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Comparison of effects of a new dihydropyridine, Bay K 8644, and nifedipine on spontaneous mechanical activity in rat portal vein

1 In isolated portal veins from rats, Bay K 8644 (methyl‐1, 4‐dihydro‐2, 6‐dimethyl‐3‐nitro‐4 (2‐trifluoromethyl‐phenyl) pyridine‐5‐carboxylate) increased the spontaneous mechanical activity in low but not in high concentrations. 2 The Bay K 8644‐induced increase in spontaneous mechanical activity was abolished in Ca‐free medium and restored by readdition of Ca. 3 Nifedipine abolished the augmenting effect of Bay K 8644 on the spontaneous mechanical activity; this effect of nifedipine could be eliminated by further increasing the concentration of Bay K 8644. 4 The results are consistant with the conclusion that in rat portal vein, Bay K 8644 increases the entry of extracellular Ca by a mechanism antagonistic to that of nifedipine and in high concentration has a Ca‐entry blocking effect.