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Zhang JC, Xie XT, Chen Q, Zou T, Wu HL, Zhu C, Dong Y, Ye L, Li Y, Zhu PL. The effect of forskolin on membrane clock and calcium clock in the hypoxic/reoxygenation of sinoatrial node cells and its mechanism. Pharmacol Rep 2020; 72:1706-1716. [PMID: 32451735 DOI: 10.1007/s43440-020-00094-2] [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: 06/17/2019] [Revised: 01/20/2020] [Accepted: 01/22/2020] [Indexed: 11/24/2022]
Abstract
BACKGROUND In this study, we investigated the effect of forskolin (FSK, a selective adenylate cyclase agonist) on the automatic diastolic depolarization of sinus node cells (SNC) with hypoxia/reoxygenation (H/R) injury. METHODS The SNC of the newborn rat was randomly assigned into the control group, the H/R (H/R injury) group, or the H/R + FSK (H/R injury + FSK treatment) group. Patch-clamp was performed to record the action potential and electrophysiological changes. The cellular distribution of intracellular calcium concentration was analyzed by fluorescence staining. RESULTS Compared with the control cells, spontaneous pulsation frequency (SPF) and diastolic depolarization rate (DDR) of H/R cells were reduced from 244.3 ± 10.6 times/min and 108.7 ± 7.8 mV/s to 130.5 ± 7.6 times/min and 53.4 ± 6.5 mV/s, respectively. FSK significantly increased SPF and DDR of H/R cells to 208.3 ± 8.3 times/min and 93.2 ± 8.9 mV/s (n = 15, both p < 0.01), respectively. H/R reduced the current densities of If, ICa,T and inward INCX, which were significantly increased by 10 μM FSK treatment (n = 15, p < 0.01). Furthermore, reduced expression of HCN4 and NCX1.1 channel protein were significantly increased by FSK. Inhibitor studies showed that both SQ22536 (a selective adenylate cyclase inhibitor) and H89 (a selective protein kinases A [PKA] inhibitor) blocked the effects of FSK on SPF and DDR. CONCLUSIONS H/R causes pacemaker dysfunction in newborn rat sinoatrial node cells leading to divergence of the DD and the slow of spontaneous APs, which change can be dramatically reversed by FSK through increasing INCX and If current in H/R injury.
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Affiliation(s)
- Jian-Cheng Zhang
- Provincial Clinical Medicine College of Fujian Medical University, No. 134 East Street, Gulou District, Fuzhou, Fujian, 350000, People's Republic of China.,Department of Cardiology, Fujian Provincial Hospital, No. 134 East Street, Gulou District, Fuzhou, Fujian, 350000, People's Republic of China
| | - Xiao-Ting Xie
- Provincial Clinical Medicine College of Fujian Medical University, No. 134 East Street, Gulou District, Fuzhou, Fujian, 350000, People's Republic of China.,Department of Cardiology, Fujian Provincial Hospital, No. 134 East Street, Gulou District, Fuzhou, Fujian, 350000, People's Republic of China
| | - Qian Chen
- Provincial Clinical Medicine College of Fujian Medical University, No. 134 East Street, Gulou District, Fuzhou, Fujian, 350000, People's Republic of China.,Department of Critical Care Medicine Division Four, Fujian Provincial Hospital, No. 134 East Street, Gulou District, Fuzhou, Fujian, 350000, People's Republic of China
| | - Tian Zou
- Provincial Clinical Medicine College of Fujian Medical University, No. 134 East Street, Gulou District, Fuzhou, Fujian, 350000, People's Republic of China.,Department of Cardiology, Fujian Provincial Hospital, No. 134 East Street, Gulou District, Fuzhou, Fujian, 350000, People's Republic of China
| | - Hong-Lin Wu
- Provincial Clinical Medicine College of Fujian Medical University, No. 134 East Street, Gulou District, Fuzhou, Fujian, 350000, People's Republic of China.,Department of Cardiology, Fujian Provincial Hospital, No. 134 East Street, Gulou District, Fuzhou, Fujian, 350000, People's Republic of China
| | - Chao Zhu
- Department of Cardiology, General Hospital of People's Liberation Army, Haidian District, No. 28 Fuxing Road, Beijing, 100853, People's Republic of China
| | - Ying Dong
- Department of Cardiology, General Hospital of People's Liberation Army, Haidian District, No. 28 Fuxing Road, Beijing, 100853, People's Republic of China
| | - Lei Ye
- National Heart Research Institute, Singapore, Singapore
| | - Yang Li
- Department of Cardiology, General Hospital of People's Liberation Army, Haidian District, No. 28 Fuxing Road, Beijing, 100853, People's Republic of China.
| | - Peng-Li Zhu
- Provincial Clinical Medicine College of Fujian Medical University, No. 134 East Street, Gulou District, Fuzhou, Fujian, 350000, People's Republic of China. .,Department of Geriatric Medicine, Fujian Provincial Hospital, Fujian Provincial Center for Geriatrics, Provincial Clinical Medicine College of Fujian Medical University, No. 134 East Street, Gulou District, Fuzhou, Fujian, 350000, People's Republic of China.
