Kössler F, Lange F, Caffier G, Küchler G
Dept. of Work Physiology, Central Institute of Occupational Medicine, Berlin, FRG.
Gen Physiol Biophys. 1991 Oct;10(5):485-98.
The role of extracellular K+ concentration in the propagation velocity of action potential was tested in isolated rat skeletal muscles. Different K+ concentrations were produced by KCl additions to extracellular solution. Action potentials were measured extracellularly by means of two annular platinum electrodes. Fibre bundles of m. soleus (SOL), m. extensor digitorum longus (EDL), red (SMR) and white (SMW) part of m. sternomastoideus were maximum stimulated. The conduction velocity (c.v.) was calculated from the distance between the electrodes and the time delay of the potentials measured at 22 degrees C. In Tyrode solution containing 5 mmol/l K+, the c.v. was close to 1 m.s-1. Bundles of the fast muscle type seemed to have a somewhat higher c.v. The differences observed in these studies were not significant. At higher temperatures, the c.v. increased (Q10 of approx. 2) and a dissociation between SMR and SMW muscles appeared. An elevation of K+ concentration to 10 mmol/l induced a drop of the c.v. by approx. 25% and 15% in EDL and SOL muscles, respectively. After return to normal solution, the recovery was not complete within 30 min. In K+ free solution the c.v. of EDL and SM muscles rose by a factor of 1.5, but less in SOL muscles. The weaker response of SOL to K+ modification was related to the higher resistance of this muscle to fatigue. This suggestion was supported by experiments on fatigued fibre bundles. Immediately after a tetanic stimulation producing fatigue, the c.v. of EDL and SOL muscles dropped similarly as in 10 mmol/l K+; again, the drop was less for SOL muscles. Adrenaline (0.5-10.0 mumol/l) enhanced both the c.v. and the twitch amplitude. The results support the suggestion that extracellular K+ accumulation during activity is an essential factor of muscle fatigue.
在分离的大鼠骨骼肌中测试了细胞外钾离子浓度在动作电位传播速度中的作用。通过向细胞外溶液中添加氯化钾来产生不同的钾离子浓度。动作电位通过两个环形铂电极进行细胞外测量。对比目鱼肌（SOL）、趾长伸肌（EDL）、胸锁乳突肌红色部分（SMR）和白色部分（SMW）的肌纤维束进行最大刺激。传导速度（c.v.）根据电极之间的距离和在22摄氏度下测量的电位延迟来计算。在含有5 mmol/l钾离子的台氏液中，传导速度接近1 m·s-1。快肌类型的肌束传导速度似乎略高。这些研究中观察到的差异不显著。在较高温度下，传导速度增加（Q10约为2），并且SMR和SMW肌肉之间出现了分离。将钾离子浓度提高到10 mmol/l分别导致EDL和SOL肌肉的传导速度下降约25%和15%。回到正常溶液后，30分钟内恢复不完全。在无钾离子溶液中，EDL和SM肌肉的传导速度提高了1.5倍，但SOL肌肉提高得较少。SOL对钾离子变化的反应较弱与该肌肉对疲劳的较高抵抗力有关。这一观点得到了对疲劳肌纤维束实验的支持。在产生疲劳的强直刺激后，EDL和SOL肌肉的传导速度下降情况与在10 mmol/l钾离子溶液中相似；同样，SOL肌肉的下降幅度较小。肾上腺素（0.5 - 10.0 μmol/l）增加了传导速度和抽搐幅度。结果支持了这样的观点，即活动期间细胞外钾离子积累是肌肉疲劳的一个重要因素。
