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Hennis K, Piantoni C, Biel M, Fenske S, Wahl-Schott C. Pacemaker Channels and the Chronotropic Response in Health and Disease. Circ Res 2024; 134:1348-1378. [PMID: 38723033 PMCID: PMC11081487 DOI: 10.1161/circresaha.123.323250] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 05/13/2024]
Abstract
Loss or dysregulation of the normally precise control of heart rate via the autonomic nervous system plays a critical role during the development and progression of cardiovascular disease-including ischemic heart disease, heart failure, and arrhythmias. While the clinical significance of regulating changes in heart rate, known as the chronotropic effect, is undeniable, the mechanisms controlling these changes remain not fully understood. Heart rate acceleration and deceleration are mediated by increasing or decreasing the spontaneous firing rate of pacemaker cells in the sinoatrial node. During the transition from rest to activity, sympathetic neurons stimulate these cells by activating β-adrenergic receptors and increasing intracellular cyclic adenosine monophosphate. The same signal transduction pathway is targeted by positive chronotropic drugs such as norepinephrine and dobutamine, which are used in the treatment of cardiogenic shock and severe heart failure. The cyclic adenosine monophosphate-sensitive hyperpolarization-activated current (If) in pacemaker cells is passed by hyperpolarization-activated cyclic nucleotide-gated cation channels and is critical for generating the autonomous heartbeat. In addition, this current has been suggested to play a central role in the chronotropic effect. Recent studies demonstrate that cyclic adenosine monophosphate-dependent regulation of HCN4 (hyperpolarization-activated cyclic nucleotide-gated cation channel isoform 4) acts to stabilize the heart rate, particularly during rapid rate transitions induced by the autonomic nervous system. The mechanism is based on creating a balance between firing and recently discovered nonfiring pacemaker cells in the sinoatrial node. In this way, hyperpolarization-activated cyclic nucleotide-gated cation channels may protect the heart from sinoatrial node dysfunction, secondary arrhythmia of the atria, and potentially fatal tachyarrhythmia of the ventricles. Here, we review the latest findings on sinoatrial node automaticity and discuss the physiological and pathophysiological role of HCN pacemaker channels in the chronotropic response and beyond.
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Affiliation(s)
- Konstantin Hennis
- Institute of Cardiovascular Physiology and Pathophysiology, Biomedical Center Munich, Walter Brendel Centre of Experimental Medicine, Faculty of Medicine (K.H., C.P., C.W.-S.), Ludwig-Maximilians-Universität München, Germany
| | - Chiara Piantoni
- Institute of Cardiovascular Physiology and Pathophysiology, Biomedical Center Munich, Walter Brendel Centre of Experimental Medicine, Faculty of Medicine (K.H., C.P., C.W.-S.), Ludwig-Maximilians-Universität München, Germany
| | - Martin Biel
- Department of Pharmacy, Center for Drug Research (M.B., S.F.), Ludwig-Maximilians-Universität München, Germany
- German Centre for Cardiovascular Research (DZHK), Partner Site Munich Heart Alliance, Germany (M.B., S.F.)
| | - Stefanie Fenske
- Department of Pharmacy, Center for Drug Research (M.B., S.F.), Ludwig-Maximilians-Universität München, Germany
- German Centre for Cardiovascular Research (DZHK), Partner Site Munich Heart Alliance, Germany (M.B., S.F.)
| | - Christian Wahl-Schott
- Institute of Cardiovascular Physiology and Pathophysiology, Biomedical Center Munich, Walter Brendel Centre of Experimental Medicine, Faculty of Medicine (K.H., C.P., C.W.-S.), Ludwig-Maximilians-Universität München, Germany
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Characterization of sinoatrial automaticity in Microcebus murinus to study the effect of aging on cardiac activity and the correlation with longevity. Sci Rep 2023; 13:3054. [PMID: 36810863 PMCID: PMC9944915 DOI: 10.1038/s41598-023-29723-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2022] [Accepted: 02/09/2023] [Indexed: 02/24/2023] Open
Abstract
Microcebus murinus, or gray mouse lemur (GML), is one of the smallest primates known, with a size in between mice and rats. The small size, genetic proximity to humans and prolonged senescence, make this lemur an emerging model for neurodegenerative diseases. For the same reasons, it could help understand how aging affects cardiac activity. Here, we provide the first characterization of sinoatrial (SAN) pacemaker activity and of the effect of aging on GML heart rate (HR). According to GML size, its heartbeat and intrinsic pacemaker frequencies lie in between those of mice and rats. To sustain this fast automaticity the GML SAN expresses funny and Ca2+ currents (If, ICa,L and ICa,T) at densities similar to that of small rodents. SAN automaticity was also responsive to β-adrenergic and cholinergic pharmacological stimulation, showing a consequent shift in the localization of the origin of pacemaker activity. We found that aging causes decrease of basal HR and atrial remodeling in GML. We also estimated that, over 12 years of a lifetime, GML generates about 3 billion heartbeats, thus, as many as humans and three times more than rodents of equivalent size. In addition, we estimated that the high number of heartbeats per lifetime is a characteristic that distinguishes primates from rodents or other eutherian mammals, independently from body size. Thus, cardiac endurance could contribute to the exceptional longevity of GML and other primates, suggesting that GML's heart sustains a workload comparable to that of humans in a lifetime. In conclusion, despite the fast HR, GML replicates some of the cardiac deficiencies reported in old people, providing a suitable model to study heart rhythm impairment in aging. Moreover, we estimated that, along with humans and other primates, GML presents a remarkable cardiac longevity, enabling longer life span than other mammals of equivalent size.
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Frequency-Dependent Properties of the Hyperpolarization-Activated Cation Current, I f, in Adult Mouse Heart Primary Pacemaker Myocytes. Int J Mol Sci 2022; 23:ijms23084299. [PMID: 35457119 PMCID: PMC9024942 DOI: 10.3390/ijms23084299] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Revised: 04/05/2022] [Accepted: 04/11/2022] [Indexed: 02/04/2023] Open
Abstract
A number of distinct electrophysiological mechanisms that modulate the myogenic spontaneous pacemaker activity in the sinoatrial node (SAN) of the mammalian heart have been investigated extensively. There is agreement that several (3 or 4) different transmembrane ionic current changes (referred to as the voltage clock) are involved; and that the resulting net current interacts with direct and indirect effects of changes in intracellular Ca2+ (the calcium clock). However, significant uncertainties, and important knowledge gaps, remain concerning the functional roles in SAN spontaneous pacing of many of the individual ion channel- or exchanger-mediated transmembrane current changes. We report results from patch clamp studies and mathematical modeling of the hyperpolarization-activated current, If, in the generation/modulation of the diastolic depolarization, or pacemaker potential, produced by individual myocytes that were enzymatically isolated from the adult mouse sinoatrial node (SAN). Amphotericin-mediated patch microelectrode recordings at 35 °C were made under control conditions and in the presence of 5 or 10 nM isoproterenol (ISO). These sets of results were complemented and integrated with mathematical modeling of the current changes that take place in the range of membrane potentials (−70 to −50 mV), which corresponds to the ‘pacemaker depolarization’ in the adult mouse SAN. Our results reveal a very small, but functionally important, approximately steady-state or time-independent current generated by residual activation of If channels that are expressed in these pacemaker myocytes. Recordings of the pacemaker depolarization and action potential, combined with measurements of changes in If, and the well-known increases in the L-type Ca2+ current, ICaL, demonstrated that ICaL activation, is essential for myogenic pacing. Moreover, after being enhanced (approximately 3-fold) by 5 or 10 nM ISO, ICaL contributes significantly to the positive chronotropic effect. Our mathematical model has been developed in an attempt to better understand the underlying mechanisms for the pacemaker depolarization and action potential in adult mouse SAN myocytes. After being updated with our new experimental data describing If, our simulations reveal a novel functional component of If in adult mouse SAN. Computational work carried out with this model also confirms that in the presence of ISO the residual activation of If and opening of ICaL channels combine to generate a net current change during the slow diastolic depolarization phase that is essential for the observed accelerated pacemaking rate of these SAN myocytes.
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Al Kury LT, Chacar S, Alefishat E, Khraibi AA, Nader M. Structural and Electrical Remodeling of the Sinoatrial Node in Diabetes: New Dimensions and Perspectives. Front Endocrinol (Lausanne) 2022; 13:946313. [PMID: 35872997 PMCID: PMC9302195 DOI: 10.3389/fendo.2022.946313] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/17/2022] [Accepted: 06/14/2022] [Indexed: 11/14/2022] Open
Abstract
The sinoatrial node (SAN) is composed of highly specialized cells that mandate the spontaneous beating of the heart through self-generation of an action potential (AP). Despite this automaticity, the SAN is under the modulation of the autonomic nervous system (ANS). In diabetes mellitus (DM), heart rate variability (HRV) manifests as a hallmark of diabetic cardiomyopathy. This is paralleled by an impaired regulation of the ANS, and by a pathological remodeling of the pacemaker structure and function. The direct effect of diabetes on the molecular signatures underscoring this pathology remains ill-defined. The recent focus on the electrical currents of the SAN in diabetes revealed a repressed firing rate of the AP and an elongation of its tracing, along with conduction abnormalities and contractile failure. These changes are blamed on the decreased expression of ion transporters and cell-cell communication ports at the SAN (i.e., HCN4, calcium and potassium channels, connexins 40, 45, and 46) which further promotes arrhythmias. Molecular analysis crystallized the RGS4 (regulator of potassium currents), mitochondrial thioredoxin-2 (reactive oxygen species; ROS scavenger), and the calcium-dependent calmodulin kinase II (CaMKII) as metabolic culprits of relaying the pathological remodeling of the SAN cells (SANCs) structure and function. A special attention is given to the oxidation of CaMKII and the generation of ROS that induce cell damage and apoptosis of diabetic SANCs. Consequently, the diabetic SAN contains a reduced number of cells with significant infiltration of fibrotic tissues that further delay the conduction of the AP between the SANCs. Failure of a genuine generation of AP and conduction of their derivative waves to the neighboring atrial myocardium may also occur as a result of the anti-diabetic regiment (both acute and/or chronic treatments). All together, these changes pose a challenge in the field of cardiology and call for further investigations to understand the etiology of the structural/functional remodeling of the SANCs in diabetes. Such an understanding may lead to more adequate therapies that can optimize glycemic control and improve health-related outcomes in patients with diabetes.
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Affiliation(s)
- Lina T. Al Kury
- Department of Health Sciences, College of Natural and Health Sciences, Zayed University, Abu Dhabi, United Arab Emirates
- *Correspondence: Lina T. Al Kury, ; Moni Nader,
| | - Stephanie Chacar
- Department of Physiology and Immunology, College of Medicine and Health Sciences, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates
| | - Eman Alefishat
- Department of Pharmacology, College of Medicine and Health Sciences, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates
- Department of Biopharmaceutics and Clinical Pharmacy, School of Pharmacy, The University of Jordan, Amman, Jordan
- Center for Biotechnology, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates
| | - Ali A. Khraibi
- Department of Physiology and Immunology, College of Medicine and Health Sciences, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates
- Center for Biotechnology, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates
| | - Moni Nader
- Department of Physiology and Immunology, College of Medicine and Health Sciences, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates
- Center for Biotechnology, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates
- *Correspondence: Lina T. Al Kury, ; Moni Nader,
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Hu YF, Lee AS, Chang SL, Lin SF, Weng CH, Lo HY, Chou PC, Tsai YN, Sung YL, Chen CC, Yang RB, Lin YC, Kuo TBJ, Wu CH, Liu JD, Chung TW, Chen SA. Biomaterial-induced conversion of quiescent cardiomyocytes into pacemaker cells in rats. Nat Biomed Eng 2021; 6:421-434. [PMID: 34811487 DOI: 10.1038/s41551-021-00812-y] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2019] [Accepted: 09/17/2021] [Indexed: 02/07/2023]
Abstract
Pacemaker cells can be differentiated from stem cells or transdifferentiated from quiescent mature cardiac cells via genetic manipulation. Here we show that the exposure of rat quiescent ventricular cardiomyocytes to a silk-fibroin hydrogel activates the direct conversion of the quiescent cardiomyocytes to pacemaker cardiomyocytes by inducing the ectopic expression of the vascular endothelial cell-adhesion glycoprotein cadherin. The silk-fibroin-induced pacemaker cells exhibited functional and morphological features of genuine sinoatrial-node cardiomyocytes in vitro, and pacemaker cells generated via the injection of silk fibroin in the left ventricles of rats functioned as a surrogate in situ sinoatrial node. Biomaterials with suitable surface structure, mechanics and biochemistry could facilitate the scalable production of biological pacemakers for human use.
