Expression, localization, and regulation of aquaporin-1 to -3 in rat urothelia

Although mammalian urothelia are generally considered impermeable to constituents of urine, in vivo studies in several species indicate urothelial transport of water and solutes under certain conditions. This study investigates the expression, localization, and regulation of aquaporin (AQP)-1, -2, and -3 in ureteral and bladder tissues in 48-h dehydrated and water-loaded female Wistar rats. Immunoblots of homogenates of whole ureter and bladder identified characteristic approximately 28- and 35- to 44-kDa bands for AQP-1, -2, and -3. AQP-1 was localized to capillary and arteriole endothelial cells, whereas AQP-2 and -3 circumferentially lined the epithelial cell membranes except for the apical membrane of the epithelial cells adjacent to the lumens of both ureter and bladder. AQP-2 was also present in epithelial cell cytoplasm. Dehydration resulted in 160-200% increases of AQP-3 signal and 24-49% increases of AQP-2 signal but no change in AQP-1 signal on immunoblots of homogenates of ureters and bladders. AQPs in genitourinary tract urothelia likely play a role in the regulation of epithelial cell volume and osmolality and may play a role in bulk water movement across urothelia.