Wallace D R, Muskardin D T, Zahniser N R
Department of Pharmacology, University of Colorado Health Science Center, Denver.
Eur J Pharmacol. 1994 Jun 2;258(1-2):67-76. doi: 10.1016/0014-2999(94)90058-2.
Binding characteristics of alpha 2-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 alpha 2-adrenoceptor subtype-selective competitors, both alpha 2A/D- and alpha 2C-adrenoceptor subtypes were detected, suggesting rat cortical membranes contain approximately 90% alpha 2A/D-adrenoceptor subtype and 10% alpha 2C-adrenoceptor subtype. Only alpha 2A/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) alpha 2A/D-adrenoceptors are the predominant subtype in rat cerebral cortex, (2) demonstrate that the small number of alpha 2C-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.
使用拮抗剂放射性配体[3H]咪唑克生、[3H]2-(2-甲氧基-1,4-苯并二恶烷-2-基)-2-咪唑啉([3H]RX821002)以及部分激动剂放射性配体[125I]2-[2,6-(二氯-4-碘苯基)亚氨基]咪唑啉([125I]碘氯苯胍)，比较大鼠大脑皮质膜中α2-肾上腺素能受体的结合特性。使用[3H]RX821002和α2-肾上腺素能受体亚型选择性竞争剂时，检测到α2A/D-和α2C-肾上腺素能受体亚型，提示大鼠皮质膜含有约90%的α2A/D-肾上腺素能受体亚型和10%的α2C-肾上腺素能受体亚型。使用[3H]咪唑克生和[125I]碘氯苯胍仅检测到α2A/D-肾上腺素能受体。所有三种放射性配体均结合至单一高亲和力位点(Kd = 0.3 - 1.6 nM)。然而，[3H]咪唑克生和[125I]碘氯苯胍标记的位点密度比[3H]RX821002标记的密度高50%，这可能代表非肾上腺素能受体结合位点。甘氨酰甘氨酸缓冲液中[125I]碘氯苯胍结合位点的密度与[3H]RX821002标记的密度相似。这些结果表明：(1)α2A/D-肾上腺素能受体是大鼠大脑皮质中的主要亚型；(2)证明使用哌唑嗪取代[3H]RX821002结合可检测到该组织中少量的α2C-肾上腺素能受体；(3)使用甘氨酰甘氨酸缓冲液可使[125I]碘氯苯胍的非肾上腺素能受体结合最小化。
