Effects of amiodarone on barium-induced automatic activity in guinea pig ventricular muscle

1. The electrophysiological effects of a potent antiarrhythmic agent, amiodarone, on BaCl2-induced automaticity of guinea pig ventricular papillary muscle were studied by means of conventional microelectrode techniques. 2. BaCl2 (5 x 10(-4) M) depolarized the maximum diastolic potential of muscle preparation to about -62 mV and induced the spontaneous activity at rate of about 62 beats/min. 3. The application of amiodarone (4.4 x 10(-5) M to 1.1 x 10(-3) M) to the BaCl2-induced automatic muscle fibers decreased the spontaneous rate and slope of slow diastolic depolarization in a dose-dependent manner, associated with insignificant changes in action potential duration. 4. Amiodarone may exert the inhibitory effects of BaCl2-induced automaticity by decreasing steady-state conductance for the Na+ and Ca2+, probably thereby permitting the manifestation of antiarrhythmic properties in combination of its other actions.