Yamada S, Yamamura H I, Roeske W R
J Pharmacol Exp Ther. 1980 Oct;215(1):176-85.
To identify and characterize the cardiac alpha-adrenoceptors, a radioreceptor binding assay using the potent alpha adrenergic antagonist, [3H]WB4101 was performed in rat hearts. Specific [3H]WB4101 binding to rat left ventricular homogenates was saturable, reversible and of high affinity (Kd = 0.18 nM) with a Bmax of 2.57 fmol/mg of tissue (27.7 fmol/mg of protein). Adrenergic agonists competed for specific [3H]WB4101 binding in the order: (-)-epinephrine > (-)-norepinephrine greater than (-)-isoproterenol. Stereospecificity of the [3H]WB4101 binding sites was also demonstrated with (-)-epinephrine, (Ki = 90) nM being 270 times as potent as (+)-epinephrine, (K1 = 24 microM). Adrenergic antagonists competed for the binding in the order: WB4101 = prazosin greater than yohimbine greater than (-)-propranolol. WB4101 and prazosin exhibited a markedly greater (2000 times) affinity for [3H]WB4101 binding sites than yohimbine. The affinities (pKi) of alpha agonists and antagonists for [3H]WB4101 binding sites in the rat heart closely correlated with their pharmacological potencies in the heart. Scatchard analysis for [3H]WB4101 binding, performed in five regions from control and 6-hydroxydopamine-treated rat hearts, revealed specific [3H]WB4101 binding (Bmax) significantly greater in the ventricles and intraventricular septae than in atria. At 1 week after 6-hydroxydopamine treatment, there was a significant increase (40%) in the Bmax for [3H]WB4101 binding to ventricles and intraventricular septae without a change in Kd. We conclude: 1) [3H]Wb4101 selectively labels postsynaptic alpha-1 adrenoceptors in the rat heart; 2) there is a definite regional variation for cardiac alpha-1 adrenoceptors; and 3) 6-hydroxydopamine treatment caused a significant increase in the density of alpha-1 adrenoceptors in ventricles and intraventricular septae, compatible with a postsynaptic localization of the [3H]WB4101 binding site.
为了识别和表征心脏α-肾上腺素能受体，在大鼠心脏中使用强效α-肾上腺素能拮抗剂[3H]WB4101进行了放射受体结合试验。[3H]WB4101与大鼠左心室匀浆的特异性结合是可饱和的、可逆的且具有高亲和力（Kd = 0.18 nM），Bmax为2.57 fmol/mg组织（27.7 fmol/mg蛋白质）。肾上腺素能激动剂对[3H]WB4101特异性结合的竞争顺序为：（-）-肾上腺素 > （-）-去甲肾上腺素 > （-）-异丙肾上腺素。[3H]WB4101结合位点的立体特异性也通过（-）-肾上腺素得以证明，（Ki = 90）nM的效力是（+）-肾上腺素（K1 = 24 μM）的270倍。肾上腺素能拮抗剂对结合的竞争顺序为：WB4101 = 哌唑嗪 > 育亨宾 > （-）-普萘洛尔。WB4101和哌唑嗪对[3H]WB4101结合位点的亲和力比育亨宾显著高（2000倍）。大鼠心脏中α激动剂和拮抗剂对[3H]WB4101结合位点的亲和力（pKi）与其在心脏中的药理效力密切相关。对来自对照和6-羟基多巴胺处理的大鼠心脏的五个区域进行的[3H]WB4101结合的Scatchard分析显示，[3H]WB4101的特异性结合（Bmax）在心室和室间隔中显著高于心房。在6-羟基多巴胺处理1周后，[3H]WB4101与心室和室间隔结合的Bmax显著增加（40%），而Kd无变化。我们得出结论：1）[3H]Wb4101选择性标记大鼠心脏中的突触后α-1肾上腺素能受体；2）心脏α-1肾上腺素能受体存在明确的区域差异；3）6-羟基多巴胺处理导致心室和室间隔中α-1肾上腺素能受体密度显著增加，这与[3H]WB4101结合位点的突触后定位一致。
