KINETIC MECHANISM OF NA-PIG VENTRICULAR MYOCYTES( CHANNEL DEPRESSION BY TAURINE IN GUINEA)

To examine effects of taurine on the kinetics of the Na+ channel curre nt (I-Na), action potentials and whole-cell Na+ currents were recorded from single ventricular myocytes of guinea pigs. Kinetic parameters f or the activation and inactivation of I-Na were determined in accordan ce with the first-order kinetic model. Changes in the kinetic paramete rs were assessed before and after taurine exposure (5-50 mM). While ta urine at concentrations higher than 10 mM decreased the peak I-Na by c a 15%, the agent did not alter the reversal potential and the maximum Na+ conductance (G(Na)) Taurine shifted the steady-state inactivation (h(infinity)) curve toward the negative potential direction and decrea sed the slope of h(infinity). Concomitantly, the slope of the steady-s tate activation (m(infinity)) was also slightly decreased and the rate of inactivation in the large potential region (-40 to -30 mV) slightl y increased, whereas the rate of the activation appeared to remain unc hanged. 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 I-Na.