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Mitrokhin V, Hadzi-Petrushev N, Kazanski V, Schileyko S, Kamkina O, Rodina A, Zolotareva A, Zolotarev V, Kamkin A, Mladenov M. The Role of K ACh Channels in Atrial Fibrillation. Cells 2024; 13:1014. [PMID: 38920645 PMCID: PMC11201540 DOI: 10.3390/cells13121014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2024] [Revised: 06/05/2024] [Accepted: 06/07/2024] [Indexed: 06/27/2024] Open
Abstract
This manuscript explores the intricate role of acetylcholine-activated inward rectifier potassium (KACh) channels in the pathogenesis of atrial fibrillation (AF), a common cardiac arrhythmia. It delves into the molecular and cellular mechanisms that underpin AF, emphasizing the vital function of KACh channels in modulating the atrial action potential and facilitating arrhythmogenic conditions. This study underscores the dual nature of KACh activation and its genetic regulation, revealing that specific variations in potassium channel genes, such as Kir3.4 and K2P3.1, significantly influence the electrophysiological remodeling associated with AF. Furthermore, this manuscript identifies the crucial role of the KACh-mediated current, IKACh, in sustaining arrhythmia through facilitating shorter re-entry circuits and stabilizing the re-entrant circuits, particularly in response to vagal nerve stimulation. Experimental findings from animal models, which could not induce AF in the absence of muscarinic activation, highlight the dependency of AF induction on KACh channel activity. This is complemented by discussions on therapeutic interventions, where KACh channel blockers have shown promise in AF management. Additionally, this study discusses the broader implications of KACh channel behavior, including its ubiquitous presence across different cardiac regions and species, contributing to a comprehensive understanding of AF dynamics. The implications of these findings are profound, suggesting that targeting KACh channels might offer new therapeutic avenues for AF treatment, particularly in cases resistant to conventional approaches. By integrating genetic, cellular, and pharmacological perspectives, this manuscript offers a holistic view of the potential mechanisms and therapeutic targets in AF, making a significant contribution to the field of cardiac arrhythmia research.
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Affiliation(s)
- Vadim Mitrokhin
- Institute of Physiology, Federal State Autonomous Educational Institution of Higher Education “N.I. Pirogov, Russian National Research Medical University” Ministry of Health, 117997 Moscow, Russia; (V.M.); (V.K.); (S.S.); (O.K.); (A.R.); (A.Z.); (V.Z.); (A.K.)
| | - Nikola Hadzi-Petrushev
- Institute of Biology, Faculty of Natural Sciences and Mathematics, Ss. Cyril and Methodius University, 1000 Skopje, North Macedonia;
| | - Viktor Kazanski
- Institute of Physiology, Federal State Autonomous Educational Institution of Higher Education “N.I. Pirogov, Russian National Research Medical University” Ministry of Health, 117997 Moscow, Russia; (V.M.); (V.K.); (S.S.); (O.K.); (A.R.); (A.Z.); (V.Z.); (A.K.)
| | - Stanislav Schileyko
- Institute of Physiology, Federal State Autonomous Educational Institution of Higher Education “N.I. Pirogov, Russian National Research Medical University” Ministry of Health, 117997 Moscow, Russia; (V.M.); (V.K.); (S.S.); (O.K.); (A.R.); (A.Z.); (V.Z.); (A.K.)
| | - Olga Kamkina
- Institute of Physiology, Federal State Autonomous Educational Institution of Higher Education “N.I. Pirogov, Russian National Research Medical University” Ministry of Health, 117997 Moscow, Russia; (V.M.); (V.K.); (S.S.); (O.K.); (A.R.); (A.Z.); (V.Z.); (A.K.)
| | - Anastasija Rodina
- Institute of Physiology, Federal State Autonomous Educational Institution of Higher Education “N.I. Pirogov, Russian National Research Medical University” Ministry of Health, 117997 Moscow, Russia; (V.M.); (V.K.); (S.S.); (O.K.); (A.R.); (A.Z.); (V.Z.); (A.K.)
| | - Alexandra Zolotareva
- Institute of Physiology, Federal State Autonomous Educational Institution of Higher Education “N.I. Pirogov, Russian National Research Medical University” Ministry of Health, 117997 Moscow, Russia; (V.M.); (V.K.); (S.S.); (O.K.); (A.R.); (A.Z.); (V.Z.); (A.K.)
| | - Valentin Zolotarev
- Institute of Physiology, Federal State Autonomous Educational Institution of Higher Education “N.I. Pirogov, Russian National Research Medical University” Ministry of Health, 117997 Moscow, Russia; (V.M.); (V.K.); (S.S.); (O.K.); (A.R.); (A.Z.); (V.Z.); (A.K.)
| | - Andre Kamkin
- Institute of Physiology, Federal State Autonomous Educational Institution of Higher Education “N.I. Pirogov, Russian National Research Medical University” Ministry of Health, 117997 Moscow, Russia; (V.M.); (V.K.); (S.S.); (O.K.); (A.R.); (A.Z.); (V.Z.); (A.K.)
| | - Mitko Mladenov
- Institute of Physiology, Federal State Autonomous Educational Institution of Higher Education “N.I. Pirogov, Russian National Research Medical University” Ministry of Health, 117997 Moscow, Russia; (V.M.); (V.K.); (S.S.); (O.K.); (A.R.); (A.Z.); (V.Z.); (A.K.)
- Institute of Biology, Faculty of Natural Sciences and Mathematics, Ss. Cyril and Methodius University, 1000 Skopje, North Macedonia;
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Kayser A, Dittmann S, Šarić T, Mearini G, Verkerk AO, Schulze-Bahr E. The W101C KCNJ5 Mutation Induces Slower Pacing by Constitutively Active GIRK Channels in hiPSC-Derived Cardiomyocytes. Int J Mol Sci 2023; 24:15290. [PMID: 37894977 PMCID: PMC10607318 DOI: 10.3390/ijms242015290] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2023] [Revised: 10/13/2023] [Accepted: 10/15/2023] [Indexed: 10/29/2023] Open
Abstract
Mutations in the KCNJ5 gene, encoding one of the major subunits of cardiac G-protein-gated inwardly rectifying K+ (GIRK) channels, have been recently linked to inherited forms of sinus node dysfunction. Here, the pathogenic mechanism of the W101C KCNJ5 mutation underlying sinus bradycardia in a patient-derived cellular disease model of sinus node dysfunction (SND) was investigated. A human-induced pluripotent stem cell (hiPSCs) line of a mutation carrier was generated, and CRISPR/Cas9-based gene targeting was used to correct the familial mutation as a control line. Both cell lines were further differentiated into cardiomyocytes (hiPSC-CMs) that robustly expressed GIRK channels which underly the acetylcholine-regulated K+ current (IK,ACh). hiPSC-CMs with the W101C KCNJ5 mutation (hiPSCW101C-CM) had a constitutively active IK,ACh under baseline conditions; the application of carbachol was able to increase IK,ACh, further indicating that not all available cardiac GIRK channels were open at baseline. Additionally, hiPSCW101C-CM had a more negative maximal diastolic potential (MDP) and a slower pacing frequency confirming the bradycardic phenotype. Of note, the blockade of the constitutively active GIRK channel with XAF-1407 rescued the phenotype. These results provide further mechanistic insights and may pave the way for the treatment of SND patients with GIRK channel dysfunction.
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Affiliation(s)
- Anne Kayser
- Institute for Genetics of Heart Diseases (IfGH), University Hospital Münster, 48149 Münster, Germany (S.D.); (E.S.-B.)
| | - Sven Dittmann
- Institute for Genetics of Heart Diseases (IfGH), University Hospital Münster, 48149 Münster, Germany (S.D.); (E.S.-B.)
| | - Tomo Šarić
- Center for Physiology and Pathophysiology, Institute for Neurophysiology, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50931 Cologne, Germany;
| | - Giulia Mearini
- Institute of Experimental Pharmacology and Toxicology, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany
| | - Arie O. Verkerk
- Department of Medical Biology, Amsterdam University Medical Centers, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands
- Department of Experimental Cardiology, Amsterdam University Medical Centers, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands
| | - Eric Schulze-Bahr
- Institute for Genetics of Heart Diseases (IfGH), University Hospital Münster, 48149 Münster, Germany (S.D.); (E.S.-B.)
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Al Kury LT, Chacar S, Alefishat E, Khraibi AA, Nader M. Structural and Electrical Remodeling of the Sinoatrial Node in Diabetes: New Dimensions and Perspectives. Front Endocrinol (Lausanne) 2022; 13:946313. [PMID: 35872997 PMCID: PMC9302195 DOI: 10.3389/fendo.2022.946313] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/17/2022] [Accepted: 06/14/2022] [Indexed: 11/14/2022] Open
Abstract
The sinoatrial node (SAN) is composed of highly specialized cells that mandate the spontaneous beating of the heart through self-generation of an action potential (AP). Despite this automaticity, the SAN is under the modulation of the autonomic nervous system (ANS). In diabetes mellitus (DM), heart rate variability (HRV) manifests as a hallmark of diabetic cardiomyopathy. This is paralleled by an impaired regulation of the ANS, and by a pathological remodeling of the pacemaker structure and function. The direct effect of diabetes on the molecular signatures underscoring this pathology remains ill-defined. The recent focus on the electrical currents of the SAN in diabetes revealed a repressed firing rate of the AP and an elongation of its tracing, along with conduction abnormalities and contractile failure. These changes are blamed on the decreased expression of ion transporters and cell-cell communication ports at the SAN (i.e., HCN4, calcium and potassium channels, connexins 40, 45, and 46) which further promotes arrhythmias. Molecular analysis crystallized the RGS4 (regulator of potassium currents), mitochondrial thioredoxin-2 (reactive oxygen species; ROS scavenger), and the calcium-dependent calmodulin kinase II (CaMKII) as metabolic culprits of relaying the pathological remodeling of the SAN cells (SANCs) structure and function. A special attention is given to the oxidation of CaMKII and the generation of ROS that induce cell damage and apoptosis of diabetic SANCs. Consequently, the diabetic SAN contains a reduced number of cells with significant infiltration of fibrotic tissues that further delay the conduction of the AP between the SANCs. Failure of a genuine generation of AP and conduction of their derivative waves to the neighboring atrial myocardium may also occur as a result of the anti-diabetic regiment (both acute and/or chronic treatments). All together, these changes pose a challenge in the field of cardiology and call for further investigations to understand the etiology of the structural/functional remodeling of the SANCs in diabetes. Such an understanding may lead to more adequate therapies that can optimize glycemic control and improve health-related outcomes in patients with diabetes.
