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Yeow SQZ, Loh KWZ, Soong TW. Calcium Channel Splice Variants and Their Effects in Brain and Cardiovascular Function. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2021; 1349:67-86. [DOI: 10.1007/978-981-16-4254-8_5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Ben-Johny M, Dick IE, Sang L, Limpitikul WB, Kang PW, Niu J, Banerjee R, Yang W, Babich JS, Issa JB, Lee SR, Namkung H, Li J, Zhang M, Yang PS, Bazzazi H, Adams PJ, Joshi-Mukherjee R, Yue DN, Yue DT. Towards a Unified Theory of Calmodulin Regulation (Calmodulation) of Voltage-Gated Calcium and Sodium Channels. Curr Mol Pharmacol 2016; 8:188-205. [PMID: 25966688 DOI: 10.2174/1874467208666150507110359] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2015] [Revised: 01/29/2015] [Accepted: 04/20/2015] [Indexed: 12/13/2022]
Abstract
Voltage-gated Na and Ca(2+) channels represent two major ion channel families that enable myriad biological functions including the generation of action potentials and the coupling of electrical and chemical signaling in cells. Calmodulin regulation (calmodulation) of these ion channels comprises a vital feedback mechanism with distinct physiological implications. Though long-sought, a shared understanding of the channel families remained elusive for two decades as the functional manifestations and the structural underpinnings of this modulation often appeared to diverge. Here, we review recent advancements in the understanding of calmodulation of Ca(2+) and Na channels that suggest a remarkable similarity in their regulatory scheme. This interrelation between the two channel families now paves the way towards a unified mechanistic framework to understand vital calmodulin-dependent feedback and offers shared principles to approach related channelopathic diseases. An exciting era of synergistic study now looms.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | - David T Yue
- Department of Biomedical Engineering, The Johns Hopkins University School of Medicine, Ross Building, Room 713, 720 Rutland Avenue, Baltimore, MD 21205, USA.
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Ben-Johny M, Yue DT. Calmodulin regulation (calmodulation) of voltage-gated calcium channels. ACTA ACUST UNITED AC 2014; 143:679-92. [PMID: 24863929 PMCID: PMC4035741 DOI: 10.1085/jgp.201311153] [Citation(s) in RCA: 147] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Calmodulin regulation (calmodulation) of the family of voltage-gated CaV1-2 channels comprises a prominent prototype for ion channel regulation, remarkable for its powerful Ca(2+) sensing capabilities, deep in elegant mechanistic lessons, and rich in biological and therapeutic implications. This field thereby resides squarely at the epicenter of Ca(2+) signaling biology, ion channel biophysics, and therapeutic advance. This review summarizes the historical development of ideas in this field, the scope and richly patterned organization of Ca(2+) feedback behaviors encompassed by this system, and the long-standing challenges and recent developments in discerning a molecular basis for calmodulation. We conclude by highlighting the considerable synergy between mechanism, biological insight, and promising therapeutics.
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Affiliation(s)
- Manu Ben-Johny
- Calcium Signals Laboratory, Department of Biomedical Engineering, Department of Neuroscience, and Center for Cell Dynamics, Johns Hopkins University School of Medicine, Baltimore, MD 21205Calcium Signals Laboratory, Department of Biomedical Engineering, Department of Neuroscience, and Center for Cell Dynamics, Johns Hopkins University School of Medicine, Baltimore, MD 21205Calcium Signals Laboratory, Department of Biomedical Engineering, Department of Neuroscience, and Center for Cell Dynamics, Johns Hopkins University School of Medicine, Baltimore, MD 21205Calcium Signals Laboratory, Department of Biomedical Engineering, Department of Neuroscience, and Center for Cell Dynamics, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - David T Yue
- Calcium Signals Laboratory, Department of Biomedical Engineering, Department of Neuroscience, and Center for Cell Dynamics, Johns Hopkins University School of Medicine, Baltimore, MD 21205Calcium Signals Laboratory, Department of Biomedical Engineering, Department of Neuroscience, and Center for Cell Dynamics, Johns Hopkins University School of Medicine, Baltimore, MD 21205Calcium Signals Laboratory, Department of Biomedical Engineering, Department of Neuroscience, and Center for Cell Dynamics, Johns Hopkins University School of Medicine, Baltimore, MD 21205Calcium Signals Laboratory, Department of Biomedical Engineering, Department of Neuroscience, and Center for Cell Dynamics, Johns Hopkins University School of Medicine, Baltimore, MD 21205
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Cros C, Sallé L, Warren DE, Shiels HA, Brette F. The calcium stored in the sarcoplasmic reticulum acts as a safety mechanism in rainbow trout heart. Am J Physiol Regul Integr Comp Physiol 2014; 307:R1493-501. [PMID: 25377479 PMCID: PMC4269670 DOI: 10.1152/ajpregu.00127.2014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Cardiomyocyte contraction depends on rapid changes in intracellular Ca2+. In mammals, Ca2+ influx as L-type Ca2+ current (ICa) triggers the release of Ca2+ from sarcoplasmic reticulum (SR) and Ca2+-induced Ca2+ release (CICR) is critical for excitation-contraction coupling. In fish, the relative contribution of external and internal Ca2+ is unclear. Here, we characterized the role of ICa to trigger SR Ca2+ release in rainbow trout ventricular myocytes using ICa regulation by Ca2+ as an index of CICR. ICa was recorded with a slow (EGTA) or fast (BAPTA) Ca2+ chelator in control and isoproterenol conditions. In the absence of β-adrenergic stimulation, the rate of ICa inactivation was not significantly different in EGTA and BAPTA (27.1 ± 1.8 vs. 30.3 ± 2.4 ms), whereas with isoproterenol (1 μM), inactivation was significantly faster with EGTA (11.6 ± 1.7 vs. 27.3 ± 1.6 ms). When barium was the charge carrier, inactivation was significantly slower in both conditions (61.9 ± 6.1 vs. 68.0 ± 8.7 ms, control, isoproterenol). Quantification revealed that without isoproterenol, only 39% of ICa inactivation was due to Ca2+, while with isoproterenol, inactivation was Ca2+-dependent (∼65%) and highly reliant on SR Ca2+ (∼46%). Thus, SR Ca2+ is not released in basal conditions, and ICa is the main trigger of contraction, whereas during a stress response, SR Ca2+ is an important source of cytosolic Ca2+. This was not attributed to differences in SR Ca2+ load because caffeine-induced transients were not different in both conditions. Therefore, Ca2+ stored in SR of trout cardiomyocytes may act as a safety mechanism, allowing greater contraction when higher contractility is required, such as stress or exercise.
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Affiliation(s)
- Caroline Cros
- Faculty of Life Sciences, The University of Manchester, Core Technology Facility, Manchester, United Kingdom; and
| | | | - Daniel E Warren
- Faculty of Life Sciences, The University of Manchester, Core Technology Facility, Manchester, United Kingdom; and
| | - Holly A Shiels
- Faculty of Life Sciences, The University of Manchester, Core Technology Facility, Manchester, United Kingdom; and
| | - Fabien Brette
- Faculty of Life Sciences, The University of Manchester, Core Technology Facility, Manchester, United Kingdom; and
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Christel C, Lee A. Ca2+-dependent modulation of voltage-gated Ca2+ channels. Biochim Biophys Acta Gen Subj 2011; 1820:1243-52. [PMID: 22223119 DOI: 10.1016/j.bbagen.2011.12.012] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2011] [Revised: 12/15/2011] [Accepted: 12/16/2011] [Indexed: 01/06/2023]
Abstract
BACKGROUND Voltage-gated (Cav) Ca2+ channels are multi-subunit complexes that play diverse roles in a wide variety of tissues. A fundamental mechanism controlling Cav channel function involves the Ca2+ ions that permeate the channel pore. Ca2+ influx through Cav channels mediates feedback regulation to the channel that is both negative (Ca2+-dependent inactivation, CDI) and positive (Ca2+-dependent facilitation, CDF). SCOPE OF REVIEW This review highlights general mechanisms of CDI and CDF with an emphasis on how these processes have been studied electrophysiologically in native and heterologous expression systems. MAJOR CONCLUSIONS Electrophysiological analyses have led to detailed insights into the mechanisms and prevalence of CDI and CDF as Cav channel regulatory mechanisms. All Cav channel family members undergo some form of Ca2+-dependent feedback that relies on CaM or a related Ca2+ binding protein. Tremendous progress has been made in characterizing the role of CaM in CDI and CDF. Yet, what contributes to the heterogeneity of CDI/CDF in various cell-types and how Ca2+-dependent regulation of Cav channels controls Ca2+ signaling remain largely unexplored. GENERAL SIGNIFICANCE Ca2+ influx through Cav channels regulates diverse physiological events including excitation-contraction coupling in muscle, neurotransmitter and hormone release, and Ca2+-dependent gene transcription. Therefore, the mechanisms that regulate channels, such as CDI and CDF, can have a large impact on the signaling potential of excitable cells in various physiological contexts. This article is part of a Special Issue entitled Biochemical, biophysical and genetic approaches to intracellular calcium signaling.
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Affiliation(s)
- Carl Christel
- Department of Molecular Physiology and Biophysics, University of Iowa, Iowa City, IA 52242, USA
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Movafagh S, Cleemann L, Morad M. Regulation of cardiac Ca(2+) channel by extracellular Na(+). Cell Calcium 2011; 49:162-73. [PMID: 21349579 DOI: 10.1016/j.ceca.2011.01.008] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2011] [Accepted: 01/20/2011] [Indexed: 11/25/2022]
Abstract
Hyponatremia is a predictor of poor cardiovascular outcomes during acute myocardial infarction and in the setting of preexisting heart failure [1]. There are no definitive mechanisms as to how hyponatremia suppresses cardiac function. In this report we provide evidence for direct down-regulation of Ca(2+) channel current in response to low serum Na(+). In voltage-clamped rat ventricular myocytes or HEK 293 cells expressing the L-type Ca(2+) channel, a 15mM drop in extracellular Na(+) suppressed the Ca(2+) current by ∼15%; with maximal suppression of ∼30% when Na(+) levels were reduced to 100mM or less. The suppressive effects of low Na(+) on I(Ca), in part, depended on the substituting monovalent species (Li(+), Cs(+), TEA(+)), but were independent of phosphorylation state of the channel and possible influx of Ca(2+) on Na(+)/Ca(2+) exchanger. Acidification sensitized the Ca(2+) channel current to Na(+) withdrawal. Collectively our data suggest that Na(+) and H(+) may interact with regulatory site(s) at the outer recesses of the Ca(2+) channel pore thereby directly modulating the electro-diffusion of the permeating divalents (Ca(2+), Ba(2+)).
