Depletion of [Ca²⁺](i) inhibits hypoxia-induced vascular permeability factor (vascular endothelial growth factor) gene expression

We have investigated the role of ion channels and intracellular Ca²⁺ in the regulation of hypoxia-mediated VPF/VEGF activation. Known channel activator and blockers like lemakalim, glibenclamide, tetraethylammonium, 4-aminopyridine and nifedipine do not inhibit VPF/VEGF induction due to hypoxia. Whereas, 5 mM caffeine pretreatment of the 293 cells exhibits a complete inhibition of hypoxia inducted VPF/VEGF expression. Moreover, the cells treated with BAPTA-AM prior to hypoxia also show a dramatic decrease in the VPF/VEGF message level, which suggests an important role of intracellular Ca²⁺ in this signaling pathway. Caffeine pretreatment also inhibits hypoxia-mediated c-Src kinase activity. These findings demonstrate the importance of intracellular Ca²⁺ in the event of hypoxia-induced VPF/VEGF expression.