Abstract
Differences in the mechanisms underlying tolerance and μ-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-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO) was not reversed by PKC inhibition. The novel small-molecule GRK inhibitors β-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 μ-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 μ-opioid receptors, whereas the PKC inhibitor had no effect. These results suggest that tolerance induced by low- and moderate-efficacy μ-opioid receptor agonists is dependent on PKC, whereas tolerance induced by the high-efficacy agonist DAMGO is dependent on GRK.
Footnotes
This work was supported in part by the National Institutes of Health National Institute of Drug Abuse [Grants DA020836, K05-DA480, DA07027].
These data are a part of the dissertation work: Hull LC (July 2009) Enzymatic Regulation of Opioid Antinociception and Tolerance, Ph.D. dissertation, Virginia Commonwealth University, Richmond, VA.
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
doi:10.1124/jpet.109.161455.
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ABBREVIATIONS:
- PKC
- protein kinase C
- DAMGO
- [d-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin
- GRK
- G protein-coupled receptor kinase
- %MPE
- percentage maximal possible effect
- LC
- locus coeruleus
- β-ARK
- β-adrenergic receptor kinase
- β-ARK1 inhibitor
- β-adrenergic receptor kinase 1, methyl-5-[2-(5-nitro-2-furyl)vinyl]-2-furoate)
- PKA
- protein kinase A
- Gö6976
- 12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo(2,3-a)pyrrolo(3,4-c)carbazole
- PKI-(14-22)-amide
- Myr-N-Gly-Arg-Thr-Gly-Arg-Arg-Asn-Ala-Ile-NH2
- Ro 32-0432 HCl
- 2-(8-[(dimethylamino) methyl]-6,7,8,9-tetrahydropyridol[1,2-a]indol-3-yl)-3-(1-methylindol-3-yl)maleimide).
- Received September 8, 2009.
- Accepted December 11, 2009.
- Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics
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