Effects of small organic molecules on the cholinergic receptors of the motor endplate.

This paper deals with the effects on the endplate receptors of the electro-osmotic and bath application of compounds which, although lacking pharmacological affinity, mimic the actions caused at much lower concentrations by conventional cholinergic drugs. Small cyclic molecules containing carbonyl, ether, ester, amide, and carboxyl anhydride groups were tested. Lactones, carboxyl anhydrides, cyclic amides, and ketones depolarized the endplate membrane and, in addition, most of them potentiated the depolarizing action of acetylcholine. On the contrary, cyclic ethers behaved as neuromuscular blocking agents. Dioxane, which contains two ether oxygens, caused a marked prolongation of the time course of the potentials elicited by the iontophoretic application of acetylcholine pulses. In some instances the effects of adding the compounds to the bath were different from those observed following local electro-osmotic application.