Neurotransmitter release is a key step in synaptic transmission. However, the molecular events that trigger fusion of synaptic vesicles and neurotransmitter release are unknown. One attractive hypothesis is that Ca2+-activated channels in the vesicle membrane control fusion of vesicles. If true, such a channel would provide a simple molecular link between Ca2+ entry and vesicle fusion. Previous experiments have lead to the identification of several kinds of ion channels that are credited to the synaptic vesicle membrane. The objective of this project is to study these ion channels to determine: 1) which, if any, are from the synaptic vesicle membrane; 2) the biophysical properties of these channels; and 3) regulators of the channels (such as voltage and Ca2+). These goals are directed toward elucidation of the mechanism(s) of fusion of synaptic vesicles to the nerve terminal membrane and the possible role of vesicular ion channels in this process. Plan: Planar bilayer experiments will be used to identify and characterize ion channels from synaptic vesicles purified from the electric organ of the electric fish, Torpedo californica. Vesicle membrane will be induced to fuse with bilayers by using a new technique that both enhances fusion of all vesicles and makes it possible to estimate the prevalence of any observed channels. That is, it will be possible to determine if a particular channel is representative of the population of synaptic vesicles or if it is from a minor contaminant. Preliminary Results: Synaptic vesicles from Torpedo californica have been isolated and treated so that they fuse with planar bilayers. Two kinds of ion channels have been detected from these vesicles having estimated single channel conductances of 180 pS and 14 pS.
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