Role of glia cell during brain ischemia

目的：分析星形胶质细胞Na，K泵诱导电流及其在脑缺血中的作用方法：采用制霉菌素穿孔膜片钳技术，记录培养的大鼠大脑皮层星形胶质细胞Na，K泵电流。结果：1.在细胞内Na([Na]i)存在的情况下，细胞外K([K]o)呈剂量依赖性地激活星形胶质细胞的Na，K泵电流，Kd值为0.8 mM，Hill系数为1.7。2.哇巴因呈剂量依赖性阻断IP，IC50约为0.1 mM，提示星形胶质细胞存在哇巴因抗性异构体。3.IP在去极化电位中增加，在超极化电位中减少。因此，Ip的I-V关系呈S型。4.在没有[Na]i的情况下，IP仍可被[K]o激活，提示存在对河豚毒素不敏感的非失活Na电流。5.在[Na]i存在下，胞外Na([Na]o)的去除可增强[K]o诱导的Ip。6.代谢抑制剂氰化钠对Ip功能无影响，提示脑缺血时Ip活性保持不变。7.外源性谷氨酸通过升高[Na]i来增加Ip。在某些情况下，去除谷氨酸后Ip的增加明显，这可能是由于Na，K-ATPase通过代谢型谷氨酸受体而被磷酸化。结论：提示脑缺血时星形胶质细胞的Na，K泵功能保持不变，[K]o升高和[Na]o降低均可使其活性最大化，提示星形胶质细胞Na，K泵活性在清除脑缺血时细胞外钾积聚中具有神经保护作用。

Purpose : Analysis of Na,K-pump-induced currents in astrocytes and the role in brain ischemiaMethod : Using nystatin-perforated patch clamp techniques, Na,K-pump currents (Ip) were recorded from cultured astrocytes isolated from rat cerebral cortex.Results : 1. In the presence of intracellular Na([Na]I), Ip were activated by addition of extracellular K([K]o) in a dose-dependent manner with a Kd of O.8mM and a Hill coefficient of 1.7. 2.Ip were blocked by ouabain in a dose-dependent manner with a relatively high IC50 of about 0.1mM, suggesting the existence of a ouabain-resistant isoform in astrocytes. 3.Ip were increased in depolarized potentials and were decreased in hyperpolarized potential. Consequently, I-V relation of Ip showed a sigmoid shape. 4.Ip could be activated by [K]o even in the absence of [Na]I, suggesting the existence of non-inactivating Na currents that are not sensitive to tetrodotoxin. 5. In the presence of [Na]I, [K]o-induced Ip were augmented by removal of extracellular Na ([Na]o). 6. Metabolic inhibitor, sodium cyanide did not affect Ip function, suggesting that Ip activities are kept during brain ischemia. 7. Exogenous glutamate augmented Ip by increasing [Na]I. In some cases, the augmentation of Ip was evident after removal of glutamate, which is probably due to the phosphorylation of Na,K-ATPase via metabotropic-type glutamate receptors.Conclusion : From the all results, it is suggested that the Na,K-pump function in astrocytes is maintained during brain ischemia, and the activity is maximized by both elevation of [K]o and glutamate and reduction of [Na]o. These facts indicates that the Na,K-pump activity in astrocytes has a neuroprotective role in the removal of extracellular K accumulation during brain ischemia.