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Bartolucci C, Sala L. The Dynamic Clamp Technique: A Robust Toolkit for Investigating Potassium Channel Function. Methods Mol Biol 2024; 2796:211-227. [PMID: 38856904 DOI: 10.1007/978-1-0716-3818-7_13] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2024]
Abstract
The dynamic clamp technique has emerged as a powerful tool in the field of cardiac electrophysiology, enabling researchers to investigate the intricate dynamics of ion currents in cardiac cells. Potassium channels play a critical role in the functioning of cardiac cells and the overall electrical stability of the heart. This chapter provides a comprehensive overview of the methods and applications of dynamic clamp in the study of key potassium currents in cardiac cells. A step-by-step guide is presented, detailing the experimental setup and protocols required for implementing the dynamic clamp technique in cardiac cell studies. Special attention is given to the design and construction of a dynamic clamp setup with Real Time eXperimental Interface, configurations, and the incorporation of mathematical models to mimic ion channel behavior. The chapter's core focuses on applying dynamic clamp to elucidate the properties of various potassium channels in cardiac cells. It discusses how dynamic clamp can be used to investigate channel kinetics, voltage-dependent properties, and the impact of different potassium channel subtypes on cardiac electrophysiology. The chapter will also include examples of specific dynamic clamp experiments that studied potassium currents or their applications in cardiac cells.
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Affiliation(s)
- Chiara Bartolucci
- Department of Electrical, Electronic and Information Engineering 'Guglielmo Marconi', University of Bologna, Cesena, Italy.
| | - Luca Sala
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, Milan, Italy
- Istituto Auxologico Italiano IRCCS, Center for Cardiac Arrhythmias of Genetic Origin and Laboratory of Cardiovascular Genetics, Milan, Italy
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2
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Ma J, Niklewski PJ, Wang HS. Acute exposure to low-dose bisphenol A delays cardiac repolarization in female canine heart - Implication for proarrhythmic toxicity in large animals. Food Chem Toxicol 2023; 172:113589. [PMID: 36584932 PMCID: PMC9852101 DOI: 10.1016/j.fct.2022.113589] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2022] [Revised: 12/12/2022] [Accepted: 12/24/2022] [Indexed: 12/29/2022]
Abstract
Bisphenol A (BPA) is a common environmental chemical with a range of potential adverse health effects. The impact of environmentally-relevant low dose of BPA on the electrical properties of the hearts of large animals (e.g., dog, human) is poorly defined. Perturbation of cardiac electrical properties is a key arrhythmogenic mechanism. In particular, delay of ventricular repolarization and prolongation of the QT interval of the electrocardiogram is a marker for the risk of malignant arrhythmias. We examined the acute effect of 10-9 M BPA on the electrical properties of female canine ventricular myocytes and tissues. BPA rapidly delayed action potential repolarization and prolonged action potential duration (APD). The dose response curve of BPA on APD was nonmonotonic. BPA rapidly inhibited the IKr K+ current and ICaL Ca2+ current. Computational modeling indicated that the effect of BPA on APD can be accounted for by its suppression of IKr. At the tissue level, BPA acutely prolonged the QT interval in 4 left ventricular wedges. ERβ signaling contributed to the acute effects of BPA on ventricular repolarization. Our results demonstrate that BPA has QT prolongation liability in female canine hearts. These findings have implication for the potential proarrhythmic cardiac toxicity of BPA in large animals.
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Affiliation(s)
- Jianyong Ma
- Department of Pharmacology and Systems Physiology, University of Cincinnati, College of Medicine, Cincinnati, OH, USA
| | - Paul J Niklewski
- Department of Pharmacology and Systems Physiology, University of Cincinnati, College of Medicine, Cincinnati, OH, USA
| | - Hong-Sheng Wang
- Department of Pharmacology and Systems Physiology, University of Cincinnati, College of Medicine, Cincinnati, OH, USA.
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3
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Fowler ED, Wang N, Hezzell MJ, Chanoit G, Hancox JC, Cannell MB. Improved Ca 2+ release synchrony following selective modification of I tof and phase 1 repolarization in normal and failing ventricular myocytes. J Mol Cell Cardiol 2022; 172:52-62. [PMID: 35908686 DOI: 10.1016/j.yjmcc.2022.07.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/18/2022] [Revised: 07/18/2022] [Accepted: 07/20/2022] [Indexed: 12/14/2022]
Abstract
Loss of ventricular action potential (AP) early phase 1 repolarization may contribute to the impaired Ca2+ release and increased risk of sudden cardiac death in heart failure. Therefore, restoring AP phase 1 by augmenting the fast transient outward K+ current (Itof) might be beneficial, but direct experimental evidence to support this proposition in failing cardiomyocytes is limited. Dynamic clamp was used to selectively modulate the contribution of Itof to the AP and Ca2+ transient in both normal (guinea pig and rabbit) and in failing rabbit cardiac myocytes. Opposing native Itof in non-failing rabbit myocytes increased Ca2+ release heterogeneity, late Ca2+ sparks (LCS) frequency and AP duration. (APD). In contrast, increasing Itof in failing myocytes and guinea pig myocytes (the latter normally lacking Itof) increased Ca2+ transient amplitude, Ca2+ release synchrony, and shortened APD. Computer simulations also showed faster Ca2+ transient decay (mainly due to fewer LCS), decreased inward Na+/Ca2+ exchange current and APD. When the Itof conductance was increased to ~0.2 nS/pF in failing cells (a value slightly greater than seen in typical human epicardial myocytes), Ca2+ release synchrony improved and AP duration decreased slightly. Further increases in Itof can cause Ca2+ release to decrease as the peak of the bell-shaped ICa-voltage relationship is passed and premature AP repolarization develops. These results suggest that there is an optimal range for Itof enhancement that may support Ca2+ release synchrony and improve electrical stability in heart failure with the caveat that uncontrolled Itof enhancement should be avoided.
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Affiliation(s)
- Ewan D Fowler
- School of Physiology, Pharmacology & Neuroscience, Faculty of Biomedical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, UK
| | - Nan Wang
- School of Physiology, Pharmacology & Neuroscience, Faculty of Biomedical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, UK
| | - Melanie J Hezzell
- University of Bristol Veterinary School, Langford, Bristol BS40 5DU, UK
| | - Guillaume Chanoit
- University of Bristol Veterinary School, Langford, Bristol BS40 5DU, UK
| | - Jules C Hancox
- School of Physiology, Pharmacology & Neuroscience, Faculty of Biomedical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, UK
| | - Mark B Cannell
- School of Physiology, Pharmacology & Neuroscience, Faculty of Biomedical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, UK.
