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Livshitz L, Acsai K, Antoons G, Sipido K, Rudy Y. Data-based theoretical identification of subcellular calcium compartments and estimation of calcium dynamics in cardiac myocytes. J Physiol 2012; 590:4423-46. [PMID: 22547631 DOI: 10.1113/jphysiol.2012.228791] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
In cardiac cells, Ca(2+) release flux (J(rel)) via ryanodine receptors (RyRs) from the sarcoplasmic reticulum (SR) has a complex effect on the action potential (AP). Coupling between J(rel) and the AP occurs via L-type Ca(2+) channels (I(Ca)) and the Na(+)/Ca(2+) exchanger (I(NCX)). We used a combined experimental and modelling approach to study interactions between J(rel), I(Ca) and I(NCX) in porcine ventricular myocytes.We tested the hypothesis that during normal uniform J(rel), the interaction between these fluxes can be represented as occurring in two myoplasmic subcompartments for Ca(2+) distribution, one (T-space) associated with RyR and enclosed by the junctional portion of the SR membrane and corresponding T-tubular portion of the sarcolemma, the other (M-space) encompassing the rest of the myoplasm. I(Ca) and I(NCX) were partitioned into subpopulations in the T-space and M-space sarcolemma. We denoted free Ca(2+) concentrations in T-space and M-space Ca(t) and Ca(m), respectively. Experiments were designed to allow separate measurements of I(Ca) and I(NCX) as a function of J(rel). Inclusion of T-space in themodel allowed us to reproduce in silico the following important experimental results: (1) hysteresis of I(NCX) dependence on Ca(m); (2) delay between peak I(NCX) and peak Ca(m) during caffeine application protocol; (3) delay between I(NCX) and Ca(m) during Ca(2+)-induced-Ca(2+)-release; (4) rapid I(Ca) inactivation (within 2 ms) due to J(rel), with magnitude graded as a function of the SR Ca(2+) content; (5) time delay between I(Ca) inactivation due to J(rel) and Ca(m). Partition of 25% NCX in T-space and 75% in M-space provided the best fit to the experimental data. Measured Ca(m) and I(Ca) or I(NCX) were used as input to the model for estimating Ca(t). The actual model-computed Ca(t), obtained by simulating specific experimental protocols, was used as a gold standard for comparison. The model predicted peak Ca(t) in the range of 6–25 μM, with time to equilibrium of Ca(t) with Ca(m) of ~350 ms. These Ca(t) values are in the range of LCC and RyR sensitivity to Ca(2+). An increase of the SR Ca(2+) load increased the time to equilibrium. The I(Ca)-based estimation method was most accurate during the ascending phase of Ca(t). The I(NCX)-based method provided a good estimate for the descending phase of Ca(t). Thus, application of both methods in combination provides the best estimate of the entire Ca(t) time course.
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Affiliation(s)
- Leonid Livshitz
- Cardiac Bioelectricity and Arrhythmia Centre, Washington University in St Louis, St Louis, MO 63130-4899, USA
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Kawamura Y, Ishiwata T, Takizawa M, Ishida H, Asano Y, Nonoyama S. Fetal and neonatal development of Ca2+ transients and functional sarcoplasmic reticulum in beating mouse hearts. Circ J 2010; 74:1442-50. [PMID: 20526040 DOI: 10.1253/circj.cj-09-0793] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
BACKGROUND It is generally accepted that Ca(2+)-induced Ca(2+) release is not the predominant mechanism during embryonic stages. Most studies have been conducted either on primary cultures or acutely isolated cells, in which an apparent reduction of ryanodine receptor density and alterations in the cell shape have been reported. The aim of the present study was to investigate developmental changes in Ca(2+) transients using whole hearts of mouse embryos and neonates. METHODS AND RESULTS Fluo-3 fluorescence signals from stimulated whole hearts were detected using a photomultiplier and stored as Ca(2+) transients. The upstroke and decay of Ca(2+) transients became more rapid from the late embryonic stages to the neonatal stage. After thapsigargin application (an inhibitor of the sarcoplasmic Ca(2+)-ATPase [SERCA]), time to 50% relaxation (T(50)) of Ca(2+) transients was significantly prolonged. There were no significant changes in T(50) after Ru360 application (an inhibitor of mitochondrial Ca(2+) uniporter). The rate of increase in the amplitude of Ca(2+) transients after caffeine application became larger during developmental stages. CONCLUSIONS Ca(2+) homeostasis developmentally changes from a slow rise and decay of Ca(2+) transients to rapid kinetics after the mid-embryonic stage. SERCA began to contribute significantly to Ca(2+) homeostasis at early embryonic stages and sarcoplasmic reticulum Ca(2+) contents increased from embryonic to neonatal stages, whereas mitochondrial Ca(2+) uptake did not contribute to Ca(2+) transients on a beat-to-beat basis.
