101
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Rueda A, de Alba-Aguayo DR, Valdivia HH. [Ryanodine receptor, calcium leak and arrhythmias]. ARCHIVOS DE CARDIOLOGIA DE MEXICO 2014; 84:191-201. [PMID: 25103920 DOI: 10.1016/j.acmx.2013.12.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2013] [Revised: 10/30/2013] [Accepted: 12/02/2013] [Indexed: 11/28/2022] Open
Abstract
The participation of the ionic Ca(2+) release channel/ryanodine receptor in cardiac excitation-contraction coupling is well known since the late '80s, when various seminal papers communicated its purification for the first time and its identity with the "foot" structures located at the terminal cisternae of the sarcoplasmic reticulum. In addition to its main role as the Ca(2+) channel responsible for the transient Ca(2+) increase that activates the contractile machinery of the cardiomyocytes, the ryanodine receptor releases Ca(2+) during the relaxation phase of the cardiac cycle, giving rise to a diastolic Ca(2+) leak. In normal physiological conditions, diastolic Ca(2+) leak regulates the proper level of luminal Ca(2+), but in pathological conditions it participates in the generation of both, acquired and hereditary arrhythmias. Very recently, several groups have focused their efforts into the development of pharmacological tools to control the altered diastolic Ca(2+) leak via ryanodine receptors. In this review, we focus our interest on describing the participation of cardiac ryanodine receptor in the diastolic Ca(2+) leak under physiological or pathological conditions and also on the therapeutic approaches to control its undesired exacerbated activity during diastole.
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Affiliation(s)
- Angélica Rueda
- Departamento de Bioquímica, Centro de Investigación y de Estudios Avanzados del IPN, Unidad Zacatenco, México D.F., México.
| | - David R de Alba-Aguayo
- Departamento de Bioquímica, Centro de Investigación y de Estudios Avanzados del IPN, Unidad Zacatenco, México D.F., México
| | - Héctor H Valdivia
- Center for Arrhythmia Research, University of Michigan, Ann Arbor, MI, Estados Unidos
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102
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Verheule S, Eckstein J, Linz D, Maesen B, Bidar E, Gharaviri A, Schotten U. Role of endo-epicardial dissociation of electrical activity and transmural conduction in the development of persistent atrial fibrillation. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2014; 115:173-85. [DOI: 10.1016/j.pbiomolbio.2014.07.007] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2014] [Accepted: 07/19/2014] [Indexed: 10/25/2022]
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103
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Domeier TL, Roberts CJ, Gibson AK, Hanft LM, McDonald KS, Segal SS. Dantrolene suppresses spontaneous Ca2+ release without altering excitation-contraction coupling in cardiomyocytes of aged mice. Am J Physiol Heart Circ Physiol 2014; 307:H818-29. [PMID: 25038147 DOI: 10.1152/ajpheart.00287.2014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cardiac dysfunction in the aged heart reflects abnormalities in cardiomyocyte Ca(2+) homeostasis including altered Ca(2+) cycling through the sarcoplasmic reticulum (SR). The ryanodine receptor antagonist dantrolene exerts antiarrhythmic effects by preventing spontaneous diastolic Ca(2+) release from the SR. We tested the hypothesis that dantrolene prevents spontaneous Ca(2+) release without altering excitation-contraction coupling in aged myocardium. Left ventricular cardiomyocytes isolated from young (3 to 4 mo) and aged (24-26 mo) C57BL/6 mice were loaded with the Ca(2+) indicator fluo-4. Amplitudes of action potential-induced Ca(2+) transients at 1-Hz pacing were similar between young and aged mice, yet cell shortening was impaired in aged mice. Isoproterenol (1 μM) increased Ca(2+) transient amplitude and cell shortening to identical levels in young and aged; dantrolene (1 μM) had no effect on Ca(2+) transients or cell shortening during pacing. Under Ca(2+) overload conditions induced with 10 mM extracellular Ca(2+) concentration, spontaneous Ca(2+) waves were of diminished amplitude and associated with lower SR Ca(2+) content in aged versus young mice. Despite no effect in young mice, dantrolene increased SR Ca(2+) content and Ca(2+) wave amplitude in aged mice. In the presence of isoproterenol following rest from 1-Hz pacing, Ca(2+) spark frequency was elevated in aged mice, yet the time to spontaneous Ca(2+) wave was similar between young and aged mice; dantrolene decreased Ca(2+) spark frequency and prolonged the time to Ca(2+) wave onset in aged mice with no effect in young mice. Thus dantrolene attenuates diastolic Ca(2+) release in the aged murine heart that may prove useful in preventing cardiac dysfunction.
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Affiliation(s)
- Timothy L Domeier
- Department of Medical Pharmacology and Physiology, University of Missouri School of Medicine, Columbia, Missouri; and
| | - Cale J Roberts
- Department of Medical Pharmacology and Physiology, University of Missouri School of Medicine, Columbia, Missouri; and
| | - Anne K Gibson
- Department of Medical Pharmacology and Physiology, University of Missouri School of Medicine, Columbia, Missouri; and
| | - Laurin M Hanft
- Department of Medical Pharmacology and Physiology, University of Missouri School of Medicine, Columbia, Missouri; and
| | - Kerry S McDonald
- Department of Medical Pharmacology and Physiology, University of Missouri School of Medicine, Columbia, Missouri; and
| | - Steven S Segal
- Department of Medical Pharmacology and Physiology, University of Missouri School of Medicine, Columbia, Missouri; and Dalton Cardiovascular Research Center, University of Missouri School of Medicine, Columbia, Missouri
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104
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Choudhuri I, Pinninti M, Marwali MR, Sra J, Akhtar M. Polymorphic ventricular tachycardia--part II: the channelopathies. Curr Probl Cardiol 2014; 38:503-48. [PMID: 24262155 DOI: 10.1016/j.cpcardiol.2013.07.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
In this article, we explore the clinical and cellular phenomena of primary electrical diseases of the heart, that is, conditions purely related to ion channel dysfunction and not structural heart disease or reversible acquired causes. This growing classification of conditions, once considered together as "idiopathic ventricular fibrillation," continues to evolve and segregate into diseases that are phenotypically, molecularly, and genetically unique.
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105
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Di Pino A, Caruso E, Costanzo L, Guccione P. A novel RyR2 mutation in a 2-year-old baby presenting with atrial fibrillation, atrial flutter, and atrial ectopic tachycardia. Heart Rhythm 2014; 11:1480-3. [PMID: 24793461 DOI: 10.1016/j.hrthm.2014.04.037] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/25/2014] [Indexed: 01/08/2023]
Affiliation(s)
- Alfredo Di Pino
- Department of Pediatric Cardiology and Cardiac Surgery, Bambino Gesù Children's Hospital Centro Cardiologico Pediatrico del Mediterraneo, San Vincenzo Hospital, Taormina (ME), Italy.
| | - Elio Caruso
- Department of Pediatric Cardiology and Cardiac Surgery, Bambino Gesù Children's Hospital Centro Cardiologico Pediatrico del Mediterraneo, San Vincenzo Hospital, Taormina (ME), Italy
| | - Luca Costanzo
- Department of Pediatric Cardiology and Cardiac Surgery, Bambino Gesù Children's Hospital Centro Cardiologico Pediatrico del Mediterraneo, San Vincenzo Hospital, Taormina (ME), Italy; Cardiotoracovascular Department, Ferrarotto-Policlinic Hospital, University of Catania, Catania, Italy
| | - Paolo Guccione
- Department of Pediatric Cardiology and Cardiac Surgery, Bambino Gesù Children's Hospital Centro Cardiologico Pediatrico del Mediterraneo, San Vincenzo Hospital, Taormina (ME), Italy
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106
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Abstract
Calcium sparks in cardiac myocytes are brief, localized calcium releases from the sarcoplasmic reticulum (SR) believed to be caused by locally regenerative calcium-induced calcium release (CICR) via couplons, clusters of ryanodine receptors (RyRs). How such regeneration is terminated is uncertain. We performed numerical simulations of an idealized stochastic model of spark production, assuming a RyR gating scheme with only two states (open and closed). Local depletion of calcium in the SR was inevitable during a spark, and this could terminate sparks by interrupting CICR, with or without assumed modulation of RyR gating by SR lumenal calcium. Spark termination by local SR depletion was not robust: under some conditions, sparks could be greatly and variably prolonged, terminating by stochastic attrition-a phenomenon we dub "spark metastability." Spark fluorescence rise time was not a good surrogate for the duration of calcium release. Using a highly simplified, deterministic model of the dynamics of a couplon, we show that spark metastability depends on the kinetic relationship of RyR gating and junctional SR refilling rates. The conditions for spark metastability resemble those produced by known mutations of RyR2 and CASQ2 that cause life-threatening triggered arrhythmias, and spark metastability may be mitigated by altering the kinetics of the RyR in a manner similar to the effects of drugs known to prevent those arrhythmias. The model was unable to explain the distributions of spark amplitudes and rise times seen in chemically skinned cat atrial myocytes, suggesting that such sparks may be more complex events involving heterogeneity of couplons or local propagation among sub-clusters of RyRs.
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Affiliation(s)
- Michael D Stern
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA.
