Fig. 5. Schematic model for Rab27a function at membrane traffic. GTP-Rab27a functions at pre-exocytotic stages through interaction with its GTP-dependent effectors under basal conditions. Glucose triggers exocytosis via closure of the ATP-sensitive K⁺ channel, opening of the voltage-dependent Ca²⁺ channel and an eventual rise in cytosolic Ca²⁺. Glucose also causes a shift from GTP-Rab27a to GDP-Rab27a, which regulates endocytosis through interaction with coronin 3. Both GTP- and GDP-bound forms of Rab27a control a series of the insulin granule traffic at the distinct stages.