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Pluteanu F, Glaser D, Massing F, Schulte JS, Kirchhefer U. Loss of protein phosphatase 2A regulatory subunit PPP2R5A is associated with increased incidence of stress-induced proarrhythmia. Front Cardiovasc Med 2024; 11:1419597. [PMID: 38863902 PMCID: PMC11165201 DOI: 10.3389/fcvm.2024.1419597] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2024] [Accepted: 05/16/2024] [Indexed: 06/13/2024] Open
Abstract
Background Protein phosphatase 2A (PP2A) is a serine/threonine-selective holoenzyme that controls Ca2+ homeostasis and contractility of the heart via dephosphorylation of regulatory proteins. In some genetically modified mouse models with increased arrhythmogenicity, a reduced expression of the regulatory subunit B56α of PP2A was found as a concomitant effect. Whether there is a general correlation between the abundance of B56α and the promotion of cardiac arrhythmogenesis remains unclear. Methods The aim of this study was therefore to investigate the role of PP2A-B56α in the propensity for arrhythmic activity in the heart. The experimental analysis of this question has been addressed by using a mouse model with deletion of the PP2A-B56α gene, PPP2R5A (KO), in comparison to wild-type animals (WT). Evidence for arrhythmogenicity was investigated in whole animal, isolated heart and cardiomyocytes by ECG, recording of monophasic action potential (MAP) induced by programmed electrical stimulation (PES), measurement of Ca2+ transients under increased pacing frequencies and determination of total K+ channel currents (I K). Results ECG measurements showed a prolongation of QT time in KO vs. WT. KO mice exhibited a higher rate of premature ventricular contractions in the ECG. MAP measurements in Langendorff-perfused KO hearts showed increased episodes of ventricular tachyarrhythmia induced by PES. However, the KO hearts showed values for MAP duration that were similar to those in WT hearts. In contrast, KO showed more myocardial cells with spontaneous arrhythmogenic Ca2+ transient events compared to WT. The whole-cell patch-clamp technique applied to ventricular cardiomyocytes revealed comparable peak potassium channel current densities between KO and WT. Conclusion These findings support the assumption that a decrease or even the loss of PP2A-B56α leads to an increased propensity of triggered arrhythmias. This could be based on the increased spontaneous Ca2+ tansients observed.
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Affiliation(s)
- Florentina Pluteanu
- Department of Anatomy, Animal Physiology and Biophysics, University of Bucharest, Bucharest, Romania
| | - Dennis Glaser
- Institut für Pharmakologie und Toxikologie, Universitätsklinikum Münster, Universität Münster, Münster, Germany
| | - Fabian Massing
- Institut für Pharmakologie und Toxikologie, Universitätsklinikum Münster, Universität Münster, Münster, Germany
| | - Jan S. Schulte
- Institut für Pharmakologie und Toxikologie, Universitätsklinikum Münster, Universität Münster, Münster, Germany
| | - Uwe Kirchhefer
- Institut für Pharmakologie und Toxikologie, Universitätsklinikum Münster, Universität Münster, Münster, Germany
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2
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Lei M, Salvage SC, Jackson AP, Huang CLH. Cardiac arrhythmogenesis: roles of ion channels and their functional modification. Front Physiol 2024; 15:1342761. [PMID: 38505707 PMCID: PMC10949183 DOI: 10.3389/fphys.2024.1342761] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2023] [Accepted: 01/22/2024] [Indexed: 03/21/2024] Open
Abstract
Cardiac arrhythmias cause significant morbidity and mortality and pose a major public health problem. They arise from disruptions in the normally orderly propagation of cardiac electrophysiological activation and recovery through successive cardiomyocytes in the heart. They reflect abnormalities in automaticity, initiation, conduction, or recovery in cardiomyocyte excitation. The latter properties are dependent on surface membrane electrophysiological mechanisms underlying the cardiac action potential. Their disruption results from spatial or temporal instabilities and heterogeneities in the generation and propagation of cellular excitation. These arise from abnormal function in their underlying surface membrane, ion channels, and transporters, as well as the interactions between them. The latter, in turn, form common regulatory targets for the hierarchical network of diverse signaling mechanisms reviewed here. In addition to direct molecular-level pharmacological or physiological actions on these surface membrane biomolecules, accessory, adhesion, signal transduction, and cytoskeletal anchoring proteins modify both their properties and localization. At the cellular level of excitation-contraction coupling processes, Ca2+ homeostatic and phosphorylation processes affect channel activity and membrane excitability directly or through intermediate signaling. Systems-level autonomic cellular signaling exerts both acute channel and longer-term actions on channel expression. Further upstream intermediaries from metabolic changes modulate the channels both themselves and through modifying Ca2+ homeostasis. Finally, longer-term organ-level inflammatory and structural changes, such as fibrotic and hypertrophic remodeling, similarly can influence all these physiological processes with potential pro-arrhythmic consequences. These normal physiological processes may target either individual or groups of ionic channel species and alter with particular pathological conditions. They are also potentially alterable by direct pharmacological action, or effects on longer-term targets modifying protein or cofactor structure, expression, or localization. Their participating specific biomolecules, often clarified in experimental genetically modified models, thus constitute potential therapeutic targets. The insights clarified by the physiological and pharmacological framework outlined here provide a basis for a recent modernized drug classification. Together, they offer a translational framework for current drug understanding. This would facilitate future mechanistically directed therapeutic advances, for which a number of examples are considered here. The latter are potentially useful for treating cardiac, in particular arrhythmic, disease.
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Affiliation(s)
- Ming Lei
- Department of Pharmacology, University of Oxford, Oxford, United Kingdom
| | - Samantha C. Salvage
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - Antony P. Jackson
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - Christopher L.-H. Huang
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
- Physiological Laboratory, University of Cambridge, Cambridge, United Kingdom
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3
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Huang CLH, Lei M. Cardiomyocyte electrophysiology and its modulation: current views and future prospects. Philos Trans R Soc Lond B Biol Sci 2023; 378:20220160. [PMID: 37122224 PMCID: PMC10150219 DOI: 10.1098/rstb.2022.0160] [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: 01/16/2023] [Accepted: 03/10/2023] [Indexed: 05/02/2023] Open
Abstract
Normal and abnormal cardiac rhythms are of key physiological and clinical interest. This introductory article begins from Sylvio Weidmann's key historic 1950s microelectrode measurements of cardiac electrophysiological activity and Singh & Vaughan Williams's classification of cardiotropic targets. It then proceeds to introduce the insights into cardiomyocyte function and its regulation that subsequently emerged and their therapeutic implications. We recapitulate the resulting view that surface membrane electrophysiological events underlying cardiac excitation and its initiation, conduction and recovery constitute the final common path for the cellular mechanisms that impinge upon this normal or abnormal cardiac electrophysiological activity. We then consider progress in the more recently characterized successive regulatory hierarchies involving Ca2+ homeostasis, excitation-contraction coupling and autonomic G-protein signalling and their often reciprocal interactions with the surface membrane events, and their circadian rhythms. Then follow accounts of longer-term upstream modulation processes involving altered channel expression, cardiomyocyte energetics and hypertrophic and fibrotic cardiac remodelling. Consideration of these developments introduces each of the articles in this Phil. Trans. B theme issue. The findings contained in these articles translate naturally into recent classifications of cardiac electrophysiological targets and drug actions, thereby encouraging future iterations of experimental cardiac electrophysiological discovery, and testing directed towards clinical management. This article is part of the theme issue 'The heartbeat: its molecular basis and physiological mechanisms'.
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Affiliation(s)
- Christopher L.-H. Huang
- Physiological Laboratory, University of Cambridge, Downing Street, Cambridge CB2 3EG, UK
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK
| | - Ming Lei
- Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, UK
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4
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Zhao C, Li S, Zhang J, Huang Y, Zhang L, Zhao F, Du X, Hou J, Zhang T, Shi C, Wang P, Huo R, Woodman OL, Qin CX, Xu H, Huang L. Current state and future perspective of cardiovascular medicines derived from natural products. Pharmacol Ther 2020; 216:107698. [PMID: 33039419 DOI: 10.1016/j.pharmthera.2020.107698] [Citation(s) in RCA: 37] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2020] [Revised: 09/25/2020] [Accepted: 09/28/2020] [Indexed: 02/06/2023]
Abstract
The contribution of natural products (NPs) to cardiovascular medicine has been extensively documented, and many have been used for centuries. Cardiovascular disease (CVD) is the leading cause of morbidity and mortality worldwide. Over the past 40 years, approximately 50% of newly developed cardiovascular drugs were based on NPs, suggesting that NPs provide essential skeletal structures for the discovery of novel medicines. After a period of lower productivity since the 1990s, NPs have recently regained scientific and commercial attention, leveraging the wealth of knowledge provided by multi-omics, combinatorial biosynthesis, synthetic biology, integrative pharmacology, analytical and computational technologies. In addition, as a crucial part of complementary and alternative medicine, Traditional Chinese Medicine has increasingly drawn attention as an important source of NPs for cardiovascular drug discovery. Given their structural diversity and biological activity NPs are one of the most valuable sources of drugs and drug leads. In this review, we briefly described the characteristics and classification of NPs in CVDs. Then, we provide an up to date summary on the therapeutic potential and the underlying mechanisms of action of NPs in CVDs, and the current view and future prospect of developing safer and more effective cardiovascular drugs based on NPs.
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Affiliation(s)
- Chunhui Zhao
- Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing 100700, China
| | - Sen Li
- National Resource Center for Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing 100700, China; College of Chinese Medicinal Materials, Jilin Agricultural University, Changchun 130118, China
| | - Junhong Zhang
- Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing 100700, China
| | - Yuanyun Huang
- Biology Department, Cornell University, Ithaca, NY 14850, United States of America
| | - Luoqi Zhang
- National Resource Center for Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing 100700, China; College of Chinese Medicinal Materials, Jilin Agricultural University, Changchun 130118, China
| | - Feng Zhao
- Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing 100700, China
| | - Xia Du
- Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing 100700, China; Shaanxi Academy of Traditional Chinese Medicine, Xi'an 710003, China
| | - Jinli Hou
- Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing 100700, China
| | - Tong Zhang
- Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing 100700, China
| | - Chenjing Shi
- Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing 100700, China
| | - Ping Wang
- Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing 100700, China
| | - Ruili Huo
- China Academy of Chinese Medical Sciences, Beijing 100700, China
| | - Owen L Woodman
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC 3800, Australia
| | - Cheng Xue Qin
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC 3800, Australia; School of Pharmaceutical Science, Shandong University, Shandong 250100, China; Qilu Hospital, Cheeloo College of Medicine, Shandong University, Shandong 250100, China.
| | - Haiyu Xu
- Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing 100700, China.
| | - Luqi Huang
- National Resource Center for Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing 100700, China; China Academy of Chinese Medical Sciences, Beijing 100700, China.
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5
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Juang JMJ, Binda A, Lee SJ, Hwang JJ, Chen WJ, Liu YB, Lin LY, Yu CC, Ho LT, Huang HC, Chen CYJ, Lu TP, Lai LC, Yeh SFS, Lai LP, Chuang EY, Rivolta I, Antzelevitch C. GSTM3 variant is a novel genetic modifier in Brugada syndrome, a disease with risk of sudden cardiac death. EBioMedicine 2020; 57:102843. [PMID: 32645615 PMCID: PMC7341360 DOI: 10.1016/j.ebiom.2020.102843] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2020] [Revised: 05/28/2020] [Accepted: 06/03/2020] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND Brugada syndrome (BrS) is a rare inherited disease causing sudden cardiac death (SCD). Copy number variants (CNVs) can contribute to disease susceptibility, but their role in Brugada syndrome (BrS) is unknown. We aimed to identify a CNV associated with BrS and elucidated its clinical implications. METHODS We enrolled 335 unrelated BrS patients from 2000 to 2018 in the Taiwanese population. Microarray and exome sequencing were used for discovery phase whereas Sanger sequencing was used for the validation phase. HEK cells and zebrafish were used to characterize the function of the CNV variant. FINDINGS A copy number deletion of GSTM3 (chr1:109737011-109737301, hg38) containing the eighth exon and the transcription stop codon was observed in 23.9% of BrS patients versus 0.8% of 15,829 controls in Taiwan Biobank (P < 0.001), and 0% in gnomAD. Co-segregation analysis showed that the co-segregation rate was 20%. Patch clamp experiments showed that in an oxidative stress environment, GSTM3 down-regulation leads to a significant decrease of cardiac sodium channel current amplitude. Ventricular arrhythmia incidence was significantly greater in gstm3 knockout zebrafish at baseline and after flecainide, but was reduced after quinidine, consistent with clinical observations. BrS patients carrying the GSTM3 deletion had higher rates of sudden cardiac arrest and syncope compared to those without (OR: 3.18 (1.77-5.74), P<0.001; OR: 1.76 (1.02-3.05), P = 0.04, respectively). INTERPRETATION This GSTM3 deletion is frequently observed in BrS patients and is associated with reduced INa, pointing to this as a novel potential genetic modifier/risk predictor for the development of the electrocardiographic and arrhythmic manifestations of BrS. FUNDING This work was supported by the Ministry of Science and Technology (107-2314-B-002-261-MY3 to J.M.J. Juang), and by grants HL47678, HL138103 and HL152201 from the National Institutes of Health to CA.
