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Yang Q, Tadros HJ, Sun B, Bidzimou MT, Ezekian JE, Li F, Ludwig A, Wehrens XH, Landstrom AP. Junctional Ectopic Tachycardia Caused by Junctophilin-2 Expression Silencing Is Selectively Sensitive to Ryanodine Receptor Blockade. JACC Basic Transl Sci 2023; 8:1577-1588. [PMID: 38205351 PMCID: PMC10774596 DOI: 10.1016/j.jacbts.2023.07.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/15/2023] [Revised: 07/10/2023] [Accepted: 07/10/2023] [Indexed: 01/12/2024]
Abstract
Junctional ectopic tachycardia (JET) is a potentially fatal cardiac arrhythmia. Hcn4:shJph2 mice serve as a model of nodal arrhythmias driven by ryanodine type 2 receptor (RyR2)-mediated Ca2+ leak. EL20 is a small molecule that blocks RyR2 Ca2+ leak. In a novel in vivo model of JET, Hcn4:shJph2 mice demonstrated rapid conversion of JET to sinus rhythm with infusion of EL20. Primary atrioventricular nodal cells demonstrated increased Ca2+ transient oscillation frequency and increased RyR2-mediated stored Ca2+ leak which was normalized by EL20. EL20 was found to be rapidly degraded in mouse and human plasma, making it a potential novel therapy for JET.
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Affiliation(s)
- Qixin Yang
- Division of Cardiology, Department of Pediatrics, Duke University School of Medicine, Durham, North Carolina, USA
- Department of Cardiology, The First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, China
| | - Hanna J. Tadros
- Section of Cardiology, Department of Pediatrics, Baylor College of Medicine, Houston, Texas, USA
| | - Bo Sun
- Division of Cardiology, Department of Pediatrics, Duke University School of Medicine, Durham, North Carolina, USA
| | - Minu-Tshyeto Bidzimou
- Division of Cardiology, Department of Pediatrics, Duke University School of Medicine, Durham, North Carolina, USA
| | - Jordan E. Ezekian
- Division of Cardiology, Department of Pediatrics, Duke University School of Medicine, Durham, North Carolina, USA
| | - Feng Li
- Center for Drug Discovery and Department of Pathology and Immunology, Baylor College of Medicine, Houston, Texas, USA
| | - Andreas Ludwig
- Institut für Experimentelle und Klinische Pharmakologie, und Toxikologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Xander H.T. Wehrens
- Section of Cardiology, Department of Pediatrics, Baylor College of Medicine, Houston, Texas, USA
- Cardiovascular Research Institute, Departments of Medicine (Cardiology), Molecular Physiology and Biophysics, and Neuroscience and Center for Space Medicine, Baylor College of Medicine, Houston, Texas, USA
| | - Andrew P. Landstrom
- Division of Cardiology, Department of Pediatrics, Duke University School of Medicine, Durham, North Carolina, USA
- Department of Cell Biology, Duke University School of Medicine, Durham, North Carolina, USA
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2
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Pereira CH, Bare DJ, Rosas PC, Dias FAL, Banach K. The role of P21-activated kinase (Pak1) in sinus node function. J Mol Cell Cardiol 2023; 179:90-101. [PMID: 37086972 PMCID: PMC10294268 DOI: 10.1016/j.yjmcc.2023.04.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/25/2022] [Revised: 04/11/2023] [Accepted: 04/11/2023] [Indexed: 04/24/2023]
Abstract
Sinoatrial node (SAN) dysfunction (SND) and atrial arrhythmia frequently occur simultaneously with a hazard ratio of 4.2 for new onset atrial fibrillation (AF) in SND patients. In the atrial muscle attenuated activity of p21-activated kinase 1 (Pak1) increases the risk for AF by enhancing NADPH oxidase 2 dependent production of reactive oxygen species (ROS). However, the role of Pak1 dependent ROS regulation in SAN function has not yet been determined. We hypothesize that Pak1 activity maintains SAN activity by regulating the expression of the hyperpolarization activated cyclic nucleotide gated cation channel (HCN). To determine Pak1 dependent changes in heart rate (HR) regulation we quantified the intrinsic sinus rhythm in wild type (WT) and Pak1 deficient (Pak1-/-) mice of both sexes in vivo and in isolated Langendorff perfused hearts. Pak1-/- hearts displayed an attenuated HR in vivo after autonomic blockage and in isolated hearts. The contribution of the Ca2+ clock to pacemaker activity remained unchanged, but Ivabradine (3 μM), a blocker of HCN channels that are a membrane clock component, eliminated the differences in SAN activity between WT and Pak1-/- hearts. Reduced HCN4 expression was confirmed in Pak1-/- right atria. The reduced HCN activity in Pak1-/- could be rescued by class II HDAC inhibition (LMK235), ROS scavenging (TEMPOL) or attenuation of Extracellular Signal-Regulated Kinase (ERK) 1/2 activity (SCH772984). No sex specific differences in Pak1 dependent SAN regulation were determined. Our results establish Pak1 as a class II HDAC regulator and a potential therapeutic target to attenuate SAN bradycardia and AF susceptibility.
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Affiliation(s)
- Carlos H Pereira
- Dept. of Internal Medicine/Cardiology, Rush University Medical Center, 1750 W. Harrison St., Chicago, IL 60612, USA; Biological Science Center, Department of Physiology, Av. Cel Francisco H. dos Santos 100, 19031 Centro Politécnico-Curitiba, Brazil.
| | - Dan J Bare
- Dept. of Physiology & Biophysics, The Ohio State University, 5018 Graves Hall, 333 W.10th Ave., Columbus, OH 4321, USA.
| | - Paola C Rosas
- Dept. of Pharmacy Practice, College of Pharmacy, 833 S Wood St., Chicago, IL 60612, USA.
| | - Fernando A L Dias
- Biological Science Center, Department of Physiology, Av. Cel Francisco H. dos Santos 100, 19031 Centro Politécnico-Curitiba, Brazil.
| | - Kathrin Banach
- Dept. of Internal Medicine/Cardiology, Rush University Medical Center, 1750 W. Harrison St., Chicago, IL 60612, USA.
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3
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Ock S, Choi SW, Choi SH, Kang H, Kim SJ, Lee WS, Kim J. Insulin signaling is critical for sinoatrial node maintenance and function. Exp Mol Med 2023:10.1038/s12276-023-00988-0. [PMID: 37121973 DOI: 10.1038/s12276-023-00988-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2022] [Revised: 02/12/2023] [Accepted: 02/12/2023] [Indexed: 05/02/2023] Open
Abstract
Insulin and insulin-like growth factor 1 (IGF-1) signaling regulate cellular growth and glucose metabolism in the myocardium. However, their physiological role in the cells of the cardiac conduction system has never been explored. Therefore, we sought to determine the spatiotemporal function of insulin/IGF-1 receptors in the sinoatrial node (SAN). We generated cardiac conduction cell-specific inducible IGF-1 receptor (IGF-1R) knockout (KO) (CSIGF1RKO), insulin receptor (IR) KO (CSIRKO), and IR/IGF-1R double-KO (CSDIRKO) mice and evaluated their phenotypes. Telemetric electrocardiography revealed regular sinus rhythm in CSIGF1RKO mice, indicating that IGF-1R is dispensable for normal pacemaking. In contrast, CSIRKO and CSDIRKO mice exhibited profound sinus bradycardia. CSDIRKO mice showed typical sinus node dysfunction characterized by junctional rhythm and sinus pauses on electrocardiography. Interestingly, the lack of an insulin receptor in the SAN cells of CSIRKO and CSDIRKO mice caused sinus nodal fibrosis. Mechanistically, hyperpolarization-activated cyclic nucleotide-gated channel 4 (HCN4) protein expression significantly decreased in the CSIRKO and CSDIRKO mice relative to the controls. A patch-clamp study of the SAN cells of CSIRKO mice revealed a significant decrease in the funny current, which is responsible for spontaneous diastolic depolarization in the SAN. This result suggested that insulin receptor loss reduces the heart rate via downregulation of the HCN4 channel. Additionally, HCN1 expression was decreased in CSDIRKO mice, explaining their sinus node dysfunction. Our results reveal a previously unrecognized role of insulin/IGF-1 signaling in sinus node structural maintenance and pacemaker function.
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Affiliation(s)
- Sangmi Ock
- Division of Endocrinology and Metabolism, Department of Internal Medicine, College of Medicine, Chung-Ang University, Seoul, Korea
| | - Seong Woo Choi
- Departments of Physiology and Biomedical Sciences, College of Medicine, Seoul National University, Seoul, Korea
- Department of Physiology, Dongguk University College of Medicine, Gyeongju, Korea
| | - Seung Hee Choi
- Division of Endocrinology and Metabolism, Departments of Internal Medicine and Biochemistry and Cell Biology, Kyungpook National University School of Medicine, Daegu, Korea
| | - Hyun Kang
- Department of Anesthesiology, College of Medicine, Chung-Ang University, Seoul, Korea
| | - Sung Joon Kim
- Departments of Physiology and Biomedical Sciences, College of Medicine, Seoul National University, Seoul, Korea
| | - Wang-Soo Lee
- Division of Cardiology, Department of Internal Medicine, College of Medicine, Chung-Ang University, Seoul, Korea.
| | - Jaetaek Kim
- Division of Endocrinology and Metabolism, Department of Internal Medicine, College of Medicine, Chung-Ang University, Seoul, Korea.
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4
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Weisbrod D. Small and Intermediate Calcium Activated Potassium Channels in the Heart: Role and Strategies in the Treatment of Cardiovascular Diseases. Front Physiol 2020; 11:590534. [PMID: 33329039 PMCID: PMC7719780 DOI: 10.3389/fphys.2020.590534] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2020] [Accepted: 10/02/2020] [Indexed: 12/11/2022] Open
Abstract
Calcium-activated potassium channels are a heterogeneous family of channels that, despite their different biophysical characteristics, structures, and pharmacological signatures, play a role of transducer between the ubiquitous intracellular calcium signaling and the electric variations of the membrane. Although this family of channels was extensively described in various excitable and non-excitable tissues, an increasing amount of evidences shows their functional role in the heart. This review aims to focus on the physiological role and the contribution of the small and intermediate calcium-activated potassium channels in cardiac pathologies.
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5
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Ramírez Hurtado AL, Martínez FV, Diaz Galindo CA, Cuellar KG, Villareal Reyna SZ, Sánchez Herrera DP, Rodríguez González J. Noisy stimulation effect in calcium dynamics on cardiac cells. Exp Cell Res 2020; 396:112319. [PMID: 33039368 DOI: 10.1016/j.yexcr.2020.112319] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Revised: 10/05/2020] [Accepted: 10/07/2020] [Indexed: 11/24/2022]
Abstract
Noise is present in nature, and it affects the nervous and cardiovascular system. Noise added to stimuli may change the performance of excitable cells. In this paper, we study the effect of noise on the two main heart cell types: pacemaker and myocardial cells. This study investigates whether noise can induce changes in calcium dynamics on the two main heart cell types: pacemaker and myocardial cells, when stimuli with periodic electrical signals are disturbed by Gaussian white noise. Calcium dynamic parameters were obtained using imaging signals. Our results show that low intensities of noise favor amplitude and raise rate calcium dynamics, although our results show that the pacemaker cells are not affected by a noisy stimulus. Altogether, these findings suggest that noise plays a key role in calcium dynamics.
