The effect of verapamil on neuromuscular transmission and muscle contraction was studied in the skeletal muscle of chick in vitro. The interactions of verapamil with d-tubocurarine (d-TC)-induced neuromuscular blockade, acetylcholine (ACh) and tetraethylammonium (TEA)-induced contractures were also studied. The purpose of the present investigation was to see if verapamil: intensified the neuromuscular blockade produced by d-TC; modified the cholinergic responses to ACh, TEA; and inhibited both directly and indirectly elicited twitch contractions. The results showed that verapamil (1-100 micrograms/ml, 2-200 mumol/l) had a neuromuscular blocking activity on its own; i.e. it reduced both directly and indirectly evoked twitch contractions, and intensified the neuromuscular blockade produced by d-TC. In addition, verapamil reduced the contractures produced by ACh and TEA in the chick muscle. The results are in favour of the possibility that verapamil acts by a mixture of pre- and post-junctional effects at the chick neuromuscular junction.

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