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Abstract
Cardiac alternans arises from dynamical instabilities in the electrical and calcium cycling systems of the heart, and often precedes ventricular arrhythmias and sudden cardiac death. In this review, we integrate clinical observations with theory and experiment to paint a holistic portrait of cardiac alternans: the underlying mechanisms, arrhythmic manifestations and electrocardiographic signatures. We first summarize the cellular and tissue mechanisms of alternans that have been demonstrated both theoretically and experimentally, including 3 voltage-driven and 2 calcium-driven alternans mechanisms. Based on experimental and simulation results, we describe their relevance to mechanisms of arrhythmogenesis under different disease conditions, and their link to electrocardiographic characteristics of alternans observed in patients. Our major conclusion is that alternans is not only a predictor, but also a causal mechanism of potentially lethal ventricular and atrial arrhythmias across the full spectrum of arrhythmia mechanisms that culminate in functional reentry, although less important for anatomic reentry and focal arrhythmias.
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Affiliation(s)
- Zhilin Qu
- Departments of Medicine (Cardiology), Physiology, and Computational Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA
| | - James N. Weiss
- Departments of Medicine (Cardiology), Physiology, and Computational Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA
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Huang C, Song Z, Qu Z. Synchronization of spatially discordant voltage and calcium alternans in cardiac tissue. Phys Rev E 2022; 106:024406. [PMID: 36109882 PMCID: PMC11316446 DOI: 10.1103/physreve.106.024406] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2022] [Accepted: 07/18/2022] [Indexed: 06/01/2023]
Abstract
The heart is an excitable medium which is excited by membrane potential depolarization and propagation. Membrane potential depolarization brings in calcium (Ca) through the Ca channels to trigger intracellular Ca release for contraction of the heart. Ca also affects voltage via Ca-dependent ionic currents, and thus, voltage and Ca are bidirectionally coupled. It has been shown that the voltage subsystem or the Ca subsystem can generate its own dynamical instabilities which are affected by their bidirectional couplings, leading to complex dynamics of action potential and Ca cycling. Moreover, the dynamics become spatiotemporal in tissue in which cells are diffusively coupled through voltage. A widely investigated spatiotemporal dynamics is spatially discordant alternans (SDA) in which action potential duration (APD) or Ca amplitude exhibits temporally period-2 and spatially out-of-phase patterns, i.e., APD-SDA and Ca-SDA patterns, respectively. However, the mechanisms of formation, stability, and synchronization of APD-SDA and Ca-SDA patterns remain incompletely understood. In this paper, we use cardiac tissue models described by an amplitude equation, coupled iterated maps, and reaction-diffusion equations with detailed physiology (the ionic model) to perform analytical and computational investigations. We show that, when the Ca subsystem is stable, the Ca-SDA pattern always follows the APD-SDA pattern, and thus, they are always synchronized. When the Ca subsystem is unstable, synchronization of APD-SDA and Ca-SDA patterns depends on the stabilities of both subsystems, their coupling strengths, and the spatial scales of the initial Ca-SDA patterns. Spontaneous (initial condition-independent) synchronization is promoted by enhancing APD instability and reducing Ca instability as well as stronger Ca-to-APD and APD-to-Ca coupling, a pattern formation caused by dynamical instabilities. When Ca is more unstable and APD is less unstable or APD-to-Ca coupling is weak, synchronization of APD-SDA and Ca-SDA patterns is promoted by larger initially synchronized Ca-SDA clusters, i.e., initial condition-dependent synchronization. The synchronized APD-SDA and Ca-SDA patterns can be locked in-phase, antiphase, or quasiperiodic depending on the coupling relationship between APD and Ca. These theoretical and simulation results provide mechanistic insights into the APD-SDA and Ca-SDA dynamics observed in experimental studies.
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Affiliation(s)
- Chunli Huang
- School of Mathematics and Statistics, Guangdong University of Foreign Studies, Guangzhou 510420, China
- Department of Medicine, University of California, Los Angeles, California 90095, USA
| | - Zhen Song
- Peng Cheng Laboratory, Shenzhen, Guangdong, China
| | - Zhilin Qu
- Department of Medicine, University of California, Los Angeles, California 90095, USA
- Department of Computational Medicine, University of California, Los Angeles, California 90095, USA
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Wang X, Chen X, Dobrev D, Li N. The crosstalk between cardiomyocyte calcium and inflammasome signaling pathways in atrial fibrillation. Pflugers Arch 2021; 473:389-405. [PMID: 33511453 DOI: 10.1007/s00424-021-02515-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2020] [Revised: 12/14/2020] [Accepted: 01/04/2021] [Indexed: 02/07/2023]
Abstract
Atrial fibrillation (AF) is the most frequent arrhythmia in adults. The prevalence and incidence of AF is going to increase substantially over the next few decades. Because AF increases the risk of stroke, heart failure, dementia, and others, it severely impacts the quality of life, morbidity, and mortality. Although the pathogenesis of AF is multifaceted and complex, focal ectopic activity and reentry are considered as the fundamental proarrhythmic mechanisms underlying AF development. Over the past 2 decades, large amount of evidence points to the key role of intracellular Ca2+ dysregulation in both initiation and maintenance of AF. More recently, emerging evidence reveal that NLRP3 (NACHT, LRR, PYD domain-containing 3) inflammasome pathway contributes to the substrate of both triggered activity and reentry, ultimately promoting AF. In this article, we review the current state of knowledge on Ca2+ signaling and NLRP3 inflammasome activity in AF. We also discuss the potential crosstalk between these two quintessential contributors to AF promotion.
