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Trus M, Atlas D. Non-ionotropic voltage-gated calcium channel signaling. Channels (Austin) 2024; 18:2341077. [PMID: 38601983 PMCID: PMC11017947 DOI: 10.1080/19336950.2024.2341077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2024] [Accepted: 04/04/2024] [Indexed: 04/12/2024] Open
Abstract
Voltage-gated calcium channels (VGCCs) are the major conduits for calcium ions (Ca2+) within excitable cells. Recent studies have highlighted the non-ionotropic functionality of VGCCs, revealing their capacity to activate intracellular pathways independently of ion flow. This non-ionotropic signaling mode plays a pivotal role in excitation-coupling processes, including gene transcription through excitation-transcription (ET), synaptic transmission via excitation-secretion (ES), and cardiac contraction through excitation-contraction (EC). However, it is noteworthy that these excitation-coupling processes require extracellular calcium (Ca2+) and Ca2+ occupancy of the channel ion pore. Analogous to the "non-canonical" characterization of the non-ionotropic signaling exhibited by the N-methyl-D-aspartate receptor (NMDA), which requires extracellular Ca2+ without the influx of ions, VGCC activation requires depolarization-triggered conformational change(s) concomitant with Ca2+ binding to the open channel. Here, we discuss the contributions of VGCCs to ES, ET, and EC coupling as Ca2+ binding macromolecules that transduces external stimuli to intracellular input prior to elevating intracellular Ca2+. We emphasize the recognition of calcium ion occupancy within the open ion-pore and its contribution to the excitation coupling processes that precede the influx of calcium. The non-ionotropic activation of VGCCs, triggered by the upstroke of an action potential, provides a conceptual framework to elucidate the mechanistic aspects underlying the microseconds nature of synaptic transmission, cardiac contractility, and the rapid induction of first-wave genes.
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Affiliation(s)
- Michael Trus
- Department of Biological Chemistry, Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Daphne Atlas
- Department of Biological Chemistry, Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
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Kong CHT, Cannell MB. Ca 2+ spark latency and control of intrinsic Ca 2+ release dyssynchrony in rat cardiac ventricular muscle cells. J Mol Cell Cardiol 2023; 182:44-53. [PMID: 37433391 DOI: 10.1016/j.yjmcc.2023.07.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/04/2023] [Revised: 06/12/2023] [Accepted: 07/06/2023] [Indexed: 07/13/2023]
Abstract
Cardiac excitation-contraction coupling (ECC) depends on Ca2+ release from intracellular stores via ryanodine receptors (RyRs) triggered by L-type Ca2+ channels (LCCs). Uncertain numbers of RyRs and LCCs form 'couplons' whose activation produces Ca2+ sparks, which summate to form a cell-wide Ca2+ transient that switches on contraction. Voltage (Vm) changes during the action potential (AP) and stochasticity in channel gating should create variability in Ca2+ spark timing, but Ca2+ transient wavefronts have remarkable uniformity. To examine how this is achieved, we measured the Vm-dependence of evoked Ca2+ spark probability (Pspark) and latency over a wide voltage range in rat ventricular cells. With depolarising steps, Ca2+ spark latency showed a U-shaped Vm-dependence, while repolarising steps from 50 mV produced Ca2+ spark latencies that increased monotonically with Vm. A computer model based on reported channel gating and geometry reproduced our experimental data and revealed a likely RyR:LCC stoichiometry of ∼ 5:1 for the Ca2+ spark initiating complex (IC). Using the experimental AP waveform, the model revealed a high coupling fidelity (Pcpl ∼ 0.5) between each LCC opening and IC activation. The presence of ∼ 4 ICs per couplon reduced Ca2+ spark latency and increased Pspark to match experimental data. Variability in AP release timing is less than that seen with voltage steps because the AP overshoot and later repolarization decrease Pspark due to effects on LCC flux and LCC deactivation respectively. This work provides a framework for explaining the Vm- and time-dependence of Pspark, and indicates how ion channel dispersion in disease can contribute to dyssynchrony in Ca2+ release.
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Affiliation(s)
- Cherrie H T Kong
- School of Physiology, Pharmacology and Neuroscience, Faculty of Biomedical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, United Kingdom.
| | - Mark B Cannell
- School of Physiology, Pharmacology and Neuroscience, Faculty of Biomedical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, United Kingdom.
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Hoang-Trong MT, Ullah A, Lederer WJ, Jafri MS. Cardiac Alternans Occurs through the Synergy of Voltage- and Calcium-Dependent Mechanisms. MEMBRANES 2021; 11:794. [PMID: 34677560 PMCID: PMC8539281 DOI: 10.3390/membranes11100794] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/03/2021] [Revised: 10/08/2021] [Accepted: 10/12/2021] [Indexed: 11/24/2022]
Abstract
Cardiac alternans is characterized by alternating weak and strong beats of the heart. This signaling at the cellular level may appear as alternating long and short action potentials (APs) that occur in synchrony with alternating large and small calcium transients, respectively. Previous studies have suggested that alternans manifests itself through either a voltage dependent mechanism based upon action potential restitution or as a calcium dependent mechanism based on refractoriness of calcium release. We use a novel model of cardiac excitation-contraction (EC) coupling in the rat ventricular myocyte that includes 20,000 calcium release units (CRU) each with 49 ryanodine receptors (RyR2s) and 7 L-type calcium channels that are all stochastically gated. The model suggests that at the cellular level in the case of alternans produced by rapid pacing, the mechanism requires a synergy of voltage- and calcium-dependent mechanisms. The rapid pacing reduces AP duration and magnitude reducing the number of L-type calcium channels activating individual CRUs during each AP and thus increases the population of CRUs that can be recruited stochastically. Elevated myoplasmic and sarcoplasmic reticulum (SR) calcium, [Ca2+]myo and [Ca2+]SR respectively, increases ryanodine receptor open probability (Po) according to our model used in this simulation and this increased the probability of activating additional CRUs. A CRU that opens in one beat is less likely to open the subsequent beat due to refractoriness caused by incomplete refilling of the junctional sarcoplasmic reticulum (jSR). Furthermore, the model includes estimates of changes in Na+ fluxes and [Na+]i and thus provides insight into how changes in electrical activity, [Na+]i and sodium-calcium exchanger activity can modulate alternans. The model thus tracks critical elements that can account for rate-dependent changes in [Na+]i and [Ca2+]myo and how they contribute to the generation of Ca2+ signaling alternans in the heart.
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Affiliation(s)
- Minh Tuan Hoang-Trong
- Krasnow Institute for Advanced Study and School of Systems Biology, George Mason University, Fairfax, VA 22030, USA; (M.T.H.-T.); (A.U.)
| | - Aman Ullah
- Krasnow Institute for Advanced Study and School of Systems Biology, George Mason University, Fairfax, VA 22030, USA; (M.T.H.-T.); (A.U.)
| | - William Jonathan Lederer
- Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, MD 21201, USA;
| | - Mohsin Saleet Jafri
- Krasnow Institute for Advanced Study and School of Systems Biology, George Mason University, Fairfax, VA 22030, USA; (M.T.H.-T.); (A.U.)
- Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, MD 21201, USA;
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Celestino-Montes A, Pérez-Treviño P, Sandoval-Herrera MD, Gómez-Víquez NL, Altamirano J. Relative role of T-tubules disruption and decreased SERCA2 on contractile dynamics of isolated rat ventricular myocytes. Life Sci 2021; 264:118700. [PMID: 33130073 DOI: 10.1016/j.lfs.2020.118700] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2020] [Revised: 10/25/2020] [Accepted: 10/28/2020] [Indexed: 10/23/2022]
Abstract
AIMS Ventricular myocytes (VM) depolarization activates L-type Ca2+ channels (LCC) allowing Ca2+ influx (ICa) to synchronize sarcoplasmic reticulum (SR) Ca2+ release, via Ca2+-release channels (RyR2). The resulting whole-cell Ca2+ transient triggers contraction, while cytosolic Ca2+ removal by SR Ca2+ pump (SERCA2) and sarcolemmal Na+/Ca2+ exchanger (NCX) allows relaxation. In diseased hearts, extensive VM remodeling causes heterogeneous, blunted and slow Ca2+ transients. Among remodeling changes are: A) T-tubules disorganization. B) Diminished SERCA2 and low SR Ca2+. However, those often overlap, hindering their relative contribution to contractile dysfunction (CD). Furthermore, few studies have assessed their specific impact on the spatiotemporal Ca2+ transient properties and contractile dynamics simultaneously. Therefore, we sought to perform a quantitative comparison of how heterogeneous and slow Ca2+ transients, with different underlying determinants, affect contractile performance. METHODS We used two experimental models: A) formamide-induced acute "detubulation", where VM retain functional RyR2 and SERCA2, but lack T-tubules-associated LCC and NCX. B) Intact VM from hypothyroid rats, presenting decreased SERCA2 and SR Ca2+, but maintained T-tubules. By confocal imaging of Fluo-4-loaded VM, under field-stimulation, simultaneously acquired Ca2+ transients and shortening, allowing direct correlations. KEY FINDINGS We found near-linear correlations among key parameters of altered Ca2+ transients, caused independently by T-tubules disruption or decreased SR Ca2+, and shortening and relaxation, SIGNIFICANCE: Unrelated structural and molecular alterations converge in similarly abnormal Ca2+ transients and CD, highlighting the importance of independently reproduce disease-specific alterations, to quantitatively assess their impact on Ca2+ signaling and contractility, which would be valuable to determine potential disease-specific therapeutic targets.
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Affiliation(s)
- Antonio Celestino-Montes
- Tecnologico de Monterrey, Escuela de Medicina y Ciencias de la Salud, Av. Morones Prieto No. 3000 Pte., Monterrey, N.L. 64710, Mexico
| | - Perla Pérez-Treviño
- Tecnologico de Monterrey, Escuela de Medicina y Ciencias de la Salud, Av. Morones Prieto No. 3000 Pte., Monterrey, N.L. 64710, Mexico
| | - Maya D Sandoval-Herrera
- Tecnologico de Monterrey, Escuela de Medicina y Ciencias de la Salud, Av. Morones Prieto No. 3000 Pte., Monterrey, N.L. 64710, Mexico
| | - Norma L Gómez-Víquez
- Departamento de Farmacobiologia, CINVESTAV-IPN sede Sur, Mexico, D.F. 14330, Mexico
| | - Julio Altamirano
- Tecnologico de Monterrey, Escuela de Medicina y Ciencias de la Salud, Av. Morones Prieto No. 3000 Pte., Monterrey, N.L. 64710, Mexico.
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Yang HQ, Zhou P, Wang LP, Zhao YT, Ren YJ, Guo YB, Xu M, Wang SQ. Compartmentalized β1-adrenergic signalling synchronizes excitation-contraction coupling without modulating individual Ca2+ sparks in healthy and hypertrophied cardiomyocytes. Cardiovasc Res 2020; 116:2069-2080. [PMID: 32031586 DOI: 10.1093/cvr/cvaa013] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/18/2019] [Revised: 11/20/2019] [Accepted: 01/30/2020] [Indexed: 12/21/2022] Open
Abstract
AIMS β-adrenergic receptors (βARs) play pivotal roles in regulating cardiac excitation-contraction (E-C) coupling. Global signalling of β1ARs up-regulates both the influx of Ca2+ through sarcolemmal L-type Ca2+ channels (LCCs) and the release of Ca2+ from the sarcoplasmic reticulum (SR) through the ryanodine receptors (RyRs). However, we recently found that β2AR stimulation meditates 'offside compartmentalization', confining β1AR signalling into subsarcolemmal nanodomains without reaching SR proteins. In the present study, we aim to investigate the new question, whether and how compartmentalized β1AR signalling regulates cardiac E-C coupling. METHODS AND RESULTS By combining confocal Ca2+ imaging and patch-clamp techniques, we investigated the effects of compartmentalized βAR signalling on E-C coupling at both cellular and molecular levels. We found that simultaneous activation of β2 and β1ARs, in contrast to global signalling of β1ARs, modulated neither the amplitude and spatiotemporal properties of Ca2+ sparks nor the kinetics of the RyR response to LCC Ca2+ sparklets. Nevertheless, by up-regulating LCC current, compartmentalized β1AR signalling synchronized RyR Ca2+ release and increased the functional reserve (stability margin) of E-C coupling. In circumstances of briefer excitation durations or lower RyR responsivity, compartmentalized βAR signalling, by increasing the intensity of Ca2+ triggers, helped stabilize the performance of E-C coupling and enhanced the Ca2+ transient amplitude in failing heart cells. CONCLUSION Given that compartmentalized βAR signalling can be induced by stress-associated levels of catecholamines, our results revealed an important, yet unappreciated, heart regulation mechanism that is autoadaptive to varied stress conditions.
