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1 Division of Renal Medicine, Johns Hopkins Bayview Medical Center, Baltimore, MD, USA
2 Department of Physiology, University of Maryland School of Medicine, Baltimore, MD, USA
* To whom correspondence should be addressed. E-mail: dspector{at}jhmi.edu.
Although mammalian urothelia are generally considered impermeable to urinary constituents, invivo studies in several species suggest urothelial transport of water, urea, and solutes under certain conditions. This study investigates the expression, localization, and regulation of urea transporter B (UT-B) in rat renal pelvis, ureter, and bladder tissues. Immunoblots of homogenates of tissues identified characteristic ~40-55 and ~32 kDa bands in ureter, bladder and renal inner medulla, but not renal cortex. UT-B was localized by immunocytochemistry and was strongly expressed in all cell membranes (and to a limited extent in intracellular vesicles in the cytoplasm) of epithelial cells lining rat bladder, ureter, and renal pelvis lumens except the apical membrane of the umbrella cells. It was also present in the single layer papillary surface epithelial cell. There was no difference in immunoblot expression of UT-B in bladder or ureteral homogenates between groups of rats fed high or low protein, or high or low sodium diets. Water restriction resulted in an increase of UT-B expression in ureters (49%, p=0.001), but not in bladders (14%, p=NS). The functional role of UT-B in GU tract epithelia is unknown. UT-B may participate in regulation of epithelial cell volume and osmolality, in dissipation of urea gradients, and in possible net urea transport across uroepithelia.
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