Dulhunty A F, Gage P W
J Physiol. 1983 Aug;341:213-31. doi: 10.1113/jphysiol.1983.sp014802.
Asymmetrical charge movements (Q) were recorded from the voltage-clamped ends of muscle fibres in extensor digitorum longus (e.d.l.) and soleus muscles from rats. Tetracaine (2 mM) was added to solutions to prevent contraction. In both muscles the relationship between Q and membrane potential (V) was S-shaped and could be described by the Boltzmann-type equation Q = Qm/(1 + exp[-(v - V)/k]) where Qm was the maximum charge, V the membrane potential at which Q = Qm/2, and k a 'slope factor'. On average, Qm was 5-6 times greater in e.d..l. than in soleus fibres and charge movement occurred at more negative potentials in soleus than in e.d.l. fibres, V being -36.7 mV in the former and -19.0 mV in the latter, a difference of about 18 mV. The threshold for contraction, determined using a two-electrode voltage clamp, was more negative in soleus than in e.d.l. fibres. For 500 ms depolarizations, the difference was 12 mV. The relationship between tension and membrane potential during potassium contractures was S-shaped and, when fitted by the Boltzmann-type equation, gave V values of -25 mV for soleus and -14 mV for e.d.l. fibres. In paraplegic rats, the threshold for contraction in soleus fibres shifted about 12 mV to more positive potentials, but there was no change in e.d.l. fibres so that there was no significant difference between the two muscles. In paraplegic rats the relationship between tension and membrane potential during potassium contractures also shifted to more positive potentials in soleus fibres, whereas there was no change in e.d.l. fibres. These changes in the voltage sensitivity of contractile activation in soleus fibres from paraplegic rats were associated with a parallel shift in the voltage sensitivity of charge movement so that the average V shifted from -36.7 mV in normal rats to a value of -14.2 mV in paraplegic rats. There was also a four-fold increase in Qm in soleus fibres from paraplegic rats. The difference between the voltage sensitivity of contractile activation and charge movement in e.d.l. and soleus fibres in normal rats supports the hypothesis that the two are closely related: even stronger support comes from the observation of the parallel shift in the voltage sensitivity of contractile activation and charge movement in soleus fibres in paraplegic rats.
在大鼠的趾长伸肌（e.d.l.）和比目鱼肌中，从电压钳制的肌纤维末端记录到不对称的电荷移动（Q）。在溶液中加入丁卡因（2 mM）以防止收缩。在这两种肌肉中，Q与膜电位（V）之间的关系呈S形，可用玻尔兹曼型方程Q = Qm/(1 + exp[-(v - V)/k])来描述，其中Qm是最大电荷，V是Q = Qm/2时的膜电位，k是“斜率因子”。平均而言，e.d.l.肌纤维中的Qm比比目鱼肌纤维中的大5 - 6倍，且比目鱼肌纤维中的电荷移动发生在比e.d.l.肌纤维更负的电位，前者的V为-36.7 mV，后者为-19.0 mV，相差约18 mV。使用双电极电压钳测定的收缩阈值，比目鱼肌纤维比e.d.l.肌纤维更负。对于500 ms的去极化，差异为12 mV。钾离子挛缩期间张力与膜电位之间的关系呈S形，用玻尔兹曼型方程拟合时，比目鱼肌纤维的V值为-25 mV，e.d.l.肌纤维为-1 mV。在截瘫大鼠中，比目鱼肌纤维的收缩阈值向更正的电位移动了约12 mV，但e.d.l.肌纤维没有变化，因此两种肌肉之间没有显著差异。在截瘫大鼠中，钾离子挛缩期间比目鱼肌纤维的张力与膜电位之间的关系也向更正的电位移动，而e.d.l.肌纤维没有变化。截瘫大鼠比目鱼肌纤维收缩激活的电压敏感性的这些变化与电荷移动的电压敏感性的平行移动相关，因此平均V从正常大鼠的-36.7 mV移至截瘫大鼠的-14.2 mV。截瘫大鼠比目鱼肌纤维中的Qm也增加了四倍。正常大鼠中e.d.l.肌纤维和比目鱼肌纤维收缩激活与电荷移动的电压敏感性之间的差异支持了两者密切相关的假设：截瘫大鼠比目鱼肌纤维收缩激活与电荷移动的电压敏感性平行移动的观察结果提供了更强的支持。
