Ion channels in synaptic vesicles from Torpedo electric organ.

A simple method has been developed for fusing synaptic vesicles into spherical structures 20-50 micron in diameter. The method has been applied to purified cholinergic synaptic vesicles from Torpedo electric organ, and the membrane properties of these fused structures have been studied by the "cell"-attached version of the patch clamp technique. A large conductance potassium-preferring channel, termed the P channel, was consistently observed in preparations of fused synaptic vesicles. The selectivity of the channel for potassium over sodium was approximately equal to 2.8-fold. Two major conductance levels were observed during P-channel activity, and their relative proportion was dependent on the voltage applied to the membrane through the patch pipette. P channels were not seen in fused preparations of purified Torpedo lipids, nor was the frequency of their occurrence increased in preparations enriched with plasma membrane or nonvesicular membranes. We suggest, therefore, that the P channels are components of the synaptic vesicle membrane. Their function in synaptic transmission physiology is still unknown.