Dulhunty A F
J Membr Biol. 1980 Dec 30;57(3):223-33. doi: 10.1007/BF01869590.
Potassium (K-) contractures were recorded from slow-twitch (mouse soleus and fast-twitch (mouse extensor digitorum longus (EDL) and rat sternomastoid) muscles. The mouse limb muscles responded to a maintained increase in external potassium concentration with a rapid increase in tension (fast contracture) which inactivated and was followed by a slow contracture. Rat sternomastoid muscles responded with fast contractures only. The threshold potassium concentration for contraction was higher in fast-twitch muscles than in soleus muscles, at 22 and at 37 degrees C. After corrections had been made for the more rapid depolarization of soleus fibers, the threshold potential for soleus fiber contraction was 15mV closer to the resting membrane potential than the threshold for fast-twitch fiber contraction. The K-contracture results were confirmed by two microelectrode voltage-clamp experiments. Activation of fast twitch fibers required depolarizing pulses that were 15 to 20mV greater than the pulses required to activate soleus fibers. When the time courses of K-contractures were compared it was evident that inactivation with prolonged depolarization was much faster in the fast-twitch muscles than in the soleus muscles. The results suggest that the voltage dependence and kinetics of the process coupling T-tubule depolarization with calcium release from the sarcoplasmic reticulum may depend on fiber atype in mammalian skeletal muscle.
在慢肌（小鼠比目鱼肌）和快肌（小鼠趾长伸肌（EDL）和大鼠胸锁乳突肌）中记录到钾离子（K-）挛缩。小鼠肢体肌肉对外界钾离子浓度持续升高的反应是张力迅速增加（快速挛缩），随后失活并出现缓慢挛缩。大鼠胸锁乳突肌仅出现快速挛缩。在22℃和37℃时，快肌收缩的阈钾浓度高于比目鱼肌。在对比目鱼肌纤维更快的去极化进行校正后，比目鱼肌纤维收缩的阈电位比快肌纤维收缩的阈电位更接近静息膜电位15mV。钾离子挛缩结果通过两个微电极电压钳实验得到证实。激活快肌纤维所需的去极化脉冲比激活比目鱼肌纤维所需的脉冲高15至20mV。当比较钾离子挛缩的时间进程时，很明显，长时间去极化导致的失活在快肌中比在比目鱼肌中快得多。结果表明，将横管去极化与肌浆网钙释放相偶联的过程的电压依赖性和动力学可能取决于哺乳动物骨骼肌的纤维类型。