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107
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Effects of the Selective KACh Channel Blocker NTC-801 on Atrial Fibrillation in a Canine Model of Atrial Tachypacing. J Cardiovasc Pharmacol 2014; 63:421-7. [DOI: 10.1097/fjc.0000000000000065] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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108
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Heijman J, Voigt N, Wehrens XHT, Dobrev D. Calcium dysregulation in atrial fibrillation: the role of CaMKII. Front Pharmacol 2014; 5:30. [PMID: 24624086 PMCID: PMC3940963 DOI: 10.3389/fphar.2014.00030] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2014] [Accepted: 02/15/2014] [Indexed: 12/19/2022] Open
Abstract
Atrial fibrillation (AF) is the most frequently encountered clinical arrhythmia and is associated with increased morbidity and mortality. Ectopic activity and reentry are considered major arrhythmogenic mechanisms contributing to the initiation and maintenance of AF. In addition, AF is self-reinforcing through progressive electrical and structural remodeling which stabilize the arrhythmia and make it more difficult to treat. Recent research has suggested an important role for Ca(2+)-dysregulation in AF. Ca(2+)-handling abnormalities may promote ectopic activity, conduction abnormalities facilitating reentry, and AF-related remodeling. In this review article, we summarize the Ca(2+)-handling derangements occurring in AF and discuss their impact on fundamental arrhythmogenic mechanisms. We focus in particular on the role of the multifunctional Ca(2+)/calmodulin-dependent protein kinase type-II (CaMKII), which acts as a major link between Ca(2+)-dysregulation and arrhythmogenesis. CaMKII expression and activity are increased in AF and promote arrhythmogenesis through phosphorylation of various targets involved in cardiac electrophysiology and excitation-contraction coupling. We discuss the implications for potential novel therapeutic strategies for AF based on CaMKII and Ca(2+)-handling abnormalities.
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Affiliation(s)
- Jordi Heijman
- Institute of Pharmacology, Faculty of Medicine, University Duisburg-Essen Essen, Germany
| | - Niels Voigt
- Institute of Pharmacology, Faculty of Medicine, University Duisburg-Essen Essen, Germany
| | - Xander H T Wehrens
- Cardiovascular Research Institute, Departments of Molecular Physiology and Biophysics, and Medicine-Cardiology, Baylor College of Medicine Houston, TX, USA
| | - Dobromir Dobrev
- Institute of Pharmacology, Faculty of Medicine, University Duisburg-Essen Essen, Germany
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109
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Frommeyer G, Schmidt M, Clauß C, Kaese S, Stypmann J, Pott C, Eckardt L, Milberg P. Further insights into the underlying electrophysiological mechanisms for reduction of atrial fibrillation by ranolazine in an experimental model of chronic heart failure. Eur J Heart Fail 2014; 14:1322-31. [DOI: 10.1093/eurjhf/hfs163] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Affiliation(s)
- Gerrit Frommeyer
- Division of Electrophysiology, Department of Cardiovascular Medicine; University Hospital of Münster; Germany
| | - Marco Schmidt
- Division of Electrophysiology, Department of Cardiovascular Medicine; University Hospital of Münster; Germany
| | - Catharina Clauß
- Division of Electrophysiology, Department of Cardiovascular Medicine; University Hospital of Münster; Germany
| | - Sven Kaese
- Division of Electrophysiology, Department of Cardiovascular Medicine; University Hospital of Münster; Germany
| | - Jörg Stypmann
- Division of Cardiology, Department of Cardiovascular Medicine; University Hospital of Münster; Germany
| | - Christian Pott
- Division of Electrophysiology, Department of Cardiovascular Medicine; University Hospital of Münster; Germany
| | - Lars Eckardt
- Division of Electrophysiology, Department of Cardiovascular Medicine; University Hospital of Münster; Germany
| | - Peter Milberg
- Division of Electrophysiology, Department of Cardiovascular Medicine; University Hospital of Münster; Germany
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110
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Steele EM, Steele DS. Automated detection and analysis of Ca(2+) sparks in x-y image stacks using a thresholding algorithm implemented within the open-source image analysis platform ImageJ. Biophys J 2014; 106:566-76. [PMID: 24507597 PMCID: PMC3944640 DOI: 10.1016/j.bpj.2013.12.040] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2013] [Revised: 11/28/2013] [Accepted: 12/23/2013] [Indexed: 11/25/2022] Open
Abstract
Previous studies have used analysis of Ca(2+) sparks extensively to investigate both normal and pathological Ca(2+) regulation in cardiac myocytes. The great majority of these studies used line-scan confocal imaging. In part, this is because the development of open-source software for automatic detection of Ca(2+) sparks in line-scan images has greatly simplified data analysis. A disadvantage of line-scan imaging is that data are collected from a single row of pixels, representing only a small fraction of the cell, and in many instances x-y confocal imaging is preferable. However, the limited availability of software for Ca(2+) spark analysis in two-dimensional x-y image stacks presents an obstacle to its wider application. This study describes the development and characterization of software to enable automatic detection and analysis of Ca(2+) sparks within x-y image stacks, implemented as a plugin within the open-source image analysis platform ImageJ. The program includes methods to enable precise identification of cells within confocal fluorescence images, compensation for changes in background fluorescence, and options that allow exclusion of events based on spatial characteristics.
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Affiliation(s)
- Elliot M Steele
- School of Biomedical Sciences, University of Leeds, Leeds, England
| | - Derek S Steele
- School of Biomedical Sciences, University of Leeds, Leeds, England.
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111
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The ryanodine receptor store-sensing gate controls Ca2+ waves and Ca2+-triggered arrhythmias. Nat Med 2014; 20:184-92. [PMID: 24441828 DOI: 10.1038/nm.3440] [Citation(s) in RCA: 155] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2013] [Accepted: 12/03/2013] [Indexed: 12/12/2022]
Abstract
Spontaneous Ca(2+) release from intracellular stores is important for various physiological and pathological processes. In cardiac muscle cells, spontaneous store overload-induced Ca(2+) release (SOICR) can result in Ca(2+) waves, a major cause of ventricular tachyarrhythmias (VTs) and sudden death. The molecular mechanism underlying SOICR has been a mystery for decades. Here we show that a point mutation, E4872A, in the helix bundle crossing region (the proposed gate) of the cardiac ryanodine receptor (RyR2) completely abolishes luminal, but not cytosolic, Ca(2+) activation of RyR2. The introduction of metal-binding histidines at this site converts RyR2 into a luminal Ni(2+)-gated channel. Mouse hearts harboring a heterozygous RyR2 mutation at this site (E4872Q) are resistant to SOICR and are completely protected against Ca(2+)-triggered VTs. These data show that the RyR2 gate directly senses luminal (store) Ca(2+), explaining the regulation of RyR2 by luminal Ca(2+), the initiation of Ca(2+) waves and Ca(2+)-triggered arrhythmias. This newly identified store-sensing gate structure is conserved in all RyR and inositol 1,4,5-trisphosphate receptor isoforms.
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112
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Gillespie D. Computing the partition function, ensemble averages, and density of states for lattice spin systems by sampling the mean. JOURNAL OF COMPUTATIONAL PHYSICS 2013; 250:1-12. [PMID: 23935210 PMCID: PMC3737008 DOI: 10.1016/j.jcp.2013.05.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
An algorithm to approximately calculate the partition function (and subsequently ensemble averages) and density of states of lattice spin systems through non-Monte-Carlo random sampling is developed. This algorithm (called the sampling-the-mean algorithm) can be applied to models where the up or down spins at lattice nodes interact to change the spin states of other lattice nodes, especially non-Ising-like models with long-range interactions such as the biological model considered here. Because it is based on the Central Limit Theorem of probability, the sampling-the-mean algorithm also gives estimates of the error in the partition function, ensemble averages, and density of states. Easily implemented parallelization strategies and error minimizing sampling strategies are discussed. The sampling-the-mean method works especially well for relatively small systems, systems with a density of energy states that contains sharp spikes or oscillations, or systems with little a priori knowledge of the density of states.
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Affiliation(s)
- Dirk Gillespie
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, IL
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113
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Flecainide reduces ventricular arrhythmias via a mechanism that differs from that of β-blockers in catecholaminergic polymorphic ventricular tachycardia. J Arrhythm 2013. [DOI: 10.1016/j.joa.2013.01.011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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114
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Santiago DJ, Ríos E, Shannon TR. Isoproterenol increases the fraction of spark-dependent RyR-mediated leak in ventricular myocytes. Biophys J 2013; 104:976-85. [PMID: 23473480 DOI: 10.1016/j.bpj.2013.01.026] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2012] [Revised: 12/21/2012] [Accepted: 01/17/2013] [Indexed: 10/27/2022] Open
Abstract
Recent research suggests that the diastolic ryanodine-receptor-mediated release of Ca(2+) (J(leak)) from the sarcoplasmic reticulum of ventricular myocytes occurs in spark and nonspark forms. Further information about the role(s) of these release manifestations is scarce, however. This study addresses whether the fraction of spark-mediated J(leak) increases due to β-adrenergic stimulation. Confocal microscopy was used to simultaneously image Ca(2+) sparks and quantify J(leak) in intact rabbit myocytes, either in the absence or in the presence of 125 nM isoproterenol. It was found that isoproterenol treatment shifts the spark-frequency-J(leak) relationship toward an increased sensitivity to a [Ca(2+)] trigger. In agreement, a small but significant increase in spark width was found for cells with matched baseline [Ca(2+)] and total SR [Ca(2+)]. The reconstruction of release fluxes, when applied to the average sparks from those selected cells, yielded a wider release source in the isoproterenol event, indicating the recruitment of peripheral ryanodine receptors. Overall, the results presented here indicate that β-adrenergic stimulation increases the spark-dependent fraction of J(leak). Working together, the increased Ca(2+) sensitivity and the greater spark width found during isoproterenol treatment may increase the probability of Ca(2+) wave generation.
