title: An investigation on the inactivation process of sodium currents in single frog ventricular cells.
abstract: The characteristics of sodium currents (INa) in single frog ventricular cells were studied with the oil gap method. This method improves time- and space-control of the membrane potential under the voltage clamp, thereby making possible accurate analysis of fast events of INa. In this preparation the threshold of INa was about -60 mV and the reversal potential was 58 mV, which is close to the value calculated by the Nernst equation for sodium ions. Because the instantaneous current-voltage (I-V) relationship is linear, the ease of permeation of sodium ions through Na+ channels is well expressed by the chord conductance. The falling phase of INa and the time course of recovery from inactivation follow a time course of single exponential function. The time constants for on- and off-processes of inactivation at the same membrane potential are very close to each other, indicating only a single state of inactivation. Though almost all properties of INa were well described by Hodgkin-Huxley's model, a clear delay of onset of inactivation was demonstrated by two-pulse experiment. In this report the modified kinetics scheme was proposed which can account for both a delay of onset of inactivation development and a falling phase of INa that follows a single exponential time course.
authors.affiliation: Department of Physiology, Hiroshima University School of Medicine, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Miyoshi
authors.forename: I
authors.initials: I
authors.lastname: Seyama
mesh_terms: D000818:Animals; D004553:Electric Conductivity; D006352:Heart Ventricles; D007700:Kinetics; D008564:Membrane Potentials; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D011892:Rana catesbeiana; D015222:Sodium Channels / Q000378:metabolism*; D013997:Time Factors
chemical_list: D015222:Sodium Channels