Inhibition by amiodarone of slow response action potentials and contraction in guinea pig ventricular muscle

Abstract

1. 1. Effects of an antiarrhythmic agent, amiodarone (AM), on slow response action potentials and contraction of guinea pig ventricular muscle were examined. 2. 2. AM (4.4 × 10 −5 M, 1.1 × 10 −4 M) significantly inhibited the maximum upstroke velocity of slow response action potentials and contraction. 3. 3. As for action potential duration (APD), higher concentration (1.1 × 10 −4 M) of AM significantly shortened the APD, while low concentration (4.4 × 10 −5 M) had little effect on it. 4. 4. These findings strongly suggest that AM blocks slow inward current inflow via Ca 2+ channels in the ventricular muscle.