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 mechanisms of hypoxic inhibition of ion transport of alveolar epithelial cells (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 hypoxia-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 menadione, and diethyldithiocarbamate inhibited Rb-86 uptake. N-acetyl-L-cysteine, diphenyleneiodonium, and tetramethylpiperidine-N-oxyl, used to reduce ROS, inhibited Rb-86 uptake, thus mimicking the hypoxic effects, whereas deferoxamine, superoxide dismutase, and catalase were ineffective. Also, hypoxic effects on ion transport were not prevented in the presence of H2O2, diethyldithiocarbamate, and N-acetyl-L-cysteine. These results indicate that ion transport of A549 cells is significantly affected by decreasing or increasing cellular ROS levels and that it is possible that certain species of ROS might mediate the hypoxic effects on ion transport of alveolar epithelial cells.