1
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Sy MR, Keefe JA, Sutton JP, Wehrens XHT. Cardiac function, structural, and electrical remodeling by microgravity exposure. Am J Physiol Heart Circ Physiol 2023; 324:H1-H13. [PMID: 36399385 PMCID: PMC9762974 DOI: 10.1152/ajpheart.00611.2022] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/25/2022] [Revised: 11/14/2022] [Accepted: 11/15/2022] [Indexed: 11/19/2022]
Abstract
Space medicine is key to the human exploration of outer space and pushes the boundaries of science, technology, and medicine. Because of harsh environmental conditions related to microgravity and other factors and hazards in outer space, astronauts and spaceflight participants face unique health and medical challenges, including those related to the heart. In this review, we summarize the literature regarding the effects of spaceflight on cardiac structure and function. We also provide an in-depth review of the literature regarding the effects of microgravity on cardiac calcium handling. Our review can inform future mechanistic and therapeutic studies and is applicable to other physiological states similar to microgravity such as prolonged horizontal bed rest and immobilization.
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Affiliation(s)
- Mary R Sy
- Cardiovascular Research Institute, Baylor College of Medicine, Houston, Texas
- Department of Integrative Physiology, Baylor College of Medicine, Houston, Texas
| | - Joshua A Keefe
- Cardiovascular Research Institute, Baylor College of Medicine, Houston, Texas
- Department of Integrative Physiology, Baylor College of Medicine, Houston, Texas
| | - Jeffrey P Sutton
- Center for Space Medicine, Baylor College of Medicine, Houston, Texas
- Department of Medicine, Baylor College of Medicine, Houston, Texas
| | - Xander H T Wehrens
- Cardiovascular Research Institute, Baylor College of Medicine, Houston, Texas
- Department of Integrative Physiology, Baylor College of Medicine, Houston, Texas
- Center for Space Medicine, Baylor College of Medicine, Houston, Texas
- Department of Medicine, Baylor College of Medicine, Houston, Texas
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas
- Department of Pediatrics, Baylor College of Medicine, Houston, Texas
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2
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Borile G, Zaglia T, E. Lehnart S, Mongillo M. Multiphoton Imaging of Ca 2+ Instability in Acute Myocardial Slices from a RyR2R2474S Murine Model of Catecholaminergic Polymorphic Ventricular Tachycardia. J Clin Med 2021; 10:jcm10132821. [PMID: 34206855 PMCID: PMC8269190 DOI: 10.3390/jcm10132821] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2021] [Revised: 06/18/2021] [Accepted: 06/21/2021] [Indexed: 12/27/2022] Open
Abstract
Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT) is a familial stress-induced arrhythmia syndrome, mostly caused by mutations in Ryanodine receptor 2 (RyR2), the sarcoplasmic reticulum (SR) Ca2+ release channel in cardiomyocytes. Pathogenetic mutations lead to gain of function in the channel, causing arrhythmias by promoting diastolic spontaneous Ca2+ release (SCR) from the SR and delayed afterdepolarizations. While the study of Ca2+ dynamics in single cells from murine CPVT models has increased our understanding of the disease pathogenesis, questions remain on the mechanisms triggering the lethal arrhythmias at tissue level. Here, we combined subcellular analysis of Ca2+ signals in isolated cardiomyocytes and in acute thick ventricular slices of RyR2R2474S knock-in mice, electrically paced at different rates (1–5 Hz), to identify arrhythmogenic Ca2+ dynamics, from the sub- to the multicellular perspective. In both models, RyR2R2474S cardiomyocytes had increased propensity to develop SCR upon adrenergic stimulation, which manifested, in the slices, with Ca2+ alternans and synchronous Ca2+ release events in neighboring cardiomyocytes. Analysis of Ca2+ dynamics in multiple cells in the tissue suggests that SCRs beget SCRs in contiguous cells, overcoming the protective electrotonic myocardial coupling, and potentially generating arrhythmia triggering foci. We suggest that intercellular interactions may underscore arrhythmic propensity in CPVT hearts with ‘leaky’ RyR2.
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Affiliation(s)
- Giulia Borile
- Department of Biomedical Sciences, University of Padova, Via Ugo Bassi 58/B, 35131 Padova, Italy; (G.B.); (T.Z.)
- Veneto Institute of Molecular Medicine, Via Orus 2, 35129 Padova, Italy
| | - Tania Zaglia
- Department of Biomedical Sciences, University of Padova, Via Ugo Bassi 58/B, 35131 Padova, Italy; (G.B.); (T.Z.)
- Veneto Institute of Molecular Medicine, Via Orus 2, 35129 Padova, Italy
| | - Stephan E. Lehnart
- Heart Research Heart Research Center Göttingen, Cellular Biophysics and Translational Cardi-Ology Section, Department of Cardiology & Pulmonology, University Medical Center Göttingen, 37073 Göttingen, Germany;
- DZHK (German Centre for Cardiovascular Research), Partner Site Göttingen, 37073 Göttingen, Germany
| | - Marco Mongillo
- Department of Biomedical Sciences, University of Padova, Via Ugo Bassi 58/B, 35131 Padova, Italy; (G.B.); (T.Z.)
