Mechanisms of airway epithelial ion transport.

Airway epithelia contain the transport mechanisms required to effect either chloride secretion or sodium absorption. Thus, depending on the local neurohumoral environment, they have the ability to either secrete or absorb fluid. Therefore, they are in a unique position to precisely regulate the quantity and composition of the respiratory tract fluid. The importance of the respiratory tract fluid as a pulmonary defense mechanism is clear. This point is emphasized by the substantial morbidity and mortality that result from abnormalities of airway epithelial function in controlling the quantity and composition of fluid in diseases such as cystic fibrosis and asthma, and in conditions such as cigarette smoking. Therefore, it is essential to understand the function of the epithelium, its regulation, and the mechanism of ion transport at the level of the individual transport processes on the two cell membranes. As our understanding of the mechanism of ion transport increases, we may be able to define a more rational therapy of disease.