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Affiliation(s)
- Alberto Luis Ramírez Hurtado
- Centro de Investigación y de Estudios Avanzados del I.P.N - Unidad Monterrey, Vía del Conocimiento 201, Parque de Investigación e Innovación Tecnológica, C.P.: 66600, Apodaca, Nuevo León, Mexico
| | - Fernando Villafranca Martínez
- Centro de Investigación y de Estudios Avanzados del I.P.N - Unidad Monterrey, Vía del Conocimiento 201, Parque de Investigación e Innovación Tecnológica, C.P.: 66600, Apodaca, Nuevo León, Mexico
| | - Carlos Alberto Diaz Galindo
- Centro de Investigación y de Estudios Avanzados del I.P.N - Unidad Monterrey, Vía del Conocimiento 201, Parque de Investigación e Innovación Tecnológica, C.P.: 66600, Apodaca, Nuevo León, Mexico
| | - Karen Garza Cuellar
- Centro de Investigación y de Estudios Avanzados del I.P.N - Unidad Monterrey, Vía del Conocimiento 201, Parque de Investigación e Innovación Tecnológica, C.P.: 66600, Apodaca, Nuevo León, Mexico
| | - Sandra Zue Villareal Reyna
- Centro de Investigación y de Estudios Avanzados del I.P.N - Unidad Monterrey, Vía del Conocimiento 201, Parque de Investigación e Innovación Tecnológica, C.P.: 66600, Apodaca, Nuevo León, Mexico
| | - Daniel Paulo Sánchez Herrera
- Centro de Investigación y de Estudios Avanzados del I.P.N - Unidad Monterrey, Vía del Conocimiento 201, Parque de Investigación e Innovación Tecnológica, C.P.: 66600, Apodaca, Nuevo León, Mexico.
| | - Jesús Rodríguez González
- Centro de Investigación y de Estudios Avanzados del I.P.N - Unidad Monterrey, Vía del Conocimiento 201, Parque de Investigación e Innovación Tecnológica, C.P.: 66600, Apodaca, Nuevo León, Mexico.
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6
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Kohajda Z, Loewe A, Tóth N, Varró A, Nagy N. The Cardiac Pacemaker Story-Fundamental Role of the Na +/Ca 2+ Exchanger in Spontaneous Automaticity. Front Pharmacol 2020; 11:516. [PMID: 32410993 PMCID: PMC7199655 DOI: 10.3389/fphar.2020.00516] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2019] [Accepted: 04/01/2020] [Indexed: 01/01/2023] Open
Abstract
The electrophysiological mechanism of the sinus node automaticity was previously considered exclusively regulated by the so-called "funny current". However, parallel investigations increasingly emphasized the importance of the Ca2+-homeostasis and Na+/Ca2+ exchanger (NCX). Recently, increasing experimental evidence, as well as insight through mechanistic in silico modeling demonstrates the crucial role of the exchanger in sinus node pacemaking. NCX had a key role in the exciting story of discovery of sinus node pacemaking mechanisms, which recently settled with a consensus on the coupled-clock mechanism after decades of debate. This review focuses on the role of the Na+/Ca2+ exchanger from the early results and concepts to recent advances and attempts to give a balanced summary of the characteristics of the local, spontaneous, and rhythmic Ca2+ releases, the molecular control of the NCX and its role in the fight-or-flight response. Transgenic animal models and pharmacological manipulation of intracellular Ca2+ concentration and/or NCX demonstrate the pivotal function of the exchanger in sinus node automaticity. We also highlight where specific hypotheses regarding NCX function have been derived from computational modeling and require experimental validation. Nonselectivity of NCX inhibitors and the complex interplay of processes involved in Ca2+ handling render the design and interpretation of these experiments challenging.
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Affiliation(s)
- Zsófia Kohajda
- MTA-SZTE Research Group of Cardiovascular Pharmacology, Hungarian Academy of Sciences, Szeged, Hungary.,Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary
| | - Axel Loewe
- Institute of Biomedical Engineering, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
| | - Noémi Tóth
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary
| | - András Varró
- MTA-SZTE Research Group of Cardiovascular Pharmacology, Hungarian Academy of Sciences, Szeged, Hungary.,Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary
| | - Norbert Nagy
- MTA-SZTE Research Group of Cardiovascular Pharmacology, Hungarian Academy of Sciences, Szeged, Hungary.,Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary
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7
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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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8
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El Khoury N, Ross JL, Long V, Thibault S, Ethier N, Fiset C. Pregnancy and oestrogen regulate sinoatrial node calcium homeostasis and accelerate pacemaking. Cardiovasc Res 2019; 114:1605-1616. [PMID: 29800268 PMCID: PMC6148331 DOI: 10.1093/cvr/cvy129] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/21/2017] [Accepted: 05/17/2018] [Indexed: 12/24/2022] Open
Abstract
Aims During pregnancy, there is a significant increase in heart rate (HR) potentially associated with an increased risk of arrhythmias or exacerbation of pre-existing cardiac conditions endangering both mother and foetus. Calcium homeostasis plays an important role in regulating automaticity of the sinoatrial node (SAN); however, its contribution to the accelerated HR during pregnancy remains unknown. Methods and results Using murine SAN cells, we showed that pregnancy increased L-type Ca2+ current (ICaL) and CaV1.3 mRNA expression, whereas T-type Ca2+ current (ICaT) and its underlying channel were unchanged. Analysis of SAN intra-cellular Ca2+ oscillations showed that the rate of spontaneous Ca2+ transients was significantly higher in pregnant mice along with a higher mRNA expression of ryanodine receptor. Assessment of supra-ventricular arrhythmias using programmed electrical stimulation protocols on anaesthetized mice revealed higher susceptibility in pregnancy. Of note, the modifications associated with pregnancy were reversible following delivery. Furthermore, chronic administration of 17β-estradiol (E2) to nodal-like human-induced pluripotent stem cell-derived cardiomyocytes (N-hiPSC-CM), control mice, oestrogen-receptor-β knockout (ERKOβ) but not ERKOα mice, accelerated cardiac automaticity, recapitulating the pregnancy phenotype in both mouse and human SAN cell models. Conclusion Together, these results indicate that pregnancy considerably alters intra-cellular Ca2+ homeostasis sustaining faster HR during pregnancy. Importantly, these changes were dependent on an oestrogen receptor α (ERα) mechanism that resulted in increased ICaL and spontaneous Ca2+ release from the sarcoplasmic reticulum, highlighting a novel role for oestrogen in regulating HR.
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Affiliation(s)
- Nabil El Khoury
- Montreal Heart Institute, Research Center, 5000 Bélanger, Montréal, Québec, Canada.,Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, Montréal, Québec, Canada
| | - Jenna L Ross
- Montreal Heart Institute, Research Center, 5000 Bélanger, Montréal, Québec, Canada.,Faculty of Pharmacy, Université de Montréal, Montréal, Québec, Canada
| | - Valérie Long
- Montreal Heart Institute, Research Center, 5000 Bélanger, Montréal, Québec, Canada.,Faculty of Pharmacy, Université de Montréal, Montréal, Québec, Canada
| | - Simon Thibault
- Montreal Heart Institute, Research Center, 5000 Bélanger, Montréal, Québec, Canada.,Faculty of Pharmacy, Université de Montréal, Montréal, Québec, Canada
| | - Nathalie Ethier
- Montreal Heart Institute, Research Center, 5000 Bélanger, Montréal, Québec, Canada
| | - Céline Fiset
- Montreal Heart Institute, Research Center, 5000 Bélanger, Montréal, Québec, Canada.,Faculty of Pharmacy, Université de Montréal, Montréal, Québec, Canada
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9
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Canine and human sinoatrial node: differences and similarities in the structure, function, molecular profiles, and arrhythmia. J Vet Cardiol 2018; 22:2-19. [PMID: 30559056 DOI: 10.1016/j.jvc.2018.10.004] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Revised: 10/02/2018] [Accepted: 10/02/2018] [Indexed: 12/17/2022]
Abstract
The sinoatrial node (SAN) is the primary pacemaker in canine and human hearts. The SAN in both species has a unique three-dimensional heterogeneous structure characterized by small pacemaker myocytes enmeshed within fibrotic strands, which partially insulate the cells from aberrant atrial activation. The SAN pacemaker tissue expresses a unique signature of proteins and receptors that mediate SAN automaticity, ion channel currents, and cell-to-cell communication, which are predominantly similar in both species. Recent intramural optical mapping, integrated with structural and molecular studies, has revealed the existence of up to five specialized SAN conduction pathways that preferentially conduct electrical activation to atrial tissues. The intrinsic heart rate, intranodal leading pacemaker shifts, and changes in conduction in response to physiological and pathophysiological stimuli are similar. Structural and/or functional impairments due to cardiac diseases including heart failure cause SAN dysfunctions (SNDs) in both species. These dysfunctions are usually manifested as severe bradycardia, tachy-brady arrhythmias, and conduction abnormalities including exit block and SAN reentry, which could lead to atrial tachycardia and fibrillation, cardiac arrest, and heart failure. Pharmaceutical drugs and implantable pacemakers are only partially successful in managing SNDs, emphasizing a critical need to develop targeted mechanism-based therapies to treat SNDs. Because several structural and functional characteristics are similar between the canine and human SAN, research in these species may be mutually beneficial for developing novel treatment approaches. This review describes structural, functional, and molecular similarities and differences between the canine and human SAN, with special emphasis on arrhythmias and unique causal mechanisms of SND in diseased hearts.
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10
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Lang D, Glukhov AV. Functional Microdomains in Heart's Pacemaker: A Step Beyond Classical Electrophysiology and Remodeling. Front Physiol 2018; 9:1686. [PMID: 30538641 PMCID: PMC6277479 DOI: 10.3389/fphys.2018.01686] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Accepted: 11/09/2018] [Indexed: 12/12/2022] Open
Abstract
Spontaneous beating of the sinoatrial node (SAN), the primary pacemaker of the heart, is initiated, sustained, and regulated by a complex system that integrates ion channels and transporters on the cell membrane surface (often referred to as "membrane clock") with subcellular calcium handling machinery (by parity of reasoning referred to as an intracellular "Ca2+ clock"). Stable, rhythmic beating of the SAN is ensured by a rigorous synchronization between these two clocks highlighted in the coupled-clock system concept of SAN timekeeping. The emerging results demonstrate that such synchronization of the complex pacemaking machinery at the cellular level depends on tightly regulated spatiotemporal signals which are restricted to precise sub-cellular microdomains and associated with discrete clusters of different ion channels, transporters, and regulatory receptors. It has recently become evident that within the microdomains, various proteins form an interacting network and work together as a part of a macromolecular signaling complex. These protein-protein interactions are tightly controlled and regulated by a variety of neurohormonal signaling pathways and the diversity of cellular responses achieved with a limited pool of second messengers is made possible through the organization of essential signal components in particular microdomains. In this review, we highlight the emerging understanding of the functionality of distinct subcellular microdomains in SAN myocytes and their functional role in the accumulation and neurohormonal regulation of proteins involved in cardiac pacemaking. We also demonstrate how changes in scaffolding proteins may lead to microdomain-targeted remodeling and regulation of pacemaker proteins contributing to SAN dysfunction.
