神经肌肉传递过程中钙作用的时机。

The timing of calcium action during neuromuscular transmission.

Katz B, Miledi R

J Physiol. 1967 Apr;189(3):535-44. doi: 10.1113/jphysiol.1967.sp008183.

Abstract

When a nerve-muscle preparation is paralysed by tetrodotoxin, brief depolarizing pulses applied to a motor nerve ending cause packets of acetylcholine to be released and evoke end-plate potentials (e.p.p.s), provided calcium ions are present in the extracellular fluid.2. By ionophoretic discharge from a 1 M-CaCl(2) pipette, it is possible to produce a sudden increase in the local calcium concentration at the myoneural junction, at varying times before or after the depolarizing pulse.3. A brief application of calcium facilitates transmitter release if it occurs immediately before the depolarizing pulse. If the calcium pulse is applied a little later, during the period of the synaptic delay, it is ineffective.4. It is concluded that the utilization of external calcium ions at the neuromuscular junction is restricted to a brief period which barely outlasts the depolarization of the nerve ending, and which precedes the transmitter release itself.5. The suppressing effect of magnesium on transmitter release was studied by a similar method, with ionophoretic discharges from a 1 M-MgCl(2)-filled pipette. The results, though not quite as clear as with calcium, indicate that Mg pulses also are only effective if they precede the depolarizing pulses.

摘要

当神经 - 肌肉标本被河豚毒素麻痹时，若细胞外液中存在钙离子，施加于运动神经末梢的短暂去极化脉冲会致使乙酰胆碱小包被释放并引发终板电位（e.p.p.s）。
通过从1M - CaCl₂移液管进行离子电泳放电，有可能在去极化脉冲之前或之后的不同时间，使肌神经接头处的局部钙浓度突然升高。
如果在去极化脉冲之前立即施加钙脉冲，短暂施加钙会促进递质释放。如果钙脉冲稍晚些施加，即在突触延迟期间施加，则无效。
可以得出结论，神经肌肉接头处对外部钙离子的利用仅限于一个短暂时期，该时期仅比神经末梢去极化持续时间稍长，且先于递质释放本身。
用类似方法研究了镁对递质释放的抑制作用，即从装有1M - MgCl₂的移液管进行离子电泳放电。结果虽然不像钙那样清晰，但表明镁脉冲也只有在去极化脉冲之前施加才有效。