title: Transgenic Restoration of Urea Transporter A1 Confers Maximal Urinary Concentration in the Absence of Urea Transporter A3.
abstract: Urea has a critical role in urinary concentration. Mice lacking the inner medullary collecting duct (IMCD) urea transporter A1 (UT-A1) and urea transporter A3 (UT-A3) have very low levels of urea permeability and are unable to concentrate urine. To investigate the role of UT-A1 in the concentration of urine, we transgenically expressed UT-A1 in knockout mice lacking UT-A1 and UT-A3 using a construct with a UT-A1 gene that cannot be spliced to produce UT-A3. This construct was inserted behind the original UT-A promoter to yield a mouse expressing only UT-A1 (UT-A1(+/+)/UT-A3(-/-)). Western blot analysis demonstrated UT-A1 in the inner medulla of UT-A1(+/+)/UT-A3(-/-) and wild-type mice, but not in UT-A1/UT-A3 knockout mice, and an absence of UT-A3 in UT-A1(+/+)/UT-A3(-/-) and UT-A1/UT-A3 knockout mice. Immunohistochemistry in UT-A1(+/+)/UT-A3(-/-) mice also showed negative UT-A3 staining in kidney and other tissues and positive UT-A1 staining only in the IMCD. Urea permeability in isolated perfused IMCDs showed basal permeability in the UT-A1(+/+)/UT-A3(-/-) mice was similar to levels in wild-type mice, but vasopressin stimulation of urea permeability in wild-type mice was significantly greater (100% increase) than in UT-A1(+/+)/UT-A3(-/-) mice (8% increase). Notably, basal urine osmolalities in both wild-type and UT-A1(+/+)/UT-A3(-/-) mice increased upon overnight water restriction. We conclude that transgenic expression of UT-A1 restores basal urea permeability to the level in wild-type mice but does not restore vasopressin-stimulated levels of urea permeability. This information suggests that transgenic expression of UT-A1 alone in mice lacking UT-A1 and UT-A3 is sufficient to restore urine-concentrating ability.
authors.affiliation: Renal Division, Department of Medicine, and Department of Physiology, Emory University, Atlanta, Georgia janet.klein@emory.edu.
authors.forename: Janet D
authors.initials: JD
authors.lastname: Klein
authors.affiliation: Renal Division, Department of Medicine, and.
authors.forename: Yanhua
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Renal Division, Department of Medicine, and.
authors.forename: Abinash
authors.initials: A
authors.lastname: Mistry
authors.affiliation: Renal Division, Department of Medicine, and.
authors.forename: Lauren M
authors.initials: LM
authors.lastname: LaRocque
authors.affiliation: Renal Division, Department of Medicine, and.
authors.forename: Patrick A
authors.initials: PA
authors.lastname: Molina
authors.affiliation: Renal Division, Department of Medicine, and.
authors.forename: Richard T
authors.initials: RT
authors.lastname: Rogers
authors.affiliation: Renal Division, Department of Medicine, and Department of Physiology, Emory University, Atlanta, Georgia.
authors.forename: Mitsi A
authors.initials: MA
authors.lastname: Blount
authors.affiliation: Renal Division, Department of Medicine, and Department of Physiology, Emory University, Atlanta, Georgia.
authors.forename: Jeff M
authors.initials: JM
authors.lastname: Sands
mesh_terms: D000818:Animals; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D014508:Urea / Q000652:urine*; D014553:Urinary Tract Physiological Phenomena; D000096982:Urea Transporters
chemical_list: D026901:Membrane Transport Proteins; D014508:Urea; D000096982:Urea Transporters
keywords: IMCD; aquaporin; concentrating mechanism; transgenic mice; urea transporter; urine; vasopressin