Reconstitution of a chemically excitable membrane.

Membrane fragments rich in cholinergic (nicotinic) receptor sites, purified from homogenates of Torpedo marmorata electric organ, are dissolved in high concentrations of Na cholate and Tris buffer in the presence of Na ethylenediaminetetraacetate, without loss of the ability to bind Naja nigricollis [(3)H]alpha-toxin. After extensive dialysis to remove cholate, the solution is supplemented with crude lipids extracted from native membrane fragments and MgCl(2)-CaCl(2) added dropwise to the mixture as a concentrated solution. The reconstituted membranes obtained retain (22)Na(+). Release of Na from these microsacs increases in the presence of carbamylcholine and the alpha-toxin from N. nigricollis blocks this effect.