Centre for Human and Applied Physiological Sciences, Faculty of Life Sciences & Medicine, King's College London, London, United Kingdom.
Randall Centre for Cell and Molecular Biophysics, Faculty of Life Sciences & Medicine, King's College London, London, United Kingdom.
Am J Physiol Cell Physiol. 2023 Jul 1;325(1):C172-C185. doi: 10.1152/ajpcell.00525.2022. Epub 2023 May 22.
Specific force (SF) has been shown to be reduced in some but not all studies of human aging using chemically skinned single muscle fibers. This may be due, in part, not only to the health status/physical activity levels of different older cohorts, but also from methodological differences in studying skinned fibers. The aim of the present study was to compare SF in fibers from older hip fracture patients (HFP), healthy master cyclists (MC), and healthy nontrained young adults (YA) using two different activating solutions. Quadriceps muscle samples and 316 fibers were obtained from HFPs (74.6 ± 4 years, = 5), MCs (74.8 ± 1, = 5), and YA (25.5 ± 2, = 6). Fibers were activated (pCa 4.5, 15°C) in solutions containing either 60 mM N-tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid pH buffer (TES) or 20 mM imidazole. SF was determined by normalizing force to fiber cross-sectional area (CSA) assuming either an elliptical or circular shape and to fiber myosin heavy chain content. Activation in TES resulted in significantly higher MHC-I SF in all groups and YA MHC-IIA fibers, irrespective of normalization method. Although there were no differences in SF between the participant groups, the ratio of SF between the TES and imidazole solutions was lower in HFPs compared with YAs (MHC-I < 0.05; MHC-IIA = 0.055). Activating solution composition, as opposed to donor characteristics, had a more notable effect on single fiber SF. However, this two-solution approach revealed an age-related difference in sensitivity in HFPs, which was not shown in MCs. This suggests further novel approaches may be required to probe age/activity-related differences in muscle contractile quality. Whether specific force (SF) decreases with advancing age in human single skeletal muscle fibers is uncertain. Equivocal published findings may be due to the different physical activity levels of the elderly cohorts studied and/or different chemical solutions used to measure force. We compared single fiber SF between young adults, elderly cyclists, and hip fracture patients (HFP) using two solutions. The solution used significantly affected force and revealed a difference in sensitivity of HFP muscle fibers.
特定力（SF）在一些但不是所有研究人类衰老的化学剥皮单肌纤维研究中均显示降低。这可能部分归因于不同老年队列的健康状况/身体活动水平，也归因于研究剥皮纤维的方法学差异。本研究的目的是使用两种不同的激活溶液比较来自老年髋部骨折患者（HFP）、健康的大师自行车手（MC）和健康的非训练年轻成年人（YA）的纤维中的 SF。从 HFP（74.6±4 岁，n=5）、MC（74.8±1，n=5）和 YA（25.5±2，n=6）获得股四头肌样本和 316 根纤维。纤维在含有 60 mM N-三（羟甲基）甲基-2-氨基乙磺酸 pH 缓冲液（TES）或 20 mM 咪唑的溶液中（pCa4.5，15°C）被激活。通过将力归一化为纤维横截面积（CSA）并假定为椭圆形或圆形来确定 SF，并将纤维肌球蛋白重链含量归一化为 SF。在 TES 中激活会导致所有组和 YA MHC-IIA 纤维的 MHC-I SF 显著增加，而与归一化方法无关。尽管参与者组之间的 SF 没有差异，但与 YA 相比，HFP 中的 TES 和咪唑溶液之间的 SF 比降低（MHC-I<0.05；MHC-IIA=0.055）。激活溶液组成，而不是供体特征，对单纤维 SF 有更显著的影响。然而，这种双溶液方法在 HFP 中揭示了与年龄相关的敏感性差异，而在 MC 中则没有显示。这表明可能需要进一步的新方法来探究肌肉收缩质量与年龄/活动相关的差异。在人类单骨骼肌纤维中，SF 是否随年龄增长而降低尚不确定。有争议的已发表结果可能归因于所研究的老年队列的不同身体活动水平和/或用于测量力的不同化学溶液。我们使用两种溶液比较了年轻成年人、老年自行车手和髋部骨折患者（HFP）之间的单纤维 SF。使用的溶液显著影响力，并揭示了 HFP 肌肉纤维的敏感性差异。
