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Jang J, Kim SH, Um KB, Kim HJ, Park MK. Somatodendritic organization of pacemaker activity in midbrain dopamine neurons. THE KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY : OFFICIAL JOURNAL OF THE KOREAN PHYSIOLOGICAL SOCIETY AND THE KOREAN SOCIETY OF PHARMACOLOGY 2024; 28:165-181. [PMID: 38414399 PMCID: PMC10902590 DOI: 10.4196/kjpp.2024.28.2.165] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Revised: 01/08/2024] [Accepted: 01/08/2024] [Indexed: 02/29/2024]
Abstract
The slow and regular pacemaking activity of midbrain dopamine (DA) neurons requires proper spatial organization of the excitable elements between the soma and dendritic compartments, but the somatodendritic organization is not clear. Here, we show that the dynamic interaction between the soma and multiple proximal dendritic compartments (PDCs) generates the slow pacemaking activity in DA neurons. In multipolar DA neurons, spontaneous action potentials (sAPs) consistently originate from the axon-bearing dendrite. However, when the axon initial segment was disabled, sAPs emerge randomly from various primary PDCs, indicating that multiple PDCs drive pacemaking. Ca2+ measurements and local stimulation/perturbation experiments suggest that the soma serves as a stably-oscillating inertial compartment, while multiple PDCs exhibit stochastic fluctuations and high excitability. Despite the stochastic and excitable nature of PDCs, their activities are balanced by the large centrally-connected inertial soma, resulting in the slow synchronized pacemaking rhythm. Furthermore, our electrophysiological experiments indicate that the soma and PDCs, with distinct characteristics, play different roles in glutamate- induced burst-pause firing patterns. Excitable PDCs mediate excitatory burst responses to glutamate, while the large inertial soma determines inhibitory pause responses to glutamate. Therefore, we could conclude that this somatodendritic organization serves as a common foundation for both pacemaker activity and evoked firing patterns in midbrain DA neurons.
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Affiliation(s)
- Jinyoung Jang
- Department of Physiology, Sungkyunkwan University School of Medicine, Suwon 16419, Korea
| | - Shin Hye Kim
- Department of Physiology, Sungkyunkwan University School of Medicine, Suwon 16419, Korea
| | - Ki Bum Um
- Department of Physiology, Sungkyunkwan University School of Medicine, Suwon 16419, Korea
| | - Hyun Jin Kim
- Department of Physiology, Sungkyunkwan University School of Medicine, Suwon 16419, Korea
| | - Myoung Kyu Park
- Department of Physiology, Sungkyunkwan University School of Medicine, Suwon 16419, Korea
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2
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Segal S, Shemla O, Shapira R, Peretz NK, Lukyanenko Y, Brosh I, Behar J, Lakatta EG, Tsutsui K, Yaniv Y. cAMP signaling affects age-associated deterioration of pacemaker beating interval dynamics. GeroScience 2023; 45:2589-2600. [PMID: 37084120 PMCID: PMC10651572 DOI: 10.1007/s11357-023-00787-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2022] [Accepted: 03/27/2023] [Indexed: 04/22/2023] Open
Abstract
Sinoatrial node (SAN) beating interval variability (BIV) and the average beating interval (BI) are regulated by a coupled-clock system, driven by Ca2+-calmodulin activated adenylyl cyclase, cAMP, and downstream PKA signaling. Reduced responsiveness of the BI and BIV to submaximal, [X]50, β-adrenergic receptor (β-AR) stimulation, and phosphodiesterase inhibition (PDEI) have been documented in aged SAN tissue, whereas the maximal responses, [X]max, do not differ by age. To determine whether age-associated dysfunction in cAMP signaling leads to altered responsiveness of BI and BIV, we measured cAMP levels and BI in adult (2-4 months n = 27) and aged (22-26 months n = 25) C57/BL6 mouse SAN tissue in control and in response to β-AR or PDEI at X50 and [X]max. Both cAMP and average BI in adult SAN were reduced at X50, whereas cAMP and BI at Xmax did not differ by age. cAMP levels and average BI were correlated both within and between adult and aged SAN. BIV parameters in long- and short-range terms were correlated with cAMP levels for adult SAN. However, due to reduced cAMP within aged tissues at [X]50, these correlations were diminished in advanced age. Thus, cAMP level generated by the coupled clock mechanisms is tightly linked to average BI. Reduced cAMP level at X50 in aged SAN explains the reduced responsiveness of the BI and BIV to β-AR stimulation and PDEI.
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Affiliation(s)
- Sofia Segal
- Laboratory of Bioelectric and Bioenegetic, The Faculty of Biomedical Engineering, Technion-IIT, Haifa, Israel
| | - Ori Shemla
- Laboratory of Bioelectric and Bioenegetic, The Faculty of Biomedical Engineering, Technion-IIT, Haifa, Israel
| | - Rotem Shapira
- Laboratory of Bioelectric and Bioenegetic, The Faculty of Biomedical Engineering, Technion-IIT, Haifa, Israel
| | - Noa Kirschner Peretz
- Laboratory of Bioelectric and Bioenegetic, The Faculty of Biomedical Engineering, Technion-IIT, Haifa, Israel
| | | | - Inbar Brosh
- Laboratory of Bioelectric and Bioenegetic, The Faculty of Biomedical Engineering, Technion-IIT, Haifa, Israel
| | - Joachim Behar
- Laboratory of Bioelectric and Bioenegetic, The Faculty of Biomedical Engineering, Technion-IIT, Haifa, Israel
| | - Edward G Lakatta
- Intramural Research Program, National Institute On Aging, Baltimore, MD, USA
| | - Kenta Tsutsui
- Intramural Research Program, National Institute On Aging, Baltimore, MD, USA.
- Department of Cardiovascular Medicine, Saitama Medical University International Medical Center, Saitama, Japan.
| | - Yael Yaniv
- Laboratory of Bioelectric and Bioenegetic, The Faculty of Biomedical Engineering, Technion-IIT, Haifa, Israel.
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Shrestha N, Zorn-Pauly K, Mesirca P, Koyani CN, Wölkart G, Di Biase V, Torre E, Lang P, Gorischek A, Schreibmayer W, Arnold R, Maechler H, Mayer B, von Lewinski D, Torrente AG, Mangoni ME, Pelzmann B, Scheruebel S. Lipopolysaccharide-induced sepsis impairs M2R-GIRK signaling in the mouse sinoatrial node. Proc Natl Acad Sci U S A 2023; 120:e2210152120. [PMID: 37406102 PMCID: PMC10334783 DOI: 10.1073/pnas.2210152120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2022] [Accepted: 05/15/2023] [Indexed: 07/07/2023] Open
Abstract
Sepsis has emerged as a global health burden associated with multiple organ dysfunction and 20% mortality rate in patients. Numerous clinical studies over the past two decades have correlated the disease severity and mortality in septic patients with impaired heart rate variability (HRV), as a consequence of impaired chronotropic response of sinoatrial node (SAN) pacemaker activity to vagal/parasympathetic stimulation. However, the molecular mechanism(s) downstream to parasympathetic inputs have not been investigated yet in sepsis, particularly in the SAN. Based on electrocardiography, fluorescence Ca2+ imaging, electrophysiology, and protein assays from organ to subcellular level, we report that impaired muscarinic receptor subtype 2-G protein-activated inwardly-rectifying potassium channel (M2R-GIRK) signaling in a lipopolysaccharide-induced proxy septic mouse model plays a critical role in SAN pacemaking and HRV. The parasympathetic responses to a muscarinic agonist, namely IKACh activation in SAN cells, reduction in Ca2+ mobilization of SAN tissues, lowering of heart rate and increase in HRV, were profoundly attenuated upon lipopolysaccharide-induced sepsis. These functional alterations manifested as a direct consequence of reduced expression of key ion-channel components (GIRK1, GIRK4, and M2R) in the mouse SAN tissues and cells, which was further evident in the human right atrial appendages of septic patients and likely not mediated by the common proinflammatory cytokines elevated in sepsis.
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Affiliation(s)
- Niroj Shrestha
- Gottfried Schatz Research Center for Cell Signaling, Metabolism and Aging, Medical Physics and Biophysics, Medical University of Graz, 8010Graz, Austria
| | - Klaus Zorn-Pauly
- Gottfried Schatz Research Center for Cell Signaling, Metabolism and Aging, Medical Physics and Biophysics, Medical University of Graz, 8010Graz, Austria
| | - Pietro Mesirca
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, Inserm, 34094Montpellier, France
- Laboratory of Excellence in Ion Channels Science and Therapeutics, 34094Montpellier, France
| | - Chintan N. Koyani
- Division of Cardiology, Medical University of Graz, 8036Graz, Austria
| | - Gerald Wölkart
- Department of Pharmacology and Toxicology, University of Graz, 8010Graz, Austria
| | - Valentina Di Biase
- Institute of Pharmacology, Medical University of Innsbruck, 6020Innsbruck, Austria
| | - Eleonora Torre
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, Inserm, 34094Montpellier, France
- Laboratory of Excellence in Ion Channels Science and Therapeutics, 34094Montpellier, France
| | - Petra Lang
- Gottfried Schatz Research Center for Cell Signaling, Metabolism and Aging, Medical Physics and Biophysics, Medical University of Graz, 8010Graz, Austria
| | - Astrid Gorischek
- Gottfried Schatz Research Center for Cell Signaling, Metabolism and Aging, Medical Physics and Biophysics, Medical University of Graz, 8010Graz, Austria
| | - Wolfgang Schreibmayer
- Gottfried Schatz Research Center for Cell Signaling, Metabolism and Aging, Medical Physics and Biophysics, Medical University of Graz, 8010Graz, Austria
| | - Robert Arnold
- Gottfried Schatz Research Center for Cell Signaling, Metabolism and Aging, Medical Physics and Biophysics, Medical University of Graz, 8010Graz, Austria
| | - Heinrich Maechler
- Division of Cardiac Surgery, Medical University of Graz, 8036Graz, Austria
| | - Bernd Mayer
- Department of Pharmacology and Toxicology, University of Graz, 8010Graz, Austria
| | - Dirk von Lewinski
- Division of Cardiology, Medical University of Graz, 8036Graz, Austria
| | - Angelo G. Torrente
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, Inserm, 34094Montpellier, France
- Laboratory of Excellence in Ion Channels Science and Therapeutics, 34094Montpellier, France
| | - Matteo E. Mangoni
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, Inserm, 34094Montpellier, France
- Laboratory of Excellence in Ion Channels Science and Therapeutics, 34094Montpellier, France
| | - Brigitte Pelzmann
- Gottfried Schatz Research Center for Cell Signaling, Metabolism and Aging, Medical Physics and Biophysics, Medical University of Graz, 8010Graz, Austria
| | - Susanne Scheruebel
- Gottfried Schatz Research Center for Cell Signaling, Metabolism and Aging, Medical Physics and Biophysics, Medical University of Graz, 8010Graz, Austria
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Arbel Ganon L, Davoodi M, Alexandrovich A, Yaniv Y. Synergy between Membrane Currents Prevents Severe Bradycardia in Mouse Sinoatrial Node Tissue. Int J Mol Sci 2023; 24:ijms24065786. [PMID: 36982861 PMCID: PMC10051777 DOI: 10.3390/ijms24065786] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2023] [Revised: 03/04/2023] [Accepted: 03/13/2023] [Indexed: 03/30/2023] Open
Abstract
Bradycardia is initiated by the sinoatrial node (SAN), which is regulated by a coupled-clock system. Due to the clock coupling, reduction in the 'funny' current (If), which affects SAN automaticity, can be compensated, thus preventing severe bradycardia. We hypothesize that this fail-safe system is an inherent feature of SAN pacemaker cells and is driven by synergy between If and other ion channels. This work aimed to characterize the connection between membrane currents and their underlying mechanisms in SAN cells. SAN tissues were isolated from C57BL mice and Ca2+ signaling was measured in pacemaker cells within them. A computational model of SAN cells was used to understand the interactions between cell components. Beat interval (BI) was prolonged by 54 ± 18% (N = 16) and 30 ± 9% (N = 21) in response to If blockade, by ivabradine, or sodium current (INa) blockade, by tetrodotoxin, respectively. Combined drug application had a synergistic effect, manifested by a BI prolonged by 143 ± 25% (N = 18). A prolongation in the local Ca2+ release period, which reports on the level of crosstalk within the coupled-clock system, was measured and correlated with the prolongation in BI. The computational model predicted that INa increases in response to If blockade and that this connection is mediated by changes in T and L-type Ca2+ channels.
