Conclusion: Expression of AQPs in the vocal folds and the parasympathetic regulation of AQPs in the laryngeal glands may be important for controlling laryngeal secretion and vocal fold hydration. These findings are thought to be an initial step towards understanding potential mechanisms of water flow through the vocal fold surface.
Objectives: Lubrication of the vocal folds is important for phonation and laryngeal defense. However, the system of water transport in the laryngeal epithelium has not yet been clarified. The discovery of aquaporins (AQPs), a family of small, integral membrane proteins that facilitate water transport in response to osmotic gradients, has revealed a molecular mechanism for rapid water transport across the cell membranes of various tissues. We investigated the expression of nine AQP subtypes (AQP1-9) in the murine larynx and examined the neural regulating mechanisms of these subtypes.
Materials and methods: Distribution of AQPs (AQP1-9) in the murine larynx was examined by immunohistochemistry. Next, the neural mechanism regulating AQPs in the larynx was investigated using unilateral vagotomized mice.
Results: Expression of eight AQP subtypes (AQP1-8) was detected in the murine larynx, while AQP9 expression was not detected. AQP1, AQP4, and AQP5 were expressed in the vocal folds. AQP1 immunoreactivity was localized to the subepithelial connective tissue. AQP4 was densely expressed around the anterior commissure and was sparse at the squamous epithelium of the vocal fold, while AQP5 was expressed throughout the vocal fold epithelium. Vocal fold AQP expression was minimal at the vocal process. AQP2, AQP3, AQP5, AQP6, AQP7, and AQP8 were localized to the submucosal glands. Expression of AQPs in the vagotomized region was significantly decreased compared to the contralateral intact side, indicating the involvement of AQPs in parasympathetic regulation of laryngeal gland secretion.