effects of verapamil on chicken biventer - cervicis muscle

- verapamil produces a sustained contraction in isolated biventer-cervicis muscle of chickens between 2-8 days old. from cumulative dose-response curves, ed50 of was calculated for this effect of verapamil. when isolated chicken biventer-cervicis muscle was electrically stimulated, verapamil had no effect on twitch contractures but increased the base line tone of the muscle. glycerol treatment of the muscle reduced the responses to acetylcholine and kcl but had little effect on contracture produced by verapamil, and no effect on contracture produced by caffeine. incubation of the muscles with calcium-free krcbs solution omitted the responses of the muscle to acetylcholine and reduced the response to caffeine. again, the responses to caffeine and verapamil were less affected compared to kcl. addition of ethylene glycol tetra-acetic acid (egta) (2.5 mm) abolished the responses of muscle to all compounds. it was concluded that verapamil produces contracture of the muscle by release of calcium from intracellular stores.