[3H]-idazoxan binds with high affinity to two sites on hamster adipocytes: an alpha 2-adrenoceptor and a non-adrenoceptor site

Br J Pharmacol. 1989 Dec;98(4):1143-50. doi: 10.1111/j.1476-5381.1989.tb12658.x.

Abstract

1. [3H]-idazoxan labels a single population of high affinity sites (Kd 2.26 +/- 0.02 nM; Bmax 372 +/- 25 fmol mg-1 protein) in hamster adipocyte membranes. In the presence of 1 microM yohimbine to preclude binding to alpha 2-adrenoceptors, the density of [3H]-idazoxan binding sites was reduced (287 +/- 18 fmol mg-1 protein) without an apparent decrease in the affinity (Kd 2.19 +/- 0.24 nM) of the radioligand. 2. Displacement studies indicate that alpha-adrenoceptor ligands with an imidazoline side chain completely inhibit [3H]-idazoxan binding to hamster adipocyte membranes; in contrast, the alpha 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 alpha 2-adrenoceptors. 3. The low potency of noradrenaline and adrenaline in displacing [3H]-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 suggest that [3H]-idazoxan binds with high affinity to two sites in hamster adipocytes: an alpha 2-adrenoceptor and a non-adrenoceptor imidazoline site.

MeSH terms

  • Adipose Tissue / cytology
  • Adipose Tissue / metabolism*
  • Animals
  • Binding, Competitive
  • Cerebral Cortex / drug effects
  • Cerebral Cortex / metabolism
  • Cricetinae
  • Dioxanes / metabolism*
  • Dioxins / metabolism*
  • Idazoxan
  • Imidazoline Receptors
  • In Vitro Techniques
  • Kinetics
  • Male
  • Mesocricetus
  • Rats
  • Rats, Inbred Strains
  • Receptors, Adrenergic, alpha / metabolism*
  • Receptors, Drug / metabolism*

Substances

  • Dioxanes
  • Dioxins
  • Imidazoline Receptors
  • Receptors, Adrenergic, alpha
  • Receptors, Drug
  • Idazoxan