Deighan Clare, Woollhead Alison M, Colston Janet F, McGrath John C
Autonomic Physiology Unit, Division of Neuroscience and Biomedical Systems, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, G12-8QQ.
Br J Pharmacol. 2004 Jul;142(6):1031-7. doi: 10.1038/sj.bjp.0705872. Epub 2004 Jun 21.
1 Alpha1-adrenoceptors (ARs) play an important functional role in the liver; yet little is known about their cellular location. We identified the subtypes present in wild-type (WT) and alpha1B-AR knockout (KO) mice livers at 3 and 4 months of age, and investigated their distribution in hepatocytes. 2 The fluorescent alpha1-AR antagonist quinazolinyl piperazine borate-dipyrromethene (QAPB) was used to visualise hepatic alpha1-ARs and radioligand binding with [3H]-prazosin was used to quantify the alpha1-AR population. 3 QAPB and [3H]-prazosin bound specifically to hepatic alpha1-ARs with nanomolar affinity. The cellular distribution of alpha1-ARs was similar in WT and alpha1B-AR KO hepatocytes; QAPB binding was distributed diffusely throughout the cell with no binding evident on the plasma membrane. Radioligand binding produced Bmax values as follows: 3-month WT - 76+/-3.3 fmol mg(-1); 4-month WT - 50+/-3.1 fmol mg(-1); 3-month alpha1B-AR KO - 7.4+/-0.73 fmol mg(-1); 4-month alpha1B-AR KO - 30+/-2.0 fmol mg(-1). 4 In 3- and 4-month WT liver, all antagonists acted competitively. RS100329 (alpha1A-selective) and BMY7378 (alpha1D-selective) bound with low affinities, indicating the presence of alpha1B-ARs. In 4-month alpha1B-AR KO liver prazosin produced a biphasic curve, whereas RS100329 and BMY7378 produced monophasic curves of high and low affinity, respectively, indicating the presence of alpha1A-ARs. 5 In conclusion, we have made the novel observation that alpha1-ARs can compensate for one another in the absence of the endogenously expressed receptor; yet there appears to be no subtype-specific subcellular location of alpha1-ARs; the WT livers express alpha1B-ARs, while alpha1B-AR KO livers express alpha1A-ARs. This study provides new insights into both hepatocyte and alpha1-AR biology.
1 α1肾上腺素能受体（ARs）在肝脏中发挥着重要的功能作用；然而，关于它们的细胞定位却知之甚少。我们鉴定了3月龄和4月龄野生型（WT）及α1B-AR基因敲除（KO）小鼠肝脏中存在的亚型，并研究了它们在肝细胞中的分布。2 荧光α1-AR拮抗剂喹唑啉基哌嗪硼酸-二吡咯亚甲基（QAPB）用于可视化肝脏α1-ARs，[3H]-哌唑嗪放射性配体结合用于定量α1-AR群体。3 QAPB和[3H]-哌唑嗪以纳摩尔亲和力特异性结合肝脏α1-ARs。WT和α1B-AR KO肝细胞中α1-ARs的细胞分布相似；QAPB结合在整个细胞中呈弥漫性分布，质膜上无明显结合。放射性配体结合产生的Bmax值如下：3月龄WT - 76±3.3 fmol mg(-1)；4月龄WT - 50±3.1 fmol mg(-1)；3月龄α1B-AR KO - 7.4±0.73 fmol mg(-1)；4月龄α1B-AR KO - 30±2.0 fmol mg(-1)。4 在3月龄和4月龄WT肝脏中，所有拮抗剂均表现出竞争性作用。RS100329（α1A选择性）和BMY7378（α1D选择性）以低亲和力结合，表明存在α1B-ARs。在4月龄α1B-AR KO肝脏中，哌唑嗪产生双相曲线，而RS100329和BMY7378分别产生高亲和力和低亲和力的单相曲线，表明存在α1A-ARs。5 总之，我们有了一个新的发现，即α1-ARs在缺乏内源性表达受体的情况下可以相互补偿；然而，α1-ARs似乎没有亚型特异性的亚细胞定位；WT肝脏表达α1B-ARs，而α1B-AR KO肝脏表达α1A-ARs。这项研究为肝细胞生物学和α1-AR生物学提供了新的见解。
