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Table 2 Efficacy and potency of opioid agonists for the stimulation of [35S] GTPγS binding in HEK 293 cells stably expressing hMOR or Ala348,353 hMOR. Agonist efficacy was calculated as the maximal difference between specific [35S] GTPγS binding in the presence and absence of agonist and is expressed in fmol/mg. EC50 values were obtained from curve fitting of dose response curves shown in Figure 3. Receptor densities were 4.13 ± 0.26 and 1.5 ± 0.20 pmol/mg membrane protein for hMOR and Ala348,353 hMOR, respectively. Statistical analysis was performed using Student's t test: the asterisks (**p < 0.01, ***p < 0,001) refer to values significantly different from corresponding values for hMOR (Student's t test,)

From: Enhanced spontaneous activity of the mu opioid receptor by cysteine mutations: characterization of a tool for inverse agonist screening.

  Basal DAMGO Morphine
   Efficacy EC50 Efficacy EC50
  fmol/mg fmol/mg nM fmol/mg nM
hMOR 25 ± 2 98 ± 10 81 ± 2 48 ± 7 176 ± 2
  (n = 32) (n = 10) (n = 5) (n = 3) (n = 3)
Ala348,353 hMOR 41 ± 2.5*** 58 ± 6 *** 9.1 ± 2.4** 48 ± 5 60 ± 2**
  (n = 18) (n = 9) (n = 4) (n = 4) (n = 4)