Skeletal muscle force production is increased at longer compared to shorter muscle lengths because of length-dependent priming of thick filament proteins in the contractile unit before contraction. Using small-angle X-ray diffraction in combination with a mouse model that specifically cleaves the stretch-sensitive titin protein, we found that titin cleavage diminished the length-dependent priming of the thick filament. Strikingly, a titin-sensitive, length-dependent priming was also present in thin filaments, which seems only possible via bridge proteins between thick and thin filaments in resting muscle, potentially myosin-binding protein C. We further show that these bridges can be forcibly ruptured via high-speed stretches. Our results advance a paradigm shift to the fundamental regulation of length-dependent priming, with titin as the key driver.

中文翻译：

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肌肉细胞中的 Titin 力改变晶格顺序，粗细丝蛋白形成

与较短的肌肉长度相比，由于收缩前收缩单位中粗丝蛋白的长度依赖性启动，与较短的肌肉长度相比，骨骼肌力的产生增加。使用小角度 X 射线衍射结合专门切割拉伸敏感肌联蛋白的小鼠模型，我们发现肌联蛋白切割减少了粗丝的长度依赖性启动。引人注目的是，肌动蛋白敏感的、长度依赖性的启动也存在于细丝中，这似乎只能通过静息肌肉中粗细丝之间的桥蛋白，可能是肌球蛋白结合蛋白 C。我们进一步表明，这些桥可以被强行通过高速拉伸破裂。我们的结果推动了范式转变为长度依赖性启动的基本调节，