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Affiliation(s)
- Shahrzad Movafagh
- Department of Pharmacology, Georgetown University Medical Center, Washington, DC 20007, USA
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Abstract
Triggered activity in cardiac muscle and intracellular Ca2+ have been linked in the past. However, today not only are there a number of cellular proteins that show clear Ca2+ dependence but also there are a number of arrhythmias whose mechanism appears to be linked to Ca2+-dependent processes. Thus we present a systematic review of the mechanisms of Ca2+ transport (forward excitation-contraction coupling) in the ventricular cell as well as what is known for other cardiac cell types. Second, we review the molecular nature of the proteins that are involved in this process as well as the functional consequences of both normal and abnormal Ca2+ cycling (e.g., Ca2+ waves). Finally, we review what we understand to be the role of Ca2+ cycling in various forms of arrhythmias, that is, those associated with inherited mutations and those that are acquired and resulting from reentrant excitation and/or abnormal impulse generation (e.g., triggered activity). Further solving the nature of these intricate and dynamic interactions promises to be an important area of research for a better recognition and understanding of the nature of Ca2+ and arrhythmias. Our solutions will provide a more complete understanding of the molecular basis for the targeted control of cellular calcium in the treatment and prevention of such.
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Affiliation(s)
- Henk E D J Ter Keurs
- Department of Medicine, Physiology and Biophysics, University of Calgary, Alberta, Canada
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Boyden PA, ter Keurs H. Would modulation of intracellular Ca2+ be antiarrhythmic? Pharmacol Ther 2005; 108:149-79. [PMID: 16038982 DOI: 10.1016/j.pharmthera.2005.03.011] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2005] [Accepted: 03/22/2005] [Indexed: 01/10/2023]
Abstract
Under several types of conditions, reversal of steps of excitation-contraction coupling (RECC) can give rise to nondriven electrical activity. In this review we explore those conditions for several cardiac cell types (SA, atrial, Purkinje, ventricular cells). We find that abnormal spontaneous Ca2+ release from intracellular Ca2+ stores, aberrant Ca2+ influx from sarcolemmal channels or abnormal Ca2+ surges in nonuniform muscle can be the initiators of the RECC. Often, with such increases in Ca2+, spontaneous Ca2+ waves occur and lead to membrane depolarizations. Because the change in membrane voltage is produced by Ca2+-dependent changes in ion channel function, we also review here what is known about the molecular interaction of Ca2+ and several Ca2+-dependent processes, including the intracellular Ca2+ release channels implicated in the genetic basis of some forms of human arrhythmias. Finally, we review what is known about the effectiveness of several agents in modifying such Ca2+-dependent arrhythmias.
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Affiliation(s)
- Penelope A Boyden
- Department of Pharmacology, Center for Molecular Therapeutics, Columbia University, NY 10032, USA.
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Brette F, Leroy J, Le Guennec JY, Sallé L. Ca2+ currents in cardiac myocytes: Old story, new insights. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2005; 91:1-82. [PMID: 16503439 DOI: 10.1016/j.pbiomolbio.2005.01.001] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Calcium is a ubiquitous second messenger which plays key roles in numerous physiological functions. In cardiac myocytes, Ca2+ crosses the plasma membrane via specialized voltage-gated Ca2+ channels which have two main functions: (i) carrying depolarizing current by allowing positively charged Ca2+ ions to move into the cell; (ii) triggering Ca2+ release from the sarcoplasmic reticulum. Recently, it has been suggested than Ca2+ channels also participate in excitation-transcription coupling. The purpose of this review is to discuss the physiological roles of Ca2+ currents in cardiac myocytes. Next, we describe local regulation of Ca2+ channels by cyclic nucleotides. We also provide an overview of recent studies investigating the structure-function relationship of Ca2+ channels in cardiac myocytes using heterologous system expression and transgenic mice, with descriptions of the recently discovered Ca2+ channels alpha(1D) and alpha(1E). We finally discuss the potential involvement of Ca2+ currents in cardiac pathologies, such as diseases with autoimmune components, and cardiac remodeling.
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Affiliation(s)
- Fabien Brette
- School of Biomedical Sciences, University of Leeds, Worsley Building Leeds, LS2 9NQ, UK.
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Abstract
The relative contributions of voltage- and Ca(2+)-dependent mechanisms of inactivation to the decay of L-type Ca(2+) channel currents (I(CaL)) is an old story to which recent results have given an unexpected twist. In cardiac myocytes voltage-dependent inactivation (VDI) was thought to be slow and Ca(2+)-dependent inactivation (CDI) resulting from Ca(2+) influx and Ca(2+)-induced Ca(2+)-release (CICR) from the sarcoplasmic reticulum provided an automatic negative feedback mechanism to limit Ca(2+) entry and the contribution of I(CaL) to the cardiac action potential. Physiological modulation of I(CaL) by Beta-adrenergic and muscarinic agonists then involved essentially more or less of the same by enhancing or reducing Ca(2+) channel activity, Ca(2+) influx, sarcoplasmic reticulum load and thus CDI. Recent results on the other hand place VDI at the centre of the regulation of I(CaL). Under basal conditions it has been found that depolarization increases the probability that an ion channel will show rapid VDI. This is prevented by Beta-adrenergic stimulation. Evidence also suggests that a channel which shows rapid VDI inactivates before CDI can become effective. Therefore the contributions of VDI and CDI to the decay of I(CaL) are determined by the turning on, by depolarization, and the turning off, by phosphorylation, of the mechanism of rapid VDI. The physiological implications of these ideas are that under basal conditions the contribution of I(CaL) to the action potential will be determined largely by voltage and by Ca(2+) following Beta-adrenergic stimulation.
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Affiliation(s)
- Ian Findlay
- CNRS UMR 6542, Faculté des Sciences, Université de Tours, Parc de Grandmont, 37200 Tours, France.
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11
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Brette F, Lacampagne A, Sallé L, Findlay I, Le Guennec JY. Intracellular Cs+ activates the PKA pathway, revealing a fast, reversible, Ca2+-dependent inactivation of L-type Ca2+ current. Am J Physiol Cell Physiol 2003; 285:C310-8. [PMID: 12686515 DOI: 10.1152/ajpcell.00368.2002] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Inactivation of the L-type Ca2+ current (ICaL) was studied in isolated guinea pig ventricular myocytes with different ionic solutions. Under basal conditions, ICaL of 82% of cells infused with Cs+-based intracellular solutions showed enhanced amplitude with multiphasic decay and diastolic depolarization-induced facilitation. The characteristics of ICaL in this population of cells were not due to contamination by other currents or an artifact. These phenomena were reduced by ryanodine, caffeine, cyclopiazonic acid, the protein kinase A inhibitor H-89, and the cAMP-dependent protein kinase inhibitor. Forskolin and isoproterenol increased ICaL by only approximately 60% in these cells. Cells infused with either N-methyl-d-glucamine or K+-based intracellular solutions did not show multiphasic decay or facilitation under basal conditions. Isoproterenol increased ICaL by approximately 200% in these cells. In conclusion, we show that multiphasic inactivation of ICaL is due to Ca2+-dependent inactivation that is reversible on a time scale of tens of milliseconds. Cs+ seems to activate the cAMP-dependent protein kinase pathway when used as a substitute for K+ in the pipette solution.
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Affiliation(s)
- Fabien Brette
- Centre National de la Recherche Scientifique Unité Mixte de Recherche 6542, Université de Tours, France.
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12
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Abstract
A unique transient outward K(+) current (I(to)) has been described to result from the removal of extracellular Ca(2+) from ventricular myocytes of the guinea pig (15). This study addressed the question of whether this current represented K(+)-selective I(to) or the efflux of K(+) via L-type Ca(2+) channels. This outward current was inhibited by Cd(2+), Ni(2+), Co(2+), and La(3+) as well as by nifedipine. All of these compounds were equally effective inhibitors of the L-type Ca(2+) current. The current was not inhibited by 4-aminopyridine. Apparent inhibition of the outward current by extracellular Ca(2+) was shown to result from the displacement of the reversal potential of cation flux through L-type Ca(2+) channels. The current was found not to be K(+) selective but also permeant to Cs(+). The voltage dependence of inactivation of the outward current was identical to that of the L-type Ca(2+) current. It is concluded that extracellular Ca(2+) does not mask an A-type K(+) current in guinea pig ventricular myocytes.
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Affiliation(s)
- Ian Findlay
- Faculté des Sciences, Centre National de la Recherche Scientifique UMR 6542, Université de Tours, France.
