The urea transporter UT-A1 plays a predominant role in a urea-dependent urine-concentrating mechanism.

Urea transporters are a family of urea-selective channel proteins expressed in multiple tissues and play an important role in the urine-concentrating mechanism of the mammalian kidney. Previous studies have shown that knockout of urea transporter-B (UT-B), UT-A1/A3, or all-UT lead to urea-selective diuresis, indicating that urea transporters have important roles in urine concentration. Here, we sought to determine the role of UT-A1 in the urine-concentrating mechanism in a newly developed UT-A1-knockout mouse model. Phenotypically, daily urine output in UT-A1-knockout mice was nearly 3-fold that of wild-type mice and 82% of all-UT-knockout mice, and the UT-A1-knockout mice had significantly lower urine osmolality than wild-type mice. After 24 h water restriction, acute urea loading, or high-protein (40%) intake, UT-A1 knockout mice were unable to increase urine-concentrating ability. Compared with all-UT-knockout mice, the UT-A1-null mice exhibited similarly elevated daily urine output and decreased urine osmolality, indicating impaired urea-selective urine concentration. Our experimental findings reveal that UT-A1 has a predominant role in urea-dependent urine-concentrating mechanisms, suggesting that UT-A1 represents a promising diuretic target.