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Affiliation(s)
- Di Lang
- Department of Medicine, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, United States
| | - Alexey V Glukhov
- Department of Medicine, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, United States
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11
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Huang SY, Chen YC, Kao YH, Hsieh MH, Lin YK, Chung CC, Lee TI, Tsai WC, Chen SA, Chen YJ. Fibroblast growth factor 23 dysregulates late sodium current and calcium homeostasis with enhanced arrhythmogenesis in pulmonary vein cardiomyocytes. Oncotarget 2018; 7:69231-69242. [PMID: 27713141 PMCID: PMC5342473 DOI: 10.18632/oncotarget.12470] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2016] [Accepted: 09/29/2016] [Indexed: 12/19/2022] Open
Abstract
Fibroblast growth factor 23 (FGF23), elevated in chronic renal failure, increases atrial arrhythmogenesis and dysregulates calcium homeostasis. Late sodium currents (INa-Late) critically induces ectopic activity of pulmoanry vein (the most important atrial fibrillation trigger). This study was to investigate whether FGF23 activates the INa-Late leading to calcium dysregulation and increases PV arrhythmogenesis. Patch clamp, western blot, and confocal microscopy were used to evaluate the electrical activities, calcium homeostasis, and mitochondrial reactive oxygen species (ROS) in PV cardiomyocytes with or without FGF23 (0.1 or 1 ng/mL) incubation for 4~6 h. Compared to the control, FGF23 (1 ng/mL, but not 0.1 ng/mL)-treated PV cardiomyocytes had a faster beating rate. FGF23 (1 ng/mL)-treated PV cardiomyocytes had larger INa-Late, calcium transients, and mitochondrial ROS than controls. However, ranolazine (an inhibitor of INa-Late) attenuated FGF23 (1 ng/mL)-increased beating rates, calcium transients and mitochondrial ROS. FGF23 (1 ng/mL)-treated PV cardiomyocytes exhibited larger phosphorylation of calcium/calmodulin-dependent protein kinase II (CaMKII). Chelerythrine chloride (an inhibitor of protein kinase C) decreased INa-Late in FGF23 (1 ng/mL)-treated PV cardiomyocytes. However, KN93 (a selective CaMKII blocker) decreased INa-Late in control and FGF23 (1 ng/mL)-treated PV cardiomyocytes to a similar extent. In conclusion, FGF23 increased PV arrhythmogenesis through sodium and calcium dysregulation by acting protein kinase C signaling.
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Affiliation(s)
- Shih-Yu Huang
- Graduate Institute of Clinical Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan.,Division of Cardiology, Department of Internal Medicine, Cathay General Hospital, Taipei, Taiwan
| | - Yao-Chang Chen
- Department of Biomedical Engineering, National Defense Medical Center, Taipei, Taiwan
| | - Yu-Hsun Kao
- Graduate Institute of Clinical Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan.,Department of Medical Education and Research, Wan Fang Hospital, Taipei Medical University, Taipei, Taiwan
| | - Ming-Hsiung Hsieh
- Division of Cardiovascular Medicine, Department of Internal Medicine, Wan Fang Hospital, Taipei Medical University, Taipei, Taiwan.,Division of Cardiology, Department of Internal Medicine, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan
| | - Yung-Kuo Lin
- Division of Cardiovascular Medicine, Department of Internal Medicine, Wan Fang Hospital, Taipei Medical University, Taipei, Taiwan.,Division of Cardiology, Department of Internal Medicine, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan
| | - Cheng-Chih Chung
- Graduate Institute of Clinical Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan.,Division of Cardiovascular Medicine, Department of Internal Medicine, Wan Fang Hospital, Taipei Medical University, Taipei, Taiwan
| | - Ting-I Lee
- Department of General Medicine, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan.,Division of Endocrinology and Metabolism, Department of Internal Medicine, Wan Fang Hospital, Taipei Medical University, Taipei, Taiwan
| | - Wen-Chin Tsai
- Division of Cardiology, Tzu-Chi General Hospital, Institute of Medical Sciences, Tzu-Chi University, Hualien, Taiwan
| | - Shih-Ann Chen
- Division of Cardiology and Cardiovascular Research Center, Veterans General Hospital-Taipei, Taipei, Taiwan
| | - Yi-Jen Chen
- Graduate Institute of Clinical Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan.,Division of Cardiovascular Medicine, Department of Internal Medicine, Wan Fang Hospital, Taipei Medical University, Taipei, Taiwan
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12
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Ionic mechanisms of the action of anaesthetics on sinoatrial node automaticity. Eur J Pharmacol 2017; 814:63-72. [DOI: 10.1016/j.ejphar.2017.08.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2017] [Revised: 07/06/2017] [Accepted: 08/07/2017] [Indexed: 12/11/2022]
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13
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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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14
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Robertson GA. It's not funny: How changes in If limit maximum heart rate with aging. J Gen Physiol 2017; 149:177-179. [PMID: 28057841 PMCID: PMC5299625 DOI: 10.1085/jgp.201611746] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Robertson highlights recent work showing how aging limits pacemaking by the funny current, If, in the sinoatrial node.
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Affiliation(s)
- Gail A Robertson
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705 .,Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
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15
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Logantha SJRJ, Stokke MK, Atkinson AJ, Kharche SR, Parveen S, Saeed Y, Sjaastad I, Sejersted OM, Dobrzynski H. Ca(2+)-Clock-Dependent Pacemaking in the Sinus Node Is Impaired in Mice with a Cardiac Specific Reduction in SERCA2 Abundance. Front Physiol 2016; 7:197. [PMID: 27313537 PMCID: PMC4889599 DOI: 10.3389/fphys.2016.00197] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Accepted: 05/17/2016] [Indexed: 12/23/2022] Open
Abstract
Background: The sarcoplasmic reticulum Ca2+-ATPase (SERCA2) pump is an important component of the Ca2+-clock pacemaker mechanism that provides robustness and flexibility to sinus node pacemaking. We have developed transgenic mice with reduced cardiac SERCA2 abundance (Serca2 KO) as a model for investigating SERCA2's role in sinus node pacemaking. Methods and Results: In Serca2 KO mice, ventricular SERCA2a protein content measured by Western blotting was 75% (P < 0.05) lower than that in control mice (Serca2 FF) tissue. Immunofluorescent labeling of SERCA2a in ventricular, atrial, sinus node periphery and center tissue sections revealed 46, 45, 55, and 34% (all P < 0.05 vs. Serca2 FF) lower labeling, respectively and a mosaic pattern of expression. With telemetric ECG surveillance, we observed no difference in basal heart rate, but the PR-interval was prolonged in Serca2 KO mice: 49 ± 1 vs. 40 ± 1 ms (P < 0.001) in Serca2 FF. During exercise, heart rate in Serca2 KO mice was elevated to 667 ± 22 bpm, considerably less than 780 ± 17 bpm (P < 0.01) in Serca2 FF. In isolated sinus node preparations, 2 mM Cs+ caused bradycardia that was equally pronounced in Serca2 KO and Serca2 FF (32 ± 4% vs. 29 ± 5%), indicating no change in the pacemaker current, If. Disabling the Ca2+-clock with 2 μM ryanodine induced bradycardia that was less pronounced in Serca2 KO preparations (9 ± 1% vs. 20 ± 3% in Serca2 FF; P < 0.05), suggesting a disrupted Ca2+-clock. Mathematical modeling was used to dissect the effects of membrane- and Ca2+-clock components on Serca2 KO mouse heart rate and sinus node action potential. Computer modeling predicted a slowing of heart rate with SERCA2 downregulation and the heart rate slowing was pronounced at >70% reduction in SERCA2 activity. Conclusions:Serca2 KO mice show a disrupted Ca2+-clock-dependent pacemaker mechanism contributing to impaired sinus node and atrioventricular node function.
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Affiliation(s)
| | - Mathis K Stokke
- Institute for Experimental Medical Research, Oslo University Hospital and University of OsloOslo, Norway; Center for Heart Failure Research, University of OsloOslo, Norway; Clinic for Internal Medicine, Lovisenberg Deaconess Hospital ASOslo, Norway
| | - Andrew J Atkinson
- Institute of Cardiovascular Sciences, University of Manchester Manchester, UK
| | - Sanjay R Kharche
- Institute of Cardiovascular Sciences, University of Manchester Manchester, UK
| | - Sajida Parveen
- Institute of Cardiovascular Sciences, University of Manchester Manchester, UK
| | - Yawer Saeed
- Institute of Cardiovascular Sciences, University of Manchester Manchester, UK
| | - Ivar Sjaastad
- Institute for Experimental Medical Research, Oslo University Hospital and University of OsloOslo, Norway; Center for Heart Failure Research, University of OsloOslo, Norway
| | - Ole M Sejersted
- Institute for Experimental Medical Research, Oslo University Hospital and University of OsloOslo, Norway; Center for Heart Failure Research, University of OsloOslo, Norway
| | - Halina Dobrzynski
- Institute of Cardiovascular Sciences, University of Manchester Manchester, UK
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16
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Weisbrod D, Khun SH, Bueno H, Peretz A, Attali B. Mechanisms underlying the cardiac pacemaker: the role of SK4 calcium-activated potassium channels. Acta Pharmacol Sin 2016; 37:82-97. [PMID: 26725737 PMCID: PMC4722971 DOI: 10.1038/aps.2015.135] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2015] [Accepted: 11/25/2015] [Indexed: 12/25/2022] Open
Abstract
The proper expression and function of the cardiac pacemaker is a critical feature of heart physiology. The sinoatrial node (SAN) in human right atrium generates an electrical stimulation approximately 70 times per minute, which propagates from a conductive network to the myocardium leading to chamber contractions during the systoles. Although the SAN and other nodal conductive structures were identified more than a century ago, the mechanisms involved in the generation of cardiac automaticity remain highly debated. In this short review, we survey the current data related to the development of the human cardiac conduction system and the various mechanisms that have been proposed to underlie the pacemaker activity. We also present the human embryonic stem cell-derived cardiomyocyte system, which is used as a model for studying the pacemaker. Finally, we describe our latest characterization of the previously unrecognized role of the SK4 Ca(2+)-activated K(+) channel conductance in pacemaker cells. By exquisitely balancing the inward currents during the diastolic depolarization, the SK4 channels appear to play a crucial role in human cardiac automaticity.
