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

Abstract

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.