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Affiliation(s)
- Limor Arbel Ganon
- Laboratory of Bioelectric and Bioenergetic Systems, Faculty of Biomedical Engineering, Technion-IIT, Haifa 3200003, Israel
| | - Moran Davoodi
- Laboratory of Bioelectric and Bioenergetic Systems, Faculty of Biomedical Engineering, Technion-IIT, Haifa 3200003, Israel
| | - Alexandra Alexandrovich
- Laboratory of Bioelectric and Bioenergetic Systems, Faculty of Biomedical Engineering, Technion-IIT, Haifa 3200003, Israel
| | - Yael Yaniv
- Laboratory of Bioelectric and Bioenergetic Systems, Faculty of Biomedical Engineering, Technion-IIT, Haifa 3200003, Israel
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Wirth AN, Tsutsui K, Maltsev VA, Lakatta EG. Adenosine reduces sinoatrial node cell action potential firing rate by uncoupling its membrane and calcium clocks. Front Physiol 2022; 13:977807. [PMID: 36505046 PMCID: PMC9730041 DOI: 10.3389/fphys.2022.977807] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2022] [Accepted: 11/01/2022] [Indexed: 11/25/2022] Open
Abstract
The spontaneous action potential (AP) firing rate of sinoatrial nodal cells (SANC) is regulated by a system of intracellular Ca2+ and membrane ion current clocks driven by Ca2+-calmodulin-activated adenylyl cyclase-protein kinase-A signaling. The mean AP-cycle length (APCL) and APCL variability inform on the effectiveness of clock coupling. Endogenous ATP metabolite adenosine binds to adenosine receptors (A1, A3) that couple to Gi protein-coupled receptors, reducing spontaneous AP firing rate via Gβγ signaling that activates IKAch,Ado. Adenosine also inhibits adenylyl cyclase activity via Gαi signaling, impacting cAMP-mediated protein kinase-A-dependent protein phosphorylation. We hypothesize that in addition to IKAch,Ado activation, adenosine impacts also Ca2+ via Gαi signaling and that both effects reduce AP firing rate by reducing the effectiveness of the Ca2+ and membrane clock coupling. To this end, we measured Ca2+ and membrane potential characteristics in enzymatically isolated single rabbit SANC. 10 µM adenosine substantially increased both the mean APCL (on average by 43%, n = 10) and AP beat-to-beat variability from 5.1 ± 1.7% to 7.2 ± 2.0% (n = 10) measured via membrane potential and 5.0 ± 2.2% to 10.6 ± 5.9% (n = 40) measured via Ca2+ (assessed as the coefficient of variability = SD/mean). These effects were mediated by hyperpolarization of the maximum diastolic membrane potential (membrane clock effect) and suppression of diastolic local Ca2+releases (LCRs) (Ca2+-clock effect): as LCR size distributions shifted to smaller values, the time of LCR occurrence during diastolic depolarization (LCR period) became prolonged, and the ensemble LCR signal became reduced. The tight linear relationship of coupling between LCR period to the APCL in the presence of adenosine "drifted" upward and leftward, i.e. for a given LCR period, APCL was prolonged, becoming non-linear indicating clock uncoupling. An extreme case of uncoupling occurred at higher adenosine concentrations (>100 µM): small stochastic LCRs failed to self-organize and synchronize to the membrane clock, thus creating a failed attempt to generate an AP resulting in arrhythmia and cessation of AP firing. Thus, the effects of adenosine to activate Gβγ and IKACh,Ado and to activate Gαi, suppressing adenylyl cyclase activity, both contribute to the adenosine-induced increase in the mean APCL and APCL variability by reducing the fidelity of clock coupling and AP firing rate.
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Bychkov R, Juhaszova M, Calvo-Rubio Barrera M, Donald LAH, Coletta C, Shumaker C, Moorman K, Sirenko ST, Maltsev AV, Sollott SJ, Lakatta EG. The Heart's Pacemaker Mimics Brain Cytoarchitecture and Function: Novel Interstitial Cells Expose Complexity of the SAN. JACC Clin Electrophysiol 2022; 8:1191-1215. [PMID: 36182566 DOI: 10.1016/j.jacep.2022.07.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2022] [Revised: 05/27/2022] [Accepted: 07/01/2022] [Indexed: 10/14/2022]
Abstract
BACKGROUND The sinoatrial node (SAN) of the heart produces rhythmic action potentials, generated via calcium signaling within and among pacemaker cells. Our previous work has described the SAN as composed of a hyperpolarization-activated cyclic nucleotide-gated potassium channel 4 (HCN4)-expressing pacemaker cell meshwork, which merges with a network of connexin 43+/F-actin+ cells. It is also known that sympathetic and parasympathetic innervation create an autonomic plexus in the SAN that modulates heart rate and rhythm. However, the anatomical details of the interaction of this plexus with the pacemaker cell meshwork have yet to be described. OBJECTIVES This study sought to describe the 3-dimensional cytoarchitecture of the mouse SAN, including autonomic innervation, peripheral glial cells, and pacemaker cells. METHODS The cytoarchitecture of SAN whole-mount preparations was examined by three-dimensional confocal laser-scanning microscopy of triple immunolabeled with combinations of antibodies for HCN4, S100 calcium-binding protein B (S100B), glial fibrillary acidic protein (GFAP), choline acetyltransferase, or vesicular acetylcholine transporter, and tyrosine hydroxylase, and transmission electron microscopy. RESULTS The SAN exhibited heterogeneous autonomic innervation, which was accompanied by a web of peripheral glial cells and a novel S100B+/GFAP- interstitial cell population, with a unique morphology and a distinct distribution pattern, creating complex interactions with other cell types in the node, particularly with HCN4-expressing cells. Transmission electron microscopy identified a similar population of interstitial cells as telocytes, which appeared to secrete vesicles toward pacemaker cells. Application of S100B to SAN preparations desynchronized Ca2+ signaling in HCN4-expressing cells and increased variability in SAN impulse rate and rhythm. CONCLUSIONS The autonomic plexus, peripheral glial cell web, and a novel S100B+/GFAP- interstitial cell type embedded within the HCN4+ cell meshwork increase the structural and functional complexity of the SAN and provide a new regulatory pathway of rhythmogenesis.
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Affiliation(s)
- Rostislav Bychkov
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
| | - Magdalena Juhaszova
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
| | - Miguel Calvo-Rubio Barrera
- Translational Gerontology Branch, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
| | - Lorenzo A H Donald
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
| | - Christopher Coletta
- Laboratory of Genetics and Genomics, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
| | - Chad Shumaker
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
| | - Kayla Moorman
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
| | - Syevda Tagirova Sirenko
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
| | - Alexander V Maltsev
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
| | - Steven J Sollott
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
| | - Edward G Lakatta
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA.
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Guarina L, Moghbel AN, Pourhosseinzadeh MS, Cudmore RH, Sato D, Clancy CE, Santana LF. Biological noise is a key determinant of the reproducibility and adaptability of cardiac pacemaking and EC coupling. J Gen Physiol 2022; 154:213185. [PMID: 35482009 PMCID: PMC9059386 DOI: 10.1085/jgp.202012613] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2021] [Revised: 03/16/2022] [Accepted: 04/07/2022] [Indexed: 12/23/2022] Open
Abstract
Each heartbeat begins with the generation of an action potential in pacemaking cells in the sinoatrial node. This signal triggers contraction of cardiac muscle through a process termed excitation-contraction (EC) coupling. EC coupling is initiated in dyadic structures of cardiac myocytes, where ryanodine receptors in the junctional sarcoplasmic reticulum come into close apposition with clusters of CaV1.2 channels in invaginations of the sarcolemma. Cooperative activation of CaV1.2 channels within these clusters causes a local increase in intracellular Ca2+ that activates the juxtaposed ryanodine receptors. A salient feature of healthy cardiac function is the reliable and precise beat-to-beat pacemaking and amplitude of Ca2+ transients during EC coupling. In this review, we discuss recent discoveries suggesting that the exquisite reproducibility of this system emerges, paradoxically, from high variability at subcellular, cellular, and network levels. This variability is attributable to stochastic fluctuations in ion channel trafficking, clustering, and gating, as well as dyadic structure, which increase intracellular Ca2+ variance during EC coupling. Although the effects of these large, local fluctuations in function and organization are sometimes negligible at the macroscopic level owing to spatial-temporal summation within and across cells in the tissue, recent work suggests that the "noisiness" of these intracellular Ca2+ events may either enhance or counterintuitively reduce variability in a context-dependent manner. Indeed, these noisy events may represent distinct regulatory features in the tuning of cardiac contractility. Collectively, these observations support the importance of incorporating experimentally determined values of Ca2+ variance in all EC coupling models. The high reproducibility of cardiac contraction is a paradoxical outcome of high Ca2+ signaling variability at subcellular, cellular, and network levels caused by stochastic fluctuations in multiple processes in time and space. This underlying stochasticity, which counterintuitively manifests as reliable, consistent Ca2+ transients during EC coupling, also allows for rapid changes in cardiac rhythmicity and contractility in health and disease.