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Affiliation(s)
- Lina T. Al Kury
- Department of Health Sciences, College of Natural and Health Sciences, Zayed University, Abu Dhabi, United Arab Emirates
- *Correspondence: Lina T. Al Kury, ; Moni Nader,
| | - Stephanie Chacar
- Department of Physiology and Immunology, College of Medicine and Health Sciences, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates
| | - Eman Alefishat
- Department of Pharmacology, College of Medicine and Health Sciences, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates
- Department of Biopharmaceutics and Clinical Pharmacy, School of Pharmacy, The University of Jordan, Amman, Jordan
- Center for Biotechnology, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates
| | - Ali A. Khraibi
- Department of Physiology and Immunology, College of Medicine and Health Sciences, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates
- Center for Biotechnology, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates
| | - Moni Nader
- Department of Physiology and Immunology, College of Medicine and Health Sciences, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates
- Center for Biotechnology, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates
- *Correspondence: Lina T. Al Kury, ; Moni Nader,
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Impaired regulation of heart rate and sinoatrial node function by the parasympathetic nervous system in type 2 diabetic mice. Sci Rep 2021; 11:12465. [PMID: 34127743 PMCID: PMC8203800 DOI: 10.1038/s41598-021-91937-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2021] [Accepted: 05/31/2021] [Indexed: 01/01/2023] Open
Abstract
Heart rate (HR) and sinoatrial node (SAN) function are modulated by the autonomic nervous system. HR regulation by the parasympathetic nervous system (PNS) is impaired in diabetes mellitus (DM), which is denoted cardiovascular autonomic neuropathy. Whether blunted PNS effects on HR in type 2 DM are related to impaired responsiveness of the SAN to PNS agonists is unknown. This was investigated in type 2 diabetic db/db mice in vivo and in isolated SAN myocytes. The PNS agonist carbachol (CCh) had a smaller inhibitory effect on HR, while HR recovery time after CCh removal was accelerated in db/db mice. In isolated SAN myocytes CCh reduced spontaneous action potential firing frequency but this effect was reduced in db/db mice due to blunted effects on diastolic depolarization slope and maximum diastolic potential. Impaired effects of CCh occurred due to enhanced desensitization of the acetylcholine-activated K+ current (IKACh) and faster IKACh deactivation. IKACh alterations were reversed by inhibition of regulator of G-protein signaling 4 (RGS4) and by the phospholipid PIP3. SAN expression of RGS4 was increased in db/db mice. Impaired PNS regulation of HR in db/db mice occurs due to reduced responsiveness of SAN myocytes to PNS agonists in association with enhanced RGS4 activity.
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Kula R, Bébarová M, Matejovič P, Šimurda J, Pásek M. Current density as routine parameter for description of ionic membrane current: is it always the best option? PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2020; 157:24-32. [DOI: 10.1016/j.pbiomolbio.2019.11.011] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2019] [Revised: 09/20/2019] [Accepted: 11/26/2019] [Indexed: 12/17/2022]
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Zhang H, Zhang S, Wang W, Wang K, Shen W. A Mathematical Model of the Mouse Atrial Myocyte With Inter-Atrial Electrophysiological Heterogeneity. Front Physiol 2020; 11:972. [PMID: 32848887 PMCID: PMC7425199 DOI: 10.3389/fphys.2020.00972] [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: 04/16/2020] [Accepted: 07/16/2020] [Indexed: 12/20/2022] Open
Abstract
Biophysically detailed mathematical models of cardiac electrophysiology provide an alternative to experimental approaches for investigating possible ionic mechanisms underlying the genesis of electrical action potentials and their propagation through the heart. The aim of this study was to develop a biophysically detailed mathematical model of the action potentials of mouse atrial myocytes, a popular experimental model for elucidating molecular and cellular mechanisms of arrhythmogenesis. Based on experimental data from isolated mouse atrial cardiomyocytes, a set of mathematical equations for describing the biophysical properties of membrane ion channel currents, intracellular Ca2+ handling, and Ca2+-calmodulin activated protein kinase II and β-adrenergic signaling pathways were developed. Wherever possible, membrane ion channel currents were modeled using Markov chain formalisms, allowing detailed representation of channel kinetics. The model also considered heterogeneous electrophysiological properties between the left and the right atrial cardiomyocytes. The developed model was validated by its ability to reproduce the characteristics of action potentials and Ca2+ transients, matching quantitatively to experimental data. Using the model, the functional roles of four K+ channel currents in atrial action potential were evaluated by channel block simulations, results of which were quantitatively in agreement with existent experimental data. To conclude, this newly developed model of mouse atrial cardiomyocytes provides a powerful tool for investigating possible ion channel mechanisms of atrial electrical activity at the cellular level and can be further used to investigate mechanisms underlying atrial arrhythmogenesis.
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Affiliation(s)
- Henggui Zhang
- Department of Physics and Astronomy, Biological Physics Group, School of Physics & Astronomy, The University of Manchester, Manchester, United Kingdom.,Peng Cheng Laboratory, Shenzhen, China
| | - Shanzhuo Zhang
- Department of Physics and Astronomy, Biological Physics Group, School of Physics & Astronomy, The University of Manchester, Manchester, United Kingdom.,School of Computer Science and Technology, Harbin Institute of Technology, Harbin, China
| | - Wei Wang
- Department of Physics and Astronomy, Biological Physics Group, School of Physics & Astronomy, The University of Manchester, Manchester, United Kingdom.,Peng Cheng Laboratory, Shenzhen, China.,Shenzhen Key Laboratory of Visual Object Detection and Recognition, Harbin Institute of Technology, Shenzhen, China
| | - Kuanquan Wang
- School of Computer Science and Technology, Harbin Institute of Technology, Harbin, China
| | - Weijian Shen
- Department of Physics and Astronomy, Biological Physics Group, School of Physics & Astronomy, The University of Manchester, Manchester, United Kingdom
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Yamada N, Asano Y, Fujita M, Yamazaki S, Inanobe A, Matsuura N, Kobayashi H, Ohno S, Ebana Y, Tsukamoto O, Ishino S, Takuwa A, Kioka H, Yamashita T, Hashimoto N, Zankov DP, Shimizu A, Asakura M, Asanuma H, Kato H, Nishida Y, Miyashita Y, Shinomiya H, Naiki N, Hayashi K, Makiyama T, Ogita H, Miura K, Ueshima H, Komuro I, Yamagishi M, Horie M, Kawakami K, Furukawa T, Koizumi A, Kurachi Y, Sakata Y, Minamino T, Kitakaze M, Takashima S. Mutant KCNJ3 and KCNJ5 Potassium Channels as Novel Molecular Targets in Bradyarrhythmias and Atrial Fibrillation. Circulation 2020; 139:2157-2169. [PMID: 30764634 DOI: 10.1161/circulationaha.118.036761] [Citation(s) in RCA: 46] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Bradyarrhythmia is a common clinical manifestation. Although the majority of cases are acquired, genetic analysis of families with bradyarrhythmia has identified a growing number of causative gene mutations. Because the only ultimate treatment for symptomatic bradyarrhythmia has been invasive surgical implantation of a pacemaker, the discovery of novel therapeutic molecular targets is necessary to improve prognosis and quality of life. METHODS We investigated a family containing 7 individuals with autosomal dominant bradyarrhythmias of sinus node dysfunction, atrial fibrillation with slow ventricular response, and atrioventricular block. To identify the causative mutation, we conducted the family-based whole exome sequencing and genome-wide linkage analysis. We characterized the mutation-related mechanisms based on the pathophysiology in vitro. After generating a transgenic animal model to confirm the human phenotypes of bradyarrhythmia, we also evaluated the efficacy of a newly identified molecular-targeted compound to upregulate heart rate in bradyarrhythmias by using the animal model. RESULTS We identified one heterozygous mutation, KCNJ3 c.247A>C, p.N83H, as a novel cause of hereditary bradyarrhythmias in this family. KCNJ3 encodes the inwardly rectifying potassium channel Kir3.1, which combines with Kir3.4 (encoded by KCNJ5) to form the acetylcholine-activated potassium channel ( IKACh channel) with specific expression in the atrium. An additional study using a genome cohort of 2185 patients with sporadic atrial fibrillation revealed another 5 rare mutations in KCNJ3 and KCNJ5, suggesting the relevance of both genes to these arrhythmias. Cellular electrophysiological studies revealed that the KCNJ3 p.N83H mutation caused a gain of IKACh channel function by increasing the basal current, even in the absence of m2 muscarinic receptor stimulation. We generated transgenic zebrafish expressing mutant human KCNJ3 in the atrium specifically. It is interesting to note that the selective IKACh channel blocker NIP-151 repressed the increased current and improved bradyarrhythmia phenotypes in the mutant zebrafish. CONCLUSIONS The IKACh channel is associated with the pathophysiology of bradyarrhythmia and atrial fibrillation, and the mutant IKACh channel ( KCNJ3 p.N83H) can be effectively inhibited by NIP-151, a selective IKACh channel blocker. Thus, the IKACh channel might be considered to be a suitable pharmacological target for patients who have bradyarrhythmia with a gain-of-function mutation in the IKACh channel.
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Affiliation(s)
- Noriaki Yamada
- Departments of Cardiovascular Medicine (N.Y., Y.A., A.T., H. Kioka, Y.M., H.S., Y.S.), Osaka University Graduate School of Medicine, Suita, Japan
| | - Yoshihiro Asano
- Departments of Cardiovascular Medicine (N.Y., Y.A., A.T., H. Kioka, Y.M., H.S., Y.S.), Osaka University Graduate School of Medicine, Suita, Japan
| | - Masashi Fujita
- Department of Onco-cardiology, Osaka International Cancer Institute, Japan (M.F.)
| | - Satoru Yamazaki
- Departments of Cell Biology (S.Y.), National Cerebral and Cardiovascular Center, Suita, Japan
| | - Atsushi Inanobe
- Pharmacology (A.I., Y.K.), Osaka University Graduate School of Medicine, Suita, Japan
| | - Norio Matsuura
- Departments of Health and Environmental Sciences (N.M.), Kyoto University Graduate School of Medicine, Japan
| | - Hatasu Kobayashi
- Department of Biomedical Sciences, College of Life and Health Sciences Chubu University, Kasugai, Japan (H. Kobayashi)
| | - Seiko Ohno
- Bioscience and Genetics (S.O.), National Cerebral and Cardiovascular Center, Suita, Japan.,Center for Epidemiologic Research in Asia (S.O., K.M., H.U., M.H.), Shiga University of Medical Science, Otsu, Japan
| | - Yusuke Ebana
- Life Science and Bioethics Research Center (Y.E.), Tokyo Medical and Dental University, Japan
| | - Osamu Tsukamoto
- Medical Biochemistry (O.T., H. Kato, Y.N., S.T.), Osaka University Graduate School of Medicine, Suita, Japan
| | - Saki Ishino
- Center of Medical Innovation and Translational Research (S.I.), Osaka University Graduate School of Medicine, Suita, Japan
| | - Ayako Takuwa
- Departments of Cardiovascular Medicine (N.Y., Y.A., A.T., H. Kioka, Y.M., H.S., Y.S.), Osaka University Graduate School of Medicine, Suita, Japan
| | - Hidetaka Kioka
- Departments of Cardiovascular Medicine (N.Y., Y.A., A.T., H. Kioka, Y.M., H.S., Y.S.), Osaka University Graduate School of Medicine, Suita, Japan
| | - Toru Yamashita
- Pharmaceuticals Division, Nissan Chemical Corporation, Tokyo, Japan (T.Y., N.H.)
| | - Norio Hashimoto
- Pharmaceuticals Division, Nissan Chemical Corporation, Tokyo, Japan (T.Y., N.H.)
