title: Mu-type opioid receptors in rat periaqueductal gray-enriched P2 membrane are coupled to guanine nucleotide binding proteins.
abstract: The periaqueductal gray (PAG) region of the midbrain has been implicated in both stimulation-produced and opioid-induced analgesia. High affinity mu-selective opioid binding sites presumably associated with mu-type opioid receptors have been detected in rat PAG-enriched P2 membrane. In the present study the signal transduction mechanism of mu-type opioid receptors in the PAG was examined utilizing both in vitro radioligand binding and GTPase assays. The non-hydrolyzable guanine triphosphate (GTP) analog guanyl-5'-yl beta-gamma-imidodiphosphate (GppNHp) inhibited specific high affinity [3H][D-Ala2,N-MethylPhe4,Glyol5]enkephalin (DAGO) binding in rat PAG-enriched P2 membrane in a dose-dependent manner. DAGO stimulated total GTPase activity in rat PAG-enriched P2 membrane in a saturable, dose-dependent, ligand-selective, stereoselective, and naloxone-reversible manner. This DAGO stimulation of total GTPase activity was also dependent on Na+ and Mg2+, and was abolished by pertussis toxin pretreatment of the membrane. Overall these data suggest that mu-type opioid receptors in the PAG are coupled to guanine nucleotide binding proteins (G proteins).
authors.affiliation: Department of Pharmacology, University of California, San Francisco 94143.
authors.forename: J P
authors.initials: JP
authors.lastname: Fedynyshyn
authors.forename: N M
authors.initials: NM
authors.lastname: Lee
mesh_terms: D000818:Animals; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D004745:Enkephalins / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism* / Q000502:physiology; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D008297:Male; D010487:Periaqueductal Gray / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D017450:Receptors, Opioid, mu; D015398:Signal Transduction
chemical_list: D004745:Enkephalins; D011957:Receptors, Opioid; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D006165:Guanylyl Imidodiphosphate; D010744:Phosphoric Monoester Hydrolases; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins