Study of glial cell function during brain ischemia

目的：研究星形胶质细胞在体外缺血过程中电膜特性和化学感受性的功能变化。方法：采用全细胞膜片钳技术监测单个培养星形胶质细胞的膜电流，观察体外缺血对星形胶质细胞电膜特性和对神经递质谷氨酸感受性的影响。用无葡萄糖、含代谢抑制剂的脑脊液代替正常的人工脑脊液，使细胞处于缺血状态。结果：在记录的星形胶质细胞膜上，缺血液引起短暂的内向电流，然后是缓慢的外向电流。从反转电位来看，氯通道和钾通道可能分别参与了瞬时内向电流和慢向外电流的产生。谷氨酸引起星形胶质细胞的内向电流。N-甲基-D-天冬氨酸和非N-甲基-D-天冬氨酸受体拮抗剂对谷氨酸诱发电流的抑制作用约为50%，表明星形胶质细胞不仅具有离子型谷氨酸受体，还具有代谢型谷氨酸受体和/或谷氨酸转运体。谷氨酸诱发电流早期不受缺血状态的影响。由于连续记录困难，无法监测缺血的后期效应。结论：星形胶质细胞似乎是一种耐缺血细胞，在抗缺血的电膜特性上表现出与神经元相似的行为。这表明，在脑缺血期间，神经胶质细胞的功能可能会改变，因此神经胶质细胞维持细胞外钾和神经递质的浓度可能会受到干扰。

Purpose : Study of functional changes in electrical membrane properties and chemical receptivity of astrocytes during in vitro ischemia.Method : Using whole-cell patch-clamp techniques, membrane currents were monitored from single cultured astrocyte, and the effects of in vitro ischemia on the electrical membrane properties and receptivity for neurotransmitter, glutamate were examined. Ischemic condition was made by perfusing cells with glucose-free and metabolic inhibitor-containing solution instead of normal artificial cerebrospinal fluid.Results : Ischemic solution caused a transient inward current followed by a slow outward current in the membrane of astrocytes recorded. From the reversal potential, it was suggested that chloride channels and potassium channels might be involved in the generation of the transient inward currents and the slow outward currents, respectively. Glutamate caused inward currents in the astrocyte. The glutamate-induced currents were inhibited by NMDA and non-NMDA glutamate receptor antagonists by about 50%, indicating that astrocytes have not only ionotropic glutamate receptor but also metabotropic glutamate receptors and/or glutamate transporters. The glutamate-induced currents were not modified by ischemic condition in the early time. Due to difficulties of continuous recording, the late effect of ischemia could not be monitored.Conclusion : The astrocyte that has been seemed to be a ischemia-resistant cell, behaves like as the neuron in the electrical membrane properties against ischemia. This suggests that glial cell function can be altered during ischamia, so that maintenance of extracellular concentrations of potassium and neurotransmitters by glial cells might be disturbed.