Effects of reactive oxygen species on intracellular calcium in bovine tracheal epithelium: modulation by nitric oxide

We studied the effects of reactive oxygen species (ROS) on intracellular Ca2+ concentration ([Ca2+]i) and their possible modulation by nitric oxide (NO) in fura-2-loaded cultured bovine tracheal epithelium. Hypoxanthine (HX) and xanthine oxidase (XO), which generate superoxide anion (O2-) and hydrogen peroxide (H2O2), dose dependently increased [Ca2+]i. The increase in [Ca2+]i was reduced in the presence of superoxide dismutase (SOD, 200 U/mL) and catalase (200 U/mL) by 29% and 43%, respectively. The iron chelator o-phenanthroline and the hydroxyl radical (.OH) scavenger dimethylthiourea (DMTU) more potently inhibited the response of [Ca2+]i. H2O2-derived .OH generated by the Fenton reaction caused a marked [Ca2+]i elevation, but exogenous H2O2 did not. Sodium nitroprusside (100 microM), an NO donor, potentiated HX-XO-induced [Ca2+]i rise by 50%, an effect that was abolished in the presence of SOD or DMTU. These results suggest that .OH formed by interaction of O2- and H2O2 in the presence of iron may play a major role in the HX-XO-induced disruption of airway epithelial Ca2+ homeostasis, and that NO potentiates ROS-induced [Ca2+]i response, presumably by reacting with O2- and producing .OH.