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Chen Q, Chen JQ, Zhu PL, Wu HL, Xie XT, Dong Y, Xiang GJ, Chen MY, Li Y, Zhang JC. Inhibitory Effects of Cyclopiazonic Acid on the Pacemaker Current in Sinoatrial Nodal Cells. Neuroscience 2020; 433:230-240. [PMID: 31982470 DOI: 10.1016/j.neuroscience.2020.01.018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2019] [Revised: 01/09/2020] [Accepted: 01/10/2020] [Indexed: 10/25/2022]
Abstract
OBJECTIVE The spontaneous action potential of isolated sinoatrial node (SAN) cells is regulated by a coupled-clock system of two clocks: the calcium clock and membrane clock. However, it remains unclear whether calcium clock inhibitors have a direct effect on the membrane clock. The purpose of this study was to investigate the direct effect of cyclopiazonic acid (CPA), a selective calcium clock inhibitor, on the function of the membrane clock of SAN cells. METHODS at SAN cells were isolated by trypsinization and identified based on morphology and electrophysiology. If and HCN currents were recorded via patch clamp technique. The expression of the HCN channel protein was determined by Western blotting analysis. RESULTS The diastolic depolarization rate of spontaneous action potentials and the current densities of If were reduced by exposure to 10 μM CPA. The inhibitory effect of CPA was concentration-dependent with an IC50 value of 16.3 μM and a Hill coefficient of 0.98. The effect of CPA on If current was also time-dependent, and the If current amplitude was partially restored after washout. Furthermore, the steady-state activation curve of the If current was shifted to a negative potential, indicating that channel activation slowed down. Finally, the protein expression of HCN4 in HEK293 cells was markedly downregulated by CPA. CONCLUSIONS These results indicate that the direct inhibition effect of CPA on the If current in SAN cells is both concentration- and time-dependent. The underlying mechanisms may involve slowing down steady-state activation and the downregulation of pacemaker channel protein expression.
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Affiliation(s)
- Qian Chen
- Provincial Clinical Medicine College of Fujian Medical University, No.134 East Street, Gulou District, Fuzhou, Fujian 350000, PR China; Department of Critical Care Medicine Division Four, Fujian Provincial Hospital, No.134 East Street, Gulou Distric, Fuzhou, Fujian 350000, PR China.
| | - Jian-Quan Chen
- Provincial Clinical Medicine College of Fujian Medical University, No.134 East Street, Gulou District, Fuzhou, Fujian 350000, PR China; Department of Cardiology, Fujian Provincial Hospital, No.134 East Street, Gulou District, Fuzhou, Fujian 350000, PR China.
| | - Peng-Li Zhu
- Provincial Clinical Medicine College of Fujian Medical University, No.134 East Street, Gulou District, Fuzhou, Fujian 350000, PR China; Department of Geriatric Medicine, Fujian Provincial Hospital, Fujian Provincial Center for Geriatrics, No.134 East Street, Gulou District, Fuzhou, Fujian 350000, PR China.
| | - Hong-Lin Wu
- Provincial Clinical Medicine College of Fujian Medical University, No.134 East Street, Gulou District, Fuzhou, Fujian 350000, PR China; Department of Cardiology, Fujian Provincial Hospital, No.134 East Street, Gulou District, Fuzhou, Fujian 350000, PR China.
| | - Xiao-Ting Xie
- Provincial Clinical Medicine College of Fujian Medical University, No.134 East Street, Gulou District, Fuzhou, Fujian 350000, PR China; Department of Cardiology, Fujian Provincial Hospital, No.134 East Street, Gulou District, Fuzhou, Fujian 350000, PR China.
| | - Ying Dong
- Department of Cardiology, General Hospital of People's Liberation Army, No.28 Fuxing Road, Haidian District, Beijing 100853, PR China.
| | - Guo-Jian Xiang
- Provincial Clinical Medicine College of Fujian Medical University, No.134 East Street, Gulou District, Fuzhou, Fujian 350000, PR China; Department of Critical Care Medicine Division Four, Fujian Provincial Hospital, No.134 East Street, Gulou Distric, Fuzhou, Fujian 350000, PR China.