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Affiliation(s)
- Demetrio J Santiago
- Department of Molecular Biophysics & Physiology, Rush University, Chicago, Illinois, USA
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115
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Chen H, Valle G, Furlan S, Nani A, Gyorke S, Fill M, Volpe P. Mechanism of calsequestrin regulation of single cardiac ryanodine receptor in normal and pathological conditions. ACTA ACUST UNITED AC 2013; 142:127-36. [PMID: 23858002 PMCID: PMC3727306 DOI: 10.1085/jgp.201311022] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Release of Ca2+ from the sarcoplasmic reticulum (SR) drives contractile function of cardiac myocytes. Luminal Ca2+ regulation of SR Ca2+ release is fundamental not only in physiology but also in physiopathology because abnormal luminal Ca2+ regulation is known to lead to arrhythmias, catecholaminergic polymorphic ventricular tachycardia (CPVT), and/or sudden cardiac arrest, as inferred from animal model studies. Luminal Ca2+ regulates ryanodine receptor (RyR)2-mediated SR Ca2+ release through mechanisms localized inside the SR; one of these involves luminal Ca2+ interacting with calsequestrin (CASQ), triadin, and/or junctin to regulate RyR2 function. CASQ2-RyR2 regulation was examined at the single RyR2 channel level. Single RyR2s were incorporated into planar lipid bilayers by the fusion of native SR vesicles isolated from either wild-type (WT), CASQ2 knockout (KO), or R33Q-CASQ2 knock-in (KI) mice. KO and KI mice have CPVT-like phenotypes. We show that CASQ2(WT) action on RyR2 function (either activation or inhibition) was strongly influenced by the presence of cytosolic MgATP. Function of the reconstituted CASQ2(WT)–RyR2 complex was unaffected by changes in luminal free [Ca2+] (from 0.1 to 1 mM). The inhibition exerted by CASQ2(WT) association with the RyR2 determined a reduction in cytosolic Ca2+ activation sensitivity. RyR2s from KO mice were significantly more sensitive to cytosolic Ca2+ activation and had significantly longer mean open times than RyR2s from WT mice. Sensitivity of RyR2s from KI mice was in between that of RyR2 channels from KO and WT mice. Enhanced cytosolic RyR2 Ca2+ sensitivity and longer RyR2 open times likely explain the CPVT-like phenotype of both KO and KI mice.
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Affiliation(s)
- Haiyan Chen
- Department of Molecular Physiology and Biophysics, Rush University Medical Center, Chicago, IL 60612, USA
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116
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Bai Y, Jones PP, Guo J, Zhong X, Clark RB, Zhou Q, Wang R, Vallmitjana A, Benitez R, Hove-Madsen L, Semeniuk L, Guo A, Song LS, Duff HJ, Chen SRW. Phospholamban knockout breaks arrhythmogenic Ca²⁺ waves and suppresses catecholaminergic polymorphic ventricular tachycardia in mice. Circ Res 2013; 113:517-26. [PMID: 23856523 DOI: 10.1161/circresaha.113.301678] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
RATIONALE Phospholamban (PLN) is an inhibitor of cardiac sarco(endo)plasmic reticulum Ca²⁺ ATPase. PLN knockout (PLN-KO) enhances sarcoplasmic reticulum Ca²⁺ load and Ca²⁺ leak. Conversely, PLN-KO accelerates Ca²⁺ sequestration and aborts arrhythmogenic spontaneous Ca²⁺ waves (SCWs). An important question is whether these seemingly paradoxical effects of PLN-KO exacerbate or protect against Ca²⁺-triggered arrhythmias. OBJECTIVE We investigate the impact of PLN-KO on SCWs, triggered activities, and stress-induced ventricular tachyarrhythmias (VTs) in a mouse model of cardiac ryanodine-receptor (RyR2)-linked catecholaminergic polymorphic VT. METHODS AND RESULTS We generated a PLN-deficient, RyR2-mutant mouse model (PLN-/-/RyR2-R4496C+/-) by crossbreeding PLN-KO mice with catecholaminergic polymorphic VT-associated RyR2-R4496C mutant mice. Ca²⁺ imaging and patch-clamp recording revealed cell-wide propagating SCWs and triggered activities in RyR2-R4496C+/- ventricular myocytes during sarcoplasmic reticulum Ca²⁺ overload. PLN-KO fragmented these cell-wide SCWs into mini-waves and Ca²⁺ sparks and suppressed the triggered activities evoked by sarcoplasmic reticulum Ca²⁺ overload. Importantly, these effects of PLN-KO were reverted by partially inhibiting sarco(endo)plasmic reticulum Ca²⁺ ATPase with 2,5-di-tert-butylhydroquinone. However, Bay K, caffeine, or Li⁺ failed to convert mini-waves to cell-wide SCWs in PLN-/-/RyR2-R4496C+/- ventricular myocytes. Furthermore, ECG analysis showed that PLN-KO mice are not susceptible to stress-induced VTs. On the contrary, PLN-KO protected RyR2-R4496C mutant mice from stress-induced VTs. CONCLUSIONS Our results demonstrate that despite severe sarcoplasmic reticulum Ca²⁺ leak, PLN-KO suppresses triggered activities and stress-induced VTs in a mouse model of catecholaminergic polymorphic VT. These data suggest that breaking up cell-wide propagating SCWs by enhancing Ca²⁺ sequestration represents an effective approach for suppressing Ca²⁺-triggered arrhythmias.
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Affiliation(s)
- Yunlong Bai
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada
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117
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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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118
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Greiser M, Schotten U. Dynamic remodeling of intracellular Ca2+ signaling during atrial fibrillation. J Mol Cell Cardiol 2013; 58:134-42. [DOI: 10.1016/j.yjmcc.2012.12.020] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/17/2012] [Revised: 12/14/2012] [Accepted: 12/17/2012] [Indexed: 12/23/2022]
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Steele DS, Hwang HS, Knollmann BC. Triple mode of action of flecainide in catecholaminergic polymorphic ventricular tachycardia. Cardiovasc Res 2013; 98:326-7. [PMID: 23512981 PMCID: PMC3657388 DOI: 10.1093/cvr/cvt059] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
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Sikkel MB, Collins TP, Rowlands C, Shah M, O'Gara P, Williams AJ, Harding SE, Lyon AR, MacLeod KT. Triple mode of action of flecainide in catecholaminergic polymorphic ventricular tachycardia: reply. Cardiovasc Res 2013; 98:327-8. [PMID: 23536607 DOI: 10.1093/cvr/cvt068] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
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Dependency of calcium alternans on ryanodine receptor refractoriness. PLoS One 2013; 8:e55042. [PMID: 23390511 PMCID: PMC3563653 DOI: 10.1371/journal.pone.0055042] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2012] [Accepted: 12/17/2012] [Indexed: 11/25/2022] Open
Abstract
Background Rapid pacing rates induce alternations in the cytosolic calcium concentration caused by fluctuations in calcium released from the sarcoplasmic reticulum (SR). However, the relationship between calcium alternans and refractoriness of the SR calcium release channel (RyR2) remains elusive. Methodology/Principal Findings To investigate how ryanodine receptor (RyR2) refractoriness modulates calcium handling on a beat-to-beat basis using a numerical rabbit cardiomyocyte model. We used a mathematical rabbit cardiomyocyte model to study the beat-to-beat calcium response as a function of RyR2 activation and inactivation. Bi-dimensional maps were constructed depicting the beat-to-beat response. When alternans was observed, a novel numerical clamping protocol was used to determine whether alternans was caused by oscillations in SR calcium loading or by RyR2 refractoriness. Using this protocol, we identified regions of RyR2 gating parameters where SR calcium loading or RyR2 refractoriness underlie the induction of calcium alternans, and we found that at the onset of alternans both mechanisms contribute. At low inactivation rates of the RyR2, calcium alternans was caused by alternation in SR calcium loading, while at low activation rates it was caused by alternation in the level of available RyR2s. Conclusions/Significance We have mapped cardiomyocyte beat-to-beat responses as a function of RyR2 activation and inactivation, identifying domains where SR calcium load or RyR2 refractoriness underlie the induction of calcium alternans. A corollary of this work is that RyR2 refractoriness due to slow recovery from inactivation can be the cause of calcium alternans even when alternation in SR calcium load is present.
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Sikkel MB, Collins TP, Rowlands C, Shah M, O'Gara P, Williams AJ, Harding SE, Lyon AR, MacLeod KT. Flecainide reduces Ca(2+) spark and wave frequency via inhibition of the sarcolemmal sodium current. Cardiovasc Res 2013; 98:286-96. [PMID: 23334259 PMCID: PMC3714924 DOI: 10.1093/cvr/cvt012] [Citation(s) in RCA: 70] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
Aims Ca2+ waves are thought to be important in the aetiology of
ventricular tachyarrhythmias. There have been conflicting results regarding
whether flecainide reduces Ca2+ waves in isolated
cardiomyocytes. We sought to confirm whether flecainide inhibits waves in
the intact cardiomyocyte and to elucidate the mechanism. Methods and results We imaged spontaneous sarcoplasmic reticulum (SR) Ca2+
release events in healthy adult rat cardiomyocytes. Variation in stimulation
frequency was used to produce Ca2+ sparks or waves. Spark
frequency, wave frequency, and wave velocity were reduced by flecainide in
the absence of a reduction of SR Ca2+ content. Inhibition
of INa via alternative pharmacological agents
(tetrodotoxin, propafenone, or lidocaine) produced similar changes. To
assess the contribution of INa to spark and wave
production, voltage clamping was used to activate contraction from holding
potentials of −80 or −40 mV. This confirmed that reducing
Na+ influx during myocyte stimulation is sufficient to
reduce waves and that flecainide only causes Ca2+ wave
reduction when INa is active. It was found that
Na+/Ca2+-exchanger (NCX)-mediated
Ca2+ efflux was significantly enhanced by flecainide
and that the effects of flecainide on wave frequency could be reversed by
reducing [Na+]o, suggesting an important
downstream role for NCX function. Conclusion Flecainide reduces spark and wave frequency in the intact rat cardiomyocyte
at therapeutically relevant concentrations but the mechanism involves
INa reduction rather than direct ryanodine
receptor (RyR2) inhibition. Reduced INa results
in increased Ca2+ efflux via NCX across the sarcolemma,
reducing Ca2+ concentration in the vicinity of the
RyR2.