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Affiliation(s)
- Hua-Qian Yang
- State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, 5 Yiheyuan Rd, Beijing 100871, China
| | - Peng Zhou
- State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, 5 Yiheyuan Rd, Beijing 100871, China
| | - Li-Peng Wang
- State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, 5 Yiheyuan Rd, Beijing 100871, China
| | - Yan-Ting Zhao
- State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, 5 Yiheyuan Rd, Beijing 100871, China
| | - Yu-Jie Ren
- State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, 5 Yiheyuan Rd, Beijing 100871, China
| | - Yun-Bo Guo
- State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, 5 Yiheyuan Rd, Beijing 100871, China
| | - Ming Xu
- State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, 5 Yiheyuan Rd, Beijing 100871, China
| | - Shi-Qiang Wang
- State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, 5 Yiheyuan Rd, Beijing 100871, China
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Zhang XH, Morad M. Ca 2+ signaling of human pluripotent stem cells-derived cardiomyocytes as compared to adult mammalian cardiomyocytes. Cell Calcium 2020; 90:102244. [PMID: 32585508 PMCID: PMC7483365 DOI: 10.1016/j.ceca.2020.102244] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2020] [Revised: 06/10/2020] [Accepted: 06/11/2020] [Indexed: 12/23/2022]
Abstract
Human induced pluripotent stem cells derived cardiomyocytes (hiPSC-CMs) have been extensively used for in vitro modeling of human cardiovascular disease, drug screening and pharmacotherapy, but little rigorous studies have been reported on their biophysical or Ca2+ signaling properties. There is also considerable concern as to the level of their maturity and whether they can serve as reliable models for adult human cardiac myocytes. Ultrastructural difference such as lack of t-tubular network, their polygonal shapes, disorganized sarcomeric myofilament, and their rhythmic automaticity, among others, have been cited as evidence for immaturity of hiPSC-CMs. In this review, we will deal with Ca2+ signaling, its regulation, and its stage of maturity as compared to the mammalian adult cardiomyocytes. We shall summarize the data on functional aspects of Ca2+signaling and its parameters that include: L-type calcium channel (Cav1.2), ICa-induced Ca2+release, CICR, and its parameters, cardiac Na/Ca exchanger (NCX1), the ryanodine receptors (RyR2), sarco-reticular Ca2+pump, SERCA2a/PLB, and the contribution of mitochondrial Ca2+ to hiPSC-CMs excitation-contraction (EC)-coupling as compared with adult mammalian cardiomyocytes. The comparative studies suggest that qualitatively hiPSC-CMs have similar Ca2+signaling properties as those of adult cardiomyocytes, but quantitative differences do exist. This review, we hope, will allow the readers to judge for themselves to what extent Ca2+signaling of hiPSC-CMs represents the adult form of this signaling pathway, and whether these cells can be used as good models of human cardiomyocytes.
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Affiliation(s)
- Xiao-Hua Zhang
- Cardiac Signaling Center of University of South Carolina, Medical University of South Carolina, Clemson University, Charleston SC, United States
| | - Martin Morad
- Cardiac Signaling Center of University of South Carolina, Medical University of South Carolina, Clemson University, Charleston SC, United States.
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7
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Shen CP, Romero M, Brunelle A, Wolfe C, Dobyns A, Francis M, Taylor MS, Puglisi JL, Longo LD, Zhang L, Wilson CG, Wilson SM. Long-term high-altitude hypoxia influences pulmonary arterial L-type calcium channel-mediated Ca 2+ signals and contraction in fetal and adult sheep. Am J Physiol Regul Integr Comp Physiol 2017; 314:R433-R446. [PMID: 29167165 DOI: 10.1152/ajpregu.00154.2017] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Long-term hypoxia (LTH) has a profound effect on pulmonary arterial vasoconstriction in the fetus and adult. Dysregulation in Ca2+ signaling is important during the development of LTH-induced pulmonary hypertension. In the present study, we tested the hypothesis that L-type Ca2+ channels (CaL), which are voltage dependent and found in smooth, skeletal, and cardiac muscle, are important in the adaptation of pulmonary arterial contractions in postnatal maturation and in response to LTH. Pulmonary arteries were isolated from fetal or adult sheep maintained at low or high altitude (3,801 m) for >100 days. The effects were measured using an L-type Ca2+ channel opener FPL 64176 (FPL) in the presence or absence of an inhibitor, Nifedipine (NIF) on arterial contractions, intracellular Ca2+ oscillations, and ryanodine receptor-driven Ca2+ sparks. FPL induced pulmonary arterial contractions in all groups were sensitive to NIF. However, when compared with 125 mM K+, FPL contractions were greater in fetuses than in adults. FPL reduced Ca2+ oscillations in myocytes of adult but not fetal arteries, independently of altitude. The FPL effects on Ca2+ oscillations were reversed by NIF in myocytes of hypoxic but not normoxic adults. FPL failed to enhance Ca2+ spark frequency and had little impact on spatiotemporal firing characteristics. These data suggest that CaL-dependent contractions are largely uncoupled from intracellular Ca2+ oscillations and the development of Ca2+ sparks. This raises questions regarding the coupling of pulmonary arterial contractility to membrane depolarization, attendant CaL facilitation, and the related associations with the activation of Ca2+ oscillations and Ca2+ sparks.
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Affiliation(s)
- Christine P Shen
- Lawrence D. Longo, MD Center for Perinatal Biology, Loma Linda University School of Medicine , Loma Linda, California
| | - Monica Romero
- Advanced Imaging and Microscopy Core, Loma Linda University School of Medicine , Loma Linda, California
| | - Alexander Brunelle
- Lawrence D. Longo, MD Center for Perinatal Biology, Loma Linda University School of Medicine , Loma Linda, California
| | - Craig Wolfe
- Lawrence D. Longo, MD Center for Perinatal Biology, Loma Linda University School of Medicine , Loma Linda, California
| | - Abigail Dobyns
- Lawrence D. Longo, MD Center for Perinatal Biology, Loma Linda University School of Medicine , Loma Linda, California
| | - Michael Francis
- Department of Physiology, University of South Alabama College of Medicine , Mobile, Alabama
| | - Mark S Taylor
- Department of Physiology, University of South Alabama College of Medicine , Mobile, Alabama
| | - Jose L Puglisi
- Department of Biostatistics, California Northstate University School of Medicine , Elk Grove, California
| | - Lawrence D Longo
- Lawrence D. Longo, MD Center for Perinatal Biology, Loma Linda University School of Medicine , Loma Linda, California
| | - Lubo Zhang
- Lawrence D. Longo, MD Center for Perinatal Biology, Loma Linda University School of Medicine , Loma Linda, California
| | - Christopher G Wilson
- Lawrence D. Longo, MD Center for Perinatal Biology, Loma Linda University School of Medicine , Loma Linda, California
| | - Sean M Wilson
- Lawrence D. Longo, MD Center for Perinatal Biology, Loma Linda University School of Medicine , Loma Linda, California
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8
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Vierheller J, Neubert W, Falcke M, Gilbert SH, Chamakuri N. A multiscale computational model of spatially resolved calcium cycling in cardiac myocytes: from detailed cleft dynamics to the whole cell concentration profiles. Front Physiol 2015; 6:255. [PMID: 26441674 PMCID: PMC4585174 DOI: 10.3389/fphys.2015.00255] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2015] [Accepted: 09/01/2015] [Indexed: 11/13/2022] Open
Abstract
Mathematical modeling of excitation-contraction coupling (ECC) in ventricular cardiac myocytes is a multiscale problem, and it is therefore difficult to develop spatially detailed simulation tools. ECC involves gradients on the length scale of 100 nm in dyadic spaces and concentration profiles along the 100 μm of the whole cell, as well as the sub-millisecond time scale of local concentration changes and the change of lumenal Ca2+ content within tens of seconds. Our concept for a multiscale mathematical model of Ca2+ -induced Ca2+ release (CICR) and whole cardiomyocyte electrophysiology incorporates stochastic simulation of individual LC- and RyR-channels, spatially detailed concentration dynamics in dyadic clefts, rabbit membrane potential dynamics, and a system of partial differential equations for myoplasmic and lumenal free Ca2+ and Ca2+-binding molecules in the bulk of the cell. We developed a novel computational approach to resolve the concentration gradients from dyadic space to cell level by using a quasistatic approximation within the dyad and finite element methods for integrating the partial differential equations. We show whole cell Ca2+-concentration profiles using three previously published RyR-channel Markov schemes.
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Affiliation(s)
- Janine Vierheller
- Mathematical Cell Physiology, Max Delbrück Center for Molecular Medicine Berlin, Germany
| | - Wilhelm Neubert
- Mathematical Cell Physiology, Max Delbrück Center for Molecular Medicine Berlin, Germany
| | - Martin Falcke
- Mathematical Cell Physiology, Max Delbrück Center for Molecular Medicine Berlin, Germany
| | - Stephen H Gilbert
- Mathematical Cell Physiology, Max Delbrück Center for Molecular Medicine Berlin, Germany
| | - Nagaiah Chamakuri
- Johann Radon Institute for Computational and Applied Mathematics (RICAM), Austrian Academy of Sciences Linz, Austria
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9
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Bito V, Macquaide N, Sipido KR. Characterizing the trigger for sarcoplasmic reticulum Ca2+ release in cardiac myocytes. Cold Spring Harb Protoc 2015; 2015:398-402. [PMID: 25834258 DOI: 10.1101/pdb.prot076968] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Here, we describe a method for characterizing the L-type Ca(2+) current, ICaL, which is a major trigger for Ca(2+) release from the sarcoplasmic reticulum (SR). The protocol includes measuring ICaL amplitude and voltage dependence and the elicited SR Ca(2+) release. The procedure for measuring ICaL activity is performed using solutions (internal and external) and voltage control such that other ionic currents are eliminated. The resultant relationship between the Ca(2+) current and the associated internal [Ca(2+)]i transient is a first approach for evaluating coupling gain. We discuss which parameters are most appropriate for this analysis and how an evaluation of gain needs to be further explored by measuring the SR Ca(2+) content.
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Affiliation(s)
- Virginie Bito
- Division of Experimental Cardiology, Department of Cardiovascular Sciences, KU Leuven, Belgium
| | - Niall Macquaide
- Division of Experimental Cardiology, Department of Cardiovascular Sciences, KU Leuven, Belgium
| | - Karin R Sipido
- Division of Experimental Cardiology, Department of Cardiovascular Sciences, KU Leuven, Belgium
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10
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Edwards JN, Blatter LA. Cardiac alternans and intracellular calcium cycling. Clin Exp Pharmacol Physiol 2015; 41:524-32. [PMID: 25040398 DOI: 10.1111/1440-1681.12231] [Citation(s) in RCA: 66] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2013] [Revised: 03/12/2014] [Accepted: 03/17/2014] [Indexed: 12/20/2022]
Abstract
Cardiac alternans refers to a condition in which there is a periodic beat-to-beat oscillation in electrical activity and the strength of cardiac muscle contraction at a constant heart rate. Clinically, cardiac alternans occurs in settings that are typical for cardiac arrhythmias and has been causally linked to these conditions. At the cellular level, alternans is defined as beat-to-beat alternations in contraction amplitude (mechanical alternans), action potential duration (APD; electrical or APD alternans) and Ca(2+) transient amplitude (Ca(2+) alternans). The cause of alternans is multifactorial; however, alternans always originate from disturbances of the bidirectional coupling between membrane voltage (Vm ) and intracellular calcium ([Ca(2+) ]i ). Bidirectional coupling refers to the fact that, in cardiac cells, Vm depolarization and the generation of action potentials cause the elevation of [Ca(2+) ]i that is required for contraction (a process referred to as excitation-contraction coupling); conversely, changes of [Ca(2+) ]i control Vm because important membrane currents are Ca(2+) dependent. Evidence is mounting that alternans is ultimately caused by disturbances of cellular Ca(2+) signalling. Herein we review how two key factors of cardiac cellular Ca(2+) cycling, namely the release of Ca(2+) from internal stores and the capability of clearing the cytosol from Ca(2+) after each beat, determine the conditions under which alternans occurs. The contributions from key Ca(2+) -handling proteins (i.e. surface membrane channels, ion pumps and transporters and internal Ca(2+) release channels) are discussed.
