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 Ca 2+ concentration ([Ca2+]i) and their possible modulation by nitric oxide (N O) in fura-2-loaded cultured bovine tracheal epithelium. Hypoxanthine (HX) and xanthine oxidase (XO), which generate superoxide anion (O-2(-)) and hyd rogen peroxide (H2O2), dose dependently increased [Ca2+]i. The increase [Ca 2+]i was reduced in the presence of superoxide dismutase (SOD, 200 U/mL) an d catalase (200 U/mL) by 29% and 43%, respectively. The ion chelator o-phen anthroline and the hydroxyl radical ((OH)-O-.) scavenger dimethylthiourea ( DMTU) more potently inhibited the response of [Ca2+]i. H2O2-derived (OH)-O- . generated by the Fenton reaction caused a marked [Ca2+]i elevation, but e xogenous H2O2 dud bit. Sodium nitroprusside (100 mu M), an NO donor, potent iated HX-XO-induced [Ca2+]i rise by 50%, an effect that was abolished in th e presence of SOD or DMTU. These results suggest that (OH)-O-. formed by in teraction of O-2(-) 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 wi th O-2(-) and producing (OH)-O-..