Brooks S V, Faulkner J A
Department of Physiology, University of Michigan, Ann Arbor 48109-2007.
Am J Physiol. 1994 Aug;267(2 Pt 1):C507-13. doi: 10.1152/ajpcell.1994.267.2.C507.
In old animals, skeletal muscle force decreases during both isometric and shortening contractions. In contrast, force during lengthening appears to be unaffected by aging. We hypothesized that with aging single permeabilized muscle fibers would demonstrate the same impairments in force as are observed for whole muscles. For single permeabilized fibers from extensor digitorum longus muscles of adult and old mice, forces were measured during isometric, shortening, and lengthening contractions performed at 15 degrees C. Maximum isometric forces normalized for fiber area were not different for fibers from adult and old mice. During submaximal isometric contractions a decreased calcium sensitivity resulted in lower forces for fibers from old compared with adult mice. In contrast to a lack of difference in forces developed by fibers from old and adult mice during shortening contractions, during lengthening contractions fibers from old mice developed forces approximately 30% higher than those of adult mice. We conclude that the impairments in force of whole muscles with aging are not the result of impairments in intrinsic force-generating capacity of cross bridges, but changes do occur in single permeabilized muscle fibers of old mice that result in higher forces during stretch.
在老年动物中，等长收缩和缩短收缩期间骨骼肌力量都会下降。相比之下，延长收缩期间的力量似乎不受衰老影响。我们推测，随着年龄增长，单个通透化肌纤维会表现出与完整肌肉中观察到的相同的力量损伤。对于成年和老年小鼠趾长伸肌的单个通透化纤维，在15摄氏度下进行等长、缩短和延长收缩时测量力量。按纤维面积归一化的最大等长力量在成年和老年小鼠的纤维之间没有差异。在次最大等长收缩期间，与成年小鼠相比，老年小鼠纤维的钙敏感性降低导致力量更低。与老年和成年小鼠纤维在缩短收缩期间产生的力量没有差异相反，在延长收缩期间，老年小鼠的纤维产生的力量比成年小鼠高约30%。我们得出结论，衰老导致的完整肌肉力量损伤不是横桥内在力量产生能力损伤的结果，但老年小鼠的单个通透化肌纤维确实发生了变化，导致拉伸期间力量更高。
