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Abstract:
[Arg8]vasopressin and oxytocin are the two main members of the neurohypophysial hormone family found to be present in nearly all mammals. [Lys8]vasopressin ([Lys8]VP) has been identified as the antidiuretic hormone in pig and some marsupial families. The porcine‐derived kidney epithelial cell line, LLC‐PK1, expresses both [Lys8]VP receptors coupled to the activation of adenylate cyclase (V2 receptors) and oxytocin receptors. Here we report the molecular cloning of the V2 [Lys8]VP receptor and the oxytocin receptor from LLC‐PK1 cells. The cloned V2 [Lys8]VP receptor differs from human and rat V2 [Arg8] receptors mainly in its N‐terminal region, in residues located in the extracellular loops and in intracellular phosphorylation sites. When expressed in COS7 cells, the V2 [Lys8]VP receptor exhibits the relative order of ligand affinity [Lys8]VP = [Arg8]VP ≫ 1‐deamino[d‐Arg8]VP ≥ oxytocin and adenylate‐cyclase stimulation, expected for the porcine V2 [Lys8]VP receptor but different from V2 [Arg8]VP receptors. Adenylate‐cyclase activation by [Lys8]VP was inhibited in COS7 cells by a V2 antagonist. The cloned oxytocin receptor exhibits in COS7 cells a ligand specificity typical of mammalian oxytocin receptors. mRNA‐distribution analysis revealed a single 5.5‐kb transcript in the uterus from pregnant guinea pig.
