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Tóth N, Loewe A, Szlovák J, Kohajda Z, Bitay G, Levijoki J, Papp JG, Varró A, Nagy N. The reverse mode of the Na +/Ca 2+ exchanger contributes to the pacemaker mechanism in rabbit sinus node cells. Sci Rep 2022; 12:21830. [PMID: 36528651 PMCID: PMC9759562 DOI: 10.1038/s41598-022-25574-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2021] [Accepted: 12/01/2022] [Indexed: 12/23/2022] Open
Abstract
Sinus node (SN) pacemaking is based on a coupling between surface membrane ion-channels and intracellular Ca2+-handling. The fundamental role of the inward Na+/Ca2+ exchanger (NCX) is firmly established. However, little is known about the reverse mode exchange. A simulation study attributed important role to reverse NCX activity, however experimental evidence is still missing. Whole-cell and perforated patch-clamp experiments were performed on rabbit SN cells supplemented with fluorescent Ca2+-tracking. We established 2 and 8 mM pipette NaCl groups to suppress and enable reverse NCX. NCX was assessed by specific block with 1 μM ORM-10962. Mechanistic simulations were performed by Maltsev-Lakatta minimal computational SN model. Active reverse NCX resulted in larger Ca2+-transient amplitude with larger SR Ca2+-content. Spontaneous action potential (AP) frequency increased with 8 mM NaCl. When reverse NCX was facilitated by 1 μM strophantin the Ca2+i and spontaneous rate increased. ORM-10962 applied prior to strophantin prevented Ca2+i and AP cycle change. Computational simulations indicated gradually increasing reverse NCX current, Ca2+i and heart rate with increasing Na+i. Our results provide further evidence for the role of reverse NCX in SN pacemaking. The reverse NCX activity may provide additional Ca2+-influx that could increase SR Ca2+-content, which consequently leads to enhanced pacemaking activity.
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Affiliation(s)
- Noémi Tóth
- grid.9008.10000 0001 1016 9625Department of Pharmacology and Pharmacotherapy, Albert Szent-Györgyi Medical School, University of Szeged, Dóm tér 12, P.O. Box 427, Szeged, 6720 Hungary
| | - Axel Loewe
- grid.7892.40000 0001 0075 5874Institute of Biomedical Engineering, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
| | - Jozefina Szlovák
- grid.9008.10000 0001 1016 9625Department of Pharmacology and Pharmacotherapy, Albert Szent-Györgyi Medical School, University of Szeged, Dóm tér 12, P.O. Box 427, Szeged, 6720 Hungary
| | - Zsófia Kohajda
- ELKH-SZTE Research Group of Cardiovascular Pharmacology, Szeged, Hungary
| | - Gergő Bitay
- grid.9008.10000 0001 1016 9625Department of Pharmacology and Pharmacotherapy, Albert Szent-Györgyi Medical School, University of Szeged, Dóm tér 12, P.O. Box 427, Szeged, 6720 Hungary
| | - Jouko Levijoki
- grid.419951.10000 0004 0400 1289Orion Pharma, Espoo, Finland
| | - Julius Gy. Papp
- grid.9008.10000 0001 1016 9625Department of Pharmacology and Pharmacotherapy, Albert Szent-Györgyi Medical School, University of Szeged, Dóm tér 12, P.O. Box 427, Szeged, 6720 Hungary ,ELKH-SZTE Research Group of Cardiovascular Pharmacology, Szeged, Hungary
| | - András Varró
- grid.9008.10000 0001 1016 9625Department of Pharmacology and Pharmacotherapy, Albert Szent-Györgyi Medical School, University of Szeged, Dóm tér 12, P.O. Box 427, Szeged, 6720 Hungary ,ELKH-SZTE Research Group of Cardiovascular Pharmacology, Szeged, Hungary
| | - Norbert Nagy
- grid.9008.10000 0001 1016 9625Department of Pharmacology and Pharmacotherapy, Albert Szent-Györgyi Medical School, University of Szeged, Dóm tér 12, P.O. Box 427, Szeged, 6720 Hungary ,ELKH-SZTE Research Group of Cardiovascular Pharmacology, Szeged, Hungary
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Horváth B, Szentandrássy N, Almássy J, Dienes C, Kovács ZM, Nánási PP, Banyasz T. Late Sodium Current of the Heart: Where Do We Stand and Where Are We Going? Pharmaceuticals (Basel) 2022; 15:ph15020231. [PMID: 35215342 PMCID: PMC8879921 DOI: 10.3390/ph15020231] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2022] [Revised: 02/07/2022] [Accepted: 02/09/2022] [Indexed: 02/05/2023] Open
Abstract
Late sodium current has long been linked to dysrhythmia and contractile malfunction in the heart. Despite the increasing body of accumulating information on the subject, our understanding of its role in normal or pathologic states is not complete. Even though the role of late sodium current in shaping action potential under physiologic circumstances is debated, it’s unquestioned role in arrhythmogenesis keeps it in the focus of research. Transgenic mouse models and isoform-specific pharmacological tools have proved useful in understanding the mechanism of late sodium current in health and disease. This review will outline the mechanism and function of cardiac late sodium current with special focus on the recent advances of the area.
