Loaiza Anitsi, Porras Omar H, Barros Luis Felipe
Centro de Estudios Científicos, Casilla 1469, Valdivia, Chile.
J Neurosci. 2003 Aug 13;23(19):7337-42. doi: 10.1523/JNEUROSCI.23-19-07337.2003.
Glutamate stimulates glycolysis in astrocytes, a phenomenon that couples astrocytic metabolism with neuronal activity. However, it is not known whether glutamate also affects glucose transporter-1 (GLUT1), the transporter responsible for glucose entry into astrocytes. To address this question, two different real-time single-cell hexose uptake assays were applied to cultured hippocampal astrocytes using confocal epifluorescence microscopy. Glutamate caused a twofold to threefold increase in the zero-trans uptake rates of the fluorescent hexoses 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxyglucose (2-NBDG) and 6-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-6-deoxyglucose (6-NBDG). Galactose uptake, determined by the calcein volumetric assay, was stimulated to a similar extent, confirming the fluorescent hexose data, and also demonstrating that glutamate stimulation is a Vmax effect. Remarkably, glucose transport stimulation developed fully inside 10 sec, which is 100 times faster than acute stimulations of glucose transport in other cell types. Glutamate did not significantly affect the rate of 6-NBDG uptake by GLUT1-expressing epithelial Clone 9 cells, suggesting that an astrocyte-specific factor is required for transport stimulation. We conclude that glucose transport stimulation occurs early during astrocytic activation by glutamate, which provides a novel regulatory node to current models of brain energy metabolism. This mechanism should also be considered for the interpretation of functional imaging data based on hexoses.
谷氨酸可刺激星形胶质细胞中的糖酵解，这一现象将星形胶质细胞的代谢与神经元活动联系起来。然而，目前尚不清楚谷氨酸是否也会影响葡萄糖转运蛋白1（GLUT1），即负责葡萄糖进入星形胶质细胞的转运蛋白。为了解决这个问题，我们使用共聚焦落射荧光显微镜对培养的海马星形胶质细胞应用了两种不同的实时单细胞己糖摄取测定法。谷氨酸使荧光己糖2-[N-(7-硝基苯并-2-恶唑-1,3-二氮杂-4-基)氨基]-2-脱氧葡萄糖（2-NBDG）和6-[N-(7-硝基苯并-2-恶唑-1,3-二氮杂-4-基)氨基]-6-脱氧葡萄糖（6-NBDG）的零转运摄取率提高了两倍至三倍。通过钙黄绿素容量测定法测定的半乳糖摄取也受到了类似程度的刺激，这证实了荧光己糖数据，同时也表明谷氨酸刺激是一种Vmax效应。值得注意的是，葡萄糖转运刺激在10秒内就完全显现出来，这比其他细胞类型中葡萄糖转运的急性刺激快100倍。谷氨酸对表达GLUT1的上皮克隆9细胞摄取6-NBDG的速率没有显著影响，这表明转运刺激需要一种星形胶质细胞特异性因子。我们得出结论，谷氨酸激活星形胶质细胞时会早期发生葡萄糖转运刺激，这为当前的脑能量代谢模型提供了一个新的调节节点。在解释基于己糖的功能成像数据时也应考虑这一机制。
