title: Urea transporters and renal function: lessons from knockout mice.
abstract: OBJECTIVE
  Gene knockout mice have been created for the collecting duct urea transporters UT-A1 and UT-A3, the descending thin-limb urea transporter UT-A2 and the descending vasa recta isoform, UT-B. In this brief review, the new insights in our understanding of the role of urea in the urinary concentrating mechanism and kidney function resulting from studies in these mice are discussed.
  
  
  RESULTS
  The major findings in studies on urea transporter knockout mice are as follows: rapid transport of urea from the inner medulla collecting duct lumen via UT-A1 or UT-A3 is essential for urea accumulation in the inner medullary interstitium; inner medulla collecting duct urea transporters are essential in water conservation by preventing urea-induced osmotic diuresis; an absence of inner medulla collecting duct urea transport does not prevent the concentration of sodium chloride in the inner medulla interstitium; deletion of the vasa recta isoform UT-B has a much greater effect on urinary concentration than deleting the descending limb isoform UT-A2.
  
  
  CONCLUSIONS
  Multiple urea transport mechanisms within the kidney are essential for producing maximally concentrated urine.
authors.affiliation: Water and Salt Research Center, Institute of Anatomy, University of Aarhus, Aarhus, Denmark. ROFE@ana.au.dk
authors.forename: Robert A
authors.initials: RA
authors.lastname: Fenton
mesh_terms: D000818:Animals; D001692:Biological Transport; D007668:Kidney / Q000502:physiology*; D007671:Kidney Concentrating Ability; D007679:Kidney Medulla / Q000378:metabolism; D007685:Kidney Tubules, Collecting / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D012965:Sodium Chloride / Q000378:metabolism; D014508:Urea / Q000378:metabolism; D000096982:Urea Transporters
chemical_list: D026901:Membrane Transport Proteins; D012965:Sodium Chloride; D014508:Urea; D000096982:Urea Transporters