Reconstitution of purified acetylcholine receptors with functional ion channels in planar lipid bilayers

Acetylcholine receptor, solubilized and purified from Torpedo californica electric organ under conditions that preserve the activity of its ion channel, was reconstituted into vesicles of soybean lipid by the cholate-dialysis technique. The reconstituted vesicles were then spread into monolayers at an air-water interface and planar bilayers were subsequently formed by apposition of two monolayers. Addition of carbamoylcholine caused an increase in membrane conductance that was transient and relaxed spontaneously to the base level (i.e., became desensitized). The response to carbamoylcholine was dose dependent and competitively inhibited by curare. Fluctuations of membrane conductance corresponding to the opening and closing of receptor channels were observed. Fluctuation analysis indicated a single-channel conductance of 16 ± 3 pS (in 0.1 M NaCl) with a mean channel open time estimated to be 35 ± 5 ms. Thus, purified acetylcholine receptor reconstituted into lipid bilayers exhibited the pharmacological specificity, activation, and desensitization properties expected of this receptor in native membranes.