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Affiliation(s)
- Markus B Sikkel
- Myocardial Function Section, National Heart and Lung Institute, Fourth Floor, Imperial Centre for Translational and Experimental Medicine, Imperial College, Hammersmith Campus, Du Cane Road, London W12 0NN, UK.
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Hsiao PY, Tien HC, Lo CP, Juang JMJ, Wang YH, Sung RJ. Gene mutations in cardiac arrhythmias: a review of recent evidence in ion channelopathies. APPLICATION OF CLINICAL GENETICS 2013; 6:1-13. [PMID: 23837003 PMCID: PMC3699290 DOI: 10.2147/tacg.s29676] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Over the past 15 years, molecular genetic studies have linked gene mutations to many inherited arrhythmogenic disorders, in particular, “ion channelopathies”, in which mutations in genes encode functional units of ion channels and/or their transporter-associated proteins in patients without primary cardiac structural abnormalities. These disorders are exemplified by congenital long QT syndrome (LQTS), short QT syndrome, Brugada syndrome (BrS) and catecholaminergic polymorphic ventricular tachycardia (CPVT). Functional and pathophysiological studies have led to better understanding of the clinical spectrum, ion channel structures and cellular electrophysiology involving dynamics of intracellular calcium cycling in many subtypes of these disorders and more importantly, development of potentially more effective pharmacological agents and even curative gene therapy. In this review, we have summarized (1) the significance of unveiling mutations in genes encoding transporter-associated proteins as the cause of congenital LQTS, (2) the technique of catheter ablation applied at the right ventricular outflow tract may be curative for severely symptomatic BrS, (3) mutations with channel function modulated by protein Kinase A-dependent phosphorylation can be the culprit of CPVT mimicry in Andersen-Tawil syndrome (LQT7), (4) ablation of the ion channel anchoring protein may prevent arrhythmogenesis in Timothy syndrome (LQT8), (5) altered intracellular Ca2+ cycling can be the basis of effective targeted pharmacotherapy in CPVT, and (6) the technology of induced pluripotent stem cells is a promising diagnostic and research tool as it has become a new paradigm for pathophysiological study of patient- and disease-specific cells aimed at screening new drugs and eventual clinical application of gene therapy. Lastly, we have discussed (7) genotype-phenotype correlation in relation to risk stratification of patients with congenital LQTS in clinical practice.
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Affiliation(s)
- Pi-Yin Hsiao
- Institute of Life Sciences, National Central University, Taoyuan, Taiwan
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Kim JJ, Němec J, Papp R, Strongin R, Abramson JJ, Salama G. Bradycardia alters Ca(2+) dynamics enhancing dispersion of repolarization and arrhythmia risk. Am J Physiol Heart Circ Physiol 2013; 304:H848-60. [PMID: 23316064 DOI: 10.1152/ajpheart.00787.2012] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Bradycardia prolongs action potential (AP) durations (APD adaptation), enhances dispersion of repolarization (DOR), and promotes tachyarrhythmias. Yet, the mechanisms responsible for enhanced DOR and tachyarrhythmias remain largely unexplored. Ca(2+) transients and APs were measured optically from Langendorff rabbit hearts at high (150 × 150 μm(2)) or low (1.5 × 1.5 cm(2)) magnification while pacing at a physiological (120 beats/min) or a slow heart rate (SHR = 50 beats/min). Western blots and pharmacological interventions were used to elucidate the regional effects of bradycardia. As a result, bradycardia (SHR 50 beats/min) increased APDs gradually (time constant τf→s = 48 ± 9.2 s) and caused a secondary Ca(2+) release (SCR) from the sarcoplasmic reticulum during AP plateaus, occurring at the base on average of 184.4 ± 9.7 ms after the Ca(2+) transient upstroke. In subcellular imaging, SCRs were temporally synchronous and spatially homogeneous within myocytes. In diastole, SHR elicited variable asynchronous sarcoplasmic reticulum Ca(2+) release events leading to subcellular Ca(2+) waves, detectable only at high magnification. SCR was regionally heterogeneous, correlated with APD prolongation (P < 0.01, n = 5), enhanced DOR (r = 0.9277 ± 0.03, n = 7), and was gradually reversed by pacing at 120 beats/min along with APD shortening (P < 0.05, n = 5). A stabilizer of leaky ryanodine receptors (RyR2), 3-(4-benzylcyclohexyl)-1-(7-methoxy-2,3-dihydrobenzo[f][1,4]thiazepin-4(5H)-yl)propan-1-one (K201; 1 μM), suppressed SCR and reduced APD at the base, thereby reducing DOR (P < 0.02, n = 5). Ventricular ectopy induced by bradycardia (n = 5/15) was suppressed by K201. Western blot analysis revealed spatial differences of voltage-gated L-type Ca(2+) channel protein (Cav1.2α), Na(+)-Ca(2+) exchange (NCX1), voltage-gated Na(+) channel (Nav1.5), and rabbit ether-a-go-go-related (rERG) protein [but not RyR2 or sarcoplasmic reticulum Ca(2+) ATPase 2a] that correlate with the SCR distribution and explain the molecular basis for SCR heterogeneities. In conclusion, acute bradycardia elicits synchronized subcellular SCRs of sufficient magnitude to overcome the source-sink mismatch and to promote afterdepolarizations.
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Affiliation(s)
- Jong J Kim
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15261, USA
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Faggioni M, Hwang HS, van der Werf C, Nederend I, Kannankeril PJ, Wilde AAM, Knollmann BC. Accelerated sinus rhythm prevents catecholaminergic polymorphic ventricular tachycardia in mice and in patients. Circ Res 2013; 112:689-97. [PMID: 23295832 DOI: 10.1161/circresaha.111.300076] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
RATIONALE Catecholaminergic polymorphic ventricular tachycardia (CPVT) is caused by mutations in cardiac ryanodine receptor (RyR2) or calsequestrin (Casq2) genes. Sinoatrial node dysfunction associated with CPVT may increase the risk for ventricular arrhythmia (VA). OBJECTIVE To test the hypothesis that CPVT is suppressed by supraventricular overdrive stimulation. METHODS AND RESULTS Using CPVT mouse models (Casq2(-/-) and RyR2(R4496C/+) mice), the effect of increasing sinus heart rate was tested by pretreatment with atropine and by atrial overdrive pacing. Increasing intrinsic sinus rate with atropine before catecholamine challenge suppressed ventricular tachycardia in 86% of Casq2(-/-) mice (6/7) and significantly reduced the VA score (atropine: 0.6±0.2 versus vehicle: 1.7±0.3; P<0.05). Atrial overdrive pacing completely prevented VA in 16 of 19 (84%) Casq2(-/-) and in 7 of 8 (88%) RyR2(R4496C/+) mice and significantly reduced ventricular premature beats in both CPVT models (P<0.05). Rapid pacing also prevented spontaneous calcium waves and triggered beats in isolated CPVT myocytes. In humans, heart rate dependence of CPVT was evaluated by screening a CPVT patient registry for antiarrhythmic drug-naïve individuals that reached >85% of their maximum-predicted heart rate during exercise testing. All 18 CPVT patients who fulfilled the inclusion criteria exhibited VA before reaching 87% of maximum heart rate. In 6 CPVT patients (33%), VA were paradoxically suppressed as sinus heart rates increased further with continued exercise. CONCLUSIONS Accelerated supraventricular rates suppress VAs in 2 CPVT mouse models and in a subset of CPVT patients. Hypothetically, atrial overdrive pacing may be a therapy for preventing exercise-induced ventricular tachycardia in treatment-refractory CPVT patients.
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Affiliation(s)
- Michela Faggioni
- Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN 37232-0575, USA
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Watanabe H, van der Werf C, Roses-Noguer F, Adler A, Sumitomo N, Veltmann C, Rosso R, Bhuiyan ZA, Bikker H, Kannankeril PJ, Horie M, Minamino T, Viskin S, Knollmann BC, Till J, Wilde AAM. Effects of flecainide on exercise-induced ventricular arrhythmias and recurrences in genotype-negative patients with catecholaminergic polymorphic ventricular tachycardia. Heart Rhythm 2012; 10:542-7. [PMID: 23286974 DOI: 10.1016/j.hrthm.2012.12.035] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/10/2012] [Indexed: 02/08/2023]
Abstract
BACKGROUND Conventional therapy with beta-blockers is incompletely effective in preventing arrhythmic events in patients with catecholaminergic polymorphic ventricular tachycardia (CPVT). We have previously discovered that flecainide in addition to conventional drug therapy prevents ventricular arrhythmias in patients with genotype-positive CPVT. OBJECTIVE To study the efficacy of flecainide in patients with genotype-negative CPVT. METHODS We studied the efficacy of flecainide for reducing ventricular arrhythmias during exercise testing and preventing arrhythmia events during long-term follow-up. RESULTS Twelve patients with genotype-negative CPVT were treated with flecainide. Conventional therapy failed to control ventricular arrhythmias in all patients. Flecainide was initiated because of significant ventricular arrhythmias (n = 8), syncope (n = 3), or cardiac arrest (n = 1). At the baseline exercise test before flecainide, 6 patients had ventricular tachycardia and 5 patients had bigeminal or frequent ventricular premature beats. Flecainide reduced ventricular arrhythmias at the exercise test in 8 patients compared to conventional therapy, similar to that in patients with genotype-positive CPVT in our previous report. Notably, flecainide completely prevented ventricular arrhythmias in 7 patients. Flecainide was continued in all patients except for one who had ventricular tachycardia at the exercise test on flecainide. During a follow-up of 48±94 months, arrhythmia events (sudden cardiac death and aborted cardiac arrest) associated with noncompliance occurred in 2 patients. Flecainide was not discontinued owing to side effects in any of the patients. CONCLUSIONS Flecainide was effective in patients with genotype-negative CPVT, suggesting that spontaneous Ca(2+) release from ryanodine channels plays a role in arrhythmia susceptibility, similar to that in patients with genotype-positive CPVT.
