Melastatin-like transient receptor potential channel 2 (TRPM2) is an oxidant-sensitive, non-selective cation charmel which has been shown to be widely expressed in mammalian tissues, including the vascular endothelium.Here we investigated the functional role of TRPM2 channels in hydrogen peroxide (H2O2)-induced endothelial Ca2+ responses and cell apoptosis in microvessel endothelial cells (H5V).We found that, application of H2O2 caused a significant increase in intracellular Ca2+ concentration ([Ca2+]i), which was inhibited by TM2E3, a TRPM2 specific blocking antibody, or by TRPM2 shRNA.In addition, DNA ladder formation assay showed that pretreatment of TM2E3 successfully protected the cells from H2O2-induced apoptosis, which was also confirmed by TRPM2 shRNA.Moreover, overexpression of TRPM2 in H5V cells significantly increased cell sensitivity to Ca2+ overload and cell apoptosis under H2O2 treatment.Taken together, these data strongly suggest that TRPM2 channels are involved in important intrinsic mechanisms, which mediate H2O2-induced Ca2+ overload and cell apoptosis in H5V cells.Inhibition of endogenous ROS-sensitive TRPM2 channels with TM2E3 or their specific shRNA significantly protects the vascular cells from apoptotic cell death.