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Affiliation(s)
- Joshua N Edwards
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, IL, USA
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11
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High-mobility group box 1 (HMGB1) impaired cardiac excitation–contraction coupling by enhancing the sarcoplasmic reticulum (SR) Ca2+ leak through TLR4–ROS signaling in cardiomyocytes. J Mol Cell Cardiol 2014; 74:260-73. [DOI: 10.1016/j.yjmcc.2014.06.003] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/25/2014] [Revised: 05/04/2014] [Accepted: 06/08/2014] [Indexed: 10/25/2022]
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12
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Janicek R, Hotka M, Zahradníková A, Zahradníková A, Zahradník I. Quantitative analysis of calcium spikes in noisy fluorescent background. PLoS One 2013; 8:e64394. [PMID: 23741324 PMCID: PMC3669300 DOI: 10.1371/journal.pone.0064394] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2013] [Accepted: 04/12/2013] [Indexed: 12/25/2022] Open
Abstract
Intracellular calcium signals are studied by laser-scanning confocal fluorescence microscopy. The required spatio-temporal resolution makes description of calcium signals difficult because of the low signal-to-noise ratio. We designed a new procedure of calcium spike analysis based on their fitting with a model. The accuracy and precision of calcium spike description were tested on synthetic datasets generated either with randomly varied spike parameters and Gaussian noise of constant amplitude, or with constant spike parameters and Gaussian noise of various amplitudes. Statistical analysis was used to evaluate the performance of spike fitting algorithms. The procedure was optimized for reliable estimation of calcium spike parameters and for dismissal of false events. A new algorithm was introduced that corrects the acquisition time of pixels in line-scan images that is in error due to sequential acquisition of individual pixels along the space coordinate. New software was developed in Matlab and provided for general use. It allows interactive dissection of temporal profiles of calcium spikes from x-t images, their fitting with predefined function(s) and acceptance of results on statistical grounds, thus allowing efficient analysis and reliable description of calcium signaling in cardiac myocytes down to the in situ function of ryanodine receptors.
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Affiliation(s)
- Radoslav Janicek
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Matej Hotka
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Bratislava, Slovakia
- Department of Biophysics, Faculty of Natural Sciences, Pavol Jozef Šafárik University, Košice, Slovakia
| | - Alexandra Zahradníková
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Alexandra Zahradníková
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Ivan Zahradník
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Bratislava, Slovakia
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Zhang XH, Haviland S, Wei H, Sarić T, Fatima A, Hescheler J, Cleemann L, Morad M. Ca2+ signaling in human induced pluripotent stem cell-derived cardiomyocytes (iPS-CM) from normal and catecholaminergic polymorphic ventricular tachycardia (CPVT)-afflicted subjects. Cell Calcium 2013; 54:57-70. [PMID: 23684427 DOI: 10.1016/j.ceca.2013.04.004] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2013] [Revised: 04/10/2013] [Accepted: 04/12/2013] [Indexed: 12/16/2022]
Abstract
Derivation of cardiomyocytes from induced pluripotent stem cells (iPS-CMs) allowed us to probe the Ca(2+)-signaling parameters of human iPS-CMs from healthy- and catecholaminergic polymorphic ventricular tachycardia (CPVT1)-afflicted individuals carrying a novel point mutation p.F2483I in ryanodine receptors (RyR2). iPS-CMs were dissociated on day 30-40 of differentiation and patch-clamped within 3-6 days. Calcium currents (ICa) averaged ∼8pA/pF in control and mutant iPS-CMs. ICa-induced Ca(2+)-transients in control and mutant cells had bell-shaped voltage-dependence similar to that of ICa, consistent with Ca(2+)-induced Ca(2+)-release (CICR) mechanism. The ratio of ICa-activated to caffeine-triggered Ca(2+)-transients was ∼0.3 in both cell types. Caffeine-induced Ca(2+)-transients generated significantly smaller Na(+)-Ca(2+) exchanger current (INCX) in mutant cells, reflecting their smaller Ca(2+)-stores. The gain of CICR was voltage-dependent as in adult cardiomyocytes. Adrenergic agonists enhanced ICa, but differentially altered the CICR gain, diastolic Ca(2+), and Ca(2+)-sparks in mutant cells. The mutant cells, when Ca(2+)-overloaded, showed longer and wandering Ca(2+)-sparks that activated adjoining release sites, had larger CICR gain at -30mV yet smaller Ca(2+)-stores. We conclude that control and mutant iPS-CMs express the adult cardiomyocyte Ca(2+)-signaling phenotype. RyR2 F2483I mutant myocytes have aberrant unitary Ca(2+)-signaling, smaller Ca(2+)-stores, higher CICR gains, and sensitized adrenergic regulation, consistent with functionally altered Ca(2+)-release profile of CPVT syndrome.
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Affiliation(s)
- X-H Zhang
- Cardiac Signaling Center of USC, MUSC, & Clemson University, Charleston, SC 29403, USA
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14
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Lu X, Ginsburg KS, Kettlewell S, Bossuyt J, Smith GL, Bers DM. Measuring local gradients of intramitochondrial [Ca(2+)] in cardiac myocytes during sarcoplasmic reticulum Ca(2+) release. Circ Res 2012; 112:424-31. [PMID: 23243207 DOI: 10.1161/circresaha.111.300501] [Citation(s) in RCA: 99] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
RATIONALE Mitochondrial [Ca(2+)] ([Ca(2+)](mito)) regulates mitochondrial energy production, provides transient Ca(2+) buffering under stress, and can be involved in cell death. Mitochondria are near the sarcoplasmic reticulum (SR) in cardiac myocytes, and evidence for crosstalk exists. However, quantitative measurements of [Ca(2+)](mito) are limited, and spatial [Ca(2+)](mito) gradients have not been directly measured. OBJECTIVE To directly measure local [Ca(2+)](mito) during normal SR Ca release in intact myocytes, and evaluate potential subsarcomeric spatial [Ca(2+)](mito) gradients. METHODS AND RESULTS Using the mitochondrially targeted inverse pericam indicator Mitycam, calibrated in situ, we directly measured [Ca(2+)](mito) during SR Ca(2+) release in intact rabbit ventricular myocytes by confocal microscopy. During steady state pacing, Δ[Ca(2+)](mito) amplitude was 29±3 nmol/L, rising rapidly (similar to cytosolic free [Ca(2+)]) but declining much more slowly. Taking advantage of the structural periodicity of cardiac sarcomeres, we found that [Ca(2+)](mito) near SR Ca(2+) release sites (Z-line) versus mid-sarcomere (M-line) reached a high peak amplitude (37±4 versus 26±4 nmol/L, respectively P<0.05) which occurred earlier in time. This difference was attributed to ends of mitochondria being physically closer to SR Ca(2+) release sites, because the mitochondrial Ca(2+) uniporter was homogeneously distributed, and elevated [Ca(2+)] applied laterally did not produce longitudinal [Ca(2+)](mito) gradients. CONCLUSIONS We developed methods to measure spatiotemporal [Ca(2+)](mito) gradients quantitatively during excitation-contraction coupling. The amplitude and kinetics of [Ca(2+)](mito) transients differ significantly from those in the cytosol and are respectively higher and faster near the Z-line versus M-line. This approach will help clarify SR-mitochondrial Ca(2+) signaling.
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Affiliation(s)
- Xiyuan Lu
- Department of Pharmacology, University of California, Davis, CA 95616, USA
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15
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Deng J, Liu W, Wang Y, Dong M, Zheng M, Liu J. Polydatin modulates Ca2+ handling, excitation–contraction coupling and β-adrenergic signaling in rat ventricular myocytes. J Mol Cell Cardiol 2012; 53:646-56. [DOI: 10.1016/j.yjmcc.2012.08.009] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/23/2012] [Revised: 07/31/2012] [Accepted: 08/10/2012] [Indexed: 11/30/2022]
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16
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Chen L, Xu Y, Li W, Wu H, Luo Z, Li X, Huang F, Young C, Liu Z, Zhou S. The novel compound liguzinediol exerts positive inotropic effects in isolated rat heart via sarcoplasmic reticulum Ca2+ ATPase-dependent mechanism. Life Sci 2012; 91:402-408. [PMID: 22906633 DOI: 10.1016/j.lfs.2012.08.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2012] [Revised: 06/27/2012] [Accepted: 08/02/2012] [Indexed: 11/15/2022]
Abstract
AIMS The present work investigated the underlying mechanism for the positive inotropic effect of liguzinediol (LZDO) in isolated rat hearts. MAIN METHODS Isolated rat heart perfusion, intracellular action potential recording, patch clamp and Ca2+ imaging were used to measure the isolated rat heart contractility, action potential duration, L-type Ca2+ current and sarcoplasmic reticulum (SR) Ca2+ transient in rat cardiomyocyte, respectively. KEY FINDINGS LZDO (1, 10, and 100μM) significantly enhanced the inotropy of isolated rat hearts, but not heart rates. Nimodipine (1μM, an L-type Ca2+ channel antagonist), ruthenium red (5μM, a ryanodine receptor inhibitor) and thapsigargin (2μM, an irreversible SR Ca2+ ATPase inhibitor) completely blocked the positive inotropic effect of LZDO. LZDO significantly enhanced the intracellular Ca2+ transient in rat cardiomyocyte. However, LZDO (100μM) did not increase L-type Ca2+ channel current. Moreover, LZDO (100μM) restored the depletion effect of caffeine on Ca2+ transient. The following compounds also failed to block the positive inotropic effect of LZDO (100μM): β-AR antagonist (propranolol 1μM), phosphodiesterase (PDE) inhibitor (IBMX 5μM), Na+-K+ ATPase inhibitor (ouabain 1μM), α(1)-AR antagonist (prazosin 1μM), dopamine D1 receptor antagonist (SCH23390 1μM) and Na+-Ca2+ exchange inhibitor (KB-R7943 1μM). SIGNIFICANCE The positive inotropic effect of LZDO in isolated rat hearts was mediated through an elevation of SR Ca2+ transient, which may act on SR Ca2+ ATPase. LZDO has a unique biological mechanism that may prove effective in treating heart failure in clinic.
