Departments of Kinesiology and Physical Education, Physics and Physiology, McGill University, Montreal, Canada.
J Muscle Res Cell Motil. 2012 Aug;33(3-4):155-65. doi: 10.1007/s10974-012-9308-7. Epub 2012 Jun 23.
The force-length relation is one of the most prominent features of striated muscles, and predicts that the force produced by a fully activated muscle is proportional to the overlap between myosin and actin filaments within sarcomeres. However, there are situations in which the force-length relation deviates from predictions based purely on filament overlap. Notably, stretch of activated skeletal muscles induces a long-lasting increase in force, which is larger than the force produced during isometric contractions at a similar length. The mechanism behind this residual force enhancement and deviations from the original force-length relation are unknown, generating heated debate in the literature. We performed a series of experiments with short segments of myofibrils and isolated sarcomeres to investigating the mechanisms of the residual force enhancement and the force length-relation. In this paper, evidence will be presented showing that force enhancement is caused by: (i) half-sarcomere non-uniformities, and (ii) a sarcomeric component, which may be associated with Ca(2+)-induced stiffness of titin molecules. These mechanisms have large implications for understanding the basic mechanisms of muscle contraction.
力-长度关系是横纹肌最显著的特征之一，它预测完全激活的肌肉产生的力与肌球蛋白和肌动蛋白丝在肌节内的重叠成正比。然而，在某些情况下，力-长度关系会偏离纯粹基于丝重叠的预测。值得注意的是，激活的骨骼肌的拉伸会引起持久的力增加，其大于在相似长度下进行等长收缩时产生的力。这种剩余力增强和偏离原始力-长度关系的机制尚不清楚，这在文献中引发了激烈的争论。我们使用肌原纤维的短段和分离的肌节进行了一系列实验，以研究剩余力增强和力-长度关系的机制。本文将提出证据表明，力增强是由以下原因引起的：（i）半肌节的不均匀性，和（ii）一个肌节成分，它可能与肌联蛋白分子的 Ca(2+)-诱导的刚性有关。这些机制对理解肌肉收缩的基本机制有很大的影响。
