Acetylcholine release from proteoliposomes equipped with synaptosomal membrane constituents.

A lyophilized presynaptic membrane powder prepared from Torpedo electric organ synaptosomes was incorporated into liposomes. These proteoliposomes had a large internal volume. The P and E faces of their membrane showed particles which were comparable to the presynaptic membrane ones. The synaptosomal ecto-esterase activity was also incorporated. A large amount of acetylcholine could be entrapped in the proteoliposome which became permeable to acetylcholine in the presence of calcium. Acetylcholine was released in preference to choline. The calcium-induced acetylcholine release depended on the incorporation of a presynaptic membrane constituent. Proteoliposomes prepared from postsynaptic membrane powders gave a much slower acetylcholine efflux. The protein pattern of presynaptic and postsynaptic membrane proteoliposomes were compared.