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Findlay I. Voltage- and cation-dependent inactivation of L-type Ca2+ channel currents in guinea-pig ventricular myocytes. J Physiol 2002; 541:731-40. [PMID: 12068036 PMCID: PMC2290374 DOI: 10.1113/jphysiol.2002.019729] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
L-type Ca2+ channel currents in native ventricular myocytes inactivate according to voltage- and Ca2+-dependent processes. This study sought to examine the effect of beta-adrenergic stimulation on the contributions of voltage and Ca2+ to Ca2+ current decay. Ventricular myocytes were enzymatically isolated from guinea-pig hearts. Inward whole-cell Cd2+-sensitive L-type Ca2+ channel currents were recorded with the patch clamp technique and comparison was made between inward currents carried by Ca2+ and either Ba2+, Sr2+ or Na+. In control conditions the decay of Ca2+ currents was faster than Ba2+, Sr2+ or Na+ currents at negative voltages while at positive voltages there was no difference. The relationship between voltage and inactivation for Ca2+ currents was bell-shaped, while that for Ba2+, Sr2+, and Na+ currents was sigmoid. Thus depolarisation progressively replaced Ca2+-dependent inactivation in the fast phase of decay of Ca2+ channel currents with rapid voltage-dependent inactivation. In the presence of isoproterenol (isoprenaline) the decay of Ca2+ currents was faster than Ba2+, Sr2+ or Na+ currents at all measured voltages (-40 to +30 mV). The relationship between voltage and inactivation for Ca2+, Ba2+ and Sr2+ currents was bell-shaped, while that for Na+ currents was sigmoid with less inactivation than under control conditions. Therefore the fast phase of decay of Ca2+ channel currents was now almost entirely due to Ca2+. It is concluded that the relative contributions of Ca2+- and voltage-dependent mechanisms of inactivation of L-type Ca2+ channels in native cardiac myocytes are modulated by beta-adrenergic stimulation influencing the amount of rapid voltage-dependent inactivation.
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Affiliation(s)
- Ian Findlay
- CNRS UMR 6542, Faculté des Sciences, Université de Tours, France.
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15
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Kneller J, Ramirez RJ, Chartier D, Courtemanche M, Nattel S. Time-dependent transients in an ionically based mathematical model of the canine atrial action potential. Am J Physiol Heart Circ Physiol 2002; 282:H1437-51. [PMID: 11893581 DOI: 10.1152/ajpheart.00489.2001] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Ionically based cardiac action potential (AP) models are based on equations with singular Jacobians and display time-dependent AP and ionic changes (transients), which may be due to this mathematical limitation. The present study evaluated transients during long-term simulated activity in a mathematical model of the canine atrial AP. Stimulus current assignment to a specific ionic species contributed to stability. Ionic concentrations were least disturbed with the K(+) stimulus current. All parameters stabilized within 6-7 h. Inward rectifier, Na(+)/Ca(2+) exchanger, L-type Ca(2+), and Na(+)-Cl(-) cotransporter currents made the greatest contributions to stabilization of intracellular [K(+)], [Na(+)], [Ca(2+)], and [Cl(-)], respectively. Time-dependent AP shortening was largely due to the outward shift of Na(+)/Ca(2+) exchange related to intracellular Na(+) (Na) accumulation. AP duration (APD) reached a steady state after approximately 40 min. AP transients also occurred in canine atrial preparations, with the APD decreasing by approximately 10 ms over 35 min, compared with approximately 27 ms in the model. We conclude that model APD and ionic transients stabilize with the appropriate stimulus current assignment and that the mathematical limitation of equation singularity does not preclude meaningful long-term simulations. The model agrees qualitatively with experimental observations, but quantitative discrepancies highlight limitations of long-term model simulations.
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Affiliation(s)
- James Kneller
- Research Center, Montreal Heart Institute, Montreal, Quebec H1T 1C8, Canada
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Leroy J, Lignon JM, Gannier F, Argibay JA, Malécot CO. Caffeine-induced immobilization of gating charges in isolated guinea-pig ventricular heart cells. Br J Pharmacol 2002; 135:721-34. [PMID: 11834620 PMCID: PMC1573184 DOI: 10.1038/sj.bjp.0704520] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
The effects of 10 mM caffeine (CAF) on intramembrane charge movements (ICM) were studied in isolated guinea-pig ventricular heart cells with the whole-cell patch-clamp technique. In the presence of CAF, the properties (voltage dependence, maximum Q(ON) [Q(max)], availability with voltage) of Q(ON) charge activated from -110 mV were barely affected. Following a 100 ms prepulse to -50 mV to decrease the participation of charges originating from Na channels, the voltage dependence of Q(ON) was shifted by 5 mV (negative component) and by 10 mV (positive component) towards negative potentials, and Q(max) was depressed by 16.5%. CAF drastically reduced in a time- and voltage-dependent manner Q(OFF) on repolarization to -50 mV, the effects being greater at positive potentials. CAF-induced Q(OFF) immobilization could be almost entirely removed by repolarization to voltages as negative as -170 mV. In these conditions, the voltage-dependence of Q(OFF) (repolarization to +30 to -170 mV) was shifted by 17 mV (negative component) and 30 mV (positive component) towards negative potentials, suggesting an interconversion into charge 2. Most of CAF effects were suppressed when the sarcoplasmic reticulum (SR) was not functional or when the cells were loaded with BAPTA-AM. We conclude that CAF effects on ICM are likely due to Ca(2+) ions released from the SR, and which accumulate in the subsarcolemmal fuzzy spaces in the vicinity of the Ca channels. Because CAF effects were more pronounced on Q(OFF) than on Q(ON) the channels have likely to open before Ca(2+) ions could affect their gating properties. It is speculated that such an effect on gating charges might contribute to the Ca-induced inactivation of the Ca current.
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Affiliation(s)
- Jérôme Leroy
- CNRS UMR 6542, Physiologie des Cellules Cardiaques et Vasculaires, Faculté des Sciences, Parc de Grandmont, 37200 Tours, France
| | - Jacques M Lignon
- CNRS UMR 6542, Physiologie des Cellules Cardiaques et Vasculaires, Faculté des Sciences, Parc de Grandmont, 37200 Tours, France
| | - François Gannier
- CNRS UMR 6542, Physiologie des Cellules Cardiaques et Vasculaires, Faculté des Sciences, Parc de Grandmont, 37200 Tours, France
| | - Jorge A Argibay
- CNRS UMR 6542, Physiologie des Cellules Cardiaques et Vasculaires, Faculté des Sciences, Parc de Grandmont, 37200 Tours, France
| | - Claire O Malécot
- CNRS UMR 6542, Physiologie des Cellules Cardiaques et Vasculaires, Faculté des Sciences, Parc de Grandmont, 37200 Tours, France
- Author for correspondence:
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17
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Mitarai S, Kaibara M, Yano K, Taniyama K. Two distinct inactivation processes related to phosphorylation in cardiac L-type Ca(2+) channel currents. Am J Physiol Cell Physiol 2000; 279:C603-10. [PMID: 10942710 DOI: 10.1152/ajpcell.2000.279.3.c603] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We investigated the inactivation process of macroscopic cardiac L-type Ca(2+) channel currents using the whole cell patch-clamp technique with Na(+) as the current carrier. The inactivation process of the inward currents carried by Na(+) through the channel consisted of two components >0 mV. The time constant of the faster inactivating component (30.6 +/- 2.2 ms at 0 mV) decreased with depolarization, but the time constant of the slower inactivating component (489 +/- 21 ms at 0 mV) was not significantly influenced by the membrane potential. The inactivation process in the presence of isoproterenol (100 nM) consisted of a single component (538 +/- 60 ms at 0 mV). A protein kinase inhibitor, H-89, decreased the currents and attenuated the effects of isoproterenol. In the presence of cAMP (500 microM), the inactivation process consisted of a single slow component. We propose that the faster inactivating component represents a kinetic of the dephosphorylated or partially phosphorylated channel, and phosphorylation converts the kinetics into one with a different voltage dependency.
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Affiliation(s)
- S Mitarai
- Department of Pharmacology, Nagasaki University, School of Medicine, Nagasaki 8528523, Japan
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18
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Delgado C, Artiles A, Gómez AM, Vassort G. Frequency-dependent increase in cardiac Ca2+ current is due to reduced Ca2+ release by the sarcoplasmic reticulum. J Mol Cell Cardiol 1999; 31:1783-93. [PMID: 10525417 DOI: 10.1006/jmcc.1999.1023] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
"Ca(2+)-current facilitation" describes several features of increase in current amplitude often associated with a reduction in inactivation rate. The aim of this study was to investigate the mechanism of frequency-dependent increase in L-type Ca2+ current, I(Ca) taking advantage of recent knowledge on the control of Ca2+ current inactivation in cardiac cells. The frequency-dependent increase in I(Ca) was studied in adult rat ventricular myocytes using the whole-cell patch-clamp technique. I(Ca) was elicited by a train of 200-ms depolarizing pulses to +20 mV applied at various frequencies (0.2 up to 1.3 Hz). The increase in frequency induced a rate-dependent enhancement of I(Ca), or facilitation phenomena. In most cells, that showed two inactivation phases of I(Ca), facilitation was mainly related to slowing of the fast I(Ca) inactivation phase that occurred besides increase in peak I(Ca) amplitude. Both the decrease and slowing of the fast component of inactivation phase were attenuated on beta -adrenergic-stimulated current. Frequency-dependent I(Ca) facilitation paralleled a reduction in Ca2+ transient measured with fluo-3. After blocking sarcoplasmic reticulum-Ca2+ release by thapsigargin, the fast I(Ca) inactivation phase was reduced and facilitation was eliminated. Facilitation could not then be restored by 1 microM isoprenaline. Thus in rat ventricular myocytes, frequency-dependent facilitation of I(Ca)reflects a reduced Ca(2+)-dependent inactivation consecutive, in most part, to reduced Ca2+ load and Ca2+ release by the sarcoplasmic reticulum rather than being an intrinsic characteristic of the L-type Ca2+ channel.
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Affiliation(s)
- C Delgado
- Institute of Pharmacology and Toxicology (CSIC-UCM), Universidad Complutense, Madrid, Spain
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19
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Matsuda T, Kurata Y. Effects of nicardipine and bupivacaine on early after depolarization in rabbit sinoatrial node cells: a possible mechanism of bupivacaine-induced arrhythmias. GENERAL PHARMACOLOGY 1999; 33:115-25. [PMID: 10461849 DOI: 10.1016/s0306-3623(99)00004-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The effects of nicardipine and bupivacaine on early afterdepolarizations (EADs) were investigated in rabbit sinoatrial (SA) nodes using the conventional microelectrode technique. In a nominally Ca2+ -free, Mg2+ -free solution, addition of 0.5 mM Sr2+ produced EADs following prolongation of action potential duration. Nicardipine (10 microM) as well as Mg2+ (1 mM), both of which block the L-type Ca2+ channel current (iCa,L), abolished Sr2+ -induced EADs. Bupivacaine (5 microM), blocking the delayed rectifier K+ current (iK), facilitated the generation of EADs in the Sr2+ solution containing 1 mM Mg2+. The EADs in Sr2+ solution and the effect of bupivacaine were well simulated by the mathematical model when enhancement of slowly inactivating iCa,L and suppression of iK were assumed. Bupivacaine may cause sinus arrhythmias by facilitating EAD generation in SA node cells.