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Affiliation(s)
- Laura Guarina
- Department of Physiology and Membrane Biology, University of California Davis School of Medicine, Davis, CA
| | - Ariana Neelufar Moghbel
- Department of Physiology and Membrane Biology, University of California Davis School of Medicine, Davis, CA
| | | | - Robert H Cudmore
- Department of Physiology and Membrane Biology, University of California Davis School of Medicine, Davis, CA
| | - Daisuke Sato
- Department of Pharmacology, University of California Davis School of Medicine, Davis, CA
| | - Colleen E Clancy
- Department of Physiology and Membrane Biology, University of California Davis School of Medicine, Davis, CA
| | - Luis Fernando Santana
- Department of Physiology and Membrane Biology, University of California Davis School of Medicine, Davis, CA
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Segal S, Arbel-Ganon L, Mazgaoker S, Davoodi M, Yaniv Y. Increase in Ca2+-Activated cAMP/PKA Signaling Prevents Hydroxychloroquine-Induced Bradycardia of the Cardiac Pacemaker. Front Physiol 2022; 13:839140. [PMID: 35634151 PMCID: PMC9130770 DOI: 10.3389/fphys.2022.839140] [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: 12/20/2021] [Accepted: 04/05/2022] [Indexed: 11/13/2022] Open
Abstract
Bradycardia or tachycardia are known side effects of drugs that limit their clinical use. The heart pacemaker function which control the heart rate under normal conditions is determined by coupled clock system. Thus, interfering with specific clock mechanism will affect other clock mechanisms through changes in interconnected signaling and can lead to rhythm disturbance. However, upregulation of a different clock components can compensate for this change. We focus here on hydroxychloroquine (HCQ), which has been shown effective in treating COVID-19 patients, however its bradycardic side effect limits its clinical use. We aim to decipher the mechanisms underlying the effect of HCQ on pacemaker automaticity, to identify a potential drug that will eliminate the bradycardia. We used isolated rabbit sinoatrial node (SAN) cells, human-induced pluripotent stem cell–derived cardiomyocytes (hiPSC-CMs) and mouse SAN cells residing in SAN tissue. Further, we employed SAN cell computational model to suggest mechanistic insights of the effect of HCQ on pacemaker function. HCQ increased mean spontaneous beat interval and variability in all three models in parallel to slower intracellular kinetics. The computational model suggested that HCQ affects the pacemaker (funny) current (If), L-type Ca2+ current (ICa,L), transient outward potassium (Ito) and due to changes in Ca2+ kinetics, the sodium-calcium exchanger current (INCX). Co-application of 3’-isobutylmethylxanthine (IBMX) and HCQ prevented the increase in beat interval and variability in all three experimental models. The HCQ-induced increase in rabbit and mice SAN cell and hiPSC-CM spontaneous beat interval, can be prevented by a phosphodiester inhibitor that restores automaticity due to slower intracellular Ca2+ kinetics.
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Stoyek MR, MacDonald EA, Mantifel M, Baillie JS, Selig BM, Croll RP, Smith FM, Quinn TA. Drivers of Sinoatrial Node Automaticity in Zebrafish: Comparison With Mechanisms of Mammalian Pacemaker Function. Front Physiol 2022; 13:818122. [PMID: 35295582 PMCID: PMC8919049 DOI: 10.3389/fphys.2022.818122] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2021] [Accepted: 01/21/2022] [Indexed: 12/13/2022] Open
Abstract
Cardiac excitation originates in the sinoatrial node (SAN), due to the automaticity of this distinct region of the heart. SAN automaticity is the result of a gradual depolarisation of the membrane potential in diastole, driven by a coupled system of transarcolemmal ion currents and intracellular Ca2+ cycling. The frequency of SAN excitation determines heart rate and is under the control of extra- and intracardiac (extrinsic and intrinsic) factors, including neural inputs and responses to tissue stretch. While the structure, function, and control of the SAN have been extensively studied in mammals, and some critical aspects have been shown to be similar in zebrafish, the specific drivers of zebrafish SAN automaticity and the response of its excitation to vagal nerve stimulation and mechanical preload remain incompletely understood. As the zebrafish represents an important alternative experimental model for the study of cardiac (patho-) physiology, we sought to determine its drivers of SAN automaticity and the response to nerve stimulation and baseline stretch. Using a pharmacological approach mirroring classic mammalian experiments, along with electrical stimulation of intact cardiac vagal nerves and the application of mechanical preload to the SAN, we demonstrate that the principal components of the coupled membrane- Ca2+ pacemaker system that drives automaticity in mammals are also active in the zebrafish, and that the effects of extra- and intracardiac control of heart rate seen in mammals are also present. Overall, these results, combined with previously published work, support the utility of the zebrafish as a novel experimental model for studies of SAN (patho-) physiological function.
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Affiliation(s)
- Matthew R. Stoyek
- Department of Physiology and Biophysics, Dalhousie University, Halifax, NS, Canada
| | - Eilidh A. MacDonald
- Department of Physiology and Biophysics, Dalhousie University, Halifax, NS, Canada
- Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Melissa Mantifel
- Department of Physiology and Biophysics, Dalhousie University, Halifax, NS, Canada
| | - Jonathan S. Baillie
- Department of Physiology and Biophysics, Dalhousie University, Halifax, NS, Canada
| | - Bailey M. Selig
- Department of Physiology and Biophysics, Dalhousie University, Halifax, NS, Canada
| | - Roger P. Croll
- Department of Physiology and Biophysics, Dalhousie University, Halifax, NS, Canada
| | - Frank M. Smith
- Department of Medical Neuroscience, Dalhousie University, Halifax, NS, Canada
| | - T. Alexander Quinn
- Department of Physiology and Biophysics, Dalhousie University, Halifax, NS, Canada
- School of Biomedical Engineering, Dalhousie University, Halifax, NS, Canada
- *Correspondence: T. Alexander Quinn,
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Yang D, Morrell CH, Lyashkov AE, Tagirova Sirenko S, Zahanich I, Yaniv Y, Vinogradova TM, Ziman BD, Maltsev VA, Lakatta EG. Ca 2+ and Membrane Potential Transitions During Action Potentials Are Self-Similar to Each Other and to Variability of AP Firing Intervals Across the Broad Physiologic Range of AP Intervals During Autonomic Receptor Stimulation. Front Physiol 2021; 12:612770. [PMID: 34566668 PMCID: PMC8456031 DOI: 10.3389/fphys.2021.612770] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Accepted: 06/02/2021] [Indexed: 12/02/2022] Open
Abstract
Ca2+ and V m transitions occurring throughout action potential (AP) cycles in sinoatrial nodal (SAN) cells are cues that (1) not only regulate activation states of molecules operating within criticality (Ca2+ domain) and limit-cycle (V m domain) mechanisms of a coupled-clock system that underlies SAN cell automaticity, (2) but are also regulated by the activation states of the clock molecules they regulate. In other terms, these cues are both causes and effects of clock molecular activation (recursion). Recently, we demonstrated that Ca2+ and V m transitions during AP cycles in single SAN cells isolated from mice, guinea pigs, rabbits, and humans are self-similar (obey a power law) and are also self-similar to trans-species AP firing intervals (APFIs) of these cells in vitro, to heart rate in vivo, and to body mass. Neurotransmitter stimulation of β-adrenergic receptor or cholinergic receptor-initiated signaling in SAN cells modulates their AP firing rate and rhythm by impacting on the degree to which SAN clocks couple to each other, creating the broad physiologic range of SAN cell mean APFIs and firing interval variabilities. Here we show that Ca2+ and V m domain kinetic transitions (time to AP ignition in diastole and 90% AP recovery) occurring within given AP, the mean APFIs, and APFI variabilities within the time series of APs in 230 individual SAN cells are self-similar (obey power laws). In other terms, these long-range correlations inform on self-similar distributions of order among SAN cells across the entire broad physiologic range of SAN APFIs, regardless of whether autonomic receptors of these cells are stimulated or not and regardless of the type (adrenergic or cholinergic) of autonomic receptor stimulation. These long-range correlations among distributions of Ca2+ and V m kinetic functions that regulate SAN cell clock coupling during each AP cycle in different individual, isolated SAN cells not in contact with each other. Our numerical model simulations further extended our perspectives to the molecular scale and demonstrated that many ion currents also behave self-similar across autonomic states. Thus, to ensure rapid flexibility of AP firing rates in response to different types and degrees of autonomic input, nature "did not reinvent molecular wheels within the coupled-clock system of pacemaker cells," but differentially engaged or scaled the kinetics of gears that regulate the rate and rhythm at which the "wheels spin" in a given autonomic input context.
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Affiliation(s)
- Dongmei Yang
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States
| | - Christopher H. Morrell
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States
- Department of Mathematics and Statistics, Loyola University Maryland, Baltimore, MD, United States
| | - Alexey E. Lyashkov
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States
| | - Syevda Tagirova Sirenko
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States
| | - Ihor Zahanich
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States
| | - Yael Yaniv
- Biomedical Engineering Faculty, Technion–Israel Institute of Technology, Haifa, Israel
| | - Tatiana M. Vinogradova
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States
| | - Bruce D. Ziman
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States
| | - Victor A. Maltsev
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States
| | - Edward G. Lakatta
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States
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11
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Tagirova Sirenko S, Tsutsui K, Tarasov KV, Yang D, Wirth AN, Maltsev VA, Ziman BD, Yaniv Y, Lakatta EG. Self-Similar Synchronization of Calcium and Membrane Potential Transitions During Action Potential Cycles Predict Heart Rate Across Species. JACC Clin Electrophysiol 2021; 7:1331-1344. [PMID: 33933406 PMCID: PMC10089231 DOI: 10.1016/j.jacep.2021.02.016] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2020] [Revised: 02/23/2021] [Accepted: 02/25/2021] [Indexed: 01/23/2023]
Abstract
OBJECTIVES The purpose of this study was to discover regulatory universal mechanisms of normal automaticity in sinoatrial nodal (SAN) pacemaker cells that are self-similar across species. BACKGROUND Translation of knowledge of SAN automaticity gleaned from animal studies to human dysrhythmias (e.g., "sick sinus" syndrome [SSS]) requiring electronic pacemaker insertion has been suboptimal, largely because heart rate varies widely across species. METHODS Subcellular Ca2+ releases, whole cell action potential (AP)-induced Ca2+ transients, and APs were recorded in isolated mouse, guinea pig, rabbit, and human SAN cells. Ca2+-Vm kinetic parameters during phases of AP cycles from their ignition to recovery were quantified. RESULTS Although both action potential cycle lengths (APCLs) and Ca2+-Vm kinetic parameters during AP cycles differed across species by 10-fold, trans-species scaling of these during AP cycles and scaling of these to APCL in cells in vitro, electrocardiogram RR intervals in vivo, and body mass (BM) were self-similar (obeyed power laws) across species. Thus, APCL in vitro, heart rate in vivo, and BM of any species can be predicted by Ca2+-Vm kinetics during AP cycles in SAN cells measured in any single species in vitro. CONCLUSIONS In designing optimal heart rate to match widely different BM and energy requirements from mice to humans, nature did not "reinvent pacemaker cell wheels," but differentially scaled kinetics of gears that regulate the rates at which the "wheels spin." This discovery will facilitate the development of novel pharmacological and biological pacemakers featuring a normal, wide-range rate regulation in animal models and the translation of these to humans to target recalcitrant human SSS.
