Weiss R J, Webb R C, Smith C B
J Pharmacol Exp Ther. 1983 Jun;225(3):599-605.
The specific binding of [3H]clonidine was used to characterize alpha-2 adrenoreceptors on rat tail artery smooth muscle membranes. At 24 degrees C binding of 8 nM [3H]clonidine was rapid T 1/2 of association = 2.1 min) and reversible (T 1/2 of dissociation = 0.7 min). The binding sites for the [3H]clonidine showed the specificity required for the alpha-2 adrenoreceptor. The rank order of potency of inhibitors of [3H]clonidine binding for agonists was clonidine greater than phenylephrine greater than methoxamine and for antagonists was yohimbine and piperoxan much greater than prazosin. Scatchard analysis of the binding data indicated the existence of a single population of binding sites with the maximum number of binding sites, Bmax, equal to 33.5 +/- 0.3 fmoles/mg of protein and the dissociation constant, KD, equal to 7.3 +/- 0.4 nM. There was no evidence for cooperativity (Hill coefficient = 0.96). The inhibition constants, Ki values, of various adrenergic agonists and antagonists for the displacement of [3H]clonidine from tail artery membranes were well correlated with Ki values determined for the displacement of this ligand from rat hippocampal membranes. Similar correlations were found with the potencies of these same agents in producing contractions of isolated tail artery strips. This study confirms the presence of alpha-2 adrenoreceptors on arterial smooth muscle and suggests that these receptors might be important in vascular function.
利用[3H]可乐定的特异性结合来表征大鼠尾动脉平滑肌膜上的α2肾上腺素能受体。在24℃时，8 nM [3H]可乐定的结合迅速（结合半衰期T1/2 = 2.1分钟）且可逆（解离半衰期T1/2 = 0.7分钟）。[3H]可乐定的结合位点显示出α2肾上腺素能受体所需的特异性。[3H]可乐定结合抑制剂对激动剂的效力排序为可乐定＞去氧肾上腺素＞甲氧明，对拮抗剂的效力排序为育亨宾和哌泊昔泮远大于哌唑嗪。对结合数据进行Scatchard分析表明存在单一的结合位点群体，最大结合位点数Bmax等于33.5±0.3 fmol/mg蛋白质，解离常数KD等于7.3±0.4 nM。没有协同性的证据（希尔系数 = 0.96）。各种肾上腺素能激动剂和拮抗剂从尾动脉膜上置换[3H]可乐定的抑制常数Ki值与从大鼠海马膜上置换该配体所测定的Ki值密切相关。在使离体尾动脉条收缩方面，这些相同药物的效力也发现了类似的相关性。本研究证实了动脉平滑肌上存在α2肾上腺素能受体，并表明这些受体可能在血管功能中起重要作用。