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Affiliation(s)
- David Weisbrod
- Department of Physiology & Pharmacology, Sackler Faculty of Medicine, Sagol School of Neuroscience, Tel Aviv University, Tel Aviv 69978, Israel
| | - Shiraz Haron Khun
- Department of Physiology & Pharmacology, Sackler Faculty of Medicine, Sagol School of Neuroscience, Tel Aviv University, Tel Aviv 69978, Israel
| | - Hanna Bueno
- Department of Physiology & Pharmacology, Sackler Faculty of Medicine, Sagol School of Neuroscience, Tel Aviv University, Tel Aviv 69978, Israel
| | - Asher Peretz
- Department of Physiology & Pharmacology, Sackler Faculty of Medicine, Sagol School of Neuroscience, Tel Aviv University, Tel Aviv 69978, Israel
| | - Bernard Attali
- Department of Physiology & Pharmacology, Sackler Faculty of Medicine, Sagol School of Neuroscience, Tel Aviv University, Tel Aviv 69978, Israel
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17
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Novella Romanelli M, Sartiani L, Masi A, Mannaioni G, Manetti D, Mugelli A, Cerbai E. HCN Channels Modulators: The Need for Selectivity. Curr Top Med Chem 2016; 16:1764-91. [PMID: 26975509 PMCID: PMC5374843 DOI: 10.2174/1568026616999160315130832] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2015] [Revised: 08/04/2015] [Accepted: 08/05/2015] [Indexed: 12/27/2022]
Abstract
Hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels, the molecular correlate of the hyperpolarization-activated current (If/Ih), are membrane proteins which play an important role in several physiological processes and various pathological conditions. In the Sino Atrial Node (SAN) HCN4 is the target of ivabradine, a bradycardic agent that is, at the moment, the only drug which specifically blocks If. Nevertheless, several other pharmacological agents have been shown to modulate HCN channels, a property that may contribute to their therapeutic activity and/or to their side effects. HCN channels are considered potential targets for developing drugs to treat several important pathologies, but a major issue in this field is the discovery of isoform-selective compounds, owing to the wide distribution of these proteins into the central and peripheral nervous systems, heart and other peripheral tissues. This survey is focused on the compounds that have been shown, or have been designed, to interact with HCN channels and on their binding sites, with the aim to summarize current knowledge and possibly to unveil useful information to design new potent and selective modulators.
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Affiliation(s)
- Maria Novella Romanelli
- University of Florence, Department of Neurosciences, Psychology, Drug Research and Child's Health, Section of Pharmaceutical and Nutraceutical Sciences, via Ugo Schiff 6, 50019 Sesto Fiorentino, Italy.
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18
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Spontaneous inward currents reflecting oscillatory activation of Na+/Ca2+ exchangers in human embryonic stem cell-derived cardiomyocytes. Pflugers Arch 2015; 468:609-22. [DOI: 10.1007/s00424-015-1769-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2015] [Revised: 11/30/2015] [Accepted: 12/03/2015] [Indexed: 11/25/2022]
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19
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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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20
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Abstract
One of the main strategies for cancer therapy is to use tyrosine kinase inhibitors for inhibiting tumor proliferation. Increasing evidence has demonstrated the potential risks of cardiac arrhythmias (such as prolonged QT interval) of these drugs. We report here that a widely used selective inhibitor of Src tyrosine kinases, 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2), can inhibit and prevent β-adrenergic stimulation of cardiac pacemaker activity. First, in dissected rat sinus node, PP2 inhibited and prevented the isoproterenol-induced increase of spontaneous beating rate. Second, in isolated rat sinus node myocytes, PP2 suppressed the hyperpolarization-activated "funny" current (traditionally called cardiac pacemaker current, I(f)) by negatively shifting the activation curve and decelerating activation kinetics. Third, in isolated rat sinus node myocytes, PP2 decreased the Src kinase activity, the cell surface expression, and tyrosine phosphorylation of hyperpolarization-activated, cyclic nucleotide-modulated channel 4 (HCN4) channel proteins. Finally, in human embryonic kidney 293 cells overexpressing recombinant human HCN4 channels, PP2 reversed the enhancement of HCN4 channels by isoproterenol and inhibited 573x, a cyclic adenosine momophosphate-insensitive human HCN4 mutant. These results demonstrated that inhibition of Src kinase activity in heart by PP2 decreased and prevented β-adrenergic stimulation of cardiac pacemaker activity. These effects are mediated, at least partially, by a cAMP-independent attenuation of channel activity and cell surface expression of HCN4, the main channel protein that controls the heart rate.
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21
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Kojima A, Ito Y, Kitagawa H, Matsuura H. Ionic mechanisms underlying the negative chronotropic action of propofol on sinoatrial node automaticity in guinea pig heart. Br J Pharmacol 2014; 172:799-814. [PMID: 25220338 DOI: 10.1111/bph.12936] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2014] [Revised: 08/16/2014] [Accepted: 09/09/2014] [Indexed: 12/24/2022] Open
Abstract
BACKGROUND AND PURPOSE Propofol is a widely used intravenous anaesthetic agent, but has undesirable cardiac side effects, including bradyarrhythmia and its severe form asystole. This study examined the ionic and cellular mechanisms underlying propofol-induced bradycardia. EXPERIMENTAL APPROACH Sinoatrial node cells, isolated from guinea pig hearts, were current- and voltage-clamped to record action potentials and major ionic currents involved in their spontaneous activity, such as the hyperpolarization-activated cation current (If ), T-type and L-type Ca(2+) currents (ICa,T and ICa,L , respectively) and the rapidly and slowly activating delayed rectifier K(+) currents (IKr and IK s , respectively). ECGs were recorded from Langendorff-perfused, isolated guinea pig hearts. KEY RESULTS Propofol (≥5 μM) reversibly decreased the firing rate of spontaneous action potentials and their diastolic depolarization rate. Propofol impaired If activation by shifting the voltage-dependent activation to more hyperpolarized potentials (≥1 μM), slowing the activation kinetics (≥3 μM) and decreasing the maximal conductance (≥10 μM). Propofol decreased ICa,T (≥3 μM) and ICa,L (≥1 μM). Propofol suppressed IKs (≥3 μM), but had a minimal effect on IKr . Furthermore, propofol (≥5 μM) decreased heart rates in Langendorff-perfused hearts. The sinoatrial node cell model reasonably well reproduced the negative chronotropic action of propofol. CONCLUSIONS AND IMPLICATIONS Micromolar concentrations of propofol suppressed the slow diastolic depolarization and firing rate of sinoatrial node action potentials by impairing If activation and reducing ICa,T , ICa,L and IKs . These observations suggest that the direct inhibitory effect of propofol on sinoatrial node automaticity, mediated via multiple channel inhibition, underlies the propofol-induced bradycardia observed in clinical settings.
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Affiliation(s)
- Akiko Kojima
- Department of Anesthesiology, Shiga University of Medical Science, Otsu, Shiga, Japan
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22
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Lai MH, Wu Y, Gao Z, Anderson ME, Dalziel JE, Meredith AL. BK channels regulate sinoatrial node firing rate and cardiac pacing in vivo. Am J Physiol Heart Circ Physiol 2014; 307:H1327-38. [PMID: 25172903 DOI: 10.1152/ajpheart.00354.2014] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Large-conductance Ca(2+)- and voltage-activated K(+) (BK) channels play prominent roles in shaping muscle and neuronal excitability. In the cardiovascular system, BK channels promote vascular relaxation and protect against ischemic injury. Recently, inhibition of BK channels has been shown to lower heart rate in intact rodents and isolated hearts, suggesting a novel role in heart function. However, the underlying mechanism is unclear. In the present study, we recorded ECGs from mice injected with paxilline (PAX), a membrane-permeable BK channel antagonist, and examined changes in cardiac conduction. ECGs revealed a 19 ± 4% PAX-induced reduction in heart rate in wild-type but not BK channel knockout (Kcnma1(-/-)) mice. The heart rate decrease was associated with slowed cardiac pacing due to elongation of the sinus interval. Action potential firing recorded from isolated sinoatrial node cells (SANCs) was reduced by 55 ± 15% and 28 ± 9% by application of PAX (3 μM) and iberiotoxin (230 nM), respectively. Furthermore, baseline firing rates from Kcnma1(-/-) SANCs were 33% lower than wild-type SANCs. The slowed firing upon BK current inhibition or genetic deletion was due to lengthening of the diastolic depolarization phase of the SANC action potential. Finally, BK channel immunoreactivity and PAX-sensitive currents were identified in SANCs with HCN4 expression and pacemaker current, respectively, and BK channels cloned from SANCs recapitulated similar activation as the PAX-sensitive current. Together, these data localize BK channels to SANCs and demonstrate that loss of BK current decreases SANC automaticity, consistent with slowed sinus pacing after PAX injection in vivo. Furthermore, these findings suggest BK channels are potential therapeutic targets for disorders of heart rate.
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Affiliation(s)
- Michael H Lai
- Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland; Fischell Department of Bioengineering, University of Maryland, College Park, Maryland
| | - Yuejin Wu
- Department of Internal Medicine and the François M. Abboud Cardiovascular Research Center, University of Iowa, Iowa City, Iowa
| | - Zhan Gao
- Department of Internal Medicine and the François M. Abboud Cardiovascular Research Center, University of Iowa, Iowa City, Iowa
| | - Mark E Anderson
- Department of Internal Medicine and the François M. Abboud Cardiovascular Research Center, University of Iowa, Iowa City, Iowa; Department of Physiology and Molecular Biophysics, University of Iowa, Iowa City, Iowa; and
| | - Julie E Dalziel
- AgResearch, Grasslands Research Centre, Palmerston North, New Zealand
| | - Andrea L Meredith
- Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland; Fischell Department of Bioengineering, University of Maryland, College Park, Maryland;
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23
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Zaniboni M, Cacciani F, Lux RL. Beat-to-beat cycle length variability of spontaneously beating guinea pig sinoatrial cells: relative contributions of the membrane and calcium clocks. PLoS One 2014; 9:e100242. [PMID: 24940609 PMCID: PMC4062511 DOI: 10.1371/journal.pone.0100242] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2014] [Accepted: 05/23/2014] [Indexed: 11/18/2022] Open
Abstract
The heartbeat arises rhythmically in the sino-atrial node (SAN) and then spreads regularly throughout the heart. The molecular mechanism underlying SAN rhythm has been attributed by recent studies to the interplay between two clocks, one involving the hyperpolarization activated cation current If (the membrane clock), and the second attributable to activation of the electrogenic NaCa exchanger by spontaneous sarcoplasmic releases of calcium (the calcium clock). Both mechanisms contain, in principle, sources of beat-to-beat cycle length variability, which can determine the intrinsic variability of SAN firing and, in turn, contribute to the heart rate variability. In this work we have recorded long sequences of action potentials from patch clamped guinea pig SAN cells (SANCs) perfused, in turn, with normal Tyrode solution, with the If inhibitor ivabradine (3 µM), then back to normal Tyrode, and again with the ryanodine channels inhibitor ryanodine (3 µM). We have found that, together with the expected increase in beating cycle length (+25%), the application of ivabradine brought about a significant and dramatic increase in beat-to-beat cycle length variability (+50%). Despite the similar effect on firing rate, ryanodine did not modify significantly beat-to-beat cycle length variability. Acetylcholine was also applied and led to a 131% increase of beating cycle length, with only a 70% increase in beat-to-beat cycle length variability. We conclude that the main source of inter-beat variability of SANCs firing rate is related to the mechanism of the calcium clock, whereas the membrane clock seems to act in stabilizing rate. Accordingly, when the membrane clock is silenced by application of ivabradine, stochastic variations of the calcium clock are free to make SANCs beating rhythm more variable.