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Affiliation(s)
- Jyh-Ming Jimmy Juang
- Cardiovascular Center and Division of Cardiology, Department of Internal Medicine, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
| | - Anna Binda
- University of Milano Bicocca School of Medicine and Surgery, Via Cadore, 48, 20900 Monza (MB), Italy
| | - Shyh-Jye Lee
- Department of Life Science, National Taiwan University, Taipei, Taiwan
| | - Juey-Jen Hwang
- Cardiovascular Center and Division of Cardiology, Department of Internal Medicine, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
| | - Wen-Jone Chen
- Cardiovascular Center and Division of Cardiology, Department of Internal Medicine, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
| | - Yen-Bin Liu
- Cardiovascular Center and Division of Cardiology, Department of Internal Medicine, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
| | - Lian-Yu Lin
- Cardiovascular Center and Division of Cardiology, Department of Internal Medicine, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
| | - Chih-Chieh Yu
- Cardiovascular Center and Division of Cardiology, Department of Internal Medicine, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
| | - Li-Ting Ho
- Cardiovascular Center and Division of Cardiology, Department of Internal Medicine, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
| | - Hui-Chun Huang
- Cardiovascular Center and Division of Cardiology, Department of Internal Medicine, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
| | - Ching-Yu Julius Chen
- Cardiovascular Center and Division of Cardiology, Department of Internal Medicine, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
| | - Tzu-Pin Lu
- Institute of Epidemiology and Preventive Medicine, National Taiwan University, Taipei, Taiwan; Department of Public Health, National Taiwan University, Taipei, Taiwan.
| | - Liang-Chuan Lai
- Graduate Institute of Physiology, National Taiwan University, Taipei, Taiwan
| | - Shih-Fan Sherri Yeh
- Department of Environmental and Occupational Medicine, National Taiwan University Hospital, Hsin-Chu branch and National Taiwan University College of Medicine, Taipei, Taiwan
| | - Ling-Ping Lai
- Cardiovascular Center and Division of Cardiology, Department of Internal Medicine, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
| | - Eric Y Chuang
- Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan
| | - Ilaria Rivolta
- University of Milano Bicocca School of Medicine and Surgery, Via Cadore, 48, 20900 Monza (MB), Italy
| | - Charles Antzelevitch
- Lankenau Institute for Medical Research and Lankenau Heart Institute, Wynnewood, PA and Sidney Kimmel Medical College of Thomas Jefferson University, Philadelphia, PA, USA.
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6
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Abstract
Brugada syndrome is an inherited, rare cardiac arrhythmogenic disease, associated with sudden cardiac death. It accounts for up to 20% of sudden deaths in patients without structural cardiac abnormalities. The majority of mutations involve the cardiac sodium channel gene SCN5A and give rise to classical abnormal electrocardiogram with ST segment elevation in the right precordial leads V1 to V3 and a predisposition to ventricular fibrillation. The pathophysiological mechanisms of Brugada syndrome have been investigated using model systems including transgenic mice, canine heart preparations, and expression systems to study different SCN5A mutations. These models have a number of limitations. The recent development of pluripotent stem cell technology creates an opportunity to study cardiomyocytes derived from patients and healthy individuals. To date, only a few studies have been done using Brugada syndrome patient-specific iPS-CM, which have provided novel insights into the mechanisms and pathophysiology of Brugada syndrome. This review provides an evaluation of the strengths and limitations of each of these model systems and summarizes the key mechanisms that have been identified to date.
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7
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Quinidine Rebooted. JACC Clin Electrophysiol 2019; 5:383-386. [DOI: 10.1016/j.jacep.2019.01.015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2018] [Revised: 01/10/2019] [Accepted: 01/17/2019] [Indexed: 11/17/2022]
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8
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Espinosa Á, Ripollés-Melchor J, Brugada R, Campuzano Ó, Sarquella-Brugada G, Abad-Motos A, Zaballos-García M, Abad-Torrent A, Prieto-Gundin A, Brugada J. Brugada Syndrome: anesthetic considerations and management algorithm. Minerva Anestesiol 2018; 85:173-188. [PMID: 30394071 DOI: 10.23736/s0375-9393.18.13170-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Brugada Syndrome is characterized by arrhythmogenic risk that may be exacerbated by different metabolic and pharmacological factors. Since its first description, knowledge of this syndrome and its detection by physicians belonging to different specialties have gradually increased. The risk of arrhythmias is well known to increase in the postoperative period, and this risk is particularly accentuated in patients with Brugada Syndrome. The purpose of this review is to analyze the relationship between this syndrome and anesthesia; establish recommendations for the safe management of these patients in the surgical setting; and update the relevant concepts regarding the safety of drug administration in individuals with Brugada Syndrome.
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Affiliation(s)
- Ángel Espinosa
- Department of Cardiothoracic Anesthesia, Mohammed Bin Khalifa Bin Salman Al Khalifa Cardiac Center, Royal Medical Services, Awali, Bahrain.,Evidence Anesthesia Review Group (EAR), Department of Pharmacology, Faculty of Medicine of Complutense University of Madrid, Madrid, Spain
| | - Javier Ripollés-Melchor
- Evidence Anesthesia Review Group (EAR), Department of Pharmacology, Faculty of Medicine of Complutense University of Madrid, Madrid, Spain - .,Department of Anesthesiology and Critical Care, Infanta Leonor University Hospital, Madrid, Spain.,Madrid Complutense University, Madrid, Spain.,Spanish Perioperative Audit and Research Network (RedGERM), Zaragoza, Spain
| | - Ramón Brugada
- Cardiovascular Genetics Center, Girona Biomedical Research Institute (IDIBGI), University of Girona, Girona, Spain.,Department of Medical Sciences, School of Medicine, University of Girona, Girona, Spain.,Cardiovascular Diseases Network Biomedical Research Center (CIBERCV), Madrid, Spain.,Department of Cardiology, Josep Trueta Hospital, Girona, Spain
| | - Óscar Campuzano
- Cardiovascular Genetics Center, Girona Biomedical Research Institute (IDIBGI), University of Girona, Girona, Spain.,Department of Medical Sciences, School of Medicine, University of Girona, Girona, Spain.,Cardiovascular Diseases Network Biomedical Research Center (CIBERCV), Madrid, Spain
| | - Georgia Sarquella-Brugada
- Department of Medical Sciences, School of Medicine, University of Girona, Girona, Spain.,Unit of Pediatric Arrhythmia, Department of Cardiology, Sant Joan de Déu Hospital, Barcelona, Spain.,Section of Arrhythmia, Department of Cardiology, Clinic Hospital, University of Barcelona, Barcelona, Spain
| | - Ane Abad-Motos
- Department of Anesthesiology and Critical Care, Infanta Leonor University Hospital, Madrid, Spain.,Madrid Complutense University, Madrid, Spain.,Spanish Perioperative Audit and Research Network (RedGERM), Zaragoza, Spain
| | - Matilde Zaballos-García
- Department of Anesthesiology, Gregorio Marañón University General Hospital, Madrid, Spain.,Clinical Toxicology, Madrid Complutense University, Madrid, Spain
| | - Ana Abad-Torrent
- Department of Anesthesiology, Vall d'Hebron University Hospital, Barcelona, Spain
| | - Alejandra Prieto-Gundin
- Department of Pediatric Anesthesiology, Sant Joan de Déu Hospital, Barcelona Children's Hospital, Barcelona, Spain
| | - Josep Brugada
- Unit of Pediatric Arrhythmia, Department of Cardiology, Sant Joan de Déu Hospital, Barcelona, Spain.,Section of Arrhythmia, Department of Cardiology, Clinic Hospital, University of Barcelona, Barcelona, Spain
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9
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Salvage SC, Chandrasekharan KH, Jeevaratnam K, Dulhunty AF, Thompson AJ, Jackson AP, Huang CL. Multiple targets for flecainide action: implications for cardiac arrhythmogenesis. Br J Pharmacol 2018; 175:1260-1278. [PMID: 28369767 PMCID: PMC5866987 DOI: 10.1111/bph.13807] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2017] [Revised: 03/27/2017] [Accepted: 03/29/2017] [Indexed: 12/19/2022] Open
Abstract
Flecainide suppresses cardiac tachyarrhythmias including paroxysmal atrial fibrillation, supraventricular tachycardia and arrhythmic long QT syndromes (LQTS), as well as the Ca2+ -mediated, catecholaminergic polymorphic ventricular tachycardia (CPVT). However, flecainide can also exert pro-arrhythmic effects most notably following myocardial infarction and when used to diagnose Brugada syndrome (BrS). These divergent actions result from its physiological and pharmacological actions at multiple, interacting levels of cellular organization. These were studied in murine genetic models with modified Nav channel or intracellular ryanodine receptor (RyR2)-Ca2+ channel function. Flecainide accesses its transmembrane Nav 1.5 channel binding site during activated, open, states producing a use-dependent antagonism. Closing either activation or inactivation gates traps flecainide within the pore. An early peak INa related to activation of Nav channels followed by rapid de-activation, drives action potential (AP) upstrokes and their propagation. This is diminished in pro-arrhythmic conditions reflecting loss of function of Nav 1.5 channels, such as BrS, accordingly exacerbated by flecainide challenge. Contrastingly, pro-arrhythmic effects attributed to prolonged AP recovery by abnormal late INaL following gain-of-function modifications of Nav 1.5 channels in LQTS3 are reduced by flecainide. Anti-arrhythmic effects of flecainide that reduce triggering in CPVT models mediated by sarcoplasmic reticular Ca2+ release could arise from its primary actions on Nav channels indirectly decreasing [Ca2+ ]i through a reduced [Na+ ]i and/or direct open-state RyR2-Ca2+ channel antagonism. The consequent [Ca2+ ]i alterations could also modify AP propagation velocity and therefore arrhythmic substrate through its actions on Nav 1.5 channel function. This is consistent with the paradoxical differences between flecainide actions upon Na+ currents, AP conduction and arrhythmogenesis under circumstances of normal and increased RyR2 function. LINKED ARTICLES This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc.
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Affiliation(s)
- Samantha C Salvage
- Department of BiochemistryUniversity of CambridgeCambridgeUK
- Physiological LaboratoryUniversity of CambridgeCambridgeUK
| | | | - Kamalan Jeevaratnam
- Faculty of Health and Medical SciencesUniversity of SurreyGuildfordUK
- School of MedicinePerdana University – Royal College of Surgeons IrelandSerdangSelangor Darul EhsanMalaysia
| | - Angela F Dulhunty
- Muscle Research Group, Eccles Institute of Neuroscience, John Curtin School of Medical ResearchAustralian National UniversityActonAustralia
| | | | | | - Christopher L‐H Huang
- Department of BiochemistryUniversity of CambridgeCambridgeUK
- Physiological LaboratoryUniversity of CambridgeCambridgeUK
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10
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Jeevaratnam K, Chadda KR, Salvage SC, Valli H, Ahmad S, Grace AA, Huang CLH. Ion channels, long QT syndrome and arrhythmogenesis in ageing. Clin Exp Pharmacol Physiol 2017; 44 Suppl 1:38-45. [PMID: 28024120 PMCID: PMC5763326 DOI: 10.1111/1440-1681.12721] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Revised: 12/18/2016] [Accepted: 12/19/2016] [Indexed: 01/08/2023]
Abstract
Ageing is associated with increased prevalences of both atrial and ventricular arrhythmias, reflecting disruption of the normal sequence of ion channel activation and inactivation generating the propagated cardiac action potential. Experimental models with specific ion channel genetic modifications have helped clarify the interacting functional roles of ion channels and how their dysregulation contributes to arrhythmogenic processes at the cellular and systems level. They have also investigated interactions between these ion channel abnormalities and age-related processes in producing arrhythmic tendency. Previous reviews have explored the relationships between age and loss-of-function Nav 1.5 mutations in producing arrhythmogenicity. The present review now explores complementary relationships arising from gain-of-function Nav 1.5 mutations associated with long QT3 (LQTS3). LQTS3 patients show increased risks of life-threatening ventricular arrhythmias, particularly after 40 years of age, consistent with such interactions between the ion channel abnormailities and ageing. In turn clinical evidence suggests that ageing is accompanied by structural, particularly fibrotic, as well as electrophysiological change. These abnormalities may result from biochemical changes producing low-grade inflammation resulting from increased production of reactive oxygen species and superoxide. Experimental studies offer further insights into the underlying mechanisms underlying these phenotypes. Thus, studies in genetically modified murine models for LQTS implicated action potential recovery processes in arrhythmogenesis resulting from functional ion channel abnormalities. In addition, ageing wild type (WT) murine models demonstrated both ion channel alterations and fibrotic changes with ageing. Murine models then suggested evidence for interactions between ageing and ion channel mutations and provided insights into potential arrhythmic mechanisms inviting future exploration.
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Affiliation(s)
- Kamalan Jeevaratnam
- Faculty of Health and Medical Sciences, University of Surrey, Guildford, UK.,School of Medicine, Perdana University-Royal College of Surgeons Ireland, Serdang, Selangor Darul Ehsan, Malaysia
| | - Karan R Chadda
- Faculty of Health and Medical Sciences, University of Surrey, Guildford, UK.,Physiological Laboratory, University of Cambridge, Cambridge, UK
| | | | - Haseeb Valli
- Physiological Laboratory, University of Cambridge, Cambridge, UK
| | - Shiraz Ahmad
- Physiological Laboratory, University of Cambridge, Cambridge, UK
| | - Andrew A Grace
- Division of Cardiovascular Biology, Department of Biochemistry, University of Cambridge, Cambridge, UK
| | - Christopher L-H Huang
- Physiological Laboratory, University of Cambridge, Cambridge, UK.,Division of Cardiovascular Biology, Department of Biochemistry, University of Cambridge, Cambridge, UK
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11
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Abstract
Cardiac arrhythmias can follow disruption of the normal cellular electrophysiological processes underlying excitable activity and their tissue propagation as coherent wavefronts from the primary sinoatrial node pacemaker, through the atria, conducting structures and ventricular myocardium. These physiological events are driven by interacting, voltage-dependent, processes of activation, inactivation, and recovery in the ion channels present in cardiomyocyte membranes. Generation and conduction of these events are further modulated by intracellular Ca2+ homeostasis, and metabolic and structural change. This review describes experimental studies on murine models for known clinical arrhythmic conditions in which these mechanisms were modified by genetic, physiological, or pharmacological manipulation. These exemplars yielded molecular, physiological, and structural phenotypes often directly translatable to their corresponding clinical conditions, which could be investigated at the molecular, cellular, tissue, organ, and whole animal levels. Arrhythmogenesis could be explored during normal pacing activity, regular stimulation, following imposed extra-stimuli, or during progressively incremented steady pacing frequencies. Arrhythmic substrate was identified with temporal and spatial functional heterogeneities predisposing to reentrant excitation phenomena. These could arise from abnormalities in cardiac pacing function, tissue electrical connectivity, and cellular excitation and recovery. Triggering events during or following recovery from action potential excitation could thereby lead to sustained arrhythmia. These surface membrane processes were modified by alterations in cellular Ca2+ homeostasis and energetics, as well as cellular and tissue structural change. Study of murine systems thus offers major insights into both our understanding of normal cardiac activity and its propagation, and their relationship to mechanisms generating clinical arrhythmias.
