Pharmacological characterization of [3H]idazoxan, [3H]RX821002 and p-[125I]iodoclonidine binding to α2-adrenoceptors in rat cerebral cortical membranes

David R. Wallace, Danny T. Muskardin, Nancy R. Zahniser

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24 Scopus citations


Binding characteristics of α2-adrenoceptors in rat cerebral cortical membranes were compared using the antagonist radioligands [3H]idazoxan, [3H]2-(2-methoxy-1,4-benzodioxan-2-yl)-2-imidazoline ([3H]RX821002), and the partial agonist radioligand [125I]2-[2,6-(dichloro-4-iodophenyl)imino]imidazoline ([125I]iodoclonidine). With [3H]RX821002 and α2-adrenoceptor subtype-selective competitors, both α2A/D- and α2C-adrenoceptor subtypes were detected, suggesting rat cortical membranes contain approximately 90% α2A/D-adronoceptor subtype and 10% α2C-adrenoceptor subtype. Only α2A/D-adrenoceptors were detected with [3H]idazoxan and [125I]iodoclonidine. All three radioligands bound to a single high affinity site (Kd = 0.3-1.6 nM). However, the densities of sites labeled by [3H]idazoxan and [125I]iodoclonidine were 50% greater than the density labeled by [3H]RX821002, likely representing non-adrenoceptor binding sites. The density of [125I]iodoclonidine binding sites in glycylglycine buffer was similar to that labeled by [3H]RX821002. These results suggest that: (1) α2A/D-adrenoceptors are the predominant subtype in rat cerebral cortex, (2) demonstrate that the small number of α2C-adrenoceptors in this tissue can be detected using prazosin to displace [3H]RX821002 binding, and (3) non-adrenoceptor binding with [125I]iodoclonidine can be minimized with the use of glycylglycine buffer.

Original languageEnglish
Pages (from-to)67-76
Number of pages10
JournalEuropean Journal of Pharmacology
Issue number1-2
StatePublished - 2 Jun 1994


  • Cortex
  • Imidazoline
  • Non-adrenoceptor binding
  • α-Adrenoceptor

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