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Affiliation(s)
- Yu-Feng Hu
- Heart Rhythm Center, Division of Cardiology, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taiwan. .,Faculty of Medicine, School of Medicine, National Yang Ming Chiao Tung University, Taipei, Taiwan. .,Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan.
| | - An-Sheng Lee
- Department of Medicine, Mackay Medical College, New Taipei City, Taiwan
| | - Shih-Lin Chang
- Heart Rhythm Center, Division of Cardiology, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taiwan.,Faculty of Medicine, School of Medicine, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Shien-Fong Lin
- Institute of Biomedical Engineering, College of Electrical and Computer Engineering, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
| | - Ching-Hui Weng
- Heart Rhythm Center, Division of Cardiology, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taiwan
| | - Hsin-Yu Lo
- Department of Biomedical Engineering, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Pei-Chun Chou
- Heart Rhythm Center, Division of Cardiology, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taiwan
| | - Yung-Nan Tsai
- Heart Rhythm Center, Division of Cardiology, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taiwan
| | - Yen-Ling Sung
- Institute of Biomedical Engineering, College of Electrical and Computer Engineering, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
| | - Chien-Chang Chen
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan
| | - Ruey-Bing Yang
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan
| | - Yuh-Charn Lin
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan
| | - Terry B J Kuo
- Institute of Brain Science, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Cheng-Han Wu
- Institute of Brain Science, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Jin-Dian Liu
- Heart Rhythm Center, Division of Cardiology, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taiwan
| | - Tze-Wen Chung
- Department of Biomedical Engineering, National Yang Ming Chiao Tung University, Taipei, Taiwan. .,Center for Advanced Pharmaceutical Research and Drug Delivery, National Yang Ming Chiao Tung University, Taipei, Taiwan.
| | - Shih-Ann Chen
- Heart Rhythm Center, Division of Cardiology, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taiwan.,Faculty of Medicine, School of Medicine, National Yang Ming Chiao Tung University, Taipei, Taiwan.,Cardiovascular Center, Taichung Veterans General Hospital, Taichung, Taiwan
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6
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Poelzing S, Weinberg SH, Keener JP. Initiation and entrainment of multicellular automaticity via diffusion limited extracellular domains. Biophys J 2021; 120:5279-5294. [PMID: 34757078 DOI: 10.1016/j.bpj.2021.10.034] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2021] [Revised: 09/12/2021] [Accepted: 10/26/2021] [Indexed: 01/07/2023] Open
Abstract
Electrically excitable cells often spontaneously and synchronously depolarize in vitro and in vivo preparations. It remains unclear how cells entrain and autorhythmically activate above the intrinsic mean activation frequency of isolated cells with or without pacemaking mechanisms. Recent studies suggest that cyclic ion accumulation and depletion in diffusion-limited extracellular volumes modulate electrophysiology by ephaptic mechanisms (nongap junction or synaptic coupling). This report explores how potassium accumulation and depletion in a restricted extracellular domain induces spontaneous action potentials in two different computational models of excitable cells without gap junctional coupling: Hodgkin-Huxley and Luo-Rudy. Importantly, neither model will spontaneously activate on its own without external stimuli. Simulations demonstrate that cells sharing a diffusion-limited extracellular compartment can become autorhythmic and entrained despite intercellular electrical heterogeneity. Autorhythmic frequency is modulated by the cleft volume and potassium fluxes through the cleft. Additionally, inexcitable cells can suppress or induce autorhythmic activity in an excitable cell via a shared cleft. Diffusion-limited shared clefts can also entrain repolarization. Critically, this model predicts a mechanism by which diffusion-limited shared clefts can initiate, entrain, and modulate multicellular automaticity in the absence of gap junctions.
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Affiliation(s)
- Steven Poelzing
- Fralin Biomedical Research Institute at Virginia Tech Carilion, Center for Heart and Reparative Medicine, and the Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, Roanoke, Virginia.
| | - Seth H Weinberg
- Department of Biomedical Engineering, Davis Heart and Lung Research Institute, and the Wexner Medical Center, The Ohio State University, Columbus, Ohio
| | - James P Keener
- Department of Mathematics, University of Utah, Salt Lake City, Utah
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7
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Hu W, Clark RB, Giles WR, Shibata E, Zhang H. Physiological Roles of the Rapidly Activated Delayed Rectifier K + Current in Adult Mouse Heart Primary Pacemaker Activity. Int J Mol Sci 2021; 22:4761. [PMID: 33946248 PMCID: PMC8124469 DOI: 10.3390/ijms22094761] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2021] [Revised: 04/27/2021] [Accepted: 04/28/2021] [Indexed: 01/01/2023] Open
Abstract
Robust, spontaneous pacemaker activity originating in the sinoatrial node (SAN) of the heart is essential for cardiovascular function. Anatomical, electrophysiological, and molecular methods as well as mathematical modeling approaches have quite thoroughly characterized the transmembrane fluxes of Na+, K+ and Ca2+ that produce SAN action potentials (AP) and 'pacemaker depolarizations' in a number of different in vitro adult mammalian heart preparations. Possible ionic mechanisms that are responsible for SAN primary pacemaker activity are described in terms of: (i) a Ca2+-regulated mechanism based on a requirement for phasic release of Ca2+ from intracellular stores and activation of an inward current-mediated by Na+/Ca2+ exchange; (ii) time- and voltage-dependent activation of Na+ or Ca2+ currents, as well as a cyclic nucleotide-activated current, If; and/or (iii) a combination of (i) and (ii). Electrophysiological studies of single spontaneously active SAN myocytes in both adult mouse and rabbit hearts consistently reveal significant expression of a rapidly activating time- and voltage-dependent K+ current, often denoted IKr, that is selectively expressed in the leading or primary pacemaker region of the adult mouse SAN. The main goal of the present study was to examine by combined experimental and simulation approaches the functional or physiological roles of this K+ current in the pacemaker activity. Our patch clamp data of mouse SAN myocytes on the effects of a pharmacological blocker, E4031, revealed that a rapidly activating K+ current is essential for action potential (AP) repolarization, and its deactivation during the pacemaker potential contributes a small but significant component to the pacemaker depolarization. Mathematical simulations using a murine SAN AP model confirm that well known biophysical properties of a delayed rectifier K+ current can contribute to its role in generating spontaneous myogenic activity.
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Affiliation(s)
- Wei Hu
- Biological Physics Group, Department of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, UK;
| | - Robert B. Clark
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, AB T2N 4N1, Canada; (R.B.C.); (W.R.G.)
| | - Wayne R. Giles
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, AB T2N 4N1, Canada; (R.B.C.); (W.R.G.)
| | - Erwin Shibata
- Department of Physiology, Carver School of Medicine, University of Iowa, Iowa City, IA 52242, USA;
| | - Henggui Zhang
- Biological Physics Group, Department of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, UK;
- Key Laboratory of Medical Electrophysiology of Ministry of Education and Medical Electrophysiological Key Laboratory of Sichuan Province, Institute of Cardiovascular Research, Southwest Medical University, Luzhou 646000, China
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8
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Alghamdi AM, Boyett MR, Hancox JC, Zhang H. Cardiac Pacemaker Dysfunction Arising From Different Studies of Ion Channel Remodeling in the Aging Rat Heart. Front Physiol 2020; 11:546508. [PMID: 33343378 PMCID: PMC7744970 DOI: 10.3389/fphys.2020.546508] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2020] [Accepted: 11/13/2020] [Indexed: 12/19/2022] Open
Abstract
The function of the sinoatrial node (SAN), the pacemaker of the heart, declines with age, resulting in increased incidence of sinoatrial node dysfunction (SND) in older adults. The present study assesses potential ionic mechanisms underlying age associated SND. Two group studies have identified complex and various changes in some of membrane ion channels in aged rat SAN, the first group (Aging Study-1) indicates a considerable changes of gene expression with up-regulation of mRNA in ion channels of Cav1.2, Cav1.3 and KvLQT1, Kv4.2, and the Ca2+ handling proteins of SERCA2a, and down-regulation of Cav3.1, NCX, and HCN1 and the Ca2+-clock proteins of RYR2. The second group (Aging Study-2) suggests a different pattern of changes, including down regulation of Cav1.2, Cav1.3 and HCN4, and RYR2, and an increase of NCX and SERCA densities and proteins. Although both data sets shared a similar finding for some specific ion channels, such as down regulation of HCN4, NCX, and RYR2, there are contradictory changes for some other membrane ion channels, such as either up-regulation or down-regulation of Cav1.2, NCX and SERCA2a in aged rat SAN. The present study aims to test a hypothesis that age-related SND may arise from different ionic and molecular remodeling patterns. To test this hypothesis, a mathematical model of the electrical action potential of rat SAN myocytes was modified to simulate the functional impact of age-induced changes on membrane ion channels and intracellular Ca2+ handling as observed in Aging Study-1 and Aging Study-2. The role and relative importance of each individually remodeled ion channels and Ca2+-handling in the two datasets were evaluated. It was shown that the age-induced changes in ion channels and Ca2+-handling, based on either Aging Study-1 or Aging Study-2, produced similar bradycardic effects as manifested by a marked reduction in the heart rate (HR) that matched experimental observations. Further analysis showed that although the SND arose from an integrated action of all remodeling of ion channels and Ca2+-handling in both studies, it was the change to I CaL that played the most important influence.
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Affiliation(s)
- Aaazh M Alghamdi
- Biological Physics Group, Department of Physics and Astronomy, The University of Manchester, Manchester, United Kingdom.,Department of Physics, Faculty of Science, University of Jeddah, Jeddah, Saudi Arabia
| | - Mark R Boyett
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Jules C Hancox
- Biological Physics Group, Department of Physics and Astronomy, The University of Manchester, Manchester, United Kingdom.,School of Physiology, Pharmacology and Neuroscience, and Cardiovascular Research Laboratories, Faculty of Life Sciences, University of Bristol, Bristol, United Kingdom
| | - Henggui Zhang
- Biological Physics Group, Department of Physics and Astronomy, The University of Manchester, Manchester, United Kingdom.,Peng Cheng Laboratory, Shenzhen, China.,Key Laboratory of Medical Electrophysiology of Ministry of Education and Medical Electrophysiological Key Laboratory of Sichuan Province, Institute of Cardiovascular Research, Southwest Medical University, Luzhou, China
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9
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Ivanova AD, Samoilova DV, Razumov AA, Kuzmin VS. Rat caval vein myocardium undergoes changes in conduction characteristics during postnatal ontogenesis. Pflugers Arch 2019; 471:1493-1503. [PMID: 31654199 DOI: 10.1007/s00424-019-02320-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2019] [Revised: 09/10/2019] [Accepted: 10/07/2019] [Indexed: 01/27/2023]
Abstract
The electrophysiological properties of the superior vena cava (SVC) myocardium, which is considered a minor source of atrial arrhythmias, were studied in this study during postnatal development. Conduction properties were investigated in spontaneously active and electrically paced SVC preparations obtained from 7-60-day-old male Wistar rats using optical mapping and microelectrode techniques. The presence of high-conductance connexin 43 (Cx43) was evaluated in SVC cross-sections using immunofluorescence. It was found that SVC myocardium is excitable, electrically coupled with the atrial tissue, and conducts excitation waves at all stages of postnatal development. However, the conduction velocity (CV) of excitation and action potential (AP) upstroke velocity in SVC were significantly lower in neonatal than in adult animals and increased with postnatal maturation. Connexins Cx43 were identified in both neonatal and adult rat SVC myocardium; however, the abundance of Cx43 was significantly less in neonates. The gap junction uncoupler octanol affected conduction more profound in the neonatal than in adult SVC. We demonstrated for the first time that the conduction characteristics of SVC myocardium change from a slow-conduction (nodal) to a high-conduction (working) phenotype during postnatal ontogenesis. An age-related CV increase may occur due to changes of AP characteristics, electrical coupling, and Cx43 presence in SVC cardiomyocyte membranes. Observed changes may contribute to the low proarrhythmicity of adult caval vein cardiac tissue, while pre- or postnatal developmental abnormalities that delay the establishment of the working conduction phenotype may facilitate SVC proarrhythmia.
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Affiliation(s)
- Alexandra D Ivanova
- Department of Human and Animal Physiology, Biological Faculty, Lomonosov Moscow State University, 1-12 Leninskie Gory, Moscow, Russia, 119234.
| | - Daria V Samoilova
- N. N. Blokhin National Medical Research Centre of Oncology, Moscow, Russia
| | - Artem A Razumov
- Ural Federal University, Institute of Natural Sciences and Mathematics, Ekaterinburg, Russia
| | - Vlad S Kuzmin
- Department of Human and Animal Physiology, Biological Faculty, Lomonosov Moscow State University, 1-12 Leninskie Gory, Moscow, Russia, 119234
- Pirogov Russian National Research Medical University (RNRMU), Moscow, Russia
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10
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Sinus node-like pacemaker mechanisms regulate ectopic pacemaker activity in the adult rat atrioventricular ring. Sci Rep 2019; 9:11781. [PMID: 31409881 PMCID: PMC6692414 DOI: 10.1038/s41598-019-48276-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2018] [Accepted: 07/02/2019] [Indexed: 01/01/2023] Open
Abstract
In adult mammalian hearts, atrioventricular rings (AVRs) surround the atrial orifices of atrioventricular valves and are hotbed of ectopic activity in patients with focal atrial tachycardia. Experimental data offering mechanistic insights into initiation and maintenance of ectopic foci is lacking. We aimed to characterise AVRs in structurally normal rat hearts, identify arrhythmia predisposition and investigate mechanisms underlying arrhythmogenicity. Extracellular potential mapping and intracellular action potential recording techniques were used for electrophysiology, qPCR for gene and, Western blot and immunohistochemistry for protein expression. Conditions favouring ectopic foci were assessed by simulations. In right atrial preparations, sinus node (SN) was dominant and AVRs displayed 1:1 impulse conduction. Detaching SN unmasked ectopic pacemaking in AVRs and pacemaker action potentials were SN-like. Blocking pacemaker current If, and disrupting intracellular Ca2+ release, prolonged spontaneous cycle length in AVRs, indicating a role for SN-like pacemaker mechanisms. AVRs labelled positive for HCN4, and SERCA2a was comparable to SN. Pacemaking was potentiated by isoproterenol and abolished with carbachol and AVRs had abundant sympathetic nerve endings. β2-adrenergic and M2-muscarinic receptor mRNA and β2-receptor protein were comparable to SN. In computer simulations of a sick SN, ectopic foci in AVR were unmasked, causing transient suppression of SN pacemaking.
