Sodium channels in cultured cardiac cells.
Primary cardiac cell cultures were prepared from the hearts of neonatal rats. The patch-clamp method (Hamill, Marty, Neher, Sakmann & Sigworth, 1981) was applied for studying whole-cell Na+ currents and single-channel Na+ currents, respectively. Whole-cell recordings yielded voltage- and time-dependent Na+ currents which could be blocked by tetrodotoxin. Single-channel Na+ currents were directly compared in cell-attached patches and in inside-out patches. In cell-attached patches the elementary current was about -1 pA at -10 mV and the slope conductance over a 50 mV voltage range was 15.1 +/- 1.6 pS (mean +/- S.D.). Inactivation during depolarization and after conditioning clamp steps, in the steady state, resulted from a reduced opening probability of Na+ channels. In inside-out patches, with identical solutions at both membrane surfaces, there was a large (40-50 mV) shift of channel opening and inactivation kinetics towards more negative potentials. However, for levels of comparable opening probabilities, mean open times of Na+ channels were similar in cell-attached and inside-out patches. Tetrodotoxin (10-20 microM) had no effect on Na+ channels when applied from the inside, but blocked them completely after application to the outside membrane surface.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002478:Cells, Cultured; D007473:Ion Channels / Q000187:drug effects*; D008564:Membrane Potentials / Q000187:drug effects; D009206:Myocardium / Q000166:cytology*; D051381:Rats; D012964:Sodium / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology
D007473:Ion Channels; D013779:Tetrodotoxin; D012964:Sodium