通过[³H]RX 821002（[³H]咪唑克生的2-甲氧基类似物）结合鉴定人额叶皮质膜中的α₂肾上腺素能受体。

Identification of ?(2) adrenergic receptors in human frontal cortex membranes by binding of [(3)H]RX 821002, the 2-methoxy analog of [(3)H]idazoxan.

作者信息

Vauquelin G, De Vos H, De Backer J P, Ebinger G

机构信息

Department of Protein Chemistry, Free University Brussels (V.U.B.), 65 Paardenstraat, 1640 St Genesius-Rode, Belgium.

出版信息

Neurochem Int. 1990;17(4):537-46. doi: 10.1016/0197-0186(90)90041-q.

DOI:10.1016/0197-0186(90)90041-q

PMID:20504656

Abstract

The antagonist [(3)H]idazoxan binds with comparable affinity to ?(2) adrenergic receptors and to phentolamine-displaceable non-stereoselective sites in human frontal cortex membranes. In contrast, idazoxan analogs possessing alkyl and alkoxy substituents at the 2-position of the benzodioxan moiety (i.e. RX 821002: 2-methoxy-1,4-[6,7-(3)H]benzodioxan-2-yl-2-imidazolin HCl, 43.8 Ci/mmol) possess 300-1200 times lower affinity for the non-stereoselective sites. Their affinity for the ?(2) receptors is increased as well, resulting in more than a 1000-fold selectivity towards the receptors as compared to the non-stereoselective sites. [(3)H]RX 821002, the 2-methoxy analog of idazoxan possesses an approx. 10-fold higher affinity for the ?(2) receptors (K(D) = 2.8 nM than [(3)H]idazoxan (K(D) = 24 nM) and about equal affinity as [(3)H]rauwolscine (K(D) = 3.6 nM). [(3)H]Rauwolscine binds with comparable affinity to ?(2) receptors and to 5-HT(1A) receptors, and competition studies indicate that the K(i) value of unlabelled RX 821002 for the 5-HT(1A) receptors (30 nM) is about one order in magnitude above its K(i) value for the ?(2) receptors (4.1 nM). Labelling of the 5-HT(1A) receptors by [(3)H]RX 821002 and by [(3)H]rauwolscine can be prevented by selective masking with 8-OH-DPAT (30 nM) or 5-HT (0.3 ?M). Under these conditions, specific binding of [(3)H]RX 821002 to the ?(2) receptors represents 84% of total binding (at its K(D)), as compared to 77% for [(3)H]rauwolscine and 20% for [(3)H]idazoxan. [(3)H]RX 821002 labels the ?(2) receptors as a single class of non-cooperative sites. Association and dissociation kinetics are very fast at 37 degrees C. Antagonist competition curves are steep with Hill coefficients close to one and the agonist curves can be analysed in terms of two affinity sites, confirming the antagonistic properties of [(3)H]RX821002. About 60% of the ?(2) receptors possess high agonist affinity.

摘要

拮抗剂[（3）H]咪唑克生与人额叶皮质膜中的β（2）肾上腺素能受体以及酚妥拉明可置换的非立体选择性位点具有相当的亲和力。相比之下，在苯并二恶烷部分的2位具有烷基和烷氧基取代基的咪唑克生类似物（即RX 821002：2-甲氧基-1,4-[6,7-（3）H]苯并二恶烷-2-基-2-咪唑啉盐酸盐，43.8 Ci/mmol）对非立体选择性位点的亲和力低300 - 1200倍。它们对β（2）受体的亲和力也增加了，与非立体选择性位点相比，对受体的选择性提高了1000倍以上。[（3）H]RX 821002，咪唑克生的2-甲氧基类似物，对β（2）受体的亲和力（KD = 2.8 nM）比[（3）H]咪唑克生（KD = 24 nM）高约10倍，与[（3）H]育亨宾（KD = 3.6 nM）的亲和力大致相当。[（3）H]育亨宾与β（2）受体和5-HT（1A）受体具有相当的亲和力，竞争研究表明，未标记的RX 821002对5-HT（1A）受体的Ki值（30 nM）比其对β（2）受体的Ki值（4.1 nM）高约一个数量级。[（3）H]RX 821002和[（3）H]育亨宾对5-HT（1A）受体的标记可通过用8-OH-DPAT（30 nM）或5-HT（0.3 μM）进行选择性掩蔽来阻止。在这些条件下，[（3）H]RX 821002与β（2）受体的特异性结合占总结合的84%（在其KD时），相比之下，[（3）H]育亨宾为77%，[（3）H]咪唑克生为20%。[（3）H]RX 821002将β（2）受体标记为单一类别的非协同位点。在37℃时，结合和解离动力学非常快。拮抗剂竞争曲线陡峭，希尔系数接近1，激动剂曲线可根据两个亲和力位点进行分析，证实了[（3）H]RX821002的拮抗特性。约60%的β（2）受体具有高激动剂亲和力。