Mediates the transport of urea driven by a concentration gradient across the cell membrane of the renal inner medullary collecting duct which is critical to the urinary concentrating mechanism. Mediates the transport of urea driven by a concentration gradient across the cell membrane of the renal inner medullary collecting duct which is critical to the urinary concentrating mechanism. Mediates the transport of urea driven by a concentration gradient across the cell membrane of the renal inner medullary collecting duct which is critical to the urinary concentrating mechanism. Mediates the transport of urea driven by a concentration gradient across the cell membrane (PubMed:11029290). Implicated in the urea movement across the blood-testis barrier and does not translocate water (PubMed:11029290). urea(in) = urea(out) urea(in) = urea(out) urea(in) = urea(out) urea(in) = urea(out) Inhibited by phloretin (PubMed:12217874). Activated by forskolin, 3-isobutyl-1-methylxanthine (IBMX) and cAMP (PubMed:12217874). Inhibited by phloretin. Inhibited by phloretin (PubMed:11029290). Activated by forskolin, 3-isobutyl-1-methylxanthine (IBMX) and cAMP (PubMed:12217874). Inhibited by phloretin. Highly expressed in kidney medulla (at protein level) (PubMed:12217874). Also detected in testes, heart, brain and liver (at protein level) (PubMed:12217874). In the kidney, present in thin descending limbs of the loop of Henle and in the middle and terminal inner medullary collecting ducts. Expressed in the kidney medulla. Expressed in the kidney medulla. Expressed in the peritubular myoid cells forming the outermost layer of the seminiferous tubules within the testes and is not detected in kidney (PubMed:11029290). Expression levels are coordinated with the stage of testes development and increase 15 days postpartum, commensurate with the start of seminiferous tubule fluid movement (PubMed:11029290). Belongs to the urea transporter family. It is uncertain whether Met-1 or Met-10 is the initiator.