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Affiliation(s)
- T Matsuda
- Department of Anesthesiology, Kanazawa Medical University, Ishikawa, Japan.
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20
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Cens T, Restituito S, Charnet P. Regulation of Ca-sensitive inactivation of a 1-type Ca2+ channel by specific domains of beta subunits. FEBS Lett 1999; 450:17-22. [PMID: 10350049 DOI: 10.1016/s0014-5793(99)00463-9] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Ca2+ channel auxiliary beta subunits have been shown to modulate voltage-dependent inactivation of various types of Ca2+ channels. The beta1 and beta2 subunits, that are differentially expressed with the L-type alpha1 Ca2+ channel subunit in heart, muscle and brain, can specifically modulate the Ca2+-dependent inactivation kinetics. Their expression in Xenopus oocytes with the alpha1C subunit leads, in both cases, to biphasic Ca2+ current decays, the second phase being markedly slowed by expression of the beta2 subunit. Using a series of beta subunit deletion mutants and chimeric constructs of beta1 and beta2 subunits, we show that the inhibitory site located on the amino-terminal region of the beta2a subunit is the major element of this regulation. These results thus suggest that different splice variants of the beta2 subunit can modulate, in a specific way, the Ca2+ entry through L-type Ca2+ channels in different brain or heart regions.
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Affiliation(s)
- T Cens
- CRBM, CNRS UPR 1086, IFR 24, Montpellier, France
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21
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Cens T, Restituito S, Galas S, Charnet P. Voltage and calcium use the same molecular determinants to inactivate calcium channels. J Biol Chem 1999; 274:5483-90. [PMID: 10026161 DOI: 10.1074/jbc.274.9.5483] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
During sustained depolarization, voltage-gated Ca2+ channels progressively undergo a transition to a nonconducting, inactivated state, preventing Ca2+ overload of the cell. This transition can be triggered either by the membrane potential (voltage-dependent inactivation) or by the consecutive entry of Ca2+ (Ca2+-dependent inactivation), depending on the type of Ca2+ channel. These two types of inactivation are suspected to arise from distinct underlying mechanisms, relying on specific molecular sequences of the different pore-forming Ca2+ channel subunits. Here we report that the voltage-dependent inactivation (of the alpha1A Ca2+ channel) and the Ca2+-dependent inactivation (of the alpha1C Ca2+ channel) are similarly influenced by Ca2+ channel beta subunits. The same molecular determinants of the beta subunit, and therefore the same subunit interactions, influence both types of inactivation. These results strongly suggest that the voltage and the Ca2+-dependent transitions leading to channel inactivation use homologous structures of the different alpha1 subunits and occur through the same molecular process. A model of inactivation taking into account these new data is presented.
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Affiliation(s)
- T Cens
- Centre de Recherches de Biochimie Macromoléculaire, CNRS UPR 1086, 1919 Route de Mende, F34293 Montpellier, France
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22
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Bramich NJ, Cousins HM. Effects of sympathetic nerve stimulation on membrane potential, [Ca2+]i, and force in the toad sinus venosus. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 276:H115-28. [PMID: 9887024 DOI: 10.1152/ajpheart.1999.276.1.h115] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The effects of sympathetic nerve stimulation on beat rate, force, intracellular Ca2+ concentration ([Ca2+]i) measured using fura 2, and membrane potential were recorded from the spontaneously beating toad sinus venosus. Short trains of stimuli evoked an increase in the beat rate and force. During this tachycardia the amplitude of pacemaker action potentials was not changed, but there was an increase in the basal level of [Ca2+]i with little change in peak [Ca2+]i measured during each action potential. Depletion of intracellular Ca2+ stores with caffeine (3 mM) abolished all responses to sympathetic nerve stimulation. The effects of caffeine were fully reversible. Caffeine (3 mM), in the presence of the Ca2+-ATPase inhibitor thapsigargin (30 microM), abolished irreversibly the chronotropic and inotropic responses evoked by sympathetic nerve stimulation. Ryanodine (10 microM) attenuated, but did not abolish, these responses. These results suggest that, in the toad sinus venosus, increases in force and beat rate evoked by sympathetic nerve stimulation result from the release of Ca2+ from intracellular Ca2+ stores.
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Affiliation(s)
- N J Bramich
- Department of Zoology, University of Melbourne, Parkville, Victoria, Australia 3052
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23
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Linz KW, Meyer R. Control of L-type calcium current during the action potential of guinea-pig ventricular myocytes. J Physiol 1998; 513 ( Pt 2):425-42. [PMID: 9806993 PMCID: PMC2231304 DOI: 10.1111/j.1469-7793.1998.425bb.x] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. During an action potential the L-type Ca2+ current (ICa,L) activates rapidly, then partially declines leading to a sustained inward current during the plateau phase. The reason for the sustained part of ICa,L has been investigated here. 2. In the present study the mechanisms controlling the ICa,L during an action potential were investigated quantitatively in isolated guinea-pig ventricular myocytes by whole-cell patch clamp. To measure the actual time courses of ICa,L and the corresponding L-type channel inactivation (fAP) during an action potential, action potential-clamp protocols combined with square pulses were applied. 3. Within the first 10 ms of the action potential the ICa,L rapidly inactivated by about 50 %; during the plateau phase inactivation proceeded to 95 %. Later, during repolarization, the L-type channels recovered up to 25 %. 4. The voltage-dependent component of inactivation during an action potential was determined from measurements of L-type current carried by monovalent cations. This component of inactivation proceeded rather slowly and contributed only a little to fAP. ICa,L during an action potential is thus mainly controlled by Ca2+-dependent inactivation. 5. In order to investigate the source of the Ca2+ controlling fAP, internal Ca2+ homeostasis was manipulated by the use of Ca2+ buffers (EGTA, BAPTA), by blocking Na+-Ca2+ exchange, or by blocking Ca2+ release from the sarcoplasmic reticulum (SR). Internal BAPTA markedly reduced the L-type channel inactivation during the entire action potential, whereas EGTA affected fAP only during the middle and late plateau phases. Inhibition of Na+-Ca2+ exchange markedly increased inactivation of L-type channels. Although blocking SR Ca2+ release decreased the fura-2-measured cytoplasmic Ca2+ concentration ([Ca2+]i) transient by about 90 %, it reduced L-type channel inactivation only during the initial 50 ms of the action potential. Thus, it is Ca2+ entering the cell through the L-type channels that controls the inactivation process for the majority of the action potential. Nevertheless, SR Ca2+-release contributes 40-50 % to L-type channel inactivation during the initial period of the action potential. However, the maximum extent of inactivation reached during the plateau is independent of Ca2+ released from the SR. 6. For the first time, the actual time course of L-type channel inactivation has been directly determined during an action potential under various defined [Ca2+]i conditions. Thereby, the relative contribution to ICa,L inactivation of voltage, Ca2+ entering through L-type channels, and Ca2+ being released from the SR could be directly demonstrated.
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Affiliation(s)
- K W Linz
- Physiological Institute, University of Bonn, Wilhelmstrasse 31, D-53111 Bonn, Germany
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24
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Takagi S, Kihara Y, Sasayama S, Mitsuiye T. Slow inactivation of cardiac L-type Ca2+ channel induced by cold acclimation of guinea pig. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:R348-56. [PMID: 9486291 DOI: 10.1152/ajpregu.1998.274.2.r348] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Whole cell L-type Ca2+ current was recorded in ventricular myocytes dissociated from guinea pigs that were bred at ambient temperatures ranging between daily averages of 4 and 29 degrees C. The dynamic voltage range of inactivation, as measured using 400-ms conditioning pulses and a holding potential of -40 mV, extended from -50 to -20 mV in myocytes prepared in summer. In winter, the inactivation curve was shifted to more negative potentials than in summer. Double-pulse experiments revealed that the negative shift was due to slow-inactivation kinetics. The negative shift of inactivation could be induced in myocytes prepared from animals that had been kept at 5 degrees C for > 3 wk in the summer. The negative shift in Ca2+ current inactivation could be abolished by adding guanosine 5'-O-(2-thiodiphosphate) (5 mM) to the pipette solution, but not by adding staurosporine (2 microM) or 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (100 microM) to the bath. The cold acclimation may introduce the slow inactivation of the cardiac L-type Ca2+ channel through an unknown pertussis toxin-insensitive G protein.
