Department of Pharmacy and Pharmacology, University of Bath, Bath, UK.
Br J Pharmacol. 2011 Sep;164(2b):772-80. doi: 10.1111/j.1476-5381.2011.01417.x.
Sigma-1 receptors are atypical receptors with potentially two transmembrane domains. Antagonists require doses significantly higher than their published affinities to have biological effects. We have reassessed the binding characteristics of these ligands and found antagonists bind to high- and low-affinity states not distinguished by agonists.
The affinities of sigma-1 receptor ligands was assessed using radioligand saturation and competition binding of [³H]-(+)-pentazocine to permeabilized MDA-MB-468 cells. This was compared with the effect of ligands on metabolic activity using an MTS-based assay and calcium signalling using cells loaded with the calcium dye, Fura-2.
Sigma-1 receptor antagonists, but not agonists, show GTP- and suramin-sensitive high-affinity binding. Functional responses (calcium signalling and metabolic activity), while associated with sigma-1 receptor binding, required binding to an unidentified, low-affinity target.
Sigma-1 receptors are coupled to G proteins. This interaction is only observed when analysing antagonist binding. The identity of the G protein remains to be resolved. The concept of agonist and antagonist at the sigma-1 receptor needs to be revisited.
西格玛-1 受体是具有潜在两个跨膜结构域的非典型受体。拮抗剂需要比其公布的亲和力高得多的剂量才能产生生物学效应。我们重新评估了这些配体的结合特性，发现拮抗剂与高亲和力态和低亲和力态结合，而不能被激动剂区分。
使用放射性配体饱和和[³H]-(+)-戊甲噻嗪对透化的 MDA-MB-468 细胞的竞争结合，评估西格玛-1 受体配体的亲和力。将这与配体对代谢活性的影响进行比较，使用 MTS 基础测定法和用钙染料 Fura-2 负载的细胞中的钙信号。
西格玛-1 受体拮抗剂，但不是激动剂，显示出 GTP 和苏拉明敏感的高亲和力结合。功能反应（钙信号和代谢活性）虽然与西格玛-1 受体结合有关，但需要与未识别的低亲和力靶标结合。
西格玛-1 受体与 G 蛋白偶联。只有在分析拮抗剂结合时才会观察到这种相互作用。G 蛋白的身份仍有待解决。需要重新审视西格玛-1 受体的激动剂和拮抗剂的概念。