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Affiliation(s)
- Yoichi Kawamura
- Department of Pediatrics, National Defense Medical College, Tokorozawa, Japan
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Guo A, Yang HT. Ca2+removal mechanisms in mouse embryonic stem cell-derived cardiomyocytes. Am J Physiol Cell Physiol 2009; 297:C732-41. [DOI: 10.1152/ajpcell.00025.2009] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In mammalian adult cardiomyocytes, sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA) plays a major role in controlling the decline of cytosolic free Ca2+concentration ([Ca2+]i) in comparison with sarcolemmal Na+/Ca2+exchanger (NCX). However, the functional importance of SERCA and NCX in cytosolic Ca2+removal during early cardiomyogenesis is still debated. In this study, the functional contributions of Ca2+transporters to [Ca2+]idecline in mouse embryonic stem cell-derived cardiomyocytes (mESCMs), a suitable model for investigation of early cardiogenesis, at various differentiation stages were investigated. We estimated that even at early differentiation stages of mESCMs, SERCA was responsible for ∼76% of total Ca2+removal, while NCX was responsible for ∼21%. The contributions of SERCA and NCX to cytosolic Ca2+clearance were increased to ∼88% and decreased to ∼10%, respectively, at the late differentiation stage. Dynamical analysis of the transient decay phases in normal and Na+-free solutions suggests that the contribution of NCX to [Ca2+]idecline is more apparent in the terminal slow decay phase than that in the initial fast phase. When SR function was suppressed in type 2 ryanodine receptor-null mESCMs or with ryanodine receptor and SERCA inhibitors (ryanodine and thapsigargin), NCX acted as the main pathway for [Ca2+]idecline. We conclude that the rapid [Ca2+]idecline is mainly achieved by the SR uptake even at the early differentiation stage of mESCMs, while NCX acts as the main Ca2+remover when SR function is suppressed. These findings suggest a critical role of SR in the regulation of [Ca2+]ihomeostasis even in differentiating cardiomyocytes.
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Affiliation(s)
- Ang Guo
- Key Laboratory of Stem Cell Biology and Laboratory of Molecular Cardiology, Institute of Health Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, and Shanghai Jiao Tong University School of Medicine
| | - Huang-Tian Yang
- Key Laboratory of Stem Cell Biology and Laboratory of Molecular Cardiology, Institute of Health Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, and Shanghai Jiao Tong University School of Medicine
- Shanghai Stem Cell Institute, Shanghai Jiao Tong University School of Medicine; and
- Shanghai Key Laboratory of Vascular Biology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
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Grandi E, Pasqualini FS, Pes C, Corsi C, Zaza A, Severi S. Theoretical investigation of action potential duration dependence on extracellular Ca2+ in human cardiomyocytes. J Mol Cell Cardiol 2008; 46:332-42. [PMID: 19121322 DOI: 10.1016/j.yjmcc.2008.12.002] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/30/2008] [Revised: 11/10/2008] [Accepted: 12/03/2008] [Indexed: 12/20/2022]
Abstract
Reduction in [Ca2+]o prolongs the AP in ventricular cardiomyocytes and the QTc interval in patients. Although this phenomenon is relevant to arrhythmogenesis in the clinical setting, its mechanisms are counterintuitive and incompletely understood. To evaluate in silico the mechanisms of APD modulation by [Ca2+]o in human cardiomyocytes. We implemented the Ten Tusscher-Noble-Noble-Panfilov model of the human ventricular myocyte and modified the formulations of the rapidly and slowly activating delayed rectifier K+ currents (IKr and IKs) and L-type Ca2+ current (ICaL) to incorporate their known sensitivity to intra- or extracellular Ca2+. Simulations were run with the original and modified models at variable [Ca2+]o in the clinically relevant 1 to 3 mM range. The original model responds with APD shortening to decrease in [Ca2+]o, i.e. opposite to the experimental observations. Incorporation of Ca2+ dependency of K+ currents cannot reproduce the inverse relation between APD and [Ca2+]o. Only when ICaL inactivation process was modified, by enhancing its dependency on Ca2+, simulations predict APD prolongation at lower [Ca2+]o. Although Ca2+-dependent ICaL inactivation is the primary mechanism, secondary changes in electrogenic Ca2+ transport (by Na+/Ca2+ exchanger and plasmalemmal Ca2+-ATPase) contribute to the reversal of APD dependency on [Ca2+]o. This theoretical investigation points to Ca2+-dependent inactivation of ICaL as a mechanism primarily responsible for the dependency of APD on [Ca2+]o. The modifications implemented here make the model more suitable to analyze repolarization mechanisms when Ca2+ levels are altered.
