Some properties of Na channel inactivation in isolated ventricular cells of frog, Rana catesbeiana.
Voltage clamp method using suction pipette was applied to single ventricular cells of frog which was isolated by the enzyme dispersion method. The fast transient current started to generate in the range between -55 mV and -50 mV and was maximum at -20 mV. The polarity of this current changed at 70 mV in the medium containing 113.5 mM Na in the external solution and 8 mM Na in the internal solution, a value close to that predicted by Nernst equation. Administration of tetrodotoxin (TTX) at a concentration of 2 microns completely abolished the fast transient current. I-V curve beyond -20 mV became linear, suggesting that the membrane permeability is well expressed by the membrane cord conductance. Maximum sodium conductance was calculated to be 0.16 mS/cm2 in 113.5 mM Na solution at 5 degrees C. The development of inactivation during depolarization assumed a single exponential time course. The time course of recovery from inactivation exhibited two time constants without a delay of onset. Longer time constants are in the range of 1,204 msec to 3,860 msec at the membrane potential of -80 mV and -70 mV. These long time constants for recovery from inactivation explain the long refractory period of the action potential in the myocardium.
D000818:Animals; D004594:Electrophysiology; D006329:Heart Conduction System / Q000502:physiology*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000502:physiology*; D011892:Rana catesbeiana; D016276:Ventricular Function
D007473:Ion Channels