Skeletal muscle force modulation: length dependent factors

我的目标是更好地理解肌肉的基本特性。主动力的计算方法是：峰值力-在整个肌肉长度处测量的被动力。我们表明，被动力在收缩过程中会减少，而主动力可以通过使用超声显微术测量纤维束长度来正确计算：超声波从纤维束一端植入的晶体发出，并由另一端的晶体检测。我将研究肌肉的特性，这些特性以前可能由于主动力的错误计算而被误解。麻醉后的大鼠腓肠肌内侧进行原位检测。单个运动单元（定义为任何运动神经元及其支配的所有肌纤维）将被单独激活，或与具有不同大小运动单元的另一个运动单元组合，并以不同的长度被激活。在较长的长度处，被动力更大，因此误判更大。我相信，修正后的方法将使两个运动单元一起激活的力类似于两个单独激活的力之和。有一些报道，延长收缩导致长度和主动力之间的关系向右转移。有人认为，向更长长度的转变是由于依从性的增加，但这并没有得到直接的评估。我将测量顺应性，使用超声显微镜，并造成肌肉损伤，通过延长收缩或穿针，并比较收缩反应（包括顺应性）。假设只有当被动力因治疗而减少时才会看到向右移动，而主动力则以传统方式计算。用修正后的计算主动力的方法，向右移动将不明显。肌肉通过改变蛋白质合成来对蛋白质使用的增加或减少作出反应。据认为，细胞信号机制对肌肉中的力很敏感，导致一些关键信号分子的激活。我建议测量这些，看看以正确的方式计算的主动力是否比传统方法更敏感。提出的工作将推进我们对肌肉功能的基本理解。

It is my goal to better understand the fundamental properties of muscles. Active force has been calculated by: peak force - passive force measured at the whole muscle length. We showed that passive force can decrease during a contraction and that active force could be correctly calculated if fiber bundle length is measured using sonomicrography: ultrasound is emitted from a crystal implanted at one end of the fiber bundle and detected by a crystal at the other end. I will investigate properties of muscle that may have previously been misinterpreted due to active force miscalculation. The anesthetized rat medial gastrocnemius muscle will be tested in situ. Individual motor units (defined as any motor neuron and all muscle fibers it innervates) will be activated alone, or in combination with another one with different sized motor units, and at several lengths. Passive force is greater at long lengths, so the miscalculation is greater. I believe the corrected method will give force of two motor units activated together similar to the sum of the two activated separately. There are several reports that lengthening contractions cause the relationship between length and active force to shift to the right. It has been suggested that the shift to longer lengths is caused by increased compliance, but this has not been directly assessed. I will measure compliance, using sonomicrography, and cause damage in muscle, by lengthening contractions or needle piercing and compare the contractile response (including compliance). It is hypothesized that a shift to the right will only be seen when passive force decreases due to the treatment, and active force is calculated in the traditional manner. The rightward shift will not be evident with the corrected method of calculating active force. Muscle responds to increased or decreased use by changing protein synthesis. It is thought that cell signalling mechanisms are sensitive to the force in the muscle, resulting in activation of some key signalling molecules. I propose to measure these, to see if active force, calculated in the correct way is a more sensitive predictor of this than the traditional method. The work that is proposed will advance our fundamental understanding of how muscles function.