- Veneto Institute of Molecular Medicine, Via Orus 2, 35129 Padova, Italy
- Correspondence: ; Tel.: +39-049-7923229; Fax: +39-049-7923250
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3
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Marchena M, Echebarria B, Shiferaw Y, Alvarez-Lacalle E. Buffering and total calcium levels determine the presence of oscillatory regimes in cardiac cells. PLoS Comput Biol 2020; 16:e1007728. [PMID: 32970668 PMCID: PMC7537911 DOI: 10.1371/journal.pcbi.1007728] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2020] [Revised: 10/06/2020] [Accepted: 07/07/2020] [Indexed: 12/16/2022] Open
Abstract
Calcium oscillations and waves induce depolarization in cardiac cells which are believed to cause life-threathening arrhythimas. In this work, we study the conditions for the appearance of calcium oscillations in both a detailed subcellular model of calcium dynamics and a minimal model that takes into account just the minimal ingredients of the calcium toolkit. To avoid the effects of homeostatic changes and the interaction with the action potential we consider the somewhat artificial condition of a cell without pacing and with no calcium exchange with the extracellular medium. Both the full subcellular model and the minimal model present the same scenarios depending on the calcium load: two stationary states, one with closed ryanodine receptors (RyR) and most calcium in the cell stored in the sarcoplasmic reticulum (SR), and another, with open RyRs and a depleted SR. In between, calcium oscillations may appear. The robustness of these oscillations is determined by the amount of calsequestrin (CSQ). The lack of this buffer in the SR enhances the appearance of oscillations. The minimal model allows us to relate the stability of the oscillating state to the nullcline structure of the system, and find that its range of existence is bounded by a homoclinic and a Hopf bifurcation, resulting in a sudden transition to the oscillatory regime as the cell calcium load is increased. Adding a small amount of noise to the RyR behavior increases the parameter region where oscillations appear and provides a gradual transition from the resting state to the oscillatory regime, as observed in the subcellular model and experimentally. In cardiac cells, calcium plays a very important role. An increase in calcium levels is the trigger used by the cell to initiate contraction. Besides, calcium modulates several transmembrane currents, affecting the cell transmembrane potential. Thus, dysregulations in calcium handling have been associated with the appearance of arrhythmias. Often, this dysregulation results in the appearance of periodic calcium waves or global oscillations, providing a pro-arrhythmic substrate. In this paper, we study the onset of calcium oscillations in cardiac cells using both a detailed subcellular model of calcium dynamics and a minimal model that takes into account the essential ingredients of the calcium toolkit. Both reproduce the main experimental results and link this behavior with the presence of different steady-state solutions and bifurcations that depend on the total amount of calcium in the cell and in the level of buffering present. We expect that this work will help to clarify the conditions under which calcium oscillations appear in cardiac myocytes and, therefore, will represent a step further in the understanding of the origin of cardiac arrhythmias.
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Affiliation(s)
- Miquel Marchena
- Departament de Física, Universitat Politècnica de Catalunya-BarcelonaTech, Barcelona, Spain
| | - Blas Echebarria
- Departament de Física, Universitat Politècnica de Catalunya-BarcelonaTech, Barcelona, Spain
| | - Yohannes Shiferaw
- Physics Department, California State University, Northridge, California 91330, USA
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4
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Country MW, Campbell BFN, Jonz MG. Spontaneous action potentials in retinal horizontal cells of goldfish ( Carassius auratus) are dependent upon L-type Ca 2+ channels and ryanodine receptors. J Neurophysiol 2019; 122:2284-2293. [PMID: 31596629 DOI: 10.1152/jn.00240.2019] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Horizontal cells (HCs) are interneurons of the outer retina that undergo graded changes in membrane potential during the light response and provide feedback to photoreceptors. We characterized spontaneous Ca2+-based action potentials (APs) in isolated goldfish (Carassius auratus) HCs with electrophysiological and intracellular imaging techniques. Transient changes in intracellular Ca2+ concentration ([Ca2+]i) were observed with fura-2 and were abolished by removal of extracellular Ca2+ or by inhibition of Ca2+ channels by 50 µM Cd2+ or 100 µM nifedipine. Inhibition of Ca2+ release from stores with 20 µM ryanodine or 50 µM dantrolene abolished Ca2+ transients and increased baseline [Ca2+]i. This increased baseline was prevented by blocking L-type Ca2+ channels with nifedipine, suggesting that Ca2+-induced Ca2+ release from stores may be needed to inactivate membrane Ca2+ channels. Caffeine (3 mM) increased the frequency of Ca2+ transients, and the store-operated channel antagonist 2-aminoethyldiphenylborinate (100 μM) counteracted this effect. APs were detected with voltage-sensitive dye imaging (FluoVolt) and current-clamp electrophysiology. In current-clamp recordings, regenerative APs were abolished by removal of extracellular Ca2+ or in the presence of 5 mM Co2+ or 100 µM nifedipine, and APs were amplified with 15 mM Ba2+. Collectively, our data suggest that during APs Ca2+ enters through L-type Ca2+ channels and that Ca2+ stores (gated by ryanodine receptors) contribute to the rise in [Ca2+]i. This work may lead to further understanding of the possible role APs have in vision, such as transitioning from light to darkness or modulating feedback from HCs to photoreceptors.NEW & NOTEWORTHY Horizontal cells (HCs) are interneurons of the outer retina that provide inhibitory feedback onto photoreceptors. HCs respond to light via graded changes in membrane potential. We characterized spontaneous action potentials in HCs from goldfish and linked action potential generation to a rise in intracellular Ca2+ via plasma membrane channels and ryanodine receptors. Action potentials may play a role in vision, such as transitioning from light to darkness, or in modulating feedback from HCs to photoreceptors.
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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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5
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Murphy KR, Baggett B, Cooper LL, Lu Y, O-Uchi J, Sedivy JM, Terentyev D, Koren G. Enhancing Autophagy Diminishes Aberrant Ca 2+ Homeostasis and Arrhythmogenesis in Aging Rabbit Hearts. Front Physiol 2019; 10:1277. [PMID: 31636573 PMCID: PMC6787934 DOI: 10.3389/fphys.2019.01277] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2019] [Accepted: 09/20/2019] [Indexed: 12/19/2022] Open
Abstract
Aim Aging in humans is associated with a 10–40-fold greater incidence of sudden cardiac death from malignant tachyarrhythmia. We have reported that thiol oxidation of ryanodine receptors (RyR2s) by mitochondria-derived reactive oxygen species (mito-ROS) contributes to defective Ca2+ homeostasis in cardiomyocytes (CMs) from aging rabbit hearts. However, mechanisms responsible for the increase in mito-ROS in the aging heart remain poorly understood. Here we test the hypothesis that age-associated decrease in autophagy is a major contributor to enhanced mito-ROS production and thereby pro-arrhythmic disturbances in Ca2+ homeostasis. Methods and Results Ventricular tissues from aged rabbits displayed significant downregulation of proteins involved in mitochondrial autophagy compared with tissues from young controls. Blocking autophagy with chloroquine increased total ROS production in primary rabbit CMs and mito-ROS production in HL-1 CMs. Furthermore, chloroquine treatment of HL-1 cells depolarized mitochondrial membrane potential (Δψm) to 50% that of controls. Blocking autophagy significantly increased oxidation of RyR2, resulting in enhanced propensity to pro-arrhythmic spontaneous Ca2+ release under β-adrenergic stimulation. Aberrant Ca2+ release was abolished by treatment with the mito-ROS scavenger mito-TEMPO. Importantly, the autophagy enhancer Torin1 and ATG7 overexpression reduced the rate of mito-ROS production and restored both Δψm and defective Ca2+ handling in CMs derived from aged rabbit hearts. Conclusion Decreased autophagy is a major cause of increased mito-ROS production in the aging heart. Our data suggest that promoting autophagy may reduce pathologic mito-ROS during normal aging and reduce pro-arrhythmic spontaneous Ca2+ release via oxidized RyR2s.
