Effects of halothane on membrane potentials in single guinea pig atrial and ventricular cells

The mechanism by which cardiac arrhythmias (e.g. premature ventricular contraction) frequently occur during halothane anesthesia remains uncertain. We studied the effects of halothane on membrane potentials in single atrial and ventricular cells from guinea pig. In both atrial and ventricular cells, the overshoot and plateau phase of the action potentials were depressed by halothane administration. However, halothane had no effect on the resting membrane potential in both cells. The duration of the action potential in atrial and ventricular cells responded differently to halothane. The duration of the ventricular action potential was markedly shortened, while that of the atrial action potential was not changed significantly. These results suggest that, since the duration of the ventricular action potential is longer than that of the atrial action potential, ventricular extrasystoles may be difficult to arise. When halothane is administered, the duration of the ventricular action potential becomes almost of the same length as the atrial action potential. Therefore the tendency to induce ventricular extrasystoles may increase.