Shuai Jianwei, Rose Heather J, Parker Ian
Department of Neurobiology and Behavior, University of California, Irvine, CA 92697-4550, USA.
Biophys J. 2006 Dec 1;91(11):4033-44. doi: 10.1529/biophysj.106.088880. Epub 2006 Sep 15.
Calcium puffs are local Ca(2+) release events that arise from a cluster of inositol 1,4,5-trisphosphate receptor channels (IP(3)Rs) and serve as a basic "building block" from which global Ca(2+) waves are generated. Important questions remain as to the number of IP(3)Rs that open during a puff, their spatial distribution within a cluster, and how much Ca(2+) current flows through each channel. The recent discovery of "trigger" events-small Ca(2+) signals that immediately precede puffs and are interpreted to arise through opening of single IP(3)R channels-now provides a useful yardstick by which to calibrate the Ca(2+) flux underlying puffs. Here, we describe a deterministic numerical model to simulate puffs and trigger events. Based on confocal linescan imaging in Xenopus oocytes, we simulated Ca(2+) release in two sequential stages; representing the trigger by the opening of a single IP(3)R in the center of a cluster for 12 ms, followed by the concerted opening of some number of IP(3)Rs for 19 ms, representing the rising phase of the puff. The diffusion of Ca(2+) and Ca(2+)-bound indicator dye were modeled in a three-dimensional cytosolic volume in the presence of immobile and mobile Ca(2+) buffers, and were used to predict the observed fluorescence signal after blurring by the microscope point-spread function. Optimal correspondence with experimental measurements of puff spatial width and puff/trigger amplitude ratio was obtained assuming that puffs arise from the synchronous opening of 25-35 IP(3)Rs, each carrying a Ca(2+) current of approximately 0.4 pA, with the channels distributed through a cluster 300-800 nm in diameter.
钙瞬变是局部Ca(2+)释放事件，源于一簇肌醇1,4,5-三磷酸受体通道（IP(3)Rs），并作为产生全局Ca(2+)波的基本“构建模块”。关于在一次钙瞬变期间打开的IP(3)Rs的数量、它们在簇内的空间分布以及有多少Ca(2+)电流流过每个通道，仍然存在重要问题。最近发现的“触发”事件——紧接在钙瞬变之前的小Ca(2+)信号，被解释为通过单个IP(3)R通道的开放而产生——现在提供了一个有用的标准，可用于校准钙瞬变背后的Ca(2+)通量。在这里，我们描述了一个确定性数值模型来模拟钙瞬变和触发事件。基于非洲爪蟾卵母细胞中的共聚焦线扫描成像，我们在两个连续阶段模拟了Ca(2+)释放；通过在簇中心打开单个IP(3)R 12毫秒来表示触发，随后一些数量的IP(3)Rs协同打开19毫秒，代表钙瞬变的上升阶段。在存在固定和移动Ca(2+)缓冲剂的情况下，在三维细胞质体积中对Ca(2+)和Ca(2+)结合指示剂染料的扩散进行建模，并用于预测在被显微镜点扩散函数模糊后的观察到的荧光信号。假设钙瞬变源于25 - 35个IP(3)Rs的同步开放，每个IP(3)R携带约0.4 pA的Ca(2+)电流，且通道分布在直径为300 - 800 nm的簇中，获得了与钙瞬变空间宽度和钙瞬变/触发幅度比的实验测量的最佳对应。
