[3H]-idazoxan binds with high affinity to two sites on hamster adipocytes: An α2-adrenoceptor and a non-adrenoceptor site

A. C. MacKinnon, C. M. Brown, M. Spedding, A. T. Kilpatrick

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    [3H]-Idazoxan labels a single population of high affinity sites (K(d) 2.26 ± 0.02 nM; B(max) 372 ± 25 fmol mg-1 protein) in hamster adipocyte membranes. In the presence of 1 µM yohimbine to preclude binding to a2-adrenoceptors, the density of [3H]-idazoxan binding sites was reduced (287 ± 18 fmol mg-1 protein) without an apparent decrease in the affinity (K(d) 2.19 ± 0.24 nM) of the radioligand. Displacement studies indicate that a-adrenoceptor ligands with an imidazoline side chain completely inhibit [3H]-idazoxan binding to hamster adipocyte membranes; in contrast, the a2-adrenoceptor antagonists yohimbine, rauwolscine, BDF 6143 and phentolamine inhibited only 20-30% of the specific binding with affinity values consistent with an interaction at a2-adrenoceptors. The low potency of noradrenaline and adrenaline in displacing [3H]-idazoxan binding to the second site on hamster adipocyte membranes indicates that it is unlikelky that this site is a type of adrenoceptor. These results suggests that [3H]-idazoxan binds with high affinity to two sites in hamster adipocytes: an a2-adrenoceptor and a non-adrenoceptor imidazoline site.

    Original languageEnglish
    Pages (from-to)1143-1150
    Number of pages8
    JournalBritish Journal of Pharmacology
    Issue number4
    Publication statusPublished - 1989


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