Abstract des Autors

Gas exchange in the lung is mediated by diffusion of the respiratory gases across the alveolar epithelium. An increased diffusion distance e.g. by alveolar edema impairs gas exchange. The thickness of the layer of alveolar lining fluid is controlled by mechanisms mediating ion- and water reabsorption. The present study was designed to test whether hypoxia impairs ion transport by alveolar epithelial cells. The activity of cation transport systems was determined by measuring the unidirectional uptake of 86Rb and 22Na by normoxic and hypoxic primary-cultured rat alveolar type II pneumocytes (AII cells) and A549 cells, a human lung carcinoma cell line with functional similarities to AII cells. Hypoxia (3% O2 = 20 torr PO2 for 30 min to 20 h) inhibits total 86Rb- and Na-uptake by about 60%. Reoxygenation for 2 hours of hypoxic A549 cells restores most of the original transport rate. In both cell types the inhibition is caused by inhibition of the Na/K-pump, Na/K/2Cl cotransport and Na-channels. In A549 cells, a decrease in the amount of protein of these transporters is observed during hypoxic exposure indicating that the inhibition of transport might be caused by a decreased numher of transporters in the plasma membrane. lf similar changes occurred in vivo e.g. during exposure to high altitude, they should result in an accumulation of fluid in the alveolar space and impair pulmonary gas exchange. Verf.-Referat