| | - Dimitar P Zankov
- Division of Molecular Medical Biochemistry, Department of Biochemistry and Molecular Biology (D.P.Z., A.S., H.O.), Shiga University of Medical Science, Otsu, Japan
| | - Akio Shimizu
- Division of Molecular Medical Biochemistry, Department of Biochemistry and Molecular Biology (D.P.Z., A.S., H.O.), Shiga University of Medical Science, Otsu, Japan
| | - Masanori Asakura
- Cardiovascular Division, Department of Internal Medicine, Hyogo College of Medicine, Nishinomiya, Japan (M.A.)
| | - Hiroshi Asanuma
- Department of Internal Medicine, Meiji University of Integrative Medicine, Nantan, Japan (H.A.)
| | - Hisakazu Kato
- Medical Biochemistry (O.T., H. Kato, Y.N., S.T.), Osaka University Graduate School of Medicine, Suita, Japan
| | - Yuya Nishida
- Medical Biochemistry (O.T., H. Kato, Y.N., S.T.), Osaka University Graduate School of Medicine, Suita, Japan
| | - Yohei Miyashita
- Departments of Cardiovascular Medicine (N.Y., Y.A., A.T., H. Kioka, Y.M., H.S., Y.S.), Osaka University Graduate School of Medicine, Suita, Japan
| | - Haruki Shinomiya
- Departments of Cardiovascular Medicine (N.Y., Y.A., A.T., H. Kioka, Y.M., H.S., Y.S.), Osaka University Graduate School of Medicine, Suita, Japan
| | - Nobu Naiki
- Departments of Cardiovascular Medicine (N.N., M.H.), Shiga University of Medical Science, Otsu, Japan
| | - Kenshi Hayashi
- Department of Cardiovascular and Internal Medicine, Kanazawa University Graduate School of Medicine, Kanazawa, Japan (K.H., M.Y.)
| | - Takeru Makiyama
- Cardiovascular Medicine (T. Makiyama), Kyoto University Graduate School of Medicine, Japan
| | - Hisakazu Ogita
- Division of Molecular Medical Biochemistry, Department of Biochemistry and Molecular Biology (D.P.Z., A.S., H.O.), Shiga University of Medical Science, Otsu, Japan
| | - Katsuyuki Miura
- Center for Epidemiologic Research in Asia (S.O., K.M., H.U., M.H.), Shiga University of Medical Science, Otsu, Japan.,Public Health (K.M., H.U.), Shiga University of Medical Science, Otsu, Japan
| | - Hirotsugu Ueshima
- Center for Epidemiologic Research in Asia (S.O., K.M., H.U., M.H.), Shiga University of Medical Science, Otsu, Japan.,Public Health (K.M., H.U.), Shiga University of Medical Science, Otsu, Japan
| | - Issei Komuro
- Department of Cardiovascular Medicine, The University of Tokyo Graduate School of Medicine, Japan (I.K.)
| | - Masakazu Yamagishi
- Department of Cardiovascular and Internal Medicine, Kanazawa University Graduate School of Medicine, Kanazawa, Japan (K.H., M.Y.).,Department of Human Sciences, Osaka University of Human Sciences, Settsu, Japan (M.Y.)
| | - Minoru Horie
- Center for Epidemiologic Research in Asia (S.O., K.M., H.U., M.H.), Shiga University of Medical Science, Otsu, Japan.,Departments of Cardiovascular Medicine (N.N., M.H.), Shiga University of Medical Science, Otsu, Japan
| | - Koichi Kawakami
- Division of Molecular and Developmental Biology, National Institute of Genetics, Mishima, Japan (K.K.).,Department of Genetics, SOKENDAI (The Graduate University for Advanced Studies), Mishima, Japan (K.K.)
| | - Tetsushi Furukawa
- Department of Bioinformational Pharmacology (T.F.), Tokyo Medical and Dental University, Japan
| | - Akio Koizumi
- Public Interest Foundation Kyoto Hokenkai, Japan (A.K.)
| | - Yoshihisa Kurachi
- Pharmacology (A.I., Y.K.), Osaka University Graduate School of Medicine, Suita, Japan
| | - Yasushi Sakata
- Departments of Cardiovascular Medicine (N.Y., Y.A., A.T., H. Kioka, Y.M., H.S., Y.S.), Osaka University Graduate School of Medicine, Suita, Japan
| | - Tetsuo Minamino
- Department of Cardiorenal and Cerebrovascular Medicine, Faculty of Medicine, Kagawa University, Japan (T. Minamino)
| | - Masafumi Kitakaze
- Clinical Medicine and Development (M.K.), National Cerebral and Cardiovascular Center, Suita, Japan
| | - Seiji Takashima
- Medical Biochemistry (O.T., H. Kato, Y.N., S.T.), Osaka University Graduate School of Medicine, Suita, Japan
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8
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Ashton JL, Trew ML, LeGrice IJ, Paterson DJ, Paton JF, Gillis AM, Smaill BH. Shift of leading pacemaker site during reflex vagal stimulation and altered electrical source-to-sink balance. J Physiol 2019; 597:3297-3313. [PMID: 31087820 DOI: 10.1113/jp276876] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2019] [Accepted: 04/30/2019] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Vagal reflexes slow heart rate and can change where the heartbeat originates within the sinoatrial node (SAN). The mechanisms responsible for this process - termed leading pacemaker (LP) shift - have not been investigated fully. We used optical mapping to measure the effects of baroreflex, chemoreflex and carbachol on pacemaker entrainment and electrical conduction across the SAN. All methods of stimulation triggered shifts in LP site from the central SAN to one or two caudal pacemaker regions. These shifts were associated with reduced current generation capacity centrally and increased electrical load caudally. Previous studies suggest LP shift is a rate-dependent phenomenon whereby acetylcholine slows central pacemaker rate disproportionately, enabling caudal cells that are less acetylcholine sensitive to assume control. However, our findings indicate the LP region is defined by both pacemaker rate and capacity to drive activation. Shifts in LP site provide an important homeostatic mechanism for rapid switches in heart rate. ABSTRACT Reflex vagal activity causes abrupt heart rate slowing with concomitant caudal shifts of the leading pacemaker (LP) site within the sinoatrial node (SAN). However, neither the mechanisms responsible nor their dynamics have been investigated fully. Therefore, the objective of this study was to elucidate the mechanisms driving cholinergic LP shift. Optical maps of right atrial activation were acquired in a rat working heart-brainstem preparation during baroreflex and chemoreflex stimulation or with carbachol. All methods of stimulation triggered shifts in LP site from the central SAN to caudal pacemaker regions, which were positive for HCN4 and received uniform cholinergic innervation. During baroreflex onset, the capacity of the central region to drive activation declined with a decrease in amplitude and gradient of optical action potentials (OAPs) in the surrounding myocardium. Accompanying this decline, there was altered entrainment in the caudal SAN as shown by decreased conduction velocity, OAP amplitude, gradient and activation time. Atropine abolished these responses. Chemoreflex stimulation produced similar effects but central capacity to drive activation was preserved before the LP shift. In contrast, carbachol produced a prolonged period of reduced capacity to drive and altered entrainment. Previous studies suggest LP shift is a rate-dependent phenomenon whereby acetylcholine slows central pacemaker rate disproportionately, enabling caudal cells that are less acetylcholine sensitive to assume control. Our findings indicate that cholinergic LP shifts are also determined by altered electrical source-to-sink balance in the SAN. We conclude that the LP region is defined by both rate and capacity to drive atrial activation.
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Affiliation(s)
| | - Mark L Trew
- University of Auckland, Auckland, New Zealand
| | | | | | | | - Anne M Gillis
- University of Calgary - Libin Cardiovascular Institute of Alberta, Calgary, AB, Canada
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Nobles M, Montaigne D, Sebastian S, Birnbaumer L, Tinker A. Differential effects of inhibitory G protein isoforms on G protein-gated inwardly rectifying K + currents in adult murine atria. Am J Physiol Cell Physiol 2018; 314:C616-C626. [PMID: 29342363 DOI: 10.1152/ajpcell.00271.2016] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
G protein-gated inwardly rectifying K+ (GIRK) channels are the major inwardly rectifying K+ currents in cardiac atrial myocytes and an important determinant of atrial electrophysiology. Inhibitory G protein α-subunits can both mediate activation via acetylcholine but can also suppress basal currents in the absence of agonist. We studied this phenomenon using whole cell patch clamping in murine atria from mice with global genetic deletion of Gαi2, combined deletion of Gαi1/Gαi3, and littermate controls. We found that mice with deletion of Gαi2 had increased basal and agonist-activated currents, particularly in the right atria while in contrast those with Gαi1/Gαi3 deletion had reduced currents. Mice with global genetic deletion of Gαi2 had decreased action potential duration. Tissue preparations of the left atria studied with a multielectrode array from Gαi2 knockout mice showed a shorter effective refractory period, with no change in conduction velocity, than littermate controls. Transcriptional studies revealed increased expression of GIRK channel subunit genes in Gαi2 knockout mice. Thus different G protein isoforms have differential effects on GIRK channel behavior and paradoxically Gαi2 act to increase basal and agonist-activated GIRK currents. Deletion of Gαi2 is potentially proarrhythmic in the atria.
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Affiliation(s)
- Muriel Nobles
- The Heart Centre, William Harvey Research Institute, Barts and the London School of Medicine and Dentistry , London , United Kingdom
| | - David Montaigne
- Centre Hospitalier Régional Universitaire de Lille , Lille , France.,Université Lille 2 , Lille , France.,Institut National de la Santé et de la Recherche Médicale, U1011, Lille , France.,European Genomic Institute for Diabetes , Lille , France.,Institut Pasteur de Lille , Lille , France
| | - Sonia Sebastian
- The Heart Centre, William Harvey Research Institute, Barts and the London School of Medicine and Dentistry , London , United Kingdom
| | - Lutz Birnbaumer
- Division of Intramural Research, National Institute of Environmental Health Sciences , Research Triangle Park, North Carolina.,Institute of Biomedical Research, Catholic University of Argentina , Buenos Aires , Argentina
| | - Andrew Tinker
- The Heart Centre, William Harvey Research Institute, Barts and the London School of Medicine and Dentistry , London , United Kingdom
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Abramochkin DV, Karimova VM, Filatova TS, Kamkin A. Diadenosine pentaphosphate affects electrical activity in guinea pig atrium via activation of potassium acetylcholine-dependent inward rectifier. J Physiol Sci 2017; 67:523-529. [PMID: 27942993 PMCID: PMC10717602 DOI: 10.1007/s12576-016-0510-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2016] [Accepted: 11/30/2016] [Indexed: 11/25/2022]
Abstract
Diadenosine pentaphosphate (Ap5A) belongs to the family of diadenosine polyphosphates, endogenously produced compounds that affect vascular tone and cardiac performance when released from platelets. The previous findings indicate that Ap5A shortens action potentials (APs) in rat myocardium via activation of purine P2 receptors. The present study demonstrates alternative mechanism of Ap5A electrophysiological effects found in guinea pig myocardium. Ap5A (10-4 M) shortens APs in guinea pig working atrial myocardium and slows down pacemaker activity in the sinoatrial node. P1 receptors antagonist DPCPX (10-7 M) or selective GIRK channels blocker tertiapin (10-6 M) completely abolished all Ap5A effects, while P2 blocker PPADS (10-4 M) was ineffective. Patch-clamp experiments revealed potassium inward rectifier current activated by Ap5A in guinea pig atrial myocytes. The current was abolished by DPCPX or tertiapin and therefore was considered as potassium acetylcholine-dependent inward rectifier (I KACh). Thus, unlike rat, in guinea pig atrium Ap5A produces activation of P1 receptors and subsequent opening of KACh channels leading to negative effects on cardiac electrical activity.
