Immunolocalization of aquaporins in vocal fold epithelia.

Objective: To investigate the presence of aquaporin (AQP) water channels 1, 2, and 3 in stratified squamous vocal fold epithelium.

Design: Immunolocalization analysis of excised ovine vocal fold epithelia.

Subjects: Sheep.

Interventions: Ovine vocal fold epithelia were prepared for immunoelectron microscopy using primary antibodies directed against AQP-1, AQP-2, and AQP-3. Photographic profiles of epithelium exposed to each antibody were used to calculate the immunogold labeling density of the plasma membrane and cytoplasm.

Main Outcome Measures: Density of immunolabeling was compared across 3 regions that represent cell layers closest to the glottal lumen for the plasma membrane and cytoplasm, respectively.

Results: Labeling densities of AQP-1 and AQP-2 were significantly greater for the plasma membrane region of the luminal cells than for deeper cell layers. Cytoplasmic labeling and labeling of circular structures was greatest for cell layers 2 through 5 beneath the vocal fold surface compared with the surface cell layer. Immunogold labeling of AQP-3, an aquaglyceroporin, in vocal fold epithelium was inconclusive.

Conclusion: Aquaporins 1 and 2, associated with the plasma membrane region of ovine vocal fold epithelial cells, demonstrate the presence of an intrinsic mechanism to permit transcellular water flux in response to osmotic gradients.