Purpose: This study was designed to clarify the physiological function and tissue distribution of aquaporin 5 (AQP5) in the lacrimal and parotid glands. Methods: Saliva and tear volumes were compared in AQP5 knockout (AQP5-/-) mice and wild-type mice. Immunohistochemistry and immunoblot analysis were performed in wild-type and AQP5-/- mice. Results: Immunofluorescence of AQP5 staining showed that AQP5 was localized mainly in the ductal cells rather than in the acinar cells of the lacrimal gland. In contrast, in the parotid gland, AQP5 was observed abundantly in acinar cells with undetectable staining in ductal cells. Tear secretion was not changed in AQP5-/- mouse, although saliva secretion was significantly reduced. Conclusions: AQP5 distribution in acinar cells and ductal cells was completely opposite in the lacrimal and parotid glands. The physiological role of AQP5 might be dependent on the characteristic tissue distribution of the protein in the lacrimal and parotid glands.
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