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Inducing I to,f and phase 1 repolarization of the cardiac action potential with a Kv4.3/KChIP2.1 bicistronic transgene. J Mol Cell Cardiol 2021; 164:29-41. [PMID: 34823101 PMCID: PMC8884339 DOI: 10.1016/j.yjmcc.2021.11.004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/22/2021] [Revised: 10/22/2021] [Accepted: 11/11/2021] [Indexed: 11/22/2022]
Abstract
The fast transient outward potassium current (Ito,f) plays a key role in phase 1 repolarization of the human cardiac action potential (AP) and its reduction in heart failure (HF) contributes to the loss of contractility. Therefore, restoring Ito,f might be beneficial for treating HF. The coding sequence of a P2A peptide was cloned, in frame, between Kv4.3 and KChIP2.1 genes and ribosomal skipping was confirmed by Western blotting. Typical Ito,f properties with slowed inactivation and accelerated recovery from inactivation due to the association of KChIP2.1 with Kv4.3 was seen in transfected HEK293 cells. Both bicistronic components trafficked to the plasmamembrane and in adenovirus transduced rabbit cardiomyocytes both t-tubular and sarcolemmal construct labelling appeared. The resulting current was similar to Ito,f seen in human ventricular cardiomyocytes and was 50% blocked at ~0.8 mmol/l 4-aminopyridine and increased ~30% by 5 μmol/l NS5806 (an Ito,f agonist). Variation in the density of the expressed Ito,f, in rabbit cardiomyocytes recapitulated typical species-dependent variations in AP morphology. Simultaneous voltage recording and intracellular Ca2+ imaging showed that modification of phase 1 to a non-failing human phenotype improved the rate of rise and magnitude of the Ca2+ transient. Ito,f expression also reduced AP triangulation but did not affect ICa,L and INa magnitudes. This raises the possibility for a new gene-based therapeutic approach to HF based on selective phase 1 modification. Action potential phase 1 depends on fast transient outward current (Ito,f). Construction of a bicistronic transgene for Kv4.3 and KChIP2.1 with P2A separator Expressed bicistronic Kv4.3/KChIP2.1 proteins traffic to the cell surface membrane Viral transduction with Kv4.3/KChIP2.1 increases Ito,f in cardiomyocytes. Kv4.3/KChIP2.1 transgene expression increased AP phase 1 and EC coupling
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Morotti S, Liu C, Hegyi B, Ni H, Fogli Iseppe A, Wang L, Pritoni M, Ripplinger CM, Bers DM, Edwards AG, Grandi E. Quantitative cross-species translators of cardiac myocyte electrophysiology: Model training, experimental validation, and applications. SCIENCE ADVANCES 2021; 7:eabg0927. [PMID: 34788089 PMCID: PMC8598003 DOI: 10.1126/sciadv.abg0927] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2020] [Accepted: 09/28/2021] [Indexed: 05/13/2023]
Abstract
Animal experimentation is key in the evaluation of cardiac efficacy and safety of novel therapeutic compounds. However, interspecies differences in the mechanisms regulating excitation-contraction coupling can limit the translation of experimental findings from animal models to human physiology and undermine the assessment of drugs’ efficacy and safety. Here, we built a suite of translators for quantitatively mapping electrophysiological responses in ventricular myocytes across species. We trained these statistical operators using a broad dataset obtained by simulating populations of our biophysically detailed computational models of action potential and Ca2+ transient in mouse, rabbit, and human. We then tested our translators against experimental data describing the response to stimuli, such as ion channel block, change in beating rate, and β-adrenergic challenge. We demonstrate that this approach is well suited to predicting the effects of perturbations across different species or experimental conditions and suggest its integration into mechanistic studies and drug development pipelines.
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Affiliation(s)
- Stefano Morotti
- Department of Pharmacology, University of California Davis, Davis, CA 95616, USA
| | - Caroline Liu
- Department of Pharmacology, University of California Davis, Davis, CA 95616, USA
| | - Bence Hegyi
- Department of Pharmacology, University of California Davis, Davis, CA 95616, USA
| | - Haibo Ni
- Department of Pharmacology, University of California Davis, Davis, CA 95616, USA
| | - Alex Fogli Iseppe
- Department of Pharmacology, University of California Davis, Davis, CA 95616, USA
| | - Lianguo Wang
- Department of Pharmacology, University of California Davis, Davis, CA 95616, USA
| | - Marco Pritoni
- Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | | | - Donald M. Bers
- Department of Pharmacology, University of California Davis, Davis, CA 95616, USA
| | - Andrew G. Edwards
- Department of Pharmacology, University of California Davis, Davis, CA 95616, USA
| | - Eleonora Grandi
- Department of Pharmacology, University of California Davis, Davis, CA 95616, USA
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Verkerk AO, Wilders R. Dynamic Clamp in Electrophysiological Studies on Stem Cell-Derived Cardiomyocytes-Why and How? J Cardiovasc Pharmacol 2021; 77:267-279. [PMID: 33229908 DOI: 10.1097/fjc.0000000000000955] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Accepted: 10/31/2020] [Indexed: 12/15/2022]
Abstract
ABSTRACT Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) are supposed to be a good human-based model, with virtually unlimited cell source, for studies on mechanisms underlying cardiac development and cardiac diseases, and for identification of drug targets. However, a major drawback of hPSC-CMs as a model system, especially for electrophysiological studies, is their depolarized state and associated spontaneous electrical activity. Various approaches are used to overcome this drawback, including the injection of "synthetic" inward rectifier potassium current (IK1), which is computed in real time, based on the recorded membrane potential ("dynamic clamp"). Such injection of an IK1-like current results in quiescent hPSC-CMs with a nondepolarized resting potential that show "adult-like" action potentials on stimulation, with functional availability of the most important ion channels involved in cardiac electrophysiology. These days, dynamic clamp has become a widely appreciated electrophysiological tool. However, setting up a dynamic clamp system can still be laborious and difficult, both because of the required hardware and the implementation of the dedicated software. In the present review, we first summarize the potential mechanisms underlying the depolarized state of hPSC-CMs and the functional consequences of this depolarized state. Next, we explain how an existing manual patch clamp setup can be extended with dynamic clamp. Finally, we shortly validate the extended setup with atrial-like and ventricular-like hPSC-CMs. We feel that dynamic clamp is a highly valuable tool in the field of cellular electrophysiological studies on hPSC-CMs and hope that our directions for setting up such dynamic clamp system may prove helpful.
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Affiliation(s)
- Arie O Verkerk
- Department of Medical Biology, Amsterdam UMC, University of Amsterdam, Amsterdam, The Netherlands ; and
- Department of Experimental Cardiology, Amsterdam UMC, University of Amsterdam, Amsterdam, The Netherlands
| | - Ronald Wilders
- Department of Medical Biology, Amsterdam UMC, University of Amsterdam, Amsterdam, The Netherlands ; and
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Benson AP, Stevenson-Cocks HJ, Whittaker DG, White E, Colman MA. Multi-scale approaches for the simulation of cardiac electrophysiology: II - Tissue-level structure and function. Methods 2020; 185:60-81. [PMID: 31988002 DOI: 10.1016/j.ymeth.2020.01.010] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2019] [Revised: 11/15/2019] [Accepted: 01/14/2020] [Indexed: 02/06/2023] Open
Abstract
Computational models of the heart, from cell-level models, through one-, two- and three-dimensional tissue-level simplifications, to biophysically-detailed three-dimensional models of the ventricles, atria or whole heart, allow the simulation of excitation and propagation of this excitation, and have provided remarkable insight into the normal and pathological functioning of the heart. In this article we present equations for modelling cellular excitation (i.e. the cell action potential) from both a phenomenological and a biophysical perspective. Hodgkin-Huxley formalism is discussed, along with the current generation of biophysically-detailed cardiac cell models. Alternative Markovian formulations for modelling ionic currents are also presented. Equations describing propagation of this cellular excitation, through one-, two- and three-dimensional idealised or realistic tissues, are then presented. For all types of model, from cell to tissue, methods for discretisation and integration of the underlying equations are discussed. The article finishes with a discussion of two tissue-level experimental imaging techniques - diffusion tensor magnetic resonance imaging and optical imaging - that can be used to provide data for parameterisation and validation of cell- and tissue-level cardiac models.
