Hydrogen peroxide inhibits Ca efflux through plasma membrane Ca-ATPase in mouse parotid acinar cells.

Intracellular Ca mobilization is closely linked with the initiation of salivary secretion in parotid acinar cells. Reactive oxygen species (ROS) are known to be related to a variety of oxidative stress-induced cellular disorders and believed to be involved in salivary impairments. In this study, we investigated the underlying mechanism of hydrogen peroxide (HO) on cytosolic Ca accumulation in mouse parotid acinar cells. Intracellular Ca levels were slowly elevated when 1 mM HO was perfused in the presence of normal extracellular Ca. In a Ca-free medium, 1 mM HO still enhanced the intracellular Ca level. Ca entry tested using manganese quenching technique was not affected by perfusion of 1 mM HO. On the other hand, 10 mM HO induced more rapid Ca accumulation and facilitated Ca entry from extracellular fluid. Ca refill into intracellular Ca store and inositol 1,4,5-trisphosphate (1 µM)-induced Ca release from Ca store was not affected by 1 mM HO in permeabilized cells. Ca efflux through plasma membrane Ca-ATPase (PMCA) was markedly blocked by 1 mM HO in thapsigargin-treated intact acinar cells. Antioxidants, either catalase or dithiothreitol, completely protected HO-induced Ca accumulation through PMCA inactivation. From the above results, we suggest that excessive production of HO under pathological conditions may lead to cytosolic Ca accumulation and that the primary mechanism of HO-induced Ca accumulation is likely to inhibit Ca efflux through PMCA rather than mobilize Ca ions from extracellular medium or intracellular stores in mouse parotid acinar cells.