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11
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Kodirov SA. Tale of tail current. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2019; 150:78-97. [PMID: 31238048 DOI: 10.1016/j.pbiomolbio.2019.06.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2019] [Revised: 05/22/2019] [Accepted: 06/20/2019] [Indexed: 02/07/2023]
Abstract
The largest biomass of channel proteins is located in unicellular organisms and bacteria that have no organs. However, orchestrated bidirectional ionic currents across the cell membrane via the channels are important for the functioning of organs of organisms, and equally concern both fauna or flora. Several ion channels are activated in the course of action potentials. One of the hallmarks of voltage-dependent channels is a 'tail current' - deactivation as observed after prior and sufficient activation predominantly at more depolarized potentials e.g. for Kv while upon hyperpolarization for HCN α subunits. Tail current also reflects the timing of channel closure that is initiated upon termination of stimuli. Finally, deactivation of currents during repolarization could be a selective estimate for given channel as in case of HERG, if dedicated long and more depolarized 'tail pulse' is used. Since from a holding potential of e.g. -70 mV are often a family of outward K+ currents comprising IA and IK are simultaneously activated in native cells.
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Affiliation(s)
- Sodikdjon A Kodirov
- Pavlov Institute of Physiology, Russian Academy of Sciences, Saint Petersburg, Russia; Cardiovascular Division, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, 02115, USA; Almazov Federal Heart, Blood and Endocrinology Centre, Saint Petersburg, 197341, Russia; Institute of Experimental Medicine, I. P. Pavlov Department of Physiology, Russian Academy of Medical Sciences, Saint Petersburg, Russia; Laboratory of Emotions' Neurobiology, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, 02-093, Poland.
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12
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Umehara S, Tan X, Okamoto Y, Ono K, Noma A, Amano A, Himeno Y. Mechanisms Underlying Spontaneous Action Potential Generation Induced by Catecholamine in Pulmonary Vein Cardiomyocytes: A Simulation Study. Int J Mol Sci 2019; 20:ijms20122913. [PMID: 31207916 PMCID: PMC6628582 DOI: 10.3390/ijms20122913] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2019] [Revised: 06/11/2019] [Accepted: 06/12/2019] [Indexed: 12/24/2022] Open
Abstract
Cardiomyocytes and myocardial sleeves dissociated from pulmonary veins (PVs) potentially generate ectopic automaticity in response to noradrenaline (NA), and thereby trigger atrial fibrillation. We developed a mathematical model of rat PV cardiomyocytes (PVC) based on experimental data that incorporates the microscopic framework of the local control theory of Ca2+ release from the sarcoplasmic reticulum (SR), which can generate rhythmic Ca2+ release (limit cycle revealed by the bifurcation analysis) when total Ca2+ within the cell increased. Ca2+ overload in SR increased resting Ca2+ efflux through the type II inositol 1,4,5-trisphosphate (IP3) receptors (InsP3R) as well as ryanodine receptors (RyRs), which finally triggered massive Ca2+ release through activation of RyRs via local Ca2+ accumulation in the vicinity of RyRs. The new PVC model exhibited a resting potential of −68 mV. Under NA effects, repetitive Ca2+ release from SR triggered spontaneous action potentials (APs) by evoking transient depolarizations (TDs) through Na+/Ca2+ exchanger (APTDs). Marked and variable latencies initiating APTDs could be explained by the time courses of the α1- and β1-adrenergic influence on the regulation of intracellular Ca2+ content and random occurrences of spontaneous TD activating the first APTD. Positive and negative feedback relations were clarified under APTD generation.
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Affiliation(s)
- Shohei Umehara
- Department of Bioinformatics, College of Life Sciences, Ritsumeikan University, Shiga 525-8577, Japan.
| | - Xiaoqiu Tan
- Institute of Cardiovascular Research, Southwest Medical University, Luzhou 640000, China.
| | - Yosuke Okamoto
- Department of Cell Physiology, Graduate School of Medicine, Akita University, Akita 010-8543, Japan.
| | - Kyoichi Ono
- Department of Cell Physiology, Graduate School of Medicine, Akita University, Akita 010-8543, Japan.
| | - Akinori Noma
- Department of Bioinformatics, College of Life Sciences, Ritsumeikan University, Shiga 525-8577, Japan.
| | - Akira Amano
- Department of Bioinformatics, College of Life Sciences, Ritsumeikan University, Shiga 525-8577, Japan.
| | - Yukiko Himeno
- Department of Bioinformatics, College of Life Sciences, Ritsumeikan University, Shiga 525-8577, Japan.
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Sun Y, Timofeyev V, Dennis A, Bektik E, Wan X, Laurita KR, Deschênes I, Li RA, Fu JD. A Singular Role of I K1 Promoting the Development of Cardiac Automaticity during Cardiomyocyte Differentiation by I K1 -Induced Activation of Pacemaker Current. Stem Cell Rev Rep 2018. [PMID: 28623610 DOI: 10.1007/s12015-017-9745-1] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The inward rectifier potassium current (IK1) is generally thought to suppress cardiac automaticity by hyperpolarizing membrane potential (MP). We recently observed that IK1 could promote the spontaneously-firing automaticity induced by upregulation of pacemaker funny current (If) in adult ventricular cardiomyocytes (CMs). However, the intriguing ability of IK1 to activate If and thereby promote automaticity has not been explored. In this study, we combined mathematical and experimental assays and found that only IK1 and If, at a proper-ratio of densities, were sufficient to generate rhythmic MP-oscillations even in unexcitable cells (i.e. HEK293T cells and undifferentiated mouse embryonic stem cells [ESCs]). We termed this effect IK1-induced If activation. Consistent with previous findings, our electrophysiological recordings observed that around 50% of mouse (m) and human (h) ESC-differentiated CMs could spontaneously fire action potentials (APs). We found that spontaneously-firing ESC-CMs displayed more hyperpolarized maximum diastolic potential and more outward IK1 current than quiescent-yet-excitable m/hESC-CMs. Rather than classical depolarization pacing, quiescent mESC-CMs were able to fire APs spontaneously with an electrode-injected small outward-current that hyperpolarizes MP. The automaticity to spontaneously fire APs was also promoted in quiescent hESC-CMs by an IK1-specific agonist zacopride. In addition, we found that the number of spontaneously-firing m/hESC-CMs was significantly decreased when If was acutely upregulated by Ad-CGI-HCN infection. Our study reveals a novel role of IK1 promoting the development of cardiac automaticity in m/hESC-CMs through a mechanism of IK1-induced If activation and demonstrates a synergistic interaction between IK1 and If that regulates cardiac automaticity.
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Affiliation(s)
- Yu Sun
- Department of Medicine, Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University, 2500 Metrohealth Drive, Rammelkamp 650, Cleveland, OH, 44109, USA
| | - Valeriy Timofeyev
- Department of Internal Medicine, University of California, Davis, CA, USA
| | - Adrienne Dennis
- Department of Medicine, Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University, 2500 Metrohealth Drive, Rammelkamp 650, Cleveland, OH, 44109, USA
| | - Emre Bektik
- Department of Medicine, Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University, 2500 Metrohealth Drive, Rammelkamp 650, Cleveland, OH, 44109, USA.,Ph.D. Program in Human Biology, School of Integrative and Global Majors, University of Tsukuba, Tsukuba, Japan
| | - Xiaoping Wan
- Department of Medicine, Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University, 2500 Metrohealth Drive, Rammelkamp 650, Cleveland, OH, 44109, USA
| | - Kenneth R Laurita
- Department of Medicine, Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University, 2500 Metrohealth Drive, Rammelkamp 650, Cleveland, OH, 44109, USA
| | - Isabelle Deschênes
- Department of Medicine, Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University, 2500 Metrohealth Drive, Rammelkamp 650, Cleveland, OH, 44109, USA
| | - Ronald A Li
- Dr. Li Dak-Sum Center for Regenerative Medicine, University of Hong Kong, The Hong Kong Jockey Club Building for Interdisciplinary Research, LB 5-06, 5 Sassoon Road, Pokfulam, Hong Kong. .,Ming-Wai Lau Center for Regenerative Medicine, Karolinska Institutet, Solna, Sweden.
| | - Ji-Dong Fu
- Department of Medicine, Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University, 2500 Metrohealth Drive, Rammelkamp 650, Cleveland, OH, 44109, USA.
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Chen K, Zuo D, Wang SY, Chen H. Kir2 inward rectification-controlled precise and dynamic balances between Kir2 and HCN currents initiate pacemaking activity. FASEB J 2018; 32:3047-3057. [PMID: 29401592 DOI: 10.1096/fj.201701260r] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Spontaneous rhythmic action potential or pacemaking activity of pacemaker cells controls rhythmic signaling such as heartbeat. The mechanism underlying the origin of pacemaking activity is not well understood. In this study, we created human embryonic kidney (HEK) 293 cells that show pacemaking activity through heterologous expression of strong inward rectifier K+ subfamily 2 isoform 1 (Kir2.1) channels, hyperpolarization-activated cyclic nucleotide-gated isoform 2 (HCN2) nonselective cation channels, and voltage-gated Na+ subfamily 1 isoform 5 or Ca2+ subfamily 3 isoform 1 (Nav1.5 or Cav3.1) channels. A range of relative levels of Kir2.1 and HCN2 currents dynamically counterbalance, generating spontaneous rhythmic oscillation of resting membrane potential between -64 and -34 mV and determining oscillation rates. Each oscillation cycle begins with an autodepolarization phase, which slowly proceeds to the threshold potential that activates Nav1.5 or Cav3.1 channels and triggers action potential, causing engineered HEK293 cells to exhibit pacemaking activity at a rate of ≤67 beats/min. Engineered HEK293 cells with Kir2.1 and either HCN3 or HCN4 also show the oscillation. Engineered HEK293 cells expressing HCN2 and other Kir2 channels, which lack Kir2.1-like complete inward rectification, do not show the oscillation. Therefore, Kir2.1-like inward rectification-controlled precise and dynamic balances between Kir2 and HCN currents initiate spontaneous rhythmic action potential and form an origin of pacemaking activity; Kir2 and HCN channels play essential roles in pacemaking activity.-Chen, K., Zuo, D., Wang, S.-Y. Chen, H. Kir2 inward rectification-controlled precise and dynamic balances between Kir2 and HCN currents initiate pacemaking activity.
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Affiliation(s)
- Kuihao Chen
- Department of Biological Sciences, University at Albany, State University of New York, Albany, New York, USA
| | - Dongchuan Zuo
- Department of Biological Sciences, University at Albany, State University of New York, Albany, New York, USA
| | - Sho-Ya Wang
- Department of Biological Sciences, University at Albany, State University of New York, Albany, New York, USA
| | - Haijun Chen
- Department of Biological Sciences, University at Albany, State University of New York, Albany, New York, USA
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15
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Howarth FC, Qureshi MA, Jayaprakash P, Parekh K, Oz M, Dobrzynski H, Adrian TE. The Pattern of mRNA Expression Is Changed in Sinoatrial Node from Goto-Kakizaki Type 2 Diabetic Rat Heart. J Diabetes Res 2018; 2018:8454078. [PMID: 30246030 PMCID: PMC6139199 DOI: 10.1155/2018/8454078] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/10/2018] [Revised: 07/16/2018] [Accepted: 08/12/2018] [Indexed: 01/01/2023] Open
Abstract
BACKGROUND In vivo experiments in Goto-Kakizaki (GK) type 2 diabetic rats have demonstrated reductions in heart rate from a young age. The expression of genes encoding more than 70 proteins that are associated with the generation and conduction of electrical activity in the GK sinoatrial node (SAN) have been evaluated to further clarify the molecular basis of the low heart rate. MATERIALS AND METHODS Heart rate and expression of genes were evaluated with an extracellular electrode and real-time RT-PCR, respectively. Rats aged 12-13 months were employed in these experiments. RESULTS Isolated spontaneous heart rate was reduced in GK heart (161 ± 12 bpm) compared to controls (229 ± 11 bpm). There were many differences in expression of mRNA, and some of these differences were of particular interest. Compared to control SAN, expression of some genes were downregulated in GK-SAN: gap junction, Gja1 (Cx43), Gja5 (Cx40), Gjc1 (Cx45), and Gjd3 (Cx31.9); cell membrane transport, Trpc1 (TRPC1) and Trpc6 (TRPC6); hyperpolarization-activated cyclic nucleotide-gated channels, Hcn1 (HCN1) and Hcn4 (HCN4); calcium channels, Cacna1d (Cav1.3), Cacna1g (Cav3.1), Cacna1h (Cav3.2), Cacna2d1 (Cavα2δ1), Cacna2d3 (Cavα2δ3), and Cacng4 (Cav γ 4); and potassium channels, Kcna2 (Kv1.2), Kcna4 (Kv1.4), Kcna5 (Kv1.5), Kcnb1 (Kv2.1), Kcnd3 (Kv4.3), Kcnj2 (Kir2.1), Kcnk1 (TWIK1), Kcnk5 (K2P5.1), Kcnk6 (TWIK2), and Kcnn2 (SK2) whilst others were upregulated in GK-SAN: Ryr2 (RYR2) and Nppb (BNP). CONCLUSIONS This study provides new insight into the changing expression of genes in the sinoatrial node of diabetic heart.
