Table 1

[35S]GTPγS intrinsic efficacies and [3H]naloxoneKi values of opioid agonists in mMOR-CHO cell and rat thalamic membranes

AgonistEmax (%Max)EC50(nM)Ki(nM)nHKi/EC50Intrin. Eff
A. mMOR-CHO cells
  DAMGO100  ± 4.5a 27.3  ± 6.5108  ± 180.61  ± 0.043.94**2.47
  Methadone108  ± 4.1a 62.6  ± 8.6283  ± 890.78  ± 0.124.52**2.98
  Fentanyl§110  ± 1.1a 23.0  ± 4.16.6  ± 6.20.56  ± 0.052.89**2.13
  Morphine§106  ± 3.1a 120  ± 25286  ± 651.03  ± 0.132.38*1.79
  Alfentanil111  ± 11a 387  ± 54575  ± 1000.99  ± 0.011.491.38
  Sufentanil104  ± 11a 4.0  ± 0.73.8  ± 2.30.67  ± 0.110.931.31
  Meperidine48  ± 1.5b 2214  ± 4022153  ± 6270.76  ± 0.100.970.48
  Buprenorphine§43  ± 3.5bc 3.6  ± 1.20.38  ± 0.11.32  ± 0.430.110.43
  Nalorphine17  ± 1.1cd 7.0  ± 1.415.4  ± 2.50.72  ± 0.072.20*0.17
  Nalbuphine16  ± 0.4cd 9.0  ± 1.615.9  ± 1.40.90  ± 0.061.77*0.16
  Levallorphan§12  ± 1.0d 2.7  ± 1.21.8  ± 0.31.12  ± 0.120.660.12
B. Rat thalamus
  DAMGO100  ± 4.6a 204  ± 18143  ± 170.52  ± 0.020.701.00
  Methadone103  ± 1.4a 478  ± 6.2218  ± 400.64  ± 0.070.46*1.03
  Fentanyl§58  ± 4.6b 117  ± 2165.7  ± 7.00.75  ± 0.060.560.58
  Morphine§56  ± 3.0b 314  ± 59201  ± 280.67  ± 0.040.640.56
  Sufentanil56  ± 1.2b 3.8  ± 2.63.4  ± 0.40.70  ± 0.060.900.56
  Buprenorphine§10  ± 1.5c 0.74  ± 0.51.1  ± 0.21.20  ± 0.091.510.10
  Nalorphine8.4  ± 1.4c 13.1  ± 5.010.1  ± 2.10.82  ± 0.130.770.08

Data were obtained from experiments depicted in figures 1 and 2. For calculations of intrinsic efficacy,Ki/EC50 values for partial agonists are assumed to be 1; where Ki/EC50values are ≤1, intrinsic efficacy was determined by the fractionalEmax. Emax values containing the same letter designations are not significantly different from each other, whereas those that do not contain any similar letter designations are significantly different (P < .05). ForKi/EC50 ratios: *P < .05; **P < .01 different from 1, respectively.

  • §Emax and EC50 values are fromSelley et al. (1997).