Hydrogen peroxide increases Na+/K+-ATPase function in alveolar type II cells

We have studied the regulation of Na+/K+-ATPase function in alveolar type II cells submitted to oxidative stress, Alveolar type II cells were isolated from Sprague Dawley rats and suspended in Dulbecco's modified Eagle's medium. 500 mu M xanthine plus 0.5 or 5 mU/ml xanthine oxidase (group 1 and 2, respectively) were added to the cell suspensions, Following various exposure times the reaction was stopped by adding allopurinol and cells were processed to assay H2O2 steady state concentrations, enzymatic activity of catalase and Na+/K+-ATPase function. Hydrogen peroxide production by the xanthine-xanthine oxidase system reached maximal values at 30 min of incubation in both groups, H2O2 steady state concentration increased 2- and 10-fold, respectively. Catalase activity was not changed after slight oxidative stress (group 1) but decreased in severe oxidative stress (group 2), Decreases in the Na+/K+-ATPase activity (10 and 60% for groups 1 and 2) were found during the first hour of exposure coinciding with the peak in H2O2 steady state concentration. This early inactivation was followed by progressive increases in the activity up to 70% over the control value in group 1, and to the control value in group 2. [H-3]Ouabain binding studies showed that the increase in Na+/K+-ATPase activity after oxidative stress was due to an increase in the number of phosphorylated pump molecules in the plasma membrane of alveolar type II cells.