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Affiliation(s)
- Denis V Abramochkin
- Department of Human and Animal Physiology, Lomonosov Moscow State University, Leninskiye Gory, 1, 12, Moscow, Russia.
- Department of Physiology, Pirogov Russian National Research Medical University, Moscow, Russia.
| | - Viktoria M Karimova
- Department of Human and Animal Physiology, Lomonosov Moscow State University, Leninskiye Gory, 1, 12, Moscow, Russia
| | - Tatiana S Filatova
- Department of Human and Animal Physiology, Lomonosov Moscow State University, Leninskiye Gory, 1, 12, Moscow, Russia
| | - Andre Kamkin
- Department of Physiology, Pirogov Russian National Research Medical University, Moscow, Russia
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Holmes AP, Yu TY, Tull S, Syeda F, Kuhlmann SM, O’Brien SM, Patel P, Brain KL, Pavlovic D, Brown NA, Fabritz L, Kirchhof P. A Regional Reduction in Ito and IKACh in the Murine Posterior Left Atrial Myocardium Is Associated with Action Potential Prolongation and Increased Ectopic Activity. PLoS One 2016; 11:e0154077. [PMID: 27149380 PMCID: PMC4858288 DOI: 10.1371/journal.pone.0154077] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Accepted: 04/10/2016] [Indexed: 11/22/2022] Open
Abstract
Background The left atrial posterior wall (LAPW) is potentially an important area for the development and maintenance of atrial fibrillation. We assessed whether there are regional electrical differences throughout the murine left atrial myocardium that could underlie regional differences in arrhythmia susceptibility. Methods We used high-resolution optical mapping and sharp microelectrode recordings to quantify regional differences in electrical activation and repolarisation within the intact, superfused murine left atrium and quantified regional ion channel mRNA expression by Taqman Low Density Array. We also performed selected cellular electrophysiology experiments to validate regional differences in ion channel function. Results Spontaneous ectopic activity was observed during sustained 1Hz pacing in 10/19 intact LA and this was abolished following resection of LAPW (0/19 resected LA, P<0.001). The source of the ectopic activity was the LAPW myocardium, distinct from the pulmonary vein sleeve and LAA, determined by optical mapping. Overall, LAPW action potentials (APs) were ca. 40% longer than the LAA and this region displayed more APD heterogeneity. mRNA expression of Kcna4, Kcnj3 and Kcnj5 was lower in the LAPW myocardium than in the LAA. Cardiomyocytes isolated from the LAPW had decreased Ito and a reduced IKACh current density at both positive and negative test potentials. Conclusions The murine LAPW myocardium has a different electrical phenotype and ion channel mRNA expression profile compared with other regions of the LA, and this is associated with increased ectopic activity. If similar regional electrical differences are present in the human LA, then the LAPW may be a potential future target for treatment of atrial fibrillation.
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Affiliation(s)
- Andrew P. Holmes
- Institute of Cardiovascular Science, University of Birmingham, Birmingham, United Kingdom
| | - Ting Y. Yu
- Institute of Cardiovascular Science, University of Birmingham, Birmingham, United Kingdom
- Physical Sciences of Imaging in the Biomedical Sciences, School of Chemistry, College of Engineering Physical Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Samantha Tull
- Institute of Cardiovascular Science, University of Birmingham, Birmingham, United Kingdom
| | - Fahima Syeda
- Institute of Cardiovascular Science, University of Birmingham, Birmingham, United Kingdom
| | - Stefan M. Kuhlmann
- Institute of Cardiovascular Science, University of Birmingham, Birmingham, United Kingdom
| | - Sian-Marie O’Brien
- Institute of Cardiovascular Science, University of Birmingham, Birmingham, United Kingdom
| | - Pushpa Patel
- Institute of Cardiovascular Science, University of Birmingham, Birmingham, United Kingdom
| | - Keith L. Brain
- Institute of Cardiovascular Science, University of Birmingham, Birmingham, United Kingdom
| | - Davor Pavlovic
- Institute of Cardiovascular Science, University of Birmingham, Birmingham, United Kingdom
| | - Nigel A. Brown
- St George’s, University of London, London, United Kingdom
| | - Larissa Fabritz
- Institute of Cardiovascular Science, University of Birmingham, Birmingham, United Kingdom
- Department of Cardiovascular Medicine, Hospital of the University of Münster, Münster, Germany
- University Hospitals Birmingham NHS Foundation Trust, Birmingham, United Kingdom
- * E-mail:
| | - Paulus Kirchhof
- Institute of Cardiovascular Science, University of Birmingham, Birmingham, United Kingdom
- Department of Cardiovascular Medicine, Hospital of the University of Münster, Münster, Germany
- University Hospitals Birmingham NHS Foundation Trust, Birmingham, United Kingdom
- Sandwell and West Birmingham Hospitals NHS Trust, Birmingham, United Kingdom
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Tomson TT, Arora R. Modulation of Cardiac Potassium Current by Neural Tone and Ischemia. Card Electrophysiol Clin 2016; 8:349-60. [PMID: 27261826 DOI: 10.1016/j.ccep.2016.01.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The cardiac action potential is generated by intricate flows of ions across myocyte cell membranes in a coordinated fashion to control myocardial contraction and the heart rhythm. Modulation of the flow of these ions in response to a variety of stimuli results in changes to the action potential. Abnormal or altered ion currents can result in cardiac arrhythmias. Abnormalities of autonomic regulation of potassium current play a role in the genesis of cardiac arrhythmias, and alterations in acetylcholine-activated potassium channels may play a key role in atrial fibrillation. Ischemia is another important modulator of cardiac cellular electrophysiology.
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Affiliation(s)
- Todd T Tomson
- Bluhm Cardiovascular Institute, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
| | - Rishi Arora
- Bluhm Cardiovascular Institute, Northwestern University Feinberg School of Medicine, Chicago, IL, USA.
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13
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Bragança B, Oliveira-Monteiro N, Ferreirinha F, Lima PA, Faria M, Fontes-Sousa AP, Correia-de-Sá P. Ion Fluxes through KCa2 (SK) and Cav1 (L-type) Channels Contribute to Chronoselectivity of Adenosine A1 Receptor-Mediated Actions in Spontaneously Beating Rat Atria. Front Pharmacol 2016; 7:45. [PMID: 27014060 PMCID: PMC4780064 DOI: 10.3389/fphar.2016.00045] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2015] [Accepted: 02/18/2016] [Indexed: 11/24/2022] Open
Abstract
Impulse generation in supraventricular tissue is inhibited by adenosine and acetylcholine via the activation of A1 and M2 receptors coupled to inwardly rectifying GIRK/KIR3.1/3.4 channels, respectively. Unlike M2 receptors, bradycardia produced by A1 receptors activation predominates over negative inotropy. Such difference suggests that other ion currents may contribute to adenosine chronoselectivity. In isolated spontaneously beating rat atria, blockade of KCa2/SK channels with apamin and Cav1 (L-type) channels with nifedipine or verapamil, sensitized atria to the negative inotropic action of the A1 agonist, R-PIA, without affecting the nucleoside negative chronotropy. Patch-clamp experiments in the whole-cell configuration mode demonstrate that adenosine, via A1 receptors, activates the inwardly-rectifying GIRK/KIR3.1/KIR3.4 current resulting in hyperpolarization of atrial cardiomyocytes, which may slow down heart rate. Conversely, the nucleoside inactivates a small conductance Ca2+-activated KCa2/SK outward current, which eventually reduces the repolarizing force and thereby prolong action potentials duration and Ca2+ influx into cardiomyocytes. Immunolocalization studies showed that differences in A1 receptors distribution between the sinoatrial node and surrounding cardiomyocytes do not afford a rationale for adenosine chronoselectivity. Immunolabelling of KIR3.1, KCa2.2, KCa2.3, and Cav1 was also observed throughout the right atrium. Functional data indicate that while both A1 and M2 receptors favor the opening of GIRK/KIR3.1/3.4 channels modulating atrial chronotropy, A1 receptors may additionally restrain KCa2/SK activation thereby compensating atrial inotropic depression by increasing the time available for Ca2+ influx through Cav1 (L-type) channels.
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Affiliation(s)
- Bruno Bragança
- Laboratório de Farmacologia e Neurobiologia - Center for Drug Discovery and Innovative Medicines (MedInUP), Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto (UP) Porto, Portugal
| | - Nádia Oliveira-Monteiro
- Laboratório de Farmacologia e Neurobiologia - Center for Drug Discovery and Innovative Medicines (MedInUP), Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto (UP) Porto, Portugal
| | - Fátima Ferreirinha
- Laboratório de Farmacologia e Neurobiologia - Center for Drug Discovery and Innovative Medicines (MedInUP), Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto (UP) Porto, Portugal
| | - Pedro A Lima
- Departamento de Química e Bioquímica, Faculdade de Ciências, Centro de Química e Bioquímica, Universidade de Lisboa Lisboa, Portugal
| | - Miguel Faria
- Laboratório de Farmacologia e Neurobiologia - Center for Drug Discovery and Innovative Medicines (MedInUP), Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto (UP) Porto, Portugal
| | - Ana P Fontes-Sousa
- Laboratório de Farmacologia e Neurobiologia - Center for Drug Discovery and Innovative Medicines (MedInUP), Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto (UP) Porto, Portugal
| | - Paulo Correia-de-Sá
- Laboratório de Farmacologia e Neurobiologia - Center for Drug Discovery and Innovative Medicines (MedInUP), Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto (UP) Porto, Portugal
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14
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Krishnaswamy PS, Egom EE, Moghtadaei M, Jansen HJ, Azer J, Bogachev O, Mackasey M, Robbins C, Rose RA. Altered parasympathetic nervous system regulation of the sinoatrial node in Akita diabetic mice. J Mol Cell Cardiol 2015; 82:125-35. [DOI: 10.1016/j.yjmcc.2015.02.024] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/06/2014] [Revised: 02/21/2015] [Accepted: 02/26/2015] [Indexed: 11/26/2022]
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15
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Davies L, Jin J, Shen W, Tsui H, Shi Y, Wang Y, Zhang Y, Hao G, Wu J, Chen S, Fraser JA, Dong N, Christoffels V, Ravens U, Huang CL, Zhang H, Cartwright EJ, Wang X, Lei M. Mkk4 is a negative regulator of the transforming growth factor beta 1 signaling associated with atrial remodeling and arrhythmogenesis with age. J Am Heart Assoc 2014; 3:e000340. [PMID: 24721794 PMCID: PMC4187508 DOI: 10.1161/jaha.113.000340] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/20/2013] [Accepted: 01/07/2014] [Indexed: 12/19/2022]
Abstract
BACKGROUND Atrial fibrillation (AF), often associated with structural, fibrotic change in cardiac tissues involving regulatory signaling mediators, becomes increasingly common with age. In the present study, we explored the role of mitogen-activated protein kinase kinase 4 (Mkk4), a critical component of the stress-activated mitogen-activated protein kinase family, in age-associated AF. METHODS AND RESULTS We developed a novel mouse model with a selective inactivation of atrial cardiomyocyte Mkk4 (Mkk4(ACKO)). We characterized and compared electrophysiological, histological, and molecular features of young (3- to 4-month), adult (6-month), and old (1-year) Mkk4(ACKO) mice with age-matched control littermates (Mkk4(F/F)). Aging Mkk4(ACKO) mice were more susceptible to atrial tachyarrhythmias than the corresponding Mkk4(F/F) mice, showing characteristic slow and dispersed atrial conduction, for which modeling studies demonstrated potential arrhythmic effects. These differences paralleled increased interstitial fibrosis, upregulated transforming growth factor beta 1 (TGF-β1) signaling and dysregulation of matrix metalloproteinases in Mkk4(ACKO), compared to Mkk4(F/F), atria. Mkk4 inactivation increased the sensitivity of cultured cardiomyocytes to angiotensin II-induced activation of TGF-β1 signaling. This, in turn, enhanced expression of profibrotic molecules in cultured cardiac fibroblasts, suggesting cross-talk between these two cell types in profibrotic signaling. Finally, human atrial tissues in AF showed a Mkk4 downregulation associated with increased production of profibrotic molecules, compared to findings in tissue from control subjects in sinus rhythm. CONCLUSIONS These findings together demonstrate, for the first time, that Mkk4 is a negative regulator of the TGF-β1 signaling associated with atrial remodeling and arrhythmogenesis with age, establishing Mkk4 as a new potential therapeutic target for treating AF.