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MESH Headings
- Action Potentials
- Animals
- Arrhythmias, Cardiac/etiology
- Arrhythmias, Cardiac/genetics
- Arrhythmias, Cardiac/metabolism
- Arrhythmias, Cardiac/physiopathology
- Diabetes Mellitus, Type 2/complications
- Diabetes Mellitus, Type 2/genetics
- Diabetes Mellitus, Type 2/metabolism
- Diabetic Cardiomyopathies/etiology
- Diabetic Cardiomyopathies/genetics
- Diabetic Cardiomyopathies/metabolism
- Diabetic Cardiomyopathies/physiopathology
- Disease Models, Animal
- Gene Expression Regulation
- Heart Rate/genetics
- Isolated Heart Preparation
- Male
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Rats, Wistar
- Sinoatrial Node/metabolism
- Sinoatrial Node/physiopathology
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Affiliation(s)
- F. C. Howarth
- Department of Physiology, College of Medicine & Health Sciences, UAE University, Al Ain, UAE
| | - M. A. Qureshi
- Department of Physiology, College of Medicine & Health Sciences, UAE University, Al Ain, UAE
| | - P. Jayaprakash
- Department of Pharmacology, College of Medicine & Health Sciences, UAE University, Al Ain, UAE
| | - K. Parekh
- Department of Physiology, College of Medicine & Health Sciences, UAE University, Al Ain, UAE
| | - M. Oz
- Department of Pharmacology, College of Medicine & Health Sciences, UAE University, Al Ain, UAE
| | - H. Dobrzynski
- Cardiovascular Sciences, University of Manchester, Manchester, UK
| | - T. E. Adrian
- Department of Basic Medical Sciences, Mohammed Bin Rashid University of Medicine & Health Sciences, Dubai, UAE
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16
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Toyoda F, Ding WG, Matsuura H. Heterogeneous functional expression of the sustained inward Na + current in guinea pig sinoatrial node cells. Pflugers Arch 2017; 470:481-490. [PMID: 29197941 DOI: 10.1007/s00424-017-2091-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2017] [Revised: 11/08/2017] [Accepted: 11/21/2017] [Indexed: 11/26/2022]
Abstract
The sustained inward Na+ current (I st) identified in the sinoatrial node (SAN) cell has been suggested to play a pivotal role in cardiac pacemaking. However, the composition of cells in the SAN is heterogeneous and cell-to-cell variability in the magnitude of I st remains to be fully characterized. The present study investigated the current density of I st in morphologically different types of pacemaker cells dissociated from guinea pig SAN. I st was preferentially detected in spontaneously active spindle or spider-shaped cells, but was less well expressed in larger-sized elongated spindle-type cells and practically absent in clearly striated atrial-like cells, despite clear expression of the funny current (I f). The current density of I st in spindle and spider cells varied from 0.7 to 1.6 pA pF-1 and was significantly reduced in non-beating cells with similar morphologies. By linear regression analysis, we identified a positive correlation between the current densities of I st and the L-type Ca2+ current (I Ca,L), which was specifically observed in spindle and spider cells. These cells exhibited a more negative voltage for half maximal I Ca,L activation than atrial-like cells, suggesting a variable ratio between CaV1.2- and CaV1.3-mediated I Ca,L in SAN cells. Consistent single-cell transcript measurements confirmed a higher relative expression of CaV1.3, which activates at more negative potentials, in spindle cells than in atrial-like cells. Taken together, these results can be interpreted as indicating that I st plays a specific role in primary pacemaker cells and that its presence is closely correlated with functional levels of CaV1.3-mediated I Ca,L.
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Affiliation(s)
- Futoshi Toyoda
- Department of Physiology, Shiga University of Medical Science, Seta Tsukinowa, Otsu, Shiga, 520-2192, Japan.
| | - Wei-Guang Ding
- Department of Physiology, Shiga University of Medical Science, Seta Tsukinowa, Otsu, Shiga, 520-2192, Japan
| | - Hiroshi Matsuura
- Department of Physiology, Shiga University of Medical Science, Seta Tsukinowa, Otsu, Shiga, 520-2192, Japan
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17
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Ca V1.3 L-type Ca 2+ channel contributes to the heartbeat by generating a dihydropyridine-sensitive persistent Na + current. Sci Rep 2017; 7:7869. [PMID: 28801600 PMCID: PMC5554211 DOI: 10.1038/s41598-017-08191-8] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2017] [Accepted: 07/07/2017] [Indexed: 11/22/2022] Open
Abstract
The spontaneous activity of sinoatrial node (SAN) pacemaker cells is generated by a functional interplay between the activity of ionic currents of the plasma membrane and intracellular Ca2+ dynamics. The molecular correlate of a dihydropyridine (DHP)-sensitive sustained inward Na+ current (Ist), a key player in SAN automaticity, is still unknown. Here we show that Ist and the L-type Ca2+ current (ICa,L) share CaV1.3 as a common molecular determinant. Patch-clamp recordings of mouse SAN cells showed that Ist is activated in the diastolic depolarization range, and displays Na+ permeability and minimal inactivation and sensitivity to ICa,L activators and blockers. Both CaV1.3-mediated ICa,L and Ist were abolished in CaV1.3-deficient (CaV1.3−/−) SAN cells but the CaV1.2-mediated ICa,L current component was preserved. In SAN cells isolated from mice expressing DHP-insensitive CaV1.2 channels (CaV1.2DHP−/−), Ist and CaV1.3-mediated ICa,L displayed overlapping sensitivity and concentration–response relationships to the DHP blocker nifedipine. Consistent with the hypothesis that CaV1.3 rather than CaV1.2 underlies Ist, a considerable fraction of ICa,L was resistant to nifedipine inhibition in CaV1.2DHP−/− SAN cells. These findings identify CaV1.3 channels as essential molecular components of the voltage-dependent, DHP-sensitive Ist Na+ current in the SAN.
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18
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Weisbrod D, Khun SH, Bueno H, Peretz A, Attali B. Mechanisms underlying the cardiac pacemaker: the role of SK4 calcium-activated potassium channels. Acta Pharmacol Sin 2016; 37:82-97. [PMID: 26725737 PMCID: PMC4722971 DOI: 10.1038/aps.2015.135] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2015] [Accepted: 11/25/2015] [Indexed: 12/25/2022] Open
Abstract
The proper expression and function of the cardiac pacemaker is a critical feature of heart physiology. The sinoatrial node (SAN) in human right atrium generates an electrical stimulation approximately 70 times per minute, which propagates from a conductive network to the myocardium leading to chamber contractions during the systoles. Although the SAN and other nodal conductive structures were identified more than a century ago, the mechanisms involved in the generation of cardiac automaticity remain highly debated. In this short review, we survey the current data related to the development of the human cardiac conduction system and the various mechanisms that have been proposed to underlie the pacemaker activity. We also present the human embryonic stem cell-derived cardiomyocyte system, which is used as a model for studying the pacemaker. Finally, we describe our latest characterization of the previously unrecognized role of the SK4 Ca(2+)-activated K(+) channel conductance in pacemaker cells. By exquisitely balancing the inward currents during the diastolic depolarization, the SK4 channels appear to play a crucial role in human cardiac automaticity.
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Affiliation(s)
- David Weisbrod
- Department of Physiology & Pharmacology, Sackler Faculty of Medicine, Sagol School of Neuroscience, Tel Aviv University, Tel Aviv 69978, Israel
| | - Shiraz Haron Khun
- Department of Physiology & Pharmacology, Sackler Faculty of Medicine, Sagol School of Neuroscience, Tel Aviv University, Tel Aviv 69978, Israel
| | - Hanna Bueno
- Department of Physiology & Pharmacology, Sackler Faculty of Medicine, Sagol School of Neuroscience, Tel Aviv University, Tel Aviv 69978, Israel
| | - Asher Peretz
- Department of Physiology & Pharmacology, Sackler Faculty of Medicine, Sagol School of Neuroscience, Tel Aviv University, Tel Aviv 69978, Israel
| | - Bernard Attali
- Department of Physiology & Pharmacology, Sackler Faculty of Medicine, Sagol School of Neuroscience, Tel Aviv University, Tel Aviv 69978, Israel
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19
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Saito Y, Nakamura K, Yoshida M, Sugiyama H, Ohe T, Kurokawa J, Furukawa T, Takano M, Nagase S, Morita H, Kusano KF, Ito H. Enhancement of Spontaneous Activity by HCN4 Overexpression in Mouse Embryonic Stem Cell-Derived Cardiomyocytes - A Possible Biological Pacemaker. PLoS One 2015; 10:e0138193. [PMID: 26384234 PMCID: PMC4575154 DOI: 10.1371/journal.pone.0138193] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2015] [Accepted: 08/26/2015] [Indexed: 12/13/2022] Open
Abstract
BACKGROUND Establishment of a biological pacemaker is expected to solve the persisting problems of a mechanical pacemaker including the problems of battery life and electromagnetic interference. Enhancement of the funny current (If) flowing through hyperpolarization-activated cyclic nucleotide-gated (HCN) channels and attenuation of the inward rectifier K+ current (IK1) flowing through inward rectifier potassium (Kir) channels are essential for generation of a biological pacemaker. Therefore, we generated HCN4-overexpressing mouse embryonic stem cells (mESCs) and induced cardiomyocytes that originally show poor IK1 currents, and we investigated whether the HCN4-overexpressing mESC-derived cardiomyocytes (mESC-CMs) function as a biological pacemaker in vitro. METHODS AND RESULTS The rabbit Hcn4 gene was transfected into mESCs, and stable clones were selected. mESC-CMs were generated via embryoid bodies and purified under serum/glucose-free and lactate-supplemented conditions. Approximately 90% of the purified cells were troponin I-positive by immunostaining. In mESC-CMs, expression level of the Kcnj2 gene encoding Kir2.1, which is essential for generation of IK1 currents that are responsible for stabilizing the resting membrane potential, was lower than that in an adult mouse ventricle. HCN4-overexpressing mESC-CMs expressed about a 3-times higher level of the Hcn4 gene than did non-overexpressing mESC-CMs. Expression of the Cacna1h gene, which encodes T-type calcium channel and generates diastolic depolarization in the sinoatrial node, was also confirmed. Additionally, genes required for impulse conduction including Connexin40, Connexin43, and Connexin45 genes, which encode connexins forming gap junctions, and the Scn5a gene, which encodes sodium channels, are expressed in the cells. HCN4-overexpressing mESC-CMs showed significantly larger If currents and more rapid spontaneous beating than did non-overexpressing mESC-CMs. The beating rate of HCN4-overexpressing mESC-CMs responded to ivabradine, an If inhibitor, and to isoproterenol, a beta-adrenergic receptor agonist. Co-culture of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) with aggregates composed of mESC-CMs resulted in synchronized contraction of the cells. The beating rate of hiPSC-CMs co-cultured with aggregates of HCN4-overexpressing mESC-CMs was significantly higher than that of non-treated hiPSC-CMs and that of hiPSC-CMs co-cultured with aggregates of non-overexpressing mESC-CMs. CONCLUSIONS We generated HCN4-overexpresssing mESC-CMs expressing genes required for impulse conduction, showing rapid spontaneous beating, responding to an If inhibitor and beta-adrenergic receptor agonist, and having pacing ability in an in vitro co-culture system with other excitable cells. The results indicated that these cells could be applied to a biological pacemaker.
