Action Potential Duration-Stabilizing Action of Taurine in Guinea Pig Ventricular Myocytes

Abstract

To examine taurine actions on the rate of repolarization of action potentials (AP), L-type Ca²⁺ (I_ca), late outward K⁺ (I_K) and the inward rectifier currents as affected by the external Ca²⁺ concentrations ([Ca²⁺]_o), whole-cell voltage-clamp and current-clamp experiments were conducted in guinea pig ventricular myocytes. At a high (3.6 mM) [Ca²⁺]_o, 10 mM taurine suppressed both I_ca and I_K, shortened AP duration and decelerated the rate (−dV/dt) of terminal repolarization of AP. In contrast, at a low (0.9 mM) [Ca²⁺]_o, taurine intensified both I_ca and I_K, lengthened AP duration and accelerated −dV/dt. However, at either [Ca²⁺]_o, the resting membrane potential was slightly hyperpolarized, and the inward rectifier current examined by the ramp-pulse protocol remained unaffected by taurine. Taurine is suggested to maintain a stable AP duration by altering the inward Ca²⁺ and I_K in the opposite directions, depending on [Ca²⁺]_o. The relevance of the stabilizing action of taurine on the AP duration to its reported antiarrhythmic efficacies is discussed.