement slow-adapting power-law dynamics of the gating variables of the potassium, n, and sodium, m and h, conductances we used fractional derivatives of order η≤1. The fractional derivatives were used to solve the kinetic equations of each gate. We systematically classified the properties of each gate as a function of η. We then tested if the full model could generate action potentials with the different power-law behaving gates. Finally, we studied the patterns of action potential that emerged in each case. Our results show the model produces a wide range of action potential shapes and spiking patterns in response to constant current stimulation as a function of η. In comparison with the classical model, the action potential shapes for power-law behaving potassium conductance (n gate) showed a longer peak and shallow hyperpolarization; for power-law activation of the sodium conductance (m gate), the action potentials had a sharp rise time; and for power-law inactivation of the sodium conductance (h gate) the spikes had wider peak that for low values of η replicated pituitary- and cardiac-type action potentials. With all physiological parameters fixed a wide range of spiking patterns emerged as a function of the value of the constant input current and η, such as square wave bursting, mixed mode oscillations, and pseudo-plateau potentials. Our analyses show that the intrinsic memory trace of the fractional derivative provides a negative feedback mechanism between the voltage trace and the activity of the power-law behaving gate variable. As a consequence, power-law behaving conductances result in an increase in the number of spiking patterns a neuron can generate and, we propose, expand the computational capacity of the neuron. There is increasing evidence that the activity of individual membrane ion channels, conductances, and the firing rate of neurons are history dependent. In this work we studied how history dependent activation of membrane conductances affect the action potential activity of the Hodgkin-Huxley model, a widely used model of action potential generation. In order to implement history dependent activation, we made use of fractional order differential equations. This type of history dependent differential equations are increasingly being used in biomedical sciences to simulate complex phenomena. We use fractional order derivatives to model the kinetic dynamics of the gate variables for the potassium and sodium conductances of the Hodgkin-Huxley model. Our results show that power-law dynamics of the different gate variables result in a wide range of action potential shapes and spiking patterns, even in the case where the model was stimulated with constant current. As a consequence, power-law behaving conductances result in an increase in the number of spiking patterns a neuron can generate and, we propose, expand the computational capacity of the neuron.
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Affiliation(s)
- Wondimu Teka
- UTSA Neurosciences Institute, The University of Texas at San Antonio, San Antonio, Texas, United States of America
| | - David Stockton
- Biomedical Engineering Program, The University of Texas at San Antonio, San Antonio, Texas, United States of America
| | - Fidel Santamaria
- UTSA Neurosciences Institute, The University of Texas at San Antonio, San Antonio, Texas, United States of America
- * E-mail:
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