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Affiliation(s)
- Kevin R Murphy
- Cardiovascular Research Center at the Cardiovascular Institute, Division of Cardiology, Warren Alpert Medical School of Brown University, Providence, RI, United States.,Department of Molecular Biology, Cellular Biology and Biochemistry, Brown University, Providence, RI, United States
| | - Brett Baggett
- Cardiovascular Research Center at the Cardiovascular Institute, Division of Cardiology, Warren Alpert Medical School of Brown University, Providence, RI, United States.,Department of Molecular Biology, Cellular Biology and Biochemistry, Brown University, Providence, RI, United States
| | - Leroy L Cooper
- Cardiovascular Research Center at the Cardiovascular Institute, Division of Cardiology, Warren Alpert Medical School of Brown University, Providence, RI, United States.,Department of Biology, Vassar College, Poughkeepsie, NY, United States
| | - Yichun Lu
- Cardiovascular Research Center at the Cardiovascular Institute, Division of Cardiology, Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Jin O-Uchi
- Cardiovascular Research Center at the Cardiovascular Institute, Division of Cardiology, Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - John M Sedivy
- Department of Molecular Biology, Cellular Biology and Biochemistry, Brown University, Providence, RI, United States
| | - Dmitry Terentyev
- Cardiovascular Research Center at the Cardiovascular Institute, Division of Cardiology, Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Gideon Koren
- Cardiovascular Research Center at the Cardiovascular Institute, Division of Cardiology, Warren Alpert Medical School of Brown University, Providence, RI, United States
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6
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Fukaya H, Piktel JS, Wan X, Plummer BN, Laurita KR, Wilson LD. Arrhythmogenic Delayed Afterdepolarizations Are Promoted by Severe Hypothermia But Not Therapeutic Hypothermia. Circ J 2018; 82:62-70. [DOI: 10.1253/circj.cj-17-0145] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Hidehira Fukaya
- The Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University
- Department of Cardiovascular Medicine, Kitasato University School of Medicine
| | - Joseph S. Piktel
- The Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University
- Department of Emergency Medicine, MetroHealth Campus, Case Western Reserve University
| | - Xiaoping Wan
- The Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University
| | - Bradley N. Plummer
- The Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University
| | - Kenneth R. Laurita
- The Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University
| | - Lance D. Wilson
- The Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University
- Department of Emergency Medicine, MetroHealth Campus, Case Western Reserve University
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7
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Muszkiewicz A, Liu X, Bueno-Orovio A, Lawson BAJ, Burrage K, Casadei B, Rodriguez B. From ionic to cellular variability in human atrial myocytes: an integrative computational and experimental study. Am J Physiol Heart Circ Physiol 2017; 314:H895-H916. [PMID: 29351467 PMCID: PMC6008144 DOI: 10.1152/ajpheart.00477.2017] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Variability refers to differences in physiological function between individuals, which may translate into different disease susceptibility and treatment efficacy. Experiments in human cardiomyocytes face wide variability and restricted tissue access; under these conditions, computational models are a useful complementary tool. We conducted a computational and experimental investigation in cardiomyocytes isolated from samples of the right atrial appendage of patients undergoing cardiac surgery to evaluate the impact of variability in action potentials (APs) and subcellular ionic densities on Ca2+ transient dynamics. Results showed that 1) variability in APs and ionic densities is large, even within an apparently homogenous patient cohort, and translates into ±100% variation in ionic conductances; 2) experimentally calibrated populations of models with wide variations in ionic densities yield APs overlapping with those obtained experimentally, even if AP characteristics of the original generic model differed significantly from experimental APs; 3) model calibration with AP recordings restricts the variability in ionic densities affecting upstroke and resting potential, but redundancy in repolarization currents admits substantial variability in ionic densities; and 4) model populations constrained with experimental APs and ionic densities exhibit three Ca2+ transient phenotypes, differing in intracellular Ca2+ handling and Na+/Ca2+ membrane extrusion. These findings advance our understanding of the impact of variability in human atrial electrophysiology. NEW & NOTEWORTHY Variability in human atrial electrophysiology is investigated by integrating for the first time cellular-level and ion channel recordings in computational electrophysiological models. Ion channel calibration restricts current densities but not cellular phenotypic variability. Reduced Na+/Ca2+ exchanger is identified as a primary mechanism underlying diastolic Ca2+ fluctuations in human atrial myocytes.
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Affiliation(s)
- Anna Muszkiewicz
- Department of Computer Science, University of Oxford , Oxford , United Kingdom
| | - Xing Liu
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, John Radcliffe Hospital , Oxford , United Kingdom
| | | | - Brodie A J Lawson
- ARC Centre of Excellence for Mathematical and Statistical Frontiers, School of Mathematical Sciences, Queensland University of Technology , Brisbane, Queensland , Australia.,School of Mathematics, Queensland University of Technology , Brisbane, Queensland , Australia
| | - Kevin Burrage
- Department of Computer Science, University of Oxford , Oxford , United Kingdom.,ARC Centre of Excellence for Mathematical and Statistical Frontiers, School of Mathematical Sciences, Queensland University of Technology , Brisbane, Queensland , Australia.,School of Mathematics, Queensland University of Technology , Brisbane, Queensland , Australia
| | - Barbara Casadei
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, John Radcliffe Hospital , Oxford , United Kingdom
| | - Blanca Rodriguez
- Department of Computer Science, University of Oxford , Oxford , United Kingdom
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8
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Gambardella J, Trimarco B, Iaccarino G, Santulli G. New Insights in Cardiac Calcium Handling and Excitation-Contraction Coupling. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 1067:373-385. [PMID: 28956314 DOI: 10.1007/5584_2017_106] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Excitation-contraction (EC) coupling denotes the conversion of electric stimulus in mechanic output in contractile cells. Several studies have demonstrated that calcium (Ca2+) plays a pivotal role in this process. Here we present a comprehensive and updated description of the main systems involved in cardiac Ca2+ handling that ensure a functional EC coupling and their pathological alterations, mainly related to heart failure.
