Faculty of Kinesiology, University of Calgary, 2500 University Drive, Calgary, Alberta, Canada T2N 1N4.
J Biomech. 2010 Nov 16;43(15):3063-6. doi: 10.1016/j.jbiomech.2010.07.016. Epub 2010 Aug 21.
The purpose of this study was to determine failure stresses and failure lengths of actively and passively stretched myofibrils. As expected, myofibrils failed at average sarcomere lengths (about 6-7μm) that vastly exceeded sarcomere lengths at which actin-myosin filament overlap ceases to exist (4μm) and thus actin-myosin-based cross-bridge forces are zero at failure. Surprisingly, however, actively stretched myofibrils had much greater failure stresses and failure energies than passively stretched myofibrils, thereby providing compelling evidence for strong force production independent of actin-myosin-based cross-bridge forces. Follow-up experiments in which titin was deleted and cross-bridge formation was inhibited at high and low calcium concentrations point to titin as the regulator of this force, independent of calcium. The results of this study point to a mechanism of force production that reduces stretch-induced muscle damage at extreme length and limits injury and force loss within physiologically relevant ranges of sarcomere and muscle lengths.
本研究旨在确定主动和被动拉伸肌原纤维的失效应力和失效长度。不出所料，肌原纤维在平均肌节长度（约 6-7μm）下失效，远超过肌节长度（4μm），此时肌动球蛋白丝重叠不复存在，因此在失效时，基于肌动球蛋白的横桥力为零。然而，令人惊讶的是，主动拉伸的肌原纤维的失效应力和失效能量比被动拉伸的肌原纤维大得多，从而有力地证明了在没有肌动球蛋白横桥力的情况下也能产生强大的力。后续的实验中，当肌联蛋白缺失和在高钙和低钙浓度下抑制横桥形成时，肌联蛋白是力的调节因子，与钙无关。这项研究的结果指出了一种力产生的机制，该机制可降低极端长度下拉伸引起的肌肉损伤，并限制肌节和肌肉长度在生理相关范围内的损伤和力损失。