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Affiliation(s)
- Syevda Tagirova Sirenko
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institute of Health, Baltimore, Maryland, USA.
| | - Kenta Tsutsui
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institute of Health, Baltimore, Maryland, USA; Saitama International Medical Center, Saitama, Japan
| | - Kirill V Tarasov
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institute of Health, Baltimore, Maryland, USA
| | - Dongmei Yang
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institute of Health, Baltimore, Maryland, USA
| | - Ashley N Wirth
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institute of Health, Baltimore, Maryland, USA
| | - Victor A Maltsev
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institute of Health, Baltimore, Maryland, USA
| | - Bruce D Ziman
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institute of Health, Baltimore, Maryland, USA
| | - Yael Yaniv
- Biomedical Engineering Faculty, Technion-IIT, Haifa, Israel
| | - Edward G Lakatta
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institute of Health, Baltimore, Maryland, USA.
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12
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Lensen IS, Monfredi OJ, Andris RT, Lake DE, Moorman JR. Heart rate fragmentation gives novel insights into non-autonomic mechanisms governing beat-to-beat control of the heart's rhythm. JRSM Cardiovasc Dis 2020; 9:2048004020948732. [PMID: 32922768 PMCID: PMC7457638 DOI: 10.1177/2048004020948732] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2020] [Revised: 07/15/2020] [Accepted: 07/17/2020] [Indexed: 12/17/2022] Open
Abstract
To demonstrate how heart rate fragmentation gives novel insights into
non-autonomic mechanisms of beat-to-beat variability in cycle length, and
predicts survival of cardiology clinic patients, over and above traditional
clinical risk factors and measures of heart rate variability. Approach: We studied 2893 patients seen by cardiologists with
clinical data including 24-hour Holter monitoring. Novel measures of heart
rate fragmentation alongside canonical time and frequency domain measures of
heart rate variability, as well as an existing local dynamics score were
calculated. A proportional hazards model was utilized to relate the results
to survival. Main results: The novel heart rate fragmentation measures were
validated and characterized with respect to the effects of age, ectopy and
atrial fibrillation. Correlations between parameters were determined.
Critically, heart rate fragmentation results could not be accounted for by
undersampling respiratory sinus arrhythmia. Increased heart rate
fragmentation was associated with poorer survival (p ≪ 0.01 in the
univariate model). In multivariable analyses, increased heart rate
fragmentation and more abnormal local dynamics (p 0.045), along with
increased clinical risk factors (age (p ≪ 0.01), tobacco use (p ≪ 0.01) and
history of heart failure (p 0.019)) and lower low- to high-frequency ratio
(p 0.022) were all independent predictors of 2-year mortality. Significance: Analysis of continuous ECG data with heart rate
fragmentation indices yields information regarding non-autonomic control of
beat-to-beat variability in cycle length that is independent of and additive
to established parameters for investigating heart rate variability, and
predicts mortality in concert with measures of local dynamics, frequency
content of heart rate, and clinical risk factors.
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Affiliation(s)
- Irene S Lensen
- University of Technology Eindhoven, Noord-Brabant, Netherlands
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13
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Signatures of the autonomic nervous system and the heart's pacemaker cells in canine electrocardiograms and their applications to humans. Sci Rep 2020; 10:9971. [PMID: 32561798 PMCID: PMC7305326 DOI: 10.1038/s41598-020-66709-z] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2019] [Accepted: 03/13/2020] [Indexed: 01/21/2023] Open
Abstract
Heart rate and heart rate variability (HRV) are mainly determined by the autonomic nervous system (ANS), which interacts with receptors on the sinoatrial node (SAN; the heart’s primary pacemaker), and by the “coupled-clock” system within the SAN cells. HRV changes are associated with cardiac diseases. However, the relative contributions of the ANS and SAN to HRV are not clear, impeding effective treatment. To discern the SAN’s contribution, we performed HRV analysis on canine electrocardiograms containing basal and ANS-blockade segments. We also analyzed human electrocardiograms of atrial fibrillation and heart failure patients, as well as healthy aged subjects. Finally, we used a mathematical model to simulate HRV under decreased “coupled-clock” regulation. We found that (a) in canines, the SAN and ANS contribute mainly to long- and short-term HRV, respectively; (b) there is evidence suggesting a similar relative SAN contribution in humans; (c) SAN features can be calculated from beat-intervals obtained in-vivo, without intervention; (d) ANS contribution can be modeled by sines embedded in white noise; (e) HRV changes associated with cardiac diseases and aging can be interpreted as deterioration of both SAN and ANS; and (f) SAN clock-coupling can be estimated from changes in HRV. This may enable future non-invasive diagnostic applications.
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14
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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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15
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Moïse NS, Flanders WH, Pariaut R. Beat-to-Beat Patterning of Sinus Rhythm Reveals Non-linear Rhythm in the Dog Compared to the Human. Front Physiol 2020; 10:1548. [PMID: 32038271 PMCID: PMC6990411 DOI: 10.3389/fphys.2019.01548] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Accepted: 12/09/2019] [Indexed: 02/06/2023] Open
Abstract
The human and dog have sinus arrhythmia; however, the beat-to-beat interval changes were hypothesized to be different. Geometric analyses (R–R interval tachograms, dynamic Poincaré plots) to examine rate changes on a beat-to-beat basis were analyzed along with time and frequency domain heart rate variability from 40 human and 130 canine 24-h electrocardiographic recordings. Humans had bell-shaped beat-interval distributions, narrow interval bands across time with continuous interval change and linear changes in rate. In contrast, dogs had skewed non-singular beat distributions, wide interval bands {despite faster average heart rate of dogs [mean (range); 81 (64–119)] bpm compared to humans [74.5 (59–103) p = 0.005]} with regions displaying a paucity of intervals (zone of avoidance) and linear plus non-linear rate changes. In the dog, dynamic Poincaré plots showed linear rate changes as intervals prolonged until a point of divergence from the line of identity at a mean interval of 598.5 (95% CI: 583.5–613.5) ms (bifurcation interval). The dog had bimodal beat distribution during sleep with slower rates and greater variability than during active hours that showed singular interval distributions, higher rates and less variability. During sleep, Poincaré plots of the dog had clustered or branched patterns of intervals. A slower rate supported greater parasympathetic modulation with a branched compared to the clustered distribution. Treatment with atropine eliminated the non-linear patterns, while hydromorphone shifted the bifurcated branching and beat clustering to longer intervals. These results demonstrate the unique non-linear nature of beat-to-beat variability in the dog compared to humans with increases in interval duration (decrease heart rate). These results provoke the possibility that changes are linear with a dominant sympathetic modulation and non-linear with a dominant parasympathetic modulation. The abrupt bifurcation, zone of avoidance and beat-to-beat patterning are concordant with other studies demonstrating the development of exit block from the sinus node with parasympathetic modulation influencing not only the oscillation of the pacing cells, but conduction to the atria. Studies are required to associate the in vivo sinus node beat patterns identified in this study to the mapping of sinus impulse origin and exit from the sinus node.
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Affiliation(s)
- N Sydney Moïse
- College of Veterinary Medicine, Department of Clinical Sciences, Cornell University, Ithaca, NY, United States
| | - Wyatt H Flanders
- Department of Physics, University of Washington, Seattle, WA, United States
| | - Romain Pariaut
- College of Veterinary Medicine, Department of Clinical Sciences, Cornell University, Ithaca, NY, United States
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16
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Moen JM, Matt MG, Ramirez C, Tarasov KV, Chakir K, Tarasova YS, Lukyanenko Y, Tsutsui K, Monfredi O, Morrell CH, Tagirova S, Yaniv Y, Huynh T, Pacak K, Ahmet I, Lakatta EG. Overexpression of a Neuronal Type Adenylyl Cyclase (Type 8) in Sinoatrial Node Markedly Impacts Heart Rate and Rhythm. Front Neurosci 2019; 13:615. [PMID: 31275103 PMCID: PMC6591434 DOI: 10.3389/fnins.2019.00615] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2019] [Accepted: 05/29/2019] [Indexed: 12/21/2022] Open
Abstract
Heart rate (HR) and HR variability (HRV), predictors of over-all organism health, are widely believed to be driven by autonomic input to the sinoatrial node (SAN), with sympathetic input increasing HR and reducing HRV. However, variability in spontaneous beating intervals in isolated SAN tissue and single SAN cells, devoid of autonomic neural input, suggests that clocks intrinsic to SAN cells may also contribute to HR and HRV in vivo. We assessed contributions of both intrinsic and autonomic neuronal input mechanisms of SAN cell function on HR and HRV via in vivo, telemetric EKG recordings. This was done in both wild type (WT) mice, and those in which adenylyl cyclase type 8 (ADCY8), a main driver of intrinsic cAMP-PKA-Ca2+ mediated pacemaker function, was overexpressed exclusively in the heart (TGAC8). We hypothesized that TGAC8 mice would: (1) manifest a more coherent pattern of HRV in vivo, i.e., a reduced HRV driven by mechanisms intrinsic to SAN cells, and less so to modulation by autonomic input and (2) utilize unique adaptations to limit sympathetic input to a heart with high levels of intrinsic cAMP-Ca2+ signaling. Increased adenylyl cyclase (AC) activity in TGAC8 SAN tissue was accompanied by a marked increase in HR and a concurrent marked reduction in HRV, both in the absence or presence of dual autonomic blockade. The marked increase in intrinsic HR and coherence of HRV in TGAC8 mice occurred in the context of: (1) reduced HR and HRV responses to β-adrenergic receptor (β-AR) stimulation; (2) increased transcription of genes and expression of proteins [β-Arrestin, G Protein-Coupled Receptor Kinase 5 (GRK5) and Clathrin Adaptor Protein (Dab2)] that desensitize β-AR signaling within SAN tissue, (3) reduced transcripts or protein levels of enzymes [dopamine beta-hydorxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT)] required for catecholamine production in intrinsic cardiac adrenergic cells, and (4) substantially reduced plasma catecholamine levels. Thus, mechanisms driven by cAMP-PKA-Ca2+ signaling intrinsic to SAN cells underlie the marked coherence of TGAC8 mice HRV. Adaptations to limit additional activation of AC signaling, via decreased neuronal sympathetic input, are utilized to ensure the hearts survival and prevent Ca2+ overload.