| | - Mei-Yan Chen
- Provincial Clinical Medicine College of Fujian Medical University, No.134 East Street, Gulou District, Fuzhou, Fujian 350000, PR China; Department of Anesthesiology Division Two, Fujian Provincial Hospital, No.134 East Street, Gulou Distric, Fuzhou, Fujian 350000, PR China.
| | - Yang Li
- Department of Cardiology, General Hospital of People's Liberation Army, No.28 Fuxing Road, Haidian District, Beijing 100853, PR China.
| | - Jian-Cheng Zhang
- Provincial Clinical Medicine College of Fujian Medical University, No.134 East Street, Gulou District, Fuzhou, Fujian 350000, PR China; Department of Cardiology, Fujian Provincial Hospital, No.134 East Street, Gulou District, Fuzhou, Fujian 350000, PR China.
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3
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Hawk MA, Ritchie GD, Henderson KA, Knostman KAB, Roche BM, Ma ZJ, Matthews CM, Sabourin CL, Wakayama EJ, Sabourin PJ. Neurobehavioral and Cardiovascular Effects of Potassium Cyanide Administered Orally to Mice. Int J Toxicol 2016; 35:604-15. [PMID: 27170681 DOI: 10.1177/1091581816646974] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The Food and Drug Administration Animal Rule requires evaluation of cardiovascular and central nervous system (CNS) effects of new therapeutics. To characterize an adult and juvenile mouse model, neurobehavioral and cardiovascular effects and pathology of a single sublethal but toxic, 8 mg/kg, oral dose of potassium cyanide (KCN) for up to 41 days postdosing were investigated. This study describes the short- and long-term sensory, motor, cognitive, and behavioral changes associated with oral dosing of a sublethal but toxic dose of KCN utilizing functional observation battery and Tier II CNS testing in adult and juvenile mice of both sexes. Selected tissues (histopathology) were evaluated for changes associated with KCN exposure with special attention to brain regions. Telemetry (adult mice only) was used to evaluate cardiovascular and temperature changes. Neurobehavioral capacity, sensorimotor responsivity or spontaneous locomotor activity, and rectal temperature were significantly reduced in adult and juvenile mice at 30 minutes post-8 mg/kg KCN dose. Immediate effects of cyanide included bradycardia, adverse electrocardiogram arrhythmic events, hypotension, and hypothermia with recovery by approximately 1 hour for blood pressure and heart rate effects and by 2 hours for body temperature. Lesions consistent with hypoxia, such as mild acute tubular necrosis in the kidneys corticomedullary junction, were the only histopathological findings and occurred at a very low incidence. The mouse KCN intoxication model indicates rapid and completely reversible effects in adult and juvenile mice following a single oral 8 mg/kg dose. Neurobehavioral and cardiovascular measurements can be used in this animal model as a trigger for treatment.
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Affiliation(s)
| | | | | | | | | | | | | | - Carol L Sabourin
- Department of Health and Human Services (HHS), Office of the Assistant Secretary for Preparedness and Response (ASPR), The Biomedical Advanced Research and Development Authority (BARDA), Washington, DC, USA
| | - Edward J Wakayama
- Department of Health and Human Services (HHS), Office of the Assistant Secretary for Preparedness and Response (ASPR), The Biomedical Advanced Research and Development Authority (BARDA), Washington, DC, USA
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Ju YK, Lee BH, Trajanovska S, Hao G, Allen DG, Lei M, Cannell MB. The involvement of TRPC3 channels in sinoatrial arrhythmias. Front Physiol 2015; 6:86. [PMID: 25859221 PMCID: PMC4373262 DOI: 10.3389/fphys.2015.00086] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2014] [Accepted: 03/04/2015] [Indexed: 01/08/2023] Open
Abstract
Atrial fibrillation (AF) is a significant contributor to cardiovascular morbidity and mortality. The currently available treatments are limited and AF continues to be a major clinical challenge. Clinical studies have shown that AF is frequently associated with dysfunction in the sino-atrial node (SAN). The association between AF and SAN dysfunction is probably related to the communication between the SAN and the surrounding atrial cells that form the SAN-atrial pacemaker complex and/or pathological processes that affect both the SAN and atrial simultaneously. Recent evidence suggests that Ca2+ entry through TRPC3 (Transient Receptor Potential Canonical-3) channels may underlie several pathophysiological conditions -including cardiac arrhythmias. However, it is still not known if atrial and sinoatrial node cells are also involved. In this article we will first briefly review TRPC3 and IP3R signaling that relate to store/receptor-operated Ca2+ entry (SOCE/ROCE) mechanisms and cardiac arrhythmias. We will then present some of our recent research progress in this field. Our experiments results suggest that pacing-induced AF in angiotensin II (Ang II) treated mice are significantly reduced in mice lacking the TRPC3 gene (TRPC3−/− mice) compared to wild type controls. We also show that pacemaker cells express TRPC3 and several other molecular components related to SOCE/ROCE signaling, including STIM1 and IP3R. Activation of G-protein coupled receptors (GPCRs) signaling that is able to modulate SOCE/ROCE and Ang II induced Ca2+ homeostasis changes in sinoatrial complex being linked to TRPC3. The results provide new evidence that TRPC3 may play a role in sinoatrial and atrial arrhythmias that are caused by GPCRs activation.
