Fluid transport by airway epithelia.

Airway epithelia possess transepithelial ion transport processes which may help to regulate the fluid content of airway secretions. Chloride secretion promotes fluid movement from blood to airway lumen. Active absorption of Na favours fluid movement in the opposite direction. The balance between these two processes can be altered by a number of agents which stimulate Cl secretion. The importance of ion transport for normal mucociliary clearance is suggested by the finding that airway epithelia in patients with cystic fibrosis are unable to secrete chloride. This defect may cause the characteristically sticky and tenacious mucous secretions which are the major cause of death in this disease.