Endothelial cells of the kidney vasa recta express the urea transporter HUT11

The cell specific expression of the human urea transporter HUT11 in human and rat kidneys was investigated by immunochemistry and in situ hybridization. Using specific rabbit polyclonal antibodies directed against the N-terminal part and the C-terminal part of HUT11, we found that endothelial cells of medullary vasa recta (outer and inner medulla) express HUT11. In addition, an HUT11-related protein expressed by smooth muscle cells of cortical arterioles can be detected by the anti-HUT11 N-terminal peptide antibody but not the anti-HUT11 C-terminal peptide antibody. The endothelial expression of HUT11 was confirmed by double labeling with anti-CD31 and anti-von Willebrand factor antibodies. No HUT11-positive cells expressed alpha smooth muscle actin, Tamm Horsfall protein, cytokeratin 18, or CAM-L1, a marker of the principal cells of collecting ducts. Medullary vasa recta of developing and mature rat kidneys were also stained with the anti-HUT11 C-terminal peptide antibody. By in situ hybridization using a specific HUT11 35S-cDNA probe on human kidney sections, medullary vasa recta but not other renal structures were found to express HUT11 mRNA. We conclude that endothelial cells of medullary vasa recta express HUT11, a specific urea transporter, which may play a role in urea recycling within the kidney and in the mechanisms of urinary concentration and urea excretion.