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Affiliation(s)
- Jack M Moen
- Intramural Research Program, Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States.,Cellular and Molecular Physiology, Yale University, New Haven, CT, United States
| | - Michael G Matt
- Intramural Research Program, Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States.,School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Christopher Ramirez
- Intramural Research Program, Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States
| | - Kirill V Tarasov
- Intramural Research Program, Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States
| | - Khalid Chakir
- Intramural Research Program, Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States
| | - Yelena S Tarasova
- Intramural Research Program, Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States
| | - Yevgeniya Lukyanenko
- Intramural Research Program, Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States
| | - Kenta Tsutsui
- Intramural Research Program, Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States
| | - Oliver Monfredi
- Intramural Research Program, Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States.,Department of Cardiovascular and Electrophysiology, The Johns Hopkins Hospital, Baltimore, MD, United States
| | - Christopher H Morrell
- Intramural Research Program, Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States.,Department of Mathematics, Loyola University Maryland, Baltimore, MD, United States
| | - Syevda Tagirova
- Intramural Research Program, Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States
| | - Yael Yaniv
- Faculty of Biomedical Engineering, Technion Israel Institute of Technology, Haifa, Israel
| | - Thanh Huynh
- Section on Medical Neuroendocrinology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, United States
| | - Karel Pacak
- Section on Medical Neuroendocrinology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, United States
| | - Ismayil Ahmet
- Intramural Research Program, Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States
| | - Edward G Lakatta
- Intramural Research Program, Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States
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17
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Viner H, Nitsan I, Sapir L, Drori S, Tzlil S. Mechanical Communication Acts as a Noise Filter. iScience 2019; 14:58-68. [PMID: 30927696 PMCID: PMC6441679 DOI: 10.1016/j.isci.2019.02.030] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2018] [Revised: 12/29/2018] [Accepted: 02/26/2019] [Indexed: 11/15/2022] Open
Abstract
Cells can communicate mechanically by responding to mechanical deformations generated by their neighbors. Here, we describe a new role for mechanical communication by demonstrating that mechanical coupling between cells acts as a signaling cue that reduces intrinsic noise in the interacting cells. We measure mechanical interaction between beating cardiac cells cultured on a patterned flexible substrate and find that beat-to-beat variability decays exponentially with coupling strength. To demonstrate that such noise reduction is indeed a direct consequence of mechanical coupling, we reproduce the exponential decay in an assay where a beating cell interacts mechanically with an artificial stochastic ‘mechanical cell’. The mechanical cell consists of a probe that mimics the deformations generated by a stochastically beating neighboring cardiac cell. We show that noise reduction through mechanical coupling persists long after stimulation stops and identify microtubule integrity, NOX2, and CaMKII as mediators of noise reduction. Mechanical communication reduces intrinsic noise in interacting cells Cardiac cell beating noise decays exponentially with the strength of mechanical coupling Identical exponential decay length is obtained using a stochastic mechanical cell NOX2, ROS, and CaMKII are involved in mechanical communication-induced noise reduction
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Affiliation(s)
- Hen Viner
- Faculty of Mechanical Engineering, Technion - Israel Institute of Technology, Haifa 32000, Israel
| | - Ido Nitsan
- Faculty of Mechanical Engineering, Technion - Israel Institute of Technology, Haifa 32000, Israel
| | - Liel Sapir
- Faculty of Mechanical Engineering, Technion - Israel Institute of Technology, Haifa 32000, Israel
| | - Stavit Drori
- Faculty of Mechanical Engineering, Technion - Israel Institute of Technology, Haifa 32000, Israel
| | - Shelly Tzlil
- Faculty of Mechanical Engineering, Technion - Israel Institute of Technology, Haifa 32000, Israel.
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18
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Positive Feedback Mechanisms among Local Ca Releases, NCX, and I CaL Ignite Pacemaker Action Potentials. Biophys J 2019. [PMID: 29539403 DOI: 10.1016/j.bpj.2017.12.043] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Recent data suggest that cardiac pacemaker cell function is determined by numerous time-, voltage-, and Ca-dependent interactions of cell membrane electrogenic proteins (M-clock) and intracellular Ca cycling proteins (Ca-clock), forming a coupled-clock system. Many aspects of the coupled-clock system, however, remain underexplored. The key players of the system are Ca release channels (ryanodine receptors), generating local Ca releases (LCRs) from sarcoplasmic reticulum, electrogenic Na/Ca exchanger (NCX) current, and L-type Ca current (ICaL). We combined numerical model simulations with experimental simultaneous recordings of action potentials (APs) and Ca to gain further insight into the complex interactions within the system. Our simulations revealed a positive feedback mechanism, dubbed AP ignition, which accelerates the diastolic depolarization (DD) to reach AP threshold. The ignition phase begins when LCRs begin to occur and the magnitude of inward NCX current begins to increase. The NCX current, together with funny current and T-type Ca current accelerates DD, bringing the membrane potential to ICaL activation threshold. During the ignition phase, ICaL-mediated Ca influx generates more LCRs via Ca-induced Ca release that further activates inward NCX current, creating a positive feedback. Simultaneous recordings of membrane potential and confocal Ca images support the model prediction of the positive feedback among LCRs and ICaL, as diastolic LCRs begin to occur below and continue within the voltage range of ICaL activation. The ignition phase onset (identified within the fine DD structure) begins when DD starts to notably accelerate (∼0.15 V/s) above the recording noise. Moreover, the timing of the ignition onset closely predicted the duration of each AP cycle in the basal state, in the presence of autonomic receptor stimulation, and in response to specific inhibition of either the M-clock or Ca-clock, thus indicating general importance of the new coupling mechanism for regulation of the pacemaker cell cycle duration, and ultimately the heart rate.
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19
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Segal S, Kirschner Peretz N, Arbel-Ganon L, Liang J, Li L, Marbach D, Yang D, Wang SQ, Yaniv Y. Eliminating contraction during culture maintains global and local Ca 2+ dynamics in cultured rabbit pacemaker cells. Cell Calcium 2018; 78:35-47. [PMID: 30594820 DOI: 10.1016/j.ceca.2018.12.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Revised: 12/17/2018] [Accepted: 12/17/2018] [Indexed: 12/12/2022]
Abstract
Pacemaker cells residing in the sinoatrial node generate the regular heartbeat. Ca2+ signaling controls the heartbeat rate-directly, through the effect on membrane molecules (NCX exchange, K+ channel), and indirectly, through activation of calmodulin-AC-cAMP-PKA signaling. Thus, the physiological role of signaling in pacemaker cells can only be assessed if the Ca2+ dynamics are in the physiological range. Cultured cells that can be genetically manipulated and/or virally infected with probes are required for this purpose. Because rabbit pacemaker cells in culture experience a decrease in their spontaneous action potential (AP) firing rate below the physiological range, Ca2+ dynamics are expected to be affected. However, Ca2+ dynamics in cultured pacemaker cells have not been reported before. We aim to a develop a modified culture method that sustains the global and local Ca2+ kinetics along with the AP firing rate of rabbit pacemaker cells. We used experimental and computational tools to test the viability of rabbit pacemaker cells in culture under various conditions. We tested the effect of culture dish coating, pH, phosphorylation, and energy balance on cultured rabbit pacemaker cells function. The cells were maintained in culture for 48 h in two types of culture media: one without the addition of a contraction uncoupler and one enriched with either 10 mM BDM (2,3-Butanedione 2-monoxime) or 25 μM blebbistatin. The uncoupler was washed out from the medium prior to the experiments. Cells were successfully infected with a GFP adenovirus cultured with either BDM or blebbistatin. Using either uncoupler during culture led to the cell surface area being maintained at the same level as fresh cells. Moreover, the phospholamban and ryanodine receptor densities and their phosphorylation level remained intact in culture when either blebbistatin or BDM were present. Spontaneous AP firing rate, spontaneous Ca2+ kinetics, and spontaneous local Ca2+ release parameters were similar in the cultured cells with blebbistatin as in fresh cells. However, BDM affects these parameters. Using experimental and a computational model, we showed that by eliminating contraction, phosphorylation activity is preserved and energy is reduced. However, the side-effects of BDM render it less effective than blebbistatin.
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Affiliation(s)
- Sofia Segal
- Biomedical Engineering Faculty, Technion-IIT, Haifa, Israel
| | | | | | - Jinghui Liang
- College of Life Sciences, Peking University, Beijing, China
| | - Linlin Li
- College of Life Sciences, Peking University, Beijing, China
| | - Daphna Marbach
- Biomedical Engineering Faculty, Technion-IIT, Haifa, Israel
| | - Dongmei Yang
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, NIH, Baltimore, MD, USA
| | - Shi-Qiang Wang
- College of Life Sciences, Peking University, Beijing, China
| | - Yael Yaniv
- Biomedical Engineering Faculty, Technion-IIT, Haifa, Israel.
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20
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Ahammer H, Scheruebel S, Arnold R, Mayrhofer-Reinhartshuber M, Lang P, Dolgos Á, Pelzmann B, Zorn-Pauly K. Sinoatrial Beat to Beat Variability Assessed by Contraction Strength in Addition to the Interbeat Interval. Front Physiol 2018; 9:546. [PMID: 29867582 PMCID: PMC5968354 DOI: 10.3389/fphys.2018.00546] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2018] [Accepted: 04/27/2018] [Indexed: 12/01/2022] Open
Abstract
Beat to beat variability of cardiac tissue or isolated cells is frequently investigated by determining time intervals from electrode measurements in order to compute scale dependent or scale independent parameters. In this study, we utilize high-speed video camera recordings to investigate the variability of intervals as well as mechanical contraction strengths and relative contraction strengths with nonlinear analyses. Additionally, the video setup allowed us simultaneous electrode registrations of extracellular potentials. Sinoatrial node tissue under control and acetylcholine treated conditions was used to perform variability analyses by computing sample entropies and Higuchi dimensions. Beat to beat interval variabilities measured by the two recording techniques correlated very well, and therefore, validated the video analyses for this purpose. Acetylcholine treatment induced a reduction of beating rate and contraction strength, but the impact on interval variability was negligible. Nevertheless, the variability analyses of contraction strengths revealed significant differences in sample entropies and Higuchi dimensions between control and acetylcholine treated tissue. Therefore, the proposed high-speed video camera technique might represent a non-invasive tool that allows long-lasting recordings for detecting variations in beating behavior over a large range of scales.
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Affiliation(s)
- Helmut Ahammer
- Institute of Biophysics, Medical University of Graz, Graz, Austria
| | | | - Robert Arnold
- Institute of Biophysics, Medical University of Graz, Graz, Austria
| | | | - Petra Lang
- Institute of Biophysics, Medical University of Graz, Graz, Austria
| | - Ádám Dolgos
- Institute for eHealth, Graz University of Applied Sciences, Graz, Austria
| | | | - Klaus Zorn-Pauly
- Institute of Biophysics, Medical University of Graz, Graz, Austria
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21
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Sirenko SG, Yang D, Maltseva LA, Kim MS, Lakatta EG, Maltsev VA. Spontaneous, local diastolic subsarcolemmal calcium releases in single, isolated guinea-pig sinoatrial nodal cells. PLoS One 2017; 12:e0185222. [PMID: 28945810 PMCID: PMC5612473 DOI: 10.1371/journal.pone.0185222] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2017] [Accepted: 09/10/2017] [Indexed: 11/30/2022] Open
Abstract
Uptake and release calcium from the sarcoplasmic reticulum (SR) (dubbed “calcium clock”), in the form of spontaneous, rhythmic, local diastolic calcium releases (LCRs), together with voltage-sensitive ion channels (membrane clock) form a coupled system that regulates the action potential (AP) firing rate. LCRs activate Sodium/Calcium exchanger (NCX) that accelerates diastolic depolarization and thus participating in regulation of the time at which the next AP will occur. Previous studies in rabbit SA node cells (SANC) demonstrated that the basal AP cycle length (APCL) is tightly coupled to the basal LCR period (time from the prior AP-induced Ca2+ transient to the diastolic LCR occurrence), and that this coupling is further modulated by autonomic receptor stimulation. Although spontaneous LCRs during diastolic depolarization have been reported in SANC of various species (rabbit, cat, mouse, toad), prior studies have failed to detect LCRs in spontaneously beating SANC of guinea-pig, a species that has been traditionally used in studies of cardiac pacemaker cell function. We performed a detailed investigation of whether guinea-pig SANC generate LCRs and whether they play a similar key role in regulation of the AP firing rate. We used two different approaches, 2D high-speed camera and classical line-scan confocal imaging. Positioning the scan-line beneath sarcolemma, parallel to the long axis of the cell, we found that rhythmically beating guinea-pig SANC do, indeed, generate spontaneous, diastolic LCRs beneath the surface membrane. The average key LCR characteristics measured in confocal images in guinea-pig SANC were comparable to rabbit SANC, both in the basal state and in the presence of β-adrenergic receptor stimulation. Moreover, the relationship between the LCR period and APCL was subtended by the same linear function. Thus, LCRs in guinea-pig SANC contribute to the diastolic depolarization and APCL regulation. Our findings indicate that coupled-clock system regulation of APCL is a general, species-independent, mechanism of pacemaker cell normal automaticity. Lack of LCRs in prior studies is likely explained by technical issues, as individual LCRs are small stochastic events occurring mainly near the cell border.
