Clonazepam and Diltiazem Both Inhibit Sodium-calcium Exchange of Mitochondria, but Only Diltiazem Inhibits the Slow Action Potentials of Cardiac Muscles

Clonazepam, up to concentrations of 5 x 10(-5) M produced only 15% inhibition of contraction without effecting isoproterenol-induced slow action potentials (APs) of guinea pig papillary muscles. On the other hand, 10(-6) M diltiazem completely inhibited both slow APs and contractions. Both clonazepam and diltiazem inhibited Na+-induced Ca2+ release from isolated mitochondria. The half-maximum effect of clonazepam and diltiazem occurred at 7 and 8 x 10(-6) M respectively. The results suggest that clonazepam more specifically inhibits the Na+-induced Ca2+ release process of mitochondria.