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Affiliation(s)
- Laura Davies
- Institute of Cardiovascular Sciences, Faculty of Medicine and Human Sciences, University of Manchester, Manchester, UK (L.D., J.J., H.T., Y.W., Y.Z., G.H., E.J.C., M.L.)
| | - Jiawei Jin
- Institute of Cardiovascular Sciences, Faculty of Medicine and Human Sciences, University of Manchester, Manchester, UK (L.D., J.J., H.T., Y.W., Y.Z., G.H., E.J.C., M.L.)
- Faculty of Life Science, University of Manchester, Manchester, UK (J.J., X.W.)
| | - Weijin Shen
- School of Physics and Astronomy, University of Manchester, Manchester, UK (W.S., H.Z.)
| | - Hoyee Tsui
- Institute of Cardiovascular Sciences, Faculty of Medicine and Human Sciences, University of Manchester, Manchester, UK (L.D., J.J., H.T., Y.W., Y.Z., G.H., E.J.C., M.L.)
| | - Ying Shi
- Institute for Cardiovascular Diseases, Union Hospital, Huazhong University of Science and Technology, Wuhan, China (Y.S., J.W., S.C., N.D., M.L.)
| | - Yanwen Wang
- Institute of Cardiovascular Sciences, Faculty of Medicine and Human Sciences, University of Manchester, Manchester, UK (L.D., J.J., H.T., Y.W., Y.Z., G.H., E.J.C., M.L.)
| | - Yanmin Zhang
- Institute of Cardiovascular Sciences, Faculty of Medicine and Human Sciences, University of Manchester, Manchester, UK (L.D., J.J., H.T., Y.W., Y.Z., G.H., E.J.C., M.L.)
| | - Guoliang Hao
- Institute of Cardiovascular Sciences, Faculty of Medicine and Human Sciences, University of Manchester, Manchester, UK (L.D., J.J., H.T., Y.W., Y.Z., G.H., E.J.C., M.L.)
| | - Jingjing Wu
- Institute for Cardiovascular Diseases, Union Hospital, Huazhong University of Science and Technology, Wuhan, China (Y.S., J.W., S.C., N.D., M.L.)
| | - Si Chen
- Institute for Cardiovascular Diseases, Union Hospital, Huazhong University of Science and Technology, Wuhan, China (Y.S., J.W., S.C., N.D., M.L.)
| | - James A. Fraser
- Physiological Laboratory, University of Cambridge, Cambridge, UK (J.A.F., C.L.H.)
| | - Nianguo Dong
- Institute for Cardiovascular Diseases, Union Hospital, Huazhong University of Science and Technology, Wuhan, China (Y.S., J.W., S.C., N.D., M.L.)
| | - Vincent Christoffels
- Department of Anatomy & Embryology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands (V.C.)
| | - Ursula Ravens
- Department of Pharmacology and Toxicology, Medical Faculty, Dresden University of Technology, Dresden, Germany (U.R.)
| | | | - Henggui Zhang
- School of Physics and Astronomy, University of Manchester, Manchester, UK (W.S., H.Z.)
| | - Elizabeth J. Cartwright
- Institute of Cardiovascular Sciences, Faculty of Medicine and Human Sciences, University of Manchester, Manchester, UK (L.D., J.J., H.T., Y.W., Y.Z., G.H., E.J.C., M.L.)
| | - Xin Wang
- Faculty of Life Science, University of Manchester, Manchester, UK (J.J., X.W.)
| | - Ming Lei
- Institute of Cardiovascular Sciences, Faculty of Medicine and Human Sciences, University of Manchester, Manchester, UK (L.D., J.J., H.T., Y.W., Y.Z., G.H., E.J.C., M.L.)
- Institute for Cardiovascular Diseases, Union Hospital, Huazhong University of Science and Technology, Wuhan, China (Y.S., J.W., S.C., N.D., M.L.)
- Department of Pharmacology, University of Oxford, Mansfield Road, UK (M.L.)
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16
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Mesirca P, Marger L, Toyoda F, Rizzetto R, Audoubert M, Dubel S, Torrente AG, Difrancesco ML, Muller JC, Leoni AL, Couette B, Nargeot J, Clapham DE, Wickman K, Mangoni ME. The G-protein-gated K+ channel, IKACh, is required for regulation of pacemaker activity and recovery of resting heart rate after sympathetic stimulation. ACTA ACUST UNITED AC 2013; 142:113-26. [PMID: 23858001 PMCID: PMC3727310 DOI: 10.1085/jgp.201310996] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Parasympathetic regulation of sinoatrial node (SAN) pacemaker activity modulates multiple ion channels to temper heart rate. The functional role of the G-protein–activated K+ current (IKACh) in the control of SAN pacemaking and heart rate is not completely understood. We have investigated the functional consequences of loss of IKACh in cholinergic regulation of pacemaker activity of SAN cells and in heart rate control under physiological situations mimicking the fight or flight response. We used knockout mice with loss of function of the Girk4 (Kir3.4) gene (Girk4−/− mice), which codes for an integral subunit of the cardiac IKACh channel. SAN pacemaker cells from Girk4−/− mice completely lacked IKACh. Loss of IKACh strongly reduced cholinergic regulation of pacemaker activity of SAN cells and isolated intact hearts. Telemetric recordings of electrocardiograms of freely moving mice showed that heart rate measured over a 24-h recording period was moderately increased (10%) in Girk4−/− animals. Although the relative extent of heart rate regulation of Girk4−/− mice was similar to that of wild-type animals, recovery of resting heart rate after stress, physical exercise, or pharmacological β-adrenergic stimulation of SAN pacemaking was significantly delayed in Girk4−/− animals. We conclude that IKACh plays a critical role in the kinetics of heart rate recovery to resting levels after sympathetic stimulation or after direct β-adrenergic stimulation of pacemaker activity. Our study thus uncovers a novel role for IKACh in SAN physiology and heart rate regulation.
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Affiliation(s)
- Pietro Mesirca
- Centre National de la Recherche Scientifique UMR 5203, Institut de Génomique Fonctionnelle, Département de Physiologie, Laboratoire d'Excellence Canaux Ioniques d'Intérêt Thérapeutique, 34094 Montpellier, France
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17
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Jones DL, Tuomi JM, Chidiac P. Role of Cholinergic Innervation and RGS2 in Atrial Arrhythmia. Front Physiol 2012; 3:239. [PMID: 22754542 PMCID: PMC3386567 DOI: 10.3389/fphys.2012.00239] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2011] [Accepted: 06/12/2012] [Indexed: 01/25/2023] Open
Abstract
The heart receives sympathetic and parasympathetic efferent innervation as well as the ability to process information internally via an intrinsic cardiac autonomic nervous system (ICANS). For over a century, the role of the parasympathetics via vagal acetylcholine release was related to controlling primarily heart rate. Although in the late 1800s shown to play a role in atrial arrhythmia, the myocardium took precedence from the mid-1950s until in the last decade a resurgence of interest in the autonomics along with signaling cascades, regulators, and ion channels. Originally ignored as being benign and thus untreated, recent emphasis has focused on atrial arrhythmia as atrial fibrillation (AF) is the most common arrhythmia seen by the general practitioner. It is now recognized to have significant mortality and morbidity due to resultant stroke and heart failure. With the aging population, there will be an unprecedented increased burden on health care resources. Although it has been known for more than half a century that cholinergic stimulation can initiate AF, the classical concept focused on the M2 receptor and its signaling cascade including RGS4, as these had been shown to have predominant effects on nodal function (heart rate and conduction block) as well as contractility. However, recent evidence suggests that the M3 receptor may also playa role in initiation and perpetuation of AF and thus RGS2, a putative regulator of the M3 receptor, may be a target for therapeutic intervention. Mice lacking RGS2 (RGS2−/−), were found to have significantly altered electrophysiological atrial responses and were more susceptible to electrically induced AF. Vagally induced or programmed stimulation-induced AF could be blocked by the selective M3R antagonist, darifenacin. These results suggest a potential surgical target (ICANS) and pharmacological targets (M3R, RGS2) for the management of AF.
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Affiliation(s)
- Douglas L Jones
- Department of Physiology and Pharmacology, The University of Western Ontario London, ON, Canada
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Kharche S, Yu J, Lei M, Zhang H. A mathematical model of action potentials of mouse sinoatrial node cells with molecular bases. Am J Physiol Heart Circ Physiol 2011; 301:H945-63. [PMID: 21724866 PMCID: PMC3191499 DOI: 10.1152/ajpheart.00143.2010] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Genetically modified mice are popular experimental models for studying the molecular bases and mechanisms of cardiac arrhythmia. A postgenome challenge is to classify the functional roles of genes in cardiac function. To unveil the functional role of various genetic isoforms of ion channels in generating cardiac pacemaking action potentials (APs), a mathematical model for spontaneous APs of mouse sinoatrial node (SAN) cells was developed. The model takes into account the biophysical properties of membrane ionic currents and intracellular mechanisms contributing to spontaneous mouse SAN APs. The model was validated by its ability to reproduce the physiological exceptionally short APs and high pacing rates of mouse SAN cells. The functional roles of individual membrane currents were evaluated by blocking their coding channels. The roles of intracellular Ca2+-handling mechanisms on cardiac pacemaking were also investigated in the model. The robustness of model pacemaking behavior was evaluated by means of one- and two-parameter analyses in wide parameter value ranges. This model provides a predictive tool for cellular level outcomes of electrophysiological experiments. It forms the basis for future model development and further studies into complex pacemaking mechanisms as more quantitative experimental data become available.