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Affiliation(s)
- Jessica Gambardella
- Department of Advanced Biomedical Sciences, "Federico II" University, Naples, Italy.,Department of Medicine, Surgery and Dentistry, Scuola Medica Salernitana, University of Salerno, Fisciano, Italy
| | - Bruno Trimarco
- Department of Advanced Biomedical Sciences, "Federico II" University, Naples, Italy
| | - Guido Iaccarino
- Department of Medicine, Surgery and Dentistry, Scuola Medica Salernitana, University of Salerno, Fisciano, Italy
| | - Gaetano Santulli
- Department of Advanced Biomedical Sciences, "Federico II" University, Naples, Italy. .,Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Ave, Forch 525, 10461, New York, NY, USA.
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9
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Zheng J, Zhai K, Chen Y, Zhang X, Miao L, Wei B, Ji G. Nitric oxide mediates stretch-induced Ca2+ oscillation in smooth muscle. J Cell Sci 2016; 129:2430-7. [DOI: 10.1242/jcs.180638] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2015] [Accepted: 03/23/2016] [Indexed: 11/20/2022] Open
Abstract
The stretching of smooth muscle tissue modulates contraction via augmentation of Ca2+ transients, but the mechanism underlying stretch-induced Ca2+ transients is still unknown. We found that mechanical stretching and maintenance of mouse urinary bladder smooth muscle strips and single myocytes at the initial length of 30% and 18%, respectively, resulted in Ca2+ oscillations. Experiments indicated that mechanical stretching remarkably increases the production of nitric oxide (NO) as well as the amplitude and duration of muscle contraction. Stretch-induced Ca2+ oscillations and contractility increases were completely abolished by NO inhibitor L-NAME or eNOS gene inactivation. Moreover, exposure of eNOS knockout myocytes to exogenous NO donor induced Ca2+ oscillations. The stretch-induced Ca2+ oscillations were greatly inhibited by selective IP3R inhibitor xestospongin C and partially inhibited by ryanodine. Moreover, the stretch-induced Ca2+ oscillations were also suppressed by LY294002, but not by the soluble guanylyl cyclase (sGC) inhibitor ODQ. These results suggest that myocytes stretching and maintenance at a certain length resulted in Ca2+ oscillations that is NO dependent and sGC/cGMP independent and results from the activation of PI(3)K in smooth muscle.
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Affiliation(s)
- Ji Zheng
- Urological Surgery Research Institute, Southwest Hospital, Third Military Medical University, Gao Tanyan Rd. 30, Chongqing 400038, China
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Rd, Beijing 100101, China
| | - Kui Zhai
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Rd, Beijing 100101, China
| | - Yingxiao Chen
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Rd, Beijing 100101, China
| | - Xu Zhang
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Rd, Beijing 100101, China
| | - Lin Miao
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Rd, Beijing 100101, China
| | - Bin Wei
- Department of Physiology, Wayne State University School of Medicine, Detroit, MI 48201, United States
| | - Guangju Ji
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Rd, Beijing 100101, China
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10
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Miura M, Nagano T, Murai N, Taguchi Y, Handoh T, Satoh M, Miyata S, Miller L, Shindoh C, Stuyvers BD. Effect of Carbenoxolone on Arrhythmogenesis in Rat Ventricular Muscle. Circ J 2016; 80:76-84. [DOI: 10.1253/circj.cj-15-0401] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Masahito Miura
- Department of Clinical Physiology, Health Science, Tohoku University Graduate School of Medicine
| | - Tsuyoshi Nagano
- Department of Clinical Physiology, Health Science, Tohoku University Graduate School of Medicine
| | - Naomi Murai
- Department of Clinical Physiology, Health Science, Tohoku University Graduate School of Medicine
| | - Yuhto Taguchi
- Department of Clinical Physiology, Health Science, Tohoku University Graduate School of Medicine
| | - Tetsuya Handoh
- Department of Clinical Physiology, Health Science, Tohoku University Graduate School of Medicine
| | - Minami Satoh
- Department of Clinical Physiology, Health Science, Tohoku University Graduate School of Medicine
| | - Satoshi Miyata
- Department of Cardiovascular Medicine, Tohoku University Graduate School of Medicine
| | - Lawson Miller
- Faculty of Medicine, Biomedical Sciences, Memorial University
| | - Chiyohiko Shindoh
- Department of Clinical Physiology, Health Science, Tohoku University Graduate School of Medicine
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11
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Liu MB, de Lange E, Garfinkel A, Weiss JN, Qu Z. Delayed afterdepolarizations generate both triggers and a vulnerable substrate promoting reentry in cardiac tissue. Heart Rhythm 2015; 12:2115-24. [PMID: 26072025 PMCID: PMC4583816 DOI: 10.1016/j.hrthm.2015.06.019] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/20/2015] [Indexed: 11/23/2022]
Abstract
BACKGROUND Delayed afterdepolarizations (DADs) have been well characterized as arrhythmia triggers, but their role in generating a tissue substrate vulnerable to reentry is not well understood. OBJECTIVE The purpose of this study was to test the hypothesis that random DADs can self-organize to generate both an arrhythmia trigger and a vulnerable substrate simultaneously in cardiac tissue as a result of gap junction coupling. METHODS Computer simulations in 1-dimensional cable and 2-dimensional tissue models were performed. The cellular DAD amplitude was varied by changing the strength of sarcoplasmic reticulum calcium release. Random DAD latency and amplitude in different cells were simulated using gaussian distributions. RESULTS Depending on the strength of spontaneous sarcoplasmic reticulum calcium release and other conditions, random DADs in cardiac tissue resulted in the following behaviors: (1) triggered activity (TA); (2) a vulnerable tissue substrate causing unidirectional conduction block and reentry by inactivating sodium channels; (3) both triggers and a vulnerable substrate simultaneously by generating TA in regions next to regions with subthreshold DADs susceptible to unidirectional conduction block and reentry. The probability of the latter 2 behaviors was enhanced by reduced sodium channel availability, reduced gap junction coupling, increased tissue heterogeneity, and less synchronous DAD latency. CONCLUSION DADs can self-organize in tissue to generate arrhythmia triggers, a vulnerable tissue substrate, and both simultaneously. Reduced sodium channel availability and gap junction coupling potentiate this mechanism of arrhythmias, which are relevant to a variety of heart disease conditions.
