Comparative effects of bepridil and verapamil on isolated coronary and systemic vascular and cardiac muscle.

The relaxant effects of the antianginal agent bepridil, a drug with calcium antagonistic actions, and verapamil on isolated pig coronary (C) and rabbit aortic (A) smooth muscle were compared. Both drugs competitively antagonised calcium in Tris buffered but not in bicarbonate buffered medium. Both agents relaxed K+-depolarised C and inhibited contractile responses to noradrenaline plus anoxia. Bepridil was approximately 10 fold less potent than verapamil. The two drugs exerted similar calcium antagonistic effects in guinea pig papillary muscle but showed dissimilar profiles in atrial muscle in that responses in the presence of bepridil appeared to be frequency dependent. It is concluded that bepridil inhibits responses to anoxia and competitively antagonises calcium in vascular smooth muscle. On atrial tissue, bepridil, unlike verapamil, appears to exert additional actions possibly involving other ion channels.