Release of calcium from mitochondrial and nonmitochondrial intracellular stores in mouse pancreatic acinar cells by hydrogen peroxide

In the present study we have studied how [Ca2+](i) is influenced by H2O2 in collagenase-dispersed mouse pancreatic acinar cells and the mechanism underlying this effect by using a digital microspectrofluorimetric system. In the presence of normal extracellular calcium concentration, perfusion of pancreatic acinar cells with 1 mM H2O2 caused a slow sustained [Ca2+](i) increase, reaching a stable plateau after 10-15 min of perfusion. This increase induced by H2O2 was also observed in a nominally calcium-free medium, reflecting the release of calcium from intracellular store(s). Application of 1 mM H2O2 to acinar cells, in which nonmitochondrial agonist-releasable calcium pools had been previously depleted by a maximal concentration of CCK-8 (1 nM) or thapsigargin (0.5 muM) was still able to induce calcium release. Similar results were observed when thapsigargin was substituted for the mitochondrial uncoupler FCCP (0.5 muM). By contrast, simultaneous addition of thapsigargin and FCCP clearly abolished the H2O2-induced calcium increase. Interestingly, coincubation of intact pancreatic acinar cells with CCK-8 plus thapsigargin and FCCP in the presence of H2O2 did not significantly affect the transient calcium spike induced by the depletion of nonmitochondrial and mitochondrial agonist-releasable calcium pools, but was followed by a sustained increase of [Ca2+](i). In addition, H2O2 was able to block calcium efflux evoked by CCK and thapsigargin. Finally, the transient increase in [Ca2+](i) induced by H2O2 was abolished by an addition of 2 mM dithiothreitol (DTT), a sulfhydryl reducing agent. Our results show that H2O2 releases calcium from CCK-8- and thapsigargin-sensitive intracellular stores and from mitochondria. The action of H2O2 is likely mediated by oxidation of sulfhydryl groups of calcium-ATPases.