Beart P M, O'Shea R D, Manallack D T
University of Melbourne, Clinical Pharmacology and Therapeutics Unit, Austin Hospital, Heidelberg, Victoria.
J Neurochem. 1989 Sep;53(3):779-88. doi: 10.1111/j.1471-4159.1989.tb11773.x.
The regulation of the central sigma-binding site was investigated using both in vitro and in vivo manipulations in conjunction with radioligand binding. The displacement of the binding of R(+)-[3H]3-[3-hydroxyphenyl]-N-(1-propyl)piperidine [R(+)-[3H]3-PPP] to cortical homogenates by a range of drugs was consistent with the site labelled being a sigma-receptor. (+)-SKF 10,047, (-)-SKF 10,047, (+/-)-cyclazocine, phencyclidine, and dexoxadrol displaced R(+)-[3H]3-PPP with pseudo-Hill coefficients of less than 1. Further analysis employing nonlinear curve fitting techniques demonstrated that displacement data for these compounds were described better by a model whereby R(+)-[3H]3-PPP was displaced from two discrete sites; approximately 65% of the total sites were in the high-affinity state. In the presence of 10 mM Mg2+ and 0.3 mM GTP, displacement curves for (+)-SKF 10,047 and (+/-)-cyclazocine were shifted to the right. These findings were due to the shift of some 15% of the high-affinity binding sites to a low-affinity state. Saturation experiments revealed that 0.3 mM GTP acted competitively to decrease the affinity of R(+)-[3H]3-PPP for the sigma sites. The sigma-binding site was thus likely to be linked to a guanine nucleotide regulatory (G) protein. Thus sigma drugs could be subdivided on the basis of their GTP sensitivity and pseudo-Hill coefficients, and by analogy with other receptors R(+)-3-PPP, (+)-SKF 10,047, and (+/-)-cyclazocine, may be putative sigma-agonists. 1,3-Di(2-tolyl)guanidine (DTG), rimcazole, and haloperidol displaced R(+)-[3H]3-PPP with pseudo-Hill coefficients of approximately unity and thus may be sigma-antagonists. Subchronic treatment with rimcazole was characterized by slight sedation and a concomitant up-regulation, with a decrease in the affinity, of sigma-binding sites. The schedule of rimcazole also increased dopamine turnover in the nucleus accumbens; both the concentration of 3,4-dihydroxyphenylacetic acid (DOPAC) and the DOPAC/dopamine ratio were elevated. DTG produced similar alterations to the binding parameters of the sigma-binding site; however, changes were not observed in general behavior or accumbal dopamine turnover. sigma-Receptors are likely to be linked to a G protein and are functionally involved in the CNS.
利用体外和体内操作结合放射性配体结合法，对中枢σ结合位点的调节进行了研究。一系列药物对R(+)-[3H]3-[3-羟基苯基]-N-(1-丙基)哌啶[R(+)-[3H]3-PPP]与皮质匀浆结合的取代作用，与所标记的位点为σ受体一致。(+)-SKF 10,047、(-)-SKF 10,047、(+/-)-环唑辛、苯环利定和右吗拉胺取代R(+)-[3H]3-PPP的伪希尔系数小于1。采用非线性曲线拟合技术的进一步分析表明，这些化合物的取代数据用一个模型能更好地描述，即R(+)-[3H]3-PPP从两个离散位点被取代；约65%的总位点处于高亲和力状态。在10 mM Mg2+和0.3 mM GTP存在下，(+)-SKF 10,047和(+/-)-环唑辛的取代曲线向右移动。这些发现是由于约15%的高亲和力结合位点转变为低亲和力状态。饱和实验表明，0.3 mM GTP竞争性地降低了R(+)-[3H]3-PPP对σ位点的亲和力。因此，σ结合位点可能与鸟嘌呤核苷酸调节(G)蛋白相连。因此，σ药物可根据其对GTP的敏感性和伪希尔系数进行细分，与其他受体类似，R(+)-3-PPP、(+)-SKF 10,047和(+/-)-环唑辛可能是推定的σ激动剂。1,3-二(2-甲苯基)胍(DTG)、利咪唑和氟哌啶醇取代R(+)-[3H]3-PPP的伪希尔系数约为1，因此可能是σ拮抗剂。利咪唑的亚慢性治疗表现为轻度镇静，同时σ结合位点上调，亲和力降低。利咪唑给药方案还增加了伏隔核中的多巴胺周转率；3,4-二羟基苯乙酸(DOPAC)的浓度和DOPAC/多巴胺比值均升高。DTG对σ结合位点的结合参数产生了类似的改变；然而，在一般行为或伏隔核多巴胺周转率方面未观察到变化。σ受体可能与G蛋白相连，并在中枢神经系统中发挥功能作用。