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Affiliation(s)
- Christopher L-H Huang
- Physiological Laboratory and the Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
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Tse G, Wong ST, Tse V, Yeo JM. Depolarization vs. repolarization: what is the mechanism of ventricular arrhythmogenesis underlying sodium channel haploinsufficiency in mouse hearts? Acta Physiol (Oxf) 2016; 218:234-235. [PMID: 27084434 DOI: 10.1111/apha.12694] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
- G. Tse
- School of Biomedical Sciences; Li Ka Shing Faculty of Medicine; University of Hong Kong; Hong Kong Hong Kong
| | - S. T. Wong
- Faculty of Medicine; Imperial College London; London UK
| | - V. Tse
- Department of Physiology; McGill University; Montreal QC Canada
| | - J. M. Yeo
- Faculty of Medicine; Imperial College London; London UK
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Jeevaratnam K, Guzadhur L, Goh YM, Grace AA, Huang CLH. Response to: Depolarization vs. repolarization: what is the mechanism of ventricular arrhythmogenesis underlying sodium channel haploinsufficiency in mouse hearts? Acta Physiol (Oxf) 2016; 218:236-238. [PMID: 27272698 DOI: 10.1111/apha.12731] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- K. Jeevaratnam
- Faculty of Health and Medical Science; University of Surrey; Guildford UK
- Perdana University - Royal College of Surgeons Ireland; Serdang Selangor Darul Ehsan Malaysia
| | - L. Guzadhur
- Division of Cardiovascular Biology; Department of Biochemistry; University of Cambridge; Cambridge UK
- Niche Science & Technology; Richmond UK
| | - Y. M. Goh
- Department of Preclinical Sciences; Faculty of Veterinary Medicine; University Putra Malaysia; Serdang Selangor Darul Ehsan Malaysia
| | - A. A. Grace
- Division of Cardiovascular Biology; Department of Biochemistry; University of Cambridge; Cambridge UK
| | - C. L.-H. Huang
- Division of Cardiovascular Biology; Department of Biochemistry; University of Cambridge; Cambridge UK
- Physiological Laboratory; University of Cambridge; Cambridge UK
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Tse G, Liu T, Li KHC, Laxton V, Chan YWF, Keung W, Li RA, Yan BP. Electrophysiological Mechanisms of Brugada Syndrome: Insights from Pre-clinical and Clinical Studies. Front Physiol 2016; 7:467. [PMID: 27803673 PMCID: PMC5067537 DOI: 10.3389/fphys.2016.00467] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Accepted: 09/27/2016] [Indexed: 12/19/2022] Open
Abstract
Brugada syndrome (BrS), is a primary electrical disorder predisposing affected individuals to sudden cardiac death via the development of ventricular tachycardia and fibrillation (VT/VF). Originally, BrS was linked to mutations in the SCN5A, which encodes for the cardiac Na+ channel. To date, variants in 19 genes have been implicated in this condition, with 11, 5, 3, and 1 genes affecting the Na+, K+, Ca2+, and funny currents, respectively. Diagnosis of BrS is based on ECG criteria of coved- or saddle-shaped ST segment elevation and/or T-wave inversion with or without drug challenge. Three hypotheses based on abnormal depolarization, abnormal repolarization, and current-load-mismatch have been put forward to explain the electrophysiological mechanisms responsible for BrS. Evidence from computational modeling, pre-clinical, and clinical studies illustrates that molecular abnormalities found in BrS lead to alterations in excitation wavelength (λ), which ultimately elevates arrhythmic risk. A major challenge for clinicians in managing this condition is the difficulty in predicting the subset of patients who will suffer from life-threatening VT/VF. Several repolarization risk markers have been used thus far, but these neglect the contributions of conduction abnormalities in the form of slowing and dispersion. Indices incorporating both repolarization and conduction and based on the concept of λ have recently been proposed. These may have better predictive values than the existing markers.
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Affiliation(s)
- Gary Tse
- Department of Medicine and Therapeutics, Chinese University of Hong KongHong Kong, Hong Kong
- Li Ka Shing Institute of Health Sciences, Chinese University of Hong KongHong Kong, Hong Kong
| | - Tong Liu
- Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular Disease, Department of Cardiology, Tianjin Institute of Cardiology, Second Hospital of Tianjin Medical UniversityTianjin, China
| | - Ka H. C. Li
- Faculty of Medicine, Newcastle UniversityNewcastle, UK
| | - Victoria Laxton
- Intensive Care Department, Royal Brompton and Harefield NHS TrustLondon, UK
| | - Yin W. F. Chan
- School of Biological Sciences, University of CambridgeCambridge, UK
| | - Wendy Keung
- Stem Cell and Regenerative Medicine Consortium, Li Ka Shing Faculty of Medicine, The University of Hong KongPokfulam, Hong Kong
| | - Ronald A. Li
- Ming Wai Lau Centre for Reparative Medicine, Karolinska InstitutetSolna, Sweden
| | - Bryan P. Yan
- Department of Medicine and Therapeutics, Chinese University of Hong KongHong Kong, Hong Kong
- Department of Epidemiology and Preventive Medicine, Monash UniversityMelbourne, VIC, Australia
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Jeevaratnam K, Guzadhur L, Goh YM, Grace AA, Huang CLH. Sodium channel haploinsufficiency and structural change in ventricular arrhythmogenesis. Acta Physiol (Oxf) 2016; 216:186-202. [PMID: 26284956 DOI: 10.1111/apha.12577] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2015] [Revised: 06/11/2015] [Accepted: 07/24/2015] [Indexed: 12/19/2022]
Abstract
Normal cardiac excitation involves orderly conduction of electrical activation and recovery dependent upon surface membrane, voltage-gated, sodium (Na(+) ) channel α-subunits (Nav 1.5). We summarize experimental studies of physiological and clinical consequences of loss-of-function Na(+) channel mutations. Of these conditions, Brugada syndrome (BrS) and progressive cardiac conduction defect (PCCD) are associated with sudden, often fatal, ventricular tachycardia (VT) or fibrillation. Mouse Scn5a(+/-) hearts replicate important clinical phenotypes modelling these human conditions. The arrhythmic phenotype is associated not only with the primary biophysical change but also with additional, anatomical abnormalities, in turn dependent upon age and sex, each themselves exerting arrhythmic effects. Available evidence suggests a unified binary scheme for the development of arrhythmia in both BrS and PCCD. Previous biophysical studies suggested that Nav 1.5 deficiency produces a background electrophysiological defect compromising conduction, thereby producing an arrhythmic substrate unmasked by flecainide or ajmaline challenge. More recent reports further suggest a progressive decline in conduction velocity and increase in its dispersion particularly in ageing male Nav 1.5 haploinsufficient compared to WT hearts. This appears to involve a selective appearance of slow conduction at the expense of rapidly conducting pathways with changes in their frequency distributions. These changes were related to increased cardiac fibrosis. It is thus the combination of the structural and biophysical changes both accentuating arrhythmic substrate that may produce arrhythmic tendency. This binary scheme explains the combined requirement for separate, biophysical and structural changes, particularly occurring in ageing Nav 1.5 haploinsufficient males in producing clinical arrhythmia.
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Affiliation(s)
- K. Jeevaratnam
- Faculty of Health and Medical Science; University of Surrey; Guilford UK
- Perdana University - Royal College of Surgeons Ireland; Serdang Selangor Darul Ehsan Malaysia
| | - L. Guzadhur
- Division of Cardiovascular Biology; Department of Biochemistry; University of Cambridge; Cambridge UK
- Niche Science & Technology; Richmond UK
| | - Y. M. Goh
- Department of Preclinical Sciences; Faculty of Veterinary Medicine; University Putra Malaysia; Serdang Selangor Darul Ehsan Malaysia
| | - A. A. Grace
- Division of Cardiovascular Biology; Department of Biochemistry; University of Cambridge; Cambridge UK
| | - C. L.-H. Huang
- Division of Cardiovascular Biology; Department of Biochemistry; University of Cambridge; Cambridge UK
- Physiological Laboratory; University of Cambridge; Cambridge UK
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Ning F, Luo L, Ahmad S, Valli H, Jeevaratnam K, Wang T, Guzadhur L, Yang D, Fraser JA, Huang CLH, Ma A, Salvage SC. The RyR2-P2328S mutation downregulates Nav1.5 producing arrhythmic substrate in murine ventricles. Pflugers Arch 2015; 468:655-65. [PMID: 26545784 PMCID: PMC4792352 DOI: 10.1007/s00424-015-1750-0] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2015] [Revised: 09/25/2015] [Accepted: 10/19/2015] [Indexed: 01/05/2023]
Abstract
Catecholaminergic polymorphic ventricular tachycardia (CPVT) predisposes to ventricular arrhythmia due to altered Ca2+ homeostasis and can arise from ryanodine receptor (RyR2) mutations including RyR2-P2328S. Previous reports established that homozygotic murine RyR2-P2328S (RyR2S/S) hearts show an atrial arrhythmic phenotype associated with reduced action potential (AP) conduction velocity and sodium channel (Nav1.5) expression. We now relate ventricular arrhythmogenicity and slowed AP conduction in RyR2S/S hearts to connexin-43 (Cx43) and Nav1.5 expression and Na+ current (INa). Stimulation protocols applying extrasystolic S2 stimulation following 8 Hz S1 pacing at progressively decremented S1S2 intervals confirmed an arrhythmic tendency despite unchanged ventricular effective refractory periods (VERPs) in Langendorff-perfused RyR2S/S hearts. Dynamic pacing imposing S1 stimuli then demonstrated that progressive reductions of basic cycle lengths (BCLs) produced greater reductions in conduction velocity at equivalent BCLs and diastolic intervals in RyR2S/S than WT, but comparable changes in AP durations (APD90) and their alternans. Western blot analyses demonstrated that Cx43 protein expression in whole ventricles was similar, but Nav1.5 expression in both whole tissue and membrane fractions were significantly reduced in RyR2S/S compared to wild-type (WT). Loose patch-clamp studies similarly demonstrated reduced INa in RyR2S/S ventricles. We thus attribute arrhythmogenesis in RyR2S/S ventricles resulting from arrhythmic substrate produced by reduced conduction velocity to downregulated Nav1.5 reducing INa, despite normal determinants of repolarization and passive conduction. The measured changes were quantitatively compatible with earlier predictions of linear relationships between conduction velocity and the peak INa of the AP but nonlinear relationships between peak INa and maximum Na+ permeability.
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Affiliation(s)
- Feifei Ning
- Department of Cardiovascular Medicine, First Affiliated Hospital of Xi'an Jiaotong University, No. 277 West Yanta Road, Xi'an, Shaanxi, 710061, People's Republic of China
| | - Ling Luo
- Department of Cardiovascular Medicine, First Affiliated Hospital of Xi'an Jiaotong University, No. 277 West Yanta Road, Xi'an, Shaanxi, 710061, People's Republic of China
| | - Shiraz Ahmad
- Physiological Laboratory, University of Cambridge, Cambridge, CB2 3EG, UK
| | - Haseeb Valli
- Physiological Laboratory, University of Cambridge, Cambridge, CB2 3EG, UK
| | - Kamalan Jeevaratnam
- Faculty of Health and Medical Science, Duke of Kent Building, University of Surrey, Guildford, GU2 7TE, UK
- Perdana University-Royal College of Surgeons Ireland, 43400 Serdang, Selangor, Darul Ehsan, Malaysia
| | - Tingzhong Wang
- Department of Cardiovascular Medicine, First Affiliated Hospital of Xi'an Jiaotong University, No. 277 West Yanta Road, Xi'an, Shaanxi, 710061, People's Republic of China
- Key Laboratory of Molecular Cardiology, Shaanxi Province, People's Republic of China
- Key Laboratory of Environment and Genes Related to Diseases (Xi'an Jiaotong University), Ministry of Education, Xi'an, People's Republic of China
| | - Laila Guzadhur
- Department of Biochemistry, University of Cambridge, Cambridge, CB2 1QW, UK
- Niche Science and Technology, Falstaff House, Bardolph Road, Richmond, UK
| | - Dandan Yang
- Department of Cardiovascular Medicine, First Affiliated Hospital of Xi'an Jiaotong University, No. 277 West Yanta Road, Xi'an, Shaanxi, 710061, People's Republic of China
| | - James A Fraser
- Physiological Laboratory, University of Cambridge, Cambridge, CB2 3EG, UK
| | - Christopher L-H Huang
- Physiological Laboratory, University of Cambridge, Cambridge, CB2 3EG, UK
- Department of Biochemistry, University of Cambridge, Cambridge, CB2 1QW, UK
| | - Aiqun Ma
- Department of Cardiovascular Medicine, First Affiliated Hospital of Xi'an Jiaotong University, No. 277 West Yanta Road, Xi'an, Shaanxi, 710061, People's Republic of China.
