TitleIdentification and characterization of mesotocin and V1a-like vasotocin receptors in a urodele amphibian, Taricha granulosa
Publication TypeJournal Article
Year of Publication2011
AuthorsSearcy, BT, Bradford, CS, Thompson, RR, Filtz, TM, Moore, FL
JournalGeneral and Comparative Endocrinology
Type of ArticleJournal Article

The cDNA sequences encoding the mesotocin receptor (MTR) and vasotocin 1a receptor (VTR-1a) were identified in a urodele amphibian, the rough-skinned newt, Taricha granulosa. Saturation binding of [H-3]oxytocin (OT) to the Taricha MTR (tMTR) was best fit by a two-state model; a high affinity-low abundance site and a lower affinity-high abundance site. Competition-binding studies found the following rank-order affinities for the tMTR: mesotocin (MT) > OT approximate to vasotocin (VT) > vasopressin (VP) > isotocin (IT). Inositol phosphate (IP) accumulation studies demonstrated functional activity of both the tMTR and Taricha VTR-1a (tVTR-1a) in a heterologous cell culture system. The rank-order potencies for the tMTR were MT > OT > VT approximate to VP > IT. The combined binding and IP results indicate that VT may act as a partial agonist of the tMTR. Rank-order potencies for the tVTR-1a were VT > VP > MT approximate to OT > IT. For both receptors, stimulation of IP accumulation was blocked by d(CH2)(5)[Tyr(Me)(2)]AVP (Manning compound) and d(CH2)(5)[Tyr(Me)(2),Thr(4),Tyr-NH2]OVT (OTA). OTA was a more potent antagonist for the transiently expressed tMTR while Manning compound was relatively more potent at inhibiting IP accumulation in tVTR-1a expressing cells. In contradiction to earlier assumptions, the absolute IC50 of Manning compound was lower for the tMTR (27 nM +/- 13) than the tVTR-1a (586 nM +/- 166) indicating its potential higher affinity for the tMTR, a finding with special relevance to interpretation of comparative studies investigating the behavioral and physiological actions of neurohypophysial peptides in non-mammalian species. (C) 2010 Elsevier Inc. All rights reserved.

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