Possible role of ROS as mediators of hypoxia-induced ion transport inhibition of alveolar epithelial cells

In oxygen-sensitive excitable cells, responses to hypoxia are initiated by membrane depolarization due to closing of the K channels that is thought to be mediated by a decrease in reactive oxygen species (ROS). Because the me chanisms of hypoxic inhibition of ion transport of alveolar epithelial cell s (Planes C, Friedlander G, Loiseau A, Amiel C, and Clerici C. Am J Physiol Lung Cell Mol Physiol 271: L70-L78, 1996; Mairbaurl H, Wodopia R, Eckes S, Schulz S, and Bartsch P. Am J Physiol Lung Cell Mot Physiol 273: L797-L806 , 1997) are not yet understood, we tested the possible involvement of a hyp oxia-induced change in ROS that might control transport activity. Transport was measured as Rb-86 and Na-22 uptake in A549 cells exposed to normoxia, hyperoxia, or hypoxia together with ROS donors and scavengers. H2O2 < 1 mM did not affect transport, whereas 1 mM H2O2 activated Na-22 uptake (+200%) but inhibited Rb-86 uptake (-30%). Also hyperoxia, aminotriazole plus menad ione, and diethyldithiocarbamate inhibited Rb-86 uptake. N-acetyl-L-cystein e, diphenyleneiodonium, and tetramethylpiperidine-N-oxyl, used to reduce RO S, inhibited Rb-86 uptake, thus mimicking the hypoxic effects, whereas defe roxamine, superoxide dismutase, and catalase were ineffective. Also, hypoxi c effects on ion transport were not prevented in the presence of H2O2, diet hyldithiocarbamate, and N-acetyl-L-cysteine. These results indicate that io n transport of A549 cells is significantly affected by decreasing or increa sing cellular ROS levels and that it is possible that certain species of RO S might mediate the hypoxic effects on ion transport of alveolar epithelial cells.