Effect of antagonists on the incorporation of [35S] GTPγS binding in membranes expressing hMOR and Ala348,353 hMOR. [35S] GTPγS incorporation was measured as described in the Experimental Procedures. Panel A: membranes prepared from HEK 293 cells stably expressing hMOR. Panel B: membranes prepared from HEK 293 cells stably expressing Ala348,353 hMOR. All ligands were used at a concentration of 10 μM. Incorporation is expressed as percent variation over [35S] GTPγS binding in the absence of agonist. Data are given as the mean ± S.E.M. from 3 (except naloxone, CTOP and cyprodime where n = 5) independent experiments performed in triplicate. Statistical analysis was performed using Student's t test, *p < 0.05, **p < 0.01 compared to basal [35S] GTPγS.