Fitts R H, Winder W W, Brooke M H, Kaiser K K, Holloszy J O
Am J Physiol. 1980 Jan;238(1):C14-20. doi: 10.1152/ajpcell.1980.238.1.C15.
The effects of thyrotoxicosis on the contractile properties of soleus muscle were examined in rats given 3 mg of T4 and 1 mg of T3 per kg of diet for 6--8 wk. Thyrotoxicosis induced significant decreases in isometric twitch contraction time (CT), one-half relaxation time, and peak twitch tension. The Ca2+ uptake activity of the sarcoplasmic reticulum (SR) was increased in the thyrotoxic muscles; this adaptation in the SR provides a possible mechanism for the alterations in isometric contractile properties. Thyrotoxicosis induced a large increase in fibers classified as type 2, on the basis of an alkali-stable histochemical reaction for ATPase, in the soleus. Although this reaction is commonly interpreted as indicating that a muscle is fast, maximum shortening velocity (Vmax) and Mg2+ activated actomyosin ATPase activity were unaffected in the thyrotoxic soleus. Our findings provide evidence that CT and Vmax can vary independently and that the histochemical ATPase reaction may not always reflect the biochemical properties that make myosin fast or slow.
在每千克饮食中给予3毫克甲状腺素（T4）和1毫克三碘甲状腺原氨酸（T3），持续6 - 8周的大鼠中，研究了甲状腺毒症对比目鱼肌收缩特性的影响。甲状腺毒症导致等长收缩时的收缩时间（CT）、半松弛时间和峰值收缩张力显著降低。甲状腺毒症肌肉中肌浆网（SR）的钙离子摄取活性增加；SR的这种适应性变化为等长收缩特性的改变提供了一种可能的机制。基于对ATP酶的碱稳定组织化学反应，甲状腺毒症导致比目鱼肌中归类为2型的纤维大量增加。尽管这种反应通常被解释为表明肌肉是快肌，但甲状腺毒症比目鱼肌的最大缩短速度（Vmax）和镁离子激活的肌动球蛋白ATP酶活性并未受到影响。我们的研究结果表明，CT和Vmax可以独立变化，并且组织化学ATP酶反应可能并不总是反映使肌球蛋白快或慢的生化特性。
