Lynch Gordon S, Faulkner John A, Brooks Susan V
Basic and Clinical Myology Laboratory, Department of Physiology, The University of Melbourne, Victoria, Australia.
Am J Physiol Cell Physiol. 2008 Jul;295(1):C249-56. doi: 10.1152/ajpcell.90640.2007. Epub 2008 May 28.
The deficit in force generation is a measure of the magnitude of damage to sarcomeres caused by lengthening contractions of either single fibers or whole muscles. In addition, permeabilized single fibers may suffer breakages. Our goal was to understand the interaction between breakages and force deficits in "young" and "old" permeabilized single fibers from control muscles of young and old rats and "conditioned" fibers from muscles that completed a 6-wk program of in vivo lengthening contractions. Following single lengthening contractions of old-control fibers compared with young-control fibers, the twofold greater force deficits at a 10% strain support the concept of an age-related increase in the susceptibility of fibers to mechanical damage. In addition, the much higher breakage rates for old fibers at all strains tested indicate an increase with aging in the number of fibers at risk of being severely injured during any given stretch. Following the 6-wk program of lengthening contractions, young-conditioned fibers and old-conditioned fibers were not different with respect to force deficit or the frequency of breakages. A potential mechanism for the increased resistance to stretch-induced damage of old-conditioned fibers is that, through intracellular damage and subsequent degeneration and regeneration, weaker sarcomeres were replaced by stronger sarcomeres. These data indicate that, despite the association of high fiber breakage rates and large force deficits with aging, the detrimental characteristics of old fibers were improved by a conditioning program that altered both sarcomeric characteristics as well as the overall structural integrity of the fibers.
力量产生的不足是衡量单根纤维或整块肌肉的拉长收缩对肌节造成损伤程度的指标。此外，通透的单根纤维可能会发生断裂。我们的目标是了解来自年轻和老年大鼠对照肌肉的“年轻”和“老年”通透单根纤维以及来自完成6周体内拉长收缩计划的肌肉的“适应性”纤维中，断裂与力量不足之间的相互作用。与年轻对照纤维相比，老年对照纤维单次拉长收缩后，在10%应变下两倍大的力量不足支持了纤维对机械损伤的易感性随年龄增长而增加的概念。此外，在所有测试应变下老年纤维的断裂率都高得多，这表明随着年龄增长，在任何给定拉伸过程中面临严重损伤风险的纤维数量增加。经过6周的拉长收缩计划后，年轻适应性纤维和老年适应性纤维在力量不足或断裂频率方面没有差异。老年适应性纤维对拉伸诱导损伤抵抗力增加的一个潜在机制是，通过细胞内损伤以及随后的退化和再生，较弱的肌节被较强的肌节所取代。这些数据表明，尽管高纤维断裂率和大力量不足与衰老相关，但通过改变肌节特征以及纤维整体结构完整性的适应性计划，老年纤维的有害特征得到了改善。