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Affiliation(s)
- Yue-Kun Ju
- Department of Physiology, School of Medical Sciences, Bosch Institute, University of Sydney Sydney, NSW, Australia
| | - Bon Hyang Lee
- Department of Physiology, School of Medical Sciences, Bosch Institute, University of Sydney Sydney, NSW, Australia
| | - Sofie Trajanovska
- Department of Physiology, School of Medical Sciences, Bosch Institute, University of Sydney Sydney, NSW, Australia
| | - Gouliang Hao
- Department of Pharmacology, University of Oxford Oxford, UK
| | - David G Allen
- Department of Physiology, School of Medical Sciences, Bosch Institute, University of Sydney Sydney, NSW, Australia
| | - Ming Lei
- Department of Pharmacology, University of Oxford Oxford, UK
| | - Mark B Cannell
- Department of Physiology and Pharmacology, University of Bristol Bristol, UK
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Monfredi O, Maltsev VA, Lakatta EG. Modern concepts concerning the origin of the heartbeat. Physiology (Bethesda) 2014; 28:74-92. [PMID: 23455768 DOI: 10.1152/physiol.00054.2012] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Physiological processes governing the heart beat have been under investigation for several hundred years. Major advances have been made in the recent past. A review of the present paradigm is presented here, including a look back at important steps that led us to where we are today, alongside a glimpse into the exciting future of pacemaker research.
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Affiliation(s)
- Oliver Monfredi
- Institute of Cardiovascular Sciences, University of Manchester, Manchester, UK
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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: 52] [Impact Index Per Article: 4.0] [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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Lakatta EG, Maltsev VA, Vinogradova TM. A coupled SYSTEM of intracellular Ca2+ clocks and surface membrane voltage clocks controls the timekeeping mechanism of the heart's pacemaker. Circ Res 2010; 106:659-73. [PMID: 20203315 PMCID: PMC2837285 DOI: 10.1161/circresaha.109.206078] [Citation(s) in RCA: 453] [Impact Index Per Article: 32.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Ion channels on the surface membrane of sinoatrial nodal pacemaker cells (SANCs) are the proximal cause of an action potential. Each individual channel type has been thoroughly characterized under voltage clamp, and the ensemble of the ion channel currents reconstructed in silico generates rhythmic action potentials. Thus, this ensemble can be envisioned as a surface "membrane clock" (M clock). Localized subsarcolemmal Ca(2+) releases are generated by the sarcoplasmic reticulum via ryanodine receptors during late diastolic depolarization and are referred to as an intracellular "Ca(2+) clock," because their spontaneous occurrence is periodic during voltage clamp or in detergent-permeabilized SANCs, and in silico as well. In spontaneously firing SANCs, the M and Ca(2+) clocks do not operate in isolation but work together via numerous interactions modulated by membrane voltage, subsarcolemmal Ca(2+), and protein kinase A and CaMKII-dependent protein phosphorylation. Through these interactions, the 2 subsystem clocks become mutually entrained to form a robust, stable, coupled-clock system that drives normal cardiac pacemaker cell automaticity. G protein-coupled receptors signaling creates pacemaker flexibility, ie, effects changes in the rhythmic action potential firing rate, by impacting on these very same factors that regulate robust basal coupled-clock system function. This review examines evidence that forms the basis of this coupled-clock system concept in cardiac SANCs.
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Affiliation(s)
- Edward G Lakatta
- Laboratory of Cardiovascular Science, Gerontology Research Center, National Institute on Aging/NIH, 5600 Nathan Shock Dr., Baltimore, MD 21224-6825, USA.
