Active sodium transport and alveolar epithelial Na-K-ATPase increase during subacute hyperoxia in rats.

Active Na+ transport and lung edema clearance were studied in a model of lung injury caused by sublethal oxygen exposure. Rats exposed to 85% O2 for 7 days were studied at 0, 7, 14, and 30 days after removal from the hyperoxic chamber and compared with room air controls. In the isolated-perfused, fluid-filled rat lung, albumin flux from the perfusate into the air spaces increased after oxygen exposure and returned to control values after 7 days of recovery. However, permeability to small solutes (Na+ and mannitol) normalized only after 30 days of recovery from hyperoxia. Active Na+ transport increased immediately after oxygen exposure and returned to control values 7 days after removal from hyperoxic chamber. Na-K-adenosinetriphosphatase (ATPase) activity, and protein expression in alveolar epithelial type II cells obtained at the end of the isolated lung experiments increased significantly after the oxygen exposure compared with controls in association with the increased active Na+ transport. We conclude that active Na+ transport and lung liquid clearance are increased in the subacute hyperoxic phase of lung injury in rats, due in part to the upregulation of alveolar epithelial Na-K-ATPases. Conceivably, this behavior protects against the effects of lung injury by allowing the injured lung to clear edema more effectively. Accordingly, this upregulation may be targeted as a strategy to diminish edema in patients with lung injury.