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标题：Mutations of Arginine 222 in Pre-transmembrane Domain I of Mouse 5-HT3A Receptor Abolish 20(R)- But Not 20(S)-Ginsenoside Rg3 Inhibition of 5-HT-Mediated Ion Currents
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作者：Byung-Hwan Lee ; Jun-Ho Lee ; In-Soo Yoon 等
期刊名称：Biological and Pharmaceutical Bulletin
印刷版ISSN：0918-6158
电子版ISSN：1347-5215
出版年度：2007
卷号：30
期号：9
页码：1721-1726
DOI：10.1248/bpb.30.1721
出版社：The Pharmaceutical Society of Japan
摘要：Ginsenosides, active ingredients of Panax ginseng, exist as stereoisomers depending on the position of the hydroxyl group on carbon-20; i.e. 20( R )-ginsenoside and 20( S )-ginsenoside are epimers. We previously investigated the structure–activity relationship of the ginsenoside Rg₃ stereoisomers, 20- R -protopanaxatriol-3-[ O -β- D -glucopyranosyl (1→2)-β-glucopyranoside], (20( R )-Rg₃) and 20- S -protopanaxatriol-3-[ O -β- D -glucopyranosyl (1→2)-β-glucopyranoside], (20( S )-Rg₃) in regulating 5-HT_3A receptor-mediated ion currents ( I _5-HT) expressed in Xenopus oocytes and found that 20( S )-Rg₃ rather than 20( R )-Rg₃ was more stronger inhibitor of I _5-HT. In the present study, we further investigated the effects of 20( R )-Rg₃ and 20( S )-Rg₃ on mouse 5-HT_3A receptor channel activity after site-directed mutations of 5-HT_3A receptor facilitation site, which is located at pre-transmembrane domain I (pre-TM1). 5-HT_3A receptor was expressed in Xenopus oocytes, and I _5-HT was measured using two-electrode voltage clamp technique. In wild-type, both 20( R )-Rg₃ and 20( S )-Rg₃ inhibited I _5-HT with concentration-dependent and reversible manner. Induction of 5-HT_3A receptor facilitation by point mutations of pre-TM1 amino acid residue R222 to R222A, R222D, R222E or R222T not only decreased EC₅₀ values for I _5-HT compared to wild-type but also abolished 20( R )-Rg₃-induced inhibition of I _5-HT. Those mutations also shifted the IC₅₀ values by 20( S )-Rg₃ into right direction by 2- to 4-folds compared with wild-type. These results indicate that 5-HT_3A receptor facilitation differentially affects 20( R )-Rg₃- and 20( S )-Rg₃-mediated 5-HT_3A receptor channel regulation.
关键词：ginseng;ginsenoside stereoisomer;5-HT3A receptor;ligand-gated ion channel;Xenopus oocyte