TitleCloning, pharmacological characterization and tissue distribution of an ORL1 opioid receptor from an amphibian, the rough-skinned newt Taricha granulosa
Publication TypeJournal Article
Year of Publication2005
AuthorsWalthers, EA, Bradford, CS, Moore, FL
JournalJournal of Molecular Endocrinology
Type of ArticleJournal Article

We have cloned and characterized an opioid receptor-like (ORL1; also referred to as NOP) receptor from a urodele amphibian, the rough-skinned newt Taricha granulosa The cDNA clone encodes a protein of 368 amino acids that contains the seven hydrophobic domains characteristic of G-protein-coupled receptors, and has the highest sequence identity to the frog (Rana pipiens) nociceptin-like and human ORD1 opioid receptors (79(.)6 and 68(.)4%, respectively). Saturation binding assays on membranes from COS-7 cells transiently expressing the newt ORL1 (nORL) receptor revealed a single, high-affinity (estimated K-d, 0(.)1974 nM) binding site for the ORL1-specific agonist [H-3]orphanin FQ analog ([H-3]oFQ). In competition binding assays, the [H-3]oFQ-binding site, like the mammalian ORL1 receptor, had no affinity for the non-selective opioid receptor antagonist naloxone, the K-selective agonists U69593 and U50488, or the mu- and delta-selective opioid receptor agonists DAMGO and DPDPE, respectively. However, the nORL receptor displayed higher affinities for the K-selective agonists dynorphin A (1-13), dynorphin B, and dynorphin A (1-8) (K-i values, 2(.)8, 151(.)8, and 183(.)0 nM, respectively) than its mammalian homologue. The tissue distribution of the nORL receptor, as determined by reverse transcriplase PCR, was also found to differ from reports on the mammalian ORL1 receptor, with mRNA detected in brain, spinal cord, and lung, but not detected in a number of other peripheral tissues reported to express the receptor in mammals. This is the first report describing the expression and characterization of an amphibian ORL1 receptor, and contributes to our understanding of the evolution of the opioid system.

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