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Affiliation(s)
- Long Chen
- National Standard Laboratory of Pharmacology for Chinese Materia Medica, Department of Pharmacology, School of Pharmacy, Nanjing University of Chinese Medicine, Nanjing 210046, China; Institute of Chinese Medicine of Taizhou China Medical City, Taizhou 225300, China.
| | - Yi Xu
- National Standard Laboratory of Pharmacology for Chinese Materia Medica, Department of Pharmacology, School of Pharmacy, Nanjing University of Chinese Medicine, Nanjing 210046, China
| | - Wei Li
- Department of Chemistry and Processing for Chinese Materia Medica, School of Pharmacy, Nanjing University of Chinese Medicine, Nanjing 210046, China.
| | - Hao Wu
- Department of Chemistry and Processing for Chinese Materia Medica, School of Pharmacy, Nanjing University of Chinese Medicine, Nanjing 210046, China
| | - Zhuoka Luo
- National Standard Laboratory of Pharmacology for Chinese Materia Medica, Department of Pharmacology, School of Pharmacy, Nanjing University of Chinese Medicine, Nanjing 210046, China
| | - Xuehua Li
- National Standard Laboratory of Pharmacology for Chinese Materia Medica, Department of Pharmacology, School of Pharmacy, Nanjing University of Chinese Medicine, Nanjing 210046, China
| | - Feifei Huang
- National Standard Laboratory of Pharmacology for Chinese Materia Medica, Department of Pharmacology, School of Pharmacy, Nanjing University of Chinese Medicine, Nanjing 210046, China
| | - Clint Young
- Xenon Pharmaceuticals Inc., 3650 Gilmore Way, Burnaby, Canada BC V5G4W8
| | - Zheng Liu
- Department of Chemistry and Processing for Chinese Materia Medica, School of Pharmacy, Nanjing University of Chinese Medicine, Nanjing 210046, China
| | - Shuyuan Zhou
- Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing, 10070, China
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17
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Kekenes-Huskey PM, Cheng Y, Hake JE, Sachse FB, Bridge JH, Holst MJ, McCammon JA, McCulloch AD, Michailova AP. Modeling effects of L-type ca(2+) current and na(+)-ca(2+) exchanger on ca(2+) trigger flux in rabbit myocytes with realistic T-tubule geometries. Front Physiol 2012; 3:351. [PMID: 23060801 PMCID: PMC3463892 DOI: 10.3389/fphys.2012.00351] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2012] [Accepted: 08/16/2012] [Indexed: 12/26/2022] Open
Abstract
The transverse tubular system of rabbit ventricular myocytes consists of cell membrane invaginations (t-tubules) that are essential for efficient cardiac excitation-contraction coupling. In this study, we investigate how t-tubule micro-anatomy, L-type Ca2+ channel (LCC) clustering, and allosteric activation of Na+/Ca2+ exchanger by L-type Ca2+ current affects intracellular Ca2+ dynamics. Our model includes a realistic 3D geometry of a single t-tubule and its surrounding half-sarcomeres for rabbit ventricular myocytes. The effects of spatially distributed membrane ion-transporters (LCC, Na+/Ca2+ exchanger, sarcolemmal Ca2+ pump, and sarcolemmal Ca2+ leak), and stationary and mobile Ca2+ buffers (troponin C, ATP, calmodulin, and Fluo-3) are also considered. We used a coupled reaction-diffusion system to describe the spatio-temporal concentration profiles of free and buffered intracellular Ca2+. We obtained parameters from voltage-clamp protocols of L-type Ca2+ current and line-scan recordings of Ca2+ concentration profiles in rabbit cells, in which the sarcoplasmic reticulum is disabled. Our model results agree with experimental measurements of global Ca2+ transient in myocytes loaded with 50 μM Fluo-3. We found that local Ca2+ concentrations within the cytosol and sub-sarcolemma, as well as the local trigger fluxes of Ca2+ crossing the cell membrane, are sensitive to details of t-tubule micro-structure and membrane Ca2+ flux distribution. The model additionally predicts that local Ca2+ trigger fluxes are at least threefold to eightfold higher than the whole-cell Ca2+ trigger flux. We found also that the activation of allosteric Ca2+-binding sites on the Na+/Ca2+ exchanger could provide a mechanism for regulating global and local Ca2+ trigger fluxes in vivo. Our studies indicate that improved structural and functional models could improve our understanding of the contributions of L-type and Na+/Ca2+ exchanger fluxes to intracellular Ca2+ dynamics.
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18
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Blaich A, Pahlavan S, Tian Q, Oberhofer M, Poomvanicha M, Lenhardt P, Domes K, Wegener JW, Moosmang S, Ruppenthal S, Scholz A, Lipp P, Hofmann F. Mutation of the calmodulin binding motif IQ of the L-type Ca(v)1.2 Ca2+ channel to EQ induces dilated cardiomyopathy and death. J Biol Chem 2012; 287:22616-25. [PMID: 22589547 DOI: 10.1074/jbc.m112.357921] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cardiac excitation-contraction coupling (EC coupling) links the electrical excitation of the cell membrane to the mechanical contractile machinery of the heart. Calcium channels are major players of EC coupling and are regulated by voltage and Ca(2+)/calmodulin (CaM). CaM binds to the IQ motif located in the C terminus of the Ca(v)1.2 channel and induces Ca(2+)-dependent inactivation (CDI) and facilitation (CDF). Mutation of Ile to Glu (Ile1624Glu) in the IQ motif abolished regulation of the channel by CDI and CDF. Here, we addressed the physiological consequences of such a mutation in the heart. Murine hearts expressing the Ca(v)1.2(I1624E) mutation were generated in adult heterozygous mice through inactivation of the floxed WT Ca(v)1.2(L2) allele by tamoxifen-induced cardiac-specific activation of the MerCreMer Cre recombinase. Within 10 days after the first tamoxifen injection these mice developed dilated cardiomyopathy (DCM) accompanied by apoptosis of cardiac myocytes (CM) and fibrosis. In Ca(v)1.2(I1624E) hearts, the activity of phospho-CaM kinase II and phospho-MAPK was increased. CMs expressed reduced levels of Ca(v)1.2(I1624E) channel protein and I(Ca). The Ca(v)1.2(I1624E) channel showed "CDI" kinetics. Despite a lower sarcoplasmic reticulum Ca(2+) content, cellular contractility and global Ca(2+) transients remained unchanged because the EC coupling gain was up-regulated by an increased neuroendocrine activity. Treatment of mice with metoprolol and captopril reduced DCM in Ca(v)1.2(I1624E) hearts at day 10. We conclude that mutation of the IQ motif to IE leads to dilated cardiomyopathy and death.
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Affiliation(s)
- Anne Blaich
- Forschergruppe, Institut für Pharmakologie und Toxikologie, Technische Universität München, 80802 München, Germany
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19
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Morotti S, Grandi E, Summa A, Ginsburg KS, Bers DM. Theoretical study of L-type Ca(2+) current inactivation kinetics during action potential repolarization and early afterdepolarizations. J Physiol 2012; 590:4465-81. [PMID: 22586219 DOI: 10.1113/jphysiol.2012.231886] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Sarcoplasmic reticulum (SR) Ca(2+) release mediates excitation–contraction coupling (ECC) in cardiac myocytes. It is triggered upon membrane depolarization by entry of Ca(2+) via L-type Ca(2+) channels (LTCCs), which undergo both voltage- and Ca(2+)-dependent inactivation (VDI and CDI, respectively). We developed improved models of L-type Ca(2+) current and SR Ca(2+) release within the framework of the Shannon-Bers rabbit ventricular action potential (AP) model. The formulation of SR Ca(2+) release was modified to reproduce high ECC gain at negative membrane voltages. An existing LTCC model was extended to reflect more faithfully contributions of CDI and VDI to total inactivation. Ba(2+) current inactivation included an ion-dependent component (albeit small compared with CDI), in addition to pure VDI. Under physiological conditions (during an AP) LTCC inactivates predominantly via CDI, which is controlled mostly by SR Ca(2+) release during the initial AP phase, but by Ca(2+) through LTCCs for the remaining part. Simulations of decreased CDI or K(+) channel block predicted the occurrence of early and delayed after depolarizations. Our model accurately describes ECC and allows dissection of the relative contributions of different Ca(2+) sources to total CDI, and the relative roles of CDI and VDI, during normal and abnormal repolarization.
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Affiliation(s)
- Stefano Morotti
- Department of Pharmacology, University of California, Davis, CA 95616-8636, USA
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20
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Fares E, Parks RJ, MacDonald JK, Egar JM, Howlett SE. Ovariectomy enhances SR Ca2+ release and increases Ca2+ spark amplitudes in isolated ventricular myocytes. J Mol Cell Cardiol 2012; 52:32-42. [DOI: 10.1016/j.yjmcc.2011.09.002] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/28/2011] [Revised: 08/18/2011] [Accepted: 09/02/2011] [Indexed: 11/24/2022]
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21
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Takeda Y, Nystoriak MA, Nieves-Cintrón M, Santana LF, Navedo MF. Relationship between Ca2+ sparklets and sarcoplasmic reticulum Ca2+ load and release in rat cerebral arterial smooth muscle. Am J Physiol Heart Circ Physiol 2011; 301:H2285-94. [PMID: 21984539 PMCID: PMC3233819 DOI: 10.1152/ajpheart.00488.2011] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/12/2011] [Accepted: 09/30/2011] [Indexed: 11/22/2022]
Abstract
Ca(+) sparklets are subcellular Ca(2+) signals produced by the opening of sarcolemmal L-type Ca(2+) channels. Ca(2+) sparklet activity varies within the sarcolemma of arterial myocytes. In this study, we examined the relationship between Ca(2+) sparklet activity and sarcoplasmic reticulum (SR) Ca(2+) accumulation and release in cerebral arterial myocytes. Our data indicate that the SR is a vast organelle with multiple regions near the sarcolemma of these cells. Ca(2+) sparklet sites were located at or <0.2 μm from SR-sarcolemmal junctions. We found that while Ca(2+) sparklets increase the rate of SR Ca(2+) refilling in arterial myocytes, their activity did not induce regional variations in SR Ca(2+) content or Ca(2+) spark activity. In arterial myocytes, L-type Ca(2+) channel activity was independent of SR Ca(2+) load. This ruled out a potential feedback mechanism whereby SR Ca(2+) load regulates the activity of these channels. Together, our data suggest a model in which Ca(2+) sparklets contribute Ca(2+) influx into a cytosolic Ca(2+) pool from which sarco(endo)plasmic reticulum Ca(2+)-ATPase pumps Ca(2+) into the SR, indirectly regulating SR function.
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Affiliation(s)
- Yukari Takeda
- Department of Physiology and Biophysics, University of Washington, Seattle, 98195, USA
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22
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Sato D, Bers DM. How does stochastic ryanodine receptor-mediated Ca leak fail to initiate a Ca spark? Biophys J 2011; 101:2370-9. [PMID: 22098735 DOI: 10.1016/j.bpj.2011.10.017] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2011] [Revised: 10/06/2011] [Accepted: 10/12/2011] [Indexed: 11/15/2022] Open
Abstract
Spontaneous calcium (Ca) sparks are initiated by single ryanodine receptor (RyR) opening. Once one RyR channel opens, it elevates local [Ca] in the cleft space ([Ca](Cleft)), which opens other RyR channels in the same Ca release unit (CaRU) via Ca-induced Ca-release. Experiments by Zima et al. (J. Physiol. 588:4743-4757, 2010) demonstrate that spontaneous Ca sparks occur only when intrasarcoplasmic-reticulum (SR) [Ca] ([Ca](SR)) is above a threshold level, but that RyR-mediated SR Ca leak exists without Ca sparks well below this threshold [Ca](SR). We examine here how single RyR opening at lower [Ca](SR) can fail to recruit Ca sparks at a CaRU, while still contributing to SR Ca leak. We assess this using a physiologically detailed mathematical model of junctional SR Ca release in which RyR gating is regulated by [Ca](SR) and [Ca](Cleft). We find that several factors contribute to the failure of Ca sparks as [Ca](SR) declines: 1), lower [Ca](SR) reduces driving force and thus limits local [Ca](Cleft) achieved and the rate of rise during RyR opening; 2), low [Ca](SR) limits RyR open time (τ(O)), which further reduces local [Ca](Cleft) attained; 3), low τ(O) and fast [Ca](Cleft) dissipation after RyR closure shorten the opportunity for neighboring RyR activation; 4), at low [Ca](SR), the RyR exhibits reduced [Ca](Cleft) sensitivity. We conclude that all of these factors conspire to reduce the probability of Ca sparks as [Ca](SR) declines, despite continued RyR-mediated Ca leak. In addition, these same factors explain the much lower efficacy of L-type Ca channel opening to trigger local SR Ca release at low [Ca](SR) during excitation-contraction coupling. Conversely, all of these factors are fundamentally important for increasing the propensity for pro-arrhythmic Ca sparks and waves in cardiac myocytes at high [Ca](SR).
