Cloning and characterization of the vasopressin-regulated urea transporter

UREA is the principal end product of nitrogen metabolism in mammals¹. Movement of urea across cell membranes was originally thought to occur by lipid-phase permeation, but recent studies have revealed the existence of specialized transporters with a low affinity for urea (K_m > 200 mM)². Here we report the isolation of a complementary DNA from rabbit renal medulla that encodes a 397-amino-acid membrane glycoprotein, UT2, with the functional characteristics of the vasopressin-sensitive urea transporter previously described in in vitro-perfused inner medullary collecting ducts^3,4. UT2 is not homologous to any known protein and displays a unique pattern of hydrophobicity. Because of the central role of this transporter in fluid balance^1,3-7 and nitrogen metabolism⁸, the study of this protein will provide important insights into the urinary concentrating mechanism and nitrogen balance.