Table 4

Blocking of 10 nM etorphine-induced μ receptor internalization

DrugnEC50Maximal Surface Receptor Staining
nM % control
Morphine54900  ± 150095  ± 4
RTI-1c53000  ± 700102  ± 7
RTI-1d5421  ± 123110  ± 4
Buprenorphine413  ± 2112  ± 6
Naloxone528  ± 6114  ± 6

Surface receptor staining was determined as described inExperimental Procedures. Curves were fitted to a standard four-parametric logistic equation with SigmaPlot (SPSS Inc., Chicago, IL). EC50 values represent the concentration of drug that produced half its maximal effect on surface receptor staining. Values are mean ± S.E.