蛋白激酶C对大鼠缺血海马突触体谷氨酸摄取的调控作用

采用大鼠海马脑片体外缺血模型，观察海马突触体内蛋白激酶Ｃ（ＰＫＣ）活性的变化，以及这种变化对突触体谷氨酸（ＧＬＵ）摄取的影响。结果显示：海马脑片体外“缺血”１０ｍｉｎ，其突触体内ＰＫＣ活性基本不变，而缺血３０ｍｉｎ，突触体内ＰＫＣ活性显著上升（Ｐ＜０．０１，ｎ＝６）；非Ｎ－甲基－Ｄ－天门冬氨酸（ＮＭＤＡ）受体拮抗剂ＤＮＱＸ有效地抑制ＰＫＣ活性的同时，可降低胞外ＧＬＵ的堆积，而ＮＭＤＡ受体阻断剂ＡＰ＿５无作用。进一步实验证明，ＰＫＣ激动剂ＰＤＢ浓度依赖性地抑制突触体对３Ｈ－ＧＬＵ的摄取（ＩＣ５０＝１３１±１０μｍｏｌ／Ｌ），此抑制作用可由ＰＫＣ抑制剂Ｈ－７（１００μｍｏｌ／Ｌ）抵消。提示脑缺血诱发ＧＬＵ堆积的作用机理可能是：脑缺血引发钙内流导致ＧＬＵ过量释放，ＧＬＵ又通过突触前非ＮＭＤＡ受体激活ＰＫＣ，抑制其自身摄取，正反馈性加重胞外ＧＬＵ的堆积。

Regulation of Protein Kinase C on Glutamate Uptake into Synaptosomes in Rat Hippocampal Slices under Ischemic States

With a in vitro ischemic model, the activities of protein kinase C(PKC) and the effects of PKC on glutamate (GLU) uptake into synaptosomes in rat hippocampal slices were studied. The results showed that in synaptosomes, the PKC activity showed no changes under 10 min ischemic insult. However, the PKC avtivation was observed in presynaptic nerve terminals (from 1.30±0. 12 to 9. 34±0. 89U) following 30 min ischemia. DNQX, a nonNMDA receptor antagonist, potently reduced the PKC activation and decreased the ischemiainduced GLU accumulation, whereas NMDA receptor antagonist AP_5 showed no such effect.We further observed that the inhibition of 1-￣3H-GLU uptake into synaptosomes by addition of PDB, a PKC stimulator, was dependent on PDB concentration. These results provide direct evidence to show that the accumulation of GLU induced by cerebral ischemic conditions was under the dual control of Ca￣(2+) influx which enhances GLU release and PKC activation in presynaptic nerve terminals.