Dupuis D S, Perez M, Halazy S, Colpaert F C, Pauwels P J
Cellular and Molecular Biology Department, Centre de Recherche Pierre Fabre, 17, avenue Jean Moulin, F-81106, Castres cédex, France.
Brain Res Mol Brain Res. 1999 Apr 6;67(1):107-23. doi: 10.1016/s0169-328x(99)00052-2.
The present study reports on G-protein activation by recombinant 5-HT receptors and by native 5-HT1A and 5-HT1B receptors in guinea-pig and rat brain using agonist-stimulated [35S]GTPgammaS binding responses mediated by a new 5-HT ligand, a dimer of sumatriptan. Dimerization of sumatriptan increased the binding affinity for h 5-HT1B (pKi: 9.22 vs. 7.79 for sumatriptan), h 5-HT1D (9.07 vs. 8.08) and also h 5-HT1A receptors (7.80 vs. 6.40), while the binding affinity for h 5-ht1E (6.67 vs. 6.19) and h 5-ht1F (7.37 vs. 7.78) receptors was not affected. Sumatriptan dimer (10 microM) stimulated [35S]GTPgammaS binding mainly in the superficial gray layer of the superior colliculi, hippocampus and substantia nigra of guinea-pig and rat coronal brain sections. This fits with the labelling by the 5-HT1B/1D receptor antagonist [3H] GR 125743. The observed [35S]GTPgammaS binding responses in the substantia nigra are likely to be mediated by stimulation of the 5-HT1B receptor subtype, since they were antagonized by the 5-HT1B inverse agonist SB 224289 (10 microM), and not by the 5-HT2A/1D antagonist ketanserin (10 microM). Quantitative assessment of the [35S]GTPgammaS binding responses in the substantia nigra of rat showed highly efficacious responses for both sumatriptan dimer and its monomer. In contrast, less efficacious agonist responses (51+/-10% and 35+/-13%, respectively) were measured in the guinea-pig substantia nigra. This may suggest that the G-protein coupling efficacy of 5-HT1B receptors is different between the substantia nigra of both species. In addition, the sumatriptan dimer also activated guinea-pig and rat hippocampal 5-HT1A receptors with high efficacy in contrast to sumatriptan. Therefore, dimerization of sumatriptan can be considered as a new approach to transform a partial 5-HT1A agonist into a more efficacious agonist. In conclusion, the sumatriptan dimer stimulates G-protein activation via 5-HT1B receptors besides 5-HT1A receptors in guinea-pig and rat brain. The magnitude of the 5-HT1B receptor responses is superior for sumatriptan and its dimer in rat compared to guinea-pig substantia nigra.
本研究报道了使用一种新型5-羟色胺（5-HT）配体——舒马曲坦二聚体介导的激动剂刺激的[35S]GTPγS结合反应，对豚鼠和大鼠脑中重组5-HT受体以及天然5-HT1A和5-HT1B受体的G蛋白激活情况进行的研究。舒马曲坦二聚化增加了对人5-HT1B（pKi：9.22，而舒马曲坦为7.79）、人5-HT1D（9.07对8.08）以及人5-HT1A受体（7.80对6.40）的结合亲和力，而对人5-HT1E（6.67对6.19）和人5-HT1F（7.37对7.78）受体的结合亲和力未受影响。舒马曲坦二聚体（10微摩尔）主要在豚鼠和大鼠冠状脑切片的上丘浅层灰质、海马和黑质中刺激[35S]GTPγS结合。这与5-HT1B/1D受体拮抗剂[3H]GR 125743的标记情况相符。在黑质中观察到的[35S]GTPγS结合反应可能是由5-HT1B受体亚型的刺激介导的，因为它们被5-HT1B反向激动剂SB 224289（10微摩尔）拮抗，而未被5-HT2A/1D拮抗剂酮色林（10微摩尔）拮抗。对大鼠黑质中[35S]GTPγS结合反应的定量评估显示，舒马曲坦二聚体及其单体均有高效反应。相比之下，在豚鼠黑质中测得的激动剂反应效率较低（分别为51±10%和35±13%）。这可能表明两种物种黑质中5-HT1B受体的G蛋白偶联效率不同。此外，与舒马曲坦相比，舒马曲坦二聚体还能高效激活豚鼠和大鼠海马的5-HT1A受体。因此，舒马曲坦二聚化可被视为将部分5-HT1A激动剂转化为更有效激动剂的一种新方法。总之，舒马曲坦二聚体在豚鼠和大鼠脑中除了通过5-HT1A受体外，还通过5-HT1B受体刺激G蛋白激活。与豚鼠黑质相比，大鼠黑质中5-HT1B受体反应的幅度在舒马曲坦及其二聚体中更高。
