Figure 2.

Schematic model of GTP-bound Rab27a function in pancreatic β-cells. Insulin-containing granules transported in the cytoplasm attach to the inner surface of the cell membrane (docking). The contents of both docked and undocked granules are eventually released following elevation of intracellular Ca²⁺ levels. GTP-bound Rab27a regulates insulin secretion by modulating the granule transport and docking steps via its effector proteins. Residents are granules that are pre-docked to the plasma membrane before fusion. Passengers are granules that fused without stably docking. Visitors are granules that remain near the plasma membrane for some time before fusion.