1. The effect of protein kinase C and G protein-coupled receptor kinase inhibition on tolerance induced by mu-opioid agonists of different efficacy.
- Author
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Hull LC, Llorente J, Gabra BH, Smith FL, Kelly E, Bailey C, Henderson G, and Dewey WL
- Subjects
- Animals, Brain physiology, Drug Interactions, Drug Tolerance, Enkephalin, Ala(2)-MePhe(4)-Gly(5)- pharmacology, Fentanyl pharmacology, In Vitro Techniques, Locus Coeruleus drug effects, Locus Coeruleus physiology, Male, Meperidine pharmacology, Mice, Mice, Inbred C57BL, Morphine pharmacology, Neurons drug effects, Neurons physiology, Patch-Clamp Techniques, Analgesics, Opioid pharmacology, Brain drug effects, G-Protein-Coupled Receptor Kinases antagonists & inhibitors, Protein Kinase C antagonists & inhibitors, Receptors, Opioid, mu agonists
- 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. more...
- Published
- 2010
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