Crooks Daniel R, Welch Nicholas, Smith Donald R
Department of Environmental Toxicology, University of California, Santa Cruz, CA 95064, USA.
Neurotoxicology. 2007 May;28(3):548-54. doi: 10.1016/j.neuro.2007.01.003. Epub 2007 Jan 16.
Recent studies have suggested that the globus pallidus may be a particularly sensitive target of manganese (Mn), however, in vitro studies of the effects of Mn on GABAergic neurons have been restricted by the lack of a cell model expressing GABAergic properties. Here, we investigated the effects of low-level Mn treatment on cellular GABA and glutamate metabolism using the newly characterized AF5 rat neural-derived cell line, which displays GABAergic properties during culture in vitro. Intracellular GABA and glutamate levels were measured along with measurement of the release of GABA and glutamate into the culture medium, glutamine uptake from the culture medium, and the specific effects of Mn on the enzymes directly responsible for the synthesis and degradation of GABA, glutamate decarboxylase (GAD) and GABA transaminase (GABA-T). Our results demonstrate that Mn had no effect on the activities of GAD or GABA-T. Similarly, low-level Mn treatment of AF5 cultures had only a small effect on intracellular GABA levels (114% of control) and no effect on the release of GABA. In contrast, intracellular and extracellular glutamate levels were enhanced to 170 and 198% of control during Mn treatment, respectively, while extracellular glutamine decreased to 73% of controls. Together, these results suggest that glutamate homeostasis may be preferentially affected over GABA in AF5 cells during low-level Mn treatment, suggesting a novel mechanism by which Mn-induced excitotoxicity might arise.
最近的研究表明，苍白球可能是锰（Mn）的一个特别敏感的靶点，然而，由于缺乏表达GABA能特性的细胞模型，关于锰对GABA能神经元影响的体外研究受到了限制。在这里，我们使用新鉴定的AF5大鼠神经源性细胞系研究了低水平锰处理对细胞GABA和谷氨酸代谢的影响，该细胞系在体外培养过程中表现出GABA能特性。测量了细胞内GABA和谷氨酸水平，同时测量了GABA和谷氨酸释放到培养基中的情况、从培养基中摄取谷氨酰胺的情况，以及锰对直接负责GABA合成和降解的酶——谷氨酸脱羧酶（GAD）和GABA转氨酶（GABA-T）的具体影响。我们的结果表明，锰对GAD或GABA-T的活性没有影响。同样，对AF5培养物进行低水平锰处理对细胞内GABA水平只有很小的影响（为对照的114%），对GABA的释放没有影响。相比之下，在锰处理期间，细胞内和细胞外谷氨酸水平分别提高到对照的170%和198%，而细胞外谷氨酰胺则降至对照的73%。总之，这些结果表明，在低水平锰处理期间，AF5细胞中的谷氨酸稳态可能比GABA更容易受到影响，这提示了锰诱导的兴奋性毒性可能产生的一种新机制。
