Facilitation of Neuromuscular transmission by calcium antagonists, diltiazem, nifedipine and verapamil, in the dog.

Effects of three Ca++-antagonists, diltiazem, nifedipine and verapamil, on the neuromuscular junction were investigated in the in situ canine anterior tibial muscle preparation by close-arterial injections via the femoral artery. All these Ca++-antagonists dose-dependently augmented the twitch tension elicited by indirect stimulation applied to the common fibular nerve at a frequency of 0.1 or 0.2 Hz. The maximum of the twitch tension reached about 130% of the control by 10 mg of nifedipine, or 30 mg of diltiazem or verapamil. Nifedipine was approximately 3 times as potent as diltiazem or verapamil. Nifedipine was approximately 3 times as potent as diltiazem or verapamil in this augmentation. On the other hand, these doses of Ca++-antagonists had little effects on the twitch tension elicited by direct stimulation of the muscle. The tetanic contraction elicited by indirect stimulation of 30 Hz was partially inhibited and the post-tetanic potentiation of the twitch tension was also slightly depressed with diltiazem and verapamil. Nifedipine induced slight increases in the tetanic contraction and the post-tetanic potentiation. In addition it was demonstrated that these Ca++-antagonists depressed the acetylcholine-induced contraction of the skeletal muscle.