Detailed analysis of heterogeneity of [3H]naloxone binding sites in rat brain synaptosomes

Maria Szücs, Anna Borsodi, Anikó Bogdány, József Gaál, József Batke, Géza Toth

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The experiments reported in this paper address the question of heterogeneity of [3H]naloxone binding sites in rat brainstem synaptosomal preparations at 23°C in the presence of 100 mM sodium chloride. Kinetic analysis in the presence of 0.4, 4 and 10 nM [3H]naloxone gave pseudo-first order association rate of 0.9±0.04, 1.23±0.08 and 1.06±0.08 min-1, respectively. The dissociation of a 1 nM [3H]naloxone receptor complex was biphasic with dissociation rate constants of 1.8 and 0.4 min-1. On the other hand, dissociation of 10 nM [3H]naloxone was monophasic with a kd of 1.1 min-1. Two subpopulations of binding sites were also observed by steady state binding studies, with Kd values of 0.5 and 3.4 nM and a ratio of high to low affinity sites of 1:9. Heterogeneity of [3H]naloxone binding sites could be seen by displacement studies performed with opioid eptides and alkaloids. We suggest that our data best fits a model with two independent naloxone binding sites wherein either one or both undergo a multi-step interaction with ligand.

Original languageEnglish
Pages (from-to)581-587
Number of pages7
JournalNeurochemical research
Issue number7
Publication statusPublished - Jul 1 1987



  • Opioid receptor
  • kinetic analysis
  • multiple binding sites

ASJC Scopus subject areas

  • Biochemistry
  • Cellular and Molecular Neuroscience

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