Recognition and activation of the opioid receptor-like ORL 1 receptor by nociceptin, nociceptin analogs and opioids.
Nociceptin, also known as orphanin FQ, was recently identified as the naturally occurring agonist of orphan opioid receptor-like ORL1 receptor (Meunier et al., 1995, Nature 377, 532; Reinscheid et al., 1995, Science 270, 792). Nociceptin is a heptadecapeptide which, although it resembles dynorphin A, the endogenous agonist of the kappa-opioid receptor, displays very low potency in competing with binding of [3H]diprenorphine to or inhibiting adenylate cyclase via mu-, delta- and kappa-opioid receptors. Tritium-labeled nociceptin ([3H]nociceptin) was used here to establish a pharmacological profile in vitro of the ORL 1 receptor. In membranes from recombinant Chinese hamster ovary (CHO) cells expressing the ORL 1 receptor, equilibrium binding of [3H]nociceptin is highly specific, saturable (Bmax in the range 1.3-1.8 pmol/mg protein) and of high affinity (Kd approximately equal to 0.1 nM). It is selectively decreased in the presence of Na+ ions and/or of the GTP analog 5'-guanylylimido-diphosphate, an allosteric regulation that is analogous to that of opiate binding to opioid receptors. A few opiates, namely lofentanil, a 4-anilinopiperidine derivative and etorphine, a 6,14-endo-ethenotetrahydrothebaine derivative, were found to be quite potent not only in competing with binding of [3H]nociceptin at the ORL 1 receptor but also in inhibiting forskolin-induced accumulation of cyclic AMP in intact recombinant CHO cells. In a preliminary attempt to delineate active parts of the neuropeptide, nociceptin analogs were also tested, including N- and C-terminal truncation products. Our results suggest that the highly basic, internal core of nociceptin might be essential in conferring on the peptide both affinity for and activity at the ORL 1 receptor. In this respect, the message and address division of dynorphin A, nociceptin's closest structural analog, do not seem to apply to nociceptin.
Butour
J L
JL
Unité de Neuropharmacologie Moléculaire, Centre National de la Recherche Scientifique, Toulouse, France.
Moisand
C
C
Mazarguil
H
H
Mollereau
C
C
Meunier
J C
JC
D000067956:Adenylyl Cyclase Inhibitors; D000595:Amino Acid Sequence; D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D016466:CHO Cells; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D006224:Cricetinae; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005283:Fentanyl / Q000031:analogs & derivatives / Q000494:pharmacology; D008969:Molecular Sequence Data; D018847:Opioid Peptides / Q000494:pharmacology*; D011957:Receptors, Opioid / Q000819:agonists / Q000187:drug effects*; D000094942:Nociceptin Receptor; D000097629:Nociceptin
D000067956:Adenylyl Cyclase Inhibitors; D000701:Analgesics, Opioid; D005576:Colforsin; D004791:Enzyme Inhibitors; D005283:Fentanyl; D018847:Opioid Peptides; D011957:Receptors, Opioid; D000094942:Nociceptin Receptor; D000097629:Nociceptin; C034846:lofentanil