Khodorov B, Pinelis V, Vinskaya N, Sorokina E, Grigortsevich N, Storozhevykh T
Institute of General Pathology and Pathophysiology, Russian Academy of Medical Sciences, Moscow.
FEBS Lett. 1999 Apr 1;448(1):173-6. doi: 10.1016/s0014-5793(99)00350-6.
In experiments with fura-2 loaded cultured rat cerebellar granule cells we have compared the changes in [Ca2+]i homeostasis produced by replacement of external Na+ with the organic cation N-methyl-D-glucamine (NMDG) or Li+. The Na+/NMDG replacement caused an increase in baseline [Ca2+]i and a considerable delay in [Ca2+]i recovery following a glutamate (Glu) pulse in almost all the cells. In contrast Na+/Li+ replacement usually did not change baseline [Ca2+]i and produced only a small (if any) delay in the post-glutamate [Ca2+]i recovery. Previously [Storozhevykh et al. (1998) FEBS Lett. 431, 215-218] we revealed that perturbation of [Ca2+]i homeostasis caused by Na+/NMDG replacement cannot be explained by a reversal of the Na+/Ca2+ exchange but is mainly due to Ca2+ influx through NMDA channels activated by Na+ dependent release of endogenous excitatory amino acids ('reversed Glu uptake'). In the present work we confirmed this conclusion and obtained evidence suggesting that in contrast to NMDG Li+ interferes with the 'reversed Glu uptake' triggered by removal of external Na+. Thus it has been shown that the addition of Li+ (20 mM) to a Na+-free NMDG-containing solution suppressed both the perturbation of [Ca2+]i homeostasis and delayed neuronal death caused by Na+/NMDG replacement. Li+ is also able to abolish the [Ca2+]i response induced by PDC which at high concentrations (> 200 microM) is shown to stimulate the release of endogenous Glu. In contrast to Na+/Li+, Na+/NMDG replacement greatly enhances [Ca2+]i increase caused by PDC. Control experiments showed that Na+/Li+ replacement does not decrease the [Ca2+]i response to the Glu pulse. Therefore we concluded that a considerable quantitative difference between the effects of Na+/NMDG and Na+/Li+ replacements on both [Ca2+]i homeostasis and cell viability resulted mainly from the ability of Li+ to attenuate the release of endogenous Glu in response to the removal of external Na+.
在使用装载了fura - 2的培养大鼠小脑颗粒细胞进行的实验中，我们比较了用有机阳离子N - 甲基 - D - 葡糖胺（NMDG）或Li⁺替代细胞外Na⁺所引起的[Ca²⁺]i稳态变化。Na⁺/NMDG替代导致几乎所有细胞的基线[Ca²⁺]i升高，并且在谷氨酸（Glu）脉冲后[Ca²⁺]i恢复出现相当大的延迟。相比之下，Na⁺/Li⁺替代通常不会改变基线[Ca²⁺]i，并且在谷氨酸作用后[Ca²⁺]i恢复中仅产生很小（如果有的话）的延迟。此前[斯托罗热维赫等人（1998年），《欧洲生物化学学会联合会快报》431, 215 - 218]我们发现，Na⁺/NMDG替代引起的[Ca²⁺]i稳态扰动不能用Na⁺/Ca²⁺交换的逆转来解释，而是主要由于通过由Na⁺依赖性释放内源性兴奋性氨基酸激活的NMDA通道的Ca²⁺内流（“反向Glu摄取”）。在本研究中，我们证实了这一结论，并获得证据表明与NMDG不同，Li⁺干扰了因去除细胞外Na⁺而触发的“反向Glu摄取”。因此，已表明向不含Na⁺但含NMDG的溶液中添加Li⁺（20 mM）可抑制[Ca²⁺]i稳态的扰动以及由Na⁺/NMDG替代引起的神经元死亡延迟。Li⁺还能够消除由PDC诱导的[Ca²⁺]i反应，高浓度（> 200 μM）的PDC显示可刺激内源性Glu的释放。与Na⁺/Li⁺不同，Na⁺/NMDG替代极大地增强了由PDC引起的[Ca²⁺]i升高。对照实验表明，Na⁺/Li⁺替代不会降低对Glu脉冲的[Ca²⁺]i反应。因此我们得出结论，Na⁺/NMDG和Na⁺/Li⁺替代对[Ca²⁺]i稳态和细胞活力的影响在数量上存在相当大的差异，这主要是由于Li⁺能够减弱因去除细胞外Na⁺而引起的内源性Glu释放。