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Affiliation(s)
- Alan P Benson
- School of Biomedical Sciences University of Leeds, Leeds LS2 9JT, UK.
| | | | - Dominic G Whittaker
- School of Biomedical Sciences University of Leeds, Leeds LS2 9JT, UK; School of Mathematical Sciences, University of Nottingham, Nottingham NG7 2RD, UK
| | - Ed White
- School of Biomedical Sciences University of Leeds, Leeds LS2 9JT, UK
| | - Michael A Colman
- School of Biomedical Sciences University of Leeds, Leeds LS2 9JT, UK
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8
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Altamirano F, Schiattarella GG, French KM, Kim SY, Engelberger F, Kyrychenko S, Villalobos E, Tong D, Schneider JW, Ramirez-Sarmiento CA, Lavandero S, Gillette TG, Hill JA. Polycystin-1 Assembles With Kv Channels to Govern Cardiomyocyte Repolarization and Contractility. Circulation 2019; 140:921-936. [PMID: 31220931 DOI: 10.1161/circulationaha.118.034731] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
BACKGROUND Polycystin-1 (PC1) is a transmembrane protein originally identified in autosomal dominant polycystic kidney disease where it regulates the calcium-permeant cation channel polycystin-2. Autosomal dominant polycystic kidney disease patients develop renal failure, hypertension, left ventricular hypertrophy, and diastolic dysfunction, among other cardiovascular disorders. These individuals harbor PC1 loss-of-function mutations in their cardiomyocytes, but the functional consequences are unknown. PC1 is ubiquitously expressed, and its experimental ablation in cardiomyocyte-specific knockout mice reduces contractile function. Here, we set out to determine the pathophysiological role of PC1 in cardiomyocytes. METHODS Wild-type and cardiomyocyte-specific PC1 knockout mice were analyzed by echocardiography. Excitation-contraction coupling was assessed in isolated cardiomyocytes and human embryonic stem cell-derived cardiomyocytes, and functional consequences were explored in heterologous expression systems. Protein-protein interactions were analyzed biochemically and by means of ab initio calculations. RESULTS PC1 ablation reduced action potential duration in cardiomyocytes, decreased Ca2+ transients, and myocyte contractility. PC1-deficient cardiomyocytes manifested a reduction in sarcoendoplasmic reticulum Ca2+ stores attributable to a reduced action potential duration and sarcoendoplasmic reticulum Ca2+ ATPase (SERCA) activity. An increase in outward K+ currents decreased action potential duration in cardiomyocytes lacking PC1. Overexpression of full-length PC1 in HEK293 cells significantly reduced the current density of heterologously expressed Kv4.3, Kv1.5 and Kv2.1 potassium channels. PC1 C terminus inhibited Kv4.3 currents to the same degree as full-length PC1. Additionally, PC1 coimmunoprecipitated with Kv4.3, and a modeled PC1 C-terminal structure suggested the existence of 2 docking sites for PC1 within the N terminus of Kv4.3, supporting a physical interaction. Finally, a naturally occurring human mutant PC1R4228X manifested no suppressive effects on Kv4.3 channel activity. CONCLUSIONS Our findings uncover a role for PC1 in regulating multiple Kv channels, governing membrane repolarization and alterations in SERCA activity that reduce cardiomyocyte contractility.
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Affiliation(s)
- Francisco Altamirano
- Department of Internal Medicine, Cardiology Division (F.A., G.G.S., K.M.F., S.Y.K., S.K., E.V., D.T., J.W.S., S.L., T.G.G., J.A.H.), University of Texas Southwestern Medical Center, Dallas
| | - Gabriele G Schiattarella
- Department of Internal Medicine, Cardiology Division (F.A., G.G.S., K.M.F., S.Y.K., S.K., E.V., D.T., J.W.S., S.L., T.G.G., J.A.H.), University of Texas Southwestern Medical Center, Dallas.,Department of Advanced Biomedical Sciences, Federico II University, Naples, Italy (G.G.S.)
| | - Kristin M French
- Department of Internal Medicine, Cardiology Division (F.A., G.G.S., K.M.F., S.Y.K., S.K., E.V., D.T., J.W.S., S.L., T.G.G., J.A.H.), University of Texas Southwestern Medical Center, Dallas
| | - Soo Young Kim
- Department of Internal Medicine, Cardiology Division (F.A., G.G.S., K.M.F., S.Y.K., S.K., E.V., D.T., J.W.S., S.L., T.G.G., J.A.H.), University of Texas Southwestern Medical Center, Dallas
| | - Felipe Engelberger
- Institute for Biological and Medical Engineering, Schools of Engineering, Medicine, and Biological Sciences, Pontificia Universidad Catolica de Chile, Santiago, Chile (F.E., C.A.R.S.)
| | - Sergii Kyrychenko
- Department of Internal Medicine, Cardiology Division (F.A., G.G.S., K.M.F., S.Y.K., S.K., E.V., D.T., J.W.S., S.L., T.G.G., J.A.H.), University of Texas Southwestern Medical Center, Dallas
| | - Elisa Villalobos
- Department of Internal Medicine, Cardiology Division (F.A., G.G.S., K.M.F., S.Y.K., S.K., E.V., D.T., J.W.S., S.L., T.G.G., J.A.H.), University of Texas Southwestern Medical Center, Dallas
| | - Dan Tong
- Department of Internal Medicine, Cardiology Division (F.A., G.G.S., K.M.F., S.Y.K., S.K., E.V., D.T., J.W.S., S.L., T.G.G., J.A.H.), University of Texas Southwestern Medical Center, Dallas
| | - Jay W Schneider
- Department of Internal Medicine, Cardiology Division (F.A., G.G.S., K.M.F., S.Y.K., S.K., E.V., D.T., J.W.S., S.L., T.G.G., J.A.H.), University of Texas Southwestern Medical Center, Dallas
| | - Cesar A Ramirez-Sarmiento
- Institute for Biological and Medical Engineering, Schools of Engineering, Medicine, and Biological Sciences, Pontificia Universidad Catolica de Chile, Santiago, Chile (F.E., C.A.R.S.)
| | - Sergio Lavandero
- Department of Internal Medicine, Cardiology Division (F.A., G.G.S., K.M.F., S.Y.K., S.K., E.V., D.T., J.W.S., S.L., T.G.G., J.A.H.), University of Texas Southwestern Medical Center, Dallas.,Advanced Center for Chronic Diseases (ACCDiS), Facultad de Ciencias Químicas y Farmacéuticas & Facultad de Medicina, Universidad de Chile, Santiago, Chile (S.L.).,Corporación Centro de Estudios Científicos de las Enfermedades Crónicas (CECEC), Santiago, Chile (S.L.)
| | - Thomas G Gillette
- Department of Internal Medicine, Cardiology Division (F.A., G.G.S., K.M.F., S.Y.K., S.K., E.V., D.T., J.W.S., S.L., T.G.G., J.A.H.), University of Texas Southwestern Medical Center, Dallas
| | - Joseph A Hill
- Department of Internal Medicine, Cardiology Division (F.A., G.G.S., K.M.F., S.Y.K., S.K., E.V., D.T., J.W.S., S.L., T.G.G., J.A.H.), University of Texas Southwestern Medical Center, Dallas.,Department of Molecular Biology (J.A.H.), University of Texas Southwestern Medical Center, Dallas
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Johnson EK, Springer SJ, Wang W, Dranoff EJ, Zhang Y, Kanter EM, Yamada KA, Nerbonne JM. Differential Expression and Remodeling of Transient Outward Potassium Currents in Human Left Ventricles. Circ Arrhythm Electrophysiol 2019; 11:e005914. [PMID: 29311162 DOI: 10.1161/circep.117.005914] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/05/2017] [Accepted: 11/30/2017] [Indexed: 11/16/2022]
Abstract
BACKGROUND Myocardial, transient, outward currents, Ito, have been shown to play pivotal roles in action potential (AP) repolarization and remodeling in animal models. The properties and contribution of Ito to left ventricular (LV) repolarization in the human heart, however, are poorly defined. METHODS AND RESULTS Whole-cell, voltage-clamp recordings, acquired at physiological (35°C to 37°C) temperatures, from myocytes isolated from the LV of nonfailing human hearts identified 2 distinct transient currents, Ito,fast (Ito,f) and Ito,slow (Ito,s), with significantly (P<0.0001) different rates of recovery from inactivation and pharmacological sensitives: Ito,f recovers in ≈10 ms, 100× faster than Ito,s, and is selectively blocked by the Kv4 channel toxin, SNX-482. Current-clamp experiments revealed regional differences in AP waveforms, notably a phase 1 notch in LV subepicardial myocytes. Dynamic clamp-mediated addition/removal of modeled human ventricular Ito,f, resulted in hyperpolarization or depolarization, respectively, of the notch potential, whereas slowing the rate of Ito,f inactivation resulted in AP collapse. AP-clamp experiments demonstrated that changes in notch potentials modified the time course and amplitudes of voltage-gated Ca2+ currents, ICa. In failing LV subepicardial myocytes, Ito,f was reduced and Ito,s was increased, notch and plateau potentials were depolarized (P<0.0001) and AP durations were prolonged (P<0.001). CONCLUSIONS Ito,f and Ito,s are differentially expressed in nonfailing human LV, contributing to regional heterogeneities in AP waveforms. Ito,f regulates notch and plateau potentials and modulates the time course and amplitude of ICa. Slowing Ito,f inactivation results in dramatic AP shortening. Remodeling of Ito,f in failing human LV subepicardial myocytes attenuates transmural differences in AP waveforms.
