Acetylcholine Receptors in Muscle Membrane

Abstract

CÆSIUM depolarization of muscle membrane is further increased when choline is added to the bathing cæsium–Ringer solution^1,2. This cæsium–choline depolarization remains constant in the continued presence of cæsium, even when choline is removed from the Ringer. When cæsium is replaced by potassium following removal of choline, the cæsium–choline effect is reversed and the normal resting membrane potential is recovered². It appears that choline reacts in specific fashion with membrane ‘receptors’, the result of this reaction depending on cæsium and potassium ions; in the presence of cæsium, a depolarization results; in the presence of potassium, none. Scanning data show that when muscles are treated with cæsium–Ringer, the entire muscle surface becomes sensitive to choline. The work presented here was designed to elucidate the action of acetylcholine (ACh) on the cæsium-treated muscle membrane, in comparison with the action of choline (Ch) previously described, and to determine whether: (1) an additional depolarization is evoked only when cæsium is added before acetylcholine; (2) D-tubocurarine and eserine have any effect on the additional depolarization produced by ACh.