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Affiliation(s)
- Massimiliano Zaniboni
- Department of Life Sciences, University of Parma, Parma, Italy
- Center of Excellence for Toxicological Research, University of Parma, Parma, Italy
- * E-mail:
| | | | - Robert L. Lux
- Cardiovascular Research and Training Institute, University of Utah, Salt Lake City, Utah, United States of America
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24
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Yaniv Y, Sirenko S, Ziman BD, Spurgeon HA, Maltsev VA, Lakatta EG. New evidence for coupled clock regulation of the normal automaticity of sinoatrial nodal pacemaker cells: bradycardic effects of ivabradine are linked to suppression of intracellular Ca²⁺ cycling. J Mol Cell Cardiol 2013; 62:80-9. [PMID: 23651631 PMCID: PMC3735682 DOI: 10.1016/j.yjmcc.2013.04.026] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/07/2012] [Revised: 04/07/2013] [Accepted: 04/29/2013] [Indexed: 11/19/2022]
Abstract
Beneficial clinical bradycardic effects of ivabradine (IVA) have been interpreted solely on the basis of If inhibition, because IVA specifically inhibits If in sinoatrial nodal pacemaker cells (SANC). However, it has been recently hypothesized that SANC normal automaticity is regulated by crosstalk between an "M clock," the ensemble of surface membrane ion channels, and a "Ca(2+) clock," the sarcoplasmic reticulum (SR). We tested the hypothesis that crosstalk between the two clocks regulates SANC automaticity, and that indirect suppression of the Ca(2+) clock further contributes to IVA-induced bradycardia. IVA (3 μM) not only reduced If amplitude by 45 ± 6% in isolated rabbit SANC, but the IVA-induced slowing of the action potential (AP) firing rate was accompanied by reduced SR Ca(2+) load, slowed intracellular Ca(2+) cycling kinetics, and prolonged the period of spontaneous local Ca(2+) releases (LCRs) occurring during diastolic depolarization. Direct and specific inhibition of SERCA2 by cyclopiazonic acid (CPA) had effects similar to IVA on LCR period and AP cycle length. Specifically, the LCR period and AP cycle length shift toward longer times almost equally by either direct perturbations of the M clock (IVA) or the Ca(2+) clock (CPA), indicating that the LCR period reports the crosstalk between the clocks. Our numerical model simulations predict that entrainment between the two clocks that involves a reduction in INCX during diastolic depolarization is required to explain the experimentally AP firing rate reduction by IVA. In summary, our study provides new evidence that a coupled-clock system regulates normal cardiac pacemaker cell automaticity. Thus, IVA-induced bradycardia includes a suppression of both clocks within this system.
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Affiliation(s)
- Yael Yaniv
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, NIH, 5600 Nathan Shock Dr., Baltimore, MD 21224
| | - Syevda Sirenko
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, NIH, 5600 Nathan Shock Dr., Baltimore, MD 21224
| | - Bruce D. Ziman
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, NIH, 5600 Nathan Shock Dr., Baltimore, MD 21224
| | - Harold A. Spurgeon
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, NIH, 5600 Nathan Shock Dr., Baltimore, MD 21224
| | - Victor A. Maltsev
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, NIH, 5600 Nathan Shock Dr., Baltimore, MD 21224
| | - Edward G. Lakatta
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, NIH, 5600 Nathan Shock Dr., Baltimore, MD 21224
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25
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Le Quang K, Benito B, Naud P, Qi XY, Shi YF, Tardif JC, Gillis MA, Dobrev D, Charpentier F, Nattel S. T-Type Calcium Current Contributes to Escape Automaticity and Governs the Occurrence of Lethal Arrhythmias After Atrioventricular Block in Mice. Circ Arrhythm Electrophysiol 2013; 6:799-808. [DOI: 10.1161/circep.113.000407] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- Khai Le Quang
- From the Department of Medicine and Research Centre, Montreal Heart Institute, Université de Montréal, Montreal, Quebec, Canada (K.L.Q., B.B., P.N., X.Y.Q., Y.F.S., J.-C.T., M.-A.G., S.N.); Department of Medicine, Laval University, Quebec, Canada (K.L.Q.); IMIM Parc de Salut Mar, Hospital del Mar, Barcelona, Spain (B.B.); Institute of Pharmacology, University of Duisburg-Essen, Essen, Germany (D.D.); Division of Experimental Cardiology, University of Heidelberg, Heidelberg, Germany (D.D.); and
| | - Begoña Benito
- From the Department of Medicine and Research Centre, Montreal Heart Institute, Université de Montréal, Montreal, Quebec, Canada (K.L.Q., B.B., P.N., X.Y.Q., Y.F.S., J.-C.T., M.-A.G., S.N.); Department of Medicine, Laval University, Quebec, Canada (K.L.Q.); IMIM Parc de Salut Mar, Hospital del Mar, Barcelona, Spain (B.B.); Institute of Pharmacology, University of Duisburg-Essen, Essen, Germany (D.D.); Division of Experimental Cardiology, University of Heidelberg, Heidelberg, Germany (D.D.); and
| | - Patrice Naud
- From the Department of Medicine and Research Centre, Montreal Heart Institute, Université de Montréal, Montreal, Quebec, Canada (K.L.Q., B.B., P.N., X.Y.Q., Y.F.S., J.-C.T., M.-A.G., S.N.); Department of Medicine, Laval University, Quebec, Canada (K.L.Q.); IMIM Parc de Salut Mar, Hospital del Mar, Barcelona, Spain (B.B.); Institute of Pharmacology, University of Duisburg-Essen, Essen, Germany (D.D.); Division of Experimental Cardiology, University of Heidelberg, Heidelberg, Germany (D.D.); and
| | - Xiao Yan Qi
- From the Department of Medicine and Research Centre, Montreal Heart Institute, Université de Montréal, Montreal, Quebec, Canada (K.L.Q., B.B., P.N., X.Y.Q., Y.F.S., J.-C.T., M.-A.G., S.N.); Department of Medicine, Laval University, Quebec, Canada (K.L.Q.); IMIM Parc de Salut Mar, Hospital del Mar, Barcelona, Spain (B.B.); Institute of Pharmacology, University of Duisburg-Essen, Essen, Germany (D.D.); Division of Experimental Cardiology, University of Heidelberg, Heidelberg, Germany (D.D.); and
| | - Yan Fen Shi
- From the Department of Medicine and Research Centre, Montreal Heart Institute, Université de Montréal, Montreal, Quebec, Canada (K.L.Q., B.B., P.N., X.Y.Q., Y.F.S., J.-C.T., M.-A.G., S.N.); Department of Medicine, Laval University, Quebec, Canada (K.L.Q.); IMIM Parc de Salut Mar, Hospital del Mar, Barcelona, Spain (B.B.); Institute of Pharmacology, University of Duisburg-Essen, Essen, Germany (D.D.); Division of Experimental Cardiology, University of Heidelberg, Heidelberg, Germany (D.D.); and
| | - Jean-Claude Tardif
- From the Department of Medicine and Research Centre, Montreal Heart Institute, Université de Montréal, Montreal, Quebec, Canada (K.L.Q., B.B., P.N., X.Y.Q., Y.F.S., J.-C.T., M.-A.G., S.N.); Department of Medicine, Laval University, Quebec, Canada (K.L.Q.); IMIM Parc de Salut Mar, Hospital del Mar, Barcelona, Spain (B.B.); Institute of Pharmacology, University of Duisburg-Essen, Essen, Germany (D.D.); Division of Experimental Cardiology, University of Heidelberg, Heidelberg, Germany (D.D.); and
| | - Marc-Antoine Gillis
- From the Department of Medicine and Research Centre, Montreal Heart Institute, Université de Montréal, Montreal, Quebec, Canada (K.L.Q., B.B., P.N., X.Y.Q., Y.F.S., J.-C.T., M.-A.G., S.N.); Department of Medicine, Laval University, Quebec, Canada (K.L.Q.); IMIM Parc de Salut Mar, Hospital del Mar, Barcelona, Spain (B.B.); Institute of Pharmacology, University of Duisburg-Essen, Essen, Germany (D.D.); Division of Experimental Cardiology, University of Heidelberg, Heidelberg, Germany (D.D.); and
| | - Dobromir Dobrev
- From the Department of Medicine and Research Centre, Montreal Heart Institute, Université de Montréal, Montreal, Quebec, Canada (K.L.Q., B.B., P.N., X.Y.Q., Y.F.S., J.-C.T., M.-A.G., S.N.); Department of Medicine, Laval University, Quebec, Canada (K.L.Q.); IMIM Parc de Salut Mar, Hospital del Mar, Barcelona, Spain (B.B.); Institute of Pharmacology, University of Duisburg-Essen, Essen, Germany (D.D.); Division of Experimental Cardiology, University of Heidelberg, Heidelberg, Germany (D.D.); and
| | - Flavien Charpentier
- From the Department of Medicine and Research Centre, Montreal Heart Institute, Université de Montréal, Montreal, Quebec, Canada (K.L.Q., B.B., P.N., X.Y.Q., Y.F.S., J.-C.T., M.-A.G., S.N.); Department of Medicine, Laval University, Quebec, Canada (K.L.Q.); IMIM Parc de Salut Mar, Hospital del Mar, Barcelona, Spain (B.B.); Institute of Pharmacology, University of Duisburg-Essen, Essen, Germany (D.D.); Division of Experimental Cardiology, University of Heidelberg, Heidelberg, Germany (D.D.); and
| | - Stanley Nattel
- From the Department of Medicine and Research Centre, Montreal Heart Institute, Université de Montréal, Montreal, Quebec, Canada (K.L.Q., B.B., P.N., X.Y.Q., Y.F.S., J.-C.T., M.-A.G., S.N.); Department of Medicine, Laval University, Quebec, Canada (K.L.Q.); IMIM Parc de Salut Mar, Hospital del Mar, Barcelona, Spain (B.B.); Institute of Pharmacology, University of Duisburg-Essen, Essen, Germany (D.D.); Division of Experimental Cardiology, University of Heidelberg, Heidelberg, Germany (D.D.); and
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SK4 Ca2+ activated K+ channel is a critical player in cardiac pacemaker derived from human embryonic stem cells. Proc Natl Acad Sci U S A 2013; 110:E1685-94. [PMID: 23589888 DOI: 10.1073/pnas.1221022110] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Proper expression and function of the cardiac pacemaker is a critical feature of heart physiology. Two main mechanisms have been proposed: (i) the "voltage-clock," where the hyperpolarization-activated funny current If causes diastolic depolarization that triggers action potential cycling; and (ii) the "Ca(2+) clock," where cyclical release of Ca(2+) from Ca(2+) stores depolarizes the membrane during diastole via activation of the Na(+)-Ca(2+) exchanger. Nonetheless, these mechanisms remain controversial. Here, we used human embryonic stem cell-derived cardiomyocytes (hESC-CMs) to study their autonomous beating mechanisms. Combined current- and voltage-clamp recordings from the same cell showed the so-called "voltage and Ca(2+) clock" pacemaker mechanisms to operate in a mutually exclusive fashion in different cell populations, but also to coexist in other cells. Blocking the "voltage or Ca(2+) clock" produced a similar depolarization of the maximal diastolic potential (MDP) that culminated by cessation of action potentials, suggesting that they converge to a common pacemaker component. Using patch-clamp recording, real-time PCR, Western blotting, and immunocytochemistry, we identified a previously unrecognized Ca(2+)-activated intermediate K(+) conductance (IK(Ca), KCa3.1, or SK4) in young and old stage-derived hESC-CMs. IK(Ca) inhibition produced MDP depolarization and pacemaker suppression. By shaping the MDP driving force and exquisitely balancing inward currents during diastolic depolarization, IK(Ca) appears to play a crucial role in human embryonic cardiac automaticity.
