Regulation of aquaporin water channels in vocal fold epithelium

Vocal fold hydration is of critical importance to the initiation and maintenance of sustained phonation, although the mechanisms of ion and water transport in this system are only recently being investigated. Aquaporin water channels, present in the plasma membrane of epithelial cells, allow the passive osmotic passage of water across the cell membrane. The aim of these studies was to identify the presence and regulation of aquaporins in vocal fold epithelial cells.; Freshly excised ovine larynges were obtained from the abbatoir and exposed to either 10nM vasopressin or sham control for short-term (40 minutes) or long-term (4 hours) regulation studies. Long-term regulation of aquaporins by vasopressin was investigated using real-time RT-PCR of AQP1 (N=34) and AQP2 (N=32) mRNA of ovine vocal folds. Long-term vasopressin-treated vocal fold samples contained significantly higher levels of AQP1, but not AQP2, as compared to sham controls. Short-term regulation of aquaporins by vasopressin was investigated using immunolocalization of AQP1 and AQP2 proteins in ovine vocal folds exposed to either vasopressin (10nM, N=8) or sham control (N=8) for 40 minutes. Immunolocalization of sham controls revealed labeling of AQP1, and to a lesser extent, AQP2, in the plasma membrane and circular bodies in the cytoplasm of luminal cells. Immunolabeling densities of the plasma membrane and cytoplasm were not significantly different between vasopressin-treated and sham control samples for either AQP1 or AQP2. Light microscopy of thick sections revealed an increased cell size of vasopressin-treated samples as compared to sham controls, as well as rough luminal edges in some samples.; The pattern of labeling seen in control samples is consistent with a specialization of luminal cells for rapid fluxes of water in response to osmotic challenges at the lumen of the airway. The vasopressin-dependent increase of AQP1 mRNA in stratified squamous epithelium of the vocal fold suggests a hormonal mechanism for long-term upregulation of water permeability in luminal cells. Increases in cell volume of vocal fold epithelial cells following short-term vasopressin exposure suggested an effect of vasopressin on water permeability in these cells, although no increase in immunolabeling of aquaporins was visible in samples.