Reinés A, Zárate S, Carmona C, Negri G, Peña C, Rodríguez de Lores Arnaiz G
Instituto de Biología Celular y Neurociencias "Prof. E. De Robertis", Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires, Argentina.
Life Sci. 2005 Dec 5;78(3):245-52. doi: 10.1016/j.lfs.2005.04.046. Epub 2005 Aug 16.
We have isolated from rat cerebral cortex an endogenous Na(+), K(+)-ATPase inhibitor, termed endobain E, which modulates glutamatergic N-methyl-d-aspartate (NMDA) receptor. This endogenous factor allosterically decreases [(3)H]dizocilpine binding to NMDA receptor, most likely acting as a weak channel blocker. In the present study we investigated whether endobain E is present in the cerebral cortex of rats subjected to ischemia and modulates NMDA receptor exposed to the same conditions. Ischemia-reperfusion was carried out by bilateral occlusion of common carotid arteries followed by a 15-min reperfusion period. Elution profile of brain soluble fraction showed that endobain E is present in cerebral cortex of ischemia-reperfusion rats. On assaying its effect on synaptosomal membrane Na(+), K(+)-ATPase activity and [(3)H]dizocilpine binding to cerebral cortex membranes prepared from animals without treatment, it was found that the endogenous modulator isolated from ischemia-reperfusion rats was able to inhibit both enzyme activity and ligand binding. On the other hand, endobain E prepared from rats without treatment also decreased binding to cerebral cortex or hippocampal membranes obtained from animals exposed to ischemia-reperfusion. Since ischemia decreases tissue pH and NMDA receptor activity varies according to proton concentration, pH influence on endobain E effect was tested. Endobain E ( approximately 80 mg original tissue) decreased [(3)H]dizocilpine binding 25% at pH 7.4 or 8.0 but 90% at pH 6.5. These results demonstrate that endobain E is present and also able to modulate NMDA receptor in the short-term period that follows cerebral ischemia and that its effect depends on proton concentration, suggesting greater NMDA receptor modulation by endobain E at low pH, typical of ischemic tissues.
我们从大鼠大脑皮层中分离出一种内源性钠钾ATP酶抑制剂，称为内源性脑抑制素E，它可调节谷氨酸能N-甲基-D-天冬氨酸（NMDA）受体。这种内源性因子通过变构作用降低[³H]地卓西平与NMDA受体的结合，很可能作为一种弱通道阻滞剂发挥作用。在本研究中，我们调查了内源性脑抑制素E是否存在于缺血大鼠的大脑皮层中，并调节处于相同条件下的NMDA受体。通过双侧颈总动脉闭塞15分钟后再灌注来进行缺血再灌注。脑可溶性部分的洗脱曲线表明，内源性脑抑制素E存在于缺血再灌注大鼠的大脑皮层中。在检测其对突触体膜钠钾ATP酶活性以及[³H]地卓西平与未经处理动物制备的大脑皮层膜结合的影响时，发现从缺血再灌注大鼠中分离出的内源性调节剂能够抑制酶活性和配体结合。另一方面，从未经处理的大鼠制备的内源性脑抑制素E也降低了与从经历缺血再灌注的动物获得的大脑皮层或海马膜的结合。由于缺血会降低组织pH值，且NMDA受体活性会根据质子浓度而变化，因此测试了pH值对内源性脑抑制素E作用的影响。内源性脑抑制素E（约80毫克原始组织）在pH 7.4或8.0时使[³H]地卓西平结合降低25%，但在pH 6.5时降低90%。这些结果表明，内源性脑抑制素E在脑缺血后的短期内存在且能够调节NMDA受体，其作用取决于质子浓度，这表明在缺血组织典型的低pH值条件下，内源性脑抑制素E对NMDA受体的调节作用更强。
