Muscle and Aging Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, AB, Canada.
Exp Gerontol. 2010 Sep;45(9):662-70. doi: 10.1016/j.exger.2010.04.001. Epub 2010 Apr 14.
Although most literature suggests a relative protection of slow twitch muscle with aging, there is limited data in senescence when muscle atrophy and functional decline markedly accelerate. To address this issue we examined age-related changes in muscle mass, contractile function, mitochondrial enzyme activities, and myosin heavy chain (MHC) expression in the slow twitch soleus (Sol) and fast twitch gastrocnemius (Gas) muscle of young adult (YA) and senescent (SEN) rats. Muscle mass declined between YA and SEN in the Sol by 35% compared to 55% in the Gas muscle. After normalizing for muscle mass, tetanic force per g of muscle declined by 58% in Sol and by 36% in Gas muscle. Time-to-peak tension was increased only in the Gas (30%), whereas time-to-half relaxation was increased by 70% in Sol and 51% in Gas. Citrate synthase and complex IV activity declined in homogenates of Sol (30-36%) and red oxidative region of Gas (46-51%), but not white glycolytic region of Gas. Strikingly, the shift away from the dominant adult MHC isoform with aging was much greater in Sol (fibers positive for MHC fast: 11+/-2% in YA versus 36+/-3% in SEN) than in Gas (fibers positive for MHC slow: 12+/-1% in YA versus 26+/-3% in SEN) muscle. Collectively, these results show that the slow twitch Sol muscle undergoes large phenotypic alterations in very old age and for several measures (tetanic tension per g, time-to-half relaxation and shift in adult MHC expression) that is of greater magnitude than fast twitch muscle, underscoring the importance of including age-related changes in slow twitch muscle in seeking potential treatments for sarcopenia.
虽然大多数文献表明，随着年龄的增长，慢肌纤维相对受到保护，但在衰老过程中，肌肉萎缩和功能下降明显加速，相关数据有限。为了解决这个问题，我们研究了年轻成年（YA）和衰老（SEN）大鼠慢肌（比目鱼肌）和快肌（腓肠肌）中与年龄相关的肌肉质量、收缩功能、线粒体酶活性和肌球蛋白重链（MHC）表达的变化。与快肌相比，YA 和 SEN 大鼠比目鱼肌的肌肉质量分别下降了 35%和 55%。在肌肉质量归一化后，比目鱼肌的强直张力下降了 58%，腓肠肌下降了 36%。只有腓肠肌的峰值张力时间增加（30%），而比目鱼肌的半松弛时间增加了 70%，腓肠肌增加了 51%。柠檬酸合酶和复合物 IV 的活性在比目鱼肌（30-36%）和红区氧化腓肠肌（46-51%）匀浆中下降，但在白区糖酵解腓肠肌中没有下降。引人注目的是，随着年龄的增长，从占主导地位的成人 MHC 同工型的转变在比目鱼肌（YA 时 MHC 快阳性纤维：11+/-2%，而 SEN 时 36+/-3%）比腓肠肌（YA 时 MHC 慢阳性纤维：12+/-1%，而 SEN 时 26+/-3%）大得多。总的来说，这些结果表明，慢肌比目鱼鱼在非常老的年龄经历了巨大的表型改变，并且在几个指标（强直张力/g、半松弛时间和成人 MHC 表达的转变）上比快肌更大，这突显了在寻求治疗肌少症的潜在方法时，包括与年龄相关的慢肌变化的重要性。
