Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, AB, Canada.
Am J Physiol Cell Physiol. 2018 Sep 1;315(3):C310-C318. doi: 10.1152/ajpcell.00183.2017. Epub 2018 May 16.
The aim of this study was to determine the role of titin in preventing the development of sarcomere length nonuniformities following activation and after active and passive stretch by determining the effect of partial titin degradation on sarcomere length nonuniformities and force in passive and active myofibrils. Selective partial titin degradation was performed using a low dose of trypsin. Myofibrils were set at a sarcomere length of 2.4 µm and then passively stretched to sarcomere lengths of 3.4 and 4.4 µm. In the active condition, myofibrils were set at a sarcomere length of 2.8 µm, activated, and actively stretched by 1 µm/sarcomere. The extent of sarcomere length nonuniformities was calculated for each sarcomere as the absolute difference between sarcomere length and the mean sarcomere length of the myofibril. Our main finding is that partial titin degradation does not increase sarcomere length nonuniformities after passive stretch and activation compared with when titin is intact but increases the extent of sarcomere length nonuniformities after active stretch. Furthermore, when titin was partially degraded, active and passive stresses were substantially reduced. These results suggest that titin plays a crucial role in actively stretched myofibrils and is likely involved in active and passive force production.
本研究旨在确定titin 在预防肌节长度非均一性方面的作用，方法是通过确定部分 titin 降解对肌节长度非均一性和被动及主动肌原纤维中力的影响来实现。采用低剂量的胰蛋白酶进行有选择的部分 titin 降解。肌原纤维设定在肌节长度为 2.4 µm，然后被动拉伸至肌节长度为 3.4 µm 和 4.4 µm。在主动条件下，肌原纤维设定在肌节长度为 2.8 µm，激活并以 1 µm/sarcomere 的速度主动拉伸。为每个肌节计算肌节长度非均匀性的程度，作为肌节长度与肌原纤维的平均肌节长度之间的绝对差。我们的主要发现是，与 titin 完整时相比，部分 titin 降解不会增加被动拉伸和激活后的肌节长度非均匀性，但会增加主动拉伸后的肌节长度非均匀性程度。此外，当 titin 部分降解时，主动和被动张力大大降低。这些结果表明 titin 在主动拉伸的肌原纤维中起着至关重要的作用，并且可能参与主动和被动力的产生。
