DAMGO and morphine-stimulated [35S] GTPγS binding at hMOR and Ala348,353 hMOR. Increasing concentrations of DAMGO and morphine (10-10 to 10-4 M) were used to stimulate [35S] GTPγS binding. Panel A: DAMGO at hMOR (■) or at Ala348,353 hMOR (▼). Panel B: morphine at hMOR (◆) or Ala348,353 hMOR (▲). Data are given as the mean ± S.E.M. from at least 3 independent experiments performed in triplicate.