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Affiliation(s)
- Michael B Liu
- UCLA Cardiovascular Research Laboratory; Department of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los Angeles, California
| | - Enno de Lange
- UCLA Cardiovascular Research Laboratory; Department of Knowledge Engineering, Maastricht University, Maastricht, The Netherlands
| | - Alan Garfinkel
- UCLA Cardiovascular Research Laboratory; Department of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los Angeles, California; Department of Integrative Biology and Physiology, University of California, Los Angeles, California
| | - James N Weiss
- UCLA Cardiovascular Research Laboratory; Department of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los Angeles, California; Department of Integrative Biology and Physiology, University of California, Los Angeles, California; Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, California
| | - Zhilin Qu
- UCLA Cardiovascular Research Laboratory; Department of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los Angeles, California.
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12
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Miskolczi G, Gönczi M, Kovács M, Seprényi G, Végh Á. Further evidence for the role of gap junctions in the delayed antiarrhythmic effect of cardiac pacing. Can J Physiol Pharmacol 2015; 93:545-53. [PMID: 25943326 DOI: 10.1139/cjpp-2014-0518] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
UNLABELLED The objective of this study was to provide evidence that gap junctions are involved in the delayed antiarrhythmic effect of cardiac pacing. Twenty-four dogs were paced through the right ventricle (4 × 5 min, rate of 240 beats/min) 24 h prior to a 25 min occlusion of the left anterior descending coronary artery. Some of these paced dogs were infused with 50 (n = 7) or 100 μmol/L (n = 7) of the gap junction uncoupler carbenoxolone (CBX), prior to and during the occlusion. Ten sham-paced dogs, subjected only to occlusion, served as the controls. Cardiac pacing markedly reduced the number of ectopic beats and episodes of ventricular tachycardia (VT), as well the incidence of VT and ventricular fibrillation during occlusion. The changes in severity of ischaemia and tissue electrical resistance were also less marked compared with the unpaced controls. Pacing also preserved the permeability of gap junctions, the phosphorylation of connexin43, and the structural integrity of the intercalated discs. The closing of gap junctions with CBX prior to and during ischaemia markedly attenuated or even abolished these protective effects of pacing. CONCLUSION Our results support the previous findings that gap junctions play a role in the delayed antiarrhythmic effect of cardiac pacing.
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Affiliation(s)
- Gottfried Miskolczi
- a Department of Pharmacology and Pharmacotherapy, University of Szeged, 6720 Szeged, Dóm tér 12, Hungary
| | - Márton Gönczi
- a Department of Pharmacology and Pharmacotherapy, University of Szeged, 6720 Szeged, Dóm tér 12, Hungary
| | - Mária Kovács
- a Department of Pharmacology and Pharmacotherapy, University of Szeged, 6720 Szeged, Dóm tér 12, Hungary
| | - György Seprényi
- b Department of Medical Biology, University of Szeged, Szeged, Hungary
| | - Ágnes Végh
- a Department of Pharmacology and Pharmacotherapy, University of Szeged, 6720 Szeged, Dóm tér 12, Hungary
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13
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Greer-Short A, Poelzing S. Distinguishing between overdrive excited and suppressed ventricular beats in guinea pig ventricular myocardium. Front Physiol 2015; 6:14. [PMID: 25741282 PMCID: PMC4332283 DOI: 10.3389/fphys.2015.00014] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2014] [Accepted: 01/09/2015] [Indexed: 11/13/2022] Open
Abstract
Rapid ventricular pacing rates induces two types of beats following pacing cessation: recovery cycle length (RCL) prolongation (overdrive suppression) and RCL shortening (overdrive excitation). The goals of this study were to compare common experimental protocols for studying triggered activity in whole-heart preparations and differentiate between recovery beats using a new methodology. Post-pacing recovery beat cycle length (RCL) and QRS were normalized to pre-paced R-R and QRS intervals and analyzed using a K-means clustering algorithm. Control hearts only produced suppressed beats: RCL ratio increased with rapid pacing (25 ± 4.0%, n = 10) without changing QRS duration. Rapid pacing during hypercalcemia + hypothermia (5.5 mM and 34°C) produced significantly earlier excited beats (53 ± 14%, n = 5) with wider QRS durations (58 ± 6.3%, n = 5) than suppressed beats. Digoxin + hypothermia (0.75 μM) produced the most excited beats with significantly earlier RCL (44 ± 3.2%, n = 6) and wider QRS (60 ± 3.1%, n = 6) ratios relative to suppressed beats. Increasing pacing further shortened RCL (30 ± 7.8%, n = 6). In a prospective study, TTX (100 nM) increased RCL ratio (15 ± 6.0%, n = 10) without changing the QRS duration of excited beats. The algorithm was compared to a cross-correlation analysis with 93% sensitivity and 94% specificity. This ECG based algorithm distinguishes between triggered and automatic activity.