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Affiliation(s)
- Hiroshi Watanabe
- Division of Cardiology, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
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Mason SA, Viero C, Euden J, Bannister M, West D, Chen SRW, Williams AJ. The contribution of hydrophobic residues in the pore-forming region of the ryanodine receptor channel to block by large tetraalkylammonium cations and Shaker B inactivation peptides. ACTA ACUST UNITED AC 2012; 140:325-39. [PMID: 22930804 PMCID: PMC3434103 DOI: 10.1085/jgp.201210851] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Although no high-resolution structural information is available for the ryanodine receptor (RyR) channel pore-forming region (PFR), molecular modeling has revealed broad structural similarities between this region and the equivalent region of K+ channels. This study predicts that, as is the case in K+ channels, RyR has a cytosolic vestibule lined with predominantly hydrophobic residues of transmembrane helices (TM10). In K+ channels, this vestibule is the binding site for blocking tetraalkylammonium (TAA) cations and Shaker B inactivation peptides (ShBPs), which are stabilized by hydrophobic interactions involving specific residues of the lining helices. We have tested the hypothesis that the cytosolic vestibule of RyR fulfils a similar role and that TAAs and ShBPs are stabilized by hydrophobic interactions with residues of TM10. Both TAAs and ShBPs block RyR from the cytosolic side of the channel. By varying the composition of TAAs and ShBPs, we demonstrate that the affinity of both species is determined by their hydrophobicity, with variations reflecting alterations in the dissociation rate of the bound blockers. We investigated the role of TM10 residues of RyR by monitoring block by TAAs and ShBPs in channels in which the hydrophobicity of individual TM10 residues was lowered by alanine substitution. Although substitutions changed the kinetics of TAA interaction, they produced no significant changes in ShBP kinetics, indicating the absence of specific hydrophobic sites of interactions between RyR and these peptides. Our investigations (a) provide significant new information on both the mechanisms and structural components of the RyR PFR involved in block by TAAs and ShBPs, (b) highlight important differences in the mechanisms and structures determining TAA and ShBP block in RyR and K+ channels, and (c) demonstrate that although the PFRs of these channels contain analogous structural components, significant differences in structure determine the distinct ion-handling properties of the two species of channel.
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Affiliation(s)
- Sammy A Mason
- Institute of Molecular and Experimental Medicine, Wales Heart Research Institute, School of Medicine, Cardiff University, Cardiff CF14 4XN, Wales, UK
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128
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Ather S, Wang W, Wang Q, Li N, Anderson ME, Wehrens XHT. Inhibition of CaMKII phosphorylation of RyR2 prevents inducible ventricular arrhythmias in mice with Duchenne muscular dystrophy. Heart Rhythm 2012; 10:592-9. [PMID: 23246599 DOI: 10.1016/j.hrthm.2012.12.016] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/12/2012] [Indexed: 12/14/2022]
Abstract
BACKGROUND Ventricular tachycardia (VT) is the second most common cause of death in patients with Duchenne muscular dystrophy (DMD). Recent studies have implicated enhanced sarcoplasmic reticulum (SR) Ca(2+) leak via type 2 ryanodine receptor (RyR2) as a cause of VT in the mdx mouse model of DMD. However, the signaling mechanisms underlying induction of SR Ca(2+) leak and VT are poorly understood. OBJECTIVE To test whether enhanced Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) phosphorylation of RyR2 underlies SR Ca(2+) leak and induction of VT in mdx mice. METHODS Programmed electrical stimulation was performed on anesthetized mice and confocal imaging of Ca(2+) release events in isolated ventricular myocytes. RESULTS Programmed electrical stimulation revealed inducible VT in mdx mice, which was inhibited by CaMKII inhibition or mutation S2814A in RyR2. Myocytes from mdx mice exhibited more Ca(2+) sparks and Ca(2+) waves compared with wild-type mice, in particular at faster pacing rates. Arrhythmogenic Ca(2+) waves were inhibited by CaMKII but not by protein kinase A inhibition. Moreover, mutation S2814A but not S2808A in RyR2 suppressed spontaneous Ca(2+) waves in myocytes from mdx mice. CONCLUSIONS CaMKII blockade and genetic inhibition of RyR2-S2814 phosphorylation prevent VT induction in a mouse model of DMD. In ventricular myocytes from mdx mice, spontaneous Ca(2+) sparks and Ca(2+) waves can be suppressed by CaMKII inhibition or mutation S2814A in RyR2. Thus, the inhibition of CaMKII-induced SR Ca(2+) leak might be a new strategy to prevent arrhythmias in patients with DMD without heart failure.
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Affiliation(s)
- Sameer Ather
- Department of Medicine (Cardiology), Baylor College of Medicine, Houston, TX 77030, USA
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129
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Calcium flux balance in the heart. J Mol Cell Cardiol 2012; 58:110-7. [PMID: 23220128 DOI: 10.1016/j.yjmcc.2012.11.017] [Citation(s) in RCA: 88] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/09/2012] [Revised: 11/08/2012] [Accepted: 11/22/2012] [Indexed: 11/22/2022]
Abstract
This article reviews the consequences of the need for the cardiac cell to be in calcium flux balance in the steady state. We first discuss how this steady state condition affects the control of resting [Ca(2+)]i. The next section considers how sarcoplasmic reticulum (SR) Ca content is controlled by a feedback mechanism whereby changes of SR Ca affect the amplitude of the Ca transient and this, in turn, controls sarcolemmal Ca fluxes. Subsequent sections review the effects of altering the activity of individual Ca handling proteins. Increasing the activity of the SR Ca-ATPase (SERCA) increases both the amplitude and rate constant of decay of the systolic Ca transient. The Ca flux balance condition requires that this must be achieved with no change of Ca efflux placing constraints on the magnitude of change of amplitude and decay rate. We analyze the quantitative dependence of Ca transient amplitude and SR content on SERCA activity. Increasing the open probability of the RyR during systole is predicted to have no steady state effect on the amplitude of the systolic Ca transient. We discuss the effects of changing the amplitude of the L-type Ca current in the context of both triggering Ca release from the SR and loading the cell with calcium. These manoeuvres are considered in the context of the effects of β-adrenergic stimulation. Finally, we review calcium flux balance in the presence of Ca waves.
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Loaiza R, Benkusky NA, Powers PP, Hacker T, Noujaim S, Ackerman MJ, Jalife J, Valdivia HH. Heterogeneity of ryanodine receptor dysfunction in a mouse model of catecholaminergic polymorphic ventricular tachycardia. Circ Res 2012; 112:298-308. [PMID: 23152493 DOI: 10.1161/circresaha.112.274803] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
RATIONALE Most cardiac ryanodine receptor (RyR2) mutations associated with catecholaminergic polymorphic ventricular tachycardia (CPVT) are postulated to cause a distinctive form of Ca(2+) release dysfunction. Considering the spread distribution of CPVT mutations, we hypothesized that dysfunctional heterogeneity also was feasible. OBJECTIVE To determine the molecular and cellular mechanisms by which a novel RyR2-V2475F mutation associated with CPVT in humans triggers Ca(2+)-dependent arrhythmias in whole hearts and intact mice. METHODS AND RESULTS Recombinant channels harboring CPVT-linked RyR2 mutations were functionally characterized using tritiated ryanodine binding and single-channel recordings. Homologous recombination was used to generate a knock-in mouse bearing the RyR2-V2475F mutation. Ventricular myocytes from mice heterozygous for the mutation (RyR2-V2475F(+/-)) and their wild-type littermates were Ca(2+)-imaged by confocal microscopy under conditions that mimic stress. The propensity of wild-type and RyR2-V2475F(+/-) mice to have development of arrhythmias was tested at the whole heart level and in intact animals. Recombinant RyR2-V2475F channels displayed increased cytosolic Ca(2+) activation, abnormal protein kinase A phosphorylation, and increased activation by luminal Ca(2+). The RyR2-V2475F mutation appears embryonic-lethal in homozygous mice, but heterozygous mice have no alterations at baseline. Spontaneous Ca(2+) release events were more frequent and had shorter latency in isoproterenol-stimulated cardiomyocytes from RyR2-V2475F(+/-) hearts, but their threshold was unchanged with respect to wild-type. Adrenergically triggered tachyarrhythmias were more frequent in RyR2-V2475F(+/-) mice. CONCLUSIONS The mutation RyR2-V2475F is phenotypically strong among other CPVT mutations and produces heterogeneous mechanisms of RyR2 dysfunction. In living mice, this mutation appears too severe to be harbored in all RyR2 channels but remains undetected under basal conditions if expressed at relatively low levels. β-adrenergic stimulation breaks the delicate Ca(2+) equilibrium of RyR2-V2475F(+/-) hearts and triggers life-threatening arrhythmias.
