Rose C R, Waxman S G, Ransom B R
Department of Neurology, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
J Neurosci. 1998 May 15;18(10):3554-62. doi: 10.1523/JNEUROSCI.18-10-03554.1998.
A steep inwardly directed Na+ gradient is essential for glial functions such as glutamate reuptake and regulation of intracellular ion concentrations. We investigated the effects of glucose deprivation, chemical hypoxia, and simulated ischemia on intracellular Na+ concentration ([Na+]i) in cultured spinal cord astrocytes using fluorescence ratio imaging with sodium-binding benzofuran isophthalate (SBFI) AM. Glucose removal or chemical hypoxia (induced by 10 mM NaN3) for 60 min increased [Na+]i from a baseline of 8.3 to 11 mM. Combined glycolytic and respiratory blockage by NaN3 and 0 glucose saline caused [Na+]i to increase by 20 mM, similar to the [Na+]i increases elicited by blocking the Na+/K+-ATPase with ouabain. Recovery from large [Na+]i increases (>15 mM) induced by the glutamatergic agonist kainate was attenuated during glucose deprivation or NaN3 application and was blocked in NaN3 and 0 glucose. To mimic in vivo ischemia, we exposed astrocytes to NaN3 and 0 glucose saline containing L-lactate and glutamate with increased [K+] and decreased [Na+], [Ca2+], and pH. This induced an [Na+]i decrease followed by an [Na+]i rise and a further [Na+]i increase after reperfusion with standard saline. Similar multiphasic [Na+]i changes were observed after NaN3 and 0 glucose saline with only reduced [Na+]e. Our results suggest that the ability to maintain a low [Na+]i enables spinal cord astrocytes to continue uptake of K+ and/or glutamate at the onset of energy failure. With prolonged energy failure, however, astrocytic [Na+]i rises; with loss of their steep transmembrane Na+ gradient, astrocytes may aggravate metabolic insults by carrier reversal and release of acid, K+, and/or glutamate into the extracellular space.
陡峭的内向型钠离子梯度对于胶质细胞功能至关重要，如谷氨酸重摄取和细胞内离子浓度调节。我们使用钠结合苯并呋喃异邻苯二甲酸酯（SBFI）AM荧光比率成像技术，研究了葡萄糖剥夺、化学性缺氧和模拟缺血对培养的脊髓星形胶质细胞内钠离子浓度（[Na⁺]i）的影响。去除葡萄糖或用10 mM叠氮化钠诱导化学性缺氧60分钟，可使[Na⁺]i从基线8.3 mM增加到11 mM。叠氮化钠和无葡萄糖生理盐水联合导致糖酵解和呼吸阻滞，使[Na⁺]i增加20 mM，类似于用哇巴因阻断钠钾ATP酶引起的[Na⁺]i增加。在葡萄糖剥夺或应用叠氮化钠期间，由谷氨酸能激动剂海藻酸诱导的[Na⁺]i大幅增加（>15 mM）后的恢复减弱，在叠氮化钠和无葡萄糖条件下则被阻断。为模拟体内缺血，我们使星形胶质细胞暴露于含有L-乳酸和谷氨酸、[K⁺]升高而[Na⁺]、[Ca²⁺]和pH降低的叠氮化钠和无葡萄糖生理盐水中。这导致[Na⁺]i先降低，随后升高，在用标准生理盐水再灌注后[Na⁺]i进一步增加。在仅[Na⁺]e降低的叠氮化钠和无葡萄糖生理盐水中也观察到类似的多相[Na⁺]i变化。我们的结果表明，维持低[Na⁺]i的能力使脊髓星形胶质细胞能够在能量衰竭开始时继续摄取K⁺和/或谷氨酸。然而，随着能量衰竭时间延长，星形胶质细胞的[Na⁺]i升高；随着其陡峭的跨膜钠离子梯度丧失，星形胶质细胞可能通过载体逆转以及向细胞外空间释放酸、K⁺和/或谷氨酸而加重代谢损伤。
