Lobner D, Lipton P
Department of Physiology, University of Wisconsin, Madison 53706.
J Neurosci. 1993 Nov;13(11):4861-71. doi: 10.1523/JNEUROSCI.13-11-04861.1993.
Five minutes of oxygen and glucose deprivation (termed "in vitro ischemia") causes long-term synaptic transmission failure (LTF) in the CA1 region of the rat hippocampal slice. Dependence of LTF on cell calcium was tested by generating graded reductions in cell Ca. There was a strong correlation between the average level of exchangeable cell Ca in CA1 during ischemia, and the extent of LTF. In standard buffer, exchangeable cell Ca in CA1 increased by 35% after 3 min of ischemia and remained elevated for the entire 5 min of ischemia. Unidirectional Ca influx increased by 35% during the first 2.5 min of ischemia and remained at that level for the next 2.5 min. There were no changes in unidirectional Ca efflux during this period. Thus, the accumulation results from increased influx of Ca. Ca influx during the first 2.5 min of ischemia depended entirely on NMDA channels; it was completely blocked by the noncompetitive NMDA receptor antagonist MK-801. However MK-801 had no effect during the second 2.5 min. This inactivation of NMDA-mediated influx during ischemia appears to result from dephosphorylation. Okadaic acid increased Ca influx during the second 2.5 min of ischemia and this increase was blocked by MK-801. The ischemia-induced Ca influx during the second 2.5 min of ischemia was attenuated 25% by nifedipine (50 microM) and an additional 35% by the Na/Ca exchange inhibitor benzamil (100 microM). The AMPA/kainate antagonist DNQX had no effect on the Ca influx. Antagonists were used to relate Ca influx to LTF. Blockade of enhanced Ca entry during ischemia in standard buffer (2.4 mM Ca) had no effect on LTF, consistent with total cell Ca prior to ischemia being adequate to cause complete LTF. However, MK-801 strongly protected against LTF when the buffer contained 1.2 mM Ca, a more physiological level. MK-801 combined with DNQX prevented transmission damage in standard buffer. Thus, AMPA/kainate receptor activation contributes to ischemic damage, although not by enhancing Ca entry.
五分钟的缺氧和无糖状态（称为“体外缺血”）会导致大鼠海马切片CA1区出现长期突触传递失败（LTF）。通过逐步降低细胞内钙水平来测试LTF对细胞钙的依赖性。缺血期间CA1区可交换细胞钙的平均水平与LTF的程度之间存在很强的相关性。在标准缓冲液中，缺血3分钟后CA1区可交换细胞钙增加35%，并在整个5分钟的缺血过程中保持升高。单向钙内流在缺血的前2.5分钟增加35%，并在接下来的2.5分钟保持在该水平。在此期间单向钙外流没有变化。因此，钙的积累是由于钙内流增加所致。缺血前2.5分钟的钙内流完全依赖于NMDA通道；它被非竞争性NMDA受体拮抗剂MK-801完全阻断。然而，MK-801在第二个2.5分钟期间没有作用。缺血期间NMDA介导的内流失活似乎是由去磷酸化导致的。冈田酸增加了缺血第二个2.5分钟期间的钙内流，并且这种增加被MK-801阻断。硝苯地平（50微摩尔）使缺血第二个2.5分钟期间缺血诱导的钙内流减弱25%，钠/钙交换抑制剂苄amil（100微摩尔）使其再减弱35%。AMPA/海人酸受体拮抗剂DNQX对钙内流没有影响。使用拮抗剂来关联钙内流与LTF。在标准缓冲液（2.4毫摩尔钙）中阻断缺血期间增强的钙内流对LTF没有影响，这与缺血前细胞总钙足以导致完全LTF一致。然而，当缓冲液含有1.2毫摩尔钙（更接近生理水平）时，MK-801能强烈保护防止LTF。MK-801与DNQX联合使用可防止标准缓冲液中的传递损伤。因此，AMPA/海人酸受体激活会导致缺血性损伤，尽管不是通过增强钙内流。
