[The blocking action of snake venom polypeptides on the cholinergic mechanisms of leech dorsal muscle].

The blocking action of alpha-polypeptides from the venoms of elapid snakes (Bungarus multicinctus and Naja naja siamensis) was studied on leech dorsal muscle. It was shown that these neurotoxins failed to inhibit the responses to mononitrogen cholinomimetics (acetylcholine, nicotine, carbamylcholine, etc.). The capacity of neurotoxins to inhibit the responses to the bisquaternary cholinommimetics depended upon the length of the molecule. The neurotoxins were active against the "shorter" cholinomimetics, such as decamethonium, and bischolinic esters of malonic, succinic and glutaric acids. The "longer" cholinomimetics (bischolinic esters of adipinic, pimelic, suberic, azelaic, sebacic acids retained their full activity after the treatment of leech dorsal muscle by neurotoxins. Possible explanations of the selective action of neurotoxins are discussed.