Regulation of vocal fold transepithelial water fluxes

Vocal fold hydration is critical to phonation. We hypothesized that the vocal fold generates bidirectional water fluxes, which are regulated by activity of the Na + -K + - ATPase. Western blots and immunohistochemistry demonstrated the presence of the α-subunit Na + -K + -ATPase in the canine vocal fold ( n = 11). Luminal cells, basal and adjacent one to two layers of suprabasal cells within stratified squamous epithelium, were immunopositive, as well as basolateral membranes of submucosal seromucous glands underlying transitional epithelia. Canine ( n = 6) and ovine ( n = 14) vocal fold mucosae exhibited transepithelial potential differences of 8.1 ± 2.8 and 9.3 ± 1.3 mV (lumen negative), respectively. The potential difference and short-circuit current (ovine = 31 ± 4 μA/cm 2 ; canine = 41 ± 10 μA/cm 2 ) were substantially reduced by luminal administration of 75 μM acetylstrophanthidin ( P < 0.05). Ovine ( n = 7) transepithelial water fluxes decreased from 5.1 ± 0.3 to 4.3 ± 0.3 μl · min −1 · cm −2 from the basal to luminal chamber and from 5.2 ± 0.2 to 3.9 ± 0.3 μl · min −1 · cm −2 from the luminal to basal chamber by luminal acetylstrophanthidin ( P < 0.05). The presence of the Na + -K + -ATPase in the vocal fold epithelium and the electrolyte transport derived from its activity provide the intrinsic mechanisms to regulate cell volume as well as vocal fold hydration.