Immunolocalization of AQP5 in Salivary Glands of Rat

Kwon, Tae Hwan; Lee, Wan; Jung, Yong Wook

Abstract

Exocrine glands secrete large volumes of fluid in response to neural or hormonal stimulation. In the present studies, we examined the immunolocalization of AQP1-5 in salivary glands of rat to clarify the potential roles of these for fluid secretion. Immunohistochemistry using cryosections of rat submandibular glands revealed that AQP1 was located in the capillary endothelia between secretory gland cells. Secretory gland cells and ductal cells were not labeled with anti-AQP1, AQP2 and AQP3 were not present in either salivary gland cells, intercalated ductal cells or striated ducts. AQP4 was localized in the basolateral plasma membrane domains of the intercalated ductal cells in rat submandibular glands whereas either secretory gland cells or striated ducts were not labeled. AQP5 was abundant in the apical domains of the secretory gland cells as well as of the secretory canaliculi and intercalated ductal cells, consistent with RT-PCR analyses as well as previous data (Nielsen et al., 1997). Importantly, AQP5 labeling was associated with the apical part of the secretory gland cells, raising the possibility for trafficking of AQP5 from intracellular vesicles to the apical plasma membranes following neuronal or hormonal stimulation. In parotid and sublingual glands, the immunolabeling pattern of AQPs was identical with that seen in submandibular glands, while the AQP5 immunolabeling was sparse in the sublingual glands which is mainly composed of mucinous glands. In conclusion, the basolateral localization of AQP4 in the intercalated ductal cells and presence of AQP5 in the apical plasma membrane of secretory acinar cells, canaliculi and intercalated ductal cells of submandibular gland suggest that both AQP4 and AQP5 may provide a critical pathway for osmotic water flow into the secreted fluid.