Interaction of verapamil with d‐tubocurarine and cholinergic agonists at the avian neuromuscular junction

Abstract

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: (a) intensified the neuromuscular blockade produced by d-TC; (b) modified the cholinergic responses to ACh, TEA; and (c) inhibited both directly and indirectly elicited twitch contractions. The results showed that verapamil (1-100 .mu.g/ml, 2-200 .mu.mol/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.