Inhibitory action of 711389-S on the electrical activity of rabbit sinoatrial node

Membrane actions of ethanol on rabbit sino-atrial node studied by voltage clamp method

Electrophysiological effects of ethanol on rabbit sino-atrial node were studied by means of the double-microelectrode voltage clamp method. In spontaneously beating preparations, ethanol (above 1%) decreased the maximum rate of depolarization of the action potential. Furthermore, 3% ethanol produced a significant decrease in the action potential amplitude, the action potential duration at 50% repolarization and the rate of the diastolic depolarization. Of the current systems, voltage clamp studies showed that ethanol reduced the slow inward current, the time-dependent potassium outward current and the hyperpolarization activated inward current. These observations indicate that ethanol does not have an effect on a single current system, but directly modifies the spontaneous discharge of sino-atrial node pacemaker cells due to a reduction of the time-dependent current systems.

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.

Effects of pirmenol hydrochloride on the spontaneous action potentials and membrane current systems of rabbit sinoatrial node cells

The electrophysiologic effects of pirmenol hydrochloride on rabbit sinoatrial node cells were examined and compared with those of several class I antiarrhythmic agents. At 1 microM, pirmenol decreased the heart rate and the rate of diastolic depolarization and increased the action potential duration at half-amplitude. Above 10 microM, the agent also decreased the maximum rate of rise (Vmax) and the action potential amplitude significantly. The order of the inhibitory potency on Vmax was apridine greater than 711389-S greater than pirmenol greater than mexiletine greater than tocainide. With respect to the current systems, pirmenol decreased the slow inward current (Isi) and the time-dependent potassium outward current (IK). The agent also prolonged the recovery time constant of Isi without any changes in the decay process of the tail current (IK). These findings suggest that pirmenol depresses the spontaneous discharge of the sinoatrial node through a decrease in Isi and Ik.