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Affiliation(s)
- Sanjay Kharche
- Biological Physics Group, School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom
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Presence and functional role of the rapidly activating delayed rectifier K+ current in left and right atria of adult mice. Eur J Pharmacol 2010; 649:14-22. [DOI: 10.1016/j.ejphar.2010.08.025] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2009] [Revised: 07/24/2010] [Accepted: 08/25/2010] [Indexed: 11/22/2022]
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Voigt N, Trausch A, Knaut M, Matschke K, Varró A, Van Wagoner DR, Nattel S, Ravens U, Dobrev D. Left-to-right atrial inward rectifier potassium current gradients in patients with paroxysmal versus chronic atrial fibrillation. Circ Arrhythm Electrophysiol 2010; 3:472-80. [PMID: 20657029 DOI: 10.1161/circep.110.954636] [Citation(s) in RCA: 160] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
BACKGROUND Recent evidence suggests that atrial fibrillation (AF) is maintained by high-frequency reentrant sources with a left-to-right-dominant frequency gradient, particularly in patients with paroxysmal AF (pAF). Unequal left-to-right distribution of inward rectifier K(+) currents has been suggested to underlie this dominant frequency gradient, but this hypothesis has never been tested in humans. METHODS AND RESULTS Currents were measured with whole-cell voltage-clamp in cardiomyocytes from right atrial (RA) and left (LA) atrial appendages of patients in sinus rhythm (SR) and patients with AF undergoing cardiac surgery. Western blot was used to quantify protein expression of I(K1) (Kir2.1 and Kir2.3) and I(K,ACh) (Kir3.1 and Kir3.4) subunits. Basal current was ≈2-fold larger in chronic AF (cAF) versus SR patients, without RA-LA differences. In pAF, basal current was ≈2-fold larger in LA versus RA, indicating a left-to-right atrial gradient. In both atria, Kir2.1 expression was ≈2-fold greater in cAF but comparable in pAF versus SR. Kir2.3 levels were unchanged in cAF and RA-pAF but showed a 51% decrease in LA-pAF. In SR, carbachol-activated (2 μmol/L) I(K,ACh) was 70% larger in RA versus LA. This right-to-left atrial gradient was decreased in pAF and cAF caused by reduced I(K,ACh) in RA only. Similarly, in SR, Kir3.1 and Kir3.4 proteins were greater in RA versus LA and decreased in RA of pAF and cAF. Kir3.1 and Kir3.4 expression was unchanged in LA of pAF and cAF. CONCLUSION Our results support the hypothesis that a left-to-right gradient in inward rectifier background current contributes to high-frequency sources in LA that maintain pAF. These findings have potentially important implications for development of atrial-selective therapeutic approaches.
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Affiliation(s)
- Niels Voigt
- Department of Pharmacology and Toxicology, Dresden University of Technology, Dresden, Germany
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Zhao Q, Tang Y, Okello E, Wang X, Huang C. Changes in atrial effective refractory period and I(KACh) after vagal stimulation plus rapid pacing in the pulmonary vein. Rev Esp Cardiol 2009; 62:742-9. [PMID: 19709509 DOI: 10.1016/s1885-5857(09)72354-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
INTRODUCTION AND OBJECTIVES Recent studies have shown that rapid atrial pacing causes atrial electrical remodeling. However, the influence of the vagus nerve on atrial electrical remodeling is not clear. METHODS This study involved 24 dogs divided into three groups. In the control group, the inducibility of atrial fibrillation (AF) during vagal stimulation (VS(1)) was investigated. In the pacing group, the atrial effective refractory period (AERP) was determined before and after pacing in the left superior pulmonary vein (LSPV). In the vagal stimulation (VS) plus pacing group, the LSPV was subjected to rapid electrical pacing after vagal stimulation (VS(2)), and the AERP was measured both before VS(2) and after pacing. The I(KACh) density was measured in LSPV and atrial myocardial cells in the three groups using the patch-clamp technique. RESULTS The duration of induced AF was greater in the pacing group than in the control or VS-plus-pacing group. In the pacing group, the AERP was markedly shortened and the AERP dispersion (dAERP) was significantly increased (P< .05). However, there was no significant change in AERP in the VS-plus-pacing group, though the dAERP increased significantly (P< .05). The I(KACh) density was increased in LSPV and atrial myocardial cells after pacing. However, there was no significant change in I(KACh) density after VS(2) plus pacing. CONCLUSIONS Although shortening of the AERP may play a fundamental role, it is not in itself responsible for cholinergically induced AF. Rapid pacing in the LSPV increased the I(KACh). However, VS before rapid pacing partly protected the atria against electrical remodeling.
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Affiliation(s)
- Qingyan Zhao
- Cardiovascular Research Institute of Wuhan University, Renmin Hospital of Wuhan University, People's Republic of China.
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Hara Y, Ike A, Tanida R, Okada M, Yamawaki H. Involvement of Cyclooxygenase-2 in Carbachol-Induced Positive Inotropic Response in Mouse Isolated Left Atrium. J Pharmacol Exp Ther 2009; 331:808-15. [DOI: 10.1124/jpet.109.156992] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Anumonwo JMB, Lopatin AN. Cardiac strong inward rectifier potassium channels. J Mol Cell Cardiol 2009; 48:45-54. [PMID: 19703462 DOI: 10.1016/j.yjmcc.2009.08.013] [Citation(s) in RCA: 111] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/23/2009] [Revised: 08/13/2009] [Accepted: 08/18/2009] [Indexed: 10/20/2022]
Abstract
Cardiac I(K1) and I(KACh) are the major potassium currents displaying classical strong inward rectification, a unique property that is critical for their roles in cardiac excitability. In the last 15 years, research on I(K1) and I(KACh) has been propelled by the cloning of the underlying inwardly rectifying potassium (Kir) channels, the discovery of the molecular mechanism of strong rectification and the linking of a number of disorders of cardiac excitability to defects in genes encoding Kir channels. Disease-causing mutations in Kir genes have been shown experimentally to affect one or more of the following channel properties: structure, assembly, trafficking, and regulation, with the ultimate effect of a gain- or a loss-of-function of the channel. It is now established that I(K1) and I(KACh) channels are heterotetramers of Kir2 and Kir3 subunits, respectively. Each homomeric Kir channel has distinct biophysical and regulatory properties, and individual Kir subunits often display different patterns of regional, cellular, and membrane distribution. These differences are thought to underlie important variations in the physiological properties of I(K1) and I(KACh). It has become increasingly clear that the contribution of I(K1) and I(KACh) channels to cardiac electrical activity goes beyond their long recognized role in the stabilization of resting membrane potential and shaping the late phase of action potential repolarization in individual myocytes but extends to being critical elements determining the overall electrical stability of the heart.
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Affiliation(s)
- Justus M B Anumonwo
- Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109-5622, USA
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Zhao Q, Tang Y, Okello E, Wang X, Huang C. Cambios del periodo refractario efectivo auricular y de la IKACh tras estimulación vagal más estimulación eléctrica rápida en venas pulmonares. Rev Esp Cardiol 2009. [DOI: 10.1016/s0300-8932(09)71687-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Park HJ, Zhang Y, Du C, Welzig CM, Madias C, Aronovitz MJ, Georgescu SP, Naggar I, Wang B, Kim YB, Blaustein RO, Karas RH, Liao R, Mathews CE, Galper JB. Role of SREBP-1 in the development of parasympathetic dysfunction in the hearts of type 1 diabetic Akita mice. Circ Res 2009; 105:287-94. [PMID: 19423844 DOI: 10.1161/circresaha.109.193995] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
RATIONALE Diabetic autonomic neuropathy (DAN), a major complication of diabetes mellitus, is characterized, in part, by impaired cardiac parasympathetic responsiveness. Parasympathetic stimulation of the heart involves activation of an acetylcholine-gated K+ current, I(KAch), via a (GIRK1)2/(GIRK4)2 K+ channel. Sterol regulatory element binding protein-1 (SREBP-1) is a lipid-sensitive transcription factor. OBJECTIVE We describe a unique SREBP-1-dependent mechanism for insulin regulation of cardiac parasympathetic response in a mouse model for DAN. METHODS AND RESULTS Using implantable EKG transmitters, we demonstrated that compared with wild-type, Ins2(Akita) type I diabetic mice demonstrated a decrease in the negative chronotropic response to carbamylcholine characterized by a 2.4-fold decrease in the duration of bradycardia, a 52+/-8% decrease in atrial expression of GIRK1 (P<0.01), and a 31.3+/-2.1% decrease in SREBP-1 (P<0.05). Whole-cell patch-clamp studies of atrial myocytes from Akita mice exhibited a markedly decreased carbamylcholine stimulation of I(KAch) with a peak value of -181+/-31 pA/pF compared with -451+/-62 pA/pF (P<0.01) in cells from wild-type mice. Western blot analysis of extracts of Akita mice demonstrated that insulin treatment increased the expression of GIRK1, SREBP-1, and I(KAch) activity in atrial myocytes from these mice to levels in wild-type mice. Insulin treatment of cultured atrial myocytes stimulated GIRK1 expression 2.68+/-0.12-fold (P<0.01), which was reversed by overexpression of dominant negative SREBP-1. Finally, adenoviral expression of SREBP-1 in Akita atrial myocytes reversed the impaired I(KAch) to levels in cells from wild-type mice. CONCLUSIONS These results support a unique molecular mechanism for insulin regulation of GIRK1 expression and parasympathetic response via SREBP-1, which might play a role in the pathogenesis of DAN in response to insulin deficiency in the diabetic heart.
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Affiliation(s)
- Ho-Jin Park
- Tufts Medical Center, Molecular Cardiology Research Institute, 750 Washington St., Box 8486, Boston, MA 02111, USA.
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Vigmond EJ, Tsoi V, Yin Y, Pagé P, Vinet A. Estimating atrial action potential duration from electrograms. IEEE Trans Biomed Eng 2009; 56:1546-55. [PMID: 19237338 DOI: 10.1109/tbme.2009.2014740] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Electrogram analysis is important in clinical and experimental settings. Activation recovery interval (ARI) has been used to measure ventricular action potential duration (APD) but its suitability for the atria has not been addressed. Mapping of atrial repolarization may be especially important during nerve stimulation since large heterogenous APD changes may manifest. This study assessed the utility of estimating APD in the atria using electrograms. A computer model of the atria was used to compute electrograms. Two different atrial waveforms were used, as well as two ventricular. APD was modulated with an acetylcholine- (ACh) dependent potassium channel and varying the spatial ACh distribution. ARI was computed, as well as the area under the repolarization wave (ATa). APD was measured by four methods. Atrial electrograms were also compared to monophasic action potentials recorded from a dog. ARI computed from atrial action potentials was not very precise, with errors ranging over 30 ms. Determining changes in APD induced by changing [ACh] yielded larger errors. Conversely, ventricular action potentials produced ARIs that very closely correlated with APD, and changes in APD . Positive ATa indicated regions of shortened APD, and islands of ACh release were clearly demarcated by ATa polarity. Experimentally, ARI was able to detect changes in APD, but did not measure APD well. The faster rate of ventricular repolarization produces larger currents that are less susceptible to electrotonic coupling effects, improving correlation with APD. ARI most closely correlated with APD measured as a fixed threshold above rest. Atrial APs produce electrograms that can be used to detect changes in APD. This may be improved by decreasing coupling. The ATa is a robust measure for precisely identifying spatial APD heterogeneities.
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Affiliation(s)
- Edward J Vigmond
- Department of Electrical and Computer Engineering, University of Calgary, Calgary, AB T2N 1N4, Canada.