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Affiliation(s)
- S Takagi
- Department of Physiology, Kyoto University Graduate School of Medicine, Japan
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25
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Levi AJ, Dalton GR, Hancox JC, Mitcheson JS, Issberner J, Bates JA, Evans SJ, Howarth FC, Hobai IA, Jones JV. Role of intracellular sodium overload in the genesis of cardiac arrhythmias. J Cardiovasc Electrophysiol 1997; 8:700-21. [PMID: 9209972 DOI: 10.1111/j.1540-8167.1997.tb01834.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
A number of clinical cardiac disorders may be associated with a rise of the intracellular Na concentration (Na(i)) in heart muscle. A clear example is digitalis toxicity, in which excessive inhibition of the Na/K pump causes the Na(i) concentration to become raised above the normal level. Especially in digitalis toxicity, but also in many other situations, the rise of Na(i) may be an important (or contributory) cause of increased cardiac arrhythmias. In this review, we consider the mechanisms by which a raised Na(i) may cause cardiac arrhythmias. First, we describe the factors that regulate Na(i), and we demonstrate that the equilibrium level of Na(i) is determined by a balance between Na entry into the cell, and Na extrusion from the cell. A number of mechanisms are responsible for Na entry into the cell, whereas the Na/K pump appears to be the main mechanism for Na extrusion. We then consider the processes by which an increased level of Nai might contribute to cardiac arrhythmias. A rise of Na(i) is well known to result in an increase of intracellular Ca, via the important and influential Na/Ca exchange mechanism in the cell membrane of cardiac muscle cells. A rise of intracellular Ca modulates the activity of a number of sarcolemmal ion channels and affects release of intracellular Ca from the sarcoplasmic reticulum, all of which might be involved in causing arrhythmia. It is possible that the increase in contractile force that results from the rise of intracellular Ca may initiate or exacerbate arrhythmia, since this will increase wall stress and energy demands in the ventricle, and an increase in wall stress may be arrhythmogenic. In addition, the rise of Na(i) is anticipated to modulate directly a number of ion channels and to affect the regulation of intracellular pH, which also may be involved in causing arrhythmia. We also present experiments in this review, carried out on the working rat heart preparation, which suggest that a rise of Na(i) causes an increase of wall stress-induced arrhythmia in this model. In addition, we have investigated the effect on wall stress-induced arrhythmia of maneuvers that might be anticipated to change intracellular Ca, and this has allowed identification of some of the factors involved in causing arrhythmia in the working rat heart.
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Affiliation(s)
- A J Levi
- Department of Physiology, School of Medical Sciences, University of Bristol, United Kingdom.
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26
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27
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Delpech N, Soustre H, Potreau D. Endothelin-1 inhibits L-type Ca2+ current enhanced by isoprenaline in rat atrial myocytes. J Cardiovasc Pharmacol 1997; 29:136-43. [PMID: 9007683 DOI: 10.1097/00005344-199701000-00021] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Endothelin-1 (ET-1) was shown to exert direct cardiac effects by complex signaling pathways and to interact with neurotransmitter regulation of cardiac activity. The effect of ET-1 was investigated on the beta-adrenergic stimulation of cardiac L-type Ca2+ current (ICaL) on isolated rat atrial myocytes by using the patch-clamp technique. ET-1 (5 x 10(-8) M) reversed the increase in ICaL induced by isoprenaline (10(-6) M) but had no effect on basal ICaL and on (-) Bay K 8644-increased ICaL (10(-6) M); so ET-1 might exert an effect only when the Ca2+ channels are phosphorylated. The antiadrenergic action of ET-1, blocked by BQ-123 (10(-6) M) and unaffected by IRL 1038 (3.5 x 10(-8) M) should be mediated by ET-A receptors. The inhibitory action of ET-1 was still observed when ICaL was previously increased by forskolin (3 x 10(-6) M), 8-bromo-cyclic adenosine monophosphate (8-Br-cAMP; 200 microM), or cAMP (100 microM) in presence of isobutyl methyl xanthine (IBMX; 10(-6) M), suggesting that the antiadrenergic action of ET-1 on ICaL was exerted independent of the cAMP-dependent phosphorylation pathway. ET-1 is known to be an activator of phosphoinositide hydrolysis, resulting in an increased production of IP3 and diacylglycerol (DAG). A Ca(2+)-dependent inhibition of ICaL consequently to an elevation of the intracellular Ca2+ pool via IP3 might be excluded in the action of ET-1, because of the presence of EGTA in the intrapipette medium. ET-1 reversed the isoprenaline-induced increase in ICaL in the presence of protein kinase C inhibitor [PKC(19-31); 100 microM), making unlikely the involvement of a DAG-dependent activation of PKC. Therefore the antiadrenergic action of ET-1 might also be independent on the phosphoinositide pathway.
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Affiliation(s)
- N Delpech
- Laboratory of General Physiology, URA CNRS 1869, Faculty of Sciences, Poitiers, France
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28
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Tanaka H, Noguchi K, Shigenobu K. Myocardial action potential prolongation by calcium channel activation under calcium free-EGTA condition in rats: developmental and regional variations. GENERAL PHARMACOLOGY 1995; 26:39-43. [PMID: 7536175 DOI: 10.1016/0306-3623(94)00169-n] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
1. Prolongation of action potentials upon the addition of isoproterenol, forskolin, isobutylmethyl-xanthine (IBMX) and dibutyril cAMP (dbcAMP) under Ca-free EGTA condition was examined in isolated myocardial preparations from neonatal and adult rats, whose action potential configuration greatly differ. 2. The prolongation of the action potential was previously suggested to be produced by persistent sodium influx through calcium channel due to the lack of calcium-mediated inactivation of calcium channels under such experimental condition. 3. Preparations used were papillary muscles and free walls of the right and left ventricles from neonatal and adult rats. 4. In adult preparations, the prolongation produced by isoproterenol, forskolin and IBMX in the right free wall was smaller than those in the other three regions, while no regional difference was observed with dbcAMP. 5. The degree of prolongation by all of the four drugs were smaller in the neonate than in the adult. No regional difference was observed with any of the drugs in the neonate. 6. Our present results suggest that contribution of calcium-mediated inactivation of calcium channels to the repolarization of rat myocardium may increase postnatally to produce the developmental shortening of its action potential. Also, regional difference in the cAMP related mechanisms may appear postnatally.
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Affiliation(s)
- H Tanaka
- Department of Pharmacology, Toho University School of Pharmaceutical Sciences, Chiba, Japan
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29
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Boyett MR, Honjo H, Harrison SM, Zang WJ, Kirby MS. Ultra-slow voltage-dependent inactivation of the calcium current in guinea-pig and ferret ventricular myocytes. Pflugers Arch 1994; 428:39-50. [PMID: 7971160 DOI: 10.1007/bf00374750] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
L-type Ca2+ current, iCa, has been recorded in guinea-pig ventricular myocytes at 36 degrees C using the whole cell patch clamp technique. Intracellular Ca2+ was buffered with ethylenebis(oxonitrilo)tetraacetate (EGTA). An increase in the rate of stimulation from 0.5 to 3 Hz resulted in an abrupt decrease in iCa in the first beat at the high rate, followed by a progressive decrease (tau approx. 7 s) over the next 30 s. The changes were not the result of Ca(2+)-dependent inactivation, because similar changes occurred with either Ba2+ or Na+ as the charge carrier. During 20-s voltage clamp pulses there was an ultra-slow phase of inactivation of Ba2+ or Na+ current through the Ca2+ channel (tau approx. 6 s at 0 mV). This was confirmed by applying test pulses after conditioning pulses of different duration: the Ba2+ current during the test pulse decreased progressively when the duration of the conditioning pulse was increased progressively to 20 s. Ultra-slow inactivation of Ba2+ current was voltage dependent and increased monotonically at more positive potentials. Recovery of Ba2+ current from ultra-slow inactivation occurred with a time constant of 3.7 s at -40 mV and 0.7 s at -80 mV. The gradual decrease in iCa on increasing the rate to 3 Hz may have been the result of the development of ultra-slow voltage-dependent inactivation.
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Affiliation(s)
- M R Boyett
- Department of Physiology, University of Leeds, UK
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30
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Tanaka H, Noguchi K, Shigenobu K. Myocardial action potential prolongation by calcium channel activation under calcium-free EGTA condition in guinea pigs and rats. GENERAL PHARMACOLOGY 1994; 25:475-80. [PMID: 7926594 DOI: 10.1016/0306-3623(94)90201-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
1. Prolongation of action potentials upon the addition of isoproterenol or dbcAMP under Ca-free EGTA condition were observed in isolated myocardial preparations from both the guinea pig and the rat, whose action potential configuration greatly differ. The degree of prolongation was greater in the rat than in the guinea pig. 2. The prolongation of the action potential was rapidly reversed upon the addition of calcium ion and was dose-dependently suppressed by the addition of calcium antagonists. The sensitivity to nicardipine of this action potential was tenfold higher than of the so-called slow response action potentials. The duration of the prolonged action potential was dependent on the external sodium concentration, but was not affected by tetrodotoxin. 3. Thus, it was demonstrated in intact myocardia that sodium ion may persistently pass through the calcium channel to prolong the action potential when it is activated under the condition where the calcium-mediated inactivation of calcium channels is removed. 4. Contribution of calcium-mediated inactivation of calcium channels to the repolarization of normal myocardium may be larger in the rat than in the guinea pig.
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Affiliation(s)
- H Tanaka
- Department of Pharmacology, Toho University School of Pharmaceutical Sciences, Chiba, Japan
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31
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Haack JA, Rosenberg RL. Calcium-dependent inactivation of L-type calcium channels in planar lipid bilayers. Biophys J 1994; 66:1051-60. [PMID: 8038377 PMCID: PMC1275812 DOI: 10.1016/s0006-3495(94)80886-0] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Intracellular Ca2+ can inhibit the activity of voltage-gated Ca channels by modulating the rate of channel inactivation. Ca(2+)-dependent inactivation of these channels may be a common negative feedback process important for regulating Ca2+ entry under physiological and pathological conditions. This article demonstrates that the inactivation of cardiac L-type Ca channels, reconstituted into planar lipid bilayers and studied in the presence of a dihydropyridine agonist, is sensitive to Ca2+. The rates and extents of inactivation, determined from ensemble averages of unitary Ba2+ currents, decreased when the calcium concentration facing the intracellular surface of the channel ([Ca2+]i) was lowered from approximately 10 microM to 20 nM by the addition of Ca2+ chelators. The rates and extents of Ba2+ current inactivation could also be increased by subsequent addition of Ca2+ raising the [Ca2+]i to 15 microM, thus demonstrating that the Ca2+ dependence of inactivation could be reversibly regulated by changes in [Ca2+]i. In addition, reconstituted Ca channels inactivated more quickly when the inward current was carried by Ca2+ than when it was carried by Ba2+, suggesting that local increases in [Ca2+]i could activate Ca(2+)-dependent inactivation. These data support models in which Ca2+ binds to the channel itself or to closely associated regulatory proteins to control the rate of channel inactivation, and are inconsistent with purely enzymatic models for channel inactivation.