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Gao Z, Rasmussen TP, Li Y, Kutschke W, Koval OM, Wu Y, Wu Y, Hall DD, Joiner MLA, Wu XQ, Swaminathan PD, Purohit A, Zimmerman K, Weiss RM, Philipson KD, Song LS, Hund TJ, Anderson ME. Genetic inhibition of Na+-Ca2+ exchanger current disables fight or flight sinoatrial node activity without affecting resting heart rate. Circ Res 2013; 112:309-17. [PMID: 23192947 PMCID: PMC3562595 DOI: 10.1161/circresaha.111.300193] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/27/2012] [Accepted: 11/26/2012] [Indexed: 01/01/2023]
Abstract
RATIONALE The sodium-calcium exchanger 1 (NCX1) is predominantly expressed in the heart and is implicated in controlling automaticity in isolated sinoatrial node (SAN) pacemaker cells, but the potential role of NCX1 in determining heart rate in vivo is unknown. OBJECTIVE To determine the role of Ncx1 in heart rate. METHODS AND RESULTS We used global myocardial and SAN-targeted conditional Ncx1 knockout (Ncx1(-/-)) mice to measure the effect of the NCX current on pacemaking activity in vivo, ex vivo, and in isolated SAN cells. We induced conditional Ncx1(-/-) using a Cre/loxP system. Unexpectedly, in vivo and ex vivo hearts and isolated SAN cells showed that basal rates in Ncx1(-/-) (retaining ≈20% of control level NCX current) and control mice were similar, suggesting that physiological NCX1 expression is not required for determining resting heart rate. However, increases in heart rate and SAN cell automaticity in response to isoproterenol or the dihydropyridine Ca(2+) channel agonist BayK8644 were significantly blunted or eliminated in Ncx1(-/-) mice, indicating that NCX1 is important for fight or flight heart rate responses. In contrast, the pacemaker current and L-type Ca(2+) currents were equivalent in control and Ncx1(-/-) SAN cells under resting and isoproterenol-stimulated conditions. Ivabradine, a pacemaker current antagonist with clinical efficacy, reduced basal SAN cell automaticity similarly in control and Ncx1(-/-) mice. However, ivabradine decreased automaticity in SAN cells isolated from Ncx1(-/-) mice more effectively than in control SAN cells after isoproterenol, suggesting that the importance of NCX current in fight or flight rate increases is enhanced after pacemaker current inhibition. CONCLUSIONS Physiological Ncx1 expression is required for increasing sinus rates in vivo, ex vivo, and in isolated SAN cells, but not for maintaining resting heart rate.
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Affiliation(s)
- Zhan Gao
- Department of Internal Medicine and Cardiovascular Research Center, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA
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Kojima A, Kitagawa H, Omatsu-Kanbe M, Matsuura H, Nosaka S. Inhibitory effects of sevoflurane on pacemaking activity of sinoatrial node cells in guinea-pig heart. Br J Pharmacol 2012; 166:2117-35. [PMID: 22356456 DOI: 10.1111/j.1476-5381.2012.01914.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
BACKGROUND AND PURPOSE The volatile anaesthetic sevoflurane affects heart rate in clinical settings. The present study investigated the effect of sevoflurane on sinoatrial (SA) node automaticity and its underlying ionic mechanisms. EXPERIMENTAL APPROACH Spontaneous action potentials and four ionic currents fundamental for pacemaking, namely, the hyperpolarization-activated cation current (I(f) ), T-type and L-type Ca²⁺ currents (I(Ca,T) and I(Ca,L) , respectively), and slowly activating delayed rectifier K⁺ current (I(Ks) ), were recorded in isolated guinea-pig SA node cells using perforated and conventional whole-cell patch-clamp techniques. Heart rate in guinea-pigs was recorded ex vivo in Langendorff mode and in vivo during sevoflurane inhalation. KEY RESULTS In isolated SA node cells, sevoflurane (0.12-0.71 mM) reduced the firing rate of spontaneous action potentials and its electrical basis, diastolic depolarization rate, in a qualitatively similar concentration-dependent manner. Sevoflurane (0.44 mM) reduced spontaneous firing rate by approximately 25% and decreased I(f) , I(Ca,T) , I(Ca,L) and I(Ks) by 14.4, 31.3, 30.3 and 37.1%, respectively, without significantly affecting voltage dependence of current activation. The negative chronotropic effect of sevoflurane was partly reproduced by a computer simulation of SA node cell electrophysiology. Sevoflurane reduced heart rate in Langendorff-perfused hearts, but not in vivo during sevoflurane inhalation in guinea-pigs. CONCLUSIONS AND IMPLICATIONS Sevoflurane at clinically relevant concentrations slowed diastolic depolarization and thereby reduced pacemaking activity in SA node cells, at least partly due to its inhibitory effect on I(f) , I(Ca,T) and I(Ca,L) . These findings provide an important electrophysiological basis of alterations in heart rate during sevoflurane anaesthesia in clinical settings.
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Affiliation(s)
- Akiko Kojima
- Department of Anesthesiology, Shiga University of Medical Science, Otsu, Shiga, Japan.
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Kurtzwald-Josefson E, Hochhauser E, Katz G, Porat E, Seidman JG, Seidman CE, Chepurko Y, Shainberg A, Eldar M, Arad M. Exercise training improves cardiac function and attenuates arrhythmia in CPVT mice. J Appl Physiol (1985) 2012; 113:1677-83. [PMID: 23042908 DOI: 10.1152/japplphysiol.00818.2012] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a lethal ventricular arrhythmia evoked by physical or emotional stress. Recessively inherited CPVT is caused by either missense or null-allele mutations in the cardiac calsequestrin (CASQ2) gene. It was suggested that defects in CASQ2 cause protein deficiency and impair Ca(2+) uptake to the sarcoplasmic reticulum and Ca(2+)-dependent inhibition of ryanodine channels, leading to diastolic Ca(2+) leak, after-depolarizations, and arrhythmia. To examine the effect of exercise training on left ventricular remodeling and arrhythmia, CASQ2 knockout (KO) mice and wild-type controls underwent echocardiography and heart rhythm telemetry before and after 6 wk of training by treadmill exercise. qRT-PCR and Western blotting were used to measure gene and protein expression. Left ventricular fractional shortening was impaired in KO (33 ± 5 vs. 51 ± 7% in controls, P < 0.05) and improved after training (43 ± 12 and 51 ± 9% in KO and control mice, respectively, P = nonsignificant). The exercise tolerance was low in KO mice (16 ± 1 vs. 29 ± 2 min in controls, P < 0.01), but improved in trained animals (26 ± 2 vs. 30 ± 3 min, P = nonsignificant). The hearts of KO mice had a higher basal expression of the brain natriuretic peptide gene. After training, the expression of natriuretic peptide genes markedly decreased, with no difference between KO and controls. Exercise training was not associated with a change in ventricular tachycardia prevalence, but appeared to reduce arrhythmia load, as manifested by a decrease in ventricular beats during stress. We conclude that, in KO mice, which recapitulate the phenotype of human CPVT2, exercise training is well tolerated and could offer a strategy for heart conditioning against stress-induced arrhythmia.
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Affiliation(s)
- Efrat Kurtzwald-Josefson
- Leviev Heart Center, Sheba Medical Center, Tel Hashomer, Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel
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Yaniv Y, Maltsev VA, Ziman BD, Spurgeon HA, Lakatta EG. The "funny" current (I(f)) inhibition by ivabradine at membrane potentials encompassing spontaneous depolarization in pacemaker cells. Molecules 2012; 17:8241-54. [PMID: 22777191 PMCID: PMC4523892 DOI: 10.3390/molecules17078241] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2012] [Revised: 07/03/2012] [Accepted: 07/04/2012] [Indexed: 11/16/2022] Open
Abstract
Recent clinical trials have shown that ivabradine (IVA), a drug that inhibits the funny current (I(f)) in isolated sinoatrial nodal cells (SANC), decreases heart rate and reduces morbidity and mortality in patients with cardiovascular diseases. While IVA inhibits I(f), this effect has been reported at essentially unphysiological voltages, i.e., those more negative than the spontaneous diastolic depolarization (DD) between action potentials (APs). We tested the relative potency of IVA to block I(f) over a wide range of membrane potentials, including those that encompass DD governing to the SANC spontaneous firing rate. A clinically relevant IVA concentration of 3 μM to single, isolated rabbit SANC slowed the spontaneous AP firing rate by 15%. During voltage clamp the maximal I(f) was 18 ± 3 pA/pF (at -120 mV) and the maximal I(f) reduction by IVA was 60 ± 8% observed at -92 ± 4 mV. At the maximal diastolic depolarization (~-60 mV) I(f) amplitude was only -2.9 ± 0.4 pA/pF, and was reduced by only 41 ± 6% by IVA. Thus, I(f) amplitude and its inhibition by IVA at physiologically relevant membrane potentials are substantially less than that at unphysiological (hyperpolarized) membrane potentials. This novel finding more accurately describes how IVA affects SANC function and is of direct relevance to numerical modeling of SANC automaticity.
