Ninomiya H, Taniguchi T, Fujiwara M
Department of Neurology, Faculty of Medicine, Kyoto University, Japan.
J Neurochem. 1990 Sep;55(3):1001-7. doi: 10.1111/j.1471-4159.1990.tb04589.x.
We examined the effects of in vitro anoxia on phosphoinositide (PI) breakdown in rat hippocampal slices stimulated by glutamate and quisqualate. In addition to assays of accumulations of 3H-inositol phosphates (3H-IPs) degraded from prelabeled PI, we adopted direct assay procedures of inositol 1,4,5-triphosphate (1,4,5-IP3) using 1,4,5-IP3-specific binding protein to determine the formation of 1,4,5-IP3. The first effect, observed with anoxic incubation by itself, was the diminished quisqualate (10(-5) M)-stimulated accumulation of 3H-IPs degraded from prelabeled PI under prolonged anoxia. Quisqualate caused a transient increase in 1,4,5-IP3 formation in the early phase of anoxia, similar to that under oxygenated conditions. Glutamate (10(-5) M), under normal conditions, influenced neither the accumulation of 3H-IPs nor the formation of 1,4,5-IP3. Also, the accumulation of 3H-IPs under prolonged anoxia was unaffected. The same concentration of glutamate, however, gave rise to a transient increase in 1,4,5-IP3 content in the early phase of anoxia, similar to that caused by quisqualate. The second effect, observed by oxygenation following anoxia, was the induction of glutamate-stimulated accumulation of 3H-IPs. When the hippocampal slices were oxygenated following a sufficiently long (greater than 30-min) exposure to anoxia, glutamate (10(-5) M) caused a significant increase in accumulation of 3H-IPs degraded from prelabeled PI. Quisqualate-stimulated accumulation of 3H-IPs under oxygenated incubations was also increased by prior exposure of slices to anoxia. These results support the hypothesis that an exposure of hippocampal slices to anoxia induces a sensitivity of the PI breakdown pathway to glutamate and that, given an oxygen supply following sufficiently long exposure to anoxia, the slices maintain their sensitivity to glutamate with an apparent increase in the accumulation of 3H-IPs.
我们研究了体外缺氧对谷氨酸和喹啉酸刺激的大鼠海马切片中磷酸肌醇（PI）分解的影响。除了检测从预先标记的PI降解的3H-肌醇磷酸（3H-IPs）的积累外，我们还采用了使用1,4,5-IP3特异性结合蛋白直接检测肌醇1,4,5-三磷酸（1,4,5-IP3）的方法来测定1,4,5-IP3的形成。首先，单独进行缺氧孵育时观察到的效应是，在长时间缺氧条件下，喹啉酸（10^(-5) M）刺激的从预先标记的PI降解的3H-IPs积累减少。喹啉酸在缺氧早期引起1,4,5-IP3形成的短暂增加，类似于在有氧条件下的情况。在正常条件下，谷氨酸（10^(-5) M）既不影响3H-IPs的积累，也不影响1,4,5-IP3的形成。此外，长时间缺氧下3H-IPs的积累不受影响。然而，相同浓度的谷氨酸在缺氧早期引起1,4,5-IP3含量的短暂增加，类似于喹啉酸引起的情况。其次，缺氧后进行充氧观察到的效应是，诱导谷氨酸刺激的3H-IPs积累。当海马切片在充分长时间（大于30分钟）暴露于缺氧后进行充氧时，谷氨酸（10^(-5) M）导致从预先标记的PI降解的3H-IPs积累显著增加。切片预先暴露于缺氧也增加了充氧孵育时喹啉酸刺激的3H-IPs积累。这些结果支持以下假设：海马切片暴露于缺氧会诱导PI分解途径对谷氨酸敏感，并且在充分长时间暴露于缺氧后给予氧气供应时，切片保持对谷氨酸的敏感性，同时3H-IPs的积累明显增加。
