Urea transporter, kidney ; Specialized low-affinity vasopressin-regulated urea transporter. Mediates rapid transepithelial urea transport across the inner medullary collecting duct and plays a major role in the urinary concentrating mechanism. Vasopressin regulates urea transport by increasing isoform 1 accumulation in the plasma membrane and/or phosphorylation of isoform 1 (929 aa)