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Affiliation(s)
- Daisuke Sato
- Department of Pharmacology, University of California, Davis, California, USA
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23
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Ko ML, Shi L, Tsai JY, Young ME, Neuendorff N, Earnest DJ, Ko GYP. Cardiac-specific mutation of Clock alters the quantitative measurements of physical activities without changing behavioral circadian rhythms. J Biol Rhythms 2011; 26:412-22. [PMID: 21921295 PMCID: PMC3181102 DOI: 10.1177/0748730411414170] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Even though peripheral circadian oscillators in the cardiovascular system are known to exist, the daily rhythms of the cardiovascular system are mainly attributed to autonomic or hormonal inputs under the control of the central oscillator, the suprachiasmatic nucleus (SCN). In order to examine the role of peripheral oscillators in the cardiovascular system, we used a transgenic mouse where the Clock gene is specifically disrupted in cardiomyocytes. In this cardiomyocyte-specific CLOCK mutant (CCM) mouse model, the circadian input from the SCN remains intact. Both CCM and wild-type (WT) littermates displayed circadian rhythms in wheel-running behavior. However, the overall wheel-running activities were significantly lower in CCM mice compared to WT over the course of 5 weeks, indicating that CCM mice either have lower baseline physical activities or they have lower physical adaptation abilities because daily wheel running, like routine exercise, induces physical adaptation over a period of time. Upon further biochemical analysis, it was revealed that the diurnal oscillations of phosphorylation states of several kinases and protein expression of the L-type voltage-gated calcium channel (L-VGCC) α1D subunit found in WT hearts were abolished in CCM hearts, indicating that in mammalian hearts, the daily oscillations of the activities of these kinases and L-VGCCs were downstream elements of the cardiac core oscillators. However, the phosphorylation of p38 MAPK exhibited robust diurnal rhythms in both WT and CCM hearts, indicating that cardiac p38 could be under the influence of the central clock through neurohormonal signals or be part of the circadian input pathway in cardiomyocytes. Taken together, these results indicate that the cardiac core oscillators have an impact in regulating circadian rhythmicities and cardiac function.
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Affiliation(s)
- Michael L. Ko
- Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX
| | - Liheng Shi
- Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX
| | - Ju-Yun Tsai
- US Department of Agriculture/Agricultural Research Service Children’s Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX
| | - Martin E. Young
- Division of Cardiovascular Diseases, Department of Medicine, University of Alabama at Birmingham, Birmingham, AL
| | - Nichole Neuendorff
- Department of Neuroscience and Experimental Therapeutics, Texas A&M Health Science Center, College Station, TX
| | - David J. Earnest
- Department of Neuroscience and Experimental Therapeutics, Texas A&M Health Science Center, College Station, TX
| | - Gladys Y.-P. Ko
- Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX
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Schendel T, Thul R, Sneyd J, Falcke M. How does the ryanodine receptor in the ventricular myocyte wake up: by a single or by multiple open L-type Ca2+ channels? EUROPEAN BIOPHYSICS JOURNAL: EBJ 2011; 41:27-39. [DOI: 10.1007/s00249-011-0755-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2011] [Revised: 08/23/2011] [Accepted: 09/14/2011] [Indexed: 02/07/2023]
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25
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Acsai K, Antoons G, Livshitz L, Rudy Y, Sipido KR. Microdomain [Ca²⁺] near ryanodine receptors as reported by L-type Ca²⁺ and Na+/Ca²⁺ exchange currents. J Physiol 2011; 589:2569-83. [PMID: 21486798 DOI: 10.1113/jphysiol.2010.202663] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
During Ca²⁺ release from the sarcoplasmic reticulum triggered by Ca²⁺ influx through L-type Ca²⁺ channels (LTCCs), [Ca²⁺] near release sites ([Ca²⁺]nrs) temporarily exceeds global cytosolic [Ca²⁺]. [Ca²⁺]nrs can at present not be measured directly but the Na+/Ca2+ exchanger (NCX) near release sites and LTCCs also experience [Ca²⁺]nrs. We have tested the hypothesis that ICaL and INCX could be calibrated to report [Ca²⁺]nrs and would report different time course and values for local [Ca²⁺]. Experiments were performed in pig ventricular myocytes (whole-cell voltage-clamp, Fluo-3 to monitor global cytosolic [Ca²⁺], 37◦C). [Ca²⁺]nrs-dependent inactivation of ICaL during a step to +10 mV peaked around 10 ms. For INCX we computationally isolateda current fraction activated by [Ca²⁺]nrs; values were maximal at 10 ms into depolarization. The recovery of [Ca²⁺]nrs was comparable with both reporters (>90% within 50 ms). Calibration yielded maximal values for [Ca²⁺]nrs between 10 and 15 μmol l⁻¹ with both methods. When applied to a step to less positive potentials (-30 to -20 mV), the time course of [Ca²⁺]nrs was slower but peak values were not very different. In conclusion, both ICaL inactivation and INCX activation, using a subcomponent analysis, can be used to report dynamic changes of [Ca²⁺]nrs. Absolute values obtained by these different methods are within the same range, suggesting that they are reporting on a similar functional compartment near ryanodine receptors. Comparable [Ca²⁺]nrs at +10 mV and -20 mV suggests that, although the number of activated release sites differs at these potentials, local gradients at release sites can reach similar values.
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Affiliation(s)
- Karoly Acsai
- Lab of Experimental Cardiology, Catholic University of Leuven, Belgium
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26
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Ko ML, Shi L, Grushin K, Nigussie F, Ko GYP. Circadian profiles in the embryonic chick heart: L-type voltage-gated calcium channels and signaling pathways. Chronobiol Int 2011; 27:1673-96. [PMID: 20969517 DOI: 10.3109/07420528.2010.514631] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Circadian clocks exist in the heart tissue and modulate multiple physiological events, from cardiac metabolism to contractile function and expression of circadian oscillator and metabolic-related genes. Ample evidence has demonstrated that there are endogenous circadian oscillators in adult mammalian cardiomyocytes. However, mammalian embryos cannot be entrained independently to light-dark (LD) cycles in vivo without any maternal influence, but circadian genes are well expressed and able to oscillate in embryonic stages. The authors took advantage of using chick embryos that are independent of maternal influences to investigate whether embryonic hearts could be entrained under LD cycles in ovo. The authors found circadian regulation of L-type voltage-gated calcium channels (L-VGCCs), the ion channels responsible for the production of cardiac muscle contraction in embryonic chick hearts. The mRNA levels and protein expression of VGCCα1C and VGCCα1D are under circadian control, and the average L-VGCC current density is significantly larger when cardiomyocytes are recorded during the night than day. The phosphorylation states of several kinases involved in insulin signaling and cardiac metabolism, including extracellular signal-regulated kinase (Erk), stress-activated protein kinase (p38), protein kinase B (Akt), and glycogen synthase kinase-3β (GSK-3β), are also under circadian control. Both Erk and p38 have been implicated in regulating cardiac contractility and in the development of various pathological states, such as cardiac hypertrophy and heart failure. Even though both Erk and phosphoinositide 3-kinase (PI3K)-Akt signaling pathways participate in complex cellular processes regarding physiological or pathological states of cardiomyocytes, the circadian oscillators in the heart regulate these pathways independently, and both pathways contribute to the circadian regulation of L-VGCCs.
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Affiliation(s)
- Michael L Ko
- Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843, USA
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27
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Abstract
The goal of systems biology is to relate events at the molecular level to more integrated scales from organelle to cell, tissue, and living organism. Here, we review how normal and abnormal excitation-contraction coupling properties emerge from the protein scale, where behaviors are dominated by randomness, to the cell and tissue scales, where heart has to beat with reliable regularity for a lifetime. Beginning with the fundamental unit of excitation-contraction coupling, the couplon where L-type Ca channels in the sarcolemmal membrane adjoin ryanodine receptors in the sarcoplasmic reticulum membrane, we show how a network of couplons with 3 basic properties (random activation, refractoriness, and recruitment) produces the classic physiological properties of excitation-contraction coupling and, under pathophysiological conditions, leads to Ca alternans and Ca waves. Moving to the tissue scale, we discuss how cellular Ca alternans and Ca waves promote both reentrant and focal arrhythmias in the heart. Throughout, we emphasize the qualitatively novel properties that emerge at each new scale of integration.
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Affiliation(s)
- James N Weiss
- Department of Medicine, University of California at Los Angeles, 90095, USA.
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28
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29
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Heinzel FR, MacQuaide N, Biesmans L, Sipido K. Dyssynchrony of Ca2+ release from the sarcoplasmic reticulum as subcellular mechanism of cardiac contractile dysfunction. J Mol Cell Cardiol 2010; 50:390-400. [PMID: 21075114 DOI: 10.1016/j.yjmcc.2010.11.008] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/16/2010] [Revised: 09/30/2010] [Accepted: 11/05/2010] [Indexed: 02/05/2023]
Abstract
Cardiac contractile function depends on coordinated electrical activation throughout the heart. Dyssynchronous electrical activation of the ventricles has been shown to contribute to contractile dysfunction in heart failure, and resynchronization therapy has emerged as a therapeutic concept. At the cellular level, coupling of membrane excitation to myofilament contraction is facilitated by highly organized intracellular structures which coordinate Ca(2+) release. The cytosolic [Ca(2+)] transient triggered by depolarization-induced Ca(2+) influx is the result of a gradable and robust high gain process, Ca(2+)-induced Ca(2+) release (CICR), which integrates subcellular localized Ca(2+) release events. Lack of synchronization of these localized release events can contribute to contractile dysfunction in myocardial hypertrophy and heart failure. Different underlying mechanisms relate to functional and structural changes in sarcolemmal Ca(2+) channels, the sarcoplasmic Ca(2+) release channel or ryanodine receptor, RyR, their intracellular arrangement in close proximity in couplons and the loss of t-tubules. Dyssynchrony at the subcellular level translates in a reduction of the overall gain of CICR at the cellular level and forms an important determinant of myocyte contractility in heart failure.
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30
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Krishna A, Sun L, Valderrábano M, Palade PT, Clark JW. Modeling CICR in rat ventricular myocytes: voltage clamp studies. Theor Biol Med Model 2010; 7:43. [PMID: 21062495 PMCID: PMC3245510 DOI: 10.1186/1742-4682-7-43] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2010] [Accepted: 11/10/2010] [Indexed: 01/08/2023] Open
Abstract
Background The past thirty-five years have seen an intense search for the molecular mechanisms underlying calcium-induced calcium-release (CICR) in cardiac myocytes, with voltage clamp (VC) studies being the leading tool employed. Several VC protocols including lowering of extracellular calcium to affect Ca2+ loading of the sarcoplasmic reticulum (SR), and administration of blockers caffeine and thapsigargin have been utilized to probe the phenomena surrounding SR Ca2+ release. Here, we develop a deterministic mathematical model of a rat ventricular myocyte under VC conditions, to better understand mechanisms underlying the response of an isolated cell to calcium perturbation. Motivation for the study was to pinpoint key control variables influencing CICR and examine the role of CICR in the context of a physiological control system regulating cytosolic Ca2+ concentration ([Ca2+]myo). Methods The cell model consists of an electrical-equivalent model for the cell membrane and a fluid-compartment model describing the flux of ionic species between the extracellular and several intracellular compartments (cell cytosol, SR and the dyadic coupling unit (DCU), in which resides the mechanistic basis of CICR). The DCU is described as a controller-actuator mechanism, internally stabilized by negative feedback control of the unit's two diametrically-opposed Ca2+ channels (trigger-channel and release-channel). It releases Ca2+ flux into the cyto-plasm and is in turn enclosed within a negative feedback loop involving the SERCA pump, regulating[Ca2+]myo. Results Our model reproduces measured VC data published by several laboratories, and generates graded Ca2+ release at high Ca2+ gain in a homeostatically-controlled environment where [Ca2+]myo is precisely regulated. We elucidate the importance of the DCU elements in this process, particularly the role of the ryanodine receptor in controlling SR Ca2+ release, its activation by trigger Ca2+, and its refractory characteristics mediated by the luminal SR Ca2+ sensor. Proper functioning of the DCU, sodium-calcium exchangers and SERCA pump are important in achieving negative feedback control and hence Ca2+ homeostasis. Conclusions We examine the role of the above Ca2+ regulating mechanisms in handling various types of induced disturbances in Ca2+ levels by quantifying cellular Ca2+ balance. Our model provides biophysically-based explanations of phenomena associated with CICR generating useful and testable hypotheses.
