Ion channels from synaptic vesicle membranes studied by patch clamping and incorporation into planar lipid bilayers

Synaptic vesicles contain ion channels that may aid in neurotransmitter release or the life cycle of the vesicle. Synaptic vesicles are recycled after fusion with the presynaptic membrane, so pathways are required for acquiring acetylcholine, ATP, and maintaining osmotic stability. The concentration of acetylcholine and ATP inside the vesicle has been debated. Data is presented that shows that the difference in reported values may be due to different purification methods.;Synaptic vesicles from Torpedo californica are quite small (;Five distinct channel types were discovered using joined vesicles fused into planer lipid bilayers: Channels +3, ;Patching of pure synaptic vesicles resulted in the observation of the multiple conducting anion channel and a second channel. This second channel may represent a subconductance state of one of the joined vesicle anion channels, a different channel, or even an altered state of a transporter.;The proton pump inhibitor, DCCD, the acetylcholine transport blocker, vesimacol, and ATP were used to determine possible roles for these channels. DCCD appears to activate the anion channel both in joined vesicles and synaptic vesicles. ATP (1 mM) appears to activate the channel in synaptic vesicles. However, in joined vesicles in the presence of Channel +3, ATP is inhibiting. It is concluded that the anion channel represents an altered state of the hydrogen pump. The other channels appear to regulate osmotic conditions within the vesicle.