The medullary collecting duct urea transporters.

The terminal inner medullary collecting duct facilitated urea transporter, UT-A1, belongs to a family of four urea transporters. The inner medullary collecting duct also expresses three active urea transporters. Reducing urine concentrating ability in vivo upregulates UT-A1 and alters active urea secretion in the terminal inner medullary collecting duct, and induces active urea reabsorption in the initial inner medullary collecting duct.