Table 3

Potencies and efficacies of various ligands for stimulating [35S]GTPγS binding

DrugnEC50% Maximal Stimulation
Etorphine110.973  ± 0.195100
Morphine636.3  ± 7.182  ± 23-a
Fentanyl859.7  ± 11.177  ± 23-a
RTI-1a41.01  ± 0.25103  ± 6
RTI-1b54.46  ± 0.49105  ± 7
RTI-1c8ND13  ± 43-a
RTI-1d8ND8  ± 23-a
Buprenorphine8ND21  ± 33-a

Measurement of the ability of various ligands to stimulate [35S]GTPγS binding was performed as described inExperimental Procedures. The maximal amount of stimulation caused by each ligand is expressed as a percentage of the maximal amount of stimulation caused by etorphine. Curves were fitted to a standard four-parametric logistic equation with SigmaPlot (SPSS Inc., Chicago, IL). Results for RTI-1c, RTI-1d, and buprenorphine were based on treatment with 10 μM of each drug. Values are means ± S.E.

  • ND, not determined.

  • 3-a Significantly less than etorphine-induced stimulation,P < .05 by Student's t test.