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Affiliation(s)
- Yukihiro Saito
- Department of Cardiovascular Medicine, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama, Japan
| | - Kazufumi Nakamura
- Department of Cardiovascular Medicine, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama, Japan
- * E-mail:
| | - Masashi Yoshida
- Department of Cardiovascular Medicine, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama, Japan
| | - Hiroki Sugiyama
- Department of Cardiovascular Medicine, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama, Japan
| | - Tohru Ohe
- Sakakibara Heart Institute of Okayama, Okayama, Japan
| | - Junko Kurokawa
- Department of Bio-informational Pharmacology, Medical Research Institute, Tokyo Medical and Dental University, Tokyo, Japan
| | - Tetsushi Furukawa
- Department of Bio-informational Pharmacology, Medical Research Institute, Tokyo Medical and Dental University, Tokyo, Japan
| | - Makoto Takano
- Department of Physiology, Kurume University School of Medicine, Kurume, Japan
| | - Satoshi Nagase
- Department of Cardiovascular Medicine, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama, Japan
| | - Hiroshi Morita
- Department of Cardiovascular Medicine, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama, Japan
- Department of Cardiovascular Therapeutics, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama, Japan
| | - Kengo F. Kusano
- Department of Cardiovascular Medicine, National Cerebral and Cardiovascular Center, Osaka, Japan
| | - Hiroshi Ito
- Department of Cardiovascular Medicine, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama, Japan
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20
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Abstract
One of the main strategies for cancer therapy is to use tyrosine kinase inhibitors for inhibiting tumor proliferation. Increasing evidence has demonstrated the potential risks of cardiac arrhythmias (such as prolonged QT interval) of these drugs. We report here that a widely used selective inhibitor of Src tyrosine kinases, 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2), can inhibit and prevent β-adrenergic stimulation of cardiac pacemaker activity. First, in dissected rat sinus node, PP2 inhibited and prevented the isoproterenol-induced increase of spontaneous beating rate. Second, in isolated rat sinus node myocytes, PP2 suppressed the hyperpolarization-activated "funny" current (traditionally called cardiac pacemaker current, I(f)) by negatively shifting the activation curve and decelerating activation kinetics. Third, in isolated rat sinus node myocytes, PP2 decreased the Src kinase activity, the cell surface expression, and tyrosine phosphorylation of hyperpolarization-activated, cyclic nucleotide-modulated channel 4 (HCN4) channel proteins. Finally, in human embryonic kidney 293 cells overexpressing recombinant human HCN4 channels, PP2 reversed the enhancement of HCN4 channels by isoproterenol and inhibited 573x, a cyclic adenosine momophosphate-insensitive human HCN4 mutant. These results demonstrated that inhibition of Src kinase activity in heart by PP2 decreased and prevented β-adrenergic stimulation of cardiac pacemaker activity. These effects are mediated, at least partially, by a cAMP-independent attenuation of channel activity and cell surface expression of HCN4, the main channel protein that controls the heart rate.
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21
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Metabolic syndrome remodels electrical activity of the sinoatrial node and produces arrhythmias in rats. PLoS One 2013; 8:e76534. [PMID: 24250786 PMCID: PMC3826723 DOI: 10.1371/journal.pone.0076534] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2013] [Accepted: 09/01/2013] [Indexed: 01/08/2023] Open
Abstract
In the last ten years, the incidences of metabolic syndrome and supraventricular arrhythmias have greatly increased. The metabolic syndrome is a cluster of alterations, which include obesity, hypertension, hypertriglyceridemia, glucose intolerance and insulin resistance, that increase the risk of developing, among others, atrial and nodal arrhythmias. The aim of this study is to demonstrate that metabolic syndrome induces electrical remodeling of the sinus node and produces arrhythmias. We induced metabolic syndrome in 2-month-old male Wistar rats by administering 20% sucrose in the drinking water. Eight weeks later, the rats were anesthetized and the electrocardiogram was recorded, revealing the presence of arrhythmias only in treated rats. Using conventional microelectrode and voltage clamp techniques, we analyzed the electrical activity of the sinoatrial node. We observed that in the sinoatrial node of “metabolic syndrome rats”, compared to controls, the spontaneous firing of all cells decreased, while the slope of the diastolic depolarization increased only in latent pacemaker cells. Accordingly, the pacemaker currents If and Ist increased. Furthermore, histological analysis showed a large amount of fat surrounding nodal cardiomyocytes and a rise in the sympathetic innervation. Finally, Poincaré plot denoted irregularity in the R-R and P-P ECG intervals, in agreement with the variability of nodal firing potential recorded in metabolic syndrome rats. We conclude that metabolic syndrome produces a dysfunction SA node by disrupting normal architecture and the electrical activity, which could explain the onset of arrhythmias in rats.
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Deng X, Guan C, Wang Y, Zhang B, Li S, Sun G, Hao L, Li G. Identification and detection of the isolated sinus venosus from the Asian toad. Cell Biochem Funct 2013; 31:660-7. [PMID: 23348247 DOI: 10.1002/cbf.2952] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2012] [Revised: 11/05/2012] [Accepted: 12/11/2012] [Indexed: 11/09/2022]
Abstract
The pacemaker activity of mammalian sinoatrial node (SAN) of the heart plays a fundamental role in the integration of vital functions. Studying factors such as drugs that influence pacemaker activity of SAN has its significance. In this study, we isolated sinus venosus, SAN from toads (Bufo gargarizans), and analysed its electronic signal, histological characteristics and the influence of acetylcholine (ACh) and ivabradine on its pacemaker activity using PowerLab® and Chart® 5.0 software. We found that when isolated sinus venosus was treated with ACh, its histological distribution was disorganized and inter-beat (RR) interval was also broadened. The high frequency normalized unit (HFnu) and Poincaré plot of heart rate variability (HRV) of the isolated sinus venosus was also altered upon ACh treatment in a time-dependent and dose-dependent manner. When treated with ivabradine, these parameters of HRV such as square root of the mean of the squared differences between adjacent NN intervals (RMSSD) and HFnu were in the upward tendency, but low frequency normalized unit and low frequency/high frequency were in the opposite tendency. Taken together, we have developed a new model for studying the influences of drugs on autorhythmicity using isolated sinus venosus of the toad. With this model, we showed that ACh and ivabradine may affect the pacemaker activity by stimulating muscarinic receptor or inhibiting If current, respectively.
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Affiliation(s)
- Xin Deng
- The Experimental Center of Functional Subjects, College of Basic Medical Scientific Research, China Medical University, Shenyang, China
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Zhang H, Butters T, Adeniran I, Higham J, Holden AV, Boyett MR, Hancox JC. Modeling the chronotropic effect of isoprenaline on rabbit sinoatrial node. Front Physiol 2012; 3:241. [PMID: 23060799 PMCID: PMC3459472 DOI: 10.3389/fphys.2012.00241] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2012] [Accepted: 06/13/2012] [Indexed: 11/13/2022] Open
Abstract
Introduction: β-adrenergic stimulation increases the heart rate by accelerating the electrical activity of the pacemaker of the heart, the sinoatrial node (SAN). Ionic mechanisms underlying the actions of β-adrenergic stimulation are not yet fully understood. Isoprenaline (ISO), a β-adrenoceptor agonist, shifts voltage-dependent If activation to more positive potentials resulting in an increase of If, which has been suggested to be the main mechanism underlying the effect of β-adrenergic stimulation. However, ISO has been found to increase the firing rate of rabbit SAN cells when If is blocked. ISO also increases ICaL, Ist, IKr, and IKs; and shifts the activation of IKr to more negative potentials and increases the rate of its deactivation. ISO has also been reported to increase the intracellular Ca2+ transient, which can contribute to chronotropy by modulating the “Ca2+ clock.” The aim of this study was to analyze the ionic mechanisms underlying the positive chronotropy of β-adrenergic stimulation using two distinct and well established computational models of the electrical activity of rabbit SAN cells. Methods and results: We modified the Boyett et al. (2001) and Kurata et al. (2008) models of electrical activity for the central and peripheral rabbit SAN cells by incorporating equations for the known dose-dependent actions of ISO on various ionic channel currents (ICaL, Ist, IKr, and IKs), kinetics of IKr and If, and the intracellular Ca2+ transient. These equations were constructed from experimental data. To investigate the ionic basis of the effects of ISO, we simulated the chronotropic effect of a range of ISO concentrations when ISO exerted all its actions or just a subset of them. Conclusion: In both the Boyett et al. and Kurata et al. SAN models, the chronotropic effect of ISO was found to result from an integrated action of ISO on ICaL, If, Ist, IKr, and IKs, among which an increase in the rate of deactivation of IKr plays a prominent role, though the effect of ISO on If and [Ca2+]i also plays a role.
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Affiliation(s)
- Henggui Zhang
- Biological Physics Group, School of Physics and Astronomy, University of Manchester Manchester, UK ; School of Computer Science and Technology, Harbin Institute of Technology Harbin, China
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Nistri S, Pini A, Sassoli C, Squecco R, Francini F, Formigli L, Bani D. Relaxin promotes growth and maturation of mouse neonatal cardiomyocytes in vitro: clues for cardiac regeneration. J Cell Mol Med 2012; 16:507-19. [PMID: 21554533 PMCID: PMC3822927 DOI: 10.1111/j.1582-4934.2011.01328.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The demonstration that the adult heart contains myocardial progenitor cells which can be recruited in an attempt to replace the injured myocardium has sparkled interest towards novel molecules capable of improving the differentiation of these cells. In this context, the peptide hormone relaxin (RLX), recently validated as a cardiovascular hormone, is a promising candidate. This study was designed to test the hypothesis that RLX may promote the growth and maturation of mouse neonatal immature cardiomyocytes in primary culture. The cultures were studied at 2, 12, 24 and 48 hrs after the addition of human recombinant H2 RLX (100 ng/ml), the main circulating form of the hormone, or plain medium by combining molecular biology, morphology and electrophysiology. RLX modulated cell proliferation, promoting it at 2 and 12 hrs and inhibiting it at 24 hrs; RLX also induced the expression of both cardiac-specific transcription factors (GATA-4 and Nkx2-5) and cardiac-specific structural genes (connexin 43, troponin T and HCN4 ion channel) at both the mRNA and protein level. Consistently, RLX induced the appearance of ultrastructural and electrophysiological signs of functionally competent, mature cardiomyocytes. In conclusion, this study provides novel circumstantial evidence that RLX specifically acts on immature cardiomyocytes by promoting their proliferation and maturation. This notion suggests that RLX, for which the heart is both a source and target organ, may be an endogenous regulator of cardiac morphogenesis during pre-natal life and could participate in heart regeneration and repair, both as endogenous myocardium-derived factor and exogenous cardiotropic drug, during adult life.
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Affiliation(s)
- Silvia Nistri
- Department of Anatomy, Histology & Forensic Medicine, Section Histology, University of Florence, Florence, Italy
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Sosunov EA, Anyukhovsky EP. Differential effects of ivabradine and ryanodine on pacemaker activity in canine sinus node and purkinje fibers. J Cardiovasc Electrophysiol 2012; 23:650-5. [PMID: 22353259 DOI: 10.1111/j.1540-8167.2011.02285.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
INTRODUCTION It is generally accepted that at least 2 major mechanisms contribute to sinus node (SN) pacemaking: a membrane voltage (mainly I(f) ) clock and a calcium (Ca) clock (localized submembrane sarcoplasmic reticulum Ca(2+) release during late diastolic depolarization). The aim of this study was to compare the contributions of each mechanism to pacemaker activity in SN and Purkinje fibers (PFs) exhibiting normal or abnormal automaticity. METHODS AND RESULTS Conventional microelectrodes were used to record action potentials in isolated spontaneously beating canine SN and free running PF in control and in the presence of 0.1 μM isoproterenol. Ryanodine (0.1-3 μM) and ivabradine (3 μM) were used to inhibit sarcoplasmic reticulum Ca(2+) release or I(f), respectively. To induce automaticity at low membrane potentials, PFs were superfused with BaCl(2). In SN, ivabradine reduced the rate whereas ryanodine had no effect. Isoproterenol significantly accelerated automatic rate, which was decreased by ivabradine and ryanodine. In normally polarized PFs, ryanodine had no effects on the automatic rate in the absence or presence of isoproterenol, whereas ivabradine inhibited both control and isoproterenol-accelerated automaticity. In PF depolarized with BaCl(2), ivabradine decreased BaCl(2) -induced automatic rate while ryanodine had no effect. CONCLUSION In canine SN, I(f) contributes to both basal automaticity and β-adrenergic-induced rate acceleration while the ryanodine-inhibited Ca clock appears more involved in β-adrenergic regulation of pacemaker rate. In PF, normal automaticity depends mainly on I(f). Inhibition of basal potassium conductance results in high automatic rates at depolarized membrane potentials with SN-like responses to inhibition of membrane and Ca clocks.
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Affiliation(s)
- Eugene A Sosunov
- Department of Pharmacology, Center for Molecular Therapeutics, College of Physicians and Surgeons of Columbia University, New York, NY, USA
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Abstract
The coordinated generation and propagation of action potentials within cardiomyocytes creates the intrinsic electrical stimuli that are responsible for maintaining the electromechanical pump function of the human heart. The synchronous opening and closing of cardiac Na(+), Ca(2+), and K(+) channels corresponds with the activation and inactivation of inward depolarizing (Na(+) and Ca(2+)) and outward repolarizing (K(+)) currents that underlie the various phases of the cardiac action potential (resting, depolarization, plateau, and repolarization). Inherited mutations in pore-forming α subunits and accessory β subunits of cardiac K(+) channels can perturb the atrial and ventricular action potential and cause various cardiac arrhythmia syndromes, including long QT syndrome, short QT syndrome, Brugada syndrome, and familial atrial fibrillation. In this Review, we summarize the current understanding of the molecular and cellular mechanisms that underlie K(+)-channel-mediated arrhythmia syndromes. We also describe translational advances that have led to the emerging role of genetic testing and genotype-specific therapy in the diagnosis and clinical management of individuals who harbor pathogenic mutations in genes that encode α or β subunits of cardiac K(+) channels.