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Affiliation(s)
| | | | | | | | - Edward G. Lakatta
- Author to whom correspondence should be addressed; ; Tel.: +1-410-558-8202; Fax: +1-410-558-8150
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Zhang H, Butters T, Adeniran I, Higham J, Holden AV, Boyett MR, Hancox JC. Modeling the chronotropic effect of isoprenaline on rabbit sinoatrial node. Front Physiol 2012; 3:241. [PMID: 23060799 PMCID: PMC3459472 DOI: 10.3389/fphys.2012.00241] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2012] [Accepted: 06/13/2012] [Indexed: 11/13/2022] Open
Abstract
Introduction: β-adrenergic stimulation increases the heart rate by accelerating the electrical activity of the pacemaker of the heart, the sinoatrial node (SAN). Ionic mechanisms underlying the actions of β-adrenergic stimulation are not yet fully understood. Isoprenaline (ISO), a β-adrenoceptor agonist, shifts voltage-dependent If activation to more positive potentials resulting in an increase of If, which has been suggested to be the main mechanism underlying the effect of β-adrenergic stimulation. However, ISO has been found to increase the firing rate of rabbit SAN cells when If is blocked. ISO also increases ICaL, Ist, IKr, and IKs; and shifts the activation of IKr to more negative potentials and increases the rate of its deactivation. ISO has also been reported to increase the intracellular Ca2+ transient, which can contribute to chronotropy by modulating the “Ca2+ clock.” The aim of this study was to analyze the ionic mechanisms underlying the positive chronotropy of β-adrenergic stimulation using two distinct and well established computational models of the electrical activity of rabbit SAN cells. Methods and results: We modified the Boyett et al. (2001) and Kurata et al. (2008) models of electrical activity for the central and peripheral rabbit SAN cells by incorporating equations for the known dose-dependent actions of ISO on various ionic channel currents (ICaL, Ist, IKr, and IKs), kinetics of IKr and If, and the intracellular Ca2+ transient. These equations were constructed from experimental data. To investigate the ionic basis of the effects of ISO, we simulated the chronotropic effect of a range of ISO concentrations when ISO exerted all its actions or just a subset of them. Conclusion: In both the Boyett et al. and Kurata et al. SAN models, the chronotropic effect of ISO was found to result from an integrated action of ISO on ICaL, If, Ist, IKr, and IKs, among which an increase in the rate of deactivation of IKr plays a prominent role, though the effect of ISO on If and [Ca2+]i also plays a role.
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Affiliation(s)
- Henggui Zhang
- Biological Physics Group, School of Physics and Astronomy, University of Manchester Manchester, UK ; School of Computer Science and Technology, Harbin Institute of Technology Harbin, China
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Yaniv Y, Spurgeon HA, Lyashkov AE, Yang D, Ziman BD, Maltsev VA, Lakatta EG. Crosstalk between mitochondrial and sarcoplasmic reticulum Ca2+ cycling modulates cardiac pacemaker cell automaticity. PLoS One 2012; 7:e37582. [PMID: 22666369 PMCID: PMC3362629 DOI: 10.1371/journal.pone.0037582] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2012] [Accepted: 04/22/2012] [Indexed: 01/02/2023] Open
Abstract
Background Mitochondria dynamically buffer cytosolic Ca2+ in cardiac ventricular cells and this affects the Ca2+ load of the sarcoplasmic reticulum (SR). In sinoatrial-node cells (SANC) the SR generates periodic local, subsarcolemmal Ca2+ releases (LCRs) that depend upon the SR load and are involved in SANC automaticity: LCRs activate an inward Na+-Ca2+ exchange current to accelerate the diastolic depolarization, prompting the ensemble of surface membrane ion channels to generate the next action potential (AP). Objective To determine if mitochondrial Ca2+ (Ca2+m), cytosolic Ca2+ (Ca2+c)-SR-Ca2+ crosstalk occurs in single rabbit SANC, and how this may relate to SANC normal automaticity. Results Inhibition of mitochondrial Ca2+ influx into (Ru360) or Ca2+ efflux from (CGP-37157) decreased [Ca2+]m to 80±8% control or increased [Ca2+]m to 119±7% control, respectively. Concurrent with inhibition of mitochondrial Ca2+ influx or efflux, the SR Ca2+ load, and LCR size, duration, amplitude and period (imaged via confocal linescan) significantly increased or decreased, respectively. Changes in total ensemble LCR Ca2+ signal were highly correlated with the change in the SR Ca2+ load (r2 = 0.97). Changes in the spontaneous AP cycle length (Ru360, 111±1% control; CGP-37157, 89±2% control) in response to changes in [Ca2+]m were predicted by concurrent changes in LCR period (r2 = 0.84). Conclusion A change in SANC Ca2+m flux translates into a change in the AP firing rate by effecting changes in Ca2+c and SR Ca2+ loading, which affects the characteristics of spontaneous SR Ca2+ release.
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Affiliation(s)
- Yael Yaniv
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - Harold A. Spurgeon
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - Alexey E. Lyashkov
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - Dongmei Yang
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - Bruce D. Ziman
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - Victor A. Maltsev
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - Edward G. Lakatta
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
- * E-mail:
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Sosunov EA, Anyukhovsky EP. Differential effects of ivabradine and ryanodine on pacemaker activity in canine sinus node and purkinje fibers. J Cardiovasc Electrophysiol 2012; 23:650-5. [PMID: 22353259 DOI: 10.1111/j.1540-8167.2011.02285.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
INTRODUCTION It is generally accepted that at least 2 major mechanisms contribute to sinus node (SN) pacemaking: a membrane voltage (mainly I(f) ) clock and a calcium (Ca) clock (localized submembrane sarcoplasmic reticulum Ca(2+) release during late diastolic depolarization). The aim of this study was to compare the contributions of each mechanism to pacemaker activity in SN and Purkinje fibers (PFs) exhibiting normal or abnormal automaticity. METHODS AND RESULTS Conventional microelectrodes were used to record action potentials in isolated spontaneously beating canine SN and free running PF in control and in the presence of 0.1 μM isoproterenol. Ryanodine (0.1-3 μM) and ivabradine (3 μM) were used to inhibit sarcoplasmic reticulum Ca(2+) release or I(f), respectively. To induce automaticity at low membrane potentials, PFs were superfused with BaCl(2). In SN, ivabradine reduced the rate whereas ryanodine had no effect. Isoproterenol significantly accelerated automatic rate, which was decreased by ivabradine and ryanodine. In normally polarized PFs, ryanodine had no effects on the automatic rate in the absence or presence of isoproterenol, whereas ivabradine inhibited both control and isoproterenol-accelerated automaticity. In PF depolarized with BaCl(2), ivabradine decreased BaCl(2) -induced automatic rate while ryanodine had no effect. CONCLUSION In canine SN, I(f) contributes to both basal automaticity and β-adrenergic-induced rate acceleration while the ryanodine-inhibited Ca clock appears more involved in β-adrenergic regulation of pacemaker rate. In PF, normal automaticity depends mainly on I(f). Inhibition of basal potassium conductance results in high automatic rates at depolarized membrane potentials with SN-like responses to inhibition of membrane and Ca clocks.
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Affiliation(s)
- Eugene A Sosunov
- Department of Pharmacology, Center for Molecular Therapeutics, College of Physicians and Surgeons of Columbia University, New York, NY, USA
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Zhang H, Lau DH, Shlapakova IN, Zhao X, Danilo P, Robinson RB, Cohen IS, Qu D, Xu Z, Rosen MR. Implantation of Sinoatrial Node Cells into Canine Right Ventricle: Biological Pacing Appears Limited by the Substrate. Cell Transplant 2011. [DOI: 10.3727/096368911x565038b] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Biological pacing has been proposed as a physiologic counterpart to electronic pacing, and the sinoatrial node (SAN) is the general standard for biological pacemakers. We tested the expression of SAN pacemaker cell activity when implanted autologously in the right ventricle (RV). We induced complete heart block and implanted electronic pacemakers in the RV of adult mongrel dogs. Autologous SAN cells isolated enzymatically were studied by patch clamp to confirm SAN identity. SAN cells (400,000) were injected into the RV subepicardial free wall and dogs were monitored for 2 weeks. Pacemaker function was assessed by overdrive pacing and IV epinephrine challenge. SAN cells expressed a time-dependent inward current (If) activating on hyperpolarization: density = 4.3 ± 0.6 pA/pF at −105 mV. Four of the six dogs demonstrated >50% of beats originating from the implant site at 24 h. Biological pacemaker rates on days 7–14 = 45–55 bpm and post-overdrive escape times = 1.5–2.5 s. Brisk catecholamine responsiveness occurred. Dogs implanted with autologous SAN cells manifest biological pacing properties dissimilar from those of the anatomic SAN. This highlights the importance of cell and substrate interaction in generating biological pacemaker function.
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Affiliation(s)
- Hao Zhang
- Changhai Hospital, Second Military Medical University, Shanghai, China
| | - David H. Lau
- Department of Pharmacology, Center for Molecular Therapeutics, College of Physicians and Surgeons, Columbia University, New York, NY, USA
| | - Iryna N. Shlapakova
- Department of Pharmacology, Center for Molecular Therapeutics, College of Physicians and Surgeons, Columbia University, New York, NY, USA
| | - Xin Zhao
- Division of Cardiology, First Affiliated Hospital of Soochow University, Su Zhou, China
| | - Peter Danilo
- Department of Pharmacology, Center for Molecular Therapeutics, College of Physicians and Surgeons, Columbia University, New York, NY, USA
| | - Richard B. Robinson
- Department of Pharmacology, Center for Molecular Therapeutics, College of Physicians and Surgeons, Columbia University, New York, NY, USA
| | - Ira S. Cohen
- Department of Physiology & Biophysics, Stony Brook University, Stony Brook, NY, USA
| | - Dan Qu
- Changhai Hospital, Second Military Medical University, Shanghai, China
| | - Zhiyun Xu
- Changhai Hospital, Second Military Medical University, Shanghai, China
| | - Michael R. Rosen
- Department of Pharmacology, Center for Molecular Therapeutics, College of Physicians and Surgeons, Columbia University, New York, NY, USA
- Department of Pediatrics, College of Physicians and Surgeons, Columbia University, New York, NY, USA
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Chang SL, Chen YC, Yeh YH, Lin YK, Wu TJ, Lin CI, Chen SA, Chen YJ. Heart failure enhanced pulmonary vein arrhythmogenesis and dysregulated sodium and calcium homeostasis with increased calcium sparks. J Cardiovasc Electrophysiol 2011; 22:1378-86. [PMID: 21992547 DOI: 10.1111/j.1540-8167.2011.02126.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
UNLABELLED Late sodium currents and intracellular Ca(2+) (Ca(2+) (i)) dynamics play an important role in arrhythmogenesis of pulmonary vein (PV) and heart failure (HF). It is not clear whether HF enhances PV arrhythmogenesis through modulation of Ca(2+) homeostasis and increased late sodium currents. The aim of this study was to investigate the sodium and calcium homeostasis in PV cardiomyocytes with HF. METHODS AND RESULTS Whole-cell patch clamp was used to investigate the action potentials and ionic currents in isolated rabbit single PV cardiomyocytes with and without rapid pacing induced HF. The Ca(2+) (i) dynamics were evaluated through fluorescence and confocal microscopy. As compared to control PV cardiomyocytes (n = 18), HF PV cardiomyocytes (n = 13) had a higher incidence of delayed afterdepolarization (45% vs 13%, P < 0.05) and faster spontaneous activity (3.0 ± 0.2 vs 2.1 ± 0.2 Hz, P < 0.05). HF PV cardiomyocytes had increased late Na(+) currents, Na(+) /Ca(2+) exchanger currents, and transient inward currents, but had decreased Na(+) currents or L-type calcium currents. HF PV cardiomyocytes with pacemaker activity had larger Ca(2+) (i) transients (R410/485, 0.18 ± 0.04 vs 0.11 ± 0.02, P < 0.05), and sarcoplasmic reticulum Ca(2+) stores. Moreover, HF PV cardiomyocytes with pacemaker activity (n = 18) had higher incidence (95% vs 70%, P < 0.05), frequency (7.8 ± 3.1 vs 2.3 ± 1.2 spark/mm/s, P < 0.05), amplitude (F/F(0) , 3.2 ± 0.8 vs 1.9 ± 0.5, P < 0.05), and longer decay time (65 ± 3 vs 48 ± 4 ms, P < 0.05) of Ca(2+) sparks than control PV cardiomyocytes with pacemaker activity (n = 18). CONCLUSIONS Dysregulated sodium and calcium homeostasis, and enhanced calcium sparks promote arrhythmogenesis of PV cardiomyocytes in HF, which may play an important role in the development of atrial fibrillation.
