哺乳动物不活动化肌纤维的动作电位

用河豚毒素(TTX)慢性阻断大鼠坐骨神经的冲动传导,使后肢不活动,经过不同时间(最长7d)后离体观察了快肌伸趾长肌(EDL)和慢肌比目鱼肌(SOL)肌纤维终板区的诱发动作电位。我们发现在不活动期间动作电位超射和上升速率逐步下降,并从第4天起部分肌纤维能在含有1×10~(-7)g/ml TTX的溶液中被诱发产生动作电位(称抗TTX动作电位),待至第7天时全部SOL肌纤维和90％的EDL肌纤维都能被诱发出抗TTX动作电位。与去神经肌纤维相比,不仅抗TTX动作电位出现较晚,并且其超射和上升速率较低。在去掉TTX阻断使肌肉恢复活动后,动作电位超射和上升速率渐趋恢复,抗TTX动作电位逐渐消失。无论是动作电位的恢复还是抗TTX动作电位的消失,EDL肌纤维均快于SOL肌纤维。本文还讨论了不活动化使肌纤维动作电位变化以及快、慢肌差别的可能原因。

ACTION POTENTIAL OF INACTIVATED MAMMALIAN MUSCLE FIBRES

In the present work, tetrodotoxin (TTX) was used to chronically block theconduction of impulses of the rat sciatic nerve, and the changes of action potentialsof inactivated muscle fibres were examined. Action potentials intracellularlyelicited were recorded from the end-plate region of the fast-twitch muscle extensordigitorum longus (EDL) and slow-twitch muscle soleus (SOL) muscle fibres inactivat-ed for up to 7 days. Similar to denervation, long-term inactivation led to graduallydecreasing of the overshoot and rise rate of action potentials and appearance ofTTX-resistant action potentials in a few fibres on the fourth day. On the seventhday the TTX-resistant action potential was found in almost all of tested fibres(100%SOL and 90% EDL fibres). But, these changes induced by inactivation were lessthan those by denervation. After removal of blockade, the overshoot and riserate of action potentials gradually returned to the control level, and the actionpotentials could no longer be elicited in the presence of TTX. The time course,with which both the recovery of parameters of action potentials and the disap-pearance of TTX-resistant action potentials proceeded, was faster in EDL than inSOL. The mechanism of inactivation-induced change of action potentials ofmuscle fibres and the possible reason for the difference in the recovery processbetween EDL and SOL are discussed.