Calcium Dynamics in Exocytosis and Synaptic Facilitation

胞吐作用和突触促进中的钙动力学

• 批准号: 0817703
• 负责人: Victor Matveev
• 金额: $ 30.56万
• 依托单位: New Jersey Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-08-01 至 2013-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0817703&HistoricalAwards=false
• 关键词: Calcium; Dynamics; Exocytosis; Synaptic; Facilitation

This project will use a combination of analytical, computational and experimental techniques to gain a deeper understanding of the synaptic release of neurotransmitter, termed exocytosis. It will address such open questions as the precise sequence of steps linking calcium ion entry into the cell to exocytosis, the involvement of individual calcium channels in neurotransmitter release, and the mechanisms of transient calcium-dependent facilitation of synaptic response, presumably caused by the accumulation of calcium at the exocytosis site. More specifically, this project will focus on the impact of intrinsic and externally applied calcium binding substances termed calcium buffers on exocytosis and its facilitation, using mathematical and computational modeling of calcium diffusion inside the cell. The importance of calcium buffers stems from the fact that they absorb more than 95% of calcium ions entering the cell; further, the sensitivity of exocytosis and facilitation to applied buffers provides one of the most widely used methods to probe the intrinsic calcium sensitivity of these processes. The first specific goal of this project is to reveal the effect of such buffers on the cooperativity of individual calcium channels in triggering exocytosis of a single vesicle, and to re-examine the so-called calcium current cooperativity measurements that probe the arrangement of channels at the release site. The second specific goal is to examine the proposed non-local property of the buffer saturation phenomenon, whereby the transient whole-terminal depletion of free buffer by calcium influx through one group of channels may cause subsequent opening of the same or another group of channels to produce a greater calcium elevation. Further, the competition between two calcium buffers in their regulation of intracellular calcium will be explored. Finally, this project will examine the possible functional consequences of synaptic facilitation for the dynamics of neural circuits.Neurotransmitter release at chemical synapses (exocytosis) represents the most common form of communication between two neurons in any biological neural system, including the mammalian cortex, and the knowledge of its mechanisms is indispensable for a full understanding of inter-neuronal interactions and neural information processing. Further, the regulation of neurotransmitter release and binding to receptors represents the main pharmacological treatment method in many neurological and psychiatric pathologies. The importance of this project stems from its combined use of advanced computational tools and experimental physiological techniques in gaining deeper understanding of the neurotransmitter release process, known to depend on the action of calcium ions inside the cell. This project will focus on the precise sequence of exocytosis steps starting with the entry of calcium through cell membrane calcium channels, their subsequent accumulation and binding to intracellular calcium-binding substances, and ending with the calcium-triggered release of neurotransmitter-filled vesicles into the synapse. This investigation should also lead to a better understanding of other vital physiological processes controlled by calcium ions, from gene expression regulation to muscle cell contraction in the heart. Further, this project will involve the use and further development of a publicly accessible computational modeling tool called CalC ("Calcium Calculator"), designed by the Principle Investigator for the modeling of three-dimensional calcium ion diffusion inside the cell (http://www.calciumcalculator.org). This will contribute to the infrastructure for computational modeling in the biological sciences and will also serve as a useful training instrument in the fields of cell neurophysiology and biophysics. All modeling results obtained in the course of this project will be made publicly available through the on-line model database, ensuring the most rapid and effective dissemination of the obtained results. Finally, this project will create student training opportunities in the highly interdisciplinary fields of mathematical biology, biophysics and computational neuroscience, including the training of students from under-represented ethnic groups, since this work will be conducted in an institution with one of the most ethnically diverse student bodies in the country (NJIT).

该项目将结合分析、计算和实验技术，对突触释放神经递质（称为胞外分泌）有更深的了解。它将解决一些悬而未决的问题，如钙离子进入细胞到胞吐的确切步骤顺序，单个钙通道在神经递质释放中的参与，以及短暂的钙依赖性突触反应的促进机制，可能是由胞吐部位的钙积累引起的。更具体地说，该项目将重点关注内源性和外源性钙结合物质钙缓冲液对胞外分泌及其促进作用的影响，使用细胞内钙扩散的数学和计算模型。钙缓冲液的重要性源于它们吸收了95%以上进入细胞的钙离子；此外，胞吐和易化对应用缓冲液的敏感性为探测这些过程的内在钙敏感性提供了最广泛使用的方法之一。该项目的第一个具体目标是揭示这些缓冲液对触发单个囊泡胞外分泌的单个钙通道协同性的影响，并重新检查所谓的钙电流协同性测量，探测释放部位通道的排列。第二个具体目标是研究缓冲液饱和现象的非局部特性，即钙通过一组通道流入导致自由缓冲液的瞬时全端耗尽，可能导致随后打开相同或另一组通道，以产生更大的钙升高。此外，将探讨两种钙缓冲液在调节细胞内钙方面的竞争。最后，本项目将研究突触易化对神经回路动力学的可能功能后果。化学突触中的神经递质释放（胞吐）代表了包括哺乳动物皮层在内的任何生物神经系统中两个神经元之间最常见的交流形式，对其机制的了解对于充分理解神经元间相互作用和神经信息处理是必不可少的。此外，调节神经递质释放和与受体的结合是许多神经和精神疾病的主要药物治疗方法。这个项目的重要性源于它结合了先进的计算工具和实验生理技术，以更深入地了解神经递质释放过程，已知依赖于细胞内钙离子的作用。本项目将重点研究细胞外吐过程的精确顺序，从钙通过细胞膜钙通道进入细胞，随后积累并与细胞内钙结合物质结合，到钙触发的充满神经递质的囊泡释放到突触结束。这项研究也将有助于更好地理解钙离子控制的其他重要生理过程，从基因表达调控到心脏肌肉细胞收缩。此外，该项目将涉及使用和进一步开发一种可公开访问的计算建模工具CalC（“钙计算器”），该工具由首席研究员设计，用于模拟细胞内三维钙离子扩散（http://www.calciumcalculator.org）。这将有助于生物科学中计算建模的基础设施，也将作为细胞神经生理学和生物物理学领域的有用训练工具。在本项目过程中获得的所有建模结果都将通过在线模型数据库向公众提供，确保获得的结果得到最迅速和有效的传播。最后，该项目将为数学生物学、生物物理学和计算神经科学等高度跨学科领域的学生提供培训机会，包括培训来自代表性不足的族裔群体的学生，因为这项工作将在一个拥有全国最具种族多样性学生群体之一的机构（NJIT）进行。