Figure 4.

Putative vesicle priming events that allow vesicles to become competent for exocytosis. Once primed, vesicles ‘move’ from the reserve pool to the readily releasable pool where the increase in Ca²⁺ influx through activated VDCCs promotes exocytosis. GLP-1 may promote Cl^- ion pumping into a vesicle through Epac and a putative granule SUR protein that may regulate ClC-3 chloride channels. The influx of Cl^- ions counters the charge promoted by the action of the H⁺-ATPase pump. The increase in H⁺ allows the decrease in intragranular pH necessary for exocytosis.