Cheung Y D, Triggle C R
Division of Basic Medical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Canada.
Biochem Pharmacol. 1988 Nov 1;37(21):4055-61. doi: 10.1016/0006-2952(88)90095-0.
The properties of alpha adrenoceptors in rat-tail artery membranes were studied using tritiated ligands that are selective for the alpha 1 and alpha 2 subtypes. High-affinity saturable binding was obtained for the alpha 1 antagonist prazosin yielding a Bmax of 144 +/- 31.6 fmol/mg protein (mean +/- SEM, N = 3) and a Kd of 0.17 +/- 0.04 nM, and also for the alpha 2 antagonist rauwolscine which yielded a Bmax of 141.3 +/- 19.3 fmol/mg protein and a Kd of 1.57 +/- 0.32 nM. The [3H]prazosin-labelled sites displayed a pharmacological profile characteristic of an alpha 1 adrenoceptor, whereas the [3H]rauwolscine-labelled sites exhibited the expected alpha 2 adrenoceptor profile. Agonist affinity for [3H]rauwolscine sites was reduced by Gpp(NH)p and Na+, and the effects appeared synergistic for adrenaline, but non-interactive for UK-14304. Agonist interaction with [3H]prazosin sites in the rat-tail artery was also regulated by Gpp(NH)p and Na+, although clearly in a qualitatively and quantitatively different manner from the [3H]rauwolscine sites. These results suggest that distinct binding sites for [3H]prazosin and [3H]rauwolscine could be differentiated with antagonist ligands. These distinct antagonist recognition sites demonstrate the pharmacological profile expected for alpha 1 and alpha 2 adrenoceptors, and the quantitatively differing abilities of Na+ and Gpp(NH)p to regulate agonist interactions with these sites are suggestive, but do not necessarily prove, that different G proteins may be involved in this regulation.
利用对α1和α2亚型具有选择性的氚标记配体，研究了大鼠尾动脉膜中α肾上腺素能受体的特性。对于α1拮抗剂哌唑嗪，获得了高亲和力的饱和结合，其Bmax为144±31.6 fmol/mg蛋白质（平均值±标准误，N = 3），Kd为0.17±0.04 nM；对于α2拮抗剂利血平，也获得了高亲和力的饱和结合，其Bmax为141.3±19.3 fmol/mg蛋白质，Kd为1.57±0.32 nM。[3H]哌唑嗪标记的位点显示出α1肾上腺素能受体的药理学特征，而[3H]利血平标记的位点则表现出预期的α2肾上腺素能受体特征。Gpp(NH)p和Na+降低了激动剂对[3H]利血平位点的亲和力，肾上腺素的作用表现为协同，但对UK-14304无相互作用。尽管与[3H]利血平位点在定性和定量上明显不同，但Gpp(NH)p和Na+也调节了大鼠尾动脉中激动剂与[3H]哌唑嗪位点的相互作用。这些结果表明，[3H]哌唑嗪和[3H]利血平的不同结合位点可以用拮抗剂配体进行区分。这些不同的拮抗剂识别位点显示出α1和α2肾上腺素能受体预期的药理学特征，Na+和Gpp(NH)p调节激动剂与这些位点相互作用的定量差异能力具有提示作用，但不一定能证明不同的G蛋白可能参与了这种调节。