- Key Laboratory of Molecular Cardiology, Shaanxi Province, People's Republic of China.
- Key Laboratory of Environment and Genes Related to Diseases (Xi'an Jiaotong University), Ministry of Education, Xi'an, People's Republic of China.
| | - Samantha C Salvage
- Physiological Laboratory, University of Cambridge, Cambridge, CB2 3EG, UK.
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Salvage SC, King JH, Chandrasekharan KH, Jafferji DIG, Guzadhur L, Matthews HR, Huang CL, Fraser JA. Flecainide exerts paradoxical effects on sodium currents and atrial arrhythmia in murine RyR2-P2328S hearts. Acta Physiol (Oxf) 2015; 214:361-75. [PMID: 25850710 PMCID: PMC4510817 DOI: 10.1111/apha.12505] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2014] [Revised: 11/03/2014] [Accepted: 04/01/2015] [Indexed: 12/30/2022]
Abstract
Aims Cardiac ryanodine receptor mutations are associated with catecholaminergic polymorphic ventricular tachycardia (CPVT), and some, including RyR2-P2328S, also predispose to atrial fibrillation. Recent work associates reduced atrial Nav1.5 currents in homozygous RyR2-P2328S (RyR2S/S) mice with slowed conduction and increased arrhythmogenicity. Yet clinically, and in murine models, the Nav1.5 blocker flecainide reduces ventricular arrhythmogenicity in CPVT. We aimed to determine whether, and how, flecainide influences atrial arrhythmogenicity in RyR2S/S mice and their wild-type (WT) littermates. Methods We explored effects of 1 μm flecainide on WT and RyR2S/S atria. Arrhythmic incidence, action potential (AP) conduction velocity (CV), atrial effective refractory period (AERP) and AP wavelength (λ = CV × AERP) were measured using multi-electrode array recordings in Langendorff-perfused hearts; Na+ currents (INa) were recorded using loose patch clamping of superfused atria. Results RyR2S/S showed more frequent atrial arrhythmias, slower CV, reduced INa and unchanged AERP compared to WT. Flecainide was anti-arrhythmic in RyR2S/S but pro-arrhythmic in WT. It increased INa in RyR2S/S atria, whereas it reduced INa as expected in WT. It increased AERP while sparing CV in RyR2S/S, but reduced CV while sparing AERP in WT. Thus, RyR2S/S hearts have low λ relative to WT; flecainide then increases λ in RyR2S/S but decreases λ in WT. Conclusions Flecainide (1 μm) rescues the RyR2-P2328S atrial arrhythmogenic phenotype by restoring compromised INa and λ, changes recently attributed to increased sarcoplasmic reticular Ca2+ release. This contrasts with the increased arrhythmic incidence and reduced INa and λ with flecainide in WT.
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Affiliation(s)
- S. C. Salvage
- Physiological Laboratory University of Cambridge Cambridge UK
| | - J. H. King
- Physiological Laboratory University of Cambridge Cambridge UK
| | | | | | - L. Guzadhur
- Department of Biochemistry University of Cambridge Cambridge UK
| | - H. R. Matthews
- Physiological Laboratory University of Cambridge Cambridge UK
| | - C. L.‐H. Huang
- Physiological Laboratory University of Cambridge Cambridge UK
- Department of Biochemistry University of Cambridge Cambridge UK
| | - J. A. Fraser
- Physiological Laboratory University of Cambridge Cambridge UK
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Barsheshet A, Dotsenko O, Goldenberg I. Congenital long QT syndromes: prevalence, pathophysiology and management. Paediatr Drugs 2014; 16:447-56. [PMID: 25288402 DOI: 10.1007/s40272-014-0090-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Long QT syndrome is a genetic disorder associated with life threatening ventricular arrhythmias and sudden death. This inherited arrhythmic disorder exhibits genetic heterogeneity, incomplete penetrance, and variable expressivity. During the past two decades there have been major advancements in understanding the genotype-phenotype correlations in LQTS. This genotype-phenotype relationship can lead to improved management of LQTS. However, development of genotype-specific or mutation-specific management strategies is very challenging. This review describes the pathophysiology of LQTS, genotype-phenotype correlations, and focuses on the management of LQTS. In general, the treatment of LQTS consists of lifestyle modifications, medical therapy with beta-blockers, device and surgical therapy. We further summarize current data on the efficacy of pharmacological treatment options for the three most prevalent LQTS variants including beta-blockers in LQT1, LQT2 and LQT3, sodium channel blockers and ranolazine for LQT3, potassium supplementation and spironolactone for LQT2, and possibly sex hormone-based therapy for LQT2.
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Affiliation(s)
- Alon Barsheshet
- Cardiology Department, Rabin Medical Center, Petach Tikva, Israel
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19
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Makara MA, Curran J, Little SC, Musa H, Polina I, Smith SA, Wright PJ, Unudurthi SD, Snyder J, Bennett V, Hund TJ, Mohler PJ. Ankyrin-G coordinates intercalated disc signaling platform to regulate cardiac excitability in vivo. Circ Res 2014; 115:929-38. [PMID: 25239140 DOI: 10.1161/circresaha.115.305154] [Citation(s) in RCA: 91] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
RATIONALE Nav1.5 (SCN5A) is the primary cardiac voltage-gated Nav channel. Nav1.5 is critical for cardiac excitability and conduction, and human SCN5A mutations cause sinus node dysfunction, atrial fibrillation, conductional abnormalities, and ventricular arrhythmias. Further, defects in Nav1.5 regulation are linked with malignant arrhythmias associated with human heart failure. Consequently, therapies to target select Nav1.5 properties have remained at the forefront of cardiovascular medicine. However, despite years of investigation, the fundamental pathways governing Nav1.5 membrane targeting, assembly, and regulation are still largely undefined. OBJECTIVE Define the in vivo mechanisms underlying Nav1.5 membrane regulation. METHODS AND RESULTS Here, we define the molecular basis of an Nav channel regulatory platform in heart. Using new cardiac-selective ankyrin-G(-/-) mice (conditional knock-out mouse), we report that ankyrin-G targets Nav1.5 and its regulatory protein calcium/calmodulin-dependent kinase II to the intercalated disc. Mechanistically, βIV-spectrin is requisite for ankyrin-dependent targeting of calcium/calmodulin-dependent kinase II-δ; however, βIV-spectrin is not essential for ankyrin-G expression. Ankyrin-G conditional knock-out mouse myocytes display decreased Nav1.5 expression/membrane localization and reduced INa associated with pronounced bradycardia, conduction abnormalities, and ventricular arrhythmia in response to Nav channel antagonists. Moreover, we report that ankyrin-G links Nav channels with broader intercalated disc signaling/structural nodes, as ankyrin-G loss results in reorganization of plakophilin-2 and lethal arrhythmias in response to β-adrenergic stimulation. CONCLUSIONS Our findings provide the first in vivo data for the molecular pathway required for intercalated disc Nav1.5 targeting/regulation in heart. Further, these new data identify the basis of an in vivo cellular platform critical for membrane recruitment and regulation of Nav1.5.
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Affiliation(s)
- Michael A Makara
- From The Dorothy M. Davis Heart & Lung Research Institute (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., S.D.U., J.S., T.J.H., P.J.M. ), Departments of Internal Medicine (S.A.S., P.J.M.), and Physiology and Cell Biology (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., P.J.M.), The Ohio State University Wexner Medical Center, Columbus; Department of Biomedical Engineering, The Ohio State University College of Engineering, Columbus (S.D.U., J.S., T.J.H.); and Howard Hughes Medical Institute, Department of Biochemistry, Duke University Medical Center, Durham, NC (V.B.)
| | - Jerry Curran
- From The Dorothy M. Davis Heart & Lung Research Institute (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., S.D.U., J.S., T.J.H., P.J.M. ), Departments of Internal Medicine (S.A.S., P.J.M.), and Physiology and Cell Biology (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., P.J.M.), The Ohio State University Wexner Medical Center, Columbus; Department of Biomedical Engineering, The Ohio State University College of Engineering, Columbus (S.D.U., J.S., T.J.H.); and Howard Hughes Medical Institute, Department of Biochemistry, Duke University Medical Center, Durham, NC (V.B.)
| | - Sean C Little
- From The Dorothy M. Davis Heart & Lung Research Institute (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., S.D.U., J.S., T.J.H., P.J.M. ), Departments of Internal Medicine (S.A.S., P.J.M.), and Physiology and Cell Biology (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., P.J.M.), The Ohio State University Wexner Medical Center, Columbus; Department of Biomedical Engineering, The Ohio State University College of Engineering, Columbus (S.D.U., J.S., T.J.H.); and Howard Hughes Medical Institute, Department of Biochemistry, Duke University Medical Center, Durham, NC (V.B.)
| | - Hassan Musa
- From The Dorothy M. Davis Heart & Lung Research Institute (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., S.D.U., J.S., T.J.H., P.J.M. ), Departments of Internal Medicine (S.A.S., P.J.M.), and Physiology and Cell Biology (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., P.J.M.), The Ohio State University Wexner Medical Center, Columbus; Department of Biomedical Engineering, The Ohio State University College of Engineering, Columbus (S.D.U., J.S., T.J.H.); and Howard Hughes Medical Institute, Department of Biochemistry, Duke University Medical Center, Durham, NC (V.B.)
| | - Iuliia Polina
- From The Dorothy M. Davis Heart & Lung Research Institute (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., S.D.U., J.S., T.J.H., P.J.M. ), Departments of Internal Medicine (S.A.S., P.J.M.), and Physiology and Cell Biology (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., P.J.M.), The Ohio State University Wexner Medical Center, Columbus; Department of Biomedical Engineering, The Ohio State University College of Engineering, Columbus (S.D.U., J.S., T.J.H.); and Howard Hughes Medical Institute, Department of Biochemistry, Duke University Medical Center, Durham, NC (V.B.)
| | - Sakima A Smith
- From The Dorothy M. Davis Heart & Lung Research Institute (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., S.D.U., J.S., T.J.H., P.J.M. ), Departments of Internal Medicine (S.A.S., P.J.M.), and Physiology and Cell Biology (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., P.J.M.), The Ohio State University Wexner Medical Center, Columbus; Department of Biomedical Engineering, The Ohio State University College of Engineering, Columbus (S.D.U., J.S., T.J.H.); and Howard Hughes Medical Institute, Department of Biochemistry, Duke University Medical Center, Durham, NC (V.B.)
| | - Patrick J Wright
- From The Dorothy M. Davis Heart & Lung Research Institute (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., S.D.U., J.S., T.J.H., P.J.M. ), Departments of Internal Medicine (S.A.S., P.J.M.), and Physiology and Cell Biology (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., P.J.M.), The Ohio State University Wexner Medical Center, Columbus; Department of Biomedical Engineering, The Ohio State University College of Engineering, Columbus (S.D.U., J.S., T.J.H.); and Howard Hughes Medical Institute, Department of Biochemistry, Duke University Medical Center, Durham, NC (V.B.)
| | - Sathya D Unudurthi
- From The Dorothy M. Davis Heart & Lung Research Institute (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., S.D.U., J.S., T.J.H., P.J.M. ), Departments of Internal Medicine (S.A.S., P.J.M.), and Physiology and Cell Biology (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., P.J.M.), The Ohio State University Wexner Medical Center, Columbus; Department of Biomedical Engineering, The Ohio State University College of Engineering, Columbus (S.D.U., J.S., T.J.H.); and Howard Hughes Medical Institute, Department of Biochemistry, Duke University Medical Center, Durham, NC (V.B.)
| | - Jed Snyder
- From The Dorothy M. Davis Heart & Lung Research Institute (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., S.D.U., J.S., T.J.H., P.J.M. ), Departments of Internal Medicine (S.A.S., P.J.M.), and Physiology and Cell Biology (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., P.J.M.), The Ohio State University Wexner Medical Center, Columbus; Department of Biomedical Engineering, The Ohio State University College of Engineering, Columbus (S.D.U., J.S., T.J.H.); and Howard Hughes Medical Institute, Department of Biochemistry, Duke University Medical Center, Durham, NC (V.B.)
| | - Vann Bennett
- From The Dorothy M. Davis Heart & Lung Research Institute (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., S.D.U., J.S., T.J.H., P.J.M. ), Departments of Internal Medicine (S.A.S., P.J.M.), and Physiology and Cell Biology (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., P.J.M.), The Ohio State University Wexner Medical Center, Columbus; Department of Biomedical Engineering, The Ohio State University College of Engineering, Columbus (S.D.U., J.S., T.J.H.); and Howard Hughes Medical Institute, Department of Biochemistry, Duke University Medical Center, Durham, NC (V.B.)
| | - Thomas J Hund
- From The Dorothy M. Davis Heart & Lung Research Institute (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., S.D.U., J.S., T.J.H., P.J.M. ), Departments of Internal Medicine (S.A.S., P.J.M.), and Physiology and Cell Biology (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., P.J.M.), The Ohio State University Wexner Medical Center, Columbus; Department of Biomedical Engineering, The Ohio State University College of Engineering, Columbus (S.D.U., J.S., T.J.H.); and Howard Hughes Medical Institute, Department of Biochemistry, Duke University Medical Center, Durham, NC (V.B.)
| | - Peter J Mohler
- From The Dorothy M. Davis Heart & Lung Research Institute (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., S.D.U., J.S., T.J.H., P.J.M. ), Departments of Internal Medicine (S.A.S., P.J.M.), and Physiology and Cell Biology (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., P.J.M.), The Ohio State University Wexner Medical Center, Columbus; Department of Biomedical Engineering, The Ohio State University College of Engineering, Columbus (S.D.U., J.S., T.J.H.); and Howard Hughes Medical Institute, Department of Biochemistry, Duke University Medical Center, Durham, NC (V.B.).
