Involvement of TRPM2 and L-type Ca²⁺ channels in Ca²⁺ entry and cell death induced by hydrogen peroxide in rat β-cell line RIN-5F

Ca²⁺ overload is one of the mechanisms for H₂O₂-induced cell death in rat pancreatic β-cell line RIN-5F cells. RIN-5F cells express TRPM2, which is a Ca²⁺-permeable channel activated by H₂O₂, and voltage-dependent L-type Ca²⁺ channels, both of which induce Ca²⁺ entry by H₂O₂. This study examined the contribution of these channels to H₂O₂-induced Ca²⁺ entry and cell death in RIN-5F cells. Cytosolic Ca²⁺ concentration was measured using fura-2 as a Ca²⁺ indicator. Cell death was estimated by trypan blue exclusion. Pre-treatment with poly(ADP-ribose) polymerase (PARP) inhibitors, which inhibit TRPM2 activation, strongly reduced Ca²⁺ entry by H₂O₂. The PARP inhibitors used had no effect on the Ca²⁺ elevation by voltage-dependent L-type Ca²⁺ channels. On the other hand, pre-treatment with L-type Ca²⁺ channel blockers, which did not affect TRPM2 activation, partly reduced H₂O₂-induced Ca²⁺ entry. Treatment with PARP inhibitors but not L-type Ca²⁺ channel blockers, around the early phase in H₂O₂-induced Ca²⁺ elevation, also reduced the late phase. Moreover, H₂O₂-induced RIN-5F cell death was strongly attenuated by PARP inhibitors, in compared to L-type Ca²⁺ channel blockers. Our results suggest that TRPM2 channels rather than L-type Ca²⁺ channels primarily contribute to H₂O₂-induced Ca²⁺ entry and cell death.