LOCALIZATION AND EXPRESSION OF AQP5 IN CORNEA, SEROUS SALIVARY-GLANDS, AND PULMONARY EPITHELIAL-CELLS

Aquaporin (AQP) 5 gene was recently isolated from salivary gland and i dentified as a member of the AQP family. The mRNA expression and local ization have been examined in several organs. The present study was fo cused on elucidation of AQP5 expression and localization in the eye, s alivary gland, and lung in rat. RNase protection assay confirmed inten se expression of AQP5 mRNA in these organs but negligible expression i n other organs. To examine the mRNA expression sites in the eye, sever al portions were microdissected for total RNA isolation. AQP5 mRNA was enriched in cornea but not in other portions (retina, lens, iris/cili ary body, conjunctiva, or sclera). AQP5 was selectively localized on t he surface of corneal epithelium in the eye by immunohistochemistry an d immunoelectron microscopy using an affinity-purified anti-AQP5 antib ody. AQP5 was also localized on apical membranes of acinar cells in th e lacrimal gland and on the microvilli protruding into intracellular s ecretory canaliculi of the serous salivary gland. In the lung, apical membranes of type I pulmonary epithelial cells were also immunostained with the antibody. These findings suggest a role of AQP5 in water tra nsport to prevent dehydration or to secrete watery products in these t issues.