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Affiliation(s)
- Balázs Horváth
- Department of Physiology, University of Debrecen, 4032 Debrecen, Hungary; (B.H.); (N.S.); (J.A.); (C.D.); (Z.M.K.); (P.P.N.)
| | - Norbert Szentandrássy
- Department of Physiology, University of Debrecen, 4032 Debrecen, Hungary; (B.H.); (N.S.); (J.A.); (C.D.); (Z.M.K.); (P.P.N.)
- Department of Basic Medical Sciences, Faculty of Dentistry, University of Debrecen, 4032 Debrecen, Hungary
| | - János Almássy
- Department of Physiology, University of Debrecen, 4032 Debrecen, Hungary; (B.H.); (N.S.); (J.A.); (C.D.); (Z.M.K.); (P.P.N.)
| | - Csaba Dienes
- Department of Physiology, University of Debrecen, 4032 Debrecen, Hungary; (B.H.); (N.S.); (J.A.); (C.D.); (Z.M.K.); (P.P.N.)
| | - Zsigmond Máté Kovács
- Department of Physiology, University of Debrecen, 4032 Debrecen, Hungary; (B.H.); (N.S.); (J.A.); (C.D.); (Z.M.K.); (P.P.N.)
| | - Péter P. Nánási
- Department of Physiology, University of Debrecen, 4032 Debrecen, Hungary; (B.H.); (N.S.); (J.A.); (C.D.); (Z.M.K.); (P.P.N.)
- Department of Dental Physiology and Pharmacology, University of Debrecen, 4032 Debrecen, Hungary
| | - Tamas Banyasz
- Department of Physiology, University of Debrecen, 4032 Debrecen, Hungary; (B.H.); (N.S.); (J.A.); (C.D.); (Z.M.K.); (P.P.N.)
- Correspondence: ; Tel.: +36-(52)-255-575; Fax: +36-(52)-255-116
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Hegyi B, Shimkunas R, Jian Z, Izu LT, Bers DM, Chen-Izu Y. Mechanoelectric coupling and arrhythmogenesis in cardiomyocytes contracting under mechanical afterload in a 3D viscoelastic hydrogel. Proc Natl Acad Sci U S A 2021; 118:e2108484118. [PMID: 34326268 PMCID: PMC8346795 DOI: 10.1073/pnas.2108484118] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The heart pumps blood against the mechanical afterload from arterial resistance, and increased afterload may alter cardiac electrophysiology and contribute to life-threatening arrhythmias. However, the cellular and molecular mechanisms underlying mechanoelectric coupling in cardiomyocytes remain unclear. We developed an innovative patch-clamp-in-gel technology to embed cardiomyocytes in a three-dimensional (3D) viscoelastic hydrogel that imposes an afterload during regular myocyte contraction. Here, we investigated how afterload affects action potentials, ionic currents, intracellular Ca2+ transients, and cell contraction of adult rabbit ventricular cardiomyocytes. We found that afterload prolonged action potential duration (APD), increased transient outward K+ current, decreased inward rectifier K+ current, and increased L-type Ca2+ current. Increased Ca2+ entry caused enhanced Ca2+ transients and contractility. Moreover, elevated afterload led to discordant alternans in APD and Ca2+ transient. Ca2+ alternans persisted under action potential clamp, indicating that the alternans was Ca2+ dependent. Furthermore, all these afterload effects were significantly attenuated by inhibiting nitric oxide synthase 1 (NOS1). Taken together, our data reveal a mechano-chemo-electrotransduction (MCET) mechanism that acutely transduces afterload through NOS1-nitric oxide signaling to modulate the action potential, Ca2+ transient, and contractility. The MCET pathway provides a feedback loop in excitation-Ca2+ signaling-contraction coupling, enabling autoregulation of contractility in cardiomyocytes in response to afterload. This MCET mechanism is integral to the individual cardiomyocyte (and thus the heart) to intrinsically enhance its contractility in response to the load against which it has to do work. While this MCET is largely compensatory for physiological load changes, it may also increase susceptibility to arrhythmias under excessive pathological loading.
