It is becoming increasingly recognized that G protein-coupled receptors physically interact. These interactions may provide a mechanism for allosteric modulation of receptor function. In this study, we examined this possibility by using an established model system of a receptor heteromer consisting of μ and δ opioid receptors. We examined the effect of a number of μ receptor ligands on the binding equilibrium and association and dissociation kinetics of a radiolabeled δ receptor agonist, [3H]deltorphin II. We also examined the effect of δ receptor ligands on the binding equilibrium and association and dissociation kinetics of a radiolabeled μ receptor agonist, [3H][d-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin ([3H]DAMGO). We show that μ receptor ligands are capable of allosterically enhancing δ receptor radioligand binding and vice versa. Thus, there is strong positive cooperativity between the two receptor units with remarkable consequences for ligand pharmacology. We find that the data can be simulated by adapting an allosteric receptor model previously developed for small molecules, suggesting that the ligand-occupied protomers function as allosteric modulators of the partner receptor's activity.
This work was supported by National Institutes of Health National Institute on Drug Abuse [Grants DA08863, DA019251] (to L.A.D.); and by the Dutch Top Institute Pharma project [Grant D1-105] (to A.P.IJ.)
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
- G protein-coupled receptor
- opioid receptor
- deltorphin II
- 7-benzylidenenaltrexone maleate
- Chinese hamster ovary
- ICI 174,864
- analysis of variance
- (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl) pyrrolo-[1,2,3-d,e]-1,4-benzoxazin-6-yl]-1-naphthalenyl-methanone.
- Received December 28, 2010.
- Accepted March 17, 2011.
- Copyright © 2011 The American Society for Pharmacology and Experimental Therapeutics