Shalabi Nabil, Cornachione Anabelle, de Souza Leite Felipe, Vengallatore Srikar, Rassier Dilson E
Department of Mechanical Engineering, McGill University, 817 Sherbrooke Street West, Montreal, Quebec, Canada, H3A 2K6.
Department of Kinesiology and Physical Education, McGill University, 475 Pine Avenue West, Montreal, Quebec, Canada, H2W 1S4.
J Physiol. 2017 Mar 15;595(6):2085-2098. doi: 10.1113/JP272983. Epub 2017 Feb 19.
When a skeletal muscle is stretched while it contracts, the muscle produces a relatively higher force than the force from an isometric contraction at the same length: a phenomenon referred to as residual force enhancement. Residual force enhancement is puzzling because it cannot be directly explained by the classical force-length relationship and the sliding filament theory of contraction, the main paradigms in the muscle field. We used custom-built instruments to measure residual force enhancement in skeletal myofibrils, and, for the first time, in cardiac myofibrils. Our data report that residual force enhancement is present in skeletal muscles, but not cardiac muscles, and is regulated by the different isoforms of the titin protein filaments.
When a skeletal muscle contracts isometrically, the muscle produces a force that is relative to the final isometric sarcomere length (SL). However, when the same final SL is reached by stretching the muscle while it contracts, the muscle produces a relatively higher force: a phenomenon commonly referred to as residual force enhancement. In this study, we investigated residual force enhancement in rabbit skeletal psoas myofibrils and, for the first time, cardiac papillary myofibrils. A custom-built atomic force microscope was used in experiments that stretched myofibrils before and after inhibiting myosin and actin interactions to determine whether the different cardiac and skeletal titin isoforms regulate residual force enhancement. At SLs ranging from 2.24 to 3.13 μm, the skeletal myofibrils enhanced the force by an average of 9.0%, and by 29.5% after hindering myosin and actin interactions. At SLs ranging from 1.80 to 2.29 μm, the cardiac myofibrils did not enhance the force before or after hindering myosin and actin interactions. We conclude that residual force enhancement is present only in skeletal muscles and is dependent on the titin isoforms.
当骨骼肌在收缩时被拉伸，该肌肉产生的力比在相同长度下等长收缩产生的力相对更高：这种现象被称为残余力增强。残余力增强令人困惑，因为它无法用肌肉领域的主要范式——经典的力-长度关系和收缩的滑行细丝理论直接解释。我们使用定制仪器测量骨骼肌肌原纤维以及首次测量心肌肌原纤维中的残余力增强。我们的数据表明，残余力增强存在于骨骼肌中，但不存在于心肌中，并且由肌联蛋白丝的不同同工型调节。
当骨骼肌进行等长收缩时，肌肉产生的力与最终等长肌节长度（SL）相关。然而，当通过在肌肉收缩时拉伸使其达到相同的最终SL时，肌肉会产生相对更高的力：这种现象通常被称为残余力增强。在本研究中，我们研究了兔腰大肌骨骼肌肌原纤维以及首次研究了乳头肌心肌肌原纤维中的残余力增强。在抑制肌球蛋白和肌动蛋白相互作用前后拉伸肌原纤维的实验中，使用了定制的原子力显微镜，以确定不同的心脏和骨骼肌肌联蛋白同工型是否调节残余力增强。在2.24至3.13μm的SL范围内，骨骼肌肌原纤维平均将力增强了9.0%，在阻碍肌球蛋白和肌动蛋白相互作用后增强了29.5%。在1.80至2.29μm的SL范围内，心肌肌原纤维在阻碍肌球蛋白和肌动蛋白相互作用前后均未增强力。我们得出结论，残余力增强仅存在于骨骼肌中，并且依赖于肌联蛋白同工型。