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Affiliation(s)
- Bence Hegyi
- Department of Pharmacology, University of California, Davis, CA 95616
| | - Rafael Shimkunas
- Department of Pharmacology, University of California, Davis, CA 95616
- Department of Biomedical Engineering, University of California, Davis, CA 95616
| | - Zhong Jian
- Department of Pharmacology, University of California, Davis, CA 95616
| | - Leighton T Izu
- Department of Pharmacology, University of California, Davis, CA 95616
| | - Donald M Bers
- Department of Pharmacology, University of California, Davis, CA 95616
| | - Ye Chen-Izu
- Department of Pharmacology, University of California, Davis, CA 95616;
- Department of Biomedical Engineering, University of California, Davis, CA 95616
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, CA 95616
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4
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Morotti S, Ni H, Peters CH, Rickert C, Asgari-Targhi A, Sato D, Glukhov AV, Proenza C, Grandi E. Intracellular Na + Modulates Pacemaking Activity in Murine Sinoatrial Node Myocytes: An In Silico Analysis. Int J Mol Sci 2021; 22:5645. [PMID: 34073281 PMCID: PMC8198068 DOI: 10.3390/ijms22115645] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Revised: 05/21/2021] [Accepted: 05/25/2021] [Indexed: 12/19/2022] Open
Abstract
Background: The mechanisms underlying dysfunction in the sinoatrial node (SAN), the heart's primary pacemaker, are incompletely understood. Electrical and Ca2+-handling remodeling have been implicated in SAN dysfunction associated with heart failure, aging, and diabetes. Cardiomyocyte [Na+]i is also elevated in these diseases, where it contributes to arrhythmogenesis. Here, we sought to investigate the largely unexplored role of Na+ homeostasis in SAN pacemaking and test whether [Na+]i dysregulation may contribute to SAN dysfunction. Methods: We developed a dataset-specific computational model of the murine SAN myocyte and simulated alterations in the major processes of Na+ entry (Na+/Ca2+ exchanger, NCX) and removal (Na+/K+ ATPase, NKA). Results: We found that changes in intracellular Na+ homeostatic processes dynamically regulate SAN electrophysiology. Mild reductions in NKA and NCX function increase myocyte firing rate, whereas a stronger reduction causes bursting activity and loss of automaticity. These pathologic phenotypes mimic those observed experimentally in NCX- and ankyrin-B-deficient mice due to altered feedback between the Ca2+ and membrane potential clocks underlying SAN firing. Conclusions: Our study generates new testable predictions and insight linking Na+ homeostasis to Ca2+ handling and membrane potential dynamics in SAN myocytes that may advance our understanding of SAN (dys)function.
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Affiliation(s)
- Stefano Morotti
- Department of Pharmacology, University of California Davis, Davis, CA 95616, USA; (H.N.); (A.A.-T.); (D.S.)
| | - Haibo Ni
- Department of Pharmacology, University of California Davis, Davis, CA 95616, USA; (H.N.); (A.A.-T.); (D.S.)
| | - Colin H. Peters
- Department of Physiology and Biophysics, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA; (C.H.P.); (C.R.); (C.P.)
| | - Christian Rickert
- Department of Physiology and Biophysics, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA; (C.H.P.); (C.R.); (C.P.)
| | - Ameneh Asgari-Targhi
- Department of Pharmacology, University of California Davis, Davis, CA 95616, USA; (H.N.); (A.A.-T.); (D.S.)
| | - Daisuke Sato
- Department of Pharmacology, University of California Davis, Davis, CA 95616, USA; (H.N.); (A.A.-T.); (D.S.)
| | - Alexey V. Glukhov
- Department of Medicine, Cardiovascular Medicine, University of Wisconsin Madison School of Medicine and Public Health, Madison, WI 53705, USA;
| | - Catherine Proenza
- Department of Physiology and Biophysics, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA; (C.H.P.); (C.R.); (C.P.)