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Affiliation(s)
- Eric K Johnson
- From the Cardiovascular Division, Department of Medicine (E.K.J., S.J.S., W.W., E.J.D., Y.Z., E.M.K., K.A.Y., J.M.N.) and Department of Developmental Biology (J.M.N.), Washington University School of Medicine, St. Louis, MO
| | - Steven J Springer
- From the Cardiovascular Division, Department of Medicine (E.K.J., S.J.S., W.W., E.J.D., Y.Z., E.M.K., K.A.Y., J.M.N.) and Department of Developmental Biology (J.M.N.), Washington University School of Medicine, St. Louis, MO
| | - Wei Wang
- From the Cardiovascular Division, Department of Medicine (E.K.J., S.J.S., W.W., E.J.D., Y.Z., E.M.K., K.A.Y., J.M.N.) and Department of Developmental Biology (J.M.N.), Washington University School of Medicine, St. Louis, MO
| | - Edward J Dranoff
- From the Cardiovascular Division, Department of Medicine (E.K.J., S.J.S., W.W., E.J.D., Y.Z., E.M.K., K.A.Y., J.M.N.) and Department of Developmental Biology (J.M.N.), Washington University School of Medicine, St. Louis, MO
| | - Yan Zhang
- From the Cardiovascular Division, Department of Medicine (E.K.J., S.J.S., W.W., E.J.D., Y.Z., E.M.K., K.A.Y., J.M.N.) and Department of Developmental Biology (J.M.N.), Washington University School of Medicine, St. Louis, MO
| | - Evelyn M Kanter
- From the Cardiovascular Division, Department of Medicine (E.K.J., S.J.S., W.W., E.J.D., Y.Z., E.M.K., K.A.Y., J.M.N.) and Department of Developmental Biology (J.M.N.), Washington University School of Medicine, St. Louis, MO
| | - Kathryn A Yamada
- From the Cardiovascular Division, Department of Medicine (E.K.J., S.J.S., W.W., E.J.D., Y.Z., E.M.K., K.A.Y., J.M.N.) and Department of Developmental Biology (J.M.N.), Washington University School of Medicine, St. Louis, MO
| | - Jeanne M Nerbonne
- From the Cardiovascular Division, Department of Medicine (E.K.J., S.J.S., W.W., E.J.D., Y.Z., E.M.K., K.A.Y., J.M.N.) and Department of Developmental Biology (J.M.N.), Washington University School of Medicine, St. Louis, MO.
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10
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López Alarcón MM, Rodríguez de Yurre A, Felice JI, Medei E, Escobar AL. Phase 1 repolarization rate defines Ca 2+ dynamics and contractility on intact mouse hearts. J Gen Physiol 2019; 151:771-785. [PMID: 31000581 PMCID: PMC6571993 DOI: 10.1085/jgp.201812269] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Revised: 02/15/2019] [Accepted: 03/15/2019] [Indexed: 01/06/2023] Open
Abstract
Intact heart physiology assessed by local-field optical techniques helps decipher cardiac function at the organ level. Here, we found that the phase 1 repolarization rate of the mouse ventricular action potential defines contractility by regulating the deactivation of an L-type Ca2+ current. In the heart, Ca2+ influx through L-type Ca2+ channels triggers Ca2+ release from the sarcoplasmic reticulum. In most mammals, this influx occurs during the ventricular action potential (AP) plateau phase 2. However, in murine models, the influx through L-type Ca2+ channels happens in early repolarizing phase 1. The aim of this work is to assess if changes in the open probability of 4-aminopyridine (4-AP)–sensitive Kv channels defining the outward K+ current during phase 1 can modulate Ca2+ currents, Ca2+ transients, and systolic pressure during the cardiac cycle in intact perfused beating hearts. Pulsed local-field fluorescence microscopy and loose-patch photolysis were used to test the hypothesis that a decrease in a transient K+ current (Ito) will enhance Ca2+ influx and promote a larger Ca2+ transient. Simultaneous recordings of Ca2+ transients and APs by pulsed local-field fluorescence microscopy and loose-patch photolysis showed that a reduction in the phase 1 repolarization rate increases the amplitude of Ca2+ transients due to an increase in Ca2+ influx through L-type Ca2+ channels. Moreover, 4-AP induced an increase in the time required for AP to reach 30% repolarization, and the amplitude of Ca2+ transients was larger in epicardium than endocardium. On the other hand, the activation of Ito with NS5806 resulted in a reduction of Ca2+ current amplitude that led to a reduction of the amplitude of Ca2+ transients. Finally, the 4-AP effect on AP phase 1 was significantly smaller when the L-type Ca2+ current was partially blocked with nifedipine, indicating that the phase 1 rate of repolarization is defined by the competition between an outward K+ current and an inward Ca2+ current.
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Affiliation(s)
| | | | - Juan Ignacio Felice
- Centro de Investigaciones Cardiovasculares, Universidad Nacional de La Plata, La Plata, Argentina
| | - Emiliano Medei
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Brazil
| | - Ariel L Escobar
- Department of Bioengineering, School of Engineering, University of California, Merced, CA
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11
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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 DOI: 10.1103/physreve.97.042414] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [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, David Geffen School of Medicine, 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, David Geffen School of Medicine, University of California, Los Angeles, California 90095, USA and Department of Biomathematics, University of California, Los Angeles, California 90095, USA
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12
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Ortega FA, Grandi E, Krogh-Madsen T, Christini DJ. Applications of Dynamic Clamp to Cardiac Arrhythmia Research: Role in Drug Target Discovery and Safety Pharmacology Testing. Front Physiol 2018; 8:1099. [PMID: 29354069 PMCID: PMC5758594 DOI: 10.3389/fphys.2017.01099] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2017] [Accepted: 12/13/2017] [Indexed: 12/31/2022] Open
Abstract
Dynamic clamp, a hybrid-computational-experimental technique that has been used to elucidate ionic mechanisms underlying cardiac electrophysiology, is emerging as a promising tool in the discovery of potential anti-arrhythmic targets and in pharmacological safety testing. Through the injection of computationally simulated conductances into isolated cardiomyocytes in a real-time continuous loop, dynamic clamp has greatly expanded the capabilities of patch clamp outside traditional static voltage and current protocols. Recent applications include fine manipulation of injected artificial conductances to identify promising drug targets in the prevention of arrhythmia and the direct testing of model-based hypotheses. Furthermore, dynamic clamp has been used to enhance existing experimental models by addressing their intrinsic limitations, which increased predictive power in identifying pro-arrhythmic pharmacological compounds. Here, we review the recent advances of the dynamic clamp technique in cardiac electrophysiology with a focus on its future role in the development of safety testing and discovery of anti-arrhythmic drugs.
