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Effects of intracellular calcium on sodium current density in cultured neonatal rat cardiac myocytes.
Author(s) -
Chiamvimonvat N,
Kargacin M E,
Clark R B,
Duff H J
Publication year - 1995
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1995.sp020587
Subject(s) - myocyte , intracellular , biophysics , patch clamp , bapta , chemistry , gating , conductance , calcium , cytosol , membrane potential , reversal potential , sodium , voltage clamp , medicine , endocrinology , electrophysiology , biology , biochemistry , enzyme , mathematics , organic chemistry , combinatorics
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+.