Studies on a reconstituted acetylcholine receptor system: effect of agonists

An impure preparation of acetylcholinesterase from electroplax of the electric eel can be incorporated into a bimolecular lipid membrane. The acetylcholinesterase-modified bimolecular lipid membrane shows a concentration-dependent increase in membrane conductance elicited by several agonists (acetylcholine, carbamylcholine, phenyltrimethylammonium ion, tetraethylammonium ion, decamethonium ion, and nicotine) added to the compartment opposite that to which acetylcholinesterase was originally added. Affinity and efficacy of the various agonists in generating the conductance increase were measured from dose-response curves; these are in good quantitative agreement with corresponding values observed for depolarization of intact eel electroplax. The ion conduction pathways induced by agonists in the modified bimolecular lipid membrane show a slight cation selectivity, Na ? K > Cl (3:3:1), similar to that observed for the depolarized electroplax membrane. Evidence is presented that suggests that some components other than acetylcholinesterase induce the acetylcholine receptor response in the bimolecular lipid membrane.