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Affiliation(s)
- Randall Loaiza
- Center for Arrhythmia Research, Cardiovascular Division, Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109, USA
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Li N, Wehrens XHT. Extinguishing intracellular calcium leak: a promising antiarrhythmic approach. Heart Rhythm 2012; 10:108-9. [PMID: 23085093 DOI: 10.1016/j.hrthm.2012.10.018] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/05/2012] [Indexed: 01/12/2023]
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Perrin MJ, Gollob MH. Genetics of cardiac electrical disease. Can J Cardiol 2012; 29:89-99. [PMID: 23062665 DOI: 10.1016/j.cjca.2012.07.847] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2012] [Revised: 07/27/2012] [Accepted: 07/30/2012] [Indexed: 10/27/2022] Open
Abstract
Few tragedies compare to the sudden death of a family member. Sadly, this may represent the first sign of a familial vulnerability to such events. One common cause is an inherited cardiac arrhythmia syndrome. Sufferers are prone to premature sudden cardiac death due to altered ion channel function in the heart. Typical causes include Brugada syndrome, long QT syndrome, short QT syndrome, catecholaminergic polymorphic ventricular tachycardia, and the newly recognized early repolarization syndrome. Our knowledge of the genetic underpinnings of each of these disorders has increased markedly in recent years. Genetic screening is now a routine part of clinical care and promises more accurate diagnosis and efficient family screening. This review summarizes the diagnosis and management of each of the listed syndromes in the context of currently available genetic testing.
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Affiliation(s)
- Mark J Perrin
- Division of Cardiology, Department of Medicine, University of Ottawa Heart Institute, Ottawa, Ontario, Canada
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133
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Radwański PB, Greer-Short A, Poelzing S. Inhibition of Na+ channels ameliorates arrhythmias in a drug-induced model of Andersen-Tawil syndrome. Heart Rhythm 2012; 10:255-63. [PMID: 23041575 DOI: 10.1016/j.hrthm.2012.10.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/14/2012] [Indexed: 10/27/2022]
Abstract
BACKGROUND Andersen-Tawil syndrome (ATS1)-associated ventricular tachycardias (VTs) are initiated by frequent, hypokalemia-exacerbated, premature ventricular activity (PVA). We previously demonstrated that a guinea pig model of drug-induced ATS1 (DI-ATS1) evidenced increased arrhythmias from regions with high Na(+)/Ca(2+)-exchange expression. OBJECTIVE Therefore, we hypothesize that reduced cytosolic Na(+) entry through either cardiac isoform of or tetrodotoxin (TTX)-sensitive Na(+) channels during DI-ATS1 can ameliorate arrhythmia burden. METHODS DI-ATS1 was induced with 10 μM BaCl(2) and 2 mM extracellular K(+). Ca(2+) transients and conduction velocity (CV) were optically mapped with indo-1 and di-4-ANEPPS, respectively, from Langendorff-perfused guinea pig ventricles. RESULTS Nonselective Na(+) channel blockade with 1 μM flecainide reduced amplitude (Ca(A)), slowed left ventricular CV, reduced tissue excitability, and abolished the incidence of VT while decreasing the incidence of PVA relative to DI-ATS1. Selective, TTX-sensitive Na(+) channel blockade with TTX (100 nM) during DI-ATS1 decreased Ca(A) and decreased the inducibility of VTs and PVA relative to DI-ATS1 without slowing CV. Ranolazine altered Ca(A), left ventricular CV, tissue excitability, and reduced inducibility of VT and PVA in a concentration-dependent manner. None of the aforementioned interventions altered diastolic Ca(2+) levels or Ca(2+) transient decay time constant. CONCLUSIONS These data suggest that cytosolic Na(+) entry and its modulation of Ca(2+) handling are necessary for arrhythmogenesis. During the loss of inward-rectifier K(+) current function, not only Na(+)/Ca(2+)-exchange dominance but Na(+) flux may determine arrhythmia burden. Therefore, selective inhibition of TTX-sensitive Na(+) channels may offer a potential therapeutic target to alleviate arrhythmias during states of Ca(2+) overload secondary to loss of inward-rectifier K(+) current function without compromising the excitability reserve.
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Affiliation(s)
- Przemysław B Radwański
- Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City, Utah 84112-5000, USA
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Silva JNA, Silva JR. Updates on the inherited cardiac ion channelopathies: from cell to clinical. CURRENT TREATMENT OPTIONS IN CARDIOVASCULAR MEDICINE 2012; 14:473-89. [PMID: 22865245 DOI: 10.1007/s11936-012-0198-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
OPINION STATEMENT The inherited channelopathies are a rare, heterogeneous group of diseases with widely variable clinical presentations and courses. Systematic clinical and experimental work has led to identification of disease-causing genetic mutations and their biophysical manifestation. The process by which the knowledge base is developed, from genetic mutation, to cardiac myocyte, to whole heart, and finally to clinical presentation, has dramatically expanded our understanding of these diseases. Most importantly, we can now begin to comprehend how small changes at the genetic level can dramatically influence a patient's clinical course.
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Affiliation(s)
- Jennifer N A Silva
- Department of Pediatrics, Washington University School of Medicine/Saint Louis Children's Hospital, Saint Louis, MO, USA,
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135
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Maruyama M, Xiao J, Zhou Q, Vembaiyan K, Chua SK, Rubart-von der Lohe M, Lin SF, Back TG, Chen SRW, Chen PS. Carvedilol analogue inhibits triggered activities evoked by both early and delayed afterdepolarizations. Heart Rhythm 2012; 10:101-7. [PMID: 22982970 DOI: 10.1016/j.hrthm.2012.09.006] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/16/2012] [Indexed: 12/22/2022]
Abstract
BACKGROUND Carvedilol and its analogues suppress delayed afterdepolarizations (DADs) and catecholaminergic polymorphic ventricular tachycardias by direct action on the cardiac ryanodine receptor type 2 (RyR2). OBJECTIVE To test a hypothesis that carvedilol analogue may also prevent triggered activities (TAs) through the suppression of early afterdepolarizations (EADs). METHODS Intracellular Ca(2+) and membrane voltage were simultaneously recorded by using optical mapping technique in Langendorff-perfused mouse and rabbit hearts to study the effect of carvedilol analogue VK-II-36, which does not have significant beta-blocking effects. RESULTS Spontaneous intracellular Ca(2+) elevations (SCaEs) during diastole were induced by rapid ventricular pacing and isoproterenol infusion in intact rabbit ventricles. Systolic and diastolic SCaEs were simultaneously noted in Langendorff-perfused RyR2 R4496(+/-) mouse hearts after creating atrioventricular block. VK-II-36 effectively suppressed SCaEs and eliminated TAs observed in both mouse and rabbit ventricles. We tested the effect of VK-II-36 on EADs by using a rabbit model of acquired long QT syndrome, in which phase 2 and phase 3 EADs were observed in association with systolic SCaEs. VK-II-36 abolished the systolic SCaEs and phase 2 EADs, and greatly decreased the dispersion of repolarization and the amplitude of phase 3 EADs. VK-II-36 completely prevented EAD-mediated TAs in all ventricles studied. CONCLUSIONS A carvedilol analogue, VK-II-36, inhibits ventricular tachyarrhythmias in intact mouse and rabbit ventricles by the suppression of SCaEs, independent of beta-blocking activity. The RyR2 may be a potential target for treating focal ventricular arrhythmias triggered by either EADs or DADs.
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Affiliation(s)
- Mitsunori Maruyama
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA
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136
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Ryanodine receptor phosphorylation, calcium/calmodulin-dependent protein kinase II, and life-threatening ventricular arrhythmias. Trends Cardiovasc Med 2012; 21:48-51. [PMID: 22578240 DOI: 10.1016/j.tcm.2012.02.004] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ryanodine receptor (RyR2) dysfunction, which may result from a variety of mechanisms, has been implicated in the pathogenesis of cardiac arrhythmias and heart failure. In this review, we discuss the important role of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) in the regulation of RyR2-mediated Ca(2+) release. In particular, we examine how pathological activation of CaMKII can lead to an increased risk of sudden arrhythmic death. Finally, we discuss how reduction of CaMKII-mediated RyR2 hyperactivity might reduce the risk of arrhythmias and may serve as a rationale for future pharmacotherapeutic approaches.
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137
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Liu N, Napolitano C, Venetucci LA, Priori SG. Flecainide and antiarrhythmic effects in a mouse model of catecholaminergic polymorphic ventricular tachycardia. Trends Cardiovasc Med 2012; 22:35-9. [PMID: 22867967 DOI: 10.1016/j.tcm.2012.06.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Recent studies have shown that flecainide may be an effective therapy to prevent life-threatening arrhythmias in patients with catecholaminergic polymorphic ventricular tachycardia. Several hypotheses have been advanced to explain the antiarrhythmic mechanism of flecainide, including Na(+) channel blockade and a direct inhibitory action on the ryanodine receptor. In this article, we review the current literature on the topic and summarize the elements of the existing debate.