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Zhang Y, Guzadhur L, Jeevaratnam K, Salvage SC, Matthews GDK, Lammers WJ, Lei M, Huang CL, Fraser JA. Arrhythmic substrate, slowed propagation and increased dispersion in conduction direction in the right ventricular outflow tract of murine Scn5a+/- hearts. Acta Physiol (Oxf) 2014; 211:559-73. [PMID: 24913289 PMCID: PMC4296345 DOI: 10.1111/apha.12324] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2013] [Revised: 05/23/2014] [Accepted: 06/03/2014] [Indexed: 12/18/2022]
Abstract
Aim To test a hypothesis attributing arrhythmia in Brugada Syndrome to right ventricular (RV) outflow tract (RVOT) conduction abnormalities arising from Nav1.5 insufficiency and fibrotic change. Methods Arrhythmic properties of Langendorff-perfused Scn5a+/− and wild-type mouse hearts were correlated with ventricular effective refractory periods (VERPs), multi-electrode array (MEA) measurements of action potential (AP) conduction velocities and dispersions in conduction direction (CD), Nav1.5 expression levels, and fibrotic change, as measured at the RVOT and RV. Two-way anova was used to test for both independent and interacting effects of anatomical region and genotype on these parameters. Results Scn5a+/− hearts showed greater arrhythmic frequencies during programmed electrical stimulation at the RVOT but not the RV. The Scn5a+/− genotype caused an independent increase of VERP regardless of whether the recording site was the RVOT or RV. Effective AP conduction velocities (CV†s), derived from fitting regression planes to arrays of observed local activation times were reduced in Scn5a+/− hearts and at the RVOT independently. AP conduction velocity magnitudes derived by averaging MEA results from local vector analyses, CV*, were reduced by the Scn5a+/− genotype alone. In contrast, dispersions in conduction direction, were greater in the RVOT than the RV, when the atrioventricular node was used as the pacing site. The observed reductions in Nav1.5 expression were attributable to Scn5a+/−, whereas increased levels of fibrosis were associated with the RVOT. Conclusions The Scn5a+/− RVOT recapitulates clinical findings of increased arrhythmogenicity through reduced CV† reflecting reduced CV* attributable to reduced Nav1.5 expression and increased CD attributable to fibrosis.
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Affiliation(s)
- Y. Zhang
- Physiological Laboratory University of Cambridge Cambridge UK
- Heart Centre Northwest Women's and Children's Hospital Xi'an China
| | - L. Guzadhur
- Physiological Laboratory University of Cambridge Cambridge UK
| | - K. Jeevaratnam
- Physiological Laboratory University of Cambridge Cambridge UK
- Perdana University‐Royal College of Surgeons Ireland Selangor Malaysia
| | - S. C. Salvage
- Physiological Laboratory University of Cambridge Cambridge UK
| | | | - W. J. Lammers
- Department of Physiology College of Medicine and Health Sciences Al Ain UAE
| | - M. Lei
- Department of Pharmacology University of Oxford Oxford UK
| | - C. L.‐H. Huang
- Physiological Laboratory University of Cambridge Cambridge UK
- Department of Biochemistry University of Cambridge Cambridge UK
| | - J. A. Fraser
- Physiological Laboratory University of Cambridge Cambridge UK
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Matthews GDK, Guzadhur L, Sabir IN, Grace AA, Huang CLH. Action potential wavelength restitution predicts alternans and arrhythmia in murine Scn5a(+/-) hearts. J Physiol 2013; 591:4167-88. [PMID: 23836691 PMCID: PMC3779110 DOI: 10.1113/jphysiol.2013.254938] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Reductions in cardiac action potential wavelength, and the consequent wavebreak, have been implicated in arrhythmogenesis. Tachyarrhythmias are more common in the Brugada syndrome, particularly following pharmacological challenge, previously modelled using Scn5a+/− murine hearts. Propagation latencies and action potential durations (APDs) from monophasic action potential recordings were used to assess wavelength changes with heart rate in Langendorff-perfused wild-type (WT) and Scn5a+/− hearts. Recordings were obtained from right (RV) and left (LV) ventricular, epicardial and endocardial surfaces during incremental pacing, before and following flecainide or quinidine challenge. Conduction velocities (θ′), action potential wavelengths (λ′= APD ×θ′), and their corresponding alternans depended non-linearly upon diastolic interval (DI). Maximum θ′ was lower in Scn5a+/− RV epicardium than endocardium. Flecainide further reduced θ′, accentuating this RV conduction block. Quinidine reduced maximum θ′ in WT and caused earlier conduction failure in the RV of both Scn5a+/− and WT. Use of recovery wavelengths (λ′0= DI ×θ′) rather than DI, provided novel λ restitution plots of λ′ against λ′0, which sum to a basic cycle distance permitting feedback analysis. λ′ restitution gradient better correlated with alternans magnitude than either APD or θ restitution gradient. The large differences in θ′ and APD restitution contrasted with minor differences in maximum λ′ between epi- and endocardia of untreated hearts, and quinidine-treated WT hearts. Strikingly, all regions and conditions converged to a common instability point, implying a conserved relationship. Flecainide or quinidine decreased the pacing rates at which this occurred, through reducing basic cycle distance, in the Scn5a+/− RV epicardium, directly predictive of its arrhythmic phenotype.
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Affiliation(s)
- Gareth D K Matthews
- G. D. K. Matthews: Physiological Laboratory, University of Cambridge, Downing Street, Cambridge CB2 3EG, UK.
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Jeevaratnam K, Rewbury R, Zhang Y, Guzadhur L, Grace AA, Lei M, Huang CLH. Frequency distribution analysis of activation times and regional fibrosis in murine Scn5a+/- hearts: the effects of ageing and sex. Mech Ageing Dev 2012; 133:591-9. [PMID: 22968175 PMCID: PMC3466423 DOI: 10.1016/j.mad.2012.07.006] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2011] [Revised: 07/17/2012] [Accepted: 07/31/2012] [Indexed: 12/21/2022]
Abstract
Both Brugada Syndrome (BrS) and progressive cardiac conduction defect (PCCD) are associated respectively with diffuse and discrete alterations in conduction pathways affected by ageing and sex. This study assessed for contributions of such processes to the mechanism of conduction changes in Scn5a+/− and WT hearts stratified by age (3 and 12 months) and sex. In vivo electrocardiographic chest-lead assessment demonstrated greater incidences of bundle branch block in all Scn5a+/− mice compared to WT. Frequency analysis of right ventricular (RV) epicardial activation obtained from a 64-channel multi-electrode array demonstrated greater prominence of late conducting components in Scn5a+/− compared to WT male, and in male compared to female Scn5a+/− following stratification by genotype and sex. Similar differences were observed between old male Scn5a+/− and young male Scn5a+/−, old female Scn5a+/−, and old male WT, following stratification by genotype, age and sex. These findings directly correlated with histomorphometric assessment of regional fibrosis in both septa and free walls preferentially involving the RV. We demonstrate complex alterations in conduction distributions suggesting a conversion of normal to slow-conducting tissue, modulated by ageing and sex, coupled with fibrosis in Scn5a+/− hearts. These features suggest an overlap between pathophysiological processes related to BrS and PCCD in Scn5a+/− hearts.
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Affiliation(s)
- Kamalan Jeevaratnam
- Physiological Laboratory, University of Cambridge, Downing Street, Cambridge CB2 3EG, United Kingdom.
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23
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Cerrone M, Noorman M, Lin X, Chkourko H, Liang FX, van der Nagel R, Hund T, Birchmeier W, Mohler P, van Veen TA, van Rijen HV, Delmar M. Sodium current deficit and arrhythmogenesis in a murine model of plakophilin-2 haploinsufficiency. Cardiovasc Res 2012; 95:460-8. [PMID: 22764151 DOI: 10.1093/cvr/cvs218] [Citation(s) in RCA: 148] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
AIMS The shRNA-mediated loss of expression of the desmosomal protein plakophilin-2 leads to sodium current (I(Na)) dysfunction. Whether pkp2 gene haploinsufficiency leads to I(Na) deficit in vivo remains undefined. Mutations in pkp2 are detected in arrhythmogenic right ventricular cardiomyopathy (ARVC). Ventricular fibrillation and sudden death often occur in the 'concealed phase' of the disease, prior to overt structural damage. The mechanisms responsible for these arrhythmias remain poorly understood. We sought to characterize the morphology, histology, and ultrastructural features of PKP2-heterozygous-null (PKP2-Hz) murine hearts and explore the relation between PKP2 abundance, I(Na) function, and cardiac electrical synchrony. METHODS AND RESULTS Hearts of PKP2-Hz mice were characterized by multiple methods. We observed ultrastructural but not histological or gross anatomical differences in PKP2-Hz hearts compared with wild-type (WT) littermates. Yet, in myocytes, decreased amplitude and a shift in gating and kinetics of I(Na) were observed. To further unmask I(Na) deficiency, we exposed myocytes, Langendorff-perfused hearts, and anaesthetized animals to a pharmacological challenge (flecainide). In PKP2-Hz hearts, the extent of flecainide-induced I(Na) block, impaired ventricular conduction, and altered electrocardiographic parameters were larger than controls. Flecainide provoked ventricular arrhythmias and death in PKP2-Hz animals, but not in the WT. CONCLUSIONS PKP2 haploinsufficiency leads to I(Na) deficit in murine hearts. Our data support the notion of a cross-talk between desmosome and sodium channel complex. They also suggest that I(Na) dysfunction may contribute to generation and/or maintenance of arrhythmias in PKP2-deficient hearts. Whether pharmacological challenges could help unveil arrhythmia risk in patients with mutations or variants in PKP2 remains undefined.
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Affiliation(s)
- Marina Cerrone
- Division of Cardiology, New York University School of Medicine, New York, NY, USA
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Derangeon M, Montnach J, Baró I, Charpentier F. Mouse Models of SCN5A-Related Cardiac Arrhythmias. Front Physiol 2012; 3:210. [PMID: 22737129 PMCID: PMC3381239 DOI: 10.3389/fphys.2012.00210] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2012] [Accepted: 05/29/2012] [Indexed: 12/19/2022] Open
Abstract
Mutations of SCN5A gene, which encodes the α-subunit of the voltage-gated Na+ channel NaV1.5, underlie hereditary cardiac arrhythmic syndromes such as the type 3 long QT syndrome, cardiac conduction diseases, the Brugada syndrome, the sick sinus syndrome, a trial standstill, and numerous overlap syndromes. Patch-clamp studies in heterologous expression systems have provided important information to understand the genotype-phenotype relationships of these diseases. However, they could not clarify how SCN5A mutations can be responsible for such a large spectrum of diseases, for the late age of onset or the progressiveness of some of these diseases and for the overlapping syndromes. Genetically modified mice rapidly appeared as promising tools for understanding the pathophysiological mechanisms of cardiac SCN5A-related arrhythmic syndromes and several mouse models have been established. This review presents the results obtained on these models that, for most of them, recapitulate the clinical phenotypes of the patients. This includes two models knocked out for Nav1.5 β1 and β3 auxiliary subunits that are also discussed. Despite their own limitations that we point out, the mouse models still appear as powerful tools to elucidate the pathophysiological mechanisms of SCN5A-related diseases and offer the opportunity to investigate the secondary cellular consequences of SCN5A mutations such as the expression remodeling of other genes. This points out the potential role of these genes in the overall human phenotype. Finally, they constitute useful tools for addressing the role of genetic and environmental modifiers on cardiac electrical activity.
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Guzadhur L, Jiang W, Pearcey SM, Jeevaratnam K, Duehmke RM, Grace AA, Lei M, Huang CLH. The Age-dependence of atrial arrhythmogenicity in Scn5a+/−murine hearts reflects alterations in action potential propagation and recovery. Clin Exp Pharmacol Physiol 2012; 39:518-27. [DOI: 10.1111/j.1440-1681.2012.05706.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Laila Guzadhur
- Physiological Laboratory; University of Cambridge; Cambridge; UK
| | - Wenhui Jiang
- Medical College of Xi'an Jiaotong University; Xi'an; China
| | - Sarah M Pearcey
- Physiological Laboratory; University of Cambridge; Cambridge; UK
| | | | - Rudy M Duehmke
- Physiological Laboratory; University of Cambridge; Cambridge; UK
| | - Andrew A Grace
- Department of Biochemistry; University of Cambridge; Cambridge; UK
| | - Ming Lei
- Institute of Cardiovascular Sciences; University of Manchester; Manchester; UK
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Matthews GDK, Guzadhur L, Grace A, Huang CLH. Nonlinearity between action potential alternans and restitution, which both predict ventricular arrhythmic properties in Scn5a+/- and wild-type murine hearts. J Appl Physiol (1985) 2012; 112:1847-63. [PMID: 22461438 DOI: 10.1152/japplphysiol.00039.2012] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Electrocardiographic QT- and T-wave alternans, presaging ventricular arrhythmia, reflects compromised adaptation of action potential (AP) duration (APD) to altered heart rate, classically attributed to incomplete Na(v)1.5 channel recovery prior to subsequent stimulation. The restitution hypothesis suggests a function whose slope directly relates to APD alternans magnitude, predicting a critical instability condition, potentially generating arrhythmia. The present experiments directly test for such correlations among arrhythmia, APD alternans and restitution. Mice haploinsufficient in the Scn5a, cardiac Na(+) channel gene (Scn5a(+/-)), previously used to replicate Brugada syndrome, were used, owing to their established arrhythmic properties increased by flecainide and decreased by quinidine, particularly in right ventricular (RV) epicardium. Monophasic APs, obtained during pacing with progressively decrementing cycle lengths, were systematically compared at RV and left ventricular epicardial and endocardial recording sites in Langendorff-perfused Scn5a(+/-) and wild-type hearts before and following flecainide (10 μM) or quinidine (5 μM) application. The extent of alternans was assessed using a novel algorithm. Scn5a(+/-) hearts showed greater frequencies of arrhythmic endpoints with increased incidences of ventricular tachycardia, diminished by quinidine, and earlier onsets of ventricular fibrillation, particularly following flecainide challenge. These features correlated directly with increased refractory periods, specifically in the RV, and abnormal restitution and alternans properties in the RV epicardium. The latter variables were related by a unique, continuous higher-order function, rather than a linear relationship with an unstable threshold. These findings demonstrate a specific relationship between alternans and restitution, as well as confirming their capacity to predict arrhythmia, but implicate mechanisms additional to the voltage feedback suggested in the restitution hypothesis.
