title: Effects of intracellular calcium on sodium current density in cultured neonatal rat cardiac myocytes.
abstract: 1. Na+ channel mRNA levels in the heart can be modulated by changes in intracellular Ca2+ ([Ca2+]i). We have investigated whether this regulation of Na+ channel biosynthesis by cytosolic Ca2+ translates into functional Na+ channels that can be detected electrophysiologically. 2. Whole-cell Na+ currents (INa) were recorded using patch-clamp techniques from single ventricular myocytes isolated from neonatal rats and maintained in tissue culture for 24 h. Na+ current density, measured at a membrane potential of -10 mV, was significantly decreased in the cells which were exposed for 24 h to culture medium containing 10 mM of both external Ca2+ and K+ in order to raise [Ca2+]i compared with control cells which were maintained in culture medium containing 2 and 5 mM of Ca2+ and K+, respectively. In contrast, Na+ current density (at -10 mV) was significantly increased in cells exposed for 24 h to 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid tetraacetoxymethyl ester (BAPTA AM; a cell membrane-permeable Ca2+ chelator) which lowered the average [Ca2+]i compared with control. 3. Changes in current density were not associated with changes in the voltage dependence of activation and inactivation of INa. There were no changes in single-channel conductances. 4. It is concluded that Na+ current density in neonatal rat cardiac myocytes is modulated by [Ca2+]i. The findings suggest that the differences in current density are attributable to a change in Na+ channel numbers rather than to changes in single-channel conductance or gating. These changes are consistent with the previously documented modulation of Na+ channel biosynthesis by cytosolic Ca2+.
authors.affiliation: Department of Medicine and Medical Physiology, University of Calgary, Alberta, Canada.
authors.forename: N
authors.initials: N
authors.lastname: Chiamvimonvat
authors.forename: M E
authors.initials: ME
authors.lastname: Kargacin
authors.forename: R B
authors.initials: RB
authors.lastname: Clark
authors.forename: H J
authors.initials: HJ
authors.lastname: Duff
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D002478:Cells, Cultured / Q000502:physiology; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004553:Electric Conductivity; D007700:Kinetics; D009206:Myocardium / Q000166:cytology* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D015222:Sodium Channels / Q000187:drug effects; D013997:Time Factors
chemical_list: D002614:Chelating Agents; D015222:Sodium Channels; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D011188:Potassium; D002118:Calcium