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Affiliation(s)
- Eleonora Grandi
- Biomedical Engineering Laboratory-D.E.I.S., University of Bologna, Cesena, Italy
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Snopko RM, Ramos-Franco J, Di Maio A, Karko KL, Manley C, Piedras-Rentería E, Mejía-Alvarez R. Ca2+ sparks and cellular distribution of ryanodine receptors in developing cardiomyocytes from rat. J Mol Cell Cardiol 2008; 44:1032-1044. [PMID: 18468619 DOI: 10.1016/j.yjmcc.2008.03.015] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/25/2007] [Revised: 03/18/2008] [Accepted: 03/18/2008] [Indexed: 10/22/2022]
Abstract
Although abundant ryanodine receptors (RyRs) exist in cardiomyocytes from newborn (NB) rat and despite the maturity of their single-channel properties, the RyR contribution to excitation-contraction (E-C) coupling is minimal. Immature arrangement of RyRs in the Ca(2+) release site of the sarcoplasmic reticulum and/or distant RyRs location from the sarcolemmal Ca(2+) signal could explain this quiescence. Consequently, Ca(2+) sparks and their cellular distribution were studied in NB myocytes and correlated with the formation of dyads and transverse (T) tubules. Ca(2+) sparks were recorded in fluo-4-loaded intact ventricular myocytes acutely dissociated from adult and NB rats (0-9 days old). Sparks were defined/compared in the center and periphery of the cell. Co-immunolocalization of RyRs with dihydropyridine receptors (DHPR) was used to estimate dyad formation, while the development of T tubules was studied using di-8-ANEPPS and diIC12. Our results indicate that in NB cells, Ca(2+) sparks exhibited lower amplitude (1.7+/-0.5 vs. 3.6+/-1.7 F/F(0)), shorter duration (47+/-3.2 vs. 54.1+/-3 ms), and larger width (1.7+/-0.8 vs. 1.2+/-0.4 microm) than in adult. Although no significant changes were observed in the overall frequency, central sparks increased from approximately 60% at 0-1 day to 82% at 7-9 days. While immunolocalization revealed many central release sites at 7-8 days, fluorescence labeling of the plasma membrane showed less abundant internal T tubules. This could imply that although during the first week, release sites emerge forming dyads with DHPR-containing T tubules; some of these T tubules may not be connected to the surface, explaining the RyR quiescence during E-C coupling in NB.
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Affiliation(s)
- Rose M Snopko
- Department of Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153, USA
| | - Josefina Ramos-Franco
- Department of Molecular Biophysics and Physiology, Rush University, Chicago, IL 60612, USA
| | - Alessandro Di Maio
- Department of Cell and Developmental Biology, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Kimberly L Karko
- Department of Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153, USA
| | - Christopher Manley
- Department of Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153, USA
| | - Erika Piedras-Rentería
- Department of Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153, USA
| | - Rafael Mejía-Alvarez
- Department of Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153, USA.
