Low performance of fatigued skeletal muscle accompanies large difference in the state of water : test of hypothesis.

用核磁共振仪观察到，强直神经刺激引起的蛙肌反复收缩导致肌肉水的横向松弛过程普遍迟缓。在直接刺激的大鼠腰肌中也观察到类似的变化。因此，类似的变化预计会伴随着人类的肌肉疲劳。为了阐明这种水状态变化的本质，我们对肌原纤维悬浮液进行了实验。肌原纤维影响远离其表面的水分子。这种被抑制的水的比例随着肌原纤维浓度的增加而以依赖温度的方式增加。这种依赖关系表明水与肌肉之间的相互作用是疏水相互作用。这种相互作用还影响了水的物理性质，影响了肌原纤维的沉降极限。在BTS和BDM诱导的疲劳肌肉的模型肌纤维中，有一部分僵硬与收缩力量的发展无关。肌肉的这种僵硬可能与疲劳引起的水状态的变化有关。对于肌内水组分，我们以横向松弛来区分水组分的亚细胞定位。为了模拟肌肉中的水环境，我们成功地开发出了低至中等分子量的碳氢化合物溶液。结合分子动力学模拟，我们可以估计伴随着骨骼肌疲劳过程的分子事件。根据这些结果，我们提出了一种检测人体骨骼肌疲劳过程的灵敏方法。也就是说，剔除骨骼肌核磁共振信号中缓慢松弛的部分，就可以将细胞内的水成分描绘为密度图。疲劳引起的横向松弛过程的延迟被认为是随着疲劳过程的进行而增加CPMG可见水分的原因。

Repetitive contraction of frog muscle elicited by tetanic nerve stimuli induced general retardation of transverse relaxation process of muscle water observed with NMR. Similar change was observed in lumbrical muscle of rat stimulated directly. Therefore, similar change is expected to accompany muscle fatigue in humans. To elucidate the entity of this change in water state, we performed experiments on myofibril suspension. Myofibrils affected water molecules far from its surface. The fraction of this suppressed water increased with myofibril concentration in a temperature dependent manner. The dependency indicated the interaction between water and muscle is the hydrophobic interaction. The interaction also affected physical property of water affecting the sedimentation limit for myofibrils. In the model muscle fiber of fatigued muscle induced by BTS and BDM, there is a fraction of stiffness that is not linked with contractile force development. This stiffness in muscle may be related with the fatigue-induced change in water state. As for the intramuscular water components, we assigned subcellular localization of water components distinguished by the transverse relaxation. To mimic the water milieu in muscle, we succeeded to develop hydrocarbon solution of low to intermediate molecular weight. Combined with the molecular dynamics simulation, we could estimate the molecular events accompanying fatiguing process of skeletal muscle. From these results, we proposed a sensitive method to detect fatiguing process in human skeletal muscle. That is, eliminating slowly relaxing part of the NMR signals from skeletal muscle, one can depict intracellular water components as a density map. Fatigue-induced retardation of the transverse relaxation process is considered to increase CPMG visible water as fatiguing process proceeds.