MOLECULAR-CLONING AND FUNCTIONAL-CHARACTERIZATION OF V2 [8-LYSINE] VASOPRESSIN AND OXYTOCIN RECEPTORS FROM A PIG-KIDNEY CELL-LINE

[Arg8]vasopressin and oxytocin are the two main members of the neurohy pophysial hormone family found to be present in nearly all mammals. [L ys8]vasopressin ([Lys8]VP) has been identified as the antidiuretic hor mone in pig and some marsupial families. The porcine-derived kidney ep ithelial cell line, LLC-PK1, expresses both [Lys8]VP receptors coupled to the activation of adenylate cyclase (V2 receptors) and oxytocin re ceptors. Here we report the molecular cloning of the V2 [Lys8]VP recep tor and the oxytocin receptor from LLC-PK, cells. The cloned V2 [Lys8] VP receptor differs from human and rat V2 [Arg8] receptors mainly in i ts N-terminal region, in residues located in the extracellular loops a nd in intracellular phosphorylation sites. When expressed in COS7 cell s, the V2 [Lys8]VP receptor exhibits the relative order of ligand affi nity [Lys8]VP = [Are]VP much greater than 1-deamino[D-Arg8]VP greater- than-or-equal-to oxytocin and adenylate-cyclase stimulation, expected for the porcine V2 [Lys8]VP receptor but different from V2 [Arg8]VP re ceptors. Adenylate-cyclase activation by [Lys8]VP was inhibited in COS 7 cells by a V2 antagonist. The cloned oxytocin receptor exhibits in C OS7 cells a ligand specificity typical of mammalian oxytocin receptors . mRNA-distribution analysis revealed a single 5.5-kb transcript in th e uterus from pregnant guinea pig.