Stockbridge N, Moore J W
J Neurosci. 1984 Mar;4(3):803-11. doi: 10.1523/JNEUROSCI.04-03-00803.1984.
We have developed a mechanistic model for intracellular influx, diffusion, and efflux of calcium, and we compare its predictions to the dynamics of transmitter release at the frog's motor nerve terminal. The model includes a square wave influx of calcium, a linear or saturable pump for the efflux of calcium, and slow diffusion of calcium within the terminal due to rapid equilibrium binding of the major portion of the influx to fixed, nonsaturable sites in the cytoplasm. Transmitter release is taken as proportional to the fourth power of the calcium concentration in a region within 100 A of the surface membrane. The model predicts phasic release of transmitter with a time course similar to that of the endplate current--it turns on with a lag, rises rapidly to a peak, and then declines more slowly. It also predicts facilitation, the increased transmitter release in response to a second stimulus for many milliseconds after the initial transmitter release has ceased. This facilitation is similar to that reported at the frog neuromuscular junction in its initial amplitude and time course.
我们建立了一个关于钙的细胞内流入、扩散和流出的机制模型，并将其预测结果与青蛙运动神经末梢递质释放的动力学进行比较。该模型包括钙的方波流入、用于钙流出的线性或饱和泵，以及由于流入的大部分与细胞质中固定的、非饱和位点快速平衡结合而导致的钙在末梢内的缓慢扩散。递质释放被认为与距表面膜100埃范围内区域的钙浓度的四次方成正比。该模型预测递质的阶段性释放，其时程与终板电流相似——它有一个延迟开启，迅速上升到峰值，然后下降得更慢。它还预测了易化作用，即在初始递质释放停止后的许多毫秒内，对第二个刺激的反应中递质释放增加。这种易化作用在其初始幅度和时程上与青蛙神经肌肉接头处报道的相似。
