[Alveolar epithelial barrier in patients with acute respiratory distress syndrome (ARDS)]

The clearance of alveolar fluid depends on the anatomic and physiologic integrity of alveolar epithelial barrier. The vectorial transport of sodium begins at the apical surface in the type II cell through amiloride-sensitive sodium channel. Sodium is pumping by Na, K-ATPasa from the basolateral surface of type II cell to the interstice. Water passes through specialized channels in the type I cell membrane by the osmotic gradient created by sodium. The activity of the sodium transporters is regulated actively by genetics and depends on molecular processes that involve the hormonal stimulation. The damage to the epithelial membrane produces an increased of the permeability of great molecules, which favors generation of edema in the alveolar space, delay in the resolution and incapacity to regenerate epithelium. More clinic trials are required to demonstrate the paper of the transport of chloride and to clarify the true function of the specialized water channels in the regulation of the alveolar fluid clearance.