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Tao T, Paterson DJ, Smith NP. A model of cellular cardiac-neural coupling that captures the sympathetic control of sinoatrial node excitability in normotensive and hypertensive rats. Biophys J 2011; 101:594-602. [PMID: 21806927 DOI: 10.1016/j.bpj.2011.05.069] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2011] [Revised: 05/12/2011] [Accepted: 05/31/2011] [Indexed: 11/16/2022] Open
Abstract
Hypertension is associated with sympathetic hyperactivity. To represent this neural-myocyte coupling, and to elucidate the mechanisms underlying sympathetic control of the cardiac pacemaker, we developed a new (to our knowledge) cellular mathematical model that incorporates signaling information from cell-to-cell communications between the sympathetic varicosity and sinoatrial node (SAN) in both normotensive (WKY) and hypertensive (SHR) rats. Features of the model include 1), a description of pacemaker activity with specific ion-channel functions and Ca(2+) handling elements; 2), dynamic β-adrenergic modulation of the excitation of the SAN; 3), representation of ionic activity of sympathetic varicosity with NE release dynamics; and 4), coupling of the varicosity model to the SAN model to simulate presynaptic transmitter release driving postsynaptic excitability. This framework captures neural-myocyte coupling and the modulation of pacemaking by nitric oxide and cyclic GMP. It also reproduces the chronotropic response to brief sympathetic stimulations. Finally, the SHR model quantitatively suggests that the impairment of cyclic GMP regulation at both sides of the sympathetic cleft is crucial for development of the autonomic phenotype observed in hypertension.
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Affiliation(s)
- T Tao
- Computing Laboratory, University of Oxford, Oxford, United Kingdom
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Kharche S, Yu J, Lei M, Zhang H. A mathematical model of action potentials of mouse sinoatrial node cells with molecular bases. Am J Physiol Heart Circ Physiol 2011; 301:H945-63. [PMID: 21724866 PMCID: PMC3191499 DOI: 10.1152/ajpheart.00143.2010] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Genetically modified mice are popular experimental models for studying the molecular bases and mechanisms of cardiac arrhythmia. A postgenome challenge is to classify the functional roles of genes in cardiac function. To unveil the functional role of various genetic isoforms of ion channels in generating cardiac pacemaking action potentials (APs), a mathematical model for spontaneous APs of mouse sinoatrial node (SAN) cells was developed. The model takes into account the biophysical properties of membrane ionic currents and intracellular mechanisms contributing to spontaneous mouse SAN APs. The model was validated by its ability to reproduce the physiological exceptionally short APs and high pacing rates of mouse SAN cells. The functional roles of individual membrane currents were evaluated by blocking their coding channels. The roles of intracellular Ca2+-handling mechanisms on cardiac pacemaking were also investigated in the model. The robustness of model pacemaking behavior was evaluated by means of one- and two-parameter analyses in wide parameter value ranges. This model provides a predictive tool for cellular level outcomes of electrophysiological experiments. It forms the basis for future model development and further studies into complex pacemaking mechanisms as more quantitative experimental data become available.
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Affiliation(s)
- Sanjay Kharche
- Biological Physics Group, School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom
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Tellez JO, Mczewski M, Yanni J, Sutyagin P, Mackiewicz U, Atkinson A, Inada S, Beresewicz A, Billeter R, Dobrzynski H, Boyett MR. Ageing-dependent remodelling of ion channel and Ca2+ clock genes underlying sino-atrial node pacemaking. Exp Physiol 2011; 96:1163-78. [PMID: 21724736 DOI: 10.1113/expphysiol.2011.057752] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The function of the sino-atrial node (SAN), the pacemaker of the heart, is known to decline with age, resulting in pacemaker disease in the elderly. The aim of the study was to investigate the effects of ageing on the SAN by characterizing electrophysiological changes and determining whether changes in gene expression are involved. In young and old rats, SAN function was characterized in the anaesthetized animal, isolated heart and isolated right atrium using ECG and action potential recordings; gene expression was characterized using quantitative PCR. The SAN function declined with age as follows: the intrinsic heart rate declined by 18 ± 3%; the corrected SAN recovery time increased by 43 ± 13%; and the SAN action potential duration increased by 11 ± 3% (at 75% repolarization). Gene expression in the SAN changed considerably with age, e.g. there was an age-dependent decrease in the Ca(2+) clock gene, RYR2, and changes in many ion channels (e.g. increases in Na(v)1.5, Na(v)β1 and Ca(v)1.2 and decreases in K(v)1.5 and HCN1). In conclusion, with age, there are changes in the expression of ion channel and Ca(2+) clock genes in the SAN, and the changes may provide a partial explanation for the age-dependent decline in pacemaker function.
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Brahmajothi MV, Morales MJ, Campbell DL, Steenbergen C, Strauss HC. Expression and distribution of voltage-gated ion channels in ferret sinoatrial node. Physiol Genomics 2010; 42A:131-40. [PMID: 20682846 DOI: 10.1152/physiolgenomics.00049.2010] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Spontaneous diastolic depolarization in the sinoatrial (SA) node enables it to serve as pacemaker of the heart. The variable cell morphology within the SA node predicts that ion channel expression would be heterogeneous and different from that in the atrium. To evaluate ion channel heterogeneity within the SA node, we used fluorescent in situ hybridization to examine ion channel expression in the ferret SA node region and atrial appendage. SA nodal cells were distinguished from surrounding cardiac myocytes by expression of the slow (SA node) and cardiac (surrounding tissue) forms of troponin I. Nerve cells in the sections were identified by detection of GAP-43 and cytoskeletal middle neurofilament. Transcript expression was characterized for the 4 hyperpolarization-activated cation channels, 6 voltage-gated Na(+) channels, 3 voltage-gated Ca(2+) channels, 24 voltage-gated K(+) channel α-subunits, and 3 ancillary subunits. To ensure that transcript expression was representative of protein expression, immunofluorescence was used to verify localization patterns of voltage-dependent K(+) channels. Colocalizations were performed to observe any preferential patterns. Some overlapping and nonoverlapping binding patterns were observed. Measurement of different cation channel transcripts showed heterogeneous expression with many different patterns of expression, attesting to the complexity of electrical activity in the SA node. This study provides insight into the possible role ion channel heterogeneity plays in SA node pacemaker activity.
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Affiliation(s)
- Mulugu V Brahmajothi
- Division of Neonatology, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA
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Role of polyamines and cAMP-dependent mechanisms on 5alpha-dihydrotestosterone-elicited functional effects in isolated right atria of rat. J Cardiovasc Pharmacol 2010; 54:310-8. [PMID: 19661811 DOI: 10.1097/fjc.0b013e3181b6e57f] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Androgens produce acute vasodilation of systemic, pulmonary, and coronary arteries in several mammal preparations and increase cardiomyocyte contractility. A decrease of the spontaneous beating of sinoatrial cells has also been described. The aim of this study was to characterize the direct effect of 5alpha-dihydrotestosterone on the spontaneous chronotropism and inotropism in the same preparation as an approach to establish the effect on cardiac output and their mechanism of action. The effects were studied on isolated right atria of Wistar rats placed in an organ bath in Tyrode solution at 37 degrees C and bubbled with carbogen. In male rats, the acute administration of 5alpha-dihydrotestosterone, a nonaromatizable derivate of testosterone, elicited a positive inotropism, which was associated with a negative chronotropism. As reported in the left atria, polyamines and beta-adrenoceptors played a role in 5alpha-dihydrotestosterone-elicited positive inotropism because the effect was antagonized by alpha-difluoromethylornithine, an inhibitor of polyamine synthesis, and atenolol, a beta1-adrenoceptor blocker, but not on the negative effect on chronotropism. The androgen increased the sinoatrial node recovery time, suggesting an effect on the mechanisms of spontaneous diastolic depolarization involved in atria pacemaking. These effects of 5alpha-dihydrotestosterone are not hormonally regulated because they are similarly produced in estrogenized females and gonadectomized male and female rats. These results suggest that the androgen could acutely improve cardiac performance.
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Vinogradova TM, Lakatta EG. Regulation of basal and reserve cardiac pacemaker function by interactions of cAMP-mediated PKA-dependent Ca2+ cycling with surface membrane channels. J Mol Cell Cardiol 2009; 47:456-74. [PMID: 19573534 PMCID: PMC2757791 DOI: 10.1016/j.yjmcc.2009.06.014] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/03/2009] [Accepted: 06/23/2009] [Indexed: 01/01/2023]
Abstract
Decades of intensive research of primary cardiac pacemaker, the sinoatrial node, have established potential roles of specific membrane channels in the generation of the diastolic depolarization, the major mechanism allowing sinoatrial node cells to generate spontaneous beating. During the last three decades, multiple studies made either in the isolated sinoatrial node or sinoatrial node cells have demonstrated a pivotal role of Ca(2+) and, specifically Ca(2+) release from sarcoplasmic reticulum, for spontaneous beating of cardiac pacemaker. Recently, spontaneous, rhythmic local subsarcolemmal Ca(2+) releases from ryanodine receptors during late half of the diastolic depolarization have been implicated as a vital factor in the generation of sinoatrial node cell spontaneous firing. Local Ca(2+) releases are driven by a unique combination of high basal cAMP production by adenylyl cyclases, high basal cAMP degradation by phosphodiesterases and a high level of cAMP-mediated PKA-dependent phosphorylation. These local Ca(2+) releases activate an inward Na(+)-Ca(2+) exchange current which accelerates the terminal diastolic depolarization rate and, thus, controls the spontaneous pacemaker firing. Both the basal primary pacemaker beating rate and its modulation via beta-adrenergic receptor stimulation appear to be critically dependent upon intact RyR function and local subsarcolemmal sarcoplasmic reticulum generated Ca(2+) releases. This review aspires to integrate the traditional viewpoint that has emphasized the supremacy of the ensemble of surface membrane ion channels in spontaneous firing of the primary cardiac pacemaker, and these novel perspectives of cAMP-mediated PKA-dependent Ca(2+) cycling in regulation of the heart pacemaker clock, both in the basal state and during beta-adrenergic receptor stimulation.
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Affiliation(s)
- Tatiana M Vinogradova
- Laboratory of Cardiovascular Science, Gerontology Research Center, NIA, NIH, 5600 Nathan Shock Drive, Baltimore, MD 21224-6825, USA
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Anumonwo JMB, Lopatin AN. Cardiac strong inward rectifier potassium channels. J Mol Cell Cardiol 2009; 48:45-54. [PMID: 19703462 DOI: 10.1016/j.yjmcc.2009.08.013] [Citation(s) in RCA: 111] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/23/2009] [Revised: 08/13/2009] [Accepted: 08/18/2009] [Indexed: 10/20/2022]
Abstract
Cardiac I(K1) and I(KACh) are the major potassium currents displaying classical strong inward rectification, a unique property that is critical for their roles in cardiac excitability. In the last 15 years, research on I(K1) and I(KACh) has been propelled by the cloning of the underlying inwardly rectifying potassium (Kir) channels, the discovery of the molecular mechanism of strong rectification and the linking of a number of disorders of cardiac excitability to defects in genes encoding Kir channels. Disease-causing mutations in Kir genes have been shown experimentally to affect one or more of the following channel properties: structure, assembly, trafficking, and regulation, with the ultimate effect of a gain- or a loss-of-function of the channel. It is now established that I(K1) and I(KACh) channels are heterotetramers of Kir2 and Kir3 subunits, respectively. Each homomeric Kir channel has distinct biophysical and regulatory properties, and individual Kir subunits often display different patterns of regional, cellular, and membrane distribution. These differences are thought to underlie important variations in the physiological properties of I(K1) and I(KACh). It has become increasingly clear that the contribution of I(K1) and I(KACh) channels to cardiac electrical activity goes beyond their long recognized role in the stabilization of resting membrane potential and shaping the late phase of action potential repolarization in individual myocytes but extends to being critical elements determining the overall electrical stability of the heart.
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Affiliation(s)
- Justus M B Anumonwo
- Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109-5622, USA
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Pacemaker activity of the human sinoatrial node: role of the hyperpolarization-activated current, I(f). Int J Cardiol 2009; 132:318-36. [PMID: 19181406 DOI: 10.1016/j.ijcard.2008.12.196] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/02/2008] [Revised: 12/16/2008] [Accepted: 12/22/2008] [Indexed: 11/20/2022]
Abstract
The mechanism of primary, spontaneous cardiac pacemaker activity of the sinoatrial node (SAN) has extensively been studied in several animal species, but is virtually unexplored in man. Understanding the mechanisms of human SAN pacemaker activity is important for developing new therapeutic approaches for controlling the heart rate in the sick sinus syndrome and in diseased myocardium. Here we review the functional role of the hyperpolarization-activated 'funny' current, I(f), in human SAN pacemaker activity. Despite the many animal studies performed over the years, the contribution of I(f) to pacemaker activity is still controversial and not fully established. However, recent clinical data on mutations in the I(f) encoding HCN4 gene, which is thought to be the most abundant isoform of the HCN gene family in SAN, suggest a functional role of I(f) in human pacemaker activity. These clinical findings are supported by recent experimental data from single isolated human SAN cells that provide direct evidence that I(f) contributes to human SAN pacemaker activity. Therefore, controlling heart rate in clinical practice via I(f) blockers offers a valuable approach to lowering heart rate and provides an attractive alternative to conventional treatment for a wide range of patients with confirmed stable angina, while upregulation or artificial expression of I(f) may relieve disease-causing bradycardias.
