Identification of a high-affinity orphanin FQ/nociceptin(1-11) binding site in mouse brain.
The presence of pairs of basic amino acids within the orphanin FQ/Nociceptin (OFQ/N) sequence has raised the possibility that truncated versions of the peptide might be physiologically important. OFQ/N(1-11) is pharmacologically active in mice, despite its poor affinity in binding assays (K(i) > 250 nM) for the OFQ/N receptor. Using an analog of OFQ/N(1-11), [(125)I][Tyr(10)]OFQ/N(1-11), we identified a high-affinity binding site (K(D) 234 pM; B(max) 43 fmol/mg protein) with a selectivity profile distinct from the OFQ/N receptor and all the traditional opioid receptors. This site had very high affinity for OFQ/N and its related peptides. The most striking differences between the new site and the OFQ/N receptor previously observed in brain were seen with traditional opioids. Dynorphin A analogs and alpha-neoendorphin competed with [(125)I][Tyr(10)]OFQ/N(1-11) binding in mouse brain with K(i) values below 10 nM, while naloxone benzoylhydrazone (K(i) 3.9 nM) labeled the [(125)I][Tyr(10)]OFQ/N(1-11) binding site as potently as many traditional opioid receptors. Several other opioids, including fentanyl, (-)cyclazocine, levallorphan, naltrindole, and diprenorphine, also displayed moderate affinities for this site. Finally, the [(125)I][Tyr(10)]OFQ/N(1-11) site had a unique regional distribution consistent with a distinct receptor. Thus, [(125)I][Tyr(10)]OFQ/N(1-11) labels a novel site in brain with a selectivity profile intermediate between that of either opioid or OFQ/N receptors.
Mathis
J P
JP
The Cotzias Laboratory of Neuro-Oncology, Memorial Sloan Kettering Cancer Center, New York, NY 10021, USA.
Goldberg
I E
IE
Letchworth
S R
SR
Ryan-Moro
J P
JP
Pasternak
G W
GW
D000818:Animals; D001345:Autoradiography; D001665:Binding Sites / Q000187:drug effects* / Q000502:physiology; D001923:Brain Chemistry; D004399:Dynorphins / Q000494:pharmacology; D051379:Mice; D008815:Mice, Inbred Strains; D009294:Narcotics / Q000494:pharmacology; D018847:Opioid Peptides / Q000032:analysis / Q000494:pharmacology*; D011869:Radioligand Assay; D011957:Receptors, Opioid / Q000378:metabolism*; D014665:Vasodilator Agents / Q000494:pharmacology; D000094942:Nociceptin Receptor; D000097629:Nociceptin
D004399:Dynorphins; D009294:Narcotics; D018847:Opioid Peptides; D011957:Receptors, Opioid; D014665:Vasodilator Agents; D000094942:Nociceptin Receptor; D000097629:Nociceptin; C000722287:Oprl1 protein, mouse