- Department of Medicine, Division of Cardiology, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA
| | - Eleonora Grandi
- Department of Pharmacology, University of California Davis, Davis, CA 95616, USA; (H.N.); (A.A.-T.); (D.S.)
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Tsuchida K. [Electrophysiological Effects of Ionophore-induced Increases in Intracellular Na + in Cardiomyocytes]. YAKUGAKU ZASSHI 2021; 141:705-710. [PMID: 33952755 DOI: 10.1248/yakushi.20-00235] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Na ionophores increase intracellular Na+ ([Na+]i). Membrane potentials and currents were measured using microelectrode and whole-cell patch-clamp techniques. Monensin (10-6-3×10-5 M) reduced the slope of the pacemaker potentials and shortened the action potential duration (APD) in sino-atrial nodal and Purkinje cells. Monensin (10-5 M) shortened the APD and reduced the amplitude of the plateau phase in ventricular myocytes. Monensin decreased the hyperpolarization-activated inward current (If), and it increased the transient outward potassium current (Ito) in Purkinje cells. In addition, monensin decreased the sodium current (INa), shifting the inactivation curve to the hyperpolarized direction. Moreover, monensin decreased the L-type calcium current (ICa) in ventricular myocytes. The Na+-Ca2+ exchange current (INa-Ca) was augmented particularly in the reverse mode, and the Na+-K+ pump current (INa-K) was also activated by monensin in cardiomyocytes. The ATP-activated potassium current (IK,ATP) could be induced by monensin. Notably, the inward rectifying K+ current (IK1), and the slow delayed outward K+ current (IKs) were not affected evidently by monensin. Collectively, alteration of [Na+]i can influence the activities of various ion channels and transporters. Thus, the significance of altered [Na+]i should be taken into consideration in the action of drugs affecting [Na+]i such as digitalis, Na+ channel blockers, and Na+ channel activating agents.
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Affiliation(s)
- Katsuharu Tsuchida
- Department of Rational Medicinal Science, Faculty of Pharmaceutical Sciences, Doshisha Women's College of Liberal Arts
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6
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Hamilton S, Terentyeva R, Clements RT, Belevych AE, Terentyev D. Sarcoplasmic reticulum-mitochondria communication; implications for cardiac arrhythmia. J Mol Cell Cardiol 2021; 156:105-113. [PMID: 33857485 DOI: 10.1016/j.yjmcc.2021.04.002] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/03/2021] [Revised: 03/15/2021] [Accepted: 04/05/2021] [Indexed: 12/11/2022]
Abstract
Sudden cardiac death due to ventricular tachyarrhythmias remains the major cause of mortality in the world. Heart failure, diabetic cardiomyopathy, old age-related cardiac dysfunction and inherited disorders are associated with enhanced propensity to malignant cardiac arrhythmias. Both defective mitochondrial function and abnormal intracellular Ca2+ homeostasis have been established as the key contributing factors in the pathophysiology and arrhythmogenesis in these conditions. This article reviews current advances in understanding of bidirectional control of ryanodine receptor-mediated sarcoplasmic reticulum Ca2+ release and mitochondrial function, and how defects in crosstalk between these two organelles increase arrhythmic risk in cardiac disease.
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Affiliation(s)
- Shanna Hamilton
- Department of Physiology and Cell Biology, Davis Heart and Lung Research Institute, Wexner Medical Center, The Ohio State University, Columbus, OH, United States of America
| | - Radmila Terentyeva
- Department of Physiology and Cell Biology, Davis Heart and Lung Research Institute, Wexner Medical Center, The Ohio State University, Columbus, OH, United States of America
| | - Richard T Clements
- Biomedical & Pharmaceutical Sciences, University of Rhode Island, Kingston, RI, United States of America
| | - Andriy E Belevych
- Department of Physiology and Cell Biology, Davis Heart and Lung Research Institute, Wexner Medical Center, The Ohio State University, Columbus, OH, United States of America
| | - Dmitry Terentyev
- Department of Physiology and Cell Biology, Davis Heart and Lung Research Institute, Wexner Medical Center, The Ohio State University, Columbus, OH, United States of America.
