It has been accepted that the force produced by a skeletal muscle myofibril depends on its cross-sectional area but not on the number of active sarcomeres because they are arranged in series. However, a previous study performed by our group showed that blocking actomyosin interactions within an activated myofibril and depleting the thick filaments in one sarcomere unexpectedly reduced force production. In this study, we examined in detail how consecutive depletion of thick filaments in individual sarcomeres within a myofibril affects force production. Myofibrils isolated from rabbit psoas were activated and relaxed using a perfusion system. An extra microperfusion needle filled with a high-ionic strength solution was used to erase thick filaments in individual sarcomeres in real time before myofibril activation. The isometric forces were measured upon activation. The force produced by myofibrils with intact sarcomeres was significantly higher than the force produced by myofibrils with one or more sarcomeres lacking thick filaments (p < 0.0001) irrespective of the number of contractions imposed on the myofibrils and their initial sarcomere length. Our results suggest that the myofibril force is affected by intersarcomere dynamics and the number of active sarcomeres in series.

中文翻译：

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单个肌节中粗丝的提取影响单个肌原纤维的力产生

人们普遍认为，骨骼肌肌原纤维产生的力取决于其横截面积，而不取决于活动肌节的数量，因为它们是串联排列的。然而，我们小组之前进行的一项研究表明，阻断激活的肌原纤维内的肌动球蛋白相互作用并消耗一个肌节中的粗丝意外地降低了力的产生。在这项研究中，我们详细研究了肌原纤维内单个肌节中粗丝的连续消耗如何影响力的产生。使用灌注系统激活和松弛从兔腰大肌中分离的肌原纤维。在肌原纤维激活之前，使用装有高离子强度溶液的额外微灌注针实时擦除单个肌节中的粗丝。在激活时测量等长力。具有完整肌节的肌原纤维产生的力显着高于具有一个或多个缺乏粗细丝的肌原纤维产生的力 (p < 0.0001)，而不管施加在肌原纤维上的收缩次数和它们的初始肌节长度如何。我们的研究结果表明，肌原纤维力受肌节间动力学和活动肌节数量的影响。