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Affiliation(s)
- Amara Greer-Short
- Department of Biomedical Engineering and Mechanics, Center for Heart and Regenerative Medicine, Virginia Polytechnic Institute and State University, Virginia Tech Carilion Research Institute Roanoke, VA, USA ; School of Biomedical Engineering and Sciences, Virginia Polytechnic Institute and State University Blacksburg, VA, USA
| | - Steven Poelzing
- Department of Biomedical Engineering and Mechanics, Center for Heart and Regenerative Medicine, Virginia Polytechnic Institute and State University, Virginia Tech Carilion Research Institute Roanoke, VA, USA ; School of Biomedical Engineering and Sciences, Virginia Polytechnic Institute and State University Blacksburg, VA, USA
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14
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Hammer KP, Hohendanner F, Blatter LA, Pieske BM, Heinzel FR. Variations in local calcium signaling in adjacent cardiac myocytes of the intact mouse heart detected with two-dimensional confocal microscopy. Front Physiol 2015; 5:517. [PMID: 25628569 PMCID: PMC4290493 DOI: 10.3389/fphys.2014.00517] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2014] [Accepted: 12/18/2014] [Indexed: 11/13/2022] Open
Abstract
Dyssynchronous local Ca release within individual cardiac myocytes has been linked to cellular contractile dysfunction. Differences in Ca kinetics in adjacent cells may also provide a substrate for inefficient contraction and arrhythmias. In a new approach we quantify variation in local Ca transients between adjacent myocytes in the whole heart. Langendorff-perfused mouse hearts were loaded with Fluo-8 AM to detect Ca and Di-4-ANEPPS to visualize cell membranes. A spinning disc confocal microscope with a fast camera allowed us to record Ca signals within an area of 465 μm by 315 μm with an acquisition speed of 55 fps. Images from multiple transients recorded at steady state were registered to their time point in the cardiac cycle to restore averaged local Ca transients with a higher temporal resolution. Local Ca transients within and between adjacent myocytes were compared with regard to amplitude, time to peak and decay at steady state stimulation (250 ms cycle length). Image registration from multiple sequential Ca transients allowed reconstruction of high temporal resolution (2.4 ± 1.3 ms) local CaT in 2D image sets (N = 4 hearts, n = 8 regions). During steady state stimulation, spatial Ca gradients were homogeneous within cells in both directions and independent of distance between measured points. Variation in CaT amplitudes was similar across the short and the long side of neighboring cells. Variations in TAU and TTP were similar in both directions. Isoproterenol enhanced the CaT but not the overall pattern of spatial heterogeneities. Here we detected and analyzed local Ca signals in intact mouse hearts with high temporal and spatial resolution, taking into account 2D arrangement of the cells. We observed significant differences in the variation of CaT amplitude along the long and short axis of cardiac myocytes. Variations of Ca signals between neighboring cells may contribute to the substrate of cardiac remodeling.
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Affiliation(s)
- Karin P Hammer
- Department of Cardiology, Medical University of Graz Graz, Austria ; Department of Internal Medicine II, University Hospital Regensburg Regensburg, Germany
| | - Felix Hohendanner
- Molecular Biophysics and Physiology, Rush Medical College, Rush University Chicago, IL, USA
| | - Lothar A Blatter
- Molecular Biophysics and Physiology, Rush Medical College, Rush University Chicago, IL, USA
| | - Burkert M Pieske
- Department of Cardiology, Medical University of Graz Graz, Austria ; Department of Cardiology, Charité-Universitaetsmedizin Berlin Berlin, Germany
| | - Frank R Heinzel
- Department of Cardiology, Medical University of Graz Graz, Austria ; Department of Cardiology, Charité-Universitaetsmedizin Berlin Berlin, Germany
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15
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Zamiri N, Massé S, Ramadeen A, Kusha M, Hu X, Azam MA, Liu J, Lai PFH, Vigmond EJ, Boyle PM, Behradfar E, Al-Hesayen A, Waxman MB, Backx P, Dorian P, Nanthakumar K. Dantrolene improves survival after ventricular fibrillation by mitigating impaired calcium handling in animal models. Circulation 2014; 129:875-85. [PMID: 24403563 DOI: 10.1161/circulationaha.113.005443] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Resistant ventricular fibrillation, refibrillation. and diminished myocardial contractility are important factors leading to poor survival after cardiac arrest. We hypothesized that dantrolene improves survival after ventricular fibrillation (VF) by rectifying the calcium dysregulation caused by VF. METHODS AND RESULTS VF was induced in 26 Yorkshire pigs for 4 minutes. Cardiopulmonary resuscitation was then commenced for 3 minutes, and dantrolene or isotonic saline was infused at the onset of cardiopulmonary resuscitation. Animals were defibrillated and observed for 30 minutes. To study the effect of VF on calcium handling and its modulation by dantrolene, hearts from 14 New Zealand rabbits were Langendorff-perfused. The inducibility of VF after dantrolene administration was documented. Optical mapping was performed to evaluate diastolic spontaneous calcium elevations as a measure of cytosolic calcium leak. The sustained return of spontaneous circulation (systolic blood pressure ≥60 mm Hg) was achieved in 85% of the dantrolene group in comparison with 39% of controls (P=0.02). return of spontaneous circulation was achieved earlier in dantrolene-treated pigs after successful defibrillation (21 ± 6 s versus 181 ± 57 s in controls, P=0.005). The median number of refibrillation episodes was lower in the dantrolene group (0 versus 1, P=0.04). In isolated rabbit hearts, the successful induction of VF was achieved in 83% of attempts in controls versus 41% in dantrolene-treated hearts (P=0.007). VF caused diastolic calcium leaks in the form of spontaneous calcium elevations. Administration of 20 μmol/L dantrolene significantly decreased spontaneous calcium elevation amplitude versus controls. (0.024 ± 0.013 versus 0.12 ± 0.02 arbitrary unit [200-ms cycle length], P=0.001). CONCLUSIONS Dantrolene infusion during cardiopulmonary resuscitation facilitates successful defibrillation, improves hemodynamics postdefibrillation, decreases refibrillation, and thus improves survival after cardiac arrest. The effects are mediated through normalizing VF-induced dysfunctional calcium cycling.
