Zhang Y, Lipton P
Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA.
J Neurosci. 1999 May 1;19(9):3307-15. doi: 10.1523/JNEUROSCI.19-09-03307.1999.
This work determined Ca2+ transport processes that contribute to the rise in cytosolic Ca2+ during in vitro ischemia (deprivation of oxygen and glucose) in the hippocampus. The CA1 striatum radiatum of rat hippocampal slices was monitored by confocal microscopy of calcium green-1. There was a 50-60% increase in fluorescence during 10 min of ischemia after a 3 min lag period. During the first 5 min of ischemia the major contribution was from Ca2+ entering via NMDA receptors; most of the fluorescence increase was blocked by MK-801. Approximately one-half of the sustained increase in fluorescence during 10 min of ischemia was caused by activation of Ca2+ release from mitochondria via the mitochondrial 2Na+-Ca2+ exchanger. Inhibition of Na+ influx across the plasmalemma using lidocaine, low extracellular Na+, or the AMPA/kainate receptor blocker CNQX reduced the fluorescence increase by 50%. The 2Na+-Ca2+ exchange blocker CGP37157 also blocked the increase, and this effect was not additive with the effects of blocking Na+ influx. When added together, CNQX and lidocaine inhibited the fluorescence increase more than CGP37157 did. Thus, during ischemia, Ca2+ entry via NMDA receptors accounts for the earliest rise in cytosolic Ca2+. Approximately 50% of the sustained rise is attributable to Na+ entry and subsequent Ca2+ release from the mitochondria via the 2Na+-Ca2+ exchanger. Sodium entry is also hypothesized to compromise clearance of cytosolic Ca2+ by routes other than mitochondrial uptake, probably by enhancing ATP depletion, accounting for the large inhibition of the Ca2+ increase by the combination of CNQX and lidocaine.
这项研究确定了在体外海马缺血（缺氧和缺葡萄糖）期间导致胞质钙离子浓度升高的钙离子转运过程。用钙绿 -1 共聚焦显微镜监测大鼠海马切片的 CA1 放射层。在 3 分钟的延迟期后，缺血 10 分钟期间荧光增加了 50 - 60%。在缺血的最初 5 分钟内，主要的钙离子增加来自通过 N - 甲基 - D - 天冬氨酸（NMDA）受体进入的钙离子；大部分荧光增加被 MK - 801 阻断。在缺血 10 分钟期间荧光持续增加的大约一半是由通过线粒体 2Na⁺ - Ca²⁺ 交换器激活线粒体释放钙离子所致。使用利多卡因、低细胞外钠离子或 AMPA/海人藻酸受体阻断剂 CNQX 抑制钠离子跨质膜内流可使荧光增加减少 50%。2Na⁺ - Ca²⁺ 交换阻断剂 CGP37157 也可阻断荧光增加，且这种作用与阻断钠离子内流的作用无叠加效应。当 CNQX 和利多卡因一起添加时，它们对荧光增加的抑制作用比 CGP37157 更强。因此，在缺血期间，通过 NMDA 受体进入的钙离子是胞质钙离子最早升高的原因。大约 50%的持续升高归因于钠离子进入以及随后通过 2Na⁺ - Ca²⁺ 交换器从线粒体释放钙离子。还推测钠离子进入可能通过增强 ATP 消耗而损害除线粒体摄取外的其他途径对胞质钙离子的清除，这解释了 CNQX 和利多卡因联合使用对钙离子增加的强烈抑制作用。
