Mediates the transport of urea driven by a concentration gradient across the cell membrane (PubMed:15845882, PubMed:22733730). Mediates the transport of urea across the cell membranes of erythrocytes and the renal inner medullary collecting duct which is critical to the urinary concentrating mechanism (By similarity). Facilitates water transport in erythrocytes (By similarity). urea(in) = urea(out) The rate of urea conduction is increased by hypotonic stress. Homotrimer; each subunit contains a pore through which urea permeates (PubMed:22733730). Identified in a complex with STOM (By similarity). Restricted to the basolateral membrane in various portions of the urothelium. Expressed in both kidney and rumen (at protein level). Expressed in both kidney and rumen and is the predominant isoform in the rumen (at protein level). Belongs to the urea transporter family.