Comparison of binding affinities determined from competitive displacement binding against [3H][Dmt1]DALDA and [3H]DAMGO in mouse brain membranes Competitive displacement binding by various opioid ligands was carried out by incubating mouse brain membranes with 0.100 to 0.150 nM [3H][Dmt1]DALDA in the presence of increasing concentrations of unlabeled opioid ligands for 60 min at 25°C. Ki values were calculated from the obtained IC50 values by the Cheng and Prusoff equation. The Kd for [3H][Dmt1]DALDA was 0.156 nM. All values represent the mean ± S.E.M. of four to six experiments.
[3H][Dmt1]DALDA | [3H]DAMGOa | |||||
|---|---|---|---|---|---|---|
| Ki (nM) | Rel. Affinityb | Ki (nM) | Rel. Affinityb | |||
| Morphine | 5.64 ± 0.24 | 1.0 | 1.00 ± 0.04 | 1.0 | ||
| DAMGO | 2.83 ± 0.14 | 2.0 | 1.22 ± 0.12 | 0.8 | ||
| DALDA | 12.9 ± 1.0 | 0.4 | 1.69 ± 0.25 | 0.6 | ||
| [Dmt1]DALDA | 0.163 ± 0.011 | 34.6 | 0.143 ± 0.015 | 7.0 | ||
| Tyr-d-Ala-Phe-Phe-NH2 | 3.44 ± 0.50 | 1.6 | 1.53 ± 0.59 | 0.7 | ||
| Dmt-d-Ala-Phe-Phe-NH2 | 0.174 ± 0.028 | 32.4 | 0.173 ± 0.027 | 5.8 | ||
| Tyr-d-Arg-Phe-Orn-NH2 | 10.38 ± 0.09 | 0.5 | 1.2 ± 0.26 | 0.8 | ||
| Dmt-d-Arg-Phe-Orn-NH2 | 0.161 ± 0.028 | 35.0 | 0.151 ± 0.018 | 6.6 | ||
| Tyr-d-Arg-Phe-A2pr-NH2 | 12.73 ± 0.09 | 0.4 | 2.55 ± 0.27 | 0.6 | ||
| Dmt-d-Arg-Phe-A2pr-NH2 | 0.145 ± 0.021 | 38.9 | 0.0636 ± 0.0110 | 15.7 | ||
↵ a Data previously published (Schiller et al., 2000).
↵ b Rel. affinity is affinity relative to morphine.