Molecular Regulation of Quantal Release
Quantal Release or synaptic vesicle fusion is a complex and highly regulated process at the last step of vesicle trafficking. At the presynaptic terminals, the synaptic vesicles are attached to the plasma membrane by the formation of the SNARE complex. The SNARE complex is a tertiary structure formed by the vesicle SNARE VAMP1/2 (a.k.a synaptobrevin) and its acceptor at the terminal plasma membrane which is pre-formed by the t-SNAREs syntaxin1 and SNAP-25. The SNARE complex formation is a functional process termed priming crucial for spontaneous and nerve-evoked quantal release. At this point, the SNARE binding protein complexin prevents the premature vesicle fusion until the Ca2+ influx evoked by the action potential. At the active sites, the rise in the Ca2+ nano domains changes the conformation of the Ca2+ sensor synaptotagmin 1/2, increases the affinity for the SANRE complex and releases the clamping function exerted by complexin driving finally the action potential evoked vesicle fusion.
