ENDOTHELIAL-CELLS OF THE KIDNEY VASA-RECTA EXPRESS THE UREA TRANSPORTER HUT11

The cell specific expression of the human urea transporter HUT11 in hu man and rat kidneys was investigated by immunochemistry and iii situ h ybridization. Using specific rabbit polyclonal antibodies directed aga inst the N-terminal part and thr C-terminal part of HUT11. we found th at endothelial cells of medullar?; vasa recta (outer and inner medulla ) express HUT11. In addition, an HUT11-related protein expressed by sm ooth muscle cells of cortical arterioles can be detected by the anti-H UT11 N-terminal peptide antibody but not the anti-HUT11 C-terminal pep tide antibody. The endothelial expression of HUT11 was confirmed by do uble lab;ling with anti-CD31 and anti-von Willebrand factor antibodies . No HUT11-positive cells expressed alpha smooth muscle actin, Tamm Ho rsfall protein. cytokeratin 18, or CAM-L1, a marker of the principal c ells of collecting ducts. Medullary vasa recta of developing and matur e rat kidneys were also stained with the anti-HUT11 C-terminal peptide antibody. By in situ hybridization using a specific HUT11 S-35-cDNA p robe on human kidney sections. medullary vasa recta but not other rena l structures were found to express HUT11 mRNA. We conclude that endoth elial cells of medullary vasa recta express HUT11. a specific urea tra nsporter, which may play a role in urea recycling within thr kidney an d in the mechanisms of urinary concentration and urea excretion.