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Affiliation(s)
- Francis A Ortega
- Physiology, Biophysics, and Systems Biology Graduate Program, Weill Cornell Graduate School of Medical Sciences, New York, NY, United States
| | - Eleonora Grandi
- Department of Pharmacology, University of California, Davis, Davis, CA, United States
| | - Trine Krogh-Madsen
- Greenberg Division of Cardiology, Weill Cornell Medical College, New York, NY, United States
| | - David J Christini
- Physiology, Biophysics, and Systems Biology Graduate Program, Weill Cornell Graduate School of Medical Sciences, New York, NY, United States.,Greenberg Division of Cardiology, Weill Cornell Medical College, New York, NY, United States
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13
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Chiamvimonvat N, Chen-Izu Y, Clancy CE, Deschenes I, Dobrev D, Heijman J, Izu L, Qu Z, Ripplinger CM, Vandenberg JI, Weiss JN, Koren G, Banyasz T, Grandi E, Sanguinetti MC, Bers DM, Nerbonne JM. Potassium currents in the heart: functional roles in repolarization, arrhythmia and therapeutics. J Physiol 2017; 595:2229-2252. [PMID: 27808412 DOI: 10.1113/jp272883] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Accepted: 10/11/2016] [Indexed: 12/19/2022] Open
Abstract
This is the second of the two White Papers from the fourth UC Davis Cardiovascular Symposium Systems Approach to Understanding Cardiac Excitation-Contraction Coupling and Arrhythmias (3-4 March 2016), a biennial event that brings together leading experts in different fields of cardiovascular research. The theme of the 2016 symposium was 'K+ channels and regulation', and the objectives of the conference were severalfold: (1) to identify current knowledge gaps; (2) to understand what may go wrong in the diseased heart and why; (3) to identify possible novel therapeutic targets; and (4) to further the development of systems biology approaches to decipher the molecular mechanisms and treatment of cardiac arrhythmias. The sessions of the Symposium focusing on the functional roles of the cardiac K+ channel in health and disease, as well as K+ channels as therapeutic targets, were contributed by Ye Chen-Izu, Gideon Koren, James Weiss, David Paterson, David Christini, Dobromir Dobrev, Jordi Heijman, Thomas O'Hara, Crystal Ripplinger, Zhilin Qu, Jamie Vandenberg, Colleen Clancy, Isabelle Deschenes, Leighton Izu, Tamas Banyasz, Andras Varro, Heike Wulff, Eleonora Grandi, Michael Sanguinetti, Donald Bers, Jeanne Nerbonne and Nipavan Chiamvimonvat as speakers and panel discussants. This article summarizes state-of-the-art knowledge and controversies on the functional roles of cardiac K+ channels in normal and diseased heart. We endeavour to integrate current knowledge at multiple scales, from the single cell to the whole organ levels, and from both experimental and computational studies.
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Affiliation(s)
- Nipavan Chiamvimonvat
- Department of Internal Medicine, University of California, Davis, Genome and Biomedical Science Facility, Rm 6315, Davis, CA, 95616, USA.,Department of Veterans Affairs, Northern California Health Care System, Mather, CA, 95655, USA
| | - Ye Chen-Izu
- Department of Internal Medicine, University of California, Davis, Genome and Biomedical Science Facility, Rm 6315, Davis, CA, 95616, USA.,Department of Pharmacology, University of California, Davis, Genome and Biomedical Science Facility, Rm 3503, Davis, CA, 95616, USA.,Department of Biomedical Engineering, University of California, Davis, Genome and Biomedical Science Facility, Rm 2303, Davis, CA, 95616, USA
| | - Colleen E Clancy
- Department of Pharmacology, University of California, Davis, Genome and Biomedical Science Facility, Rm 3503, Davis, CA, 95616, USA
| | - Isabelle Deschenes
- Department of Physiology and Biophysics, and Biomedical Engineering, Case Western Reserve University, Cleveland, OH, 44109, USA.,Heart and Vascular Research Center, MetroHealth Medical Center, Cleveland, OH, 44109, USA
| | - Dobromir Dobrev
- Institute of Pharmacology, West German Heart and Vascular Center, University Duisburg-Essen, Hufelandstrasse 55, 45122, Essen, Germany
| | - Jordi Heijman
- Department of Cardiology, Cardiovascular Research Institute Maastricht, Faculty of Health, Medicine, and Life Sciences, Maastricht University, Maastricht, The Netherlands
| | - Leighton Izu
- Department of Pharmacology, University of California, Davis, Genome and Biomedical Science Facility, Rm 3503, Davis, CA, 95616, USA
| | - Zhilin Qu
- Division of Cardiology, Cardiovascular Research Laboratory, David Geffen School of Medicine at UCLA, 3645 MRL, Los Angeles, CA, 90095, USA
| | - Crystal M Ripplinger
- Department of Pharmacology, University of California, Davis, Genome and Biomedical Science Facility, Rm 3503, Davis, CA, 95616, USA
| | - Jamie I Vandenberg
- Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, NSW, 2010, Australia
| | - James N Weiss
- Division of Cardiology, Cardiovascular Research Laboratory, David Geffen School of Medicine at UCLA, 3645 MRL, Los Angeles, CA, 90095, USA
| | - Gideon Koren
- Cardiovascular Research Center, Rhode Island Hospital and the Cardiovascular Institute, The Warren Alpert Medical School of Brown University, Providence, RI, 02903, USA
| | - Tamas Banyasz
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Eleonora Grandi
- Department of Pharmacology, University of California, Davis, Genome and Biomedical Science Facility, Rm 3503, Davis, CA, 95616, USA
| | - Michael C Sanguinetti
- Department of Internal Medicine, University of Utah, Nora Eccles Harrison Cardiovascular Research & Training Institute, Salt Lake City, UT, 84112, USA
| | - Donald M Bers
- Department of Pharmacology, University of California, Davis, Genome and Biomedical Science Facility, Rm 3503, Davis, CA, 95616, USA
| | - Jeanne M Nerbonne
- Departments of Developmental Biology and Internal Medicine, Cardiovascular Division, Washington University Medical School, St Louis, MO, 63110, USA
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14
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Ravagli E, Bucchi A, Bartolucci C, Paina M, Baruscotti M, DiFrancesco D, Severi S. Cell-specific Dynamic Clamp analysis of the role of funny If current in cardiac pacemaking. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2015; 120:50-66. [PMID: 26718599 DOI: 10.1016/j.pbiomolbio.2015.12.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2015] [Revised: 11/18/2015] [Accepted: 12/16/2015] [Indexed: 01/01/2023]
Abstract
We used the Dynamic Clamp technique for i) comparative validation of conflicting computational models of the hyperpolarization-activated funny current, If, and ii) quantification of the role of If in mediating autonomic modulation of heart rate. Experimental protocols based on the injection of a real-time recalculated synthetic If current in sinoatrial rabbit cells were developed. Preliminary results of experiments mimicking the autonomic modulation of If demonstrated the need for a customization procedure to compensate for cellular heterogeneity. For this reason, we used a cell-specific approach, scaling the maximal conductance of the injected current based on the cell's spontaneous firing rate. The pacemaking rate, which was significantly reduced after application of Ivabradine, was restored by the injection of synthetic current based on the Severi-DiFrancesco formulation, while the injection of synthetic current based on the Maltsev-Lakatta formulation did not produce any significant variation. A positive virtual shift of the If activation curve, mimicking the Isoprenaline effects, led to a significant increase in pacemaking rate (+17.3 ± 6.7%, p < 0.01), although of lower magnitude than that induced by real Isoprenaline (+45.0 ± 26.1%). Similarly, a negative virtual shift of the activation curve significantly lowered the pacemaking rate (-11.8 ± 1.9%, p < 0.001), as did the application of real Acetylcholine (-20.5 ± 5.1%). The Dynamic Clamp approach, applied to the If study in cardiomyocytes for the first time and rate-adapted to manage intercellular variability, indicated that: i) the quantitative description of the If current in the Severi-DiFrancesco model accurately reproduces the effects of the real current on rabbit sinoatrial cell pacemaking rate and ii) a significant portion (50-60%) of the physiological autonomic rate modulation is due to the shift of the If activation curve.
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Affiliation(s)
- E Ravagli
- Computational Physiopathology Unit, Laboratory of Cellular and Molecular Engineering, D.E.I., University of Bologna, Via Venezia 52, 47521 Cesena, Italy
| | - A Bucchi
- The PaceLab, Department of Biosciences, University of Milan, Via Celoria 26, 20133 Milano, Italy
| | - C Bartolucci
- Computational Physiopathology Unit, Laboratory of Cellular and Molecular Engineering, D.E.I., University of Bologna, Via Venezia 52, 47521 Cesena, Italy
| | - M Paina
- The PaceLab, Department of Biosciences, University of Milan, Via Celoria 26, 20133 Milano, Italy
| | - M Baruscotti
- The PaceLab, Department of Biosciences, University of Milan, Via Celoria 26, 20133 Milano, Italy
| | - D DiFrancesco
- The PaceLab, Department of Biosciences, University of Milan, Via Celoria 26, 20133 Milano, Italy
| | - S Severi
- Computational Physiopathology Unit, Laboratory of Cellular and Molecular Engineering, D.E.I., University of Bologna, Via Venezia 52, 47521 Cesena, Italy.
