Antifibrillatory actions of bepridil and butyl-MDI, two intracellular calcium antagonists

The antifibrillatory and electrophysiologic actions of bepridil and butyl-methylenedioxyindene (BU-MDI), two intracellular calcium antagonists, were examined in anesthetized dogs. The administration of bepridil (1.0-10.0 mg/kg i.v.) significantly increased the electrical threshold for ventricular fibrillation determined during unobstructed coronary flow, and was associated with a significant decrease in ventricular excitability and a progressive depression in ventricular myocardial conduction. BU-MDI (3.0-30.0 mg/kg i.v.) did not significantly alter ventricular fibrillation thresholds during unobstructed coronary flow, nor did it significantly alter electrophysiologic properties such as ventricular excitability, conduction or refractoriness. The administration of either bepridil (10 mg/kg i.v.) or BU-MDI (30 mg/kg i.v.), however, resulted in significant increases in the ventricular fibrillation thresholds determined during transient myocardial ischemia, restoring the threshold values to corresponding non-ischemic levels. These results suggest that an inhibition of the action and/or availability of intracellular calcium may play a role in the antifibrillatory actions of BU-MDI and bepridil during transient ischemia.