Immunohistochemical localization of aquaporins-2, 3 and 4 in epithelial cells of different organs of adult male albino rat

ABSTRACT

The aquaporins [AQPs] are a family of small membrane-spanning proteins that are expressed at plasma membranes of many cell types involved in fluid transport. More than 10 mammalian aquaporins have been identified, and these are selectively permeated by water [aquaporins] or water plus glycerol [aquaglyceroporins]. The aquaporin family of water channels plays a fundamental role in transmembrane water movement in numerous plant and animal tissues. However, the localization and expression of the AQP family members in different tissues have not been entirely elucidated. This work aimed to demonstrate the distribution and localization of some members of the aquaporin family [AQP2, AQP3 and AQP4] and to speculate on their possible roles in water balance regulation in different tissues. For this purpose, twenty adult male albino rats were used and specimens of different organs were removed. Specific aquaporin-2, aquaporin-3 and aquaporin-4 antibodies were utilized to characterize the localization of AQP2, AQP3, and AQP4 respectively in some epithelial cells of the rat by immunohistochemistry. Interestingly, AQP2 was confined to the apical plasma membranes of collecting duct principal cells. On the other hand, AQP3 was localized at the basolateral membranes of collecting duct principal cells and tracheal epithelial cells as well as at the plasma membranes of the basal and intermediate cells in the stratified epithelia of ureter, urinary bladder, urethra and oesophagus. Meanwhile, AQP4 was colocalized with AQP3 in collecting duct principal cells and was specifically localized in the basolateral membrane of parietal cells of gastric glands. It is suggested that these aquaporins may cooperate to maintain water balance in different cells