These channels could be ClC-2, CFTR, or other yet unidentified chloride channels. The process is driven by the Na,K-ATPase that pumps sodium out from the cell across the basolateral membrane. The sodium concentration outside the basolateral membrane will therefore be higher than inside the cell, which is necessary for the Na,K,2Cl-cotransporter to function. Potassium is re-circulated across the basolateral membrane through potassium channels. Sodium probably also moves paracellularly across the epithelium to maintain the secretion electroneutral.
Water passively follows the ion gradient.
English abstract below . List of included articles below . Development and regulation of alveolar fluid clearance in the guinea pig Alveolar fluid clearance is driven by active absorption of sodium across the alveolar epithelium. Development and hormonal regulation of alveolar fluid clearance over 1 hour was studied by instillation of a protein-containing, isosmolar fluid into lungs of fetal, newborn, and adult guinea pigs. After 1 hour, a sample of remaining alveolar fluid was collected and the change in protein concentration was used to calculate secretion or absorption of fluid.