The oxidative deamination of serotonin (5-HT) to 5-hydroxyindoleacetic acid (5-HIAA) by rat primary astrocyte cultures was investigated in intact cells using HPLC. All detectable 5-HIAA accumulated in the extracellular medium, and its rate of production was proportional to the 5-HT concentration over the tested range of 5 x 10(-7) to 10(-4) M. At 5 x 10(-7) M 5-HT, intracellular 5-HT was detectable only in astrocytes treated with monoamine oxidase (MAO) inhibitors. These findings are consistent with the idea that 5-HT taken up into astrocytes is not stored for re-release, but is rapidly metabolized to 5-HIAA, which is then extruded from the cell. At 5 x 10(-7) M 5-HT, 5-HIAA formation in intact cells was blocked 63% by the selective high-affinity 5-HT uptake inhibitor fluoxetine. 5-HT oxidation to 5-HIAA is carried out principally by MAO-A, because clorgyline was more effective at inhibiting the production of 5-HIAA than was pargyline. Radioenzymatic determinations of MAO activity in cell homogenates supported these findings, because under these conditions clorgyline was 1,000-fold more effective than pargyline at inhibiting MAO activity toward 14C-labelled 5-HT. However, the relatively selective MAO-B substrate beta-phenylethylamine (PEA) was also oxidized, showing that these cultures also contained MAO-B activity; the Km values for MAO-A oxidation of 5-HT and MAO-B oxidation of PEA were 135 and 45 microM, and Vmax values were 88 and 91 nmol/mg of total cell protein/h, respectively. Higher concentrations of PEA (greater than 20 microM) were oxidized by both MAO-A and MAO-B isozymes.(ABSTRACT TRUNCATED AT 250 WORDS)

译文

使用HPLC在完整细胞中研究了大鼠原代星形胶质细胞培养物将5-羟色胺 (5-HT) 氧化脱氨为5-羟基吲哚乙酸 (5-HIAA)。所有可检测到的5-HIAA都积累在细胞外培养基中,在5x10(-7) 至10(-4) M的测试范围内,其产生速率与5-HT浓度成正比。在5x10(-7) M 5-HT时,仅在用单胺氧化酶 (MAO) 抑制剂处理的星形胶质细胞中可检测到细胞内5-HT。这些发现与以下观点一致: 吸收到星形胶质细胞中的5-HT不会储存以重新释放,而是会迅速代谢为5-HIAA,然后从细胞中挤出。在5 × 10(-7) m5-ht时,选择性高亲和力5-HT摄取抑制剂氟西汀63% 阻断完整细胞中的5-HIAA形成。5-HT氧化为5-HIAA主要由MAO-A进行,因为clorgyline比pargyline更有效地抑制5-HIAA的产生。细胞匀浆中MAO活性的放射酶测定支持了这些发现,因为在这些条件下,clorgyline在抑制针对14c标记的5-HT的MAO活性方面比pargyline有效1,000倍。然而,相对选择性的MAO-B底物 β-苯乙胺 (PEA) 也被氧化,表明这些培养物也含有MAO-B活性; 5-HT的MAO-A氧化和PEA的MAO-B氧化的Km值分别为135和45微米,vmax值分别为88和91 nmol/mg的总细胞蛋白/h。较高浓度的豌豆 (大于20微米) 被MAO-A和MAO-B同工酶氧化。(摘要截短于250字)

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