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[ 3 H]‐idazoxan binds with high affinity to two sites on hamster adipocytes: an α 2 ‐adrenoceptor and a non‐adrenoceptor site
Author(s) -
MacKin A.C.,
Brown C.M.,
Spedding M.,
Kilpatrick A.T.
Publication year - 1989
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1989.tb12658.x
Subject(s) - idazoxan , hamster , rauwolscine , yohimbine , imidazoline receptor , binding site , chemistry , radioligand , endocrinology , medicine , adrenergic receptor , population , adipocyte , biology , receptor , prazosin , biochemistry , antagonist , adipose tissue , demography , sociology
1 [ 3 H]‐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 μ m yohimbine to preclude binding to α 2 ‐adrenoceptors, the density of [ 3 H]‐idazoxan binding sites was reduced (287 ± 18 fmol mg −1 protein) without an apparent decrease in the affinity ( K d 2.19 ± 0.24 n m ) of the radioligand. 2 Displacement studies indicate that α‐adrenoceptor ligands with an imidazoline side chain completely inhibit [ 3 H]‐idazoxan binding to hamster adipocyte membranes; in contrast, the α 2 ‐adrenoceptor antagonists yohimbine, rauwolscine, BDF 6143 and phentolamine inhibited only 20–30% of the specific binding with affinity values consistent with an interaction at α 2 ‐adrenoceptors. 3 The low potency of noradrenaline and adrenaline in displacing [ 3 H]‐idazoxan binding to the second site on hamster adipocyte membranes indicates that it is unlikely that this site is a type of adrenoceptor. 4 These results suggests that [ 3 H]‐idazoxan binds with high affinity to two sites in hamster adipocytes: an α 2 ‐adrenoceptor and a non‐adrenoceptor imidazoline site.