Effect of bile acid on electrophysiological properties of rabbit sino-atrial node in vitro.

1 In order to examine the action of bile acid on cardiac pacemaker activity, the effect of sodium taurocholate (NTC) was studied on the membrane potential and current of rabbit sino-atrial node preparations by means of a double microelectrode voltage clamp technique. 2 In spontaneously beating sino-atrial node preparations, NTC (above 30 microM) decreased the maximum rate of rise of the action potential. Above 100 microM, the compound also exerted a bradycardiac effect and decreased the rate of diastolic depolarization significantly. 3 On the current systems, NTC produced dose-related decreases in the slow inward Ca2+ current and the time-dependent outward K+ current. 4 It is concluded that NTC depresses the spontaneous discharge of the sino-atrial node through decreases in both inward and outward current systems.