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Affiliation(s)
- Syevda G. Sirenko
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - Dongmei Yang
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - Larissa A. Maltseva
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - Mary S. Kim
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - Edward G. Lakatta
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - Victor A. Maltsev
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
- * E-mail:
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22
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Krogh-Madsen T, Kold Taylor L, Skriver AD, Schaffer P, Guevara MR. Regularity of beating of small clusters of embryonic chick ventricular heart-cells: experiment vs. stochastic single-channel population model. CHAOS (WOODBURY, N.Y.) 2017; 27:093929. [PMID: 28964156 DOI: 10.1063/1.5001200] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The transmembrane potential is recorded from small isopotential clusters of 2-4 embryonic chick ventricular cells spontaneously generating action potentials. We analyze the cycle-to-cycle fluctuations in the time between successive action potentials (the interbeat interval or IBI). We also convert an existing model of electrical activity in the cluster, which is formulated as a Hodgkin-Huxley-like deterministic system of nonlinear ordinary differential equations describing five individual ionic currents, into a stochastic model consisting of a population of ∼20 000 independently and randomly gating ionic channels, with the randomness being set by a real physical stochastic process (radio static). This stochastic model, implemented using the Clay-DeFelice algorithm, reproduces the fluctuations seen experimentally: e.g., the coefficient of variation (standard deviation/mean) of IBI is 4.3% in the model vs. the 3.9% average value of the 17 clusters studied. The model also replicates all but one of several other quantitative measures of the experimental results, including the power spectrum and correlation integral of the voltage, as well as the histogram, Poincaré plot, serial correlation coefficients, power spectrum, detrended fluctuation analysis, approximate entropy, and sample entropy of IBI. The channel noise from one particular ionic current (IKs), which has channel kinetics that are relatively slow compared to that of the other currents, makes the major contribution to the fluctuations in IBI. Reproduction of the experimental coefficient of variation of IBI by adding a Gaussian white noise-current into the deterministic model necessitates using an unrealistically high noise-current amplitude. Indeed, a major implication of the modelling results is that, given the wide range of time-scales over which the various species of channels open and close, only a cell-specific stochastic model that is formulated taking into consideration the widely different ranges in the frequency content of the channel-noise produced by the opening and closing of several different types of channels will be able to reproduce precisely the various effects due to membrane noise seen in a particular electrophysiological preparation.
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Affiliation(s)
- Trine Krogh-Madsen
- Division of Cardiology, Department of Medicine, Weill Cornell Medicine, New York, New York 10065, USA
| | - Louise Kold Taylor
- Department of Physiology and Centre for Applied Mathematics in Biology and Medicine, McGill University, Montreal, Quebec H3G 1Y6, Canada
| | - Anne D Skriver
- Department of Physiology and Centre for Applied Mathematics in Biology and Medicine, McGill University, Montreal, Quebec H3G 1Y6, Canada
| | - Peter Schaffer
- Institute of Biophysics, Medical University Graz, A-8010 Graz, Austria
| | - Michael R Guevara
- Department of Physiology and Centre for Applied Mathematics in Biology and Medicine, McGill University, Montreal, Quebec H3G 1Y6, Canada
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23
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Comlekoglu T, Weinberg SH. Memory in a fractional-order cardiomyocyte model alters properties of alternans and spontaneous activity. CHAOS (WOODBURY, N.Y.) 2017; 27:093904. [PMID: 28964143 DOI: 10.1063/1.4999351] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Cardiac memory is the dependence of electrical activity on the prior history of one or more system state variables, including transmembrane potential (Vm), ionic current gating, and ion concentrations. While prior work has represented memory either phenomenologically or with biophysical detail, in this study, we consider an intermediate approach of a minimal three-variable cardiomyocyte model, modified with fractional-order dynamics, i.e., a differential equation of order between 0 and 1, to account for history-dependence. Memory is represented via both capacitive memory, due to fractional-order Vm dynamics, that arises due to non-ideal behavior of membrane capacitance; and ionic current gating memory, due to fractional-order gating variable dynamics, that arises due to gating history-dependence. We perform simulations for varying Vm and gating variable fractional-orders and pacing cycle length and measure action potential duration (APD) and incidence of alternans, loss of capture, and spontaneous activity. In the absence of ionic current gating memory, we find that capacitive memory, i.e., decreased Vm fractional-order, typically shortens APD, suppresses alternans, and decreases the minimum cycle length (MCL) for loss of capture. However, in the presence of ionic current gating memory, capacitive memory can prolong APD, promote alternans, and increase MCL. Further, we find that reduced Vm fractional order (typically less than 0.75) can drive phase 4 depolarizations that promote spontaneous activity. Collectively, our results demonstrate that memory reproduced by a fractional-order model can play a role in alternans formation and pacemaking, and in general, can greatly increase the range of electrophysiological characteristics exhibited by a minimal model.
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Affiliation(s)
- T Comlekoglu
- Virginia Commonwealth University, 401 West Main Street, Richmond, Virginia 23284, USA
| | - S H Weinberg
- Virginia Commonwealth University, 401 West Main Street, Richmond, Virginia 23284, USA
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24
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Davoodi M, Segal S, Kirschner Peretz N, Kamoun D, Yaniv Y. Semi-automated program for analysis of local Ca 2+ spark release with application for classification of heart cell type. Cell Calcium 2017; 64:83-90. [PMID: 28216082 DOI: 10.1016/j.ceca.2017.02.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2017] [Revised: 02/07/2017] [Accepted: 02/07/2017] [Indexed: 01/30/2023]
Abstract
Local Ca2+ spark releases are essential to the Ca2+ cycling process. Thus, they play an important role in ventricular and atrial cell contraction, as well as in sinoatrial cell automaticity. Characterizing their properties in healthy cells from different regions in the heart can reveal the basic biophysical differences among these regions. We designed a semi-automatic Matlab Graphical User Interface (called Sparkalyzer) to characterize parameters of Ca2+ spark release from any major cardiac tissue, as recorded in line-scan mode with a confocal laser-scanning microscope. We validated the algorithm on experimental images from rabbit sinoatrial, atrial, and ventricular cells loaded with Fluo-4 AM. The program characterizes general image parameters of Ca2+ transients and sparks: spark duration, which indicates for how long the spark provides Ca2+ to the closed intracellular mechanisms (typical value: 25±1, 23±1, 26±1ms for sinoatrial, atrial, and ventricular cells, respectively); spark amplitude, which indicates the amount of Ca2+ released by a single spark (1.6±0.1, 1.6±0.2, 1.4±0.1F/F0 for sinoatrial, atrial, and ventricular cells, respectively); spark length, which is the length of the Ca2+ wavelets fired out of a row of ryanodine receptors (5±0.1, 5±0.2, 3.4±0.3μm for sinoatrial, atrial, or ventricular cells, respectively) and number of sparks (0.14±0.02, 0.025±0.01, 0.02±0.01 for 1μm in 1s for sinoatrial, atrial, and ventricular cells, respectively). This method is reliable for Ca2+ spark analysis of sinoatrial, atrial, or ventricular cells. Moreover, by examining the average value of Ca2+ spark characteristics and their scattering around the mean, atrial, ventricular and sinoatrial cells can be differentiated.
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Affiliation(s)
- Moran Davoodi
- Biomedical Engineering Faculty, Technion-IIT, Haifa, Israel
| | - Sofia Segal
- Biomedical Engineering Faculty, Technion-IIT, Haifa, Israel
| | | | - David Kamoun
- Biomedical Engineering Faculty, Technion-IIT, Haifa, Israel
| | - Yael Yaniv
- Biomedical Engineering Faculty, Technion-IIT, Haifa, Israel.
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25
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Müller-Werdan U, Stöckl G, Werdan K. Advances in the management of heart failure: the role of ivabradine. Vasc Health Risk Manag 2016; 12:453-470. [PMID: 27895488 PMCID: PMC5118024 DOI: 10.2147/vhrm.s90383] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
A high resting heart rate (≥70–75 b.p.m.) is a risk factor for patients with heart failure (HF) with reduced ejection fraction (EF), probably in the sense of accelerated atherosclerosis, with an increased morbidity and mortality. Beta-blockers not only reduce heart rate but also have negative inotropic and blood pressure-lowering effects, and therefore, in many patients, they cannot be given in the recommended dose. Ivabradine specifically inhibits the pacemaker current (funny current, If) of the sinoatrial node cells, resulting in therapeutic heart rate lowering without any negative inotropic and blood pressure-lowering effect. According to the European Society of Cardiology guidelines, ivabradine should be considered to reduce the risk of HF hospitalization and cardiovascular death in symptomatic patients with a reduced left ventricular EF ≤35% and sinus rhythm ≥70 b.p.m. despite treatment with an evidence-based dose of beta-blocker or a dose below the recommended dose (recommendation class “IIa” = weight of evidence/opinion is in favor of usefulness/efficacy: “should be considered”; level of evidence “B” = data derived from a single randomized clinical trial or large nonrandomized studies). Using a heart rate cutoff of ≥ 75 b.p.m., as licensed by the European Medicines Agency, treatment with ivabradine 5–7.5 mg b.i.d. reduces cardiovascular mortality by 17%, HF mortality by 39% and HF hospitalization rate by 30%. A high resting heart rate is not only a risk factor in HF with reduced EF but also at least a risk marker in HF with preserved EF, in acute HF and also in special forms of HF. In this review, we discuss the proven role of ivabradine in the validated indication “HF with reduced EF” together with interesting preliminary findings, and the potential role of ivabradine in further, specific forms of HF.