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Affiliation(s)
- J A Haack
- Department of Pharmacology and Physiology, University of North Carolina at Chapel Hill 27599
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32
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Abstract
A low threshold, voltage-gated calcium current is reported in most cardiac tissues but rarely in ventricular cells. This article reports some recently described characteristics and discusses their possible pathophysiologic implications. It also reviews the alterations induced in this current by a variety of chemical agents including several neuromediators in cardiac and other tissues.
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Affiliation(s)
- G Vassort
- Laboratoire de Physiologie Cellulaire Cardiaque, INSERM U-241, Université de Paris-Sud, Orsay, France
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33
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Levi AJ, Boyett MR, Lee CO. The cellular actions of digitalis glycosides on the heart. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 1994; 62:1-54. [PMID: 8085015 DOI: 10.1016/0079-6107(94)90005-1] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- A J Levi
- Department of Physiology, School of Medical Sciences, University of Bristol, University Walk, U.K
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34
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Jourdon P, Feuvray D. Calcium and potassium currents in ventricular myocytes isolated from diabetic rats. J Physiol 1993; 470:411-29. [PMID: 8308734 PMCID: PMC1143925 DOI: 10.1113/jphysiol.1993.sp019866] [Citation(s) in RCA: 112] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
1. The whole-cell voltage-clamp technique was applied to ventricular myocytes isolated from normal and streptozotocin-induced diabetic rat hearts to investigate the contribution of the calcium current and of the calcium-independent potassium currents to diabetes-induced alterations of the action potential. 2. In single calcium-tolerant isolated myocytes diabetes induced a lengthening of the action potential similar to that previously described in intact ventricular muscles. 3. Only L-type calcium current was present both in normal and diabetic cells. Inactivation of ICa was described in both preparations by two exponentials, whose time constants were not modified by diabetes. 4. Calcium current density-voltage relationships and steady-state inactivation curves were not significantly affected by diabetes. 5. Potassium background inward rectifier current was not modified by diabetes. 6. Calcium-independent outward potassium current inactivated, in both cell types, according to a biexponential process whose time constants were not affected by diabetes. 7. The transient outward potassium current density was significantly reduced by diabetes whereas neither the voltage dependence of the inactivation nor the time dependence of recovery from inactivation was modified. 8. A 4-aminopyridine-insensitive potassium current was also reduced by diabetes. 9. Our results show that in isolated ventricular myocytes the lengthening of the action potential induced by diabetes results mainly from a decrease of the transmembrane calcium-independent potassium permeability.
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Affiliation(s)
- P Jourdon
- Laboratoire de Physiologie Cellulaire, URA CNRS 1121, Université Paris-Sud, Orsay, France
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35
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Risso S, DeFelice LJ. Ca channel kinetics during the spontaneous heart beat in embryonic chick ventricle cells. Biophys J 1993; 65:1006-18. [PMID: 8241381 PMCID: PMC1225817 DOI: 10.1016/s0006-3495(93)81147-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The ability of Ca ions to inhibit Ca channels presents one of the most intriguing problems in membrane biophysics. Because of this negative feedback, Ca channels can regulate the current that flows through them. The kinetics of the channels depend on voltage, and, because the voltage controls the current, a strong interaction exists between voltage dependence and Ca dependence. In addition to this interaction, the proximity of pores and the local concentration of ions also determine how effectively the Ca ions influence channel kinetics. The present article proposes a model that incorporates voltage-dependent kinetics, current-dependent kinetics, and channel clustering. We have based the model on previous voltage-clamp data and on Ca and Ba action currents measured during the action potential in beating heart cells. In general we observe that great variability exists in channel kinetics from patch to patch: Ba or Ca currents have low or high amplitudes and slow or fast kinetics during essentially the same voltage regime, either applied step-protocols or spontaneous cell action potentials. To explain this variability, we have postulated that Ca channels interact through shared ions. The model we propose expands on our previous model for Ba currents. We use the same voltage-dependent rate constants for the Ca currents that we did for the Ba currents. However, we vary the current-dependent rate constants according to the species of the conducting ion. The model reproduces the main features of our data, and we use it to predict Ca channel kinetics under physiological conditions. Preliminary reports of this work have appeared (DeFelice et al., 1991, Biophys. J. 59:551a; Risso et al., 1992, Biophys. J. 61:248a).
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Affiliation(s)
- S Risso
- Department of Anatomy and Cell Biology, Emory University, Atlanta, Georgia 30322
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36
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DeFelice LJ. Molecular and biophysical view of the Ca channel: a hypothesis regarding oligomeric structure, channel clustering, and macroscopic current. J Membr Biol 1993; 133:191-202. [PMID: 8392582 DOI: 10.1007/bf00232019] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- L J DeFelice
- Department of Anatomy and Cell Biology, Emory University School of Medicine, Atlanta, Georgia 30322
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37
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Peineau N, Mongo KG, Le Guennec JY, Garnier D, Argibay JA. Alteration of the L-type calcium current in guinea-pig single ventricular myocytes by heptaminol hydrochloride. Br J Pharmacol 1992; 107:104-8. [PMID: 1422567 PMCID: PMC1907608 DOI: 10.1111/j.1476-5381.1992.tb14470.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
1. The effects of heptaminol on calcium current amplitude and characteristics were studied in single ventricular myocytes of guinea-pig by use of the whole cell configuration of the patch clamp technique. 2. A concentration-dependent decrease in ICa amplitude was observed. At heptaminol concentration as low as 10(-6) M, this effect was observed in only two cells (n = 6). At 10(-5) M the reduction of ICa was of 30 +/- 15% (n = 11). 3. The current recovery from inactivation at -40 mV holding potential (HP) seemed less sensitive to perfusion with heptaminol (greater than 10(-6) M). However, at -80 mV HP the overshoot of the recovery curve was decreased by heptaminol. 4. Both at -40 mV and -80 mV HP, heptaminol (10(-5) M) significantly increased the steady state inactivation of ICa. 5. As previously proposed by others to explain the effects of membrane active substances, the effects of heptaminol may result from alterations in cell membrane properties and possibly from an increase in intracellular free calcium ion concentration.
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Affiliation(s)
- N Peineau
- Laboratoire d'électrophysiologie, et de pharmacologie cellulaires, Faculté des Sciences, Tours, France
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38
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Bénitah JP, Bailly P, D'Agrosa MC, Da Ponte JP, Delgado C, Lorente P. Slow inward current in single cells isolated from adult human ventricles. Pflugers Arch 1992; 421:176-87. [PMID: 1356263 DOI: 10.1007/bf00374825] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Characteristics of the slow inward current (Isi) in human ventricular myocytes isolated from septal specimens obtained in patients undergoing corrective cardiac surgery were studied using the whole-cell clamp method. A first series of experiments was performed under normal standard superfusion. Clamping from -60 mV evoked an inward current with a threshold at about -35 mV, a maximum around +10 mV and an apparent reversal potential at about +55 mV. No overlapping transient or background outward currents were detected in the -60 to +30 mV potential range, but time-dependent and steady-state outward currents were elicited at potentials above +30 mV. An overlap of steady-state activation and inactivation curves was present between -30 and +10 mV and a slight relief from inactivation was observed for voltages positive to +10 mV. The time course of inactivation consisted of fast and slow phases with time constants differing by a factor of eight. Slow time constants of inactivation were shorter at potentials that elicited larger Isi, and longer at potentials inducing smaller Isi. Recovery from inactivation evolved slowly with 100% reactivation occurring in about 4000 ms. Switching the holding potential from -60 to -40 mV led to a reversible decline of Isi without any change of the decay time constants. Isi was significantly increased by 0.1 microM isoproterenol. Total or partial inhibition by inorganic (2 mM Mn2+, 3 mM Co2+, 1 mM Cd2+) and organic (1 microM methoxyverapamil, 5 microM diltiazem) calcium antagonists did not unmask any transient outward current. However, a consistent increase of Isi was reversibly observed with 3 mM 4-aminopyridine while using standard solutions. A second series of experiments carried out with K(+)- and Na(+)-free solutions did not demonstrate any significant change from data observed with standard solutions except a reduction of outward currents at steps above +30 mV and alteration of inactivation kinetics. In this experimental setting, 4-aminopyridine also increased Isi but to a lesser degree. We conclude that Isi, as compared to the outward currents, is dominant in the diseased human ventricular cells we have studied.
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Francini F, Pizza L, Traina G. Inactivation of the slow calcium current in twitch skeletal muscle fibres of the frog. J Physiol 1992; 448:633-53. [PMID: 1593482 PMCID: PMC1176220 DOI: 10.1113/jphysiol.1992.sp019062] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
1. We investigated inactivation of the slow calcium current (ICa) at very positive potentials (over 30-40 mV) and recovery from inactivation in cut twitch skeletal muscle fibres of the frog, using the double-vaseline-gap technique. External solutions were buffered against changes in [Ca2+] (Ca(2+)-buffered) with malate. Internal solutions were Ca(2+)-buffered with high concentrations of either EGTA (60 mM) or BAPTA (30 mM). 2. ICa decayed to a steady-state level somewhat less than zero. Inactivation was most rapid at a potential 10 mV more negative than that which elicited the maximal ICa. 3. Involvement of current-dependent processes (i.e. tubular Ca2+ depletion and Ca2+ entry-dependent inactivation) in determining the decay of ICa was excluded, since inactivation was not affected by replacing Ca2+ with Ba2+ or when the size of ICa was reduced by decreasing the [Ca2+]o. Partial block of Ca2+ channels with nifedipine slowed inactivation. This was, however, independent of the size of ICa. Furthermore, neither the peak of ICa nor its time constant of decay nor the time course of ICa recovery from inactivation were affected by changing the [Ca2+]i from pCa 10 to 6. 4. ICa was potentiated during a post-pulse preceded by a pre-pulse at potentials ranging from -60 to -30 mV, whereas a U-shaped inactivation curve was observed at pre-pulse potentials more positive than -30 mV. This curve was asymmetric, since the ascending branch stabilized at a level less than unity. The U-shaped form of the curve depended on post-pulse voltage: it became more pronounced when the post-pulse depolarization increased. Moreover, the activation and inactivation kinetics of ICa during the post-pulse differed from control values. Similar results were found when Ca2+ was replaced with Ba2+. 5. The ICa recovery from inactivation was voltage dependent from -50 to -80 mV; it was voltage independent at more negative potentials, proving that recovery includes a voltage-independent step. 6. The asymmetric U-shaped inactivation curve can be reproduced by a four-state cyclic model without assuming a Ca(2+)-dependent step. Taking into account that recovery from inactivation includes a voltage-independent step which becomes rate limiting at extreme negative potentials, and that during the post-pulse the activation kinetics is faster, we propose a model which has six states, two closed, one open and three inactivated.
