Effects of organophosphate insecticides on the cholinergic receptors of frog skeletal muscle.

The organophosphates octamethyl pyrophosphoramide, Bidrin, and phosphoric acid 2,2-dichlorovinyl dimethyl ester inhibit the membrane voltage response of frog sartorius muscles to carbamylcholine in a manner expected of either a slowly reversing competitive inhibitor or a noncompetitive inhibitor. The inhibition reverses with a time course of minutes, depending upon the temperature. The inhibition by these compounds is reduced by d-tubocurarine but is unaffected by hexamethonium. This may indicate that the organophosphate binding sites are near the cholinergic binding site since both d-tubocurarine and hexamethonium are competitive inhibitors of cholinergic agonists and d-tubocurarine is the larger compound.