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Abstract
The heart automaticity is a fundamental physiological function in higher organisms. The spontaneous activity is initiated by specialized populations of cardiac cells generating periodical electrical oscillations. The exact cascade of steps initiating the pacemaker cycle in automatic cells has not yet been entirely elucidated. Nevertheless, ion channels and intracellular Ca(2+) signaling are necessary for the proper setting of the pacemaker mechanism. Here, we review the current knowledge on the cellular mechanisms underlying the generation and regulation of cardiac automaticity. We discuss evidence on the functional role of different families of ion channels in cardiac pacemaking and review recent results obtained on genetically engineered mouse strains displaying dysfunction in heart automaticity. Beside ion channels, intracellular Ca(2+) release has been indicated as an important mechanism for promoting automaticity at rest as well as for acceleration of the heart rate under sympathetic nerve input. The potential links between the activity of ion channels and Ca(2+) release will be discussed with the aim to propose an integrated framework of the mechanism of automaticity.
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Affiliation(s)
- Matteo E Mangoni
- Institute of Functional Genomics, Department of Physiology, Centre National de la Recherche Scientifique UMR5203, INSERM U661, University of Montpellier I and II, Montpellier, France.
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van Borren MMJ, Zegers JG, Verkerk AO, Wilders R. Computational model of rabbit SA node pacemaker activity probed with action potential and calcium transient clamp. ACTA ACUST UNITED AC 2008; 2007:156-9. [PMID: 18001912 DOI: 10.1109/iembs.2007.4352246] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
In the past decades, various computational models of the pacemaker activity of single sinoatrial (SA) nodal cells have been developed, building on data obtained in patch-clamp experiments on isolated SA nodal myocytes. These models show widely different results regarding the contribution of individual ionic currents to diastolic depolarization and pacemaker activity of the SA nodal myocyte. Because several of these ionic currents are strongly dependent on time, voltage and/or intracellular free calcium concentration ([Ca(2+)](i), one may argue that the apparent differences in the contribution of a particular ionic current to pacemaker activity between SA nodal cell models reflect differences in action potential shape and calcium transient between models rather than intrinsic differences in the ionic current of interest. To better appreciate the contribution of individual ionic currents to pacemaker activity in a computational model of an SA nodal cell, we imposed a realistic action potential shape and calcium transient on the model cell. This was achieved by first simultaneously recording membrane potential and ([Ca(2+)](i) from single isolated SA nodal myocytes and then subjecting the model cell to a combined ;action potential clamp' and ;calcium transient clamp' using a data file with a train of experimentally recorded SA nodal action potentials and associated calcium transients. The thus computed individual ionic currents should then more closely resemble the ;true' ionic currents during pacemaker activity of an SA nodal myocyte. Also, differences between the recorded and the computed net membrane current may prove helpful in identifying shortcomings of the computational model.
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Affiliation(s)
- Marcel M J van Borren
- Department of Physiology, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands
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Cardiac pacemaker function of HCN4 channels in mice is confined to embryonic development and requires cyclic AMP. EMBO J 2008; 27:692-703. [PMID: 18219271 DOI: 10.1038/emboj.2008.3] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2007] [Accepted: 12/21/2007] [Indexed: 11/08/2022] Open
Abstract
Important targets for cAMP signalling in the heart are hyperpolarization-activated and cyclic nucleotide-gated (HCN) channels that underlie the depolarizing 'pacemaker' current, I(f). We studied the role of I(f) in mice, in which binding of cAMP to HCN4 channels was abolished by a single amino-acid exchange (R669Q). Homozygous HCN4(R669Q/R669Q) mice die during embryonic development. Prior to E12, homozygous and heterozygous embryos display reduced heart rates and show no or attenuated responses to catecholaminergic stimulation. Adult heterozygous mice display normal heart rates at rest and during exercise. However, following beta-adrenergic stimulation, hearts exhibit pauses and sino-atrial node block. Our results demonstrate that in the embryo, HCN4 is a true cardiac pacemaker and elevation of HCN4 channel activity by cAMP is essential for viability. In adult mice, an important function of HCN4 channels is to prevent sinus pauses during and after stress while their role as a pacemaker of the murine heart is put into question. Most importantly, our results indicate that HCN4 channels can fulfil their physiological function only when cAMP is bound.
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Wilders R. Computer modelling of the sinoatrial node. Med Biol Eng Comput 2007; 45:189-207. [PMID: 17115219 DOI: 10.1007/s11517-006-0127-0] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2006] [Accepted: 10/17/2006] [Indexed: 11/26/2022]
Abstract
Over the past decades patch-clamp experiments have provided us with detailed information on the different types of ion channels that are present in the cardiac cell membrane. Sophisticated cardiac cell models based on these data can help us understand how the different types of ion channels act together to produce the cardiac action potential. In the field of biological pacemaker engineering, such models provide important instruments for the assessment of the functional implications of changes in density of specific ion channels aimed at producing stable pacemaker activity. In this review, an overview is given of the progress made in cardiac cell modelling, with particular emphasis on the development of sinoatrial (SA) nodal cell models. Also, attention is given to the increasing number of publicly available tools for non-experts in computer modelling to run cardiac cell models.
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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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Li SZ, Wu F, Wang B, Wei GZ, Jin ZX, Zang YM, Zhou JJ, Wong TM. Role of reverse mode Na+/Ca2+ exchanger in the cardioprotection of metabolic inhibition preconditioning in rat ventricular myocytes. Eur J Pharmacol 2007; 561:14-22. [PMID: 17306252 DOI: 10.1016/j.ejphar.2006.12.036] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2006] [Revised: 12/11/2006] [Accepted: 12/15/2006] [Indexed: 01/08/2023]
Abstract
This study determined the role of the reverse mode Na(+)/Ca(2+) exchanger (NCX) in cardioprotection of metabolic inhibition preconditioning in isolated ventricular myocyctes. Activity of the reverse mode NCX was assessed by changes of [Ca(2+)](i) upon withdrawal of extracellular Na(+). [Ca(2+)](i) was measured by spectrofluorometry, using Fura-2 as Ca(2+) indicator. The amplitude of contraction and exclusion of trypan blue by myocytes served as indices of contractile function and viability, respectively. Firstly, NCX activity significantly decreased during simulated reperfusion after severe metabolic inhibition (index ischaemia) in myocytes subjected to metabolic inhibition preconditioning. This inhibitory effect on NCX activity correlated with the enhancing effect of metabolic inhibition preconditioning on cell viability following ischaemic insult. Treatment myocytes with E4031, an activator of reverse mode NCX, during index ischaemia and reperfusion attenuated the enhancing effects of metabolic inhibition preconditioning on cell contraction and viability. Secondly, NCX activity was significantly higher at the end of metabolic inhibition preconditioning. More importantly, E4031 pretreatment mimicked the beneficial effects of metabolic inhibition preconditioning in myocytes and ischaemic preconditioning in the isolated perfused heart, respectively, and these effects were abolished by KB-R7943, an inhibitor of reverse mode NCX. The results indicate that increased reverse mode NCX activity during preconditioning triggered cardioprotection, and reduced reverse mode NCX activity during reperfusion after index ischaemia conferred cardioprotection.
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Affiliation(s)
- Shu-Zhuang Li
- Department of Physiology, Fourth Military Medical University, Xi'an, 710032, China
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Kurata Y, Matsuda H, Hisatome I, Shibamoto T. Effects of pacemaker currents on creation and modulation of human ventricular pacemaker: theoretical study with application to biological pacemaker engineering. Am J Physiol Heart Circ Physiol 2007; 292:H701-18. [PMID: 16997892 DOI: 10.1152/ajpheart.00426.2006] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A cardiac biological pacemaker (BP) has been created by suppression of the inward rectifier K+ current ( IK1) or overexpression of the hyperpolarization-activated current ( Ih). We theoretically investigated the effects of incorporating Ih, T-type Ca2+ current ( ICa,T), sustained inward current ( Ist), and/or low-voltage-activated L-type Ca2+ channel current ( ICa,LD) on 1) creation of BP cells, 2) robustness of BP activity to electrotonic loads of nonpacemaking (NP) cells, and 3) BP cell ability to drive NP cells. We used a single-cell model for human ventricular myocytes (HVMs) and also coupled-cell models composed of BP and NP cells. Bifurcation structures of the model cells were explored during changes in conductance of the currents and gap junction. Incorporating the pacemaker currents did not yield BP activity in HVM with normal IK1 but increased the critical IK1 conductance for BP activity to emerge. Expressing Ih appeared to be most helpful in facilitating creation of BP cells via IK1 suppression. In the coupled-cell model, Ist significantly enlarged the gap conductance ( GC) region where stable BP cell pacemaking and NP cell driving occur, reducing the number of BP cells required for robust pacemaking and driving. In contrast, Ih enlarged the GC region of pacemaking and driving only when IK1 of the NP cell was relatively low. ICa,T or ICa,LD exerted effects similar to those of Ist but caused shrinkage or irregularity of BP oscillations. These findings suggest that expressing Ist most effectively improves the structural stability of BPs to electrotonic loads and the BP ability to drive the ventricle.
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Affiliation(s)
- Yasutaka Kurata
- Dept. of Physiology, Kanazawa Medical Univ., 1-1 Daigaku, Uchinada-machi, Kahoku-gun, Ishikawa 920-0293, Japan.
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Howarth FC, Al-Sharhan R, Al-Hammadi A, Qureshi MA. Effects of streptozotocin-induced diabetes on action potentials in the sinoatrial node compared with other regions of the rat heart. Mol Cell Biochem 2006; 300:39-46. [PMID: 17541508 DOI: 10.1007/s11010-006-9366-5] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2006] [Accepted: 10/25/2006] [Indexed: 10/23/2022]
Abstract
In vivo biotelemetry studies have demonstrated that heart rate (HR) is progressively and rapidly reduced after administration of streptozotocin (STZ) and that the reduction in HR can be partially normalized with insulin replacement. Reductions in HR have also been reported in isolated perfused heart and superfused right atrial preparations suggesting that intrinsic defects in the heart are at least partly responsible for the bradycardia. The regional effects of STZ-induced diabetes mellitus (DM) on action potentials (APs) in the sinoatrial node (SAN), right and left atria and ventricles have been compared in the spontaneously beating Langendorff perfused rat heart 10-12 weeks after treatment. HR was significantly reduced in STZ-induced diabetic rat heart (174 +/- 9 BPM) compared to controls (241 +/- 12 BPM). The duration of AP repolarization at 50% and 70% from peak AP was significantly prolonged in SAN, right atrium and right ventricle from STZ-induced diabetic rat compared to age-matched controls. In the SAN AP duration (APD) at 50% and 70% were 51.7 +/- 2.2 and 59.5 +/- 2.3 ms in diabetic rat heart compared to 45.2 +/- 1.7 and 50.0 +/- 1.6 ms in controls, respectively. In contrast APD at 50% and 70% were not significantly altered in the left atrium and left ventricle. Regional defects in the expression and/or electrophysiology of SAN ion channels, and in particular those involved in AP repolarization, might underlie heart rhythm disturbances in the STZ-induced DM rat.
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Affiliation(s)
- F C Howarth
- Department of Physiology, Faculty of Medicine & Health Sciences, United Arab Emirates University, Al Ain, Abu Dhabi, United Arab Emirates.
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Cohen IS, Robinson RB. Pacemaker current and automatic rhythms: toward a molecular understanding. Handb Exp Pharmacol 2006:41-71. [PMID: 16610340 DOI: 10.1007/3-540-29715-4_2] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
The ionic basis of automaticity in the sinoatrial node and His-Purkinje system, the primary and secondary cardiac pacemaking regions, is discussed. Consideration is given to potential targets for pharmacologic or genetic therapies of rhythm disorders. An ideal target would be an ion channel that functions only during diastole, so that action potential repolarization is not affected, and one that exhibits regional differences in expression and/or function so that the primary and secondary pacemakers can be selectively targeted. The so-called pacemaker current, If, generated by the HCN gene family, best fits these criteria. The biophysical and molecular characteristics of this current are reviewed, and progress to date in developing selective pharmacologic agents targeting If and in using gene and cell-based therapies to modulate the current are reviewed.
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Affiliation(s)
- I S Cohen
- Department of Physiology and Biophysics, Stony Brook University, Room 150 Basic Science Tower, Stony Brook, NY 11794-8661, USA
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Ono K, Iijima T. Pathophysiological significance of T-type Ca2+ channels: properties and functional roles of T-type Ca2+ channels in cardiac pacemaking. J Pharmacol Sci 2005; 99:197-204. [PMID: 16272791 DOI: 10.1254/jphs.fmj05002x2] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
Abstract
Calcium channels are essential for excitation-contraction coupling and pacemaker activity in cardiac myocytes. While L-type Ca(2+) channels (LCC) have been extensively studied, functional roles of T-type channels (TCC) in native cardiac myocytes are still debatable. TCC are activated at more negative membrane potentials than LCC and therefore facilitate slow diastolic depolarization in sinoatrial node cells. Recent studies showed that selective inhibition of TCC produced a marked slowing of the pacemaker rhythm, indicating that contribution of TCC to cardiac automaticity was relatively larger than what had been speculated in previous studies. To re-evaluate TCC, we measured current density and kinetics of TCC in sinoatrial node cells of various mammalian species. Current density of TCC was larger in mice and guinea pigs than in rabbit and porcine sinoatrial node cells. Interestingly, few or no obvious TCC were recorded in porcine sinoatrial node cells. Furthermore, it was demonstrated that TCC could be enhanced by several vasoactive substances, thereby increasing spontaneous firing rate of sinoatrial node cells. TCC may, at least in part, account for different heart rates among various mammalian species. In addition, TCC might be involved in physiological and/or pathophysiological modulations of the heart rate.