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Affiliation(s)
- Nian Liu
- Cardiovascular Genetic Program, The Leon H. Charney Division of Cardiology, New York University School of Medicine, New York, NY 10016, USA
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138
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Mezu UL, Singh P, Shusterman V, Hwang HS, Knollmann BC, Němec J. Accelerated junctional rhythm and nonalternans repolarization lability precede ventricular tachycardia in Casq2-/- mice. J Cardiovasc Electrophysiol 2012; 23:1355-63. [PMID: 22860618 DOI: 10.1111/j.1540-8167.2012.02406.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
BACKGROUND Calsequestrin-2 (CASQ2) is a Ca(2+) buffering protein of myocardial sarcoplasmic reticulum. CASQ2 mutations underlie a form of catecholaminergic polymorphic ventricular tachycardia (CPVT). The CPVT phenotype is recapitulated in Casq2 -/- mice. Repolarization lability (RL)-beat-to-beat variability in the T wave morphology-has been reported in long-QT syndrome, but has not been evaluated in CPVT. METHODS AND RESULTS ECG from Casq2 -/- mice was evaluated with respect to heart rate (HR) and RL changes prior to onset of ventricular tachycardia (VT) to gain insight into arrhythmogenesis in CPVT. Telemetry from unrestrained mice (3-month-old males, 5 animals of each genotype) and ECG before and after isoproterenol administration in anesthetized mice was analyzed. Average HR in sinus rhythm (SR), occurrence of nonsinus rhythm and RL were quantified. HR was slower in Casq2 -/- animals. Accelerated junctional rhythm (JR) occurred more frequently in Casq2 -/- mice and often preceded VT. In Casq2 -/- mice, HR increased prior to VT onset, prior to onset of JR and on transition from JR to VT. RL increased during progression from SR to VT and after isoproterenol administration in Casq2 -/-, but not in Casq2+/+ animals. Isoproterenol did not increase repolarization alternans in either genotype. CONCLUSIONS Accelerated JR, likely caused by triggered activity in His/Purkinje system, occurs frequently in Casq2 -/- mice. The absence of CASQ2 results in increased RL. The increase in HR and in RL precede onset of arrhythmias in this CPVT model. Nonalternans RL precedes ventricular arrhythmia in wider range of conditions than previously appreciated.
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Affiliation(s)
- Ure L Mezu
- Heart and Vascular Institute, School of Medicine, University of Pittsburgh, 200 Lothrop Street, Pittsburgh, PA 15213, USA
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139
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Calsequestrin mutations and catecholaminergic polymorphic ventricular tachycardia. Pediatr Cardiol 2012; 33:959-67. [PMID: 22421959 PMCID: PMC3393815 DOI: 10.1007/s00246-012-0256-1] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/31/2012] [Accepted: 02/16/2012] [Indexed: 10/28/2022]
Abstract
Cardiac calsequestrin (Casq2) is the major Ca2+ binding protein in the sarcoplasmic reticulum, which is the principle Ca2+ storage organelle of cardiac muscle. During the last decade, experimental studies have provided new concepts on the role of Casq2 in the regulation of cardiac muscle Ca2+ handling. Furthermore, mutations in the gene encoding for cardiac calsequestrin, CASQ2, cause a rare but severe form of catecholaminergic polymorphic ventricular tachycardia (CPVT). Here, we review the physiology of Casq2 in cardiac Ca2+ handling and discuss pathophysiological mechanisms that lead to CPVT caused by CASQ2 mutations. We also describe the clinical aspects of CPVT and provide an update of its contemporary clinical management.
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140
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Left cardiac sympathetic denervation for the management of life-threatening ventricular tachyarrhythmias in young patients with catecholaminergic polymorphic ventricular tachycardia and long QT syndrome. Clin Res Cardiol 2012; 102:33-42. [PMID: 22821214 PMCID: PMC3536998 DOI: 10.1007/s00392-012-0492-7] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/09/2012] [Accepted: 07/04/2012] [Indexed: 10/28/2022]
Abstract
BACKGROUND Left cardiac sympathetic denervation (LCSD) may be a therapeutic adjunct for young patients with catecholaminergic polymorphic ventricular tachycardia (CPVT) and long QT syndrome (LQTS) who are not fully protected by beta-blockade. OBJECTIVE The objective of this analysis was to report our institutional experience with LSCD in young patients for the management of life-threatening ventricular arrhythmias in CPVT and LQTS. METHODS Ten young patients with CPVT and LQTS underwent transaxillary LSCD at our institution. Mean age at surgery was 14.0 (range 3.9-42) years, mean body weight was 45.7 (range 15.5-90) kg. Five patients had the clinical diagnosis of CPVT, three were genotype positive for a mutation in the ryanodine-receptor-2-gene. Four of five LQTS patients were genotype positive. Indications for LCSD were recurrent syncope, symptomatic episodes of ventricular tachycardias and/or internal cardioverter-defibrillator (ICD) discharges, and aborted cardiac arrest despite high doses of beta-blockers. RESULTS LCSD was performed via the transaxillary approach. No significant complications were observed. Two patients already had an ICD, 6 patients received an ICD at the same operation or shortly thereafter. Median length of follow-up after LCSD was 2.3 (range 0.6-3.9) years. After LCSD a marked reduction in arrhythmia burden and cardiac events was observed in all patients while medication was continued. None of the patients had any further ICD discharge for sustained VT. CONCLUSIONS After LCSD, arrhythmia burden could significantly be reduced in all our young patients with CPVT and LQTS.
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141
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Itzhaki I, Maizels L, Huber I, Gepstein A, Arbel G, Caspi O, Miller L, Belhassen B, Nof E, Glikson M, Gepstein L. Modeling of catecholaminergic polymorphic ventricular tachycardia with patient-specific human-induced pluripotent stem cells. J Am Coll Cardiol 2012; 60:990-1000. [PMID: 22749309 DOI: 10.1016/j.jacc.2012.02.066] [Citation(s) in RCA: 160] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/20/2011] [Revised: 01/25/2012] [Accepted: 02/15/2012] [Indexed: 12/23/2022]
Abstract
OBJECTIVES The goal of this study was to establish a patient-specific human-induced pluripotent stem cells (hiPSCs) model of catecholaminergic polymorphic ventricular tachycardia (CPVT). BACKGROUND CPVT is a familial arrhythmogenic syndrome characterized by abnormal calcium (Ca(2+)) handling, ventricular arrhythmias, and sudden cardiac death. METHODS Dermal fibroblasts were obtained from a CPVT patient due to the M4109R heterozygous point RYR2 mutation and reprogrammed to generate the CPVT-hiPSCs. The patient-specific hiPSCs were coaxed to differentiate into the cardiac lineage and compared with healthy control hiPSCs-derived cardiomyocytes (hiPSCs-CMs). RESULTS Intracellular electrophysiological recordings demonstrated the development of delayed afterdepolarizations in 69% of the CPVT-hiPSCs-CMs compared with 11% in healthy control cardiomyocytes. Adrenergic stimulation by isoproterenol (1 μM) or forskolin (5 μM) increased the frequency and magnitude of afterdepolarizations and also led to development of triggered activity in the CPVT-hiPSCs-CMs. In contrast, flecainide (10 μM) and thapsigargin (10 μM) eliminated all afterdepolarizations in these cells. The latter finding suggests an important role for internal Ca(2+) stores in the pathogenesis of delayed afterdepolarizations. Laser-confocal Ca(2+) imaging revealed significant whole-cell [Ca(2+)] transient irregularities (frequent local and large-storage Ca(2+)-release events, broad and double-humped transients, and triggered activity) in the CPVT cardiomyocytes that worsened with adrenergic stimulation and Ca(2+) overload and improved with beta-blockers. Store-overload-induced Ca(2+) release was also identified in the hiPSCs-CMs and the threshold for such events was significantly reduced in the CPVT cells. CONCLUSIONS This study highlights the potential of hiPSCs for studying inherited arrhythmogenic syndromes, in general, and CPVT specifically. As such, it represents a promising paradigm to study disease mechanisms, optimize patient care, and aid in the development of new therapies.
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Affiliation(s)
- Ilanit Itzhaki
- The Sohnis Family Laboratory for Cardiac Electrophysiology and Regenerative Medicine, Rappaport Faculty of Medicine and Research Institute, Technion-Israel Institute of Technology, Haifa, Israel
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142
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Venetucci L, Denegri M, Napolitano C, Priori SG. Inherited calcium channelopathies in the pathophysiology of arrhythmias. Nat Rev Cardiol 2012; 9:561-75. [DOI: 10.1038/nrcardio.2012.93] [Citation(s) in RCA: 141] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
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143
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Vogler J, Eckardt L. Pharmacology of myocardial calcium-handling. Wien Med Wochenschr 2012; 162:311-5. [PMID: 22707076 DOI: 10.1007/s10354-012-0108-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2012] [Accepted: 04/23/2012] [Indexed: 11/25/2022]
Abstract
Disturbed myocardial calcium (Ca(+)) handling is one of the pathophysiologic hallmarks of cardiovascular diseases such as congestive heart failure, cardiac hypertrophy, and certain types of tachyarrhythmias. Pharmacologic treatment of these diseases thus focuses on restoring myocardial Ca(2+) homeostasis by interacting with Ca(2+)-dependent signaling pathways. In this article, we review the currently used pharmacologic agents that are able to restore or maintain myocardial Ca(2+) homeostasis and their mechanism of action as well as emerging new substances.
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Affiliation(s)
- Julia Vogler
- Division of Rhythmology, Department of Cardiology and Angiology, University Hospital Muenster, Albert-Schweitzer-Campus 1, 48149 Muenster, Germany.
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144
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Jacquemart C, Ould Abderrahmane F, Massin MM. Effects of flecainide therapy on inappropriate shocks and arrhythmias in catecholaminergic polymorphic ventricular tachycardia. J Electrocardiol 2012; 45:736-8. [PMID: 22672791 DOI: 10.1016/j.jelectrocard.2012.05.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2012] [Indexed: 10/28/2022]
Abstract
We report the case of a child with catecholaminergic polymorphic ventricular tachycardia, who had inappropriate electric shocks by an implantable cardioverter defibrillator and from recurrence of arrhythmias despite an appropriate β-blocking treatment. An additional treatment by flecainide completely suppressed inappropriate shocks due to sinusal tachycardia and ventricular tachyarrhythmias. We briefly discuss the potentially interesting effect of flecainide in this specific arrhythmia.
