Aquaporin-5 (AQP5), a water channel protein, in the rat salivary and lacrimal glands: immunolocalization and effect of secretory stimulation

Aquaporin-5 (AQP5) is a water channel protein and is considered to play an important role in water movement across the plasma membrane. We raised anti -AQP5 antibody and examined the localization of AQP5 protein in rat salivar y and lacrimal glands by immunofluorescence microscopy. AQP5 was found in s ecretory acinar cells of submandibular, parotid, and sublingual glands, whe re it was restricted to apical membranes including intercellular secretory canaliculi. In the submandibular gland, abundant AQPS was also found additi onally at the apical membrane of intercalated duct cells. Upon stimulation by isoproterenol, apical staining for AQPS in parotid acinar cells tended t o appear as clusters of dots. These results suggest that AQPS is one of the candidate molecules responsible for the water movement in the salivary gla nds.