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Maltsev VA, Lakatta EG. Synergism of coupled subsarcolemmal Ca2+ clocks and sarcolemmal voltage clocks confers robust and flexible pacemaker function in a novel pacemaker cell model. Am J Physiol Heart Circ Physiol 2009; 296:H594-615. [PMID: 19136600 DOI: 10.1152/ajpheart.01118.2008] [Citation(s) in RCA: 145] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Recent experimental studies have demonstrated that sinoatrial node cells (SANC) generate spontaneous, rhythmic, local subsarcolemmal Ca(2+) releases (Ca(2+) clock), which occur during late diastolic depolarization (DD) and interact with the classic sarcolemmal voltage oscillator (membrane clock) by activating Na(+)-Ca(2+) exchanger current (I(NCX)). This and other interactions between clocks, however, are not captured by existing essentially membrane-delimited cardiac pacemaker cell numerical models. Using wide-scale parametric analysis of classic formulations of membrane clock and Ca(2+) cycling, we have constructed and initially explored a prototype rabbit SANC model featuring both clocks. Our coupled oscillator system exhibits greater robustness and flexibility than membrane clock operating alone. Rhythmic spontaneous Ca(2+) releases of sarcoplasmic reticulum (SR)-based Ca(2+) clock ignite rhythmic action potentials via late DD I(NCX) over much broader ranges of membrane clock parameters [e.g., L-type Ca(2+) current (I(CaL)) and/or hyperpolarization-activated ("funny") current (I(f)) conductances]. The system Ca(2+) clock includes SR and sarcolemmal Ca(2+) fluxes, which optimize cell Ca(2+) balance to increase amplitudes of both SR Ca(2+) release and late DD I(NCX) as SR Ca(2+) pumping rate increases, resulting in a broad pacemaker rate modulation (1.8-4.6 Hz). In contrast, the rate modulation range via membrane clock parameters is substantially smaller when Ca(2+) clock is unchanged or lacking. When Ca(2+) clock is disabled, the system parametric space for fail-safe SANC operation considerably shrinks: without rhythmic late DD I(NCX) ignition signals membrane clock substantially slows, becomes dysrhythmic, or halts. In conclusion, the Ca(2+) clock is a new critical dimension in SANC function. A synergism of the coupled function of Ca(2+) and membrane clocks confers fail-safe SANC operation at greatly varying rates.
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Affiliation(s)
- Victor A Maltsev
- Laboratory of Cardiovascular Science, Gerontology Research Center, NIA, NIH, 5600 Nathan Shock Dr., Baltimore, MD 21224-6825, USA
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Raj SR, Knollmann BC. The beat goes on—Driven by a cardiac calcium clock? Heart Rhythm 2008; 5:701-3. [DOI: 10.1016/j.hrthm.2008.02.027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/15/2008] [Indexed: 11/26/2022]
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Maltsev VA, Lakatta EG. Normal heart rhythm is initiated and regulated by an intracellular calcium clock within pacemaker cells. Heart Lung Circ 2007; 16:335-48. [PMID: 17827062 PMCID: PMC2078332 DOI: 10.1016/j.hlc.2007.07.005] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2007] [Accepted: 07/09/2007] [Indexed: 10/22/2022]
Abstract
For almost half a century it has been thought that the heart rhythm originates on the surface membrane of the cardiac pacemaker cells and is driven by voltage-gated ion channels (membrane clocks). Data from several recent studies, however, conclusively show that the rhythm is initiated, sustained, and regulated by oscillatory Ca(2+) releases (Ca(2+) clock) from the sarcoplasmic reticulum, a major Ca(2+) store within sinoatrial node cells, the primary heart's pacemakers. Activation of the local oscillatory Ca(2+) releases is independent of membrane depolarisation and driven by a high level of basal state phosphorylation of Ca(2+) cycling proteins. The releases produce Ca(2+) wavelets under the cell surface membrane during the later phase of diastolic depolarisation and activate the forward mode of Na(+)/Ca(2+) exchanger resulting in inward membrane current, which ignites an action potential. Phosphorylation-dependent gradation of speed at which Ca(2+) clock cycles is the essential regulatory mechanism of normal pacemaker rate and rhythm. The robust regulation of pacemaker function is insured by tight integration of Ca(2+) and membrane clocks: the action potential shape and ion fluxes are tuned by membrane clocks to sustain operation of the Ca(2+) clock which produces timely and powerful ignition of the membrane clocks to effect action potentials.
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Affiliation(s)
- Victor A. Maltsev
- Laboratory of Cardiovascular Science, Gerontology Research Center, National Institute on Aging, Intramural Research Program, National Institutes of Health, Baltimore, Maryland
| | - Edward G. Lakatta
- Laboratory of Cardiovascular Science, Gerontology Research Center, National Institute on Aging, Intramural Research Program, National Institutes of Health, Baltimore, Maryland
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