We have recently demonstrated that the α2-adrenergic radioligand [3H]idazoxan also labels additional sites that do not recognize catecholamines but bind with high affinity several chemically distinct drugs previously assumed to be highly selective for α-adrenergic receptors [Mol. Pharmacol. 35:324-330 (1989)]. We now have used three approaches to distinguish the nonadrenergic [3H]idazoxan sites from α2-adrenergic receptors. (a) No nonadrenergic [3H]idazoxan binding sites were found in COS-7 cells transfected with the genes for the two known α2-adrenergic receptor subtypes. (b) The ratio of α2-adrenergic and nonadrenergic [3H]idazoxan sites in human platelet membranes varied considerably between various donors. (c) Highly purified platelet plasma membranes were enriched for α2-adrenergic receptors but did not contain any nonadrenergic [3H]idazoxan binding sites. We conclude that the nonadrenergic [3H]idazoxan binding sites are not co-expressed with α2-adrenergic receptor and at least in human platelets may be located in an intracellular compartment.
|Original language||English (US)|
|Number of pages||4|
|State||Published - Jan 1 1990|
ASJC Scopus subject areas
- Molecular Medicine