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15
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Huo R, Sheng Y, Guo WT, Dong DL. The potential role of Kv4.3 K+ channel in heart hypertrophy. Channels (Austin) 2015; 8:203-9. [PMID: 24762397 DOI: 10.4161/chan.28972] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Transient outward K+ current (I(to)) plays a crucial role in the early phase of cardiac action potential repolarization. Kv4.3 K(+) channel is an important component of I(to). The function and expression of Kv4.3 K(+) channel decrease in variety of heart diseases, especially in heart hypertrophy/heart failure. Int his review, we summarized the changes of cardiac Kv4.3 K(+) channel in heart diseases and discussed the potential role of Kv4.3 K(+) channel in heart hypertrophy/heart failure. In heart hypertrophy/heart failure of mice and rats, down regulation of Kv4.3 K(+) channel leads to prolongation of action potential duration (APD), which is associated with increased [Ca(2+)](I), activation of calcineurin and heart hypertrophy/heart failure.However, in canine and human, Kv4.3 K(+) channel does not play a major role in setting cardiac APD. So, in addition to Kv4.3 K(+) channel/APD/[Ca(2+)](I) pathway, there exits another mechanism of Kv4.3 K(+) channel in heart hypertrophy and heart failure: downregulation of Kv4.3 K(+) channels leads to CaMKII dissociation from Kv4.3–CaMKII complex and subsequent activation of the dissociated CaMKII , which induces heart hypertrophy/heart failure. Upregulation of Kv4.3K(+) channel inhibits CaMKII activation and its related harmful consequences. We put forward a new point-of-view that Kv4.3 K(+) channel is involved in heart hypertrophy/heart failure independently of its electric function, and drugs inhibiting or upregulating Kv4.3 K(+) channel might be potentially harmful or beneficial to hearts through CaMKII.
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16
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Kim M, McKinnon D, MacCarthy T, Rosati B, McKinnon D. Regulatory evolution and voltage-gated ion channel expression in squid axon: selection-mutation balance and fitness cliffs. PLoS One 2015; 10:e0120785. [PMID: 25875483 PMCID: PMC4395378 DOI: 10.1371/journal.pone.0120785] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2014] [Accepted: 01/27/2015] [Indexed: 11/23/2022] Open
Abstract
It has been suggested that optimization of either axonal conduction velocity or the energy efficiency of action potential conduction predominates in the selection of voltage-gated sodium conductance levels in the squid axon. A population genetics model of channel gene regulatory function was used to examine the role of these and other evolutionary forces on the selection of both sodium and potassium channel expression levels. In this model, the accumulating effects of mutations result in degradation of gene regulatory function, causing channel gene expression to fall to near-zero in the absence of positive selection. In the presence of positive selection, channel expression levels fall to the lowest values consistent with the selection criteria, thereby establishing a selection-mutation balance. Within the parameter space of sodium and potassium conductance values, the physiological performance of the squid axon model showed marked discontinuities associated with conduction failure and excitability. These discontinuities in physiological function may produce fitness cliffs. A fitness cliff associated with conduction failure, combined with the effects of phenotypic noise, can account for the selection of sodium conductance levels, without considering either conduction velocity or metabolic cost. A fitness cliff associated with a transition in axonal excitability, combined with phenotypic noise, can explain the selection of potassium channel expression levels. The results suggest that voltage-gated ion channel expression will fall to low levels, consistent with key functional constraints, even in the absence of positive selection for energy efficiency. Channel expression levels and individual variation in channel expression within the population can be explained by regulatory evolution in combination with genetic variation in regulatory function and phenotypic noise, without resorting to more complex mechanisms, such as activity-dependent homeostasis. Only a relatively small region of the large, nominally isofunctional parameter space for channel expression will normally be occupied, because of the effects of mutation.
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Affiliation(s)
- Min Kim
- Department of Neurobiology and Behavior, Stony Brook University, Stony Brook, New York, United States of America
| | - Don McKinnon
- Institute of Molecular Cardiology, Stony Brook University, Stony Brook, New York, United States of America
| | - Thomas MacCarthy
- Department of Applied Mathematics and Statistics, Stony Brook University, Stony Brook, New York, United States of America
| | - Barbara Rosati
- Institute of Molecular Cardiology, Stony Brook University, Stony Brook, New York, United States of America; Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York, United States of America
| | - David McKinnon
- Department of Neurobiology and Behavior, Stony Brook University, Stony Brook, New York, United States of America; Institute of Molecular Cardiology, Stony Brook University, Stony Brook, New York, United States of America; The Department of Research, Veterans Affairs Medical Center, Northport, New York, United States of America
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17
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Cordeiro JM, Zeina T, Goodrow R, Kaplan AD, Thomas LM, Nesterenko VV, Treat JA, Hawel L, Byus C, Bett GC, Rasmusson RL, Panama BK. Regional variation of the inwardly rectifying potassium current in the canine heart and the contributions to differences in action potential repolarization. J Mol Cell Cardiol 2015; 84:52-60. [PMID: 25889894 DOI: 10.1016/j.yjmcc.2015.04.010] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/28/2014] [Revised: 03/09/2015] [Accepted: 04/08/2015] [Indexed: 10/23/2022]
Abstract
The inward rectifier potassium current, IK1, contributes to the terminal phase of repolarization of the action potential (AP), as well as the value and stability of the resting membrane potential. Regional variation in IK1 has been noted in the canine heart, but the biophysical properties have not been directly compared. We examined the properties and functional contribution of IK1 in isolated myocytes from ventricular, atrial and Purkinje tissue. APs were recorded from canine left ventricular midmyocardium, left atrial and Purkinje tissue. The terminal rate of repolarization of the AP in ventricle, but not in Purkinje, depended on changes in external K(+) ([K(+)]o). Isolated ventricular myocytes had the greatest density of IK1 while atrial myocytes had the lowest. Furthermore, the outward component of IK1 in ventricular cells exhibited a prominent outward component and steep negative slope conductance, which was also enhanced in 10 mM [K(+)]o. In contrast, both Purkinje and atrial cells exhibited little outward IK1, even in the presence of 10 mM [K(+)]o, and both cell types showed more persistent current at positive potentials. Expression of Kir2.1 in the ventricle was 76.9-fold higher than that of atria and 5.8-fold higher than that of Purkinje, whereas the expression of Kir2.2 and Kir2.3 subunits was more evenly distributed in Purkinje and atria. Finally, AP clamp data showed distinct contributions of IK1 for each cell type. IK1 and Kir2 subunit expression varies dramatically in regions of the canine heart and these regional differences in Kir2 expression likely underlie regional distinctions in IK1 characteristics, contributing to variations in repolarization in response to in [K(+)]o changes.