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Affiliation(s)
- F Francini
- Department of Physiological Sciences, University of Florence, Italy
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40
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Hadley RW, Lederer WJ. Ca2+ and voltage inactivate Ca2+ channels in guinea-pig ventricular myocytes through independent mechanisms. J Physiol 1991; 444:257-68. [PMID: 1668348 PMCID: PMC1179931 DOI: 10.1113/jphysiol.1991.sp018876] [Citation(s) in RCA: 118] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
1. L-type Ca2+ currents and Ca2+ channel gating currents were studied in isolated guinea-pig ventricular heart cells using the whole-cell patch-clamp technique, in order to investigate the mechanism of Ca(2+)-dependent inactivation. The effect of altering the intracellular Ca2+ concentration ([Ca2+]i) on these currents was studied through photorelease of intracellular Ca2+ ions using the photolabile Ca2+ chelators DM-nitrophen and nitr-5. 2. We found that step increases in [Ca2+]i produced by photorelease could either increase or decrease the L-type Ca2+ current. Specifically, Ca2+ photorelease from DM-nitrophen almost exclusively caused inactivation of the Ca2+ current. In contrast, Ca2+ photorelease from nitr-5 had a biphasic effect: a small, rapid inactivation of the Ca2+ current was followed by a slow potentiation. These two Ca(2+)-dependent processes seemed to differ in their Ca2+ dependence, as small Ca2+ photoreleases elicited potentiation without a preceding inactivation, whereas larger photoreleases elicited both inactivation and potentiation. 3. The mechanism of the Ca(2+)-dependent inactivation of Ca2+ channels was explored by comparing the effects of voltage and photoreleased Ca2+ on the Ca2+ current and the Ca2+ channel gating current. Voltage was found to reduce both the Ca2+ current and the gating current proportionally. However, Ca2+ photorelease from intracellular DM-nitrophen inactivated the Ca2+ current without having any effect on the gating current. 4. The dephosphorylation hypothesis for Ca(2+)-dependent inactivation was tested by applying isoprenaline to the cells before eliciting a maximal rise of [Ca2+]i (maximal flash intensity, zero external [Na+]i). Isoprenaline could completely prevent Ca(2+)-dependent inactivation under these conditions, even when [Ca2+]i rose so high as to cause an irreversible contracture of the cell. 5. We concluded from these experiments that voltage and Ca2+ ions inactivate the L-type Ca2+ channel through separate, independent mechanisms. In addition, we found that Ca(2+)-dependent inactivation does not result in the immobilization of gating charge, and apparently closes the Ca2+ permeation pathway through a mechanism that does not involve the voltage-sensing region of the channel. Furthermore, we found that Ca(2+)-dependent inactivation is entirely sensitive to beta-adrenergic stimulation. These facts suggest that either Ca(2+)-dependent inactivation results from Ca(2+)-dependent dephosphorylation of the Ca2+ channel, or that Ca(2+)-dependent inactivation is modulated by protein kinase A.
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Affiliation(s)
- R W Hadley
- Department of Physiology, University of Maryland School of Medicine, Baltimore 21201
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Mazzanti M, DeFelice LJ, Liu YM. Gating of L-type Ca2+ channels in embryonic chick ventricle cells: dependence on voltage, current and channel density. J Physiol 1991; 443:307-34. [PMID: 1668339 PMCID: PMC1179843 DOI: 10.1113/jphysiol.1991.sp018835] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
1. L-type calcium channels in embryonic chick heart ventricle have voltage-dependent, time-variant kinetics when they conduct inward currents carried by 20 mM-Ba2+. Depolarizing the membrane from -20 to 20 mV increases mean open time from 1.4 to 4.2 ms. Mean open time increases monotonically with voltage. The single-channel conductance, 18 +/- 2 pS, is approximately linear over this voltage range, and the extrapolated reversal potential is 38 +/- 5 mV. 2. In cell-attached patches with five or more L-type Ca2+ channels in the patch, the currents elicited by 500 ms depolarizing steps, from a -80 mV holding potential, inactivate rapidly and have large tail currents. In the same patch, currents from a -40 mV holding potential are smaller, inactivate more slowly, and have practically no tail currents. 3. In cell-attached patches containing one of two L-type Ca2+ channels, currents from -80 or -40 mV are virtually identical, and they are similar to the currents from multichannel patches held at -40 mV. 4. The voltage-dependent, time-variant kinetics of individual L-type Ca2+ channels are unaltered if the patch is removed from the cell and forms an inside-out configuration. In these experiments the internal membrane was bathed with an artificial, intracellular-like solution containing no phosphorylating enzymes or substrates. 5. Cells bathed in 20 mM-Ba2+ solutions and held at -80 mV have currents with an early phase that inactivates in tens of milliseconds, a late phase that inactivates in hundreds of milliseconds, and a large, slow tail current. Currents from -40 mV have only the late phase and practically no tails. However, if the maximum current is less than 0.1 pA pF-1, records from either -80 or -40 mV are virtually identical, and they are similar to currents from cells with higher channel density held at -40 mV. Furthermore, if cells are stimulated before full recovery from inactivation, the reduced current is accompanied by slower inactivation. 6. Whole-cell currents in 1.5 mM-Ca2+ solutions are entirely abolished by addition of 20 microM-nifedipine, and they are enhanced 2-3 times by addition of 30 microM-cyclic AMP and 3 mM-ATP to the whole-cell recording electrode. The whole-cell currents in 20 mM-Ba2+ solutions are also completely blocked by 20 microM-nifedipine, regardless of kinetics or holding potential. Thus, by definition, the cells we are studying contain only L-type channels.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- M Mazzanti
- Department of Anatomy and Cell Biology, Emory University School of Medicine, Atlanta, GA 30322
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42
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Creazzo TL, Rossignol C, Hancock L, Stadt H. Membrane ion channels in cardiac malformation and disease. Ann N Y Acad Sci 1990; 588:207-15. [PMID: 1694065 DOI: 10.1111/j.1749-6632.1990.tb13211.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- T L Creazzo
- Department of Anatomy, Medical College of Georgia, Augusta 30912
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43
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Pelzer D, Pelzer S, McDonald TF. Properties and regulation of calcium channels in muscle cells. Rev Physiol Biochem Pharmacol 1990; 114:107-207. [PMID: 2155470 DOI: 10.1007/bfb0031019] [Citation(s) in RCA: 119] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- D Pelzer
- II. Physiologisches Institut, Medizinische Fakultät der Universität des Saarlandes, Homburg/Saar, FRG
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44
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Murat I. [Mechanisms of action of halogenated anesthetics on isolated cardiac muscle]. ANNALES FRANCAISES D'ANESTHESIE ET DE REANIMATION 1990; 9:346-61. [PMID: 2169214 DOI: 10.1016/s0750-7658(05)80246-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The mechanisms responsible for the direct negative inotropic effects of the three currently used volatile anesthetics (halothane, enflurane and isoflurane) are reviewed. These agents interfere at each step of excitation-contraction coupling, i.e. sarcolemmal membrane, sarcoplasmic reticulum and contractile proteins. At the myofilament level, they decrease both calcium sensitivity and maximal developed force of cardiac skinned fibers of various species, a preparation in which all functional membranes are destroyed and thus allowing to study the direct effects of volatile anesthetics on myocardial contractile proteins. The effects of the three volatile anesthetics are similar at equipotent concentrations. The site of action seems to involve the regulatory proteins of the thin myofilament, especially troponin-tropomyosin complex. At the sarcolemmal level, all three anesthetics decrease Ca++ entry through the voltage-dependent calcium channels, an effect that seems slightly more important for both halothane and enflurane than for isoflurane. However, these two sites of action (contractile proteins and sarcolemmal membrane) are not sufficient to explain their overall negative inotropic effect. The third site of action involves the sarcoplasmic reticulum. Halothane and enflurane produce an initial liberation of Ca++ from internal stores, while isoflurane does not. All three agents decrease the net uptake of Ca++ and increase the permeability of sarcoplasmic reticulum to Ca++, similar to the effect of caffeine. However, the resulting effect, i.e. a reduction of sarcoplasmic reticulum Ca++ content occurs at clinical concentrations of halothane or enflurane, while much higher concentrations of isoflurane are required to produce a similar reduction. This differential effect on the sarcoplasmic reticulum function (which is quantitative but not qualitative) seems to be mainly responsible for the lesser negative inotropic effect of isoflurane as observed in intact cardiac muscles of various species including humans. The knowledge of the mechanisms of action of volatile anesthetics is important for understanding the potential consequences associated with their use in patients receiving cardiac drugs, especially calcium blockers and phosphodiesterase inhibitors.
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Affiliation(s)
- I Murat
- Département d'Anesthésie-Réanimation, Hôpital Saint-Vincent-de-Paul, Paris
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45
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Sauviat MP. Effect of palytoxin on the calcium current and the mechanical activity of frog heart muscle. Br J Pharmacol 1989; 98:773-80. [PMID: 2574064 PMCID: PMC1854776 DOI: 10.1111/j.1476-5381.1989.tb14605.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
1. The effect of palytoxin (PTX) on the Ca current (ICa) and the mechanical activity of frog atrial fibres was studied by use of the double sucrose gap voltage clamp technique. 2. In normal Ringer solution, PTX transiently increased the electrically-evoked peak tension which then decreased while a major contracture developed. PTX slowed the time course of the relaxation phase of the evoked tension. 3. Evidence is presented which suggests that the toxin also increased the entry of Ca and Sr via the Na-Ca exchange mechanism. It also induced the development of a Ca-dependent outward current which was inhibited by Sr. 4. In Na-free solution, PTX increased ICa and shifted the reversal potential for Ca towards more negative membrane potentials, thus suggesting that the internal Ca concentration had increased. Current-voltage, tension-voltage, time to peak-voltage and inactivation time constant-membrane potential curves were all shifted towards more negative membrane potentials in the presence of PTX. 5. These effects of PTX are similar to those caused by the increase in internal Ca concentration induced by Na ionophores by way of voltage-dependent Ca influx of the Na-Ca exchange mechanism.
