title: The effect of protein kinase C and G protein-coupled receptor kinase inhibition on tolerance induced by mu-opioid agonists of different efficacy.
abstract: Differences in the mechanisms underlying tolerance and mu-opioid receptor desensitization resulting from exposure to opioid agonists of different efficacy have been suggested previously. The objective of this study was to determine the effects of protein kinase C (PKC) and G protein-coupled receptor kinase (GRK) inhibition on antinociceptive tolerance in vivo to opioid agonists of different efficacy. A rapid (8-h) tolerance-induction model was used where each opioid was repeatedly administered to naive mice. Animals were then challenged with the opioid after injection of a kinase inhibitor to determine its effects on the level of tolerance. Tolerance to meperidine, morphine, or fentanyl was fully reversed by the PKC inhibitor 12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo(2,3-a)pyrrolo(3,4-c)carbazole (Gö6976). However, in vivo tolerance to [d-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin (DAMGO) was not reversed by PKC inhibition. The novel small-molecule GRK inhibitors beta-adrenergic receptor kinase 1 inhibitor and 2-(8-[(dimethylamino) methyl]-6,7,8,9-tetrahydropyridol[1,2-a]indol-3-yl)-3-(1-methylindol-3-yl)maleimide (Ro 32-0432) did not reverse the tolerance to meperidine, fentanyl, or morphine but did reverse the tolerance to DAMGO. To correlate GRK-dependent DAMGO-induced tolerance with mu-opioid receptor desensitization, we used in vitro whole-cell patch-clamp recording from mouse locus coeruleus neurons and observed that the GRK inhibitors reduced DAMGO-induced desensitization of mu-opioid receptors, whereas the PKC inhibitor had no effect. These results suggest that tolerance induced by low- and moderate-efficacy mu-opioid receptor agonists is dependent on PKC, whereas tolerance induced by the high-efficacy agonist DAMGO is dependent on GRK.
authors.affiliation: Department of Pharmacology and Toxicology, Virginia Commonwealth University Medical Center, Richmond, Virginia, USA.
authors.forename: L C
authors.initials: LC
authors.lastname: Hull
authors.forename: J
authors.initials: J
authors.lastname: Llorente
authors.forename: B H
authors.initials: BH
authors.lastname: Gabra
authors.forename: F L
authors.initials: FL
authors.lastname: Smith
authors.forename: E
authors.initials: E
authors.lastname: Kelly
authors.forename: C
authors.initials: C
authors.lastname: Bailey
authors.forename: G
authors.initials: G
authors.lastname: Henderson
authors.forename: W L
authors.initials: WL
authors.lastname: Dewey
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000187:drug effects* / Q000502:physiology; D004347:Drug Interactions; D004361:Drug Tolerance; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D005283:Fentanyl / Q000494:pharmacology; D054768:G-Protein-Coupled Receptor Kinases / Q000037:antagonists & inhibitors*; D066298:In Vitro Techniques; D008125:Locus Coeruleus / Q000187:drug effects / Q000502:physiology; D008297:Male; D008614:Meperidine / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D009020:Morphine / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D011493:Protein Kinase C / Q000037:antagonists & inhibitors*; D017450:Receptors, Opioid, mu / Q000819:agonists*
chemical_list: D000701:Analgesics, Opioid; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D009020:Morphine; D008614:Meperidine; D011493:Protein Kinase C; D054768:G-Protein-Coupled Receptor Kinases; D005283:Fentanyl