Power Output and Efficiency of Asynchronous Muscle

9603187能够高频操作的约瑟夫森肌肉使用两种根本不同的控制连接模式之一。这两种模式的肌肉被称为同步或异步，取决于肌肉电活动和肌肉收缩之间是否存在1:1的对应关系。在同步肌肉中，通过肌肉纤维（t小管和肌浆网）中参与钙释放和再结合的收缩激活的成分的细化，实现了短暂收缩，从而实现了高频操作的潜力。高频操作的异步方法建立在缩短失活和草图激活的基础上，这些特征在许多肌肉中都有发现，但在一些昆虫的高频肌肉中得到了特别的阐述。如果其中一块肌肉受到强直性刺激，并以适当的频率进行循环缩短和延长，则缩短时任何给定长度的力都大于重新伸展时该长度的力，这是缩短失效的结果。因此，在缩短过程中所做的功比延长肌肉所需的功要多，并且存在净功输出，当肌肉附加到适当的共振负载时，该功允许肌肉在高频下重复收缩。有人提出，异步肌肉应该有更高的质量比功率输出，比同步肌肉更有效。与同步肌肉相比，异步肌肉中的控制成分（肌浆网和t小管）需要的空间更少，因此预计它们的功率输出更大；更有效率，因为在非同步肌肉中，钙循环成本大大降低。不幸的是，关于异步肌肉的功率输出和效率的现有信息不足以知道这些假设是否正确。这些假设将通过直接测量异步肌肉的功率输出和效率来验证。所使用的肌肉是甲虫飞行肌肉，选择的尺寸和形状方便的机械研究。功率输出将使用工作循环方法来确定，在这种方法中，对肌肉施加重复的长度变化，并且每个周期的功输出作为肌肉力与肌肉长度绘制时形成的图形的面积来测量。将测量正常飞行时的收缩频率和肌肉温度特征。功率测量将与能量消耗的测量相结合，通过氧气消耗或二氧化碳产生来判断，以确定肌肉将代谢能转化为机械能的效率。＊＊＊

9603187 Josephson Muscles which are capable of high-frequency operation use one of two fundamentally different modes for controlling connection. Muscles of the two modes are termed synchronous or asynchronous, depending on whether there is or is not a 1:1 correspondence between muscle electrical activity and muscle contraction. In synchronous muscles brief contraction, and therefore the potential for high frequency operation, is achieved through the elaboration of the components within muscle fibers (the T-tubules and sarcoplasmic reticulum) which are involved in contractile activation through calcium release and rebinding. The asynchronous approach to high-frequency operation is built on shortening deactivation and sketch activation, features which are found in many muscles but which are particularly elaborated in high-frequency muscles of some insects. If one of these muscles is tetanically stimulated and subjected to cyclic shortening and lengthening at an appropriate frequency, the force at any given length during shortening is greater than the force at that length during reextension, a consequence of shortening deactivation. Thus more work is done during shortening than is required to relengthen the muscle, and there is net work output, work which allows the muscle to contract repetitively at high frequency when it is attached to an appropriate resonant load. It has been proposed that asynchronous muscles should have higher mass-specific power output and be more efficient than synchronous counterparts. They are expected to have greater power output because less space need be devoted to control components (sarcoplasmic reticulum and T-tubules) in asynchronous muscles than in synchronous ones; more efficient because calcium cycling costs are substantially less in the asynchronous muscles. Unfortunately, available information on power output and efficiency of asynchronous muscle is insufficient to know if the hypotheses are correct. These hypotheses will be tested by directly m easuring power output and efficiency of an asynchronous muscle. The muscle to be used are beetle flight muscles, chosen for being of convenient size and shape for mechanical studies. Power output will be determined using the work loop approach, in which a repetitive length change is imposed on the muscle and work output per cycle is measured as the area of the figure formed when muscle force is plotted against muscle length. Measurements will be made at a contraction frequency and muscle temperature characteristic of those during normal flight. Power measurements will be combined with measurements of energy expenditure, judged by oxygen consumption or carbon dioxide production, to determine the efficiency of the muscle in converting metabolic to mechanical energy. ***