Water permeability in human airway epithelium

Osmotic water permeability (P_f) was studied in spheroid-shaped human airway epithelia explants derived from nasal polyps by the use of a new improved tissue collection and isolation procedure. The fluid-filled spheroids were lined with a single cell layer with the ciliated apical cell membrane facing the outside. They were capable of surviving hours of experiment involving continuous superfusion of the bathing medium and changes of osmolarity. A new image analysis technique was developed for measuring the spheroid diameters, giving high time and measurement resolutions. The transepithelial P_f, determined by the changes of the apical solution osmolarity, was not influenced by the presence of glucose, Na⁺, or Na⁺/glucose-cotransport inhibitors in the bath, but was sensitive to the aquaporin (AQP) inhibitor HgCl₂. The measured P_f levels and the values of activation energy were in the range of those seen in AQP-associated water transport. Together, these results indicate the presence of an AQP in the apical membrane of the spheroids. Notably, identical values for P_f were found in CF and non-CF airway preparations, as was the case also for the calculated spontaneous fluid absorption rates.