Na+ entry via glutamate transporter activates the reverse Na+/Ca2+ exchange and triggers Ca2+i-induced Ca2+ release in rat cerebellar Type-1 astrocytes
Na+ entry via glutamate transporter activates the reverse Na+/Ca2+ exchange and triggers Ca2+i-induced Ca2+ release in rat cerebellar Type-1 astrocytes
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DOI：
10.1111/j.1471-4159.2006.04303.x
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发表时间：
2007-03-01
影响因子：
4.7
通讯作者：
DiPolo, Reinaldo
中科院分区：
文献类型：
--
作者：
Rojas, Hector;Colina, Claudia;DiPolo, Reinaldo
我们之前已经证明，大鼠小脑 1 型星形胶质细胞表达非常活跃的金雀异黄素敏感的 Na+/Ca2+ 交换器，它占质膜总 Ca2+ 通量的大部分，并负责清除生理激动剂诱导的 Ca-i(2+) 负荷。在这项工作中，我们探索了大鼠小脑星形胶质细胞中反向 Na+/Ca2+ 交换参与激动剂诱导的 Ca2+ 信号传导的机制。使用 Fluo-3 对 Ca-i(2+) 进行显微分光荧光测量表明，与 Na+/Ca2+ 交换的长 (> 20 s) 反向操作相关的 Ca-i(2+) 信号通过与钙-钙释放兼容的机制被放大，而与短 (< 20 s) 脉冲相关的信号则不会被放大。使用兰尼碱受体激动剂（4-氯间甲酚）和内质网 ATP 酶抑制剂（毒胡萝卜素）的药理学实验证实了这一点。共聚焦显微镜显示免疫荧光标记的 Na+/Ca2+ 交换剂和 RyR 的高度共定位。低浓度 (< 50 μmol/L) 或高浓度 (> 500 μmol/L) L-谷氨酸 (L-Glu) 或 L-天冬氨酸会导致浓度升高，但 Na+/Ca2+ 交换抑制剂 KB-R7943 和 SEA0400 可以完全阻断该升高。这项工作中最重要的新发现是，L-Glu 通过诱导 Na+ 通过生电 Na+-Glu 共转运蛋白而不是通过离子传递 L-Glu 受体进入，激活 Na+/Ca2+ 交换的反向模式，这一点已通过离子传递 L-Glu 受体和生电 Glu 转运蛋白的特异性阻断剂的药理学实验证实。
We have previously demonstrated that rat cerebellar Type-1 astrocytes express a very active genistein sensitive Na+/Ca2+ exchanger, which accounts for most of the total plasma membrane Ca2+ fluxes and for the clearance of Ca-i(2+) loads induced by physiological agonists. In this work, we have explored the mechanism by which the reverse Na+/Ca2+ exchange is involved in agonist-induced Ca2+ signaling in rat cerebellar astrocytes. Microspectrofluorometric measurements of Ca-i(2+) with Fluo-3 demonstrate that the Ca-i(2+) signals associated long (> 20 s) periods of reverse operation of the Na+/Ca2+ exchange are amplified by a mechanism compatible with calcium-calcium release, while those associated with short (< 20 s) pulses are not amplified. This was confirmed by pharmacological experiments using ryanodine receptors agonist (4-chloro-m-cresol) and the endoplasmic reticulum ATPase inhibitor (thapsigargin). Confocal microscopy demonstrates a high co-localization of immunofluorescent labeled Na+/Ca2+ exchanger and RyRs. Low (< 50 mu mol/L) or high (> 500 mu mol/L) concentrations of L-glutamate (L-Glu) or L-aspartate causes a rise in which is completely blocked by the Na+/Ca2+ exchange inhibitors KB-R7943 and SEA0400. The most important novel finding presented in this work is that L-Glu activates the reverse mode of the Na+/Ca2+ exchange by inducing Na+ entry through the electrogenic Na+-Glu-co-transporter and not through the ionophoric L-Glu receptors, as confirmed by pharmacological experiments with specific blockers of the ionophoric L-Glu receptors and the electrogenic Glu transporter.