title: Differential regulation by cAMP-dependent protein kinase and protein kinase C of the mu opioid receptor coupling to a G protein-activated K+ channel.
abstract: A mu opioid receptor and a G protein-activated K+ channel were coexpressed in Xenopus oocytes. Stimulation of the mu opioid receptor induced an inwardly rectifying current that was blocked by opioid receptor antagonist naloxone, indicating that the mu opioid receptor is functionally coupled to the K+ channel. The coupling is mediated by G proteins, since pertussis toxin treatment reduced the K+ current and injection of GTP gamma S (guanosine 5'-O-(thiotriphosphate)) enhanced it. Repeated stimulation of the mu receptor leads to desensitization, as the K+ current from the second stimulation was reduced to 70% of that from the first one. Both cAMP-dependent protein kinase (PKA) and protein kinase C (PKC) regulate this process, but in opposite direction. Activation of PKC by treatment of the oocyte with phorbol ester potentiated the desensitization of the mu receptor-induced current. However, incubation of the cell with a membrane-permeable cAMP analog, 8-chlorophenylthio-cAMP, completely abolished the desensitization. The cAMP effect appears to be mediated by PKA, since injection of a PKA catalytic subunit showed the same effect as cAMP incubation. These results suggest that PKA and PKC differentially regulate the mu opioid receptor coupling to the G protein-activated K+ channel.
authors.affiliation: Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis 46202.
authors.forename: Y
authors.initials: Y
authors.lastname: Chen
authors.forename: L
authors.initials: L
authors.lastname: Yu
mesh_terms: D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D017931:DNA Primers; D005260:Female; D019204:GTP-Binding Proteins / Q000096:biosynthesis / Q000187:drug effects / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D008969:Molecular Sequence Data; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D037342:Pertussis Toxin; D015221:Potassium Channels / Q000096:biosynthesis / Q000187:drug effects / Q000502:physiology*; D011493:Protein Kinase C / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017450:Receptors, Opioid, mu / Q000096:biosynthesis / Q000187:drug effects / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D014981:Xenopus
chemical_list: D017931:DNA Primers; D015221:Potassium Channels; D012333:RNA, Messenger; D017450:Receptors, Opioid, mu; D010566:Virulence Factors, Bordetella; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D037342:Pertussis Toxin; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D019204:GTP-Binding Proteins