METHYLMERCURY UPTAKE IN RAT PRIMARY ASTROCYTE CULTURES - THE ROLE OF THE NEUTRAL AMINO-ACID-TRANSPORT SYSTEM
METHYLMERCURY UPTAKE IN RAT PRIMARY ASTROCYTE CULTURES - THE ROLE OF THE NEUTRAL AMINO-ACID-TRANSPORT SYSTEM
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DOI：
10.1016/0006-8993(90)91546-s
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发表时间：
1990-06-25
期刊：
影响因子：
2.9
通讯作者：
KIMELBERG, HK
中科院分区：
文献类型：
--
作者：
ASCHNER, M;EBERLE, NB;KIMELBERG, HK
甲基汞(MeHg)在受损皮质区域星形胶质细胞上密集标记的意义尚不清楚，单个神经元因甲基汞在星形胶质细胞中积累而发生变化的程度也尚不清楚。作为了解星形胶质细胞与甲基汞S神经毒性机制之间关系的第一步，研究甲基汞是如何转运到培养的星形胶质细胞中的。原代培养的新生大鼠大脑皮质星形胶质细胞经MeHgCl孵育后摄取[203汞]MeHg符合简单的扩散过程。当星形胶质细胞以L-半胱氨酸结合物的形式加入到介质中时，星形胶质细胞对[203汞]甲基汞的摄取表现出特定运输系统的动力学标准。在这种含SH的氨基酸存在下，显示了饱和动力学、底物特异性和抑制以及反式刺激。L蛋氨酸和2-氨基二环-[2，2，1]-庚烷-2-羧酸联合给药可抑制半胱氨酸介导的甲基汞摄取。2-甲氨基异丁酸不能抑制甲基汞-半胱氨酸结合物的摄取。谷氨酸对星形胶质细胞摄取甲基汞-半胱氨酸结合物有适度的促进作用，而在没有半胱氨酸的情况下，对[203汞]甲基汞的摄取不变。这些结果表明，星形胶质细胞中存在一个中性氨基酸载体转运系统L，它能够选择性地介导半胱氨酸-甲基汞的摄取。该转运系统的底物特异性和高亲和力类似于L中性氨基酸跨越大鼠血脑屏障转运系统的特性。用100微米N-乙基马来酰亚胺或NaF预先孵育星形胶质细胞，细胞对甲基汞-半胱氨酸偶联物的摄取不受抑制。因此，在甲基汞进入星形胶质细胞的运输过程中，内吞或吞饮机制以及通过顺序的巯基膜配体交换穿梭甲基汞似乎并不起作用。
The significance of the dense labeling pattern of methylmercury (MeHg) over astrocytes in areas of damaged cortex remains obscure, and the extent to which individual neurons are altered by MeHg accumulation in astrocytes is unknown. As a first step in understanding the relationship between the astrocyte and the mechanisms of MeHg''s neurotoxicity, studies were directed at how MeHg is transported into cultured astrocytes. Uptake of [203Hg]MeHg in primary astrocyte cultures from neonatal rat cerebral cortex following incubations with MeHgCl conformed to a simple diffusion process. Uptake of [203Hg]MeHg by astrocytes exhibited the kinetic criteria of a specific transport system when added to the media as the L-cysteine conjugate. Saturation kinetics substrate specificity and inhibition, and trans-stimulation were demonstrated in the presence of this SH-containing amino acid. Cysteine-mediated uptake of MeHg was inhibited by the coadministration of L-methionine, and 2-aminobicyclo-[2,2,1]-heptane-2-carboxylic acid. 2-Methylaminoisobutyric acid was ineffective in inhibiting the uptake of the MeHg-cysteine conjugate. Preloading of the astrocytes with glutamate was moderately effective in trans-stimulating the uptake of MeHg-cysteine conjugates, while in the absence of cysteine, uptake of [203Hg]MeHg was unchanged. These results indicate the presence in astrocytes of a neutral amino acid carrier transport System L, capable of selectively mediating cysteine-MeHg uptake. The substrate specificity and high affinity of this transport system resemble the properties of the System L neutral amino acid transport across the blood-brain barrier in the rat. Cellular uptake of MeHg-cysteine conjugates was not inhibited by preincubation of astrocytes with 100 .mu.M N-ethylmaleimide or NaF. Hence, endocytotic or pinocytotic mechanisms, and shuttling of MeHg via sequential sulfhydryl membrane ligand exchange do not appear to operate in the transport of MeHg into the astrocyte.