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. 1982 Nov;77(3):461–468. doi: 10.1111/j.1476-5381.1982.tb09319.x

Spectrum of the μ-, δ- and κ-binding sites in homogenates of rat brain

MGC Gillan, HW Kosterlitz
PMCID: PMC2044623  PMID: 6291693

Abstract

1 In homogenates of rat brain, the binding characteristics of tritiated opiates and opioid peptides were examined and the relative capacities of μ-, δ- and κ-binding sites of the opiate receptor determined by saturation analysis.

2 In competition experiments, binding of the selective μ-ligand [3H]-[D-Ala2,MePhe4,Gly-ol5]enkephalin at the μ-site was displaced by [D-Ala2,D-Leu5]enkephalin with rather low affinity (KI = 12.6 nM) and more readily by the ketazocine-like compounds (-)-ethylketazocine (KI = 3.1 nM) and (-)-bremazocine (KI = 0.32 nM), which also displaced the binding of [3H]-[D-Ala2,D-Leu5]enkephalin from the δ-site. In contrast, the binding to the κ-site was easily displaced by ethylketazocine (1.0 nM) and bremazocine (0.37 nM) but not by the μ-ligand [D-Ala2,MePhe4,Gly-ol5]enkephalin (KI = 2000-3000 nM) or the δ-ligand [D-Ala2,D-Leu5]enkephalin (KI > 20,000 nM).

3 The dissociation equilibrium constant (KD) and the binding capacity (pmol/g) of the μ-binding site were determined with the selective μ-ligand [3H]-[D-Ala2,MePhe4,Gly-ol5]enkephalin. For the δ-site, [3H]-[D-Ala2,D-Leu5]enkephalin was used in the presence of unlabelled [D-Ala2,MePhe4,Gly-ol5]enkephalin in order to suppress cross-reactivity to the μ-binding site. For the estimation of κ-binding, [3H]-(±)-ethylketazocine or [3H]-(-)-bremazocine were used in the presence of unlabelled μ- and δ-ligands for the suppression of cross-reactivities to the μ- and δ-binding sites.

4 In rat brain the capacity of the μ-binding site was 7.3 pmol/g brain, that of the δ-binding site 6.7 pmol/g brain and that of the κ-binding site 2.0 pmol/g brain. Thus, the κ-binding site had the lowest value whereas in the guinea-pig brain the capacity of the μ-binding site was lower than that of the δ- or κ-binding site.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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