Pharmacological studies on the bungarotoxins: an analysis of the site of action of nicotinic agonists

The possibility that nicotinin agonists may exert an indirect action by releasing endogenous acetylcholine from nerve terminals has been examined by the use of nerve-free cultured muscle, and by the use of the specifically prejunctionally active β-type bungarotoxins. In cultured muscle the depolarizations produced by acetylcholine and carbachol were not greatly affected by treatment of the cultures with β-type bungarotoxins for 60 min. In the chick biventer cervicis nerve-muscle preparations dose-response curves to acetylcholine, carbachol, dimethylphenylpiperazinium and nicotine were not affected even after abolition of responses to nerve stimulation by the β-types toxins. As the responses to nicotinic agonists were obtainable in nerve-free muscle and were unimpaired in the chick biventer after elimination of nerve function by β-type bungarotoxins, we conclude that such agonists exert a direct action on the postjunctional acetylcholine receptors.