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Pang Y, Bounelis P, Chatham JC, Marchase RB. Hexosamine pathway is responsible for inhibition by diabetes of phenylephrine-induced inotropy. Diabetes 2004; 53:1074-81. [PMID: 15047624 DOI: 10.2337/diabetes.53.4.1074] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Hyperglycemia diminishes positive inotropic responses to agonists that activate phospholipase C (PLC) and generate inositol trisphosphate (1,4,5). The mechanisms underlying both the inotropic responses and hyperglycemia's effects on them remain undetermined, but data from isolated cardiomyocytes suggest the involvement of capacitative Ca(2+) entry (CCE), the influx of Ca(2+) through plasma membrane channels activated in response to depletion of endoplasmic or sarcoplasmic reticulum Ca(2+) stores. In neonatal rat cardiomyocytes, hyperglycemia decreased CCE induced by PLC-mediated agonists. The attenuation of CCE was also seen with glucosamine, and the inhibition by hyperglycemia was prevented by azaserine, thereby implicating hexosamine biosynthesis as the responsible metabolic pathway. In the current study, the importance of hexosamine metabolites to hyperglycemia's effects on inotropic responses was examined in isolated perfused rat hearts. The inhibition by hyperglycemia of phenylephrine-induced inotropy was reversed with azaserine and mimicked by glucosamine. An independent inhibitor of CCE, SKF96365, was also effective in blunting inotropy. These treatments did not inhibit inotropy induced by activation of adenylate cyclase through beta-adrenergic receptors. These data thus implicate CCE in responses to PLC-mediated agonists in the intact heart and point to the hexosamine pathway's negative effect on CCE as being central to the inhibition seen with hyperglycemia.
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Affiliation(s)
- Yi Pang
- Department of Cell Biology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
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Hunton DL, Zou L, Pang Y, Marchase RB. Adult rat cardiomyocytes exhibit capacitative calcium entry. Am J Physiol Heart Circ Physiol 2003; 286:H1124-32. [PMID: 14630640 DOI: 10.1152/ajpheart.00162.2003] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Capacitative Ca(2+) entry (CCE) refers to the influx of Ca(2+) through plasma membrane channels activated on depletion of endoplasmic-sarcoplasmic reticulum Ca(2+) stores. We utilized two Ca(2+)-sensitive dyes (one monitoring cytoplasmic free Ca(2+) and the other free Ca(2+) within the sarcoplasmic reticulum) to determine whether adult rat ventricular myocytes exhibit CCE. Treatments with inhibitors of the sarcoplasmic endoplasmic reticulum Ca(2+)-ATPases were not efficient in releasing Ca(2+) from stores. However, when these inhibitors were coupled with either Ca(2+) ionophores or angiotensin II (an agonist generating inositol 1,4,5 trisphosphate), depletion of stores was observed. This depletion was accompanied by a significant influx of extracellular Ca(2+) characteristic of CCE. CCE was also observed when stores were depleted with caffeine. This influx of Ca(2+) was sensitive to four inhibitors of CCE (glucosamine, lanthanum, gadolinium, and SKF-96365) but not to inhibitors of L-type channels or the Na(+)/Ca(2+) exchanger. In the whole cell configuration, an inward current of approximately 0.7 pA/pF at -90 mV was activated when a Ca(2+) chelator or inositol (1,4,5)-trisphosphate was included in the pipette or when Ca(2+) stores were depleted with a Ca(2+)-ATPase inhibitor and ionophore. The current was maximal at hyperpolarizing voltages and inwardly rectified. The channel was relatively permeant to Ca(2+) and Ba(2+) but only poorly to Mg(2+) or Mn(2+). Taken together, these data support the existence of CCE in adult cardiomyocytes, a finding with likely implications to physiological responses to phospholipase C-generating agonists.