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Affiliation(s)
- Gareth D K Matthews
- Physiological Laboratory, University of Cambridge, Cambridge, United Kingdom.
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Tse G, Hothi SS, Grace AA, Huang CLH. Ventricular arrhythmogenesis following slowed conduction in heptanol-treated, Langendorff-perfused mouse hearts. J Physiol Sci 2012; 62:79-92. [PMID: 22219003 PMCID: PMC10717265 DOI: 10.1007/s12576-011-0187-2] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2011] [Accepted: 11/28/2011] [Indexed: 10/14/2022]
Abstract
Arrhythmogenic effects of slowed action potential conduction produced by the gap junction and sodium-channel inhibitor heptanol (0.1-2 mM) were explored in Langendorff-perfused mouse hearts. Monophasic action potential recordings showed that 2 mM heptanol induced ventricular tachycardia in the absence of triggered activity arising from early or after-depolarizations during regular 8 Hz pacing and programmed electrical stimulation (PES). It also increased activation latencies and ventricular effective refractory periods (VERPs), but did not alter action potential duration (APD), thereby reducing local critical intervals for re-excitation given by APD(90) - VERP. Bipolar electrogram recordings showed that 2 mM heptanol increased electrogram duration (EGD) and ratios of EGDs obtained at the longest to those obtained at the shortest S1S2 intervals studied during PES, suggesting increased dispersion of conduction velocities. These findings show, for the first time in the mouse heart, that slowed conduction induces reversible arrhythmogenic effects despite repolarization abnormalities expected to reduce arrhythmogenicity.
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Affiliation(s)
- Gary Tse
- Section of Cardiovascular Biology, Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QW UK
| | - Sandeep S. Hothi
- The Physiological Laboratory, University of Cambridge, Downing Street, Cambridge, CB2 3EG UK
- Addenbrooke’s Hospital, Hills Road, Cambridge, CB2 0QQ UK
| | - Andrew A. Grace
- Section of Cardiovascular Biology, Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QW UK
| | - Christopher L. -H. Huang
- Section of Cardiovascular Biology, Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QW UK
- The Physiological Laboratory, University of Cambridge, Downing Street, Cambridge, CB2 3EG UK
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Martin CA, Grace AA, Huang CLH. Refractory dispersion promotes conduction disturbance and arrhythmias in a Scn5a (+/-) mouse model. Pflugers Arch 2011; 462:495-504. [PMID: 21779762 PMCID: PMC3170477 DOI: 10.1007/s00424-011-0989-3] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2011] [Revised: 06/10/2011] [Accepted: 06/15/2011] [Indexed: 11/29/2022]
Abstract
Accentuated right ventricular (RV) gradients in action potential duration (APD) have been implicated in the arrhythmogenicity observed in Brugada syndrome in studies assuming that ventricular effective refractory periods (VERPs) vary in concert with APDs. The present experiments use a genetically modified mouse model to explore spatial heterogeneities in VERP that in turn might affect conduction velocity, thereby causing arrhythmias. Activation latencies, APDs and VERPs recorded during programmed S1S2 protocols were compared in RV and left ventricular (LV) epicardia and endocardia of Langendorff-perfused wild-type (WT) and Scn5a+/− hearts. Scn5a+/− and WT hearts showed similar patterns of shorter VERPs in RV than LV epicardia, and in epicardia than endocardia. However, Scn5a+/− hearts showed longer VERPs, despite shorter APD90s, than WT in all regions examined. The pro- and anti-arrhythmic agents flecainide and quinidine increased regional VERPs despite respectively decreasing and increasing the corresponding APD90s particularly in Scn5a+/− RV epicardia. In contrast, Scn5a+/− hearts showed greater VERP gradients between neighbouring regions, particularly RV transmural gradients, than WT (9.1 ± 1.1 vs. 5.7 ± 0.5 ms, p < 0.05, n = 12). Flecainide increased (to 21 ± 0.9 ms, p < 0.05, n = 6) but quinidine decreased (to 4.5 ± 0.5 ms, p < 0.05, n = 6) these gradients, particularly across the Scn5a+/− RV. Finally, Scn5a+/− hearts showed greater conduction slowing than WT following S2 stimuli, particularly with flecainide administration. Rather than arrhythmogenesis resulting from increased transmural repolarization gradients in an early, phase 2, reentrant excitation mechanism, the present findings implicate RV VERP gradients in potential reentrant mechanisms involving impulse conduction slowed by partial refractoriness.
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Affiliation(s)
- Claire A Martin
- Physiological Laboratory, University of Cambridge, Downing Site, Cambridge, CB2 3EG, UK.
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Martin CA, Zhang Y, Grace AA, Huang CLH. Increased right ventricular repolarization gradients promote arrhythmogenesis in a murine model of Brugada syndrome. J Cardiovasc Electrophysiol 2011; 21:1153-9. [PMID: 20384647 PMCID: PMC3084998 DOI: 10.1111/j.1540-8167.2010.01767.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Repolarization Gradients in Brugada Syndrome.Introduction: Brugada syndrome (BrS) is associated with loss of Na+ channel function and increased risks of a ventricular tachycardia exacerbated by flecainide but reduced by quinidine. Previous studies in nongenetic models have implicated both altered conduction times and repolarization gradients in this arrhythmogenicity. We compared activation latencies and spatial differences in action potential recovery between different ventricular regions in a murine Scn5a+/− BrS model, and investigated the effect of flecainide and quinidine upon these. Methods and Results: Langendorff-perfused wild-type and Scn5a+/− hearts were subjected to regular pacing and a combination of programmed electrical stimulation techniques. Monophasic action potentials were recorded from the right (RV) and left ventricular (LV) epicardium and endocardium before and following flecainide (10 μM) or quinidine (5 μM) treatment, and activation latencies measured. Transmural repolarization gradients were then calculated from the difference between neighboring endocardial and epicardial action potential durations (APDs). Scn5a+/− hearts showed decreased RV epicardial APDs, accentuating RV, but not LV, transmural gradients. This correlated with increased arrhythmic tendencies compared with wild-type. Flecainide increased RV transmural gradients, while quinidine decreased them, in line with their respective pro- and antiarrhythmic effects. In contrast, Scna5+/− hearts showed slowed conduction times in both RV and LV, exacerbated not only by flecainide but also by quinidine, in contrast to their differing effects on arrhythmogenesis. Conclusion: We use a murine genetic model of BrS to systematically analyze LV and RV action potential kinetics for the first time. This establishes a key role for accentuated transmural gradients, specifically in the RV, in its arrhythmogenicity. (J Cardiovasc Electrophysiol, Vol. 21, pp. 1153-1159)
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Affiliation(s)
- Claire A Martin
- Physiological Laboratory, University of Cambridge, Downing Site, Cambridge, United Kingdom.
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Jeevaratnam K, Poh Tee S, Zhang Y, Rewbury R, Guzadhur L, Duehmke R, Grace AA, Lei M, Huang CLH. Delayed conduction and its implications in murine Scn5a(+/-) hearts: independent and interacting effects of genotype, age, and sex. Pflugers Arch 2010; 461:29-44. [PMID: 21127902 PMCID: PMC3016216 DOI: 10.1007/s00424-010-0906-1] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2010] [Revised: 10/29/2010] [Accepted: 11/12/2010] [Indexed: 11/28/2022]
Abstract
We explored for relationships between SCN5A haploinsufficiency, implicated in clinical arrhythmogenicity, and right ventricular (RV) conduction disorders in Langendorff-perfused, male and female, and young (3 months) and old (>12 month old) Scn5a+/− and wild type (WT) hearts. The investigated conditions of genotype, age, and sex affected latencies but not repolarization time courses of RV monophasic action potentials. This prompted examination of the patterns of RV epicardial activation, its dispersion, and their interrelationships as possible arrhythmic mechanisms using a 64-channel, multi-electrode array. Mean ventricular activation times (T*MEAN), spatial dispersions (D*S) between recording channels/cardiac cycle, and maximum activation times (T*MAX) representing the slowest possible conduction in any given heart were all higher in old male Scn5a+/− compared with young male and old female Scn5a+/− and old male WT. Temporal dispersions (D*T) of recording channels were similarly higher in old male Scn5a+/− compared with old male WT. All groupings of D*T, D*S, and T*MAX nevertheless linearly correlated with T*MEAN, with indistinguishable slopes. The variates explored thus influence D*T, D*S, and T*MAX through actions on T*MEAN. These findings in turn correlated with increased levels of fibrosis in young male, young female, and old male Scn5a+/− compared with the corresponding WTs. We thus demonstrate for the first time independent and interacting effects of genotype, age, and sex on epicardial conduction and its dispersions at least partially attributable to fibrotic change, resulting in the greatest effects in old male Scn5a+/− in an absence of alterations in repolarization time courses. This directly implicates altered depolarization in the clinical arrhythmogenicity associated with Scn5a+/−.
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Affiliation(s)
- Kamalan Jeevaratnam
- Physiological Laboratory, University of Cambridge, Downing Street, Cambridge, UK.
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Martin CA, Grace AA, Huang CLH. Spatial and temporal heterogeneities are localized to the right ventricular outflow tract in a heterozygotic Scn5a mouse model. Am J Physiol Heart Circ Physiol 2010; 300:H605-16. [PMID: 21097662 PMCID: PMC3044044 DOI: 10.1152/ajpheart.00824.2010] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Ventricular tachycardia (VT) in Brugada Syndrome patients often originates in the right ventricular outflow tract (RVOT). We explore the physiological basis for this observation using murine whole heart preparations. Ventricular bipolar electrograms and monophasic action potentials were recorded from seven epicardial positions in Langendorff-perfused wild-type and Scn5a+/− hearts. VT first appeared in the RVOT, implicating it as an arrhythmogenic focus in Scn5a+/− hearts. RVOTs showed the greatest heterogeneity in refractory periods, response latencies, and action potential durations, and the most fractionated electrograms. However, incidences of concordant alternans in dynamic pacing protocol recordings were unaffected by the Scn5a+/− mutation or pharmacological intervention. Conversely, particularly at the RVOT, Scn5a+/− hearts showed earlier and more frequent transitions into discordant alternans. This was accentuated by flecainide, but reduced by quinidine, in parallel with their respective pro- and anti-arrhythmic effects. Discordant alternans preceded all episodes of VT. The RVOT of Scn5a+/− hearts also showed steeper restitution curves, with the diastolic interval at which the gradient equaled one strongly correlating with the diastolic interval at which discordant alternans commenced. We attribute the arrhythmic tendency within the RVOT to the greater spatial heterogeneities in baseline electrophysiological properties. These, in turn, give rise to a tendency to drive concordant alternans phenomena into an arrhythmogenic discordant alternans. Our findings may contribute to future work investigating possible pharmacological treatments for a disease in which the current mainstay of treatment is implantable cardioverter defibrillator implantation.
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Affiliation(s)
- Claire A Martin
- Physiological Laboratory, Department of Biochemistry, University of Cambridge, Downing Site, Cambridge CB2 3EG, UK.
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Matthews GDK, Martin CA, Grace AA, Zhang Y, Huang CLH. Regional variations in action potential alternans in isolated murine Scn5a (+/-) hearts during dynamic pacing. Acta Physiol (Oxf) 2010; 200:129-46. [PMID: 20384594 DOI: 10.1111/j.1748-1716.2010.02138.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
AIM clinical observations suggest that alternans in action potential (AP) characteristics presages breakdown of normal ordered cardiac electrical activity culminating in ventricular arrhythmogenesis. We compared such temporal nonuniformities in monophasic action potential (MAP) waveforms in left (LV) and right ventricular (RV) epicardia and endocardia of Langendorff-perfused murine wild-type (WT), and Scn5a(+/-) hearts modelling Brugada syndrome (BrS) for the first time. METHODS a dynamic pacing protocol imposed successively incremented steady pacing rates between 5.5 and 33 Hz. A signal analysis algorithm detected sequences of >10 beats showing alternans. Results were compared before and following the introduction of flecainide (10 microm) and quinidine (5 microm) known to exert pro- and anti-arrhythmic effects in BrS. RESULTS sustained and transient amplitude and duration alternans were both frequently followed by ventricular ectopic beats and ventricular tachycardia or fibrillation. Diastolic intervals (DIs) that coincided with onsets of transient (tr) or sustained (ss) alternans in MAP duration (DI*) and amplitude (DI') were determined. Kruskal-Wallis tests followed by Bonferroni-corrected Mann-Whitney U-tests were applied to these DI results sorted by recording site, pharmacological conditions or experimental populations. WT hearts showed no significant heterogeneities in any DI. Untreated Scn5a (+/-) hearts showed earlier onsets of transient but not sustained duration alternans in LV endocardium compared with RV endocardium or LV epicardium. Flecainide administration caused earlier onsets of both transient and sustained duration alternans selectively in the RV epicardium in the Scn5a (+/-) hearts. CONCLUSION these findings in a genetic model thus implicate RV epicardial changes in the arrhythmogenicity produced by flecainide challenge in previously asymptomatic clinical BrS.
