神经肌接头上产生持续性去极化时小终板电位的变化

THE CHANGE OF MINIATURE ENDPLATE POTENTIALS INNEUROMUSCULAR JUNCTIONS WITH OCCURRENCE OF SUSTAINED DEPOLARIZATION

实验在大鼠膈肌标本上观察梭曼处理后，终板区持续性去极化（ｓｕｓｔａｉｎｅｄｄｅｐｏｌａｒｉｚａｔｉｏｎ，ＳＤ）产生时小终板电位（ＭＥＰＰ）的变化，以分析产生ＳＤ的机理。静息时，加入５．５μｍｏｌ／Ｌ梭曼后，ＭＥＰＰ的频率、幅度和下降时间常数分别是加药前的１．８，１．３和３．０倍（Ｐ＜０．０１）。间接强直刺激时，记录到ＳＤ，ＳＤ过程中不仅终板电位消失，ＭＥＰＰ也完全消失。ＳＤ之后一定时间ＭＥＰＰ恢复出现，然后其频率逐渐增高。从ＳＤ开始到ＭＥＰＰ明显恢复的时间与强直刺激参数有关，５０Ｈｚ×１ｓ和５０Ｈｚ×０．１ｓ强直刺激时，分别为２９．７±０．７ｓ和１１．７±３．０ｓ。结果表明，在乙酰胆碱酯酶活性被抑制后，静息时突触前自发ＡＣｈ释放增加；刺激神经时，突触后对ＡＣｈ反应性降低甚至失去反应性，是产生ＳＤ的主要机理。

In our previous study,it was observed that the sustained depolarization(SD)in endplate areamight be the predominant electrophysiological response to indirect repetitive stimulation inneuromuscular junctions treated with soman.SD was characterized by the disappearance ofendplate potentials(EPPs)and the“all or none”nature.In order to investigate the mechanism ofSD, the changes of miniature EPPs(MEPPs)were observed after exposure to soman on endplatesof isolated nonuniform stretched muscle preparation.At rest,exposure to 5.5μmol / L soman re-sulted in the increase in MEPP's frequency,amplitude and decay constant.SD occurred when theindirect stimulation was given. During SD, MEPPs disappeared as EPPs did.MEPPs reappearedand the frequency of MEPPs increased at a certain time after SD.The time from the start of SDto the reappearance of MEPPs was related to the stimulation.For 50Hz×1s and 50Hz×0.1s,itwas 29.7 ±0.7s and 11.7±3.0s respectively.It is suggested that the spontaneous presynaptic re-lease in endplates at rest might increase after exposure to soman,while during indirect stimulationwhen SD occurs, the postsynaptic response to ACh decreases or even disappears.Thepostsynaptic change may be the main mechanism of SD. It is also suggested that there may alsobe presynaptic changes during SD,but the presynaptic change is not“all or none”in nature and itis not the main mechanism of SD.