Airway surface liquid (ASL) is maintained and tightly regulated by the airway epithelium. In respiratory diseases, like Cystic Fibrosis or COPD, regulation of ASL volume is impaired. We investigated major mechanisms of water transport in H441 epithelia using a novel D₂0 dilution method and Ussing-chamber experiments.

H441 epithelia cells were cultivated at the air/liquid-interface in the presence of 30 nM Dexamethasone. Non-stimulated epithelia showed resorptive transport rates of 2.03 ±0.08 µl/h*cm², N=16 (all data given as mean ±SEM). Amiloride (30 µM) reduced relative resorption to 0.12 ±0.02 (N=6). Both Cl^- channel blockers CFTRinh-172 (50 µM) and NPPB (5-Nitro-2-[3-phenylpropylamino] benzoic acid, 100 µM) reduced relative resorption to 0.86 ±0.02 (N=15) and 0.41 ±0.03 (N=15) respectively. DIOA (30 µM) an inhibitor of K⁺/Cl^- cotransporter reduced relative resorption to 0.75 ±0.04 (N=11). An increase of relative resorption to 1.13 ±0.02 (N=15) was caused by the adenylyl cyclase activator Forskolin (50 µM). The inhibitor of Na⁺/K⁺/Cl^- cotransporter Bumetanide increased relative resorption to 1.16 ±0.01 (N=6). Carbachol had no considerable effect.

Consistent with our water transport measurements, Forskolin raised short circuit current (I_sc) in Ussing-chamber experiments. Cl^- channel blockers NPPB completely and CFTRinh-172 partially decreased Amiloride sensitive I_sc. When Cl^- -free conditions were applied apically, NPPB further reduced I_SC in the presence of Amiloride. Apically added DIOA reduced Amiloride sensitive I_SC.

Our data indicates an interdependency of Cl^- conductance and Na⁺/water resorption. In a novel approach utilizing the D₂0 dilution method we were able to correlate quantitative water transport with net ion flux.