QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: jpet.104.074641v1 312/2/809    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Clark, M. J. Articles by Traynor, J. R. Search for Related Content PubMed PubMed Citation Articles by Clark, M. J. Articles by Traynor, J. R.

CELLULAR AND MOLECULAR

Endogenous Regulator of G Protein Signaling Proteins Reduce µ-Opioid Receptor Desensitization and Down-Regulation and Adenylyl Cyclase Tolerance in C6 Cells

Pharmacology Department, University of Michigan Medical Center, Ann Arbor, Michigan

Chronic exposure of cells to µ-opioid agonists leads to tolerance which can be measured by a reduced ability to activate signaling pathways in the cell. Cell signaling through inhibitory G proteins is negatively regulated by RGS (regulator of G protein signaling) proteins. Here we examine the hypothesis that the GTPase accelerating activity of RGS proteins, by altering the lifetime of G and G, plays a role in the development of cellular tolerance to µ-opioids. C6 glioma cells were stably transfected with µ-opioid receptor and pertussis toxin (PTX)-insensitive G_o that was either sensitive or insensitive to endogenous RGS proteins. Cells were treated with PTX to uncouple endogenous G proteins followed by exposure to the µ-opioid agonists [D-Ala²,N-Me-Phe⁴,Gly⁵-ol]-enkephalin (DAMGO) or morphine. Receptor desensitization as measured by agonist-stimulated [³⁵S]GTPS binding and receptor down-regulation as measured by [³H]diprenorphine binding were increased in cells expressing RGS-insensitive G_o. Exposure to high concentrations of morphine or the peptidic µ-opioid agonist DAMGO led to a tolerance to inhibit adenylyl cyclase activity in both cell types with a rapid (30 min) and a slower component. Using a submaximal concentration of DAMGO to induce a reduced level of tolerance, a shift in the concentration-effect curve for DAMGO to inhibit adenylyl cyclase activity was seen in the cells expressing RGS-insensitive G_o, but not in the cells expressing RGS-sensitive G_o, which can be partly explained by an increased supersensitization of the adenylyl cyclase response. The results show that RGS proteins endogenously expressed in C6 cells reduce agonist-induced µ-opioid receptor desensitization, down-regulation, and sensitivity to tolerance to inhibit adenylyl cyclase activity.

Address correspondence to: Dr. John R. Traynor, Department of Pharmacology, University of Michigan Medical School, 1301 Medical Science Research Building III, 1150 West Medical Center Drive, Ann Arbor, MI 48109-0632. E-mail: jtraynor{at}umich.edu

This article has been cited by other articles:

				X. Huang, Y. Fu, R. A. Charbeneau, T. L. Saunders, D. K. Taylor, K. D. Hankenson, M. W. Russell, L. G. D'Alecy, and R. R. Neubig Pleiotropic Phenotype of a Genomic Knock-In of an RGS-Insensitive G184S Gnai2 Allele. Mol. Cell. Biol., September 1, 2006; 26(18): 6870 - 6879. [Abstract] [Full Text] [PDF]

				J. R. Traynor and R. R. Neubig REGULATORs OF G PROTEIN SIGNALING & DRUGS OF ABUSE Mol. Interv., February 1, 2005; 5(1): 30 - 41. [Abstract] [Full Text] [PDF]