ACID-BASE HOMEOSTASIS IN BRAIN INJURY

长期以来，酸碱平衡紊乱一直与 缺血性和创伤性脑损伤的病理生理学。 的有害 酸中毒的影响受到特别关注。 大量研究 表明乳酸过量产生是特别有害的 到星形胶质细胞 虽然这种易感性的基础不是 据了解，星形胶质细胞pH调节的研究表明， 这些细胞的机制与这些病理生理学 应答 特别感兴趣的是电压依赖性酸分泌 神经胶质去极化激活的机制。 的主要目的 这个建议是为了阐明这些星形胶质细胞调节的作用， 中枢神经系统急性损伤的过程。 星形胶质细胞pH调节将是 研究与pH微电极，光学记录方法和整体 细胞膜片钳技术。 细胞内pH研究将 在整个动物、脑切片和分离细胞水平上进行， 利用每个实验室提供的独特实验优势， 准备. 相比之下，神经元可以在损伤环境中受到酸中毒的保护， 因为外部氢离子阻断NMDA受体介导的活性。 然而，扩散性抑郁症和其他形式的过度兴奋 突触活动，与细胞外碱化有关， 能够解除NMDA受体的H+阻滞。 的大小 这些pH值变化取决于缓冲速度，缓冲速度由以下因素决定 碳酸酐酶的胞外活性。 这些研究将 确定这种酶在缺血性和创伤性损伤中的作用， CNS。 实验将采用最近开发的微电极技术， 这将允许第一次实时测定pH、碳酸氢盐和 受伤的大脑中的二氧化碳。 微电极研究将是 在麻醉大鼠中进行，在心脏骤停模型中（完全 皮质缺血）、中风（大脑中动脉闭塞）和脊髓 脊髓损伤 这些实验将提供一个完整的描述， 细胞外的酸碱状态。 结合 通过这些测量，我们将确定H+缓冲的动力学是否 可以通过用缓冲液处理或通过调节碳 脱水酶活性 实验将扩展到传播的研究 抑郁症和缺氧，以确定细胞外的作用， 在这些病理表现中起到缓冲作用。 这些研究利用了最近的概念和技术 大脑pH调节研究的进展。 这个广泛的目标 我们的工作是将基础研究的进展扩展到病理生理学， 设置. 我们的努力将提供洞察力和理解如何 基本的调节过程会影响心脏骤停引起的伤害， 中风和中枢神经系统损伤

Disturbances in acid-base homeostasis have long been implicated in the pathophysiology of ischemic and traumatic brain injury. The deleterious effects of acidosis have received particular attention. Numerous studies indicate that excessive production of lactic acid is particularly harmful to astrocytes. Although the basis of this susceptibility is not understood, studies of astrocyte pH regulation suggest that acid transport mechanisms of these cells are implicated in these pathophysiological responses. Of particular interest are voltage-dependent acid secretory mechanisms which are activated by glial depolarization. A principal aim of this proposal is to elucidate the role of these astrocytic regulatory processes in acute injuries to the CNS. Astrocyte pH regulation will be investigated with pH microelectrodes, optical recording methods and whole cell patch clamp techniques. The intracellular pH studies will be performed at the level of the whole animal, brain slice and isolated cell, capitalizing on the unique experimental advantages offered by each preparation. Neurons, by contrast, can be protected by acidosis in the injury setting, since external hydrogen ions block NMDA receptor-mediated activity. However, spreading depression and others forms of excessive excitory synaptic activity, are associated with extracellular alkalinization, capable of relieving the H+ block of the NMDA receptor. The magnitude of these pH shifts depends upon the speed of buffering, which is governed by the extracellular activity of carbonic anhydrase. These studies will determine the role of this enzyme in ischemic and traumatic injury to the CNS. Experiments will employ recently-developed microelectrode techniques, which will permit the first real-time determination of pH, bicarbonate and carbon dioxide in injured brain. The microelectrode studies will be conducted in anesthetized rats, in models of cardiac arrest (complete cortical ischemia), stroke (middle cerebral artery occlusion), and spinal cord injury. These experiments will provide a complete description of extracellular acid base status in these afflictions. In conjunction with these measurements, we will determine whether the kinetics of H+ buffering can be enhanced by treatment with buffers or by modulation of carbonic anhydrase activity. Experiments will be extended to the study of spreading depression, and hypoxia, in order to determine the role of extracellular buffering in the manifestation of these pathologies. These studies capitalize upon recent conceptual and technological developments in the study of brain pH regulation. The broad goal of this work is to extend our progress in basic research to the pathophysiological setting. Our efforts will provide insights and understanding into how elemental regulatory processes affect injuries arising from cardiac arrest, stroke, and CNS trauma.