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Affiliation(s)
- G D K Matthews
- Physiological Laboratory, University of Cambridge, Cambridge
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Jeevaratnam K, Zhang Y, Guzadhur L, Duehmke RM, Lei M, Grace AA, Huang CLH. Differences in sino-atrial and atrio-ventricular function with age and sex attributable to the Scn5a+/- mutation in a murine cardiac model. Acta Physiol (Oxf) 2010; 200:23-33. [PMID: 20331542 DOI: 10.1111/j.1748-1716.2010.02110.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
AIM To investigate the interacting effects of age and sex on electrocardiographic (ECG) features of Scn5a(+/-) mice modelling Brugada syndrome. METHODS Recordings were performed on anaesthetized wild-type (WT) and Scn5a(+/-) mice and differences attributable to these risk factors statistically stratified. RESULTS Scn5a(+/-) exerted sex-dependent effects upon sino-atrial function that only became apparent with age. RR intervals were greater in old male than in old female Scn5a(+/-). Atrio-ventricular (AV) conduction was slower in young female mice, whether WT and Scn5a(+/-), than the corresponding young male WT and Scn5a(+/-). However, PR intervals lengthened with age in male but not in female Scn5a(+/-) giving the greatest PR intervals in old male Scn5a(+/-) compared with either old male WT or young male Scn5a(+/-) mice. In contrast, PR intervals were similar in old female Scn5a(+/-) and in old female WT. QTc was prolonged in Scn5a(+/-) compared with WT, and female Scn5a(+/-) compared with female WT. Age-dependent alterations in durations of ventricular repolarization relative to WT affected male but not female Scn5a(+/-). Thus, T-wave durations were greater in old male Scn5a(+/-) compared with old male WT, but indistinguishable between old female Scn5a(+/-) and old female WT. Finally, analysis for combined interactions of genotype, age and sex demonstrated no effects on P wave and QRS durations and QTc intervals. CONCLUSION We demonstrate for the first time that age, sex and genotype exert both independent and interacting ECG effects. The latter suggest alterations in cardiac pacemaker function, atrio-ventricular conduction and ventricular repolarization greatest in ageing male Scn5a(+/-).
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Affiliation(s)
- K Jeevaratnam
- Physiological Laboratory, University of Cambridge, Cambridge, UK
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Dautova Y, Zhang Y, Grace AA, Huang CLH. Experimental Physiology -Research Paper: Atrial arrhythmogenic properties in wild-type andScn5a+/− murine hearts. Exp Physiol 2010; 95:994-1007. [DOI: 10.1113/expphysiol.2010.053868] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Farkas AS, Nattel S. Minimizing Repolarization-Related Proarrhythmic Risk in Drug Development and Clinical Practice. Drugs 2010; 70:573-603. [DOI: 10.2165/11535230-000000000-00000] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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Postema PG, Wolpert C, Amin AS, Probst V, Borggrefe M, Roden DM, Priori SG, Tan HL, Hiraoka M, Brugada J, Wilde AAM. Drugs and Brugada syndrome patients: review of the literature, recommendations, and an up-to-date website (www.brugadadrugs.org). Heart Rhythm 2009; 6:1335-41. [PMID: 19716089 DOI: 10.1016/j.hrthm.2009.07.002] [Citation(s) in RCA: 253] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/26/2009] [Accepted: 07/03/2009] [Indexed: 10/20/2022]
Abstract
BACKGROUND Worldwide, the Brugada syndrome has been recognized as an important cause of sudden cardiac death in individuals at a relatively young age. Importantly, many drugs have been reported to induce the characteristic Brugada syndrome-linked ECG abnormalities and/or (fatal) ventricular tachyarrhythmias. OBJECTIVE The purpose of this study was to review the literature on the use of drugs in Brugada syndrome patients, to make recommendations based on the literature and on expert opinion regarding drug safety, and to ensure worldwide online and up-to-date availability of this information to all physicians who treat Brugada syndrome patients. METHODS We performed an extensive review of the literature, formed an international expert panel to produce a consensus recommendation to each drug, and initiated a website (www.brugadadrugs.org). RESULTS The literature search yielded 506 reports for consideration. Drugs were categorized into one of four categories: (1) drugs to be avoided (n = 18); (2) drugs preferably avoided (n = 23); (3) antiarrhythmic drugs (n = 4); and (4) diagnostic drugs (n = 4). Level of evidence for most associations was C (only consensus opinion of experts, case studies, or standard-of-care) as there are no randomized studies and few nonrandomized studies in Brugada syndrome patients. CONCLUSION Many drugs have been associated with adverse events in Brugada syndrome patients. We have initiated a website (www.brugadadrugs.org) to ensure worldwide availability of information on safe drug use in Brugada syndrome patients.
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Affiliation(s)
- Pieter G Postema
- Department of Cardiology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
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Abstract
Since the identification of the first SCN5A mutation associated with long QT syndrome in 1995, several mutations in this gene for the alpha subunit of the cardiac sodium channel have been identified in a heterogeneous subset of cardiac rhythm syndromes, including Brugada syndrome, progressive cardiac conduction defect, sick sinus node syndrome, atrial fibrillation and dilated cardiomyopathy. Robust clinical evidence has been accompanied by bench studies performed in different models spanning from in vitro expression systems to transgenic mice. Together, these studies have helped establish genotype-phenotype correlations and have shaped our understanding of the role of the cardiac sodium channel in health and in disease. Remarkably, these advances in understanding have impacted on clinical management by allowing us to start developing gene-specific risk stratification schemes and mutation-specific management strategies. In this Review, we summarize the current understanding of the molecular mechanism of SCN5A-associated inherited arrhythmias, focusing on the most recent development of mutation-specific management in SCN5A-associated long QT syndrome type 3. We also briefly discuss arrhythmia-causing mutations in the genes encoding the beta subunit of the cardiac sodium channel and in those encoding proteins in the associated macromolecular complex.
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Zhang Y, Schwiening C, Killeen MJ, Zhang Y, Ma A, Lei M, Grace AA, Huang CLH. Pharmacological changes in cellular Ca2+ homeostasis parallel initiation of atrial arrhythmogenesis in murine Langendorff-perfused hearts. Clin Exp Pharmacol Physiol 2009; 36:969-80. [PMID: 19298534 PMCID: PMC2841827 DOI: 10.1111/j.1440-1681.2009.05170.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
1. Intracellular Ca(2+) overload has been associated with established atrial arrhythmogenesis. The present experiments went on to correlate acute initiation of atrial arrhythmogenesis in Langendorff-perfused mouse hearts with changes in Ca(2+) homeostasis in isolated atrial myocytes following pharmacological procedures that modified the storage or release of sarcoplasmic reticular (SR) Ca(2+) or inhibited entry of extracellular Ca(2+). 2. Caffeine (1 mmol/L) elicited diastolic Ca(2+) waves in regularly stimulated atrial myocytes immediately following addition. This was followed by a decline in the amplitude of the evoked transients and the disappearance of such diastolic events, suggesting partial SR Ca(2+) depletion. 3. Cyclopiazonic acid (CPA; 0.15 micromol/L) produced more gradual reductions in evoked Ca(2+) transients and abolished diastolic Ca(2+) events produced by the further addition of caffeine. 4. Nifedipine (0.5 micromol/L) produced immediate reductions in evoked Ca(2+) transients. Further addition of caffeine produced an immediate increase followed by a decline in the amplitude of the evoked Ca(2+) transients, without eliciting diastolic Ca(2+) events. 5. These findings correlated with changes in spontaneous and provoked atrial arrhythmogenecity in mouse isolated Langendorf-perfused hearts. Thus, caffeine was pro-arrhythmogenic immediately following but not > 5 min after application and both CPA and nifedipine pretreatment inhibited such arrhythmogenesis. 6. Together, these findings relate acute atrial arrhythmogenesis in intact hearts to diastolic Ca(2+) events in atrial myocytes that, in turn, depend upon a finite SR Ca(2+) store and diastolic Ca(2+) release following Ca(2+)-induced Ca(2+) release initiated by the entry of extracellular Ca(2+).
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Affiliation(s)
- Yanmin Zhang
- Physiological Laboratory, University of Cambridge, Cambridge, UK
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Dautova Y, Zhang Y, Sabir I, Grace AA, Huang CLH. Atrial arrhythmogenesis in wild-type and Scn5a+/delta murine hearts modelling LQT3 syndrome. Pflugers Arch 2009; 458:443-57. [PMID: 19184093 PMCID: PMC2691533 DOI: 10.1007/s00424-008-0633-z] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2008] [Accepted: 12/25/2008] [Indexed: 01/02/2023]
Abstract
Long QT(3) (LQT3) syndrome is associated with abnormal repolarisation kinetics, prolonged action potential durations (APD) and QT intervals and may lead to life-threatening ventricular arrhythmias. However, there have been few physiological studies of its effects on atrial electrophysiology. Programmed electrical stimulation and burst pacing induced atrial arrhythmic episodes in 16 out of 16 (16/16) wild-type (WT) and 7/16 genetically modified Scn5a+/Δ (KPQ) Langendorff-perfused murine hearts modelling LQT3 (P < 0.001 for both), and in 14/16 WT and 1/16 KPQ hearts (P < 0.001 for both; Fisher’s exact test), respectively. The arrhythmogenic WT hearts had significantly larger positive critical intervals (CI), given by the difference between atrial effective refractory periods (AERPs) and action potential durations at 90% recovery (APD90), compared to KPQ hearts (8.1 and 3.2 ms, respectively, P < 0.001). Flecainide prevented atrial arrhythmias in all arrhythmogenic WT (P < 0.001) and KPQ hearts (P < 0.05). It prolonged the AERP to a larger extent than it did the APD90 in both WT and KPQ groups, giving negative CIs. Quinidine similarly exerted anti-arrhythmic effects, prolonged AERP over corresponding APD90 in both WT and KPQ groups. These findings, thus, demonstrate, for the first time, inhibitory effects of the KPQ mutation on atrial arrhythmogenesis and its modification by flecainide and quinidine. They attribute these findings to differences in the CI between WT and mutant hearts, in the presence or absence of these drugs. Thus, prolongation of APD90 over AERP gave positive CI values and increased atrial arrhythmogenicity whereas lengthening of AERP over APD90 reduced such CI values and produced the opposite effect.
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Affiliation(s)
- Yana Dautova
- Cardiovascular Biology Group, Physiological Laboratory, University of Cambridge, Cambridge, UK
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Anti-arrhythmic effects of cyclopiazonic acid in Langendorff-perfused murine hearts. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2009; 98:281-8. [PMID: 19351518 DOI: 10.1016/j.pbiomolbio.2009.01.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We investigated the effects of reducing sarcoplasmic reticular (SR) Ca(2+) stores using the Ca(2+)-ATPase inhibitor cyclopiazonic acid (CPA) in Langendorff-perfused mouse hearts exposed to different pro-arrhythmic agents all known to produce Ca(2+)-mediated arrhythmogenesis. CPA (100 and 150 nM) produced progressive (beginning over approximately 1 min) and significant (P<0.0001) reductions in peak amplitudes of Ca(2+) transients evoked by regular stimulation in isolated Fluo-3 loaded myocytes from F/F(0)=3.2+/-0.16 (n=12 cells) to 1.62+/-0.012 (n=6 cells) and 1.53+/-0.06 (n=12 cells), respectively, consistent with previous reports describing reductions of store Ca(2+) in other cell systems. The corresponding effects of CPA were then examined in intact hearts exposed to isoproterenol (100 nM), elevated extracellular [Ca(2+)] (5mM) and caffeine (1mM). All three agents produced ventricular tachycardia either when added alone or simultaneously with CPA during programmed electrical stimulation. However, arrhythmogenicity was not observed when such agents were added approximately 10 min after introduction of CPA. CPA thus antagonized this Ca(2+)-mediated arrhythmogenesis but only under circumstances of SR Ca(2+) depletion. These alterations in arrhythmogenic tendency took place despite an absence of alterations in electrogram and monophasic action potential characteristics. This was in sharp contrast to previous observations in murine, DeltaKPQ-Scn5a (LQT3) and KCNE1(-/-) (LQT5), systems where re-entry has been implicated in arrhythmogenesis.
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Scn3b knockout mice exhibit abnormal ventricular electrophysiological properties. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2009; 98:251-66. [PMID: 19351516 PMCID: PMC2764399 DOI: 10.1016/j.pbiomolbio.2009.01.005] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
We report for the first time abnormalities in cardiac ventricular electrophysiology in a genetically modified murine model lacking the Scn3b gene (Scn3b−/−). Scn3b−/− mice were created by homologous recombination in embryonic stem (ES) cells. RT-PCR analysis confirmed that Scn3b mRNA was expressed in the ventricles of wild-type (WT) hearts but was absent in the Scn3b−/− hearts. These hearts also showed increased expression levels of Scn1b mRNA in both ventricles and Scn5a mRNA in the right ventricles compared to findings in WT hearts. Scn1b and Scn5a mRNA was expressed at higher levels in the left than in the right ventricles of both Scn3b−/− and WT hearts. Bipolar electrogram and monophasic action potential recordings from the ventricles of Langendorff-perfused Scn3b−/− hearts demonstrated significantly shorter ventricular effective refractory periods (VERPs), larger ratios of electrogram duration obtained at the shortest and longest S1–S2 intervals, and ventricular tachycardias (VTs) induced by programmed electrical stimulation. Such arrhythmogenesis took the form of either monomorphic or polymorphic VT. Despite shorter action potential durations (APDs) in both the endocardium and epicardium, Scn3b−/− hearts showed ΔAPD90 values that remained similar to those shown in WT hearts. The whole-cell patch-clamp technique applied to ventricular myocytes isolated from Scn3b−/− hearts demonstrated reduced peak Na+ current densities and inactivation curves that were shifted in the negative direction, relative to those shown in WT myocytes. Together, these findings associate the lack of the Scn3b gene with arrhythmic tendencies in intact perfused hearts and electrophysiological features similar to those in Scn5a+/− hearts.
