Calcium Dynamics in Exocytosis and Synaptic Facilitation

本计画将结合分析、计算与实验技术，以更深入了解神经传递素的突触释放，称为胞吐作用。 它将解决这样的开放性问题，如连接钙离子进入细胞的胞吐，参与神经递质释放的个别钙通道的步骤的精确顺序，和短暂的钙依赖性促进突触反应的机制，推测引起的钙在胞吐部位的积累。 更具体地说，该项目将重点关注称为钙缓冲液的内在和外部应用的钙结合物质对胞吐作用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。 钙缓冲剂的重要性源于它们吸收超过95%的进入细胞的钙离子的事实;此外，胞吐作用的敏感性和对所施加的缓冲剂的促进提供了最广泛使用的方法之一来探测这些过程的内在钙敏感性。 该项目的第一个具体目标是揭示这种缓冲液对单个钙通道在触发单个囊泡胞吐中的协同性的影响，并重新检查所谓的钙电流协同性测量，该测量探测释放位点处的通道布置。 第二个具体目标是检查缓冲液饱和现象的拟议非局部性质，由此通过一组通道的钙内流引起的游离缓冲液的瞬时全末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，将探讨两种钙缓冲剂在调节细胞内钙方面的竞争。 最后，本研究将探讨突触易化对神经回路动力学的可能功能影响。在任何生物神经系统（包括哺乳动物皮层）中，神经递质在化学突触（胞吐）处的释放是两个神经元之间最常见的通讯形式，了解其机制对于全面理解神经元间的相互作用和神经信息处理是必不可少的。 此外，神经递质释放和与受体结合的调节代表了许多神经和精神病理学中的主要药理学治疗方法。该项目的重要性源于其结合使用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。 该项目将重点关注胞吐步骤的精确顺序，从钙通过细胞膜钙通道进入开始，随后积累并结合细胞内钙结合物质，并以钙触发释放神经递质填充的囊泡进入突触结束。 这项研究还将有助于更好地了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中的肌肉细胞收缩。 此外，该项目将涉及使用和进一步开发一种称为CalC（“钙计算器”）的可公开访问的计算建模工具，该工具由主要研究者设计，用于对细胞内的三维钙离子扩散进行建模（http：www.calciumcalculator.org）。 这将有助于在生物科学计算建模的基础设施，也将作为一个有用的培训工具，在细胞神经生理学和生物物理学领域。在本项目过程中获得的所有建模结果将通过在线模型数据库公开提供，确保最迅速和有效地传播所获得的结果。 最后，该项目将在数学生物学、生物物理学和计算神经科学等高度跨学科领域创造学生培训机会，包括培训代表性不足的族裔群体的学生，因为这项工作将在一所拥有全国最多族裔学生的机构（NJIT）进行。

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).