Stanimirovic D B, Ball R, Durkin J P
Institute for Biological Sciences, National Research Council of Canada, Ottawa, Ontario, Canada.
Glia. 1997 Feb;19(2):123-34. doi: 10.1002/(sici)1098-1136(199702)19:2<123::aid-glia4>3.0.co;2-1.
The postsynaptic actions of glutamate are rapidly terminated by high affinity glutamate uptake into glial cells. In this study we demonstrate the stimulation of both glutamate uptake and Na,K-ATPase activity in rat astrocyte cultures in response to sublethal ischemia-like insults. Primary cultures of neonatal rat cortical astrocytes were subjected to hypoxia, or to serum- and glucose-free medium, or to both conditions (ischemia). Cell death was assessed by propidium iodide staining of cell nuclei. To measure sodium pump activity and glutamate uptake, 3H-glutamate and 86Rb were both simultaneously added to the cell culture in the presence or absence of 2 mM ouabain. Na,K-ATPase activity was defined as ouabain-sensitive 86Rb uptake. Concomitant transient increases (2-3 times above control levels) of both Na,K-ATPase and glutamate transporter activities were observed in astrocytes after 4-24 h of hypoxia, 4 h of glucose deprivation, and 2-4 h of ischemia. A 24 h ischemia caused a profound loss of both activities in parallel with significant cell death. The addition of 5 mM glucose to the cells after 4 h ischemia prevented the loss of both sodium pump activity and glutamate uptake and rescued astrocytes from death observed at the end of 24 h ischemia. Reoxygenation after the 4 h ischemic event caused the selective inhibition of Na,K-ATPase activity. The observed increases in Na,K-ATPase activity and glutamate uptake in cultured astrocytes subjected to sublethal ischemia-like insults may model an important functional response of astrocytes in vivo by which they attempt to maintain ion and glutamate homeostasis under restricted energy and oxygen supply.
谷氨酸的突触后作用通过胶质细胞对谷氨酸的高亲和力摄取而迅速终止。在本研究中，我们证明了在大鼠星形胶质细胞培养物中，亚致死性缺血样损伤可刺激谷氨酸摄取和钠钾ATP酶活性。新生大鼠皮质星形胶质细胞的原代培养物分别经历缺氧、无血清和无糖培养基处理或两种条件同时处理（缺血）。通过细胞核碘化丙啶染色评估细胞死亡情况。为了测量钠泵活性和谷氨酸摄取，在存在或不存在2 mM哇巴因的情况下，将3H-谷氨酸和86Rb同时添加到细胞培养物中。钠钾ATP酶活性定义为哇巴因敏感的86Rb摄取量。在缺氧4 - 24小时、葡萄糖剥夺4小时以及缺血2 - 4小时后，星形胶质细胞中钠钾ATP酶和谷氨酸转运体活性同时出现短暂升高（比对照水平高2 - 3倍）。24小时缺血导致两种活性显著丧失，同时伴有大量细胞死亡。缺血4小时后向细胞中添加5 mM葡萄糖可防止钠泵活性和谷氨酸摄取的丧失，并使星形胶质细胞在24小时缺血结束时免于死亡。4小时缺血事件后的复氧导致钠钾ATP酶活性受到选择性抑制。在经历亚致死性缺血样损伤的培养星形胶质细胞中观察到的钠钾ATP酶活性和谷氨酸摄取增加，可能模拟了星形胶质细胞在体内的一种重要功能反应，即它们试图在能量和氧气供应受限的情况下维持离子和谷氨酸稳态。
