Contribution of CFTR to apical-basolateral fluid transport in cultured human alveolar epithelial type II cells

Previous studies in intact lung suggest that CFTR may play a role in cAMP-regulated fluid transport from the distal air spaces of the lung. However, the potential contribution of different epithelial cells ( alveolar epithelial type I, type II, or bronchial epithelial cells) to CFTR-regulated fluid transport is unknown. In this study we determined whether the CFTR gene is expressed in human lung alveolar epithelial type II ( AT II) cells and whether the CFTR chloride channel contributes to cAMP-regulated fluid transport in cultured human AT II cells. Human AT II cells were isolated and cultured on collagen I-coated Transwell membranes for 120 - 144 h with an air-liquid interface. The cultured cells retained typical AT II-like features based on morphologic studies. Net basal fluid transport was 0.9 +/- 0.1 mu 1(.)cm(-2.)h(-1) and increased to 1.35 +/- 0.11 mu 1(.)cm(-2.)h(-1) (mean +/- SE, n = 18, P < 0.05) by stimulation with cAMP agonists. The CFTR inhibitor, CFTRinh-172, inhibited cAMP stimulated but not basal fluid transport. In short-circuit current (I-SC) studies with an apical-to-basolateral transepithelial Cl- gradient, apical application of CFTRinh-172 reversed the forskolin-induced decrease in I-SC. Real time RT-PCR demonstrated CFTR transcript expression in human AT II cells at a level similar to that in airway epithelial cells. We conclude that CFTR is expressed in cultured human AT II cells and may contribute to cAMP-regulated apical-basolateral fluid transport.