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Affiliation(s)
- Kyoichi Ono
- Department of Pharmacology, Akita University School of Medicine, Japan.
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Satoh H. Suppression of pacemaker activity by Ginkgo biloba extract and its main constituent, bilobalide in rat sino-atrial nodal cells. Life Sci 2005; 78:67-73. [PMID: 16182317 DOI: 10.1016/j.lfs.2005.04.081] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2004] [Accepted: 04/06/2005] [Indexed: 11/25/2022]
Abstract
Effects of Ginkgo biloba extract (GBE) and bilobalide (a main constituent) on the pacemaker activity and the underlying ionic currents in rat sino-atrial (SA) nodal cells were investigated using patch-clamp techniques. Both GBE and bilobalide depressed the pacemaker activity in a concentration-dependent manner. At both 0.03 mg/ml GBE and 0.3 microM bilobalide, a negative chronotropic effect was produced. Dysrhythmias often occurred. The L-type Ca(2+) current (I(Ca)) and the hyperpolarization-activated inward current (I(f)) decreased by 69.7+/-3.2% (n=6, P<0.001) and by 12.6+/-2.1% (n=7, P<0.05) at 0.03 mg/ml GBE, and by 51.2+/-3.3% (n=6, P<0.01) and by 19.8+/-2.2 % (n=6, P<0.05) at 0.3 microM bilobalide, respectively. The delayed rectifier K(+) current (I(K)) also decreased. The inhibition was 12.3+/-2.0% (n=6, P<0.05) at 0.03 mg/ml GBE, and was 28.0+/-2.9% (n=6, P<0.05) at 0.3 microM bilobalide. These results indicate that cardiac ionic channels contributing to the pacemaking are highly sensitive to GBE and bilobalide, which can sufficiently modify the spontaneous activity in rat SA nodal cells.
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Affiliation(s)
- Hiroyasu Satoh
- Department of Pharmacology, Division of Molecular and Cellular Biology, Nara Medical University, School of Medicine, Kashihara, Nara 634-8521, Japan.
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Toyoda F, Ding WG, Matsuura H. Responses of the sustained inward current to autonomic agonists in guinea-pig sino-atrial node pacemaker cells. Br J Pharmacol 2005; 144:660-8. [PMID: 15678089 PMCID: PMC1576045 DOI: 10.1038/sj.bjp.0706101] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. The present study was undertaken to examine the responses of the sustained inward current (I(st)) to beta-adrenergic and muscarinic agonists in guinea-pig sino-atrial (SA) node cells using the whole-cell patch-clamp technique. I(st) was detected as the nicardipine (1 microM)-sensitive inward current at potentials between approximately -80 and +20 mV in the presence of low concentration (0.1 mM) of extracellular Ca2+, where the L-type Ca2+ current (I(Ca,L)) was practically abolished. 2. Beta-adrenergic agonist isoprenaline (ISO) in nanomolar concentrations not only increased the amplitude of I(st) but also shifted the membrane potential producing the peak amplitude (Vpeak) to a negative direction by approximately 15 mV without appreciably affecting potential range for the current activation. The stimulatory effect of ISO was concentration-dependent with an EC50 of 2.26 nM and the maximal effect (96.4+/-22.9% increase, n=6) was obtained at 100 nM ISO, when evaluated by the responses at -50 mV. 3. Bath application of acetylcholine (ACh) significantly inhibited I(st), which had been maximally augmented by 100 nM ISO; this inhibitory effect of ACh was concentration-dependent with an IC50 of 133.9 nM. High concentration (1000 nM) of ACh depressed basal I(st) by 10.5+/-2.0% (n=3). 4. In action potential clamp experiments, I(st) was also detected under control conditions and was markedly potentiated by exposure to ISO. 5. These results strongly suggest that I(st) not only contributes to the spontaneous action potentials of mammalian SA node cells but also plays a substantial role in mediating autonomic regulation of SA node pacemaker activity.
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Affiliation(s)
- Futoshi Toyoda
- Department of Physiology, Shiga University of Medical Science, Seta-tsukinowacho, Otsu, Shiga 520-2192, Japan.
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Satoh H. Sino-atrial nodal cells of mammalian hearts: ionic currents and gene expression of pacemaker ionic channels. J Smooth Muscle Res 2004; 39:175-93. [PMID: 14695028 DOI: 10.1540/jsmr.39.175] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The cardiac pacemaker is a sino-atrial (SA) nodal cell. The signal induced by this pacemaker is distributed over the heart surface by a specialised conduction system and is clinically recorded as the ECG. The SA nodal cells are highly resistant to cardiac failure and ischemia. Under calcium overload conditions, some dysrythmias of SA nodal cells occur easily. Morphological analysis under these conditions shows swelling of the cisternae of the Golgi apparatus, with little or no other histological change or damage being observed. The rate of sinus rhythm is quite different between various species. The investigations of SA nodal cells have so far clarified the pacemaker mechanisms involved. A number of ionic channel currents or pacemaker currents, contribute to the depolarization of the pacemaker potential (phase 4). This will not occur with a single current. Recent experiments have identified several novel pacemaker currents and have also revealed several differences in the pacemaker currents between species. The marked hyperpolarization-activated inward current (I(f)) appears in SA nodal cells of most species, while the inwardly rectifying K+ current (I(K1)) with masked I(f) current is found in those of the rat and monkey. In addition, the rapidly activated current (I(Kr)) and slowly activated current (I(Ks)) of the delayed rectifier K+ current (I(K)) contribute to the pacemaker potential in guinea pig SA nodal cells, with only the I(Ks) current in porcine SA nodal cells and only the I(Kr) current in the rat and rabbit. These differences in ionic channels presumably result from differences in gene expression. Some smooth muscle cells also possess the capacity to beat spontaneously. Uterine smooth muscle cells also exhibit an I(f) current. The basal mechanism for spontaneous activity in both SA nodal cells and smooth muscle cells is almost the same, but some differences in the ionic channels and their genetic expression may contribute to their respective pacemaker currents.
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Affiliation(s)
- Hiroyasu Satoh
- Department of Pharmacology, Division of Molecular and Cellular Biology, Nara Medical University, Kashihara, Nara 634-8521, Japan.
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Satoh H. Taurine on sino-atrial nodal cells: Ca2+-dependent modulation. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2004; 526:17-23. [PMID: 12908579 DOI: 10.1007/978-1-4615-0077-3_3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/04/2023]
Affiliation(s)
- Hiroyasu Satoh
- Department of Pharmacology, Nara Medical University, Kashihara, Japan
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Cho HS, Takano M, Noma A. The electrophysiological properties of spontaneously beating pacemaker cells isolated from mouse sinoatrial node. J Physiol 2003; 550:169-80. [PMID: 12879867 PMCID: PMC2343002 DOI: 10.1113/jphysiol.2003.040501] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
In order to examine the phenotypic consequences of genetic manipulation in the function of the sinoatrial (SA) node, it is a prerequisite to record the electrical activities of a single pacemaker cell of the SA node of mouse heart. In the present study, we isolated spontaneously beating pacemaker cells from the SA node by enzymatic digestion. The rate of spontaneous action potential firing was 294 + 59 min-1 at 33-34 degrees C. The maximal diastolic potential (MDP) was -56.7 +/- 7.4 mV and the overshoot was 22.7 +/- 6.2 mV. With hyperpolarizing voltage clamp pulses, the hyperpolarization-activated, cyclic nucleotide-sensitive cation current (I(h) or I(f)) was recorded. lb started to activate at-70 to approximately -80 mV, more negative than MDP. The half-maximal activation of Ih was obtained at -107.9 +/- 10.4 mV. The inward-rectifier K+ current (IK1) was also recorded in spontaneously beating myocytes. However, the amplitude of outward IK1 was negligibly small (9.1 +/- 3.4 pA at -60 mV). With depolarization, voltage-gated Na+ current, L-type Ca2+ current and T-type Ca2+ current were consistently observed. The sustained inward current (I(st)) was also recorded in spontaneously beating pacemaker cells. E4031-sensitive, rapidly activating delayed rectifier K+ current (I(Kr)) was activated by depolarization, although the amplitude was no more than 38.3 +/- 22.2 pA at 0 mV. The chromanol 293B-sensitive, slowly activating delayed rectifier K+ current (I(Ks)) was not present. The major repolarizing current was the slowly inactivating, 4-aminopyridine-insensitive outward current. We concluded that mouse pacemaker cells possess similar membrane currents, including I(st), to those of other species.
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Affiliation(s)
- Hyun-Sung Cho
- Department of Anesthesiology, Samsung Medical Center, School of Medicine, Sungkyunkwan University, Seoul, Korea
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Matsuoka S, Sarai N, Kuratomi S, Ono K, Noma A. Role of individual ionic current systems in ventricular cells hypothesized by a model study. THE JAPANESE JOURNAL OF PHYSIOLOGY 2003; 53:105-23. [PMID: 12877767 DOI: 10.2170/jjphysiol.53.105] [Citation(s) in RCA: 146] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Individual ion channels or exchangers are described with a common set of equations for both the sinoatrial node pacemaker and ventricular cells. New experimental data are included, such as the new kinetics of the inward rectifier K+ channel, delayed rectifier K+ channel, and sustained inward current. The gating model of Shirokov et al. (J Gen Physiol 102: 1005-1030, 1993) is used for both the fast Na+ and L-type Ca2+ channels. When combined with a contraction model (Negroni and Lascano: J Mol Cell Cardiol 28: 915-929, 1996), the experimental staircase phenomenon of contraction is reconstructed. The modulation of the action potential by varying the external Ca2+ and K+ concentrations is well simulated. The conductance of I(CaL) dominates membrane conductance during the action potential so that an artificial increase of I(to), I(Kr), I(Ks), or I(KATP) magnifies I(CaL) amplitude. Repolarizing current is provided sequentially by I(Ks), I(Kr), and I(K1). Depression of ATP production results in the shortening of action potential through the activation of I(KATP). The ratio of Ca2+ released from SR over Ca2+ entering via I(CaL) (Ca2+ gain = approximately 15) in excitation-contraction coupling well agrees with the experimental data. The model serves as a predictive tool in generating testable hypotheses.
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Affiliation(s)
- Satoshi Matsuoka
- Department of Physiology and Biophysics, Kyoto University Graduate School of Medicine, Yoshidakonoe-cho, Sakyo-ku, Kyoto 606-8501, Japan
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Satoh H. Elecropharmacology of taurine on the hyperpolarization-activated inward current and the sustained inward current in spontaneously beating rat sino-atrial nodal cells. J Pharmacol Sci 2003; 91:229-38. [PMID: 12686746 DOI: 10.1254/jphs.91.229] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
Abstract
Modulation by taurine of the pacemaking activity and the underlying ionic currents, especially a hyperpolarization-activated inward current (I(f)) and a sustained inward current (I(ST)), in rat sino-atrial (SA) nodal cells was investigated at different pCa levels using a patch-clamp technique. Increasing pCa levels from 10 to 6 stimulated the spontaneous activity and simultaneously increased the I(f). Application of taurine depressed more strongly the spontaneous activity at higher pCa levels. At all pCa levels, however, taurine (20 mM) increased the I(f) by 60.1 +/- 1.7% (n = 8, P<0.001) at pCa 10 and by 48.0 +/- 1.4% (n = 8, P<0.01) at pCa 7. At pCa 7, taurine (10 and 20 mM) decreased the sustained inward current (I(ST)) by 13.3 +/- 1.1% (n = 5, P<0.05) and by 38.1 +/- 2.4% (n = 5, P<0.01), respectively. Taurine (20 mM) inhibited the L-type Ca(2+) current (I(CaL)) by 35.8 +/- 2.5% (n = 8, P<0.01), whereas taurine enhanced the T-type Ca(2+) current (I(CaT)) by 29.3 +/- 2.9% (n = 8, P<0.05). Also, taurine at pCa 7 decreased the delayed rectifier K(+) current; taurine at 20 mM inhibited the rapidly activated K(+) current (I(Kr)) by 55.6 +/- 3.3% (n = 6, P<0.001), but not the slowly activated K(+) current (I(Ks)). Taurine often elicited dysrhythmias, dependent on taurine's concentrations and pCa levels. These results indicate that taurine causes a negative chronotropic effect due to the inhibitions of the pacemaking ionic currents such as I(CaL), I(Kr) and I(ST), and suggest that the I(f) and I(CaT) currents make a minor contribution to pacemaking activity in rat SA nodal cells.
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Affiliation(s)
- Hiroyasu Satoh
- Department of Pharmacology, Division of Molecular and Cellular Biology, Nara Medical University, Japan.
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