Parker I, Yao Y
Department of Psychobiology, University of California, Irvine 92717-4550, USA.
Ciba Found Symp. 1995;188:50-60; discussion 60-5. doi: 10.1002/9780470514696.ch4.
The second messenger inositol 1,4,5-trisphosphate (InsP3) functions in large part by liberating calcium ions from intracellular stores. This release process is highly non-linear and shows a regenerative characteristic that allows production of all-or-none calcium spikes which propagate as waves. However, at low concentrations of InsP3 an additional mode of calcium liberation is seen in Xenopus oocytes, transient 'puffs' of cytosolic calcium that last for a few hundred milliseconds and are restricted to within a few micrometres. Puffs are generally of similar size and the amount of calcium released (about 3 x 10(-18) mol) suggests that they arise through the concerted opening of several InsP3-gated calcium release channels. Puff sites are present at a density of about one per 30 microns 2 in the animal hemisphere of the oocyte. Each site functions autonomously, producing puffs at largely random intervals. We conclude that calcium puffs represent 'quantal' units of InsP3-evoked calcium liberation, which may result from local regenerative feedback by cytosolic calcium ions at functionally discrete release sites.
第二信使肌醇1,4,5 - 三磷酸（InsP3）在很大程度上通过从细胞内储存库释放钙离子发挥作用。这种释放过程高度非线性，具有再生特性，能够产生全或无的钙峰，并以波的形式传播。然而，在低浓度的InsP3条件下，非洲爪蟾卵母细胞中会出现另一种钙离子释放模式，即持续几百毫秒、局限于几微米范围内的短暂胞质钙“喷发”。喷发通常大小相似，释放的钙量（约3×10⁻¹⁸摩尔）表明它们是通过几个InsP3门控钙释放通道协同开放产生的。在卵母细胞动物半球，喷发位点的密度约为每30平方微米一个。每个位点自主发挥作用，以大致随机的间隔产生喷发。我们得出结论，钙喷发代表InsP3诱发的钙离子释放的“量子”单位，这可能是由于在功能上离散的释放位点，胞质钙离子产生局部再生反馈所致。
