Effects of bepridil and of its quaternary derivative on rat tail artery

Abstract The effects of bepridil and its quaternary ammonium derivative (BN + ) were compared, showing that: (i) both drugs inhibited K + -induced contractions with similar time courses and potencies, (ii) bepridil blocked the tonic but not the phasic component of contractions elicited by noradrenaline, whereas BN + had no effect on noradrenaline-elicited contractions. These results, and the relative insensitivity of skinned taenia caeci to bepridil, suggest that this drug and BN + do not act directly on contractile proteins but affect K + - and noradrenaline-induced calcium channel activities differentially.