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Affiliation(s)
- M P Sauviat
- Laboratoire de Physiologie Comparée associé au CNRS (URA 22), Université de Paris XI, Centre d'Orsay, France
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46
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Abstract
1. A whole-cell gigaseal suction microelectrode voltage-clamp technique has been used to study slow inward tail currents in single myocytes obtained by enzymatic dispersion of rabbit ventricle and atrium. A variety of stimulation protocols, Tyrode solutions and pharmacological agents have been used to test three hypotheses: (a) that the slow inward tail current is generated by an electrogenic Na(+)-Ca2+ exchanger; (b) that a rise in [Ca2+]i, due to release from the sarcoplasmic reticulum can modulate the activity of this exchanger; and (c) that the uptake of calcium by the sarcoplasmic reticulum is a major determinant of the time course of the tail current. 2. As shown previously in amphibian atrium and guinea-pig ventricle, slow inward tail currents can be observed consistently under conditions in which action potentials and ionic currents are recorded using microelectrode constituents which only minimally disturb the intracellular milieu. 3. In ventricular cells, the envelope of these tail currents obtained by varying the duration of the preceding depolarizations shows that (a) the tail currents are activated by pulses as short as 10 ms, and reach a maximum for pulse durations of 100-200 ms, (b) the rate of decay of the tail current gradually increases as the activating depolarizations are prolonged, and (c) the tails cannot be due to deactivation of calcium currents, in agreement with other studies in frog heart. 4. When the mean level of [Ca2+]i is raised following inhibition of the Na(+)-K+ pump by strophanthidin (10(-5) M) or reductions in [K+]o (0.5 mM), the slow inward tail grows in size prior to the onset of a contracture or other signs of calcium-induced toxicity. 5. In a number of different preparations, replacement of [Ca2+]o with BaCl2 markedly or completely inhibits the Na(+)-Ca2+ exchanger, whereas Sr2+ replacement does not have this effect. In myocytes from rabbit ventricle the slow inward tails are reduced significantly and decay more slowly in 0.5-2.2 mM-BaCl2 Tyrode solution, while in 2.2 mM SrCl2 these tails are not altered. 6. The slow inward tail also shows a dependence on [K+]o, corresponding to previous data on Na(+)-Ca2+ exchange in other tissues. Increasing [K+]o in the Tyrode solution to a final concentration of 10-15 mM results in a marked inhibition of the slow tails. This effect cannot be accounted for by changes in the inwardly rectifying potassium current, IK1. 7. The slow tail currents were changed significantly by increasing the temperature of the superfusing Tyrode solution.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- W Giles
- Department of Medical Physiology, University of Calgary, Alberta, Canada
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47
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Hartzell HC, White RE. Effects of magnesium on inactivation of the voltage-gated calcium current in cardiac myocytes. J Gen Physiol 1989; 94:745-67. [PMID: 2559140 PMCID: PMC2228970 DOI: 10.1085/jgp.94.4.745] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The effects of changes in intracellular and extracellular free ionized [Mg2+] on inactivation of ICa and IBa in isolated ventricular myocytes of the frog were investigated using the whole-cell configuration of the patch-clamp technique. Intracellular [Mg2+] was varied by internal perfusion with solutions having different calculated free [Mg2+]. Increasing [Mg2+]i from 0.3 mM to 3.0 mM caused a 16% reduction in peak ICa amplitude and a 36% reduction in peak IBa amplitude, shifted the current-voltage relationship and the inactivation curve approximately 10 mV to the left, decreased relief from inactivation, and caused a dramatic increase in the rate of inactivation of IBa. The shifts in the current-voltage and inactivation curves were attributed to screening of internal surface charge by Mg2+. The increased rate of inactivation of IBa was due to an increase in both the steady-state level of inactivation as well as an increase in the rate of inactivation, as measured by two-pulse inactivation protocols. Increasing external [Mg2+] decreased IBa amplitude and shifted the current-voltage and inactivation curves to the right, but, in contrast to the effect of internal Mg2+, had little effect on the inactivation kinetics or the steady-state inactivation of IBa at potentials positive to 0 mV. These observations suggest that the Ca channel can be blocked quite rapidly by external Mg2+, whereas the block by [Mg2+]i is time and voltage dependent. We propose that inactivation of Ca channels can occur by both calcium-dependent and purely voltage-dependent mechanisms, and that a component of voltage-dependent inactivation can be modulated by changes in cytoplasmic Mg2+.
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Affiliation(s)
- H C Hartzell
- Department of Anatomy and Cell Biology, Emory University School of Medicine, Atlanta, Georgia 30322
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48
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Schouten VJ, Morad M. Regulation of Ca2+ current in frog ventricular myocytes by the holding potential, c-AMP and frequency. Pflugers Arch 1989; 415:1-11. [PMID: 2560160 DOI: 10.1007/bf00373135] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The whole-cell patch-clamp technique was used to study the effects of holding potential and frequency on the Ca2+ current in frog ventricular myocytes. INa was blocked by TTX, and ica was activated with depolarizing clamps from different holding potentials. Variation of the holding potential revealed three new effects on ica: (1) At -40 mV iCa declined with a time constant of 15 min, while at -90 mV, this irreversible decline (run down) in iCa did not occur. (2) The decline of iCa at -40 mV was biphasic: run down was preceeded by a slow inactivation with a time constant of 40 s, which was reversible upon returning the holding potential to -90 mV. (3) Increasing the frequency of the clamp pulses from 0.1 to 1 Hz led to a rapid decline of iCa when the holding potential was positive to -60 mV, but at -90 mV had either no effect or increased iCa by 35%, if c-AMP was included in the dialyzing solution. On the other hand, c-AMP did not alter the time course of the run down and the slow inactivation. Replacement of extracellular Ca2+ by Ba2+ markedly slowed iCa kinetics, but did not change the very slow inactivation or the frequency-induced enhancement of iCa. Injection of c-AMP led to a transient increase of iCa. The phosphodiesterase inhibitor theophylline enhanced the amplitude of the transient and slowed its decay. This effect was mimicked by increased frequency. It is concluded that frequency-induced enhancement of iCa is highly dependent on the holding potential, independent of Ca2+, and may involve elevation of the intracellular level of c-AMP via inhibition of phosphodiesterase activity. The new type of very slow inactivation is probably under direct voltage control and independent of Ca2+ and c-AMP.
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Affiliation(s)
- V J Schouten
- Department of Physiology, University of Pennsylvania, Philadelphia 19104-6085
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49
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Gurney AM, Charnet P, Pye JM, Nargeot J. Augmentation of cardiac calcium current by flash photolysis of intracellular caged-Ca2+ molecules. Nature 1989; 341:65-8. [PMID: 2549428 DOI: 10.1038/341065a0] [Citation(s) in RCA: 88] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The entry of calcium ions into cells through voltage-activated Ca2+ channels in the plasma membrane triggers many important cellular processes. The activity of these channels is regulated by several hormones and neurotransmitters, as well as intracellular messengers such as Ca2+ itself (for examples, see refs 1-9). In cardiac muscle, myoplasmic Ca2+ has been proposed to potentiate Ca2+ influx, although a direct effect of Ca2+ on these channels has not yet been demonstrated. Photosensitive 'caged-Ca2+' molecules such as nitr-5, however, provide powerful tools for investigating possible regulatory roles of Ca2+ on the functioning of Ca2+ channels. Because its affinity for Ca2+ is reduced by irradiation, nitr-5 can be loaded into cells and induced to release Ca2+ with a flash of light. By using this technique we found that the elevation of intracellular Ca2+ concentration directly augmented Ca2+-channel currents in isolated cardiac muscle cells from both frog and guinea pig. The time course of the current potentiation was similar to that seen with beta-adrenergic stimulation. Thus Ca2+ may work through a similar pathway, involving phosphorylation of a regulatory Ca2+-channel protein. This mechanism is probably important for the accumulation of Ca2+ and the amplification of the contractile response in cardiac muscle, and may have a role in other excitable cells.
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Affiliation(s)
- A M Gurney
- Department of Pharmacology, United Medical School, St Thomas's Hospital, London, UK
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50
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Simmons MA, Johnson EC, Becker JB, Todd DG, Reichenbecher VE, McCumbee WD, Wright GL. An endogenous 'hypertensive factor' enhances the voltage-dependent calcium current. FEBS Lett 1989; 254:137-40. [PMID: 2550274 DOI: 10.1016/0014-5793(89)81025-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The effects of an immunoaffinity-purified putative endogenous hypertensive factor (HF) on voltage-dependent calcium current in frog cardiac myocytes were assessed. In 9 out of 10 cells, HF reversibly increased the peak amplitude of the calcium current. HF increased peak calcium current density at -5 mV from a control level of 1.8 +/- 1.3 pA/pF (mean +/- SD) to 4.4 +/- 2.0 pA/pF. HF shifted the peak of the calcium current-voltage relationship in the hyperpolarizing direction. HF shifted the voltage dependence of the inactivation of the calcium current to more negative potentials with prepulses from -80 to 0 mV, but the inactivation was not affected with prepulses more positive than 0 mV. Modulation of the voltage-dependent calcium current by HF may be the mechanism underlying its pressor effects.
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Affiliation(s)
- M A Simmons
- Biomedical Sciences Graduate Program, Marshall University School of Medicine, Huntington, WV 25755
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