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Affiliation(s)
- Abhilash Krishna
- Department of Electrical and Computer Engineering, Rice University, Houston, TX 77005, USA.
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31
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González G, Zaldívar D, Carrillo E, Hernández A, García M, Sánchez J. Pharmacological preconditioning by diazoxide downregulates cardiac L-type Ca(2+) channels. Br J Pharmacol 2010; 161:1172-85. [PMID: 20636393 PMCID: PMC2998696 DOI: 10.1111/j.1476-5381.2010.00960.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2009] [Revised: 05/18/2010] [Accepted: 06/29/2010] [Indexed: 01/05/2023] Open
Abstract
BACKGROUND AND PURPOSE Pharmacological preconditioning (PPC) with mitochondrial ATP-sensitive K(+) (mitoK(ATP) ) channel openers such as diazoxide, leads to cardioprotection against ischaemia. However, effects on Ca(2+) homeostasis during PPC, particularly changes in Ca(2+) channel activity, are poorly understood. We investigated the effects of PPC on cardiac L-type Ca(2+) channels. EXPERIMENTAL APPROACH PPC was induced in isolated hearts and enzymatically dissociated cardiomyocytes from adult rats by preincubation with diazoxide. We measured reactive oxygen species (ROS) production and Ca(2+) signals associated with action potentials using fluorescent probes, and L-type currents using a whole-cell patch-clamp technique. Levels of the α(1c) subunit of L-type channels in the cellular membrane were measured by Western blot. KEY RESULTS PPC was accompanied by a 50% reduction in α(1c) subunit levels, and by a reversible fall in L-type current amplitude and Ca(2+) transients. These effects were prevented by the ROS scavenger N-acetyl-L-cysteine (NAC), or by the mitoK(ATP) channel blocker 5-hydroxydecanoate (5-HD). PPC significantly reduced infarct size, an effect blocked by NAC and 5-HD. Nifedipine also conferred protection against infarction when applied during the reperfusion period. Downregulation of the α(1c) subunit and Ca(2+) channel function were prevented in part by the protease inhibitor leupeptin. CONCLUSIONS AND IMPLICATIONS PPC downregulated the α(1c) subunit, possibly through ROS. Downregulation involved increased degradation of the Ca(2+) channel, which in turn reduced Ca(2+) influx, which may attenuate Ca(2+) overload during reperfusion.
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Affiliation(s)
- G González
- Departamento de Farmacología, Centro de Investigación y de Estudios Avanzados del I.P.N. México, México
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32
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Winslow RL, Cortassa S, O'Rourke B, Hashambhoy YL, Rice JJ, Greenstein JL. Integrative modeling of the cardiac ventricular myocyte. WILEY INTERDISCIPLINARY REVIEWS-SYSTEMS BIOLOGY AND MEDICINE 2010; 3:392-413. [PMID: 20865780 DOI: 10.1002/wsbm.122] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Cardiac electrophysiology is a discipline with a rich 50-year history of experimental research coupled with integrative modeling which has enabled us to achieve a quantitative understanding of the relationships between molecular function and the integrated behavior of the cardiac myocyte in health and disease. In this paper, we review the development of integrative computational models of the cardiac myocyte. We begin with a historical overview of key cardiac cell models that helped shape the field. We then narrow our focus to models of the cardiac ventricular myocyte and describe these models in the context of their subcellular functional systems including dynamic models of voltage-gated ion channels, mitochondrial energy production, ATP-dependent and electrogenic membrane transporters, intracellular Ca dynamics, mechanical contraction, and regulatory signal transduction pathways. We describe key advances and limitations of the models as well as point to new directions for future modeling research. WIREs Syst Biol Med 2011 3 392-413 DOI: 10.1002/wsbm.122
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Affiliation(s)
- Raimond L Winslow
- Institute of Computational Medicine and Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, USA.
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33
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Wang G, Zhu X, Xie W, Han P, Li K, Sun Z, Wang Y, Chen C, Song R, Cao C, Zhang J, Wu C, Liu J, Cheng H. Rad As a Novel Regulator of Excitation–Contraction Coupling and β-Adrenergic Signaling in Heart. Circ Res 2010; 106:317-27. [DOI: 10.1161/circresaha.109.208272] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Rationale
:
Rad (Ras associated with diabetes) GTPase, a monomeric small G protein, binds to Ca
v
β subunit of the L-type Ca
2+
channel (LCC) and thereby regulates LCC trafficking and activity. Emerging evidence suggests that Rad is an important player in cardiac arrhythmogenesis and hypertrophic remodeling. However, whether and how Rad involves in the regulation of excitation–contraction (EC) coupling is unknown.
Objective
:
This study aimed to investigate possible role of Rad in cardiac EC coupling and β-adrenergic receptor (βAR) inotropic mechanism.
Methods and Results
:
Adenoviral overexpression of Rad by 3-fold in rat cardiomyocytes suppressed LCC current (
I
Ca
), [Ca
2+
]
i
transients, and contractility by 60%, 42%, and 38%, respectively, whereas the “gain” function of EC coupling was significantly increased, due perhaps to reduced “redundancy” of LCC in triggering sarcoplasmic reticulum release. Conversely, ≈70% Rad knockdown by RNA interference increased
I
Ca
(50%), [Ca
2+
]
i
transients (52%) and contractility (58%) without altering EC coupling efficiency; and the dominant negative mutant RadS105N exerted a similar effect on
I
Ca
. Rad upregulation caused depolarizing shift of LCC activation and hastened time-dependent LCC inactivation; Rad downregulation, however, failed to alter these attributes. The Na
+
/Ca
2+
exchange activity, sarcoplasmic reticulum Ca
2+
content, properties of Ca
2+
sparks and propensity for Ca
2+
waves all remained unperturbed regardless of Rad manipulation. Rad overexpression, but not knockdown, negated βAR effects on
I
Ca
and Ca
2+
transients.
Conclusion
:
These results establish Rad as a novel endogenous regulator of cardiac EC coupling and βAR signaling and support a parsimonious model in which Rad buffers Ca
v
β to modulate LCC activity, EC coupling, and βAR responsiveness.
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Affiliation(s)
- Gang Wang
- From the Institute of Molecular Medicine (G.W., X.Z., W.X., P.H., K.L., Z.S., Y.W., C. Chen, R.S., C. Cao, C.W., J.L., H.C.) and State Key Laboratory of Biomembrane and Membrane Biotechnology (G.W., C.W.) of College of Life Science, Peking University, Beijing, China; Cardiovascular Center (J.Z.), University of Michigan, Ann Arbor, Mich; and Department of Pathophysiology (J.L.), Medical School of Shenzhen University, China
| | - Xiaojun Zhu
- From the Institute of Molecular Medicine (G.W., X.Z., W.X., P.H., K.L., Z.S., Y.W., C. Chen, R.S., C. Cao, C.W., J.L., H.C.) and State Key Laboratory of Biomembrane and Membrane Biotechnology (G.W., C.W.) of College of Life Science, Peking University, Beijing, China; Cardiovascular Center (J.Z.), University of Michigan, Ann Arbor, Mich; and Department of Pathophysiology (J.L.), Medical School of Shenzhen University, China
| | - Wenjun Xie
- From the Institute of Molecular Medicine (G.W., X.Z., W.X., P.H., K.L., Z.S., Y.W., C. Chen, R.S., C. Cao, C.W., J.L., H.C.) and State Key Laboratory of Biomembrane and Membrane Biotechnology (G.W., C.W.) of College of Life Science, Peking University, Beijing, China; Cardiovascular Center (J.Z.), University of Michigan, Ann Arbor, Mich; and Department of Pathophysiology (J.L.), Medical School of Shenzhen University, China
| | - Peidong Han
- From the Institute of Molecular Medicine (G.W., X.Z., W.X., P.H., K.L., Z.S., Y.W., C. Chen, R.S., C. Cao, C.W., J.L., H.C.) and State Key Laboratory of Biomembrane and Membrane Biotechnology (G.W., C.W.) of College of Life Science, Peking University, Beijing, China; Cardiovascular Center (J.Z.), University of Michigan, Ann Arbor, Mich; and Department of Pathophysiology (J.L.), Medical School of Shenzhen University, China
| | - Kaitao Li
- From the Institute of Molecular Medicine (G.W., X.Z., W.X., P.H., K.L., Z.S., Y.W., C. Chen, R.S., C. Cao, C.W., J.L., H.C.) and State Key Laboratory of Biomembrane and Membrane Biotechnology (G.W., C.W.) of College of Life Science, Peking University, Beijing, China; Cardiovascular Center (J.Z.), University of Michigan, Ann Arbor, Mich; and Department of Pathophysiology (J.L.), Medical School of Shenzhen University, China
| | - Zhongcui Sun
- From the Institute of Molecular Medicine (G.W., X.Z., W.X., P.H., K.L., Z.S., Y.W., C. Chen, R.S., C. Cao, C.W., J.L., H.C.) and State Key Laboratory of Biomembrane and Membrane Biotechnology (G.W., C.W.) of College of Life Science, Peking University, Beijing, China; Cardiovascular Center (J.Z.), University of Michigan, Ann Arbor, Mich; and Department of Pathophysiology (J.L.), Medical School of Shenzhen University, China
| | - Yanru Wang
- From the Institute of Molecular Medicine (G.W., X.Z., W.X., P.H., K.L., Z.S., Y.W., C. Chen, R.S., C. Cao, C.W., J.L., H.C.) and State Key Laboratory of Biomembrane and Membrane Biotechnology (G.W., C.W.) of College of Life Science, Peking University, Beijing, China; Cardiovascular Center (J.Z.), University of Michigan, Ann Arbor, Mich; and Department of Pathophysiology (J.L.), Medical School of Shenzhen University, China
| | - Chunlei Chen
- From the Institute of Molecular Medicine (G.W., X.Z., W.X., P.H., K.L., Z.S., Y.W., C. Chen, R.S., C. Cao, C.W., J.L., H.C.) and State Key Laboratory of Biomembrane and Membrane Biotechnology (G.W., C.W.) of College of Life Science, Peking University, Beijing, China; Cardiovascular Center (J.Z.), University of Michigan, Ann Arbor, Mich; and Department of Pathophysiology (J.L.), Medical School of Shenzhen University, China
| | - Ruisheng Song
- From the Institute of Molecular Medicine (G.W., X.Z., W.X., P.H., K.L., Z.S., Y.W., C. Chen, R.S., C. Cao, C.W., J.L., H.C.) and State Key Laboratory of Biomembrane and Membrane Biotechnology (G.W., C.W.) of College of Life Science, Peking University, Beijing, China; Cardiovascular Center (J.Z.), University of Michigan, Ann Arbor, Mich; and Department of Pathophysiology (J.L.), Medical School of Shenzhen University, China
| | - Chunmei Cao
- From the Institute of Molecular Medicine (G.W., X.Z., W.X., P.H., K.L., Z.S., Y.W., C. Chen, R.S., C. Cao, C.W., J.L., H.C.) and State Key Laboratory of Biomembrane and Membrane Biotechnology (G.W., C.W.) of College of Life Science, Peking University, Beijing, China; Cardiovascular Center (J.Z.), University of Michigan, Ann Arbor, Mich; and Department of Pathophysiology (J.L.), Medical School of Shenzhen University, China
| | - Jifeng Zhang
- From the Institute of Molecular Medicine (G.W., X.Z., W.X., P.H., K.L., Z.S., Y.W., C. Chen, R.S., C. Cao, C.W., J.L., H.C.) and State Key Laboratory of Biomembrane and Membrane Biotechnology (G.W., C.W.) of College of Life Science, Peking University, Beijing, China; Cardiovascular Center (J.Z.), University of Michigan, Ann Arbor, Mich; and Department of Pathophysiology (J.L.), Medical School of Shenzhen University, China
| | - Caihong Wu
- From the Institute of Molecular Medicine (G.W., X.Z., W.X., P.H., K.L., Z.S., Y.W., C. Chen, R.S., C. Cao, C.W., J.L., H.C.) and State Key Laboratory of Biomembrane and Membrane Biotechnology (G.W., C.W.) of College of Life Science, Peking University, Beijing, China; Cardiovascular Center (J.Z.), University of Michigan, Ann Arbor, Mich; and Department of Pathophysiology (J.L.), Medical School of Shenzhen University, China
| | - Jie Liu
- From the Institute of Molecular Medicine (G.W., X.Z., W.X., P.H., K.L., Z.S., Y.W., C. Chen, R.S., C. Cao, C.W., J.L., H.C.) and State Key Laboratory of Biomembrane and Membrane Biotechnology (G.W., C.W.) of College of Life Science, Peking University, Beijing, China; Cardiovascular Center (J.Z.), University of Michigan, Ann Arbor, Mich; and Department of Pathophysiology (J.L.), Medical School of Shenzhen University, China