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Affiliation(s)
- Xiaolei Wang
- Department of Medicine (Section of Cardiovascular Research), Baylor College of Medicine, Houston, TX, USA
| | - Xiaohui Chen
- Department of Medicine (Section of Cardiovascular Research), Baylor College of Medicine, Houston, TX, USA
| | - Dobromir Dobrev
- Institute of Pharmacology, West German Heart and Vascular Center, University Duisburg-Essen, Essen, Germany
| | - Na Li
- Department of Medicine (Section of Cardiovascular Research), Baylor College of Medicine, Houston, TX, USA. .,Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX, USA. .,Cardiovascular Research Institute, Baylor College of Medicine, Houston, TX, USA.
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Boyden PA. Purkinje physiology and pathophysiology. J Interv Card Electrophysiol 2018; 52:255-262. [PMID: 30056516 DOI: 10.1007/s10840-018-0414-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Accepted: 07/17/2018] [Indexed: 01/08/2023]
Abstract
There has always been an appreciation of the role of Purkinje fibers in the fast conduction of the normal cardiac impulse. Here, we briefly update our knowledge of this important set of cardiac cells. We discuss the anatomy of a Purkinje fiber strand, the importance of longitudinal conduction within a strand, circus movement within a strand, conduction, and excitability properties of Purkinjes. At the cell level, we discuss the important components of the ion channel makeup in the nonremodeled Purkinjes of healthy hearts. Finally, we discuss the role of the Purkinjes in forming the heritable arrhythmogenic substrates such as long QT, heritable conduction slowing, CPVT, sQT, and Brugada syndromes.
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Affiliation(s)
- Penelope A Boyden
- Department of Pharmacology, Columbia University, New York, NY, 10032, USA.
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Mustroph J, Wagemann O, Lebek S, Tarnowski D, Ackermann J, Drzymalski M, Pabel S, Schmid C, Wagner S, Sossalla S, Maier LS, Neef S. SR Ca 2+-leak and disordered excitation-contraction coupling as the basis for arrhythmogenic and negative inotropic effects of acute ethanol exposure. J Mol Cell Cardiol 2018; 116:81-90. [PMID: 29410242 DOI: 10.1016/j.yjmcc.2018.02.002] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/09/2017] [Revised: 01/23/2018] [Accepted: 02/01/2018] [Indexed: 02/03/2023]
Abstract
AIMS Ethanol has acute negative inotropic and arrhythmogenic effects. The underlying mechanisms, however, are largely unknown. Sarcoplasmic reticulum Ca2+-leak is an important mechanism for reduced contractility and arrhythmias. Ca2+-leak can be induced by oxidative stress and Ca2+/Calmodulin-dependent protein kinase II (CaMKII). Therefore, we investigated the influence of acute ethanol exposure on excitation-contraction coupling in atrial and ventricular cardiomyocytes. METHODS AND RESULTS Isolated human atrial and murine atrial or ventricular cardiomyocytes were preincubated for 30 min and then superfused with control solution or solution containing ethanol. Ethanol had acute negative inotropic and positive lusitropic effects in human atrial muscle strips and murine ventricular cardiomyocytes. Accordingly, Ca2+-imaging indicated lower Ca2+-transient amplitudes and increased SERCA2a activity, while myofilament Ca2+-sensitivity was reduced. SR Ca2+-leak was assessed by measuring Ca2+-sparks. Ethanol induced severe SR Ca2+-leak in human atrial cardiomyocytes (calculated leak: 4.60 ± 0.45 mF/F0 vs 1.86 ± 0.26 in control, n ≥ 80). This effect was dose-dependent, while spontaneous arrhythmogenic Ca2+-waves increased ~5-fold, as investigated in murine cardiomyocytes. Delayed afterdepolarizations, which can result from increased SR Ca2+-leak, were significantly increased by ethanol. Measurements using the reactive oxygen species (ROS) sensor CM-H2DCFDA showed increased ROS-stress in ethanol treated cells. ROS-scavenging with N-acetylcysteine prevented negative inotropic and positive lusitropic effects in human muscle strips. Ethanol-induced Ca2+-leak was abolished in mice with knockout of NOX2 (the main source for ROS in cardiomyocytes). Importantly, mice with oxidation-resistant CaMKII (Met281/282Val mutation) were protected from ethanol-induced Ca2+-leak. CONCLUSION We show for the first time that ethanol acutely induces strong SR Ca2+-leak, also altering excitation-contraction coupling. Acute negative inotropic effects of ethanol can be explained by reduced systolic Ca2+-release. Mechanistically, ROS-production via NOX2 and oxidative activation of CaMKII appear to play central roles. This provides a mechanism for the arrhythmogenic and negative inotropic effects of ethanol and suggests a druggable target (CaMKII).
