Kiedrowski L, Wroblewski J T, Costa E
Fidia-Georgetown Institute for the Neurosciences, Georgetown University, Washington D.C. 20007.
Mol Pharmacol. 1994 May;45(5):1050-4.
We monitored simultaneously the changes in the intracellular sodium concentration ([Na+]i) and intracellular calcium concentration ([Ca2+]i) in individual neurons from primary cultures of cerebellar granule cells loaded with sodium-binding benzofuran isophthalate and fluo-3. An application of glutamate (50 microM) in Mg(2+)-free medium containing 10 microM glycine evoked [Na+]i and [Ca2+]i increases that exceeded 60 mM and 1 microM, respectively. The kinetics of [Na+]i and [Ca2+]i decreases after the termination of the glutamate pulse were different. [Na+]i failed to decrease immediately after glutamate withdrawal and the delay in the onset of [Na+]i decrease after the glutamate pulse termination was proportional to the glutamate dose, the glutamate pulse duration, and the extent of [Ca2+]i elevation elicited by glutamate. The kinetics of [Ca2+]i decrease were biphasic, with the first phase occurring immediately after glutamate withdrawal and the second phase being correlated in time with a [Na+]i value lower than 15-20 mM. These results were interpreted to indicate that the glutamate-evoked calcium influx may lead to sodium homeostasis destabilization. The delay in the restoration of the sodium gradient may in turn prolong the neuronal exposure to toxic [Ca2+]i values, due to the decrease in the efficiency of the Na+/Ca2+ exchanger to extrude calcium. The glutamate effects on [Na+]i and [Ca2+]i were potentiated by glycine. Glycine (10 microM) added alone also evoked [Na+]i and [Ca2+]i increases; this effect was inhibited by a competitive inhibitor of the N-methyl-D-aspartate receptor, 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid, indicating an involvement of endogenous glutamate.
我们同时监测了用苯并呋喃异邻苯二甲酸酯钠和氟-3负载的小脑颗粒细胞原代培养物中单个神经元的细胞内钠浓度（[Na⁺]i）和细胞内钙浓度（[Ca²⁺]i）的变化。在含有10μM甘氨酸的无镁培养基中施加谷氨酸（50μM）会引起[Na⁺]i和[Ca²⁺]i分别增加超过60 mM和1μM。谷氨酸脉冲终止后[Na⁺]i和[Ca²⁺]i降低的动力学不同。谷氨酸撤药后[Na⁺]i未能立即降低，谷氨酸脉冲终止后[Na⁺]i降低开始的延迟与谷氨酸剂量、谷氨酸脉冲持续时间以及谷氨酸引起的[Ca²⁺]i升高程度成正比。[Ca²⁺]i降低的动力学是双相的，第一阶段在谷氨酸撤药后立即发生，第二阶段在时间上与低于15 - 20 mM的[Na⁺]i值相关。这些结果被解释为表明谷氨酸诱发的钙内流可能导致钠稳态不稳定。由于Na⁺/Ca²⁺交换体挤出钙的效率降低，钠梯度恢复的延迟可能反过来延长神经元暴露于有毒[Ca²⁺]i值的时间。甘氨酸增强了谷氨酸对[Na⁺]i和[Ca²⁺]i的作用。单独添加甘氨酸（10μM）也会引起[Na⁺]i和[Ca²⁺]i增加；这种作用被N-甲基-D-天冬氨酸受体的竞争性抑制剂3-(2-羧基哌嗪-4-基)丙基-1-膦酸抑制，表明内源性谷氨酸参与其中。
