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

:使用高效液相色谱法研究了大鼠原代星形胶质细胞培养物中5-羟色胺(5-HT)氧化成5-羟基吲哚乙酸(5-HIAA)的过程。所有可检测到的5-HIAA都积累在细胞外培养基中,并且其产生速率与在5 x 10(-7)至10(-4)M的测试范围内的5-HT浓度成正比。在5 x 10(- 7)仅在用单胺氧化酶(MAO)抑制剂处理过的星形胶质细胞中检测到M 5-HT,细胞内5-HT。这些发现与以下想法相一致:摄取到星形胶质细胞中的5-HT不会被存储以重新释放,而是会迅速代谢为5-HIAA,然后从细胞中挤出。在5 x 10(-7)M 5-HT处,完整细胞中5-HIAA的形成被选择性的高亲和力5-HT摄取抑制剂氟西汀阻断了63%。 5-HT氧化成5-HIAA的方法主要是通过MAO-A进行的,因为氯丁香碱在抑制5-HIAA生成方面比Pargyline更有效。放射性酶法测定细胞匀浆中MAO的活性支持了这些发现,因为在这些条件下,高粱碱在抑制MAO对14C标记的5-HT的活性方面比Pargyline高1,000倍。但是,相对选择性的MAO-B底物β-苯乙胺(PEA)也被氧化,表明这些培养物也具有MAO-B活性; PEA的5-HT的MAO-A氧化和PEA的MAO-B氧化的Km值分别为135和45 microM,Vmax值分别为88和91 nmol / mg总细胞蛋白/ h。较高浓度的PEA(大于20 microM)被MAO-A和MAO-B同工酶氧化(摘要以250字截短)

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