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Affiliation(s)
- Dacia L Hunton
- Dept. of Cell Biology, Univ. of Alabama at Birmingham, Birmingham, AL 35294-0005, USA
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Trafford AW, Díaz ME, Eisner DA. Coordinated control of cell Ca(2+) loading and triggered release from the sarcoplasmic reticulum underlies the rapid inotropic response to increased L-type Ca(2+) current. Circ Res 2001; 88:195-201. [PMID: 11157672 DOI: 10.1161/01.res.88.2.195] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The aim of this study was to investigate how sarcoplasmic reticulum (SR) Ca(2+) content and systolic Ca(2+) are controlled when Ca(2+) entry into the cell is varied. Experiments were performed on voltage-clamped rat and ferret ventricular myocytes loaded with fluo-3 to measure intracellular Ca(2+) concentration ([Ca(2+)](i)). Increasing external Ca(2+) concentration ([Ca(2+)](o)) from 1 to 2 mmol/L increased the amplitude of the systolic Ca(2+) transient with no effect on SR Ca(2+) content. This constancy of SR content is shown to result because the larger Ca(2+) transient activates a larger Ca(2+) efflux from the cell that balances the increased influx. Decreasing [Ca(2+)](o) to 0.2 mmol/L decreased systolic Ca(2+) but produced a small increase of SR Ca(2+) content. This increase of SR Ca(2+) content is due to a decreased release of Ca(2+) from the SR resulting in decreased loss of Ca(2+) from the cell. An increase of [Ca(2+)](o) has two effects: (1) increasing the fraction of SR Ca(2+) content, which is released on depolarization and (2) increasing Ca(2+) entry into the cell. The results of this study show that the combination of these effects results in rapid changes in the amplitude of the systolic Ca(2+) transient. In support of this, the changes of amplitude of the transient occur more quickly following changes of [Ca(2+)](o) than following refilling of the SR after depletion with caffeine. We conclude that the coordinated control of increased Ca(2+) entry and greater fractional release of Ca(2+) is an important factor in regulating excitation-contraction coupling.
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Affiliation(s)
- A W Trafford
- Unit of Cardiac Physiology, University of Manchester, Manchester,
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Haddock PS, Coetzee WA, Cho E, Porter L, Katoh H, Bers DM, Jafri MS, Artman M. Subcellular [Ca2+]i gradients during excitation-contraction coupling in newborn rabbit ventricular myocytes. Circ Res 1999; 85:415-27. [PMID: 10473671 DOI: 10.1161/01.res.85.5.415] [Citation(s) in RCA: 129] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The central role of T-tubule and sarcoplasmic reticulum (SR) diadic junctions in excitation-contraction (EC) coupling in adult (AD) ventricular myocytes suggests that their absence in newborn (NB) cells may manifest as an altered EC coupling phenotype. We used confocal microscopy to compare fluo-3 [Ca2+]i transients in the subsarcolemmal space and cell center of field-stimulated NB and AD rabbit ventricular myocytes. Peak systolic [Ca2+]i occurred sooner and was higher in the subsarcolemmal space compared with the cell center in NB myocytes. In AD myocytes, [Ca2+]i rose and declined with similar profiles at the cell center and subsarcolemmal space. Disabling the SR (10 micromol/L thapsigargin) slowed the rate of rise and decline of Ca2+ in AD myocytes but did not alter Ca2+ transient kinetics in NB myocytes. In contrast to adults, localized SR Ca2+ release events ("Ca2+ sparks") occurred predominantly at the cell periphery of NB myocytes. Immunolabeling experiments demonstrated overlapping distributions of the Na(+)-Ca2+ exchanger and ryanodine receptors (RyR2) in AD myocytes. In contrast, RyR2s were spatially separated from the sarcolemma in NB myocytes. Confocal sarcolemmal imaging of di-8-ANEPPS-treated myocytes confirmed an extensive T-tubule network in AD cells, and that T-tubules are absent in NB myocytes. A mathematical model of subcellular Ca2+ dynamics predicts that Ca2+ flux via the Na(+)-Ca2+ exchanger during an action potential can account for the subsarcolemmal Ca2+ gradients in NB myocytes. Spatial separation of sarcolemmal Ca2+ entry from SR Ca2+ release channels may minimize the role of SR Ca2+ release during normal EC coupling in NB ventricular myocytes.
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Affiliation(s)
- P S Haddock
- Departments of Pediatrics, New York University Medical Center, New York, NY 10016, USA
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