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Affiliation(s)
- Jonathan M Cordeiro
- Department of Experimental Cardiology, Masonic Medical Research Laboratory, Utica, NY, United States
| | - Tanya Zeina
- Department of Experimental Cardiology, Masonic Medical Research Laboratory, Utica, NY, United States
| | - Robert Goodrow
- Department of Experimental Cardiology, Masonic Medical Research Laboratory, Utica, NY, United States
| | - Aaron D Kaplan
- Department of Physiology and Biophysics, State University of New York, University of Buffalo, Buffalo, NY, United States
| | - Lini M Thomas
- Department of Experimental Cardiology, Masonic Medical Research Laboratory, Utica, NY, United States
| | - Vladislav V Nesterenko
- Department of Experimental Cardiology, Masonic Medical Research Laboratory, Utica, NY, United States
| | - Jacqueline A Treat
- Department of Experimental Cardiology, Masonic Medical Research Laboratory, Utica, NY, United States
| | - Leo Hawel
- Division of Biomedical Sciences, School of Medicine, University of California, Riverside, Riverside, CA, United States
| | - Craig Byus
- Division of Biomedical Sciences, School of Medicine, University of California, Riverside, Riverside, CA, United States
| | - Glenna C Bett
- Department of Physiology and Biophysics, State University of New York, University of Buffalo, Buffalo, NY, United States; Department of Obstetrics and Gynecology, State University of New York, University of Buffalo, Buffalo, NY, United States
| | - Randall L Rasmusson
- Department of Physiology and Biophysics, State University of New York, University of Buffalo, Buffalo, NY, United States
| | - Brian K Panama
- Department of Experimental Cardiology, Masonic Medical Research Laboratory, Utica, NY, United States.
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18
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Perspective: a dynamics-based classification of ventricular arrhythmias. J Mol Cell Cardiol 2015; 82:136-52. [PMID: 25769672 DOI: 10.1016/j.yjmcc.2015.02.017] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/09/2014] [Revised: 02/05/2015] [Accepted: 02/20/2015] [Indexed: 02/04/2023]
Abstract
Despite key advances in the clinical management of life-threatening ventricular arrhythmias, culminating with the development of implantable cardioverter-defibrillators and catheter ablation techniques, pharmacologic/biologic therapeutics have lagged behind. The fundamental issue is that biological targets are molecular factors. Diseases, however, represent emergent properties at the scale of the organism that result from dynamic interactions between multiple constantly changing molecular factors. For a pharmacologic/biologic therapy to be effective, it must target the dynamic processes that underlie the disease. Here we propose a classification of ventricular arrhythmias that is based on our current understanding of the dynamics occurring at the subcellular, cellular, tissue and organism scales, which cause arrhythmias by simultaneously generating arrhythmia triggers and exacerbating tissue vulnerability. The goal is to create a framework that systematically links these key dynamic factors together with fixed factors (structural and electrophysiological heterogeneity) synergistically promoting electrical dispersion and increased arrhythmia risk to molecular factors that can serve as biological targets. We classify ventricular arrhythmias into three primary dynamic categories related generally to unstable Ca cycling, reduced repolarization, and excess repolarization, respectively. The clinical syndromes, arrhythmia mechanisms, dynamic factors and what is known about their molecular counterparts are discussed. Based on this framework, we propose a computational-experimental strategy for exploring the links between molecular factors, fixed factors and dynamic factors that underlie life-threatening ventricular arrhythmias. The ultimate objective is to facilitate drug development by creating an in silico platform to evaluate and predict comprehensively how molecular interventions affect not only a single targeted arrhythmia, but all primary arrhythmia dynamics categories as well as normal cardiac excitation-contraction coupling.
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19
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Workman AJ, Marshall GE, Rankin AC, Smith GL, Dempster J. Transient outward K+ current reduction prolongs action potentials and promotes afterdepolarisations: a dynamic-clamp study in human and rabbit cardiac atrial myocytes. J Physiol 2012; 590:4289-305. [PMID: 22733660 DOI: 10.1113/jphysiol.2012.235986] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Human atrial transient outward K(+) current (I(TO)) is decreased in a variety of cardiac pathologies, but how I(TO) reduction alters action potentials (APs) and arrhythmia mechanisms is poorly understood, owing to non-selectivity of I(TO) blockers. The aim of this study was to investigate effects of selective I(TO) changes on AP shape and duration (APD), and on afterdepolarisations or abnormal automaticity with β-adrenergic-stimulation, using the dynamic-clamp technique in atrial cells. Human and rabbit atrial cells were isolated by enzymatic dissociation, and electrical activity recorded by whole-cell-patch clamp (35-37°C). Dynamic-clamp-simulated I(TO) reduction or block slowed AP phase 1 and elevated the plateau, significantly prolonging APD, in both species. In human atrial cells, I(TO) block (100% I(TO) subtraction) increased APD(50) by 31%, APD(90) by 17%, and APD(-61 mV) (reflecting cellular effective refractory period) by 22% (P < 0.05 for each). Interrupting I(TO) block at various time points during repolarisation revealed that the APD(90) increase resulted mainly from plateau-elevation, rather than from phase 1-slowing or any residual I(TO). In rabbit atrial cells, partial I(TO) block (∼40% I(TO) subtraction) reversibly increased the incidence of cellular arrhythmic depolarisations (CADs; afterdepolarisations and/or abnormal automaticity) in the presence of the β-agonist isoproterenol (0.1 μm; ISO), from 0% to 64% (P < 0.05). ISO-induced CADs were significantly suppressed by dynamic-clamp increase in I(TO) (∼40% I(TO) addition). ISO+I(TO) decrease-induced CADs were abolished by β(1)-antagonism with atenolol at therapeutic concentration (1 μm). Atrial cell action potential changes from selective I(TO) modulation, shown for the first time using dynamic-clamp, have the potential to influence reentrant and non-reentrant arrhythmia mechanisms, with implications for both the development and treatment of atrial fibrillation.
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Affiliation(s)
- A J Workman
- Institute of Cardiovascular and Medical Sciences, College of Medical, Veterinary and Life Sciences, University of Glasgow, 126 University Place, Glasgow G12 8TA, UK.
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20
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Zhao Z, Xie Y, Wen H, Xiao D, Allen C, Fefelova N, Dun W, Boyden PA, Qu Z, Xie LH. Role of the transient outward potassium current in the genesis of early afterdepolarizations in cardiac cells. Cardiovasc Res 2012; 95:308-16. [PMID: 22660482 DOI: 10.1093/cvr/cvs183] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
AIMS The transient outward potassium current (I(to)) plays important roles in action potential (AP) morphology and dynamics; however, its role in the genesis of early afterdepolarizations (EADs) is not well understood. We aimed to study the effects and mechanisms of I(to) on EAD genesis in cardiac cells using combined experimental and computational approaches. METHODS AND RESULTS We first carried out patch-clamp experiments in isolated rabbit ventricular myocytes exposed to H(2)O(2) (0.2 or 1 mM), in which EADs were induced at a slow pacing rate. EADs were eliminated by either increasing the pacing rate or blocking I(to) with 2 mM 4-aminopyridine. In addition to enhancing the L-type calcium current (I(Ca,L)) and the late sodium current, H(2)O(2) also increased the conductance, slowed inactivation, and accelerated recovery from the inactivation of I(to). Computer simulations showed that I(to) promoted EADs under the condition of reduced repolarization reserve, consistent with the experimental observations. However, EADs were only promoted in the intermediate ranges of the I(to) conductance and the inactivation time constant. The underlying mechanism is that I(to) lowers the AP plateau voltage into the range at which the time-dependent potassium current (namely I(Ks)) activation is further slowed and I(Ca,L) is available for reactivation, leading to voltage oscillations to manifest EADs. Further experimental studies in cardiac cells of other species validated the theoretical predictions. CONCLUSION In cardiac cells, I(to), with a proper conductance and inactivation speed, potentiates EADs by setting the AP plateau into the voltage range where I(Ca,L) reactivation is facilitated and I(Ks) activation is slowed.
