Swanson R A, Liu J, Miller J W, Rothstein J D, Farrell K, Stein B A, Longuemare M C
Department of Neurology, University of California, San Francisco, USA.
J Neurosci. 1997 Feb 1;17(3):932-40. doi: 10.1523/JNEUROSCI.17-03-00932.1997.
GLT-1, GLAST, and EAAC1 are high-affinity, Na(+)-dependent glutamate transporters identified in rat forebrain. The expression of these transporter subtypes was characterized in three preparations: undifferentiated rat cortical astrocyte cultures, astrocytes cocultured with cortical neurons, and astrocyte cultures differentiated with dibutyryl cyclic AMP (dBcAMP). The undifferentiated astrocyte monocultures expressed only the GLAST subtype. Astrocytes cocultured with neurons developed a stellate morphology and expressed both GLAST and GLT-1; neurons expressed only the EAAC1 transporter, and rare microglia in these cultures expressed GLT-1. Treatment of astrocyte cultures with dBcAMP induced expression of GLT-1 and increased expression of GLAST. These effects of dBcAMP on transporter expression were qualitatively similar to those resulting from coculture with neurons, but immunocytochemistry showed the pattern of transporter expression to be more complex in the coculture preparations. Compared with astrocytes expressing only GLAST, the dBcAMP-treated cultures expressing both GLAST and GLT-1 showed an increase in glutamate uptake Vmax, but no change in the glutamate K(m) and no increased sensitivity to inhibition by dihydrokainate. Pyrrolidine-2,4-dicarboxylic acid and threo-beta-hydroxyaspartic acid caused relatively less inhibition of transport in cultures expressing both GLAST and GLT-1, suggesting a weaker effect at GLT-1 than at GLAST. These studies show that astrocyte expression of glutamate transporter subtypes is influenced by neurons, and that dBcAMP can partially mimic this influence. Manipulation of transporter expression in astrocyte cultures may permit identification of factors regulating the expression and function of GLAST and GLT-1 in their native cell type.
GLT-1、GLAST和EAAC1是在大鼠前脑中发现的高亲和力、钠依赖性谷氨酸转运体。这些转运体亚型的表达在三种培养物中进行了表征：未分化的大鼠皮质星形胶质细胞培养物、与皮质神经元共培养的星形胶质细胞以及用二丁酰环磷腺苷（dBcAMP）分化的星形胶质细胞培养物。未分化的星形胶质细胞单培养物仅表达GLAST亚型。与神经元共培养的星形胶质细胞呈现出星状形态，并表达GLAST和GLT-1；神经元仅表达EAAC1转运体，这些培养物中罕见的小胶质细胞表达GLT-1。用dBcAMP处理星形胶质细胞培养物可诱导GLT-1的表达并增加GLAST的表达。dBcAMP对转运体表达的这些作用在性质上与与神经元共培养所产生的作用相似，但免疫细胞化学显示在共培养物中转运体的表达模式更为复杂。与仅表达GLAST的星形胶质细胞相比，同时表达GLAST和GLT-1的经dBcAMP处理的培养物显示谷氨酸摄取Vmax增加，但谷氨酸K(m)无变化，对二氢海因酸抑制的敏感性也未增加。吡咯烷-2,4-二羧酸和苏-β-羟基天冬氨酸在同时表达GLAST和GLT-1的培养物中对转运的抑制作用相对较小，表明其对GLT-1的作用比对GLAST的作用弱。这些研究表明，谷氨酸转运体亚型在星形胶质细胞中的表达受神经元影响，并且dBcAMP可以部分模拟这种影响。对星形胶质细胞培养物中转运体表达的操纵可能有助于鉴定调节天然细胞类型中GLAST和GLT-1表达及功能的因素。