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Affiliation(s)
- Shih-Lin Chang
- Institute of Clinical Medicine, National Yang-Ming University school of medicine, Taiwan
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Feliciano DF, Bassani RA, Oliveira PX, Bassani JWM. Pacemaker activity in the insect (T. molitor) heart: role of the sarcoplasmic reticulum. Am J Physiol Regul Integr Comp Physiol 2011; 301:R1838-45. [PMID: 21917905 DOI: 10.1152/ajpregu.00089.2011] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The electrophysiological properties of the myogenic cardiac cells of insects have been analyzed, but the mechanisms that regulate the pacemaker activity have not been elucidated yet. In mammalian pacemaker cells, different types of membrane ion channels seem to be sequentially activated, perhaps in a cooperative fashion with the current generated by Ca(2+) extrusion mediated by the electrogenic Na(+)/Ca(2+) exchanger, which is sustained by the diastolic sarcoplasmic reticulum (SR) Ca(2+) release. The objective of the present work was to investigate the role of the SR function on the basal beating rate (BR), and BR modulation by extracellular Ca(2+) concentration ([Ca(2+)](o)) and neurotransmitters in the in situ dorsal vessel (heart) of the mealworm beetle Tenebrio molitor. The main observations were as follows: 1) basal BR was reduced by 50% by inhibition of SR function, but not affected by perfusion with CsCl or ZD7288; 2) spontaneous activity was abolished by Cd(2+); 3) a robust positive chronotropic response could be elicited to serotonin (5-HT), but not to norepinephrine or carbamylcholine; 4) SR inhibition abolished the sustained chronotropic stimulation by [Ca(2+)](o) elevation and by 5-HT, while the latter was unaffected by CsCl. It is concluded that, in T. molitor heart, BR is markedly, but not exclusively, dependent on the SR function, and that BR control and modulation by both [Ca(2+)](o) and 5-HT requires a functional SR.
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Affiliation(s)
- Danielle F Feliciano
- Center for Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas, Campinas, Brazil
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Yaniv Y, Juhaszova M, Lyashkov AE, Spurgeon HA, Sollott SJ, Lakatta EG. Ca2+-regulated-cAMP/PKA signaling in cardiac pacemaker cells links ATP supply to demand. J Mol Cell Cardiol 2011; 51:740-8. [PMID: 21835182 DOI: 10.1016/j.yjmcc.2011.07.018] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/28/2011] [Revised: 07/12/2011] [Accepted: 07/21/2011] [Indexed: 10/17/2022]
Abstract
RATIONALE In sinoatrial node cells (SANC), Ca(2+) activates adenylate cyclase (AC) to generate a high basal level of cAMP-mediated/protein kinase A (PKA)-dependent phosphorylation of Ca(2+) cycling proteins. These result in spontaneous sarcoplasmic-reticulum (SR) generated rhythmic Ca(2+) oscillations during diastolic depolarization, that not only trigger the surface membrane to generate rhythmic action potentials (APs), but, in a feed-forward manner, also activate AC/PKA signaling. ATP is consumed to pump Ca(2+) to the SR, to produce cAMP, to support contraction and to maintain cell ionic homeostasis. OBJECTIVE Since feedback mechanisms link ATP-demand to ATP production, we hypothesized that (1) both basal ATP supply and demand in SANC would be Ca(2+)-cAMP/PKA dependent; and (2) due to its feed-forward nature, a decrease in flux through the Ca(2+)-cAMP/PKA signaling axis will reduce the basal ATP production rate. METHODS AND RESULTS O(2) consumption in spontaneous beating SANC was comparable to ventricular myocytes (VM) stimulated at 3 Hz. Graded reduction of basal Ca(2+)-cAMP/PKA signaling to reduce ATP demand in rabbit SANC produced graded ATP depletion (r(2)=0.96), and reduced O(2) consumption and flavoprotein fluorescence. Neither inhibition of glycolysis, selectively blocking contraction nor specific inhibition of mitochondrial Ca(2+) flux reduced the ATP level. CONCLUSIONS Feed-forward basal Ca(2+)-cAMP/PKA signaling both consumes ATP to drive spontaneous APs in SANC and is tightly linked to mitochondrial ATP production. Interfering with Ca(2+)-cAMP/PKA signaling not only slows the firing rate and reduces ATP consumption, but also appears to reduce ATP production so that ATP levels fall. This distinctly differs from VM, which lack this feed-forward basal cAMP/PKA signaling, and in which ATP level remains constant when the demand changes.
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Affiliation(s)
- Yael Yaniv
- Laboratory of Cardiovascular Science, Gerontology Research Center, Intramural Research Program, National Institute on Aging, NIH, Baltimore, Maryland 21224-6825, USA
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Gao Z, Singh MV, Hall DD, Koval OM, Luczak ED, Joiner MLA, Chen B, Wu Y, Chaudhary AK, Martins JB, Hund TJ, Mohler PJ, Song LS, Anderson ME. Catecholamine-independent heart rate increases require Ca2+/calmodulin-dependent protein kinase II. Circ Arrhythm Electrophysiol 2011; 4:379-87. [PMID: 21406683 PMCID: PMC3116039 DOI: 10.1161/circep.110.961771] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
BACKGROUND Catecholamines increase heart rate by augmenting the cAMP-responsive hyperpolarization-activated cyclic nucleotide-gated channel 4 pacemaker current (I(f)) and by promoting inward Na(+)/Ca(2+) exchanger current (I(NCX)) by a "Ca(2+) clock" mechanism in sinoatrial nodal cells (SANCs). The importance, identity, and function of signals that connect I(f) and Ca(2+) clock mechanisms are uncertain and controversial, but the multifunctional Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is required for physiological heart rate responses to β-adrenergic receptor (β-AR) stimulation. The aim of this study was to measure the contribution of the Ca(2+) clock and CaMKII to cardiac pacing independent of β-AR agonist stimulation. METHODS AND RESULTS We used the L-type Ca(2+) channel agonist Bay K8644 (BayK) to activate the SANC Ca(2+) clock. BayK and isoproterenol were similarly effective in increasing rates in SANCs and Langendorff-perfused hearts from wild-type control mice. In contrast, SANCs and isolated hearts from mice with CaMKII inhibition by transgenic expression of an inhibitory peptide (AC3-I) were resistant to rate increases by BayK. BayK only activated CaMKII in control SANCs but increased L-type Ca(2+) current (I(Ca)) equally in all SANCs, indicating that increasing I(Ca) was insufficient and suggesting that CaMKII activation was required for heart rate increases by BayK. BayK did not increase I(f) or protein kinase A-dependent phosphorylation of phospholamban (at Ser16), indicating that increased SANC Ca(2+) by BayK did not augment cAMP/protein kinase A signaling at these targets. Late-diastolic intracellular Ca(2+) release and I(NCX) were significantly reduced in AC3-I SANCs, and the response to BayK was eliminated by ryanodine in all groups. CONCLUSIONS The Ca(2+) clock is capable of supporting physiological fight-or-flight responses, independent of β-AR stimulation or I(f) increases. Complete Ca(2+) clock and β-AR stimulation responses require CaMKII.
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Affiliation(s)
- Zhan Gao
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, IA
| | - Madhu V Singh
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, IA
| | - Duane D Hall
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, IA
| | - Olha M. Koval
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, IA
| | - Elizabeth D. Luczak
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, IA
| | - Mei-ling A. Joiner
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, IA
| | - Biyi Chen
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, IA
| | - Yuejin Wu
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, IA
| | - Ashok K Chaudhary
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, IA
| | - James B Martins
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, IA
| | - Thomas J Hund
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, IA
| | - Peter J Mohler
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, IA
- Department of Molecular Physiology and Biophysics, Carver College of Medicine, University of Iowa, Iowa City, IA
| | - Long-Sheng Song
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, IA
| | - Mark E. Anderson
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, IA
- Department of Molecular Physiology and Biophysics, Carver College of Medicine, University of Iowa, Iowa City, IA
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Angiotensin II decreases spontaneous firing rate of guinea-pig sino-atrial node cells. Eur J Pharmacol 2011; 660:387-93. [PMID: 21510929 DOI: 10.1016/j.ejphar.2011.04.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2010] [Revised: 03/24/2011] [Accepted: 04/06/2011] [Indexed: 11/22/2022]
Abstract
Angiotensin II (Ang II) plays an important role in the regulation of cardiac function, but its electrophysiological effects on sino-atrial (SA) node are not well understood. In this study, the immediate effect of Ang II on action potentials and ionic currents were investigated by using whole-cell patch-clamps in single guinea-pig SA node pacemaker cells. We demonstrated that Ang II exerted a negative effect on spontaneous firing rate, with a concomitant reduction in the slope of diastolic depolarization. The inhibitory effect of Ang II on spontaneous activity displayed a concentration-dependent manner in the range of 1-1000 nM, with IC50 of 8.34 nM. Ang II type 1 (AT1) receptor antagonist valsartan (1 μM) abolished the inhibitory effect. In contrast, Ang II type 2 (AT2) receptor antagonist, PD123319 (1 μM) didn't affect the action of Ang II. Ang II had no significant effect on hyperpolarization-activated current (If) in SA node cells. However, it significantly slowed the deactivation of the slowly activated delayed rectifier K+ current (Iks) and increased the tail current density. Furthermore, Ang II decreased the current density of L-type Ca2+ current in SA node cells. Our data demonstrate that Ang II reduces the auto rhythm of SA node cells via enhancing Iks and reducing ICaL. The result suggests a potential mechanism by which elevated levels of Ang II may be involved in the occurrence of SA node dysfunction in cardiac pathophysiology.
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