Vasopressin regulates apical targeting of aquaporin-2 but not of UT1 urea transporter in renal collecting duct

In the renal inner medullary collecting duct (IMCD), vasopressin regulates two key transporters, namely aquaporin-2 (AQP2) and the vasopressin-regulat ed urea transporter (VRUT). Both are present in intracellular vesicles as w ell as the apical plasma membrane. Short-term regulation of AQP2 has been d emonstrated to occur by vasopressin-induced trafficking of AQP2-containing vesicles to the apical plasma membrane. Here, we have carried out studies t o determine whether short-term regulation of VRUT occurs by a similar proce ss. Cell surface labeling with NHS-LC-biotin in rat IMCD suspensions reveal ed that vasopressin causes a dose-dependent increase in the amount of AQP2 labeled at the cell surface, whereas VRUT labeled at the cell surface did n ot increase in response to vasopressin. Immunoperoxidase labeling of inner medullary thin sections from Brattleboro rats treated with 1-desamina-8-D-a rginine vasopressin (DDAVP) for 20 min revealed dramatic translocation of A QP2 to the apical region of the cell, with no change in the cellular distri bution of VRUT. in addition, differential centrifugation of inner medullary homogenates from Brattleboro rats treated with DDAVP for 60 min revealed a marked depletion of AQP2 from the low-density membrane fraction (enriched in intracellular vesicles) but did not alter the quantity of VRUT in this f raction. Finally, AQP2-containing vesicles immunoisolated from a low-densit y membrane fraction from renal inner medulla did not contain immunoreactive VRUT. Thus vasopressin-mediated regulation of AQP2, but not of VRUT, depen ds on regulated vesicular trafficking to the plasma membrane.