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Ghais NS, Zhang Y, Grace AA, Huang CLH. Arrhythmogenic actions of the Ca2+ channel agonist FPL-64716 in Langendorff-perfused murine hearts. Exp Physiol 2008; 94:240-54. [PMID: 18978037 PMCID: PMC2705814 DOI: 10.1113/expphysiol.2008.044669] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The experiments explored the extent to which alterations in L-type Ca(2+) channel-mediated Ca(2+) entry triggers Ca(2+)-mediated arrhythmogenesis in Langendorff-perfused murine hearts through use of the specific L-type Ca(2+) channel modulator FPL-64716 (FPL). Introduction of FPL (1 microm) resulted in a gradual development (>10 min) of diastolic electrical events and alternans in spontaneously beating hearts from which monophasic action potentials were recorded. In regularly paced hearts, they additionally led to non-sustained and sustained ventricular tachycardia (nsVT and sVT). Programmed electrical stimulation (PES) resulted in nsVT and sVT after 5-10 and >10 min perfusion, respectively. Pretreatments with nifedipine, diltiazem and cyclopiazonic acid abolished arrhythmogenic tendency induced by subsequent introduction of FPL, consistent with its dependence upon both extracellular Ca(2+) entry and the degree of filling of the sarcoplasmic reticular Ca(2+) store. Values for action potential duration at 90% repolarization when any of these agents were applied to FPL-treated hearts became indistinguishable from those shown by untreated control hearts, in contrast to earlier reports of their altering in long QT syndrome type 3 and hypokalaemic murine models for re-entrant arrhythmogenesis. These arrhythmic effects instead correlated with alterations in Ca(2+) homeostasis at the single-cell level found in investigations of the effects of both FPL and the same agents in regularly stimulated fluo-3 loaded myocytes. These findings are compatible with a prolonged extracellular Ca(2+) entry that potentially results in an intracellular Ca(2+) overload and produces the cardiac arrhythmogenecity following addition of FPL.
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Affiliation(s)
- Nina S Ghais
- Physiological Laboratory, University of Cambridge, UK
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Goddard CA, Ghais NS, Zhang Y, Williams AJ, Colledge WH, Grace AA, Huang CLH. Physiological consequences of the P2328S mutation in the ryanodine receptor (RyR2) gene in genetically modified murine hearts. Acta Physiol (Oxf) 2008; 194:123-40. [PMID: 18419777 PMCID: PMC2628439 DOI: 10.1111/j.1748-1716.2008.01865.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Aim To explore the physiological consequences of the ryanodine receptor (RyR2)-P2328S mutation associated with catecholaminergic polymorphic ventricular tachycardia (CPVT). Methods We generated heterozygotic (RyR2p/s) and homozygotic (RyR2s/s) transgenic mice and studied Ca2+ signals from regularly stimulated, Fluo-3-loaded, cardiac myocytes. Results were compared with monophasic action potentials (MAPs) in Langendorff-perfused hearts under both regular and programmed electrical stimulation (PES). Results Evoked Ca2+ transients from wild-type (WT), heterozygote (RyR2p/s) and homozygote (RyR2s/s) myocytes had indistinguishable peak amplitudes with RyR2s/s showing subsidiary events. Adding 100 nm isoproterenol produced both ectopic peaks and subsidiary events in WT but not RyR2p/s and ectopic peaks and reduced amplitudes of evoked peaks in RyR2s/s. Regularly stimulated WT, RyR2p/s and RyR2s/s hearts showed indistinguishable MAP durations and refractory periods. RyR2p/s hearts showed non-sustained ventricular tachycardias (nsVTs) only with PES. Both nsVTs and sustained VTs (sVTs) occurred with regular stimuli and PES with isoproterenol treatment. RyR2s/s hearts showed higher incidences of nsVTs before but mainly sVTs after introduction of isoproterenol with both regular stimuli and PES, particularly at higher pacing frequencies. Additionally, intrinsically beating RyR2s/s showed extrasystolic events often followed by spontaneous sVT. Conclusion The RyR2-P2328S mutation results in marked alterations in cellular Ca2+ homeostasis and arrhythmogenic properties resembling CPVT with greater effects in the homozygote than the heterozygote demonstrating an important gene dosage effect.
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Affiliation(s)
- C A Goddard
- Physiological Laboratory, University of Cambridge, Cambridge, UK
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Killeen MJ, Thomas G, Olesen SP, Demnitz J, Stokoe KS, Grace AA, Huang CLH. Effects of potassium channel openers in the isolated perfused hypokalaemic murine heart. Acta Physiol (Oxf) 2008; 193:25-36. [PMID: 18005217 PMCID: PMC2343060 DOI: 10.1111/j.1748-1716.2007.01773.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Aim We explored the anti-arrhythmic efficacy of K+ channel activation in the hypokalaemic murine heart using NS1643 and nicorandil, compounds which augment IKr and IKATP respectively. Methods Left ventricular epicardial and endocardial monophasic action potentials were compared in normokalaemic and hypokalaemic preparations in the absence and presence of NS1643 (30 μm) and nicorandil (20 μm). Results Spontaneously beating hypokalaemic hearts (3 mm K+) all elicited early afterdepolarizations (EADs) and episodes of ventricular tachycardia (VT). Perfusion with NS1643 and nicorandil suppressed EADs and VT in 7 of 13 and five of six hypokalaemic hearts. Provoked arrhythmia studies using programmed electrical stimulation induced VT in all hypokalaemic hearts, but failed to do so in 7 of 13 and five of six hearts perfused with NS1643 and nicorandil respectively. These anti-arrhythmic effects were accompanied by reductions in action potential duration at 90% repolarization (APD90) and changes in the transmural gradient of repolarization, reflected in ΔAPD90. NS1643 and nicorandil reduced epicardial APD90 from 68.3 ± 1.1 to 56.5 ± 4.1 and 51.5 ± 1.5 ms, respectively, but preserved endocardial APD90 in hypokalaemic hearts. NS1643 and nicorandil thus restored ΔAPD90 from −9.6 ± 4.3 ms under baseline hypokalaemic conditions to 3.9 ± 4.1 and 9.9 ± 2.1 ms, respectively, close to normokalaemic values. Conclusion These findings demonstrate, for the first time, the anti-arrhythmic efficacy of K+ channel activation in the setting of hypokalaemia. NS1643 and nicorandil are anti-arrhythmic through the suppression of EADs, reductions in APD90 and restorations of ΔAPD90.
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Affiliation(s)
- M J Killeen
- Physiological Laboratory, University of Cambridge, Cambridge, UK.
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Abstract
Sudden cardiac death stemming from ventricular arrhythmogenesis is one of the major causes of mortality in the developed world. Congenital and acquired forms of long QT syndrome (LQTS) are in turn associated with life threatening arrhythmias. Over the past decade our understanding of arrhythmogenic mechanisms in the setting of these diseases has increased greatly due to the creation of a number of animal models. Of these, the genetically amenable mouse has proved to be a particularly powerful tool. This review summarizes the congenital and acquired LQTS and describes the various mouse models that have been created to further probe arrhythmogenic mechanisms.
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Affiliation(s)
- M J Killeen
- Physiological Laboratory, University of Cambridge, Cambridge, UK.
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Killeen MJ, Gurung IS, Thomas G, Stokoe KS, Grace AA, Huang CLH. Separation of early afterdepolarizations from arrhythmogenic substrate in the isolated perfused hypokalaemic murine heart through modifiers of calcium homeostasis. Acta Physiol (Oxf) 2007; 191:43-58. [PMID: 17524066 PMCID: PMC2040229 DOI: 10.1111/j.1748-1716.2007.01715.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
AIMS We resolved roles for early afterdepolarizations (EADs) and transmural gradients of repolarization in arrhythmogenesis in Langendorff-perfused hypokalaemic murine hearts paced from the right ventricular epicardium. METHODS Left ventricular epicardial and endocardial monophasic action potentials (MAPs) and arrhythmogenic tendency were compared in the presence and absence of the L-type Ca(2+) channel blocker nifedipine (10 nm-1 microm) and the calmodulin kinase type II inhibitor KN-93 (2 microm). RESULTS All the hypokalaemic hearts studied showed prolonged epicardial and endocardial MAPs, decreased epicardial-endocardial APD(90) difference, EADs, triggered beats and ventricular tachycardia (VT) (n = 6). In all spontaneously beating hearts, 100 (but not 10) nm nifedipine reduced both the incidence of EADs and triggered beats from 66.9 +/- 15.7% to 28.3 +/- 8.7% and episodes of VT from 10.8 +/- 6.3% to 1.2 +/- 0.7% of MAPs (n = 6 hearts, P < 0.05); 1 microm nifedipine abolished all these phenomena (n = 6). In contrast programmed electrical stimulation (PES) still triggered VT in six of six hearts with 0, 10 and 100 nm but not 1 microm nifedipine. 1 microm nifedipine selectively reduced epicardial (from 66.1 +/- 3.4 to 46.2 +/- 2.5 ms) but not endocardial APD(90), thereby restoring DeltaAPD(90) from -5.9 +/- 2.5 to 15.5 +/- 3.2 ms, close to normokalaemic values. KN-93 similarly reduced EADs, triggered beats and VT in spontaneously beating hearts to 29.6 +/- 8.9% and 1.7 +/- 1.1% respectively (n = 6) yet permitted PES-induced VT (n = 6), in the presence of a persistently negative DeltaAPD(90). CONCLUSIONS These findings empirically implicate both EADs and triggered beats alongside arrhythmogenic substrate of DeltaAPD(90) in VT pathogenesis at the whole heart level.
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Affiliation(s)
- M J Killeen
- Physiological Laboratory, University of Cambridge, Cambridge, UK.
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Sabir IN, Fraser JA, Cass TR, Grace AA, Huang CLH. A quantitative analysis of the effect of cycle length on arrhythmogenicity in hypokalaemic Langendorff-perfused murine hearts. Pflugers Arch 2007; 454:925-36. [PMID: 17437126 PMCID: PMC2627988 DOI: 10.1007/s00424-007-0255-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2007] [Accepted: 03/13/2007] [Indexed: 11/09/2022]
Abstract
The clinically established proarrhythmic effect of bradycardia and antiarrhythmic effect of lidocaine (10 μM) were reproduced in hypokalaemic (3.0 mM K+) Langendorff-perfused murine hearts paced over a range (80–180 ms) of baseline cycle lengths (BCLs). Action potential durations (at 90% repolarization, APD90s), transmural conduction times and ventricular effective refractory periods (VERPs) were then determined from monophasic action potential records obtained during a programmed electrical stimulation procedure in which extrasystolic stimuli were interposed following regular stimuli at successively decreasing coupling intervals. A novel graphical analysis of epicardial and endocardial, local and transmural relationships between APD90, corrected for transmural conduction time where appropriate, and VERP yielded predictions in precise agreement with the arrhythmogenic findings obtained over the entire range of BCLs studied. Thus, in normokalaemic (5.2 mM K+) hearts a statistical analysis confirmed that all four relationships were described by straight lines of gradients not significantly (P > 0.05) different from unity that passed through the origin and thus subtended constant critical angles, θ with the abscissa (45.8° ± 0.9°, 46.6° ± 0.5°, 47.6° ± 0.5° and 44.9° ± 0.8°, respectively). Hypokalaemia shifted all points to the left of these reference lines, significantly (P < 0.05) increasing θ at BCLs of 80–120 ms where arrhythmic activity was not observed (∼63°, ∼54°, ∼55° and ∼58°, respectively) and further significantly (P < 0.05) increasing θ at BCLs of 140–180 ms where arrhythmic activity was observed (∼68°, ∼60°, ∼61° and ∼65°, respectively). In contrast, the antiarrhythmic effect of lidocaine treatment was accompanied by a significant (P < 0.05) disruption of this linear relationship and decreases in θ in both normokalaemic (∼40°, ∼33°, ∼39° and ∼41°, respectively) and hypokalaemic (∼40°, ∼44°, ∼50° and ∼48°, respectively) hearts. This extended a previous approach that had correlated alterations in transmural repolarization gradients with arrhythmogenicity in murine models of the congenital long QT syndrome type 3 and hypokalaemia at a single BCL. Thus, the analysis in terms of APD90 and VERP provided a more sensitive indication of the effect of lidocaine than one only considering transmural repolarization gradients and may be particularly applicable in physiological and pharmacological situations in which these parameters diverge.
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Affiliation(s)
- Ian N. Sabir
- Physiological Laboratory, University of Cambridge, Downing Street, Cambridge, CB2 3EG UK
| | - James A. Fraser
- Physiological Laboratory, University of Cambridge, Downing Street, Cambridge, CB2 3EG UK
| | - Thomas R. Cass
- Statistical Laboratory, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge, CB3 0WB UK
| | - Andrew A. Grace
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QW UK
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