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Affiliation(s)
- Caroline Jacquemart
- Division of Pediatric Cardiology, Queen Fabiola Children's University Hospital, HUDERF, Free University of Brussels, ULB, Brussels, Belgium
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145
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Benoist D, Stones R, Drinkhill MJ, Benson AP, Yang Z, Cassan C, Gilbert SH, Saint DA, Cazorla O, Steele DS, Bernus O, White E. Cardiac arrhythmia mechanisms in rats with heart failure induced by pulmonary hypertension. Am J Physiol Heart Circ Physiol 2012; 302:H2381-95. [PMID: 22427523 PMCID: PMC3378302 DOI: 10.1152/ajpheart.01084.2011] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/18/2011] [Accepted: 03/15/2012] [Indexed: 12/22/2022]
Abstract
Pulmonary hypertension provokes right heart failure and arrhythmias. Better understanding of the mechanisms underlying these arrhythmias is needed to facilitate new therapeutic approaches for the hypertensive, failing right ventricle (RV). The aim of our study was to identify the mechanisms generating arrhythmias in a model of RV failure induced by pulmonary hypertension. Rats were injected with monocrotaline to induce either RV hypertrophy or failure or with saline (control). ECGs were measured in conscious, unrestrained animals by telemetry. In isolated hearts, electrical activity was measured by optical mapping and myofiber orientation by diffusion tensor-MRI. Sarcoplasmic reticular Ca(2+) handling was studied in single myocytes. Compared with control animals, the T-wave of the ECG was prolonged and in three of seven heart failure animals, prominent T-wave alternans occurred. Discordant action potential (AP) alternans occurred in isolated failing hearts and Ca(2+) transient alternans in failing myocytes. In failing hearts, AP duration and dispersion were increased; conduction velocity and AP restitution were steeper. The latter was intrinsic to failing single myocytes. Failing hearts had greater fiber angle disarray; this correlated with AP duration. Failing myocytes had reduced sarco(endo)plasmic reticular Ca(2+)-ATPase activity, increased sarcoplasmic reticular Ca(2+)-release fraction, and increased Ca(2+) spark leak. In hypertrophied hearts and myocytes, dysfunctional adaptation had begun, but alternans did not develop. We conclude that increased electrical and structural heterogeneity and dysfunctional sarcoplasmic reticular Ca(2+) handling increased the probability of alternans, a proarrhythmic predictor of sudden cardiac death. These mechanisms are potential therapeutic targets for the correction of arrhythmias in hypertensive, failing RVs.
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Affiliation(s)
- David Benoist
- Institute of Membrane and Systems Biology, University of Leeds, United Kingdom
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146
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Hong RA, Rivera KK, Jittirat A, Choi JJ. Flecainide suppresses defibrillator-induced storming in catecholaminergic polymorphic ventricular tachycardia. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2012; 35:794-7. [PMID: 22553997 DOI: 10.1111/j.1540-8159.2012.03421.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited condition associated with ventricular tachycardia (VT) triggered by exercise or sympathetic stress. Incessant VT may develop due to defibrillator-induced storming-a condition where implantable cardioverter-defibrillator discharges result in a hyperadrenergic state, provoking further VT and defibrillator discharge. We describe the case of a 14-year-old boy with CPVT caused by a calsequestrin-2 mutation, who presented with defibrillator-induced storming refractory to β-blockers, calcium-channel blockers, amiodarone, and dronedarone. Flecainide and β-blocker use suppressed incessant VT and defibrillator-induced storming.
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Affiliation(s)
- Robert A Hong
- The Queen's Medical Center, John A. Burns School of Medicine, Department of Internal Medicine, Division of Cardiology John A. Burns School of Medicine, Department of Internal Medicine, Honolulu, Hawaii 96813, USA
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147
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Obeyesekere MN, Sy RW, Leong-Sit P, Gula LJ, Yee R, Skanes AC, Klein GJ, Krahn AD. Treatment of asymptomatic catecholaminergic polymorphic ventricular tachycardia. Future Cardiol 2012; 8:439-50. [DOI: 10.2217/fca.12.12] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Catecholaminergic polymorphic ventricular tachycardia is a rare genetic disorder caused by mutations in genes involved in the intracellular calcium homeostasis of cardiac cells. Affected patients typically present with life-threatening ventricular arrhythmias precipitated by emotional/physical stress. The diagnosis is based on the demonstration of polymorphic or bidirectional ventricular tachycardia associated with adrenergic stress. Genetic testing can be confirmatory in some patients. Treatment for catecholaminergic polymorphic ventricular tachycardia includes medical and surgical efforts to suppress the effects of epinephrine at the myocardial level and/or modulation of calcium homeostasis. Mortality is high when untreated and sudden cardiac death may be the first manifestation of the disease. First-degree relatives of a proband should be offered genetic testing if the causal mutation is known. If the family mutation is not known, relatives should be clinically evaluated with provocative testing. In the absence of rigorous trials, prophylactic treatment of the asymptomatic catecholaminergic polymorphic ventricular tachycardia patient appears to reduce morbidity and mortality.
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Affiliation(s)
| | - Raymond W Sy
- The University of Western Ontario, Division of Cardiology, London, Ontario, Canada
| | - Peter Leong-Sit
- The University of Western Ontario, Division of Cardiology, London, Ontario, Canada
| | - Lorne J Gula
- The University of Western Ontario, Division of Cardiology, London, Ontario, Canada
| | - Raymond Yee
- The University of Western Ontario, Division of Cardiology, London, Ontario, Canada
| | - Allan C Skanes
- The University of Western Ontario, Division of Cardiology, London, Ontario, Canada
| | - George J Klein
- The University of Western Ontario, Division of Cardiology, London, Ontario, Canada
| | - Andrew D Krahn
- The University of Western Ontario, Division of Cardiology, London, Ontario, Canada
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Abstract
Atrial fibrillation is the most common type of cardiac arrhythmia, and is responsible for substantial morbidity and mortality in the general population. Current treatments have moderate efficacy and considerable risks, especially of pro-arrhythmia, highlighting the need for new therapeutic strategies. In recent years, substantial efforts have been invested in developing novel treatments that target the underlying molecular determinants of atrial fibrillation, and several new compounds are under development. This Review focuses on the mechanistic rationale for the development of new anti-atrial fibrillation drugs, on the molecular and structural motifs that they target and on the results obtained so far in experimental and clinical studies.
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149
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Lee YS, Maruyama M, Chang PC, Park HW, Rhee KS, Hsieh YC, Hsueh CH, Shen C, Lin SF, Hwang HS, Yin H, Knollmann BC, Chen PS. Ryanodine receptor inhibition potentiates the activity of Na channel blockers against spontaneous calcium elevations and delayed afterdepolarizations in Langendorff-perfused rabbit ventricles. Heart Rhythm 2012; 9:1125-32. [PMID: 22387372 DOI: 10.1016/j.hrthm.2012.02.031] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/13/2012] [Indexed: 01/06/2023]
Abstract
BACKGROUND Na channel blockers are effective in suppressing delayed afterdepolarizations (DADs) in isolated Purkinje fibers. However, in isolated mouse ventricular myocytes lacking calsequestrin, only those Na channel blockers that also inhibit type 2 ryanodine receptor channels were effective against spontaneous Ca elevation (SCaE) and DADs. OBJECTIVE To test the hypothesis that combined Na channel and type 2 ryanodine receptor channel blocker ((R)-propafenone) is more effective than a Na channel blocker (lidocaine) in suppressing SCaE and DADs in the intact rabbit ventricles. METHODS We compared (R)-propafenone (3 μmol/L) with lidocaine (50 μmol/L) on SCaE and DADs by using epicardial optical mapping of intracellular calcium (Ca(i)) and membrane voltage in Langendorff-perfused rabbit hearts. SCaE and DADs were induced by rapid pacing trains and isoproterenol (0.3 μmol/L) infusion. One arbitrary unit is equivalent to the Ca transient amplitude of paced beats. RESULTS SCaEs were observed at the cessation of rapid pacing in all hearts at baseline. (R)-Propafenone nearly completely inhibited DADs and SCaE (0.04 arbitrary units [95% confidence interval 0.02-0.06] vs 0.23 arbitrary units [95% confidence interval 0.18-0.28] at baseline; n = 6 hearts; P <.001). Lidocaine also significantly reduced the SCaE but was significantly (P <.05) less effective than (R)-propafenone. Both drugs increased the rise time of action potential upstroke and reduced conduction velocity to a similar extent, suggesting a significant inhibition of I(Na). CONCLUSIONS Both Na channel blockers significantly reduced tachycardia-induced SCaEs in the rabbit ventricles, but (R)-propafenone was significantly more effective than lidocaine. These data suggest that type 2 ryanodine receptor inhibition potentiates the activity of Na channel blockers against SCaE and DADs in the intact hearts.
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Affiliation(s)
- Young Soo Lee
- Department of Medicine, Krannert Institute of Cardiology and Division of Cardiology, Indiana University School of Medicine, Indianapolis, Indiana, USA
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150
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Thomas NL, Williams AJ. Pharmacology of ryanodine receptors and Ca2+-induced Ca2+ release. ACTA ACUST UNITED AC 2012. [DOI: 10.1002/wmts.34] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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