| | - Heping Cheng
- From the Institute of Molecular Medicine (G.W., X.Z., W.X., P.H., K.L., Z.S., Y.W., C. Chen, R.S., C. Cao, C.W., J.L., H.C.) and State Key Laboratory of Biomembrane and Membrane Biotechnology (G.W., C.W.) of College of Life Science, Peking University, Beijing, China; Cardiovascular Center (J.Z.), University of Michigan, Ann Arbor, Mich; and Department of Pathophysiology (J.L.), Medical School of Shenzhen University, China
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34
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Fares E, Howlett SE. Effect of age on cardiac excitation-contraction coupling. Clin Exp Pharmacol Physiol 2010; 37:1-7. [DOI: 10.1111/j.1440-1681.2009.05276.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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35
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Ogrodnik J, Niggli E. Increased Ca(2+) leak and spatiotemporal coherence of Ca(2+) release in cardiomyocytes during beta-adrenergic stimulation. J Physiol 2009; 588:225-42. [PMID: 19900959 DOI: 10.1113/jphysiol.2009.181800] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
beta-Adrenergic receptor (beta-AR) stimulation of cardiac muscle has been proposed to enhance Ca(2+) release from the sarcoplasmic reticulum (SR) through ryanodine receptors (RyRs). However, the anticipated increase in RyR Ca(2+) sensitivity has proven difficult to study in intact cardiomyocytes, due to accompanying alterations in SR Ca(2+) content, inward Ca(2+) current (I(Ca)) and diastolic cytosolic Ca(2+) concentration ([Ca(2+)](i)). Here, we studied whole-cell Ca(2+) release and spontaneous Ca(2+) leak (Ca(2+) sparks) in guinea-pig ventricular myocytes with confocal Ca(2+) imaging before and during beta-AR stimulation by isoproterenol (Iso), but under otherwise nearly identical experimental conditions. The extent of SR Ca(2+) loading was controlled under whole-cell voltage-clamp conditions. UV flash-induced uncaging of Ca(2+) from DM-nitrophen was employed as an invariant trigger for whole-cell Ca(2+) release. At matched SR Ca(2+) content, we found that Iso enhanced the spatiotemporal coherence of whole-cell Ca(2+) release, evident from spatially intercorrelated release and accelerated release kinetics that resulted in moderately (20%) increased release amplitude. This may arise from higher RyR Ca(2+) sensitivity, and was also reflected in spontaneous SR Ca(2+) leak. At comparable SR Ca(2+) content and cytosolic [Ca(2+)](i), we observed an approximately 4-fold increase in Ca(2+) spark frequency in Iso that also appeared in quiescent cells within 2 min without increased SR Ca(2+) content. This was likely to have been mediated by Ca(2+)/calmodulin-dependent protein kinase (CaMKII), rather than cAMP dependent protein kinase (PKA). We conclude that Iso increases the propensity of RyRs to open, both in response to rapid elevations of [Ca(2+)](i) and at diastolic [Ca(2+)](i). While this could be beneficial in enhancing and synchronizing systolic whole-cell SR Ca(2+) release, the same behaviour could also be proarrhythmogenic during diastole.
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Affiliation(s)
- Jakob Ogrodnik
- Department of Physiology, University of Bern, Bühlplatz 5, 3012 Bern, Switzerland
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36
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Beta-adrenergic signaling accelerates and synchronizes cardiac ryanodine receptor response to a single L-type Ca2+ channel. Proc Natl Acad Sci U S A 2009; 106:18028-33. [PMID: 19815510 DOI: 10.1073/pnas.0906560106] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
As the most prototypical G protein-coupled receptor, beta-adrenergic receptor (betaAR) regulates the pace and strength of heart beating by enhancing and synchronizing L-type channel (LCC) Ca(2+) influx, which in turn elicits greater sarcoplasmic reticulum (SR) Ca(2+) release flux via ryanodine receptors (RyRs). However, whether and how betaAR-protein kinase A (PKA) signaling directly modulates RyR function remains elusive and highly controversial. By using unique single-channel Ca(2+) imaging technology, we measured the response of a single RyR Ca(2+) release unit, in the form of a Ca(2+) spark, to its native trigger, the Ca(2+) sparklet from a single LCC. We found that acute application of the selective betaAR agonist isoproterenol (1 microM, < or = 20 min) increased triggered spark amplitude in an LCC unitary current-independent manner. The increased ratio of Ca(2+) release flux underlying a Ca(2+) spark to SR Ca(2+) content indicated that betaAR stimulation helps to recruit additional RyRs in synchrony. Quantification of sparklet-spark kinetics showed that betaAR stimulation synchronized the stochastic latency and increased the fidelity (i.e., chance of hit) of LCC-RyR intermolecular signaling. The RyR modulation was independent of the increased SR Ca(2+) content. The PKA antagonists Rp-8-CPT-cAMP (100 microM) and H89 (10 microM) both eliminated these effects, indicating that betaAR acutely modulates RyR activation via the PKA pathway. These results demonstrate unequivocally that RyR activation by a single LCC is accelerated and synchronized during betaAR stimulation. This molecular mechanism of sympathetic regulation will permit more fundamental studies of altered betaAR effects in cardiovascular diseases.
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37
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Ullrich ND, Fanchaouy M, Gusev K, Shirokova N, Niggli E. Hypersensitivity of excitation-contraction coupling in dystrophic cardiomyocytes. Am J Physiol Heart Circ Physiol 2009; 297:H1992-2003. [PMID: 19783774 DOI: 10.1152/ajpheart.00602.2009] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Duchenne muscular dystrophy represents a severe inherited disease of striated muscle. It is caused by a mutation of the dystrophin gene and characterized by a progressive loss of skeletal muscle function. Most patients also develop a dystrophic cardiomyopathy, resulting in dilated hypertrophy and heart failure, but the cellular mechanisms leading to the deterioration of cardiac function remain elusive. In the present study, we tested whether defective excitation-contraction (E-C) coupling contributes to impaired cardiac performance. "E-C coupling gain" was determined in cardiomyocytes from control and dystrophin-deficient mdx mice. To this end, L-type Ca2+ currents (ICaL) were measured with the whole cell patch-clamp technique, whereas Ca2+ transients were simultaneously recorded with confocal imaging of fluo-3. Initial findings indicated subtle changes of E-C coupling in mdx cells despite matched Ca2+ loading of the sarcoplasmic reticulum (SR). However, lowering the extracellular Ca2+ concentration, a maneuver used to unmask latent E-C coupling problems, was surprisingly much better tolerated by mdx myocytes, suggesting a hypersensitive E-C coupling mechanism. Challenging the SR Ca2+ release by slow elevations of the intracellular Ca2+ concentration resulted in Ca2+ oscillations after a much shorter delay in mdx cells. This is consistent with an enhanced Ca2+ sensitivity of the SR Ca2+-release channels [ryanodine receptors (RyRs)]. The hypersensitivity could be normalized by the introduction of reducing agents, indicating that the elevated cellular ROS generation in dystrophy underlies the abnormal RyR sensitivity and hypersensitive E-C coupling. Our data suggest that in dystrophin-deficient cardiomyocytes, E-C coupling is altered due to potentially arrhythmogenic changes in the Ca2+ sensitivity of redox-modified RyRs.
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Affiliation(s)
- Nina D Ullrich
- Department of Physiology, University of Bern, Buehlplatz 5, Bern 3012, Switzerland
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38
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Shi L, Ko ML, Ko GYP. Rhythmic expression of microRNA-26a regulates the L-type voltage-gated calcium channel alpha1C subunit in chicken cone photoreceptors. J Biol Chem 2009; 284:25791-803. [PMID: 19608742 DOI: 10.1074/jbc.m109.033993] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
MicroRNAs (miRNAs) modulate gene expression by degrading or inhibiting translation of messenger RNAs (mRNAs). Here, we demonstrated that chicken microRNA-26a (gga-mir-26a) is a key posttranscriptional regulator of photoreceptor L-type voltage-gated calcium channel alpha1C subunit (L-VGCCalpha1C) expression, and its own expression has a diurnal rhythm, thereby explaining the rhythmic nature of L-VGCCalpha1Cs. Circadian oscillators in retinal photoreceptors provide a mechanism that allows photoreceptors to anticipate daily illumination changes. In photoreceptors, L-VGCC activities are under circadian control, which are higher at night and lower during the day. Interestingly, the mRNA level of VGCCalpha1D oscillates, but those for VGCCalpha1C do not. However, the protein expression of both VGCCalpha1C and alpha1D are higher at night in cone photoreceptors. The underlying mechanism regulating L-VGCCalpha1C protein expression was not clear until now. In vitro targeting reporter assays verified that gga-mir-26a specifically targeted the L-VGCCalpha1C 3'-untranslated region, and gga-mir-26a expression in the retina peaked during the day. After transfection with gga-mir-26a, L-VGCCalpha1C protein expression and L-VGCC current density decreased. Therefore, the rhythmic expression of gga-mir-26a regulated the protein expression of the L-VGCCalpha1C subunit. Additionally, both CLOCK (circadian locomoter output cycles kaput) and CREB (cAMP-response element-binding protein-1) activated gga-mir-26a expression in vitro. This result implies that gga-mir-26a might be a downstream target of circadian oscillators. Our work has uncovered new functional roles for miRNAs in the regulation of circadian rhythms in cone photoreceptors. Circadian regulated miRNAs could serve as the link between the core oscillator and output signaling that further govern biological functions.
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Affiliation(s)
- Liheng Shi
- Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, Texas 77843-4458, USA
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Chen B, Wu Y, Mohler PJ, Anderson ME, Song LS. Local control of Ca2+-induced Ca2+ release in mouse sinoatrial node cells. J Mol Cell Cardiol 2009; 47:706-15. [PMID: 19615376 DOI: 10.1016/j.yjmcc.2009.07.007] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/06/2009] [Revised: 07/06/2009] [Accepted: 07/06/2009] [Indexed: 01/01/2023]
Abstract
Emerging evidence from large animal models implicates Ca2+ regulation, particularly intracellular sarcoplasmic reticulum (SR) Ca2+ release, as essential for sinoatrial node (SAN) automaticity. However, despite the apparent importance of SR Ca2+ release to SAN cell function it is uncertain how SR Ca2+ release is controlled in SAN cells from mouse. Understanding mouse SAN SR Ca2+ release mechanism will allow improved understanding of results in studies on SAN from genetic mouse models of Ca2+ homeostatic proteins. Here we investigated the functional relationship between sarcolemmal Ca2+ influx and SR Ca2+ release at the level of single SAN cell, using simultaneous patch-clamp current recording and high resolution confocal Ca2+ imaging techniques. In mouse SAN cells, both Ca2+ channel currents and triggered SR Ca2+ transients displayed bell-shaped, graded function with the membrane potential. Moreover, the gain function for Ca2+-induced Ca2+ release (CICR) displayed a monotonically decreasing function with strong voltage dependence, consistent with a "local control" mechanism for CICR. In addition, we observed numerous discrete Ca2+ sparks at the voltage range of diastolic depolarization, in sharp contrast to the much lower frequency of sparks observed at resting potentials. We concluded that the "local control" mechanism of CICR is responsible for both local Ca2+ release during diastolic depolarization and the synchronized Ca2+ transients observed during action potential in SAN cells.
