The UT-B urea transporter is the major urea transporter in red blood cells and kidney descending vasa recta. Humans and mice that lack UT-B have a mild urine-concentrating defect. Whether deletion of UT-B altered the expression of other transporter proteins involved in urinary concentration was tested. Fluorescence-based real-time reverse transcription-PCR and Northern blot analysis showed upregulation of the UT-A2 urea transporter and the aquaporin 2 (AQP2) and AQP3 water channel transcripts

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... t no change in other urea transporters or AQP. Western blot analysis showed that UT-A2 protein abundance in the outer medulla of UT-B null mice increased to 122 Ϯ 6% of wild-type control. AQP2 protein abundance increased to 177 Ϯ 32% and 127 Ϯ 7% in the outer