Meta-Biol

• Pathways

Once vesicles are docked, primed and ready to be released fusion of the synaptic vesicle with the plasma membrane can be triggered by an influx of Ca2+ through the voltage gated Ca2+ channels (N, P/Q, R, and L type). Ca2+ influx initiates a cascade of events in which the Ca2+ sensing protein, synaptotagmin-1 (sty-1) is central. Sty-1 promotes the membrane fusion between the synaptic vesicle and the plasma membrane by Ca2+ dependant induction of membrane curvature. Synaptotagmin competes with SNARE complex binding in a Ca2+ dependent manner thereby displacing complexin-1 and causing membrane curvature and fusion of the synaptic vesicle with the plasma membrane. The fusion is characterized by the formation of a trans SNARE complex in which SNAP 25, syntaxin and synaptobrevin along with synaptotagmin, and Rab3a either become a part of the plasma membrane or membrane delimited in the vesicular membrane. Vesicle fusion ultimately results in the release of the acetylcholine into the synaptic cleft.