Kinsmen Laboratory of Neurological Research, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3.
Glia. 2011 Nov;59(11):1600-11. doi: 10.1002/glia.21202. Epub 2011 Jul 11.
We have previously demonstrated that human astrocytes are GABAergic cells. Throughout the adult human brain, they express the GABA synthesizing enzyme GAD 67, the GABA metabolizing enzyme GABA-T, and the GABA(A) and GABA(B) receptors. GABA modulates the actions of microglia, indicating an important role for astrocytes beyond that of influencing neurotransmitter function. Here we report on the mechanisms by which astrocytes release GABA. Astrocytes were found to express the mRNA and protein for multiple GABA transporters, and multiple receptors for glutamate, GABA, and glycine. In culture, untreated human astrocytes maintained an intracellular GABA level of 2.32 mM. They exported GABA into the culture medium so that an intracellular-extracellular gradient of 3.64 fold was reached. Inhibitors of the GABA transporters GAT1, GAT2, and GAT3, significantly reduced this export in a Ca(2+)-independent fashion. Intracellular GABA levels were enhanced by treatment with the GABA-T inhibitors gabaculine or vigabatrin. Treatment with glutamate increased GABA release in a concentration-dependent fashion. This was partially inhibited by blockers of N-methyl-D-aspartate and kainate receptors. Conversely, glycine and D-serine, co-agonists of NMDA receptors, enhanced the GABA release. GABA release was accompanied by an increase in intracellular Ca(2+) concentration (Ca(2+)) and was reduced by adding the Ca(2+) chelator, BAPTA-AM to the medium. These data indicate that astrocytes continuously synthesize GABA and that there are multiple mechanisms which can mediate its release. Each of these may play a role in the physiological functioning of astrocytes.
我们之前已经证明，人类星形胶质细胞是 GABA 能细胞。在整个成人脑中，它们表达 GABA 合成酶 GAD67、GABA 代谢酶 GABA-T 以及 GABA(A)和 GABA(B)受体。GABA 调节小胶质细胞的作用，表明星形胶质细胞的作用不仅影响神经递质功能。在这里，我们报告星形胶质细胞释放 GABA 的机制。发现星形胶质细胞表达多种 GABA 转运体的 mRNA 和蛋白，以及多种谷氨酸、GABA 和甘氨酸受体。在培养中，未经处理的人星形胶质细胞维持细胞内 GABA 水平为 2.32mM。它们将 GABA 输出到培养基中，从而达到细胞内-细胞外 3.64 倍的梯度。GAT1、GAT2 和 GAT3 GABA 转运体抑制剂以 Ca(2+)非依赖性方式显著降低了这种输出。用 GABA-T 抑制剂 gabaculine 或 vigabatrin 处理可增强细胞内 GABA 水平。用谷氨酸处理以浓度依赖的方式增加 GABA 释放。该作用部分被 N-甲基-D-天冬氨酸和海人藻酸受体的阻断剂抑制。相反，甘氨酸和 D-丝氨酸，NMDA 受体的共激动剂，增强了 GABA 的释放。GABA 释放伴随着细胞内 Ca(2+)浓度 (Ca(2+))的增加，并通过向培养基中添加 Ca(2+)螯合剂 BAPTA-AM 而减少。这些数据表明星形胶质细胞持续合成 GABA，并且有多种机制可以介导其释放。这些机制中的每一种都可能在星形胶质细胞的生理功能中发挥作用。