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Affiliation(s)
- Nima Zamiri
- From The Hull Family Cardiac Fibrillation Management Laboratory, University Health Network, University of Toronto, Toronto, ON, Canada (A.M., N.Z., S.M., M.K., M.A.A, P.F.H.L., M.B.W., K.N.); Keenan Research Centre, Li Ka Shing Knowledge Institute, St Michael's Hospital, Toronto, ON, Canada (A.R., X.H., A.A.-H., P.D.); Institute of Medical Science, University of Toronto, Toronto, ON, Canada (N.Z.); Department of Physiology, University of Toronto, Toronto, ON, Canada (J.L., P.B.); Institute LIRYC, Université Bordeaux 1, Bordeaux, France (E.J.V.); Institute for Computational Medicine, Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD (P.M.B.); and Department of Electrical Engineering, University of Calgary, Calgary, AB, Canada (E.B.)
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16
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Aberrant S-nitrosylation mediates calcium-triggered ventricular arrhythmia in the intact heart. Proc Natl Acad Sci U S A 2012; 109:18186-91. [PMID: 23071315 DOI: 10.1073/pnas.1210565109] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Nitric oxide (NO) derived from the activity of neuronal nitric oxide synthase (NOS1) is involved in S-nitrosylation of key sarcoplasmic reticulum (SR) Ca(2+) handling proteins. Deficient S-nitrosylation of the cardiac ryanodine receptor (RyR2) has a variable effect on SR Ca(2+) leak/sparks in isolated myocytes, likely dependent on the underlying physiological state. It remains unknown, however, whether such molecular aberrancies are causally related to arrhythmogenesis in the intact heart. Here we show in the intact heart, reduced NOS1 activity increased Ca(2+)-mediated ventricular arrhythmias only in the setting of elevated myocardial [Ca(2+)](i). These arrhythmias arose from increased spontaneous SR Ca(2+) release, resulting from a combination of decreased RyR2 S-nitrosylation (RyR2-SNO) and increased RyR2 oxidation (RyR-SOx) (i.e., increased reactive oxygen species (ROS) from xanthine oxidoreductase activity) and could be suppressed with xanthine oxidoreductase (XOR) inhibition (i.e., allopurinol) or nitric oxide donors (i.e., S-nitrosoglutathione, GSNO). Surprisingly, we found evidence of NOS1 down-regulation of RyR2 phosphorylation at the Ca(2+)/calmodulin-dependent protein kinase (CaMKII) site (S2814), suggesting molecular cross-talk between nitrosylation and phosphorylation of RyR2. Finally, we show that nitroso-redox imbalance due to decreased NOS1 activity sensitizes RyR2 to a severe arrhythmic phenotype by oxidative stress. Our findings suggest that nitroso-redox imbalance is an important mechanism of ventricular arrhythmias in the intact heart under disease conditions (i.e., elevated [Ca(2+)](i) and oxidative stress), and that therapies restoring nitroso-redox balance in the heart could prevent sudden arrhythmic death.
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17
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Cutler MJ, Wan X, Plummer BN, Liu H, Deschenes I, Laurita KR, Hajjar RJ, Rosenbaum DS. Targeted sarcoplasmic reticulum Ca2+ ATPase 2a gene delivery to restore electrical stability in the failing heart. Circulation 2012; 126:2095-104. [PMID: 23019291 DOI: 10.1161/circulationaha.111.071480] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
BACKGROUND Recently, we reported that sarcoplasmic reticulum Ca(2+) ATPase 2a (SERCA2a), the pump responsible for reuptake of cytosolic calcium during diastole, plays a central role in the molecular mechanism of cardiac alternans. Heart failure (HF) is associated with impaired myocardial calcium handling, deficient SERCA2a, and increased susceptibility to cardiac alternans. Therefore, we hypothesized that restoring deficient SERCA2a by gene transfer will significantly reduce arrhythmogenic cardiac alternans in the failing heart. METHODS AND RESULTS Adult guinea pigs were divided into 3 groups: control, HF, and HF+AAV9.SERCA2a gene transfer. HF resulted in a decrease in left ventricular fractional shortening compared with controls (P<0.001). As expected, isolated HF myocytes demonstrated slower sarcoplasmic reticulum calcium uptake, decreased Ca(2+) release, and increased diastolic Ca(2+) (P<0.05) compared with controls. Moreover, SERCA2a, cardiac ryanodine receptor 2, and sodium-calcium exchanger protein expression was decreased in HF compared with control (P<0.05). As predicted, HF increased susceptibility to cardiac alternans, as evidenced by decreased heart rate thresholds for both V(m) alternans and Ca alternans compared with controls (P<0.01). Interestingly, in vivo gene transfer of AAV9.SERCA2a in the failing heart improved left ventricular contractile function (P<0.01), suppressed cardiac alternans (P<0.01), and reduced ryanodine receptor 2 P(o) secondary to reduction of ryanodine receptor 2-P(S2814) (P<0.01). This ultimately resulted in a decreased incidence of inducible ventricular arrhythmias (P=0.05). CONCLUSIONS These data show that SERCA2a gene transfer in the failing heart not only improves contractile function but also directly restores electric stability through the amelioration of key arrhythmogenic substrate (ie, cardiac alternans) and triggers (ie, sarcoplasmic reticulum Ca(2+) leak).
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Affiliation(s)
- Michael J Cutler
- Heart and Vascular Center, MetroHealth Campus, Case Western Reserve University, 2500 MetroHealth Dr, Hamann 3, Cleveland, OH 44109-1998, USA.
