SUMMARY

ionic channel of the acetylcholine receptor: regulation by sites outside and inside the cell membrane which are sensitive to quaternary ligands. Mol. Pharmacol. 20:345-355 (1981). The actions of several quaternary molecules on the end plate region of the frog sartonius muscle were studied using bath application or intracellular injection. Tetraethylammo-nium (TEA), atropine methyl bromide, phencyclidime methiodide (PCP methiodide), piperocaine methiodide, and N-methyl pipenidine methiodide were injected into the sancoplasm just beneath the postjunctional membrane and 250-350 tm away from the end plate region. The ability of these agents to depress potassium conductance and prolong the muscle action potential was used as a measure of the efficacy of intracellular drug administration. External application of TEA (50-1000 tiM) decreased the peak amplitude of the end plate current (EPC) and its time constant of decay (TEI’c), but this agent and atropine methyl bromide were ineffective when injected internally. PCP methiodide (3-30 /2M) and piperocaine methiodide (10-60 tiM) had a potent action on EPCs and spontaneous miniature end plate currents (MEPCs) when applied to eithe