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Mathematical simulations of ligand-gated and cell-type specific effects on the action potential of human atrium. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2009; 98:161-70. [PMID: 19186188 DOI: 10.1016/j.pbiomolbio.2009.01.010] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In the mammalian heart, myocytes and fibroblasts can communicate via gap junction, or connexin-mediated current flow. Some of the effects of this electrotonic coupling on the action potential waveform of the human ventricular myocyte have been analyzed in detail. The present study employs a recently developed mathematical model of the human atrial myocyte to investigate the consequences of this heterogeneous cell-cell interaction on the action potential of the human atrium. Two independent physiological processes which alter the physiology of the human atrium have been studied. i) The effects of the autonomic transmitter acetylcholine on the atrial action potential have been investigated by inclusion of a time-independent, acetylcholine-activated K(+) current in this mathematical model of the atrial myocyte. ii) A non-selective cation current which is activated by natriuretic peptides has been incorporated into a previously published mathematical model of the cardiac fibroblast. These results identify subtle effects of acetylcholine, which arise from the nonlinear interactions between ionic currents in the human atrial myocyte. They also illustrate marked alterations in the action potential waveform arising from fibroblast-myocyte source-sink principles when the natriuretic peptide-mediated cation conductance is activated. Additional calculations also illustrate the effects of simultaneous activation of both of these cell-type specific conductances within the atrial myocardium. This study provides a basis for beginning to assess the utility of mathematical modeling in understanding detailed cell-cell interactions within the complex paracrine environment of the human atrial myocardium.
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Cifelli C, Rose RA, Zhang H, Voigtlaender-Bolz J, Bolz SS, Backx PH, Heximer SP. RGS4 regulates parasympathetic signaling and heart rate control in the sinoatrial node. Circ Res 2008; 103:527-35. [PMID: 18658048 DOI: 10.1161/circresaha.108.180984] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Heart rate is controlled by the opposing activities of sympathetic and parasympathetic inputs to pacemaker myocytes in the sinoatrial node (SAN). Parasympathetic activity on nodal myocytes is mediated by acetylcholine-dependent stimulation of M(2) muscarinic receptors and activation of Galpha(i/o) signaling. Although regulators of G protein signaling (RGS) proteins are potent inhibitors of Galpha(i/o) signaling in many tissues, the RGS protein(s) that regulate parasympathetic tone in the SAN are unknown. Our results demonstrate that RGS4 mRNA levels are higher in the SAN compared to right atrium. Conscious freely moving RGS4-null mice showed increased bradycardic responses to parasympathetic agonists compared to wild-type animals. Moreover, anesthetized RGS4-null mice had lower baseline heart rates and greater heart rate increases following atropine administration. Retrograde-perfused hearts from RGS4-null mice showed enhanced negative chronotropic responses to carbachol, whereas SAN myocytes showed greater sensitivity to carbachol-mediated reduction in the action potential firing rate. Finally, RGS4-null SAN cells showed decreased levels of G protein-coupled inward rectifying potassium (GIRK) channel desensitization and altered modulation of acetylcholine-sensitive potassium current (I(KACh)) kinetics following carbachol stimulation. Taken together, our studies establish that RGS4 plays an important role in regulating sinus rhythm by inhibiting parasympathetic signaling and I(KACh) activity.
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Affiliation(s)
- Carlo Cifelli
- Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
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Lignon JM, Bichler Z, Hivert B, Gannier FE, Cosnay P, del Rio JA, Migliore-Samour D, Malécot CO. Altered heart rate control in transgenic mice carrying the KCNJ6 gene of the human chromosome 21. Physiol Genomics 2008; 33:230-9. [PMID: 18303085 DOI: 10.1152/physiolgenomics.00143.2007] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Congenital heart defects (CHD) are common in Down syndrome (DS, trisomy 21). Recently, cardiac sympathetic-parasympathetic imbalance has also been documented in DS adults free of any CHD. The KCNJ6 gene located on human chromosome 21 encodes for the Kir3.2/GIRK2 protein subunits of G protein-regulated K(+) (K(G)) channels and could contribute to this altered cardiac regulation. To elucidate the role of its overexpression, we used homozygous transgenic (Tg(+/+)) mice carrying copies of human KCNJ6. These mice showed human Kir3.2 mRNA expression in the heart and a 2.5-fold increased translation in the atria. Phenotypic alterations were assessed by recording electrocardiogram of urethane anesthetized mice. Chronotropic responses to direct (carbachol) and indirect (methoxamine) muscarinic stimulation were enhanced in Tg(+/+) mice with respect to wild-type (WT) mice. Alternating periods of slow and fast rhythm induced by CCPA (2-chloro-N-cyclopentyl-adenosine) were amplified in Tg(+/+) mice, resulting in a reduced negative chronotropic effect. These drugs reduced the atrial P wave amplitude and area. P wave variations induced by methoxamine and CCPA were respectively increased and reduced in the Tg(+/+) mice, while PR interval and ventricular wave showed no difference between Tg(+/+) and WT. These results indicate that Tg(+/+) mice incorporating the human KCNJ6 exhibit altered Kir3.2 expression and responses to drugs that would activate K(G) channels. Moreover, these altered expression and responses are limited to sino-atrial node and atria that normally express large amounts of K(G) channels. These data suggest that KCNJ6 could play an important role in altered cardiac regulation in DS patients.
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Affiliation(s)
- Jacques M Lignon
- Centre National de la Recherche Scientifique Unité Mixte de Recherche 6542, Physiologie des Cellules Cardiaques et Vasculaires, Université François-Rabelais, Parc Grandmont, Tours, France.
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Rose RA, Kabir MG, Backx PH. Altered heart rate and sinoatrial node function in mice lacking the cAMP regulator phosphoinositide 3-kinase-gamma. Circ Res 2007; 101:1274-82. [PMID: 17975110 DOI: 10.1161/circresaha.107.158428] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Ablation of the enzyme phosphoinositide 3-kinase (PI3K)gamma (PI3Kgamma(-/-)) in mice increases cardiac contractility by elevating intracellular cAMP and enhancing sarcoplasmic reticulum Ca(2+) handling. Because cAMP is a critical determinant of heart rate, we investigated whether heart rate is altered in mice lacking PI3Kgamma. Heart rate was similar in anesthetized PI3Kgamma(-/-) and wild-type (PI3Kgamma(+/+)) mice. However, IP injection of atropine (1 mg/kg), propranolol (1 mg/kg), or both drugs in combination unmasked elevated heart rates in PI3Kgamma(-/-) mice, suggesting altered sinoatrial node (SAN) function. Indeed, spontaneous action potential frequency was approximately 35% greater in SAN myocytes isolated from PI3Kgamma(-/-) mice compared with PI3Kgamma(+/+) mice. These differences in action potential frequency were abolished by intracellular dialysis with the cAMP/protein kinase A antagonist Rp-cAMP but were unaffected by treatment with ryanodine to inhibit sarcoplasmic reticulum Ca(2+) release. Voltage-clamp experiments demonstrated that elevated action potential frequencies in PI3Kgamma(-/-) SAN myocytes were more strongly associated with cAMP-dependent increases in L-type Ca(2+) current (I(Ca,L)) than elevated hyperpolarization-activated current (I(f)). In contrast, I(Ca,L) was not increased in working atrial myocytes, suggesting distinct subcellular regulation of L-type Ca(2+) channels by PI3Kgamma in the SAN compared with the working myocardium. In summary, PI3Kgamma regulates heart rate by the cAMP-dependent modulation of SAN function. The effects of PI3Kgamma ablation in the SAN are unique from those in the working myocardium.
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Affiliation(s)
- Robert A Rose
- Department of Physiology, University of Toronto, Ontario, Canada
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Zhao QY, Huang CX, Liang JJ, Chen H, Yang B, Jiang H, Li GS. Effect of vagal stimulation and differential densities of M2 receptor and IK,ACh in canine atria. Int J Cardiol 2007; 126:352-8. [PMID: 17590455 DOI: 10.1016/j.ijcard.2007.04.050] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/03/2006] [Revised: 08/08/2006] [Accepted: 04/02/2007] [Indexed: 11/17/2022]
Abstract
OBJECTIVE We investigated the electrophysiological effect of vagal stimulation (VS) on atrial myocardium in vivo and differential densities of M(2) receptor and acetylcholine-induced inward rectifier K(+) current (I(K,ACh)) to discuss the mechanisms of atrial fibrillation (AF). METHODS With the monophasic action potential (MAP) recording technique, data from twenty-four sites, i.e. right atrial appendage (RAA), left atrial appendage (LAA), right atrium (RA) and left atrium (LA) were recorded by electrode probes, which were applied to the epicardial atrial surface of each dog. After cervical vagosympathetic cut, VS(1) (20 Hz, 0.2 ms pulse duration and at a voltage 10 V), VS(2) (20 Hz, 0.2 ms pulse duration and at a voltage 30 V) and sinus node (SN) damage were administrated respectively. MAP, dispersion of action potential duration (dAPD) and AF was recorded. Then, RAA, LAA, RA and LA were dissected. Finally, distribution of M(2) receptors and I(K,ACh) in atrial myocardium were measured by western blot and patch clamp respectively. RESULTS During VS(1) and VS(2), AF could be induced at first in right atrial appendage (RAA) and right atrium (RA) without left atrial appendage (LAA) and left atrium (LA). Compared to the parameters in control group and VS(2) group, dAPD was increased significantly by VS(1) and SN damage, but there was no significant difference between control group and VS(2) group. However, AF was not evoked after SN damage. Densities of M(2) receptor and I(K,ACh) were higher in RAA, LAA than those in LA and RA (M(2) receptor: 1 and 1.01 over 0.83 and 0.51, P<0.05; I(K,ACh): 20+/-0.89, 19+/-0.82, 14+/-0.64, 9+/-0.45 pA/pF, P<0.05). Furthermore, densities of M(2) receptor and I(K,ACh) were higher in LA than those in RA (P<0.05). CONCLUSIONS Decreased APD is the base in initiation of cholinergic AF by VS and increased dAPD alone can not induce AF. A greater abundance of M(2) receptor and I(KACh) in RAA and LAA imply atrial appendage plays an important role in initiation of cholinergic AF.
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Affiliation(s)
- Qing-Yan Zhao
- Department of Cardiology, Renmin Hospital, Wuhan University School of Medicine, JieFang Road 238, Wuhan 430060, PR China
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Arora R, Ng J, Ulphani J, Mylonas I, Subacius H, Shade G, Gordon D, Morris A, He X, Lu Y, Belin R, Goldberger JJ, Kadish AH. Unique autonomic profile of the pulmonary veins and posterior left atrium. J Am Coll Cardiol 2007; 49:1340-8. [PMID: 17394967 DOI: 10.1016/j.jacc.2006.10.075] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/09/2006] [Revised: 10/23/2006] [Accepted: 10/29/2006] [Indexed: 11/19/2022]
Abstract
OBJECTIVES The purpose of this study was to investigate the electrophysiologic profile of the pulmonary veins (PVs) and left atrium (LA) in response to autonomic manipulation. BACKGROUND The parasympathetic innervation of the PVs and posterior left atrium (PLA) is thought to contribute to focal atrial fibrillation (AF). We hypothesized that autonomic effects would be more prominent in these regions. METHODS In 14 dogs, epicardial mapping was performed in the PVs, PLA, and left atrial appendage (LAA) under the following conditions: baseline, 20-Hz cervical vagal stimulation (VS), propranolol (P), P + VS, and P + atropine. Effective refractory periods (ERPs) were measured, and conduction vectors were computed at multiple sites. Western blotting and immunostaining were performed for IKAch (Kir3.1/3.4). RESULTS The VS and P + VS caused more ERP shortening in the PV and PLA than in the LAA. The P + atropine caused greatest ERP prolongation in the LAA. Cumulative ERP change (ERP difference between P + VS and P + atropine) was greatest in the LAA and corresponded with expression of Kir3.1/3.4 (LAA > PLA > or = PV). The ERP change in response to vagal manipulation was most heterogeneous in the PLA; this corresponded with a pronounced heterogeneity of Kir3.1 distribution in the PLA. With VS and/or P, there was evidence of regional conduction delay in the PVs with a significant change in activation direction. Similar activation changes were not seen in the PLA and LAA. CONCLUSIONS The PVs and PLA demonstrate unique activation and repolarization characteristics in response to autonomic manipulation. The heterogeneity of vagal responses correlates with the pattern of IKAch distribution in the LA. The peculiar autonomic characteristics of the PVs and PLA might create substrate for re-entry and AF.
