Format

Send to

Choose Destination
Eur J Pharmacol. 2002 Sep 27;452(1):21-33.

Quantitative stoichiometry of G-proteins activated by mu-opioid receptors in postmortem human brain.

Author information

1
Department of Pharmacology, University of the Basque Country, E-48940 Leioa, Vizcaya, Spain. Javier.Maeso@mssm.edu

Abstract

Paradoxically, the potencies (EC(50)) of agonists stimulating [35S]GTPgammaS binding are several orders of magnitude lower than their affinities in receptor binding assays. We have investigated the quantitative stoichiometry of mu-opioid receptor-G-protein coupling in postmortem human brain. [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]enkephalin (DAMGO) displaced [3H]naloxone binding in a biphasic pattern. The ratio between K(i-low) and EC(50) of DAMGO stimulating [35S]GTPgammaS binding was lower than one. The K(A) of DAMGO was calculated following mu-opioid receptor alkylation by beta-funaltrexamine from [35S]GTPgammaS binding data using the "nested hyperbolic method", yielding K(A)/EC(50)>1. Thus, only 1.2 +/- 0.2% of mu-opioid receptors was needed to be occupied to achieve the half-maximal effect of DAMGO. The estimated ratio between the G-proteins activated by 10 microM DAMGO (determined by isotopic dilution curves) and the occupied-mu-opioid receptors was 1304. In conclusion, we have determined the stoichiometric and the kinetic parameters in the mu-opioid receptor-G-protein system.

PMID:
12323382
[Indexed for MEDLINE]

Supplemental Content

Full text links

Icon for Elsevier Science
Loading ...
Support Center