Dynamics of pH Regulation in the Brain

描述（由申请人提供）：神经元的电活动与脑细胞外液pH值的快速变化有关。在几毫秒内，可以检测到细胞外pH值的上升，这是由质膜钙三磷酸腺苷酶（PMCA）激活引起的，因为它泵出钙以换取细胞外氢离子。由于细胞外液无法在短时间内缓冲氢离子的通量，pH值会显著升高。这是因为催化缓冲反应的胞外碳酸酐酶活性有限。胞外pH值快速升高的意义在于几种膜通道对氢离子的敏感性。在这个应用中，我们提出单个神经元中PMCA的活性导致通过突触后n -甲基- d -天冬氨酸受体（NMDARs）的离子通量增加。初步数据表明，通过NMDARs的电流的振幅和时间过程都受到同一细胞产生的细胞外pH值升高的调节。另外的实验表明，海马中间神经元也受到调节，由于其突触后盐酸盐受体的pH敏感性。在这个应用中，中间神经元将首次在这种背景下进行研究，重点是它们的激酶和激酶

DESCRIPTION (provided by applicant): The electrical activity of neurons is associated with rapid changes in the pH of the brain extracellular fluid. Within milliseconds, a rise in extracelluar pH can be detected that is caused by activation of the plasma membrane calcium ATPase (PMCA), as it pumps out calcium in exchange for extracellular hydrogen ions. A significant increase in pH can occur due to the inability of the extracellular fluid to buffer the flux of hydrogen ions in a fast time frame. This is because the enzyme extracellular carbonic anhydrase, which catalyzes the buffering reaction, is limited in activity. The significance of the rapid elevation of extracellular pH lies in the sensitivity of several membrane channels to hydrogen ions. In this application we propose that the activity of the PMCA in a single neuron results in a boost of the ion flux through post-synaptic N-methyl-D-aspartate receptors (NMDARs). The preliminary data presented suggest that both the amplitude and time course of current through NMDARs are modulated by the rise in extracellular pH generated by the very same cell. Additional experiments suggest that hippocampal interneurons are also subject to modulation, due to the pH sensitivity of their post-synaptic kainate receptors. In this application interneurons will be studied for the first time in this context, with emphasis on their kainate and NMDAR-mediated synaptic currents, and the mechanisms that control the pH distribution across their plasma membrane. The consequences of these pH shifts for network activity are addressed in the final aim of this application, which investigates a form of short-term, post-synaptic potentiation induced by brief high frequency synaptic input. This potentiation is especially pronounced in animals with a knock out of the carbonic anhydrase 14 isoform, and is postulated to occur through a transient rise in extracellular pH, mediated via the PMCA. To accomplish these aims, experiments will be performed on acute mouse hippocampal slices, and cultured interneurons. Studies will make use of animals with a knockout of specific carbonic anhydrases, and will utilize transgenic mice with green fluorescence protein expression in specific interneuron populations. The physiological significance of these issues lies in the increased understanding of short-term plasticity in the brain, while its translational impact stems from the importance of rapid enhancements of excitability, which are a feature in the run up to seizure and spreading depression, pathologies that are implicated in the exacerbation tissue damage from stroke and traumatic brain injury.