Studies on the pharmacology of skeletal muscle in culture: specificity of receptors

The specificity of the receptors of chick embryo skeletal muscle fibres in culture was examined. Noradrenaline, histamine, dopamine and γ-aminobutyric acid had no effect on resting membrane potential or on depolarization induced by carbachol. Adrenaline and 5-hydroxytryptamine did reduce the carbachol response but were without direct effect on membrane potential. Muscarinic agonists had no action but the muscarinic antagonists, atropine and hyoscine, reduced the response to carbachol. High concentration of atropine and hyoscine produced a well-maintained depolarization of the muscle fibres and this depolarization was not inhibited by tubocurarine, α-bungarotoxin or prior cholinoreceptor desensitization. The cultured muscle fibres were depolarized by a wide range of nicotinic agonists, and gallamine acted as a competitive antagonist. It is concluded that the receptors on cultured skeletal muscle are similar to normal nicotinic receptors and that atropine and hyoscine depolarize by an action at a site other than the cholinoreceptor, possibly at the 'ion conductance modulator'.