Skeletal muscle force modulation: length dependent factors

我的目标是更好地了解肌肉的基本属性。主动力的计算方法是：峰值力--在整个肌肉长度测量的被动力。我们证明了在收缩过程中被动力可以减小，如果使用声学显微镜测量纤维束的长度，可以正确地计算出主动力：超声波是从植入纤维束一端的晶体发出的，并由另一端的晶体检测到的。我将研究肌肉的性质，这些性质以前可能由于主动力的错误计算而被误解。对麻醉后的大鼠腓肠肌内侧肌进行原位测试。单独的运动单位(定义为任何运动神经元和它所支配的所有肌肉纤维)将单独激活，或者与具有不同大小的运动单位的另一个运动单位一起激活，并且以几个长度激活。长度越长，被动力越大，因此误判越大。我相信修正后的方法会给出两个一起启动的马达单元的力，类似于两个单独启动的马达单元的总和。有几个报告说，延长收缩会导致长度和主动力量之间的关系右移。有人提出，向更长长度的转变是由于合规性增加造成的，但这一点尚未得到直接评估。我将使用声学显微摄影术测量顺应性，并通过延长收缩或穿针来导致肌肉损伤，并比较收缩反应(包括顺应性)。假设只有当被动作用力由于治疗而减少时，才会看到向右移动，而主动作用力是以传统方式计算的。用修正后的计算主动力的方法，向右移动不明显。肌肉通过改变蛋白质合成来对增加或减少的使用量做出反应。人们认为，细胞信号机制对肌肉中的力很敏感，导致一些关键的信号分子被激活。我建议测量这些，看看以正确方式计算的作用力是否比传统方法更敏感地预测这一点。这项提出的工作将促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.