Alpha-latrotoxin triggers extracellular Ca²⁺-dependent exocytosis and sensitizes fusion machinery in endocrine cells

α-from the venom of black widow spider induces and augments neurotransmitter and hormone release by way of extracellular Ca²⁺ influx and cellular signal transduction pathways. By using whole cell current and capacitance recording, the photolysis of caged Ca²⁺, and Ca ²⁺ microfluorometry and amperometry, we investigated the stimulating effect and mechanism of α-latrotoxin on exocytosis in rat pancreatic β cells, LβT2 cells and latrophilin plasmid-transfected lNS-1 cells. Our data indicated that: (1) α-latrotoxin increased cytosolic Ca ²⁺ concentration through the formation of cation-permitting pores and subsequent Ca²⁺ influx with the presence of extracellular Ca ²⁺ (2) α-latrotoxin stimulated exocytosis in normal bath solution and its stimulating effect on secretion was eradicated in Ca ²⁺-free bath solution; and (3) α_ latrotoxin sensitized the molecular machinery of fusion through activation of protein kinase C and increased the response of cells to Ca²⁺ photolysed by a flash of ultraviolet light. In α latrotoxin induced exocytosis by way of Ca ²⁺ influx and accelerated vesicle fusion by the sensitization of fusion machinery.