Hideaki Sada (1), Takashi Ban (1) and Nicholas Sperelakis (2)
(1) Department of Pharmacology, School of Medicine, Yamaguchi University, Ube 755, Japan (2) Department of Molecular and Cellular Physiology, School of Medicine, University Cincinnati, Cincinnati, Ohio 45267, U.S.A.
Abstract: To examine effects of taurine on the kinetics of the Na+ channel current (INa), action potentials and whole-cell Na+ currents were recorded from single ventricular myocytes of guinea pigs. Kinetic parameters for the activation and inactivation of INa were determined in accordance with the first-order kinetic model. Changes in the kinetic parameters were assessed before and after taurine exposure (5 - 50 mM). While taurine at concentrations higher than 10 mM decreased the peak INa by ca. 15%, the agent did not alter the reversal potential and the maximum Na+ conductance. Taurine shifted the steady-state inactivation curve toward the negative potential direction and decreased its slope. Concomitantly, the slope of the steady-state activation was also slightly decreased and the rate of inactivation in the large potential region (-40 to -30 mV) slightly increased, whereas the rate of the activation appeared to remain unchanged. It is suggested that taurine alters the surface charge of the membrane and reduces the number of charges moving upon activation and inactivation of channels, thereby reducing INa.
Keywords:
Taurine, Voltage-clamp, Na+ channel