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18
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Egorov YV, Glukhov AV, Efimov IR, Rosenshtraukh LV. Hypothermia-induced spatially discordant action potential duration alternans and arrhythmogenesis in nonhibernating versus hibernating mammals. Am J Physiol Heart Circ Physiol 2012; 303:H1035-46. [PMID: 22886418 DOI: 10.1152/ajpheart.00786.2011] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The heart of hibernating species is resistant to lethal ventricular fibrillation (VF) induced by hypothermia. Spatially discordant (SDA) cardiac alternans is a promising predictor of VF, yet its role in the mechanism of hypothermic arrhythmogenesis in both nonhibernating and hibernating mammals remains unclear. We optically mapped the posterior epicardial surface of Langendorff-perfused hearts of winter hibernating (WH, n = 13), interbout arousal (IBA; n = 4), and summer active (SA, n = 6) ground squirrels (GSs; Spermophilus undulatus) and rabbits (n = 10). Action potential duration (APD) and conduction velocity (CV) dynamic restitution and alternans were determined at 37 to 17°C. In all animals, hypothermia induced heterogeneous APD prolongation, enhanced APD dispersion, and slowed CV. In all groups, hypothermia promoted the formation of APD alternans, which was predominantly spatially concordant in GSs and SDA in rabbits (SD of APD dispersion: 4.2 ± 0.4% vs. 2.0 ± 0.3% at 37°C and 7.5 ± 1.1% vs. 3.4 ± 0.5% at 17°C, P < 0.001 for rabbits vs. the WH group, respectively). In rabbits, hypothermia significantly increased the magnitude of SDA, which enhanced the ventricular repolarization gradient, caused conduction delays (CV: 3.2 vs. 8.2 cm/s at 17°C in rabbits vs. the WH group), conduction block, and the onset of VF (0% at 37°C vs. 60% at 17°C, P < 0.01). In contrast, no arrhythmia was observed in GS hearts at any temperature. The amplitude of CV alternans was greater in rabbits (5.2 ± 0.4% versus 4.5 ± 0.3% at 37°C and 35.3 ± 4.2% vs. 14.9 ± 1.5% at 17°C in rabbits vs. the WH group, P < 0.001 at 17°C) and correlated with the amplitude of SDA. In conclusion, the mechanism underlying SDA formation during hypothermia is likely associated with CV alternans conditioned by an enhanced dispersion of repolarization. The factors of hibernating species resistance to SDA and VF seem to be the safe and dynamically stable conduction and the low dispersion of repolarization.
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Affiliation(s)
- Yuriy V Egorov
- Laboratory of Heart Electrophysiology, Cardiology Research Center, Moscow 121552, Russia
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19
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Tveito A, Lines GT, Edwards AG, Maleckar MM, Michailova A, Hake J, McCulloch A. Slow Calcium-Depolarization-Calcium waves may initiate fast local depolarization waves in ventricular tissue. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2012; 110:295-304. [PMID: 22841534 DOI: 10.1016/j.pbiomolbio.2012.07.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2012] [Accepted: 07/16/2012] [Indexed: 10/28/2022]
Abstract
Intercellular calcium waves in cardiac myocytes are a well-recognized, if incompletely understood, phenomenon. In a variety of preparations, investigators have reported multi-cellular calcium waves or triggered propagated contractions, but the mechanisms of propagation and pathological importance of these events remain unclear. Here, we review existing experimental data and present a computational approach to investigate the mechanisms of multi-cellular calcium wave propagation. Over the past 50 years, the standard modeling paradigm for excitable cardiac tissue has seen increasingly detailed models of the dynamics of individual cells coupled in tissue solely by intercellular and interstitial current flow. Although very successful, this modeling regime has been unable to capture two important phenomena: 1) the slow intercellular calcium waves observed experimentally, and 2) how intercellular calcium events resulting in delayed after depolarizations at the cellular level could overcome a source-sink mismatch to initiate depolarization waves in tissue. In this paper, we introduce a mathematical model with subcellular spatial resolution, in which we allow both inter- and intracellular current flow and calcium diffusion. In simulations of coupled cells employing this model, we observe: a) slow inter-cellular calcium waves propagating at about 0.1 mm/s, b) faster Calcium-Depolarization-Calcium (CDC) waves, traveling at about 1 mm/s, and c) CDC-waves that can set off fast depolarization-waves (50 cm/s) in tissue with varying gap-junction conductivity.
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Affiliation(s)
- Aslak Tveito
- Center for Biomedical Computing, Simula Research Laboratory, Norway
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20
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NHE-1 blockade reversed changes in calcium transient in myocardial slices from isoproterenol-induced hypertrophied rat left ventricle. Biochem Biophys Res Commun 2012; 419:431-5. [DOI: 10.1016/j.bbrc.2012.02.041] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2012] [Accepted: 02/07/2012] [Indexed: 11/24/2022]
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21
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Li N, Wang T, Wang W, Cutler MJ, Wang Q, Voigt N, Rosenbaum DS, Dobrev D, Wehrens XHT. Inhibition of CaMKII phosphorylation of RyR2 prevents induction of atrial fibrillation in FKBP12.6 knockout mice. Circ Res 2011; 110:465-70. [PMID: 22158709 DOI: 10.1161/circresaha.111.253229] [Citation(s) in RCA: 123] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
RATIONALE Abnormal calcium release from sarcoplasmic reticulum (SR) is considered an important trigger of atrial fibrillation (AF). Whereas increased Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) activity has been proposed to contribute to SR leak and AF induction, downstream targets of CaMKII remain controversial. OBJECTIVE To test the hypothesis that inhibition of CaMKII-phosphorylated type-2 ryanodine receptors (RyR2) prevents AF initiation in FKBP12.6-deficient (-/-) mice. METHODS AND RESULTS Mice lacking RyR2-stabilizing subunit FKBP12.6 had a higher incidence of spontaneous and pacing-induced AF compared with wild-type mice. Atrial myocytes from FKBP12.6-/- mice exhibited spontaneous Ca(2+) waves (SCaWs) leading to Na(+)/Ca(2+)-exchanger activation and delayed afterdepolarizations (DADs). Mutation S2814A in RyR2, which inhibits CaMKII phosphorylation, reduced Ca(2+) spark frequency, SR Ca(2+) leak, and DADs in atrial myocytes from FKBP12.6-/-:S2814A mice compared with FKBP12.6-/- mice. Moreover, FKBP12.6-/-:S2814A mice exhibited a reduced susceptibility to inducible AF, whereas FKBP12.6-/-:S2808A mice were not protected from AF. CONCLUSIONS FKBP12.6 mice exhibit AF caused by SR Ca(2+) leak, Na(+)/Ca(2+)-exchanger activation, and DADs, which promote triggered activity. Genetic inhibition of RyR2-S2814 phosphorylation prevents AF induction in FKBP12.6-/- mice by suppressing SR Ca(2+) leak and DADs. These results suggest suppression of RyR2-S2814 phosphorylation as a potential anti-AF therapeutic target.
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Affiliation(s)
- Na Li
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX 77030, USA
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