title: kappa-Opioid receptor activates an inwardly rectifying K+ channel by a G protein-linked mechanism: coexpression in Xenopus oocytes.
abstract: cRNAs encoding the kappa-opioid receptor and an inwardly rectifying, G protein-coupled, K+ channel were coinjected into Xenopus oocytes. The effects of kappa-opioid receptor agonists and antagonists on the membrane currents in these oocytes were studied using the two-electrode voltage-clamp technique. The kappa-opioid receptor agonists U69593 and dynorphin A induced a concentration-dependent inward current (EC50 of approximately 0.3 microM and approximately 30 nM, respectively) after coinjection of both cRNAs, whereas the mu-opioid receptor agonist [D-Ala2,N-MePhe4,Gly5-ol]enkephalin (10 microM) and the delta-opioid receptor agonist [D-Pen2,5]enkephalin (1 microM) had no effect. The agonist-induced inward current was reversible upon washing out of the agonists and was inhibited in the presence of the K+ channel blocker Ba2+ (0.1 mM). The specific kappa-opioid receptor antagonist norbinaltorphimine (0.1 microM) and the nonspecific opioid receptor antagonist naloxone (1 microM) abolished the agonist-induced currents. Furthermore, the agonist-induced currents exhibited rapid desensitization in the continuous presence of the agonists or after repeated application. Preincubation of the coinjected oocytes with pertussis toxin (400 ng/ml for 3 days of 1.5 microgram/ml for 24 hr) abolished most of the agonist-induced activation of the inwardly rectifying K+ current. We therefore conclude that specific stimulation of the kappa-opioid receptor can activate the inwardly rectifying K+ channel through a pertussis toxin-sensitive G protein.
authors.affiliation: Department of Pharmacology, University of Chicago, Illinois 60637, USA.
authors.forename: G H
authors.initials: GH
authors.lastname: Ma
authors.forename: R J
authors.initials: RJ
authors.lastname: Miller
authors.forename: A
authors.initials: A
authors.lastname: Kuznetsov
authors.forename: L H
authors.initials: LH
authors.lastname: Philipson
mesh_terms: D000818:Animals; D044482:Benzeneacetamides; D003001:Cloning, Molecular; D004399:Dynorphins / Q000494:pharmacology; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D020881:Enkephalin, D-Penicillamine (2,5)-; D004745:Enkephalins / Q000494:pharmacology; D005260:Female; D019204:GTP-Binding Proteins / Q000378:metabolism*; D015870:Gene Expression / Q000187:drug effects; D066298:In Vitro Techniques; D051379:Mice; D009270:Naloxone / Q000494:pharmacology; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009865:Oocytes / Q000378:metabolism; D037342:Pertussis Toxin; D015221:Potassium Channels / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D011759:Pyrrolidines / Q000494:pharmacology; D018075:RNA, Complementary / Q000235:genetics; D017473:Receptors, Opioid, kappa / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D014981:Xenopus
chemical_list: D044482:Benzeneacetamides; D004745:Enkephalins; D015221:Potassium Channels; D011759:Pyrrolidines; D018075:RNA, Complementary; D017473:Receptors, Opioid, kappa; D010566:Virulence Factors, Bordetella; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D009270:Naloxone; C051844:norbinaltorphimine; D009271:Naltrexone; D004399:Dynorphins; D020881:Enkephalin, D-Penicillamine (2,5)-; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; C045444:U 69593