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Affiliation(s)
| | - Georg Stöckl
- Department of Medical Affairs, Servier Deutschland GmbH, Munich
| | - Karl Werdan
- Department of Medicine III, University Hospital Halle (Saale), Martin-Luther-University Halle-Wittenberg, Halle (Saale), Germany
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26
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Bolea J, Pueyo E, Orini M, Bailón R. Influence of Heart Rate in Non-linear HRV Indices as a Sampling Rate Effect Evaluated on Supine and Standing. Front Physiol 2016; 7:501. [PMID: 27895588 PMCID: PMC5108795 DOI: 10.3389/fphys.2016.00501] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Accepted: 10/13/2016] [Indexed: 11/21/2022] Open
Abstract
The purpose of this study is to characterize and attenuate the influence of mean heart rate (HR) on nonlinear heart rate variability (HRV) indices (correlation dimension, sample, and approximate entropy) as a consequence of being the HR the intrinsic sampling rate of HRV signal. This influence can notably alter nonlinear HRV indices and lead to biased information regarding autonomic nervous system (ANS) modulation. First, a simulation study was carried out to characterize the dependence of nonlinear HRV indices on HR assuming similar ANS modulation. Second, two HR-correction approaches were proposed: one based on regression formulas and another one based on interpolating RR time series. Finally, standard and HR-corrected HRV indices were studied in a body position change database. The simulation study showed the HR-dependence of non-linear indices as a sampling rate effect, as well as the ability of the proposed HR-corrections to attenuate mean HR influence. Analysis in a body position changes database shows that correlation dimension was reduced around 21% in median values in standing with respect to supine position (p < 0.05), concomitant with a 28% increase in mean HR (p < 0.05). After HR-correction, correlation dimension decreased around 18% in standing with respect to supine position, being the decrease still significant. Sample and approximate entropy showed similar trends. HR-corrected nonlinear HRV indices could represent an improvement in their applicability as markers of ANS modulation when mean HR changes.
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Affiliation(s)
- Juan Bolea
- Centro de Investigación Biomédica en Red Bioingeniería, Biomateriales y NanomedicinaZaragoza, Spain
- BSICoS Group, Aragón Institute of Engineering Research (I3A), ISS Aragón, Universidad de ZaragozaZaragoza, Spain
| | - Esther Pueyo
- Centro de Investigación Biomédica en Red Bioingeniería, Biomateriales y NanomedicinaZaragoza, Spain
- BSICoS Group, Aragón Institute of Engineering Research (I3A), ISS Aragón, Universidad de ZaragozaZaragoza, Spain
| | - Michele Orini
- Institute of Cardiovascular Science, University College LondonLondon, UK
| | - Raquel Bailón
- Centro de Investigación Biomédica en Red Bioingeniería, Biomateriales y NanomedicinaZaragoza, Spain
- BSICoS Group, Aragón Institute of Engineering Research (I3A), ISS Aragón, Universidad de ZaragozaZaragoza, Spain
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27
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Yaniv Y, Lakatta EG. The end effector of circadian heart rate variation: the sinoatrial node pacemaker cell. BMB Rep 2016; 48:677-84. [PMID: 25999176 PMCID: PMC4791323 DOI: 10.5483/bmbrep.2015.48.12.061] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2015] [Indexed: 12/16/2022] Open
Abstract
Cardiovascular function is regulated by the rhythmicity of circadian, infradian and ultradian clocks. Specific time scales of different cell types drive their functions: circadian gene regulation at hours scale, activation-inactivation cycles of ion channels at millisecond scales, the heart's beating rate at hundreds of millisecond scales, and low frequency autonomic signaling at cycles of tens of seconds. Heart rate and rhythm are modulated by a hierarchical clock system: autonomic signaling from the brain releases neurotransmitters from the vagus and sympathetic nerves to the heart’s pacemaker cells and activate receptors on the cell. These receptors activating ultradian clock functions embedded within pacemaker cells include sarcoplasmic reticulum rhythmic spontaneous Ca2+ cycling, rhythmic ion channel current activation and inactivation, and rhythmic oscillatory mitochondria ATP production. Here we summarize the evidence that intrinsic pacemaker cell mechanisms are the end effector of the hierarchical brain-heart circadian clock system. [BMB Reports 2015; 48(12): 677-684]
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Affiliation(s)
- Yael Yaniv
- Biomedical Engineering Faculty, Technion-IIT, Haifa, Israel
| | - Edward G Lakatta
- Laboratory of Cardiovascular Science, Biomedical Research Center, Intramural Research Program, National Institute on Aging, NIH, Baltimore, Maryland, USA
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28
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Yaniv Y, Ahmet I, Tsutsui K, Behar J, Moen JM, Okamoto Y, Guiriba T, Liu J, Bychkov R, Lakatta EG. Deterioration of autonomic neuronal receptor signaling and mechanisms intrinsic to heart pacemaker cells contribute to age-associated alterations in heart rate variability in vivo. Aging Cell 2016; 15:716-24. [PMID: 27168363 PMCID: PMC4933656 DOI: 10.1111/acel.12483] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/18/2016] [Indexed: 12/19/2022] Open
Abstract
We aimed to determine how age‐associated changes in mechanisms extrinsic and intrinsic to pacemaker cells relate to basal beating interval variability (BIV) reduction in vivo. Beating intervals (BIs) were measured in aged (23–25 months) and adult (3–4 months) C57BL/6 male mice (i) via ECG in vivo during light anesthesia in the basal state, or in the presence of 0.5 mg mL−1 atropine + 1 mg mL−1 propranolol (in vivo intrinsic conditions), and (ii) via a surface electrogram, in intact isolated pacemaker tissue. BIV was quantified in both time and frequency domains using linear and nonlinear indices. Although the average basal BI did not significantly change with age under intrinsic conditions in vivo and in the intact isolated pacemaker tissue, the average BI was prolonged in advanced age. In vivo basal BIV indices were found to be reduced with age, but this reduction diminished in the intrinsic state. However, in pacemaker tissue BIV indices increased in advanced age vs. adults. In the isolated pacemaker tissue, the sensitivity of the average BI and BIV in response to autonomic receptor stimulation or activation of mechanisms intrinsic to pacemaker cells by broad‐spectrum phosphodiesterase inhibition declined in advanced age. Thus, changes in mechanisms intrinsic to pacemaker cells increase the average BIs and BIV in the mice of advanced age. Autonomic neural input to pacemaker tissue compensates for failure of molecular intrinsic mechanisms to preserve average BI. But this compensation reduces the BIV due to both the imbalance of autonomic neural input to the pacemaker cells and altered pacemaker cell responses to neural input.
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Affiliation(s)
- Yael Yaniv
- Biomedical Engineering Faculty Technion‐IIT Haifa Israel
| | - Ismayil Ahmet
- Laboratory of Cardiovascular Science Biomedical Research Center Intramural Research Program National Institute on Aging NIH Baltimore MD USA
| | - Kenta Tsutsui
- Laboratory of Cardiovascular Science Biomedical Research Center Intramural Research Program National Institute on Aging NIH Baltimore MD USA
| | - Joachim Behar
- Biomedical Engineering Faculty Technion‐IIT Haifa Israel
| | - Jack M. Moen
- Laboratory of Cardiovascular Science Biomedical Research Center Intramural Research Program National Institute on Aging NIH Baltimore MD USA
| | - Yosuke Okamoto
- Laboratory of Cardiovascular Science Biomedical Research Center Intramural Research Program National Institute on Aging NIH Baltimore MD USA
| | - Toni‐Rose Guiriba
- Laboratory of Cardiovascular Science Biomedical Research Center Intramural Research Program National Institute on Aging NIH Baltimore MD USA
| | - Jie Liu
- Laboratory of Cardiovascular Science Biomedical Research Center Intramural Research Program National Institute on Aging NIH Baltimore MD USA
| | - Rostislav Bychkov
- Laboratory of Cardiovascular Science Biomedical Research Center Intramural Research Program National Institute on Aging NIH Baltimore MD USA
| | - Edward G. Lakatta
- Laboratory of Cardiovascular Science Biomedical Research Center Intramural Research Program National Institute on Aging NIH Baltimore MD USA
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29
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Tse G, Lai ETH, Yeo JM, Tse V, Wong SH. Mechanisms of Electrical Activation and Conduction in the Gastrointestinal System: Lessons from Cardiac Electrophysiology. Front Physiol 2016; 7:182. [PMID: 27303305 PMCID: PMC4885840 DOI: 10.3389/fphys.2016.00182] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Accepted: 05/06/2016] [Indexed: 12/12/2022] Open
Abstract
The gastrointestinal (GI) tract is an electrically excitable organ system containing multiple cell types, which coordinate electrical activity propagating through this tract. Disruption in its normal electrophysiology is observed in a number of GI motility disorders. However, this is not well characterized and the field of GI electrophysiology is much less developed compared to the cardiac field. The aim of this article is to use the established knowledge of cardiac electrophysiology to shed light on the mechanisms of electrical activation and propagation along the GI tract, and how abnormalities in these processes lead to motility disorders and suggest better treatment options based on this improved understanding. In the first part of the article, the ionic contributions to the generation of GI slow wave and the cardiac action potential (AP) are reviewed. Propagation of these electrical signals can be described by the core conductor theory in both systems. However, specifically for the GI tract, the following unique properties are observed: changes in slow wave frequency along its length, periods of quiescence, synchronization in short distances and desynchronization over long distances. These are best described by a coupled oscillator theory. Other differences include the diminished role of gap junctions in mediating this conduction in the GI tract compared to the heart. The electrophysiology of conditions such as gastroesophageal reflux disease and gastroparesis, and functional problems such as irritable bowel syndrome are discussed in detail, with reference to ion channel abnormalities and potential therapeutic targets. A deeper understanding of the molecular basis and physiological mechanisms underlying GI motility disorders will enable the development of better diagnostic and therapeutic tools and the advancement of this field.
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Affiliation(s)
- Gary Tse
- Li Ka Shing Faculty of Medicine, School of Biomedical Sciences, University of Hong KongHong Kong, China
| | - Eric Tsz Him Lai
- Li Ka Shing Faculty of Medicine, School of Biomedical Sciences, University of Hong KongHong Kong, China
| | - Jie Ming Yeo
- School of Medicine, Imperial College LondonLondon, UK
| | - Vivian Tse
- Department of Physiology, McGill UniversityMontreal, QC, Canada
| | - Sunny Hei Wong
- Department of Medicine and Therapeutics, Institute of Digestive Disease, LKS Institute of Health Sciences, Chinese University of Hong KongHong Kong, China
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Sirenko SG, Maltsev VA, Yaniv Y, Bychkov R, Yaeger D, Vinogradova T, Spurgeon HA, Lakatta EG. Electrochemical Na+ and Ca2+ gradients drive coupled-clock regulation of automaticity of isolated rabbit sinoatrial nodal pacemaker cells. Am J Physiol Heart Circ Physiol 2016; 311:H251-67. [PMID: 27208164 DOI: 10.1152/ajpheart.00667.2015] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/20/2015] [Accepted: 05/11/2016] [Indexed: 11/22/2022]
Abstract
Coupling of an intracellular Ca(2+) clock to surface membrane ion channels, i.e., a "membrane clock, " via coupling of electrochemical Na(+) and Ca(2+) gradients (ENa and ECa, respectively) has been theorized to regulate sinoatrial nodal cell (SANC) normal automaticity. To test this hypothesis, we measured responses of [Na(+)]i, [Ca(2+)]i, membrane potential, action potential cycle length (APCL), and rhythm in rabbit SANCs to Na(+)/K(+) pump inhibition by the digitalis glycoside, digoxigenin (DG, 10-20 μmol/l). Initial small but significant increases in [Na(+)]i and [Ca(2+)]i and reductions in ENa and ECa in response to DG led to a small reduction in maximum diastolic potential (MDP), significantly enhanced local diastolic Ca(2+) releases (LCRs), and reduced the average APCL. As [Na(+)]i and [Ca(2+)]i continued to increase at longer times following DG exposure, further significant reductions in MDP, ENa, and ECa occurred; LCRs became significantly reduced, and APCL became progressively and significantly prolonged. This was accompanied by increased APCL variability. We also employed a coupled-clock numerical model to simulate changes in ENa and ECa simultaneously with ion currents not measured experimentally. Numerical modeling predicted that, as the ENa and ECa monotonically reduced over time in response to DG, ion currents (ICaL, ICaT, If, IKr, and IbNa) monotonically decreased. In parallel with the biphasic APCL, diastolic INCX manifested biphasic changes; initial INCX increase attributable to enhanced LCR ensemble Ca(2+) signal was followed by INCX reduction as ENCX (ENCX = 3ENa - 2ECa) decreased. Thus SANC automaticity is tightly regulated by ENa, ECa, and ENCX via a complex interplay of numerous key clock components that regulate SANC clock coupling.
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Affiliation(s)
- Syevda G Sirenko
- Laboratory of Cardiovascular Science, National Institutes of Health, National Institute on Aging, Intramural Research Program, Baltimore, Maryland
| | - Victor A Maltsev
- Laboratory of Cardiovascular Science, National Institutes of Health, National Institute on Aging, Intramural Research Program, Baltimore, Maryland
| | - Yael Yaniv
- Laboratory of Cardiovascular Science, National Institutes of Health, National Institute on Aging, Intramural Research Program, Baltimore, Maryland; Biomedical Engineering Faculty, Technion-IIT, Haifa, Israel
| | - Rostislav Bychkov
- Laboratory of Cardiovascular Science, National Institutes of Health, National Institute on Aging, Intramural Research Program, Baltimore, Maryland; Universidad Central del Caribe, Santa Juanita, Bayamon Puerto Rico
| | - Daniel Yaeger
- Laboratory of Cardiovascular Science, National Institutes of Health, National Institute on Aging, Intramural Research Program, Baltimore, Maryland
| | - Tatiana Vinogradova
- Laboratory of Cardiovascular Science, National Institutes of Health, National Institute on Aging, Intramural Research Program, Baltimore, Maryland
| | - Harold A Spurgeon
- Laboratory of Cardiovascular Science, National Institutes of Health, National Institute on Aging, Intramural Research Program, Baltimore, Maryland
| | - Edward G Lakatta
- Laboratory of Cardiovascular Science, National Institutes of Health, National Institute on Aging, Intramural Research Program, Baltimore, Maryland;
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Behar J, Yaniv Y. Dynamics of PKA phosphorylation and gain of function in cardiac pacemaker cells: a computational model analysis. Am J Physiol Heart Circ Physiol 2016; 310:H1259-66. [PMID: 26945074 DOI: 10.1152/ajpheart.00076.2016] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/26/2016] [Accepted: 03/02/2016] [Indexed: 11/22/2022]
Abstract
Cardiac pacemaker cell function is regulated by a coupled-clock system that integrates molecular cues on the cell-membrane surface (i.e., membrane clock) and on the sarcoplasmic reticulum (SR) (i.e., Ca(2+) clock). A recent study has shown that cotransfection of spontaneous beating cells (HEK293 cells and neonatal rat myocytes) with R524Q-mutant human hyperpolarization-activated cyclic nucleotide-gated molecules (the dominant component of funny channels) increases the funny channel's sensitivity to cAMP and leads to a decrease in spontaneous action potential (AP) cycle length (i.e., tachycardia). We hypothesize that in rabbit pacemaker cells, the same behavior is expected, and because of the coupled-clock system, the resultant steady-state decrease in AP cycle length will embody contributions from both clocks: the initial decrease in the spontaneous AP beating interval, arising from increased sensitivity of the f-channel to cAMP, will be accompanied by an increase in the adenylyl cyclase (AC)-cAMP-PKA-dependent phosphorylation activity, which will further decrease this interval. To test our hypothesis, we used the recently developed Yaniv-Lakatta pacemaker cell numerical model. This model predicts the cAMP signaling dynamics, as well as the kinetics and magnitude of protein phosphorylation in both normal and mutant pacemaker cells. We found that R524Q-mutant pacemaker cells have a shorter AP firing rate than that of wild-type cells and that gain in pacemaker function is the net effect of the R514Q mutation on the functioning of the coupled-clock system. Specifically, our results directly support the hypothesis that changes in Ca(2+)-activated AC-cAMP-PKA signaling are involved in the development of tachycardia in R524Q-mutant pacemaker cells.
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Affiliation(s)
- Joachim Behar
- Laboratory of Bioenergetic and Bioelectric Systems, Biomedical Engineering Faculty, Technion-IIT, Haifa, Israel
| | - Yael Yaniv
- Laboratory of Bioenergetic and Bioelectric Systems, Biomedical Engineering Faculty, Technion-IIT, Haifa, Israel
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Nazarov IB, Schofield CJ, Terrar DA. Contributions of cardiac "funny" (f) channels and sarcoplasmic reticulum Ca2+ in regulating beating rate of mouse and guinea pig sinoatrial node. Physiol Rep 2015; 3:3/12/e12561. [PMID: 26660545 PMCID: PMC4760437 DOI: 10.14814/phy2.12561] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The aim of this study was to investigate the effects on spontaneous beating rate of mouse atrial preparations following selective block of cardiac "funny" (f) channels, I(f), and/or suppression of sarcoplasmic reticulum (SR) function in the absence and presence of β-adrenoceptor stimulation. ZD7288 [to block I(f)] caused a substantial reduction (222 ± 13 bpm) in beating rate from 431 ± 14 to 209 ± 14 bpm, ryanodine alone (to block SR Ca(2+) release) reduced beating rate by 105 ± 11 bpm, with subsequent addition of ZD7288 further reducing rate by 57 ± 9 bpm. Cyclopiazonic acid (CPA) alone (to inhibit Ca(2+) reuptake by the SR) reduced beating rate by 148 ± 13 bpm with subsequent addition of ZD7288 further reducing rate by 79 ± 12 bpm. In additional experiments measuring Ca(2+) transients in the SA node region using Rhod-2, effects of ivabradine and ZD7288 on rate were again substantially reduced after CPA. Effects of CPA alone on rate developed much more slowly than effects on Ca(2+) transient amplitude. ZD7288, ivabradine, and CPA reduced the slope and maximum response of the log(concentration)-response curves for effects of isoprenaline on beating rate. Very little response to isoprenaline remained after treatment with CPA followed by ZD7288. Similar changes in isoprenaline log(concentration)-response curves were seen in guinea pig preparations. These observations are consistent with a role for Ca(2+) released from the SR in regulating I(f) and therefore beating rate of SA node preparations; there appear to be additional contributions of SR-derived Ca(2+) to effects of β-adrenoceptor stimulation on beating rate that are independent of I(f).
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Affiliation(s)
- Islom B Nazarov
- Department of Pharmacology, University of Oxford, Oxford, UK Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Oxford, UK
| | | | - Derek A Terrar
- Department of Pharmacology, University of Oxford, Oxford, UK
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Yaniv Y, Tsutsui K, Lakatta EG. Potential effects of intrinsic heart pacemaker cell mechanisms on dysrhythmic cardiac action potential firing. Front Physiol 2015; 6:47. [PMID: 25755643 PMCID: PMC4337365 DOI: 10.3389/fphys.2015.00047] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2014] [Accepted: 02/03/2015] [Indexed: 02/05/2023] Open
Abstract
The heart's regular electrical activity is initiated by specialized cardiac pacemaker cells residing in the sinoatrial node. The rate and rhythm of spontaneous action potential firing of sinoatrial node cells are regulated by stochastic mechanisms that determine the level of coupling of chemical to electrical clocks within cardiac pacemaker cells. This coupled-clock system is modulated by autonomic signaling from the brain via neurotransmitter release from the vagus and sympathetic nerves. Abnormalities in brain-heart clock connections or in any molecular clock activity within pacemaker cells lead to abnormalities in the beating rate and rhythm of the pacemaker tissue that initiates the cardiac impulse. Dysfunction of pacemaker tissue can lead to tachy-brady heart rate alternation or exit block that leads to long atrial pauses and increases susceptibility to other cardiac arrhythmia. Here we review evidence for the idea that disturbances in the intrinsic components of pacemaker cells may be implemented in arrhythmia induction in the heart.
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Affiliation(s)
- Yael Yaniv
- Biomedical Engineering Faculty, Technion-Israel Institute of Technology Haifa, Israel
| | - Kenta Tsutsui
- Laboratory of Cardiovascular Science, Biomedical Research Center, Intramural Research Program, National Institute on Aging, National Institutes of Health Baltimore, MD, USA
| | - Edward G Lakatta
- Laboratory of Cardiovascular Science, Biomedical Research Center, Intramural Research Program, National Institute on Aging, National Institutes of Health Baltimore, MD, USA
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Yaniv Y, Lakatta EG, Maltsev VA. From two competing oscillators to one coupled-clock pacemaker cell system. Front Physiol 2015; 6:28. [PMID: 25741284 PMCID: PMC4327306 DOI: 10.3389/fphys.2015.00028] [Citation(s) in RCA: 67] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2014] [Accepted: 01/17/2015] [Indexed: 01/01/2023] Open
Abstract
At the beginning of this century, debates regarding “what are the main control mechanisms that ignite the action potential (AP) in heart pacemaker cells” dominated the electrophysiology field. The original theory which prevailed for over 50 years had advocated that the ensemble of surface membrane ion channels (i.e., “M-clock”) is sufficient to ignite rhythmic APs. However, more recent experimental evidence in a variety of mammals has shown that the sarcoplasmic reticulum (SR) acts as a “Ca2+-clock” rhythmically discharges diastolic local Ca2+ releases (LCRs) beneath the cell surface membrane. LCRs activate an inward current (likely that of the Na+/Ca2+ exchanger) that prompts the surface membrane “M-clock” to ignite an AP. Theoretical and experimental evidence has mounted to indicate that this clock “crosstalk” operates on a beat-to-beat basis and determines both the AP firing rate and rhythm. Our review is focused on the evolution of experimental definition and numerical modeling of the coupled-clock concept, on how mechanisms intrinsic to pacemaker cell determine both the heart rate and rhythm, and on future directions to develop further the coupled-clock pacemaker cell concept.
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Affiliation(s)
- Yael Yaniv
- Biomedical Engineering Faculty, Technion-IIT Haifa, Israel
| | - Edward G Lakatta
- Laboratory of Cardiovascular Science, Biomedical Research Center, Intramural Research Program, National Institute on Aging, National Institutes of Health Baltimore, MD, USA
| | - Victor A Maltsev
- Laboratory of Cardiovascular Science, Biomedical Research Center, Intramural Research Program, National Institute on Aging, National Institutes of Health Baltimore, MD, USA
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