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Affiliation(s)
- Zhenghang Zhao
- Department of Pharmacology, School of Medicine, Xi'an Jiaotong University, Xi'an, China
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Wang HS, Arvanitis DA, Dong M, Niklewski PJ, Zhao W, Lam CK, Kranias EG, Sanoudou D. SERCA2a superinhibition by human phospholamban triggers electrical and structural remodeling in mouse hearts. Physiol Genomics 2011; 43:357-64. [PMID: 21266500 DOI: 10.1152/physiolgenomics.00032.2010] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Phospholamban (PLN), the reversible inhibitor of the sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA2a), is a key regulator of myocyte Ca(2+) cycling with a significant role in heart failure. We previously showed that the single amino acid difference between human and mouse PLN results in increased inhibition of Ca(2+) cycling and cardiac remodeling and attenuated stress responses in transgenic mice expressing the human PLN (hPLN) in the null background. Here we dissect the molecular and electrophysiological processes triggered by the superinhibitory hPLN in the mouse. Using a multidisciplinary approach, we performed global gene expression analysis, electrophysiology, and mathematical simulations on hPLN mice. We identified significant changes in a series of Na(+) and K(+) homeostasis genes/proteins (including Kcnd2, Scn9a, Slc8a1) and ionic conductance (including L-type Ca(2+) current, Na(+)/Ca(2+) exchanger, transient outward K(+) current). Simulation analysis suggests that this electrical remodeling has a critical role in rescuing cardiac function by improving sarcoplasmic reticulum Ca(2+) load and overall Ca(2+) dynamics. Furthermore, multiple structural and transcription factor gene expression changes indicate an ongoing structural remodeling process, favoring hypertrophy and myogenesis while suppressing apoptosis and progression to heart failure. Our findings expand current understanding of the hPLN function and provide additional insights into the downstream implications of SERCA2a superinhibition in the mammalian heart.
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Affiliation(s)
- Hong-Sheng Wang
- Department of Pharmacology, College of Medicine, University of Cincinnati, Cincinnati, Ohio 45267-0575, USA.
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Dong M, Niklewski PJ, Wang HS. Ionic mechanisms of cellular electrical and mechanical abnormalities in Brugada syndrome. Am J Physiol Heart Circ Physiol 2010; 300:H279-87. [PMID: 20935153 DOI: 10.1152/ajpheart.00079.2010] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The Brugada syndrome (BrS) is a right ventricular (RV) arrhythmia that is responsible for up to 12% of sudden cardiac deaths. The aims of our study were to determine the cellular mechanisms of the electrical abnormality in BrS and the potential basis of the RV contractile abnormality observed in the syndrome. Tetrodotoxin was used to reduce cardiac Na(+) current (I(Na)) to mimic a BrS-like setting in canine ventricular myocytes. Moderate reduction (<50%) of I(Na) with tetrodotoxin resulted in all-or-none repolarization in a fraction of RV epicardial myocytes. Dynamic clamp and modeling show that reduction of I(Na) shifts the action potential (AP) duration-transient outward current (I(to)) density curve to the left and has a biphasic effect on AP duration. In the presence of a large I(to), I(Na) reduction either prolongs or collapses the AP, depending on the exact density of I(to). These repolarization changes reduce Ca(2+) influx and sarcoplasmic reticulum load, resulting in marked attenuation of myocyte contraction and Ca(2+) transient in RV epicardial myocytes. We conclude that I(Na) reduction alters repolarization by reducing the threshold for I(to)-induced all-or-none repolarization. These cellular electrical changes suppress myocyte excitation-contraction coupling and contraction and may be a contributing factor to the contractile abnormality of the RV wall in BrS.
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Affiliation(s)
- Min Dong
- Department of Pharmacology and Cell Biophysics, 2Neuroscience Program, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0575, USA
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Dong M, Yan S, Chen Y, Niklewski PJ, Sun X, Chenault K, Wang HS. Role of the transient outward current in regulating mechanical properties of canine ventricular myocytes. J Cardiovasc Electrophysiol 2010; 21:697-703. [PMID: 20132386 DOI: 10.1111/j.1540-8167.2009.01708.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
INTRODUCTION The transient outward current (I(to)) is a major repolarizing current in the heart. Reduction of I(to) density is consistently observed in human heart failure (HF) and animal HF models. It has been proposed that I(to), via its influence on phase-1 repolarization of the action potential, facilitates L-type Ca(2+) current (I(Ca-L)) activation and sarcoplasmic reticulum Ca(2+) release, and that its down-regulation may contribute to the impaired contractility in failing heart. METHODS AND RESULTS We used the dynamic clamp to quantitatively examine the influence of I(to) on the mechanical properties of canine left ventricular myocytes at 34 degrees C. In endocardial myocytes, where the native I(to) is small, simulation of an epicardial-level artificial I(to) accentuated the phase-1 repolarization and significantly suppressed cell shortening. The peak amplitude of Ca(2+) transient was also reduced in the presence of simulated I(to), although the rate of rise of the Ca(2+) transient was increased. Conversely, subtraction, or "blockade" of the native I(to) enhanced contractility in epicardial cells. These results agree with the inverse correlation between I(to) levels and myocyte contractility and Ca(2+) transient amplitude in epicardial and endocardial myocytes. Action potential clamp studies showed that the phase-1 repolarization/I(to) versus I(Ca-L) relationship had an inverted-J shape; small I(to) enhanced peak I(Ca-L) while moderate-to-large I(to) decreased peak I(Ca-L) and markedly reduced early Ca(2+) influx. CONCLUSION Our results show that epicardial-level of I(to) acts as a negative, rather than positive regulator of myocyte mechanical properties in canine ventricular myocytes.
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Affiliation(s)
- Min Dong
- Department of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0575, USA
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Rosati B, Dong M, Cheng L, Liou SR, Yan Q, Park JY, Shiang E, Sanguinetti M, Wang HS, McKinnon D. Evolution of ventricular myocyte electrophysiology. Physiol Genomics 2008; 35:262-72. [PMID: 18765860 DOI: 10.1152/physiolgenomics.00159.2007] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The relative importance of regulatory versus structural evolution for the evolution of different biological systems is a subject of controversy. The primacy of regulatory evolution in the diversification of morphological traits has been promoted by many evolutionary developmental biologists. For physiological traits, however, the role of regulatory evolution has received less attention or has been considered to be relatively unimportant. To address this issue for electrophysiological systems, we examined the importance of regulatory and structural evolution in the evolution of the electrophysiological function of cardiac myocytes in mammals. In particular, two related phenomena were studied: the change in action potential morphology in small mammals and the scaling of action potential duration across mammalian phylogeny. In general, the functional properties of the ion channels involved in ventricular action potential repolarization were found to be relatively invariant. In contrast, there were large changes in the expression levels of multiple ion channel and transporter genes. For the Kv2.1 and Kv4.2 potassium channel genes, which are primary determinants of the action potential morphology in small mammals, the functional properties of the proximal promoter regions were found to vary in concordance with species-dependent differences in mRNA expression, suggesting that evolution of cis-regulatory elements is the primary determinant of this trait. Scaling of action potential duration was found to be a complex phenomenon, involving changes in the expression of a large number of channels and transporters. In this case, it is concluded that regulatory evolution is the predominant mechanism by which the scaling is achieved.
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Affiliation(s)
- Barbara Rosati
- Department of Physiology and Biophysics, Institute of Molecular Cardiology, Stony Brook University, Stony Brook, New York 11794-8661, USA
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Abstract
Dynamic clamp is a collection of closely related techniques that have been employed in cardiac electrophysiology to provide direct answers to numerous research questions regarding basic cellular mechanisms of action potential formation, action potential transfer and action potential synchronization in health and disease. Building on traditional current clamp, dynamic clamp was initially used to create virtual gap junctions between isolated myocytes. More recent applications include the embedding of a real pacemaking myocyte in a simulated network of atrial or ventricular cells and the insertion of virtual ion channels, either simulated in real time or simultaneously recorded from an expression system, into the membrane of an isolated myocyte. These applications have proven that dynamic clamp, which is characterized by the real-time evaluation and injection of simulated membrane current, is a powerful tool in cardiac electrophysiology. Here, each of the three different experimental configurations used in cardiac electrophysiology is reviewed. Also, directions are given for the implementation of dynamic clamp in the cardiac electrophysiology laboratory. With the growing interest in the application of dynamic clamp in cardiac electrophysiology, it is anticipated that dynamic clamp will also prove to be a powerful tool in basic research on biological pacemakers and in identification of specific ion channels as targets for drug development.
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Affiliation(s)
- Ronald Wilders
- Department of Physiology, Academic Medical Center, University of Amsterdam, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands.
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