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7
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Hegyi B, Chen-Izu Y, Izu LT, Bányász T. Altered K + current profiles underlie cardiac action potential shortening in hyperkalemia and β-adrenergic stimulation. Can J Physiol Pharmacol 2019; 97:773-780. [PMID: 31091413 DOI: 10.1139/cjpp-2019-0056] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Hyperkalemia is known to develop in various conditions including vigorous physical exercise. In the heart, hyperkalemia is associated with action potential (AP) shortening that was attributed to altered gating of K+ channels. However, it remains unknown how hyperkalemia changes the profiles of each K+ current under a cardiac AP. Therefore, we recorded the major K+ currents (inward rectifier K+ current, IK1; rapid and slow delayed rectifier K+ currents, IKr and IKs, respectively) using AP-clamp in rabbit ventricular myocytes. As K+ may accumulate at rapid heart rates during sympathetic stimulation, we also examined the effect of isoproterenol on these K+ currents. We found that IK1 was significantly increased in hyperkalemia, whereas the reduction of driving force for K+ efflux dominated over the altered channel gating in case of IKr and IKs. Overall, the markedly increased IK1 in hyperkalemia overcame the relative decreases of IKr and IKs during AP, resulting in an increased net repolarizing current during AP phase 3. β-Adrenergic stimulation of IKs also provided further repolarizing power during sympathetic activation, although hyperkalemia limited IKs upregulation. These results indicate that facilitation of IK1 in hyperkalemia and β-adrenergic stimulation of IKs represent important compensatory mechanisms against AP prolongation and arrhythmia susceptibility.
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Affiliation(s)
- Bence Hegyi
- a Department of Pharmacology, University of California, Davis, CA 95616, USA
| | - Ye Chen-Izu
- a Department of Pharmacology, University of California, Davis, CA 95616, USA.,b Department of Biomedical Engineering, University of California, Davis, CA 95616, USA.,c Department of Internal Medicine/Cardiology, University of California, Davis, CA 95616, USA
| | - Leighton T Izu
- a Department of Pharmacology, University of California, Davis, CA 95616, USA
| | - Tamás Bányász
- a Department of Pharmacology, University of California, Davis, CA 95616, USA.,d Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
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8
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Skogestad J, Lines GT, Louch WE, Sejersted OM, Sjaastad I, Aronsen JM. Evidence for heterogeneous subsarcolemmal Na + levels in rat ventricular myocytes. Am J Physiol Heart Circ Physiol 2019; 316:H941-H957. [PMID: 30657726 DOI: 10.1152/ajpheart.00637.2018] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The intracellular Na+ concentration ([Na+]) regulates cardiac contractility. Previous studies have suggested that subsarcolemmal [Na+] is higher than cytosolic [Na+] in cardiac myocytes, but this concept remains controversial. Here, we used electrophysiological experiments and mathematical modeling to test whether there are subsarcolemmal pools with different [Na+] and dynamics compared with the bulk cytosol in rat ventricular myocytes. A Na+ dependency curve for Na+-K+-ATPase (NKA) current was recorded with symmetrical Na+ solutions, i.e., the same [Na+] in the superfusate and internal solution. This curve was used to estimate [Na+] sensed by NKA in other experiments. Three experimental observations suggested that [Na+] is higher near NKA than in the bulk cytosol: 1) when extracellular [Na+] was high, [Na+] sensed by NKA was ~6 mM higher than the internal solution in quiescent cells; 2) long trains of Na+ channel activation almost doubled this gradient; compared with an even intracellular distribution of Na+, the increase of [Na+] sensed by NKA was 10 times higher than expected, suggesting a local Na+ domain; and 3) accumulation of Na+ near NKA after trains of Na+ channel activation dissipated very slowly. Finally, mathematical models assuming heterogeneity of [Na+] between NKA and the Na+ channel better reproduced experimental data than the homogeneous model. In conclusion, our data suggest that NKA-sensed [Na+] is higher than [Na+] in the bulk cytosol and that there are differential Na+ pools in the subsarcolemmal space, which could be important for cardiac contractility and arrhythmogenesis. NEW & NOTEWORTHY Our data suggest that the Na+-K+-ATPase-sensed Na+ concentration is higher than the Na+ concentration in the bulk cytosol and that there are differential Na+ pools in the subsarcolemmal space, which could be important for cardiac contractility and arrhythmogenesis. Listen to this article's corresponding podcast at https://ajpheart.podbean.com/e/heterogeneous-sodium-in-ventricular-myocytes/ .