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Affiliation(s)
- Julian Mustroph
- Dept. of Internal Medicine II, University Medical Center Regensburg, Regensburg, Germany
| | - Olivia Wagemann
- Dept. of Internal Medicine II, University Medical Center Regensburg, Regensburg, Germany
| | - Simon Lebek
- Dept. of Internal Medicine II, University Medical Center Regensburg, Regensburg, Germany
| | - Daniel Tarnowski
- Dept. of Internal Medicine II, University Medical Center Regensburg, Regensburg, Germany
| | - Jasmin Ackermann
- Dept. of Internal Medicine II, University Medical Center Regensburg, Regensburg, Germany
| | - Marzena Drzymalski
- Dept. of Internal Medicine II, University Medical Center Regensburg, Regensburg, Germany
| | - Steffen Pabel
- Dept. of Internal Medicine II, University Medical Center Regensburg, Regensburg, Germany
| | - Christof Schmid
- Dept. of Cardiothoracic Surgery, University Medical Center Regensburg, Regensburg, Germany
| | - Stefan Wagner
- Dept. of Internal Medicine II, University Medical Center Regensburg, Regensburg, Germany
| | - Samuel Sossalla
- Dept. of Internal Medicine II, University Medical Center Regensburg, Regensburg, Germany
| | - Lars S Maier
- Dept. of Internal Medicine II, University Medical Center Regensburg, Regensburg, Germany
| | - Stefan Neef
- Dept. of Internal Medicine II, University Medical Center Regensburg, Regensburg, Germany.
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Country MW, Jonz MG. Calcium dynamics and regulation in horizontal cells of the vertebrate retina: lessons from teleosts. J Neurophysiol 2017; 117:523-536. [PMID: 27832601 PMCID: PMC5288477 DOI: 10.1152/jn.00585.2016] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2016] [Accepted: 11/02/2016] [Indexed: 01/20/2023] Open
Abstract
Horizontal cells (HCs) are inhibitory interneurons of the vertebrate retina. Unlike typical neurons, HCs are chronically depolarized in the dark, leading to a constant influx of Ca2+ Therefore, mechanisms of Ca2+ homeostasis in HCs must differ from neurons elsewhere in the central nervous system, which undergo excitotoxicity when they are chronically depolarized or stressed with Ca2+ HCs are especially well characterized in teleost fish and have been used to unlock mysteries of the vertebrate retina for over one century. More recently, mammalian models of the retina have been increasingly informative for HC physiology. We draw from both teleost and mammalian models in this review, using a comparative approach to examine what is known about Ca2+ pathways in vertebrate HCs. We begin with a survey of Ca2+-permeable ion channels, exchangers, and pumps and summarize Ca2+ influx and efflux pathways, buffering, and intracellular stores. This includes evidence for Ca2+-permeable α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors and N-methyl-d-aspartate receptors and for voltage-gated Ca2+ channels. Special attention is given to interactions between ion channels, to differences among species, and in which subtypes of HCs these channels have been found. We then discuss a number of unresolved issues pertaining to Ca2+ dynamics in HCs, including a potential role for Ca2+ in feedback to photoreceptors, the role for Ca2+-induced Ca2+ release, and the properties and functions of Ca2+-based action potentials. This review aims to highlight the unique Ca2+ dynamics in HCs, as these are inextricably tied to retinal function.
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Affiliation(s)
- Michael W Country
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| | - Michael G Jonz
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
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Baumeister P, Quinn TA. Altered Calcium Handling and Ventricular Arrhythmias in Acute Ischemia. CLINICAL MEDICINE INSIGHTS-CARDIOLOGY 2016; 10:61-69. [PMID: 28008297 PMCID: PMC5158122 DOI: 10.4137/cmc.s39706] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Revised: 10/27/2016] [Accepted: 11/20/2016] [Indexed: 12/14/2022]
Abstract
Acute ischemia results in deadly cardiac arrhythmias that are a major contributor to sudden cardiac death (SCD). The electrophysiological changes involved have been extensively studied, yet the mechanisms of ventricular arrhythmias during acute ischemia remain unclear. What is known is that during acute ischemia both focal (ectopic excitation) and nonfocal (reentry) arrhythmias occur, due to an interaction of altered electrical, mechanical, and biochemical properties of the myocardium. There is particular interest in the role that alterations in intracellular calcium handling, which cause changes in intracellular calcium concentration and to the calcium transient, play in ischemia-induced arrhythmias. In this review, we briefly summarize the known contributors to ventricular arrhythmias during acute ischemia, followed by an in-depth examination of the potential contribution of altered intracellular calcium handling, which may include novel targets for antiarrhythmic therapy.
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Affiliation(s)
- Peter Baumeister
- Department of Physiology and Biophysics, Dalhousie University, Halifax, Canada
| | - T Alexander Quinn
- Department of Physiology and Biophysics, Dalhousie University, Halifax, Canada
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