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Affiliation(s)
- Biyi Chen
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of Iowa Carver College of Medicine, 285 Newton Road, Iowa City, IA 52242, USA
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40
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Blayney LM, Lai FA. Ryanodine receptor-mediated arrhythmias and sudden cardiac death. Pharmacol Ther 2009; 123:151-77. [PMID: 19345240 PMCID: PMC2704947 DOI: 10.1016/j.pharmthera.2009.03.006] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2009] [Accepted: 03/03/2009] [Indexed: 12/25/2022]
Abstract
The cardiac ryanodine receptor-Ca2+ release channel (RyR2) is an essential sarcoplasmic reticulum (SR) transmembrane protein that plays a central role in excitation–contraction coupling (ECC) in cardiomyocytes. Aberrant spontaneous, diastolic Ca2+ leak from the SR due to dysfunctional RyR2 contributes to the formation of delayed after-depolarisations, which are thought to underlie the fatal arrhythmia that occurs in both heart failure (HF) and in catecholaminergic polymorphic ventricular tachycardia (CPVT). CPVT is an inherited disorder associated with mutations in either the RyR2 or a SR luminal protein, calsequestrin. RyR2 shows normal function at rest in CPVT but the RyR2 dysfunction is unmasked by physical exercise or emotional stress, suggesting abnormal RyR2 activation as an underlying mechanism. Several potential mechanisms have been advanced to explain the dysfunctional RyR2 observed in HF and CPVT, including enhanced RyR2 phosphorylation status, altered RyR2 regulation at luminal/cytoplasmic sites and perturbed RyR2 intra/inter-molecular interactions. This review considers RyR2 dysfunction in the context of the structural and functional modulation of the channel, and potential therapeutic strategies to stabilise RyR2 function in cardiac pathology.
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Affiliation(s)
- Lynda M Blayney
- Wales Heart Research Institute, Cardiff University School of Medicine, Cardiff CF144XN, UK.
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Sobie EA, Ramay HR. Excitation-contraction coupling gain in ventricular myocytes: insights from a parsimonious model. J Physiol 2009; 587:1293-9. [PMID: 19153162 DOI: 10.1113/jphysiol.2008.163915] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
We present a minimal mathematical model of Ca(2+) spark triggering under voltage-clamp conditions in ventricular myocytes. The model predicts changes in excitation-contraction coupling 'gain' that result from diverse experimental interventions. We compare model results to several sets of data, and, in so doing, place apparent constraints on physiologically relevant model parameters. Specifically, the analysis suggests that many L-type Ca(2+) channel openings can potentially trigger each Ca(2+) spark, but the probability that an individual opening will trigger a spark is low. This procedure helps to reconcile contradictory results obtained in recent studies; moreover, this new model should be a useful tool for understanding changes in gain that occur physiologically and in disease.
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Affiliation(s)
- Eric A Sobie
- Department of Pharmacology and Systems Therapeutics, Mount Sinai School of Medicine, New York, NY, USA.
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Wheeler DG, Barrett CF, Groth RD, Safa P, Tsien RW. CaMKII locally encodes L-type channel activity to signal to nuclear CREB in excitation-transcription coupling. J Cell Biol 2008; 183:849-63. [PMID: 19047462 PMCID: PMC2592819 DOI: 10.1083/jcb.200805048] [Citation(s) in RCA: 149] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2008] [Accepted: 10/29/2008] [Indexed: 12/11/2022] Open
Abstract
Communication between cell surface proteins and the nucleus is integral to many cellular adaptations. In the case of ion channels in excitable cells, the dynamics of signaling to the nucleus are particularly important because the natural stimulus, surface membrane depolarization, is rapidly pulsatile. To better understand excitation-transcription coupling we characterized the dependence of cAMP response element-binding protein phosphorylation, a critical step in neuronal plasticity, on the level and duration of membrane depolarization. We find that signaling strength is steeply dependent on depolarization, with sensitivity far greater than hitherto recognized. In contrast, graded blockade of the Ca(2+) channel pore has a remarkably mild effect, although some Ca(2+) entry is absolutely required. Our data indicate that Ca(2+)/CaM-dependent protein kinase II acting near the channel couples local Ca(2+) rises to signal transduction, encoding the frequency of Ca(2+) channel openings rather than integrated Ca(2+) flux-a form of digital logic.
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Affiliation(s)
- Damian G Wheeler
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA
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Shirokova N, Niggli E. Studies of RyR function in situ. Methods 2008; 46:183-93. [PMID: 18848990 DOI: 10.1016/j.ymeth.2008.09.017] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2008] [Accepted: 09/12/2008] [Indexed: 10/21/2022] Open
Abstract
The ryanodine receptors (RyRs) are intracellular Ca2+ release channels of the sarcoplasmic reticulum (SR) involved in many cellular responses, including muscle excitation-contraction coupling. Multiple biochemical and biophysical methods are available to study RyR functions. However, most of them are somewhat limited because they can only be used to examine channels which are purified from the SR and no longer in their natural environment. In this review we discuss optical methods for studying RyR functions in situ. We describe several techniques for the investigation of local (microscopic) intracellular Ca2+ signals (a.k.a Ca2+ sparks) by means of confocal microscopy and flash photolysis of caged compounds. We discuss how these studies can and will continue to contribute to our understanding of RyR function in physiological and pathological conditions.
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Affiliation(s)
- Natalia Shirokova
- Department of Pharmacology & Physiology, UMDNJ-New Jersey Medical School, 185 South Orange Avenue, Newark, NJ 07103, USA.
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Poláková E, Zahradníková A, Pavelková J, Zahradník I, Zahradníková A. Local calcium release activation by DHPR calcium channel openings in rat cardiac myocytes. J Physiol 2008; 586:3839-54. [PMID: 18591191 DOI: 10.1113/jphysiol.2007.149989] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The principal role of calcium current in the triggering of calcium release in cardiac myocytes is well recognized. The mechanism of how calcium current (I(Ca)) controls the intensity of calcium release is not clear because of the stochastic nature of voltage-dependent gating of calcium channels (DHPRs) and of calcium-dependent gating of ryanodine receptors (RyRs). To disclose the relation between DHPR openings and the probability of calcium release, local calcium release activation by I(Ca) was investigated in rat ventricular myocytes using patch-clamp and confocal microscopy. Calcium spikes were activated by temporally synchronized DHPR calcium current triggers, generated by instantaneous 'tail' I(Ca) and modulated by prepulse duration, by tail potential, and by the DHPR agonist BayK 8644. The DHPR-RyR coupling fidelity was determined from the temporal distribution of calcium spike latencies using a model based on exponentially distributed DHPR open times. The analysis provided a DHPR mean open time of approximately 0.5 ms, RyR activation time constant of approximately 0.6 ms, and RyR activation kinetics of the 4th order. The coupling fidelity was low due to the inherent prevalence of very short DHPR openings but was increased when DHPR openings were prolonged by BayK 8644. The probability of calcium release activation was high, despite low coupling fidelity, due to the activation of many DHPRs at individual release sites. We conclude that the control of calcium release intensity by physiological stimuli can be achieved by modulating the number and duration of DHPR openings at low coupling fidelity, thus avoiding the danger of inadvertently triggering calcium release events.
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Affiliation(s)
- Eva Poláková
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Vlárska 5, 833 34 Bratislava, Slovakia
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Navedo MF, Nieves-Cintrón M, Amberg GC, Yuan C, Votaw VS, Lederer WJ, McKnight GS, Santana LF. AKAP150 is required for stuttering persistent Ca2+ sparklets and angiotensin II-induced hypertension. Circ Res 2008; 102:e1-e11. [PMID: 18174462 DOI: 10.1161/circresaha.107.167809] [Citation(s) in RCA: 108] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Hypertension is a perplexing multiorgan disease involving renal primary pathology and enhanced angiotensin II vascular reactivity. Here, we report that a novel form of a local Ca2+ signaling in arterial smooth muscle is linked to the development of angiotensin II-induced hypertension. Long openings and reopenings of L-type Ca2+ channels in arterial myocytes produce stuttering persistent Ca2+ sparklets that increase Ca2+ influx and vascular tone. These stuttering persistent Ca2+ sparklets arise from the molecular interactions between the L-type Ca2+ channel and protein kinase Calpha at only a few subsarcolemmal regions in resistance arteries. We have identified AKAP150 as the key protein, which targets protein kinase Calpha to the L-type Ca2+ channels and thereby enables its regulatory function. Accordingly, AKAP150 knockout mice (AKAP150-/-) were found to lack persistent Ca2+ sparklets and have lower arterial wall intracellular calcium ([Ca2+]i) and decreased myogenic tone. Furthermore, AKAP150-/- mice were hypotensive and did not develop angiotensin II-induced hypertension. We conclude that local control of L-type Ca2+ channel function is regulated by AKAP150-targeted protein kinase C signaling, which controls stuttering persistent Ca2+ influx, vascular tone, and blood pressure under physiological conditions and underlies angiotensin II-dependent hypertension.
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Affiliation(s)
- Manuel F Navedo
- Department of Physiology & Biophysics, University of Washington, Seattle, WA 98195, USA
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Huang J, Hove-Madsen L, Tibbits GF. Ontogeny of Ca2+-induced Ca2+ release in rabbit ventricular myocytes. Am J Physiol Cell Physiol 2007; 294:C516-25. [PMID: 18094144 DOI: 10.1152/ajpcell.00417.2007] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
It is commonly accepted that L-type Ca(2+) channel-mediated Ca(2+)-induced Ca(2+) release (CICR) is the dominant mode of excitation-contraction (E-C) coupling in the adult mammalian heart and that there is no appreciable CICR in neonates. However, we have observed that cell contraction in the neonatal heart was significantly decreased after sarcoplasmic reticulum (SR) Ca(2+) depletion with caffeine. Therefore, the present study investigated the developmental changes of CICR in rabbit ventricular myocytes at 3, 10, 20, and 56 days of age. We found that the inhibitory effect of the L-type Ca(2+) current (I(Ca)) inhibitor nifedipine (Nif; 15 microM) caused an increasingly larger reduction of Ca(2+) transients on depolarization in older age groups [from approximately 15% in 3-day-old (3d) myocytes to approximately 90% in 56-day-old (56d) myocytes]. The remaining Ca(2+) transient in the presence of Nif in younger age groups was eliminated by the inhibition of Na(+)/Ca(2+) exchanger (NCX) with the subsequent addition of 10 microM KB-R7943 (KB-R). Furthermore, Ca(2+) transients were significantly reduced in magnitude after the depletion of SR Ca(2+) with caffeine in all age groups, although the effect was significantly greater in the older age groups (from approximately 40% in 3d myocytes up to approximately 70% in 56d myocytes). This SR Ca(2+)-sensitive Ca(2+) transient in the earliest developmental stage was insensitive to Nif but was sensitive to the subsequent addition of KB-R, indicating the presence of NCX-mediated CICR that decreased significantly with age (from approximately 37% in 3d myocytes to approximately 0.5% in 56d myocytes). In contrast, the I(Ca)-mediated CICR increased significantly with age (from approximately 10% in 3d myocytes to approximately 70% in 56d myocytes). The CICR gain as estimated by the integral of the CICR Ca(2+) transient divided by the integral of its Ca(2+) transient trigger was smaller when mediated by NCX ( approximately 1.0 for 3d myocytes) than when mediated by I(Ca) ( approximately 3.0 for 56d myocytes). We conclude that the lower-efficiency NCX-mediated CICR is a predominant mode of CICR in the earliest developmental stages that gradually decreases as the more efficient L-type Ca(2+) channel-mediated CICR increases in prominence with ontogeny.
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Affiliation(s)
- Jingbo Huang
- Cardiac Membrane Research Laboratory, Simon Fraser University, Burnaby, BC, Canada
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