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Table 4 Stimulation of [35S]GTPγS binding by opioids in rMOR-1 and rMOR-1H2

From: Identification and characterization of seven new exon 11-associated splice variants of the rat mu opioid receptor gene, OPRM1

  rMOR-1 rMOR-1H2
  EC 50 EC 50/K i % Max Relative Efficacy (%) EC 50 EC 50/K i % Max Relative Efficacy (%)
Morphine 59 ± 18 39 180 ± 4 71 70 ± 24 88 225 ± 20* 90
M6G 40 ± 4 9 149 ± 3 59 44 ± 6 17 189 ± 25 75
DAMGO 35 ± 2 90 192 ± 5 76 20 ± 3* 54 209 ± 17 83
β-Endorphin 58 ± 34 21 226 ± 12 89 24 ± 8 6 241 ± 17 96
Dynorphin A 344 ± 64 22 254 ± 6 100 162 ± 12* 7 251 ± 44 100
  1. Membranes were prepared from CHO cells stably transfected with the indicated cDNA constructs and [35S]GTPγS binding carried out as described in the Methods section. The maximal stimulation, defined as the percent increase over basal binding, % Max, and the dose of drug needed to elicit 50% of the maximal response, the EC50, were calculated by nonlinear regression analysis (GraphPad Prism 4.0). Results are the means ± S.E.M. of at least three independent determinations. Significant differences of the EC50 and maximal stimulation between rMOR-1 and rMOR-1H2 were analyzed by Student t-test. Intrinsic activity (EC50/K i ) was calculated by dividing EC50 values by K i values in Table 2. The relative efficacies for the listed opioids were determined for each of the variants, based upon the maximal stimulation values. The drug with the highest level of stimulation for a specific variant was arbitrarily given an efficacy of 100%. Efficacy for all the other compounds for the indicated variant was defined relative to the drug with the greatest maximal stimulation. *: p < 0.05, when compared to rMOR-1.