Lane J Robert, Powney Ben, Wise Alan, Rees Steven, Milligan Graeme
Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, Scotland, United Kingdom.
Mol Pharmacol. 2007 May;71(5):1349-59. doi: 10.1124/mol.106.032722. Epub 2007 Feb 7.
A range of ligands displayed agonism at the long isoform of the human dopamine D(2) receptor, whether using receptor-G protein fusions or membranes of cells in which pertussis toxin-resistant mutants of individual Galpha(i)-family G proteins could be expressed in an inducible fashion. Varying degrees of efficacy were observed for individual ligands as monitored by their capacity to load [(35)S]GTPgammaS onto each of Galpha(i1),Galpha(i2),Galpha(i3), and Galpha(o1). By contrast, (S)-(-)-3-(3-hydroxyphenyl)-N-propylpiperidine was a partial agonist when Galpha(o1) was the target G protein but an antagonist/inverse agonist at Galpha(i1),Galpha(i2), and Galpha(i3). In ligand binding assays, dopamine identified both high- and low-affinity states at each of the dopamine D(2) receptor-G protein fusion proteins, and the high-affinity state was eliminated by guanine nucleotide. (S)-(-)-3-(3-hydroxyphenyl)-N-propylpiperidine bound to an apparent single state of the constructs in which the D(2) receptor was fused to Galpha(i1),Galpha(i2), or Galpha(i3). However, it bound to distinct high- and low-affinity states of the D(2) receptor-Galpha(o1) fusion, with the high-affinity state being eliminated by guanine nucleotide. Likewise, although dopamine identified guanine nucleotide-sensitive high-affinity states of the D(2) receptor when expression of pertussis toxin-resistant forms of each of Galpha(i1), Galpha(i2), Galpha(i3), and Galpha(o1) was induced, (S)-(-)-3-(3-hydroxyphenyl)-N-propylpiperidine identified a high-affinity site only in the presence of Galpha(o1). p-Tyramine displayed a protean ligand profile similar to that of (S)-(-)-3-(3-hydroxyphenyl)-N-propylpiperidine but with lower potency. These results demonstrate (S)-(-)-3-(3-hydroxyphenyl)-N-propylpiperidine to be a protean agonist at the D(2) receptor and may explain in vivo actions of this ligand.
一系列配体在人多巴胺D(2)受体的长亚型上表现出激动作用，无论是使用受体-G蛋白融合体还是在可诱导表达单个Gα(i)家族G蛋白的百日咳毒素抗性突变体的细胞的膜。通过它们将[(35)S]GTPγS加载到Gα(i1)、Gα(i2)、Gα(i3)和Gα(o1)上的能力监测，观察到各个配体有不同程度的效力。相比之下，当Gα(o1)是靶G蛋白时，(S)-(-)-3-(3-羟基苯基)-N-丙基哌啶是部分激动剂，但在Gα(i1)、Gα(i2)和Gα(i3)上是拮抗剂/反向激动剂。在配体结合试验中，多巴胺在每个多巴胺D(2)受体-G蛋白融合蛋白上都鉴定出高亲和力和低亲和力状态，并且鸟嘌呤核苷酸消除了高亲和力状态。(S)-(-)-3-(3-羟基苯基)-N-丙基哌啶与D(2)受体与Gα(i1)、Gα(i2)或Gα(i3)融合的构建体的明显单一状态结合。然而，它与D(2)受体-Gα(o1)融合体的不同高亲和力和低亲和力状态结合，高亲和力状态被鸟嘌呤核苷酸消除。同样，尽管当诱导Gα(i1)、Gα(i2)、Gα(i3)和Gα(o1)各自的百日咳毒素抗性形式的表达时，多巴胺鉴定出D(2)受体的鸟嘌呤核苷酸敏感的高亲和力状态，但(S)-(-)-3-(3-羟基苯基)-N-丙基哌啶仅在存在Gα(o1)时鉴定出一个高亲和力位点。对羟基苯乙胺显示出与(S)-(-)-3-(3-羟基苯基)-N-丙基哌啶相似的多变配体特征，但效力较低。这些结果证明(S)-(-)-3-(3-羟基苯基)-N-丙基哌啶是D(2)受体上的多变激动剂，并可能解释该配体的体内作用。
