Gallacci M, Oliveira A C
Departamento de Farmacologia, Instituto de Biociências, UNESP, Brasil.
Pharmacology. 1994 Oct;49(4):265-70. doi: 10.1159/000139242.
The mechanisms underlying the fade of the tetanic contraction induced by pancuronium were studied in vitro by means of myographical and electrophysiological techniques in the extensor digitorum longus muscle of the rat. Pancuronium (0.5 mumol/l) induced a complete fade of the tetanic contraction while leaving the twitch unaffected. At the same concentration it decreased the amplitude and increased the tetanic rundown of trains of endplate potentials (e.p.ps) evoked in the frequency of 50 Hz. The electrophysiological changes induced by pancuronium were due to decreases in both quantal sizes and quantal contents of the e.p.ps. The former effect was the result of a postsynaptic competitive action and the latter of a presynaptic inhibitory action of that compound. The decrease in quantal content affected the e.p.ps starting from the first in the train and became larger during the generation of the sequence of e.p.ps. This intensified their tetanic rundown. It is concluded that the fade of the tetanic contraction induced by pancuronium is due to a summation of pre- and postsynaptic actions and, therefore, not only to an increase in the tetanic rundown of e.p.ps. Possible explanations for the distinct abilities of neuromuscular blockers in affecting tetani and twitches in a differential manner are also discussed.
采用肌电图和电生理技术，在大鼠趾长伸肌上，对泮库溴铵诱导的强直收缩消退机制进行了体外研究。泮库溴铵（0.5μmol/L）可诱导强直收缩完全消退，而对单收缩无影响。在相同浓度下，它降低了终板电位（e.p.ps）的幅度，并增加了以50Hz频率诱发的e.p.ps串的强直衰减。泮库溴铵引起的电生理变化是由于e.p.ps的量子大小和量子含量均降低。前者是该化合物突触后竞争性作用的结果，后者是其突触前抑制作用的结果。量子含量的降低从串中的第一个e.p.ps开始影响，并在e.p.ps序列产生过程中变得更大。这加剧了它们的强直衰减。得出的结论是，泮库溴铵诱导的强直收缩消退是由于突触前和突触后作用的总和，因此，不仅仅是由于e.p.ps的强直衰减增加。还讨论了神经肌肉阻滞剂以不同方式影响强直和单收缩的不同能力的可能解释。