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Affiliation(s)
- J Skogestad
- Institute for Experimental Medical Research, Oslo University Hospital Ullevål and University of Oslo , Oslo , Norway
| | - G T Lines
- Simula Research Laboratory, Center for Cardiological Innovation , Oslo , Norway
| | - W E Louch
- Institute for Experimental Medical Research, Oslo University Hospital Ullevål and University of Oslo , Oslo , Norway.,K. G. Jebsen Center for Cardiac Research, University of Oslo , Oslo , Norway
| | - O M Sejersted
- Institute for Experimental Medical Research, Oslo University Hospital Ullevål and University of Oslo , Oslo , Norway
| | - I Sjaastad
- Institute for Experimental Medical Research, Oslo University Hospital Ullevål and University of Oslo , Oslo , Norway.,K. G. Jebsen Center for Cardiac Research, University of Oslo , Oslo , Norway
| | - J M Aronsen
- Institute for Experimental Medical Research, Oslo University Hospital Ullevål and University of Oslo , Oslo , Norway.,Bjørknes College , Oslo , Norway
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Walker MA, Gurev V, Rice JJ, Greenstein JL, Winslow RL. Estimating the probabilities of rare arrhythmic events in multiscale computational models of cardiac cells and tissue. PLoS Comput Biol 2017; 13:e1005783. [PMID: 29145393 PMCID: PMC5689829 DOI: 10.1371/journal.pcbi.1005783] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Accepted: 09/18/2017] [Indexed: 11/24/2022] Open
Abstract
Ectopic heartbeats can trigger reentrant arrhythmias, leading to ventricular fibrillation and sudden cardiac death. Such events have been attributed to perturbed Ca2+ handling in cardiac myocytes leading to spontaneous Ca2+ release and delayed afterdepolarizations (DADs). However, the ways in which perturbation of specific molecular mechanisms alters the probability of ectopic beats is not understood. We present a multiscale model of cardiac tissue incorporating a biophysically detailed three-dimensional model of the ventricular myocyte. This model reproduces realistic Ca2+ waves and DADs driven by stochastic Ca2+ release channel (RyR) gating and is used to study mechanisms of DAD variability. In agreement with previous experimental and modeling studies, key factors influencing the distribution of DAD amplitude and timing include cytosolic and sarcoplasmic reticulum Ca2+ concentrations, inwardly rectifying potassium current (IK1) density, and gap junction conductance. The cardiac tissue model is used to investigate how random RyR gating gives rise to probabilistic triggered activity in a one-dimensional myocyte tissue model. A novel spatial-average filtering method for estimating the probability of extreme (i.e. rare, high-amplitude) stochastic events from a limited set of spontaneous Ca2+ release profiles is presented. These events occur when randomly organized clusters of cells exhibit synchronized, high amplitude Ca2+ release flux. It is shown how reduced IK1 density and gap junction coupling, as observed in heart failure, increase the probability of extreme DADs by multiple orders of magnitude. This method enables prediction of arrhythmia likelihood and its modulation by alterations of other cellular mechanisms.
