[3H]idazoxan binding at non-alpha 2-adrenoceptors in rabbit adipocyte membranes.

The imidazoline ligand, [3H]idazoxan, labels a large population of high-affinity binding sites in rabbit fat cell membranes (Bmax = 1370 +/- 91 fmol/mg protein; KD = 1.6 +/- 0.6 nM) when imidazoline derivatives are used for definition of non-specific binding. [3H]Idazoxan sites are not alpha 2-adrenoceptors as assessed by competition studies which showed that epinephrine, norepinephrine and yohimbine do not inhibit [3H]idazoxan binding. Naphazoline, tramazoline and the Na+/H+ exchange inhibitor, amiloride, completely inhibited [3H]idazoxan binding. The Ki values were 9, 27 and 48 nM, respectively.