Role and regulation of lung Na,K-ATPase.

The recognition that pulmonary edema is cleared from the alveolar airspace by active Na+ transport has led to studies of the role and regulation of alveolar epithelial Na,K-ATPases. In the lung these heterodimers are predominantly composed of alpha1 and beta1-subunits and are located on the basolateral aspect of alveolar type 2 epithelial cells (AT2). Working with apically positioned epithelial Na+ channels they generate a transepithelial osmotic gradient which causes the movement of fluid out of the alveolar airspace. Accumulating data indicates that in some forms of pulmonary edema alveolar Na,K-ATPases function is reduced suggesting that pulmonary edema may be due, in part, to impairment of edema clearance mechanisms. Other studies suggest that Na,K-ATPase dysfunction or inhibition may contribute to airway reactivity. It is now recognized that lung Na,K-ATPases are positively regulated by glucocorticoids, aldosterone, catecholamines and growth hormones. These findings have led to investigations that show that enhancement of Na,K-ATPase function can accelerate pulmonary edema clearance in vitro, in normal and injured animal lungs in vivo, and in human lung explants. This review focuses on Na,K-ATPase data from lung and lung cell experiments that highlight the importance of Na,K-ATPases in airway reactivity and in maintaining a dry alveolar airspace. Review of data that suggests that there may be a role for therapeutic modulation of alveolar Na,K-ATPases for the purpose of treating patients with respiratory failure are also included.