title: Cellular and subcellular localization of the vasopressin- regulated urea transporter in rat kidney.
abstract: The renal urea transporter (RUT) is responsible for urea accumulation in the renal medulla, and consequently plays a central role in the urinary concentrating mechanism. To study its cellular and subcellular localization, we prepared affinity-purified, peptide-derived polyclonal antibodies against rat RUT based on the cloned cDNA sequence. Immunoblots using membrane fractions from rat renal inner medulla revealed a solitary 97-kDa band. Immunocytochemistry demonstrated RUT labeling of the apical and subapical regions of inner medullary collecting duct (IMCD) cells, with no labeling of outer medullary or cortical collecting ducts. Immunoelectron microscopy directly demonstrated labeling of the apical plasma membrane and of subapical intracellular vesicles of IMCD cells, but no labeling of the basolateral plasma membrane. Immunoblots demonstrated RUT labeling in both plasma membrane and intracellular vesicle-enriched membrane fractions from inner medulla, a subcellular distribution similar to that of the vasopressin-regulated water channel, aquaporin-2. In the outer medulla, RUT labeling was seen in terminal portions of short-loop descending thin limbs. Aside from IMCD and descending thin limbs, no other structures were labeled in the kidney. These results suggest that: (i) the RUT provides the apical pathway for rapid, vasopressin-regulated urea transport in the IMCD, (ii) collecting duct urea transport may be increased by vasopressin by stimulation of trafficking of RUT-containing vesicles to the apical plasma membrane, and (iii) the rat urea transporter may provide a pathway for urea entry into the descending limbs of short-loop nephrons.
authors.affiliation: Department of Cell Biology, University of Aarhus, Denmark.
authors.forename: S
authors.initials: S
authors.lastname: Nielsen
authors.forename: J
authors.initials: J
authors.lastname: Terris
authors.forename: C P
authors.initials: CP
authors.lastname: Smith
authors.forename: M A
authors.initials: MA
authors.lastname: Hediger
authors.forename: C A
authors.initials: CA
authors.lastname: Ecelbarger
authors.forename: M A
authors.initials: MA
authors.lastname: Knepper
mesh_terms: D000818:Animals; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins; D001485:Basement Membrane / Q000378:metabolism / Q000648:ultrastructure; D002352:Carrier Proteins / Q000032:analysis / Q000187:drug effects / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D015151:Immunoblotting; D007074:Immunoglobulin G; D007150:Immunohistochemistry; D007473:Ion Channels / Q000032:analysis / Q000378:metabolism; D007668:Kidney / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D007672:Kidney Cortex / Q000378:metabolism; D007679:Kidney Medulla / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000032:analysis / Q000187:drug effects / Q000378:metabolism*; D026901:Membrane Transport Proteins; D016253:Microscopy, Immunoelectron; D008970:Molecular Weight; D009399:Nephrons / Q000378:metabolism; D051381:Rats; D014508:Urea / Q000378:metabolism; D014667:Vasopressins / Q000494:pharmacology*; D000096982:Urea Transporters
chemical_list: D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins; D002352:Carrier Proteins; D007074:Immunoglobulin G; D007473:Ion Channels; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D014508:Urea; D014667:Vasopressins; D000096982:Urea Transporters; C496025:Aqp2 protein, rat