Water permeability in human airway epithelium

Abstract

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 HgCl(2). 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.

Nasospheroids permit measurements of CFTR-dependent fluid transport

“…The apical membranes face the outside, and basolateral membranes line the lumen of the spherical organoids ( Figure 1). This orientation has been observed by other groups when nondisrupted epithelial sheets are cultured in suspension (40)(41)(42)(43)(44). When CFTR is labeled with a highly specific monoclonal antibody raised against the NBD2 region of CFTR (Ab 528, provided by J.R. Riordan, UNC-Chapel Hill; refs.…”

“…Such samples provide a renewable source of differentiated airway epithelial cells from any individual with CF, regardless of their mutation, that does not require tissue expansion and multiple cell divisions prior to performing the assay. To improve the suitability of these samples for both functional and morphological tests, we have developed an organoid culture that is similar to cultures reported previously, where the apical ciliated membrane orients to the media bath (40)(41)(42)(43) but is derived from simple nasal epithelial curettage. This minimally invasive technique does not require polyp excision, which is different from the earlier reports, and utilizes normal nasal epithelial tissue.…”

Hypertonic Saline Therapy in Cystic Fibrosis

“…CF cultures had similar water permeability to non-CF cultures, consistent with our RT-PCR data (Fig. 3C) and with previous reports (8,9).…”

“…Recent data from spheroid explants of human nasal polyps provided evidence for AQP5 function in airway epithelia. In these large, spherical airway cell monolayers, with the ciliated apical membrane facing outward, Pederson et al (9) reported high membrane P f (ϳ150 m/s) that was sensitive to brief exposure to low concentration mercury. Here, our high P f values for HBE cultures and the weak temperature dependence of permeability suggest AQPmediated water movement (Fig.…”

“…Osmotically induced water transport across airways has been shown to be high and likely AQP-dependent in microperfused small airways (7) and later in cultured human tracheal epithelial cells (8) and in spheroids composed of airway epithelial cell monolayers (9). Despite this, the reduction of airway epithelial water permeability by deletion of the various lung/ airway aquaporins (AQPs 1, 3, 4 and 5) in transgenic mice did not affect ASL volume or ionic composition (10).…”