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Affiliation(s)
- Mark A. Walker
- Department of Biomedical Engineering and Institute for Computational Medicine, Johns Hopkins University, Baltimore, MD, United States of America
| | - Viatcheslav Gurev
- TJ Watson Research Center, IBM, Yorktown Heights, NY, United States of America
| | - John J. Rice
- TJ Watson Research Center, IBM, Yorktown Heights, NY, United States of America
| | - Joseph L. Greenstein
- Department of Biomedical Engineering and Institute for Computational Medicine, Johns Hopkins University, Baltimore, MD, United States of America
| | - Raimond L. Winslow
- Department of Biomedical Engineering and Institute for Computational Medicine, Johns Hopkins University, Baltimore, MD, United States of America
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10
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Lu FM, Hilgemann DW. Na/K pump inactivation, subsarcolemmal Na measurements, and cytoplasmic ion turnover kinetics contradict restricted Na spaces in murine cardiac myocytes. J Gen Physiol 2017; 149:727-749. [PMID: 28606910 PMCID: PMC5496509 DOI: 10.1085/jgp.201711780] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2017] [Accepted: 05/23/2017] [Indexed: 11/20/2022] Open
Abstract
The Na/K pump exports cytoplasmic Na ions while importing K ions, and its activity is thought to be affected by restricted intracellular Na diffusion in cardiac myocytes. Lu and Hilgemann find instead that the pump can enter an inactivated state and that inactivation can be relieved by cytoplasmic Na. Decades ago, it was proposed that Na transport in cardiac myocytes is modulated by large changes in cytoplasmic Na concentration within restricted subsarcolemmal spaces. Here, we probe this hypothesis for Na/K pumps by generating constitutive transsarcolemmal Na flux with the Na channel opener veratridine in whole-cell patch-clamp recordings. Using 25 mM Na in the patch pipette, pump currents decay strongly during continuous activation by extracellular K (τ, ∼2 s). In contradiction to depletion hypotheses, the decay becomes stronger when pump currents are decreased by hyperpolarization. Na channel currents are nearly unchanged by pump activity in these conditions, and conversely, continuous Na currents up to 0.5 nA in magnitude have negligible effects on pump currents. These outcomes are even more pronounced using 50 mM Li as a cytoplasmic Na congener. Thus, the Na/K pump current decay reflects mostly an inactivation mechanism that immobilizes Na/K pump charge movements, not cytoplasmic Na depletion. When channel currents are increased beyond 1 nA, models with unrestricted subsarcolemmal diffusion accurately predict current decay (τ ∼15 s) and reversal potential shifts observed for Na, Li, and K currents through Na channels opened by veratridine, as well as for Na, K, Cs, Li, and Cl currents recorded in nystatin-permeabilized myocytes. Ion concentrations in the pipette tip (i.e., access conductance) track without appreciable delay the current changes caused by sarcolemmal ion flux. Importantly, cytoplasmic mixing volumes, calculated from current decay kinetics, increase and decrease as expected with osmolarity changes (τ >30 s). Na/K pump current run-down over 20 min reflects a failure of pumps to recover from inactivation. Simulations reveal that pump inactivation coupled with Na-activated recovery enhances the rapidity and effectivity of Na homeostasis in cardiac myocytes. In conclusion, an autoregulatory mechanism enhances cardiac Na/K pump activity when cytoplasmic Na rises and suppresses pump activity when cytoplasmic Na declines.
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Affiliation(s)
- Fang-Min Lu
- Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX
| | - Donald W Hilgemann
- Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX
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Belardinelli L, Maleckar MM, Giles WR. Ventricular Microanatomy, Arrhythmias, and the Electrochemical Driving Force for Na +: Is There a Need for Flipped Learning? Circ Arrhythm Electrophysiol 2017; 10:e004955. [PMID: 28213509 DOI: 10.1161/circep.117.004955] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- Luiz Belardinelli
- From the InCarda Therapeutics, Inc, Clinical Research and Development, Brisbane, CA (L.B.); Allen Institute for Cell Science, Seattle, WA (M.M.M.); and Faculties of Kinesiology and Medicine (W.R.G.), The University of Calgary, Alberta, Canada
| | - Mary M Maleckar
- From the InCarda Therapeutics, Inc, Clinical Research and Development, Brisbane, CA (L.B.); Allen Institute for Cell Science, Seattle, WA (M.M.M.); and Faculties of Kinesiology and Medicine (W.R.G.), The University of Calgary, Alberta, Canada
| | - Wayne R Giles
- From the InCarda Therapeutics, Inc, Clinical Research and Development, Brisbane, CA (L.B.); Allen Institute for Cell Science, Seattle, WA (M.M.M.); and Faculties of Kinesiology and Medicine (W.R.G.), The University of Calgary, Alberta, Canada.
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