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Affiliation(s)
- Rishi Arora
- Division of Cardiology and Department of Medicine, Northwestern University-Feinberg School of Medicine, Chicago, Illinois
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Nygren A, Lomax AE, Giles WR. Optical mapping system for recording action potential durations in adult mouse left and right atrium. CONFERENCE PROCEEDINGS : ... ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL CONFERENCE 2007; 2004:3576-7. [PMID: 17271063 DOI: 10.1109/iembs.2004.1404005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
The increasing availability of murine models of the cardiovascular system has created a need for instrumentation and methods for assessing murine cardiovascular function. We have adapted an existing optical mapping system based on voltage-sensitive dyes to record from an isolated mouse atrial preparation. Initial results indicate that our approach is capable of recording action potentials from isolated mouse atria with sufficient signal quality to determine action potential duration (APD). Preliminary observations suggest that gradients in APD exist in the mouse atria and are similar to those observed in the atria of larger mammals. Future work with this technique will provide important information about mouse atrial electrophysiology and how it relates to that of larger mammals.
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Affiliation(s)
- A Nygren
- Department of Physiology & Biophysics, University of Calgary, Canada
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Huang CX, Zhao QY, Liang JJ, Chen H, Yang B, Jiang H, Li GS. Differential Densities of Muscarinic Acetylcholine Receptor and I K,ACh in Canine Supraventricular Tissues and the Effect of Amiodarone on Cholinergic Atrial Fibrillation and I K,ACh. Cardiology 2006; 106:36-43. [PMID: 16612067 DOI: 10.1159/000092597] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/20/2005] [Accepted: 01/24/2006] [Indexed: 11/19/2022]
Abstract
BACKGROUND Vagal nerve plays an important role in the induction and maintenance of atrial fibrillation (AF). This study investigated the differential densities of M2 receptor and acetylcholine-induced inward rectifier K+ current (I(K,ACh)) in atrial appendage, atrium, pulmonary vein (PV) and super vena cava (SVC) to discuss the role of atrial appendage and PV in cholinergic AF. METHODS AND RESULTS In 10 dogs, action potential duration was determined at 24 sites during bilateral cervical vagal stimulation and amiodarone administration. AF could be induced at first in right atrial appendage (RAA) and right atrium (RA) without left atrial appendage (LAA) and left atrium (LA). Amiodarone decreased the initiation of AF in vivo. Western blot and patch clamp were used to determine M2 receptor and I(K,ACh) in RAA, LAA, RA, LA, PV and SVC. The densities of M2 receptor and I(K,ACh) in LAA, RAA and LA were higher than that in RA, PV and SVC (21.34 +/- 0.92 vs. 8.24 +/- 0.45 pA/pF, p < 0.05). Furthermore, the densities of the M2 receptor and I(K,ACh) in LAA and RAA were higher than that in LA (21.34 +/- 0.92 vs. 14.17 +/- 0.65 pA/pF, p < 0.05). After amiodarone administration, densities of I(K,ACh) in LA and RA were not different, but densities of I(K,ACh )were also less in atrium than in atrial appendage. CONCLUSIONS Densities of the M2 receptor and I(K,ACh) are higher in atrial appendage than other sites. Atrial appendage perhaps plays an important role in initiation of cholinergic AF. However, PV and SVC less often play an important role in vagotonic paroxysmal AF. Reduced dispersion of I(K,ACh) is the mechanism for amiodarone to therapy AF.
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Affiliation(s)
- Cong-Xin Huang
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan, People's Republic of China.
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Makary SMY, Claydon TW, Enkvetchakul D, Nichols CG, Boyett MR. A difference in inward rectification and polyamine block and permeation between the Kir2.1 and Kir3.1/Kir3.4 K+ channels. J Physiol 2005; 568:749-66. [PMID: 16109731 PMCID: PMC1464189 DOI: 10.1113/jphysiol.2005.085746] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Inward rectification is caused by voltage-dependent block of the channel pore by intracellular Mg2+ and polyamines such as spermine. In the present study, we compared inward rectification in the Kir3.1/Kir3.4 channel, which underlies the cardiac current I(K,ACh), and the Kir2.1 channel, which underlies the cardiac current I(K,1). Sustained outward current at potentials positive to the K+ reversal potential was observed through Kir3.1/Kir3.4, but not Kir2.1, demonstrating that Kir3.1/Kir3.4 exhibits weaker inward rectification than Kir2.1. We show that Kir3.1/Kir3.4 is more sensitive to extracellular spermine block than Kir2.1, and that intracellular and extracellular polyamines can permeate Kir3.1/Kir3.4, but not Kir2.1, to a limited extent. We describe a simple kinetic model in which polyamines act as permeant blockers of Kir3.1/Kir3.4, but as relatively impermeant blockers of Kir2.1. The model shows the difference in sensitivity to extracellular spermine block, as well as the difference in the extent of inward rectification between the two channels. This suggests that Kir3.1/Kir3.4 exhibits weaker inward rectification than Kir2.1 because of the difference in the balance of polyamine block and permeation of the two channels.
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Affiliation(s)
- Samy M Y Makary
- Division of Cardiovascular and Endocrine Sciences, University of Manchester, Manchester Incubator Building, Manchester M13 9XX, UK
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Mangoni ME, Couette B, Marger L, Bourinet E, Striessnig J, Nargeot J. Voltage-dependent calcium channels and cardiac pacemaker activity: from ionic currents to genes. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2005; 90:38-63. [PMID: 15979127 DOI: 10.1016/j.pbiomolbio.2005.05.003] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
The spontaneous activity of pacemaker cells in the sino-atrial node controls the heart rhythm and rate under physiological conditions. Compared to working myocardial cells, pacemaker cells express a specific array of ionic channels. The functional importance of different ionic channels in the generation and regulation of cardiac automaticity is currently subject of an extensive research effort and has long been controversial. Among families of ionic channels, Ca(2+) channels have been proposed to substantially contribute to pacemaking. Indeed, Ca(2+) channels are robustly expressed in pacemaker cells, and influence the cell beating rate. Furthermore, they are regulated by the activity of the autonomic nervous system in both a positive and negative way. In this manuscript, we will first discuss how the concept of the involvement of Ca(2+) channels in cardiac pacemaking has been proposed and then subsequently developed by the recent advent in the domain of cardiac physiology of gene-targeting techniques. Secondly, we will indicate how the specific profile of Ca(2+) channels expression in pacemaker tissue can help design drugs which selectively regulate the heart rhythm in the absence of concomitant negative inotropism. Finally, we will indicate how the new possibility to assign a specific gene activity to a given ionic channel involved in cardiac pacemaking could implement the current postgenomic research effort in the construction of the cardiac Physiome.
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Affiliation(s)
- Matteo E Mangoni
- Departement de Physiologie, Institut de Génomique Fonctionnelle, University of Montpellier I, CNRS UMR 5203, Montpellier F-34094, France.
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Nikolov EN, Ivanova-Nikolova TT. Functional characterization of a small conductance GIRK channel in rat atrial cells. Biophys J 2005; 87:3122-36. [PMID: 15507689 PMCID: PMC1304783 DOI: 10.1529/biophysj.103.039487] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Muscarinic K+ (KACh) channels are key determinants of the inhibitory synaptic transmission in the heart. These channels are heterotetramers consisting of two homologous subunits, G-protein-gated inwardly rectifying K+ (GIRK)1 and GIRK4, and have unitary conductance of approximately 35 pS with symmetrical 150 mM KCl solutions. Activation of atrial KACh channels, however, is often accompanied by the appearance of openings with a lower conductance, suggesting a functional heterogeneity of G-protein-sensitive ion channels in the heart. Here we report the characterization of a small conductance GIRK (scGIRK) channel present in rat atria. This channel is directly activated by Gbetagamma subunits and has a unitary conductance of 16 pS. The scGIRK and KACh channels display similar affinities for Gbetagamma binding and are frequently found in the same membrane patches. Furthermore, Gbetagamma-activated scGIRK channels--like their KACh counterparts--exhibit complex gating behavior, fluctuating among four functional modes conferred by the apparent binding of a different number of Gbetagamma subunits to the channel. The electrogenic efficacy of the scGIRK channels, however, is negligible compared to that of KACh channels. Thus, Gbetagamma subunits employ the same signaling strategy to regulate two ion channels that are apparently endowed with very different functions in the atrial membrane.
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Affiliation(s)
- Emil N Nikolov
- Department of Pharmacology and Toxicology, Brody School of Medicine, East Carolina University, Greenville, North Carolina 27858, USA
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Nygren A, Lomax AE, Giles WR. Heterogeneity of action potential durations in isolated mouse left and right atria recorded using voltage-sensitive dye mapping. Am J Physiol Heart Circ Physiol 2004; 287:H2634-43. [PMID: 15271666 DOI: 10.1152/ajpheart.00380.2004] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
An imaging system for di-4-ANEPPS (4-[beta-[2-(di-n-butylamino)-6-naphthylvinyl]pyridinium]) voltage-sensitive dye recordings has been adapted for recording from an in vitro mouse heart preparation that consists of both atria in isolation. This approach has been used to study inter- and intra-atrial activation and conduction and to monitor action potential durations (APDs) in the left and right atrium. The findings from this study confirm some of our previous findings in isolated mouse atrial myocytes and demonstrate that many electrophysiological properties of mouse atria closely resemble those of larger mammals. Specifically, we made the following observations: 1) Activation in mouse atria originates in the sinoatrial node and spreads into the right atrium and, after a delay, into the left atrium. 2) APD in the left atrium is shorter than in the right atrium. 3) Sites in the posterior walls have longer APDs than sites in the atrial appendages. 4) Superfusion of this preparation with 4-aminopyridine and tetraethylammonium resulted in increases in APD, consistent with their inhibitory effects on the K+ currents known to be expressed in mouse atria. 5) The muscarinic agonist carbachol shortened APD in all areas of the preparation, except the left atrial appendage, in which carbachol had no statistically significant effect on APD. These results validate a new approach for monitoring activation, conduction, and repolarization in mouse atria and demonstrate that the physiological and pharmacological properties of mouse atria are sufficiently similar to those of larger animals to warrant further studies using this preparation.
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Affiliation(s)
- Anders Nygren
- Whitaker Institute of Biomedical Engineering, PFBG 384, Univ. of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0412, USA
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