Blei M L, Conley K E, Odderson I B, Esselman P C, Kushmerick M J
Department of Rehabilitation Medicine, University of Washington Medical Center, Seattle 98195.
Proc Natl Acad Sci U S A. 1993 Aug 1;90(15):7396-400. doi: 10.1073/pnas.90.15.7396.
This study determined the variation among individuals in ATP use during contraction and ATP synthesis after stimulation in a human limb muscle. Muscle energetics were evaluated using a metabolic stress test that separates ATP utilization from synthesis by 31P NMR spectroscopy. Epicutaneous supramaximal twitch stimulation (1 Hz) of the median and ulnar nerves was applied in combination with ischemia of the finger and wrist flexors in eight normal subjects. The linear creatine phosphate (PCr) breakdown during ischemic stimulation defined ATP use (delta PCr per twitch or approximately P/twitch) and was highly reproducible as shown by the relative standard deviation [(standard deviation/mean) x 100] of 11% in three repeated measures. The time constant of the monoexponential PCr change during aerobic recovery represented ATP synthesis rate and also showed a low relative standard deviation (9%). Individuals were found to differ significantly in both mean approximately P/twitch (PCr breakdown rates, 0.29-0.45% PCr per sec or % PCr per twitch; ANOVA, p < 0.001) and in mean recovery time constants (41-74 sec; ANOVA, P < 0.001). This range of approximately P/twitch corresponded with the range of fiber types reported for a flexor muscle. In addition, approximately P/twitch was negatively correlated with a metabolite marker of slow-twitch fiber composition (Pi/ATP). The nearly 2-fold range of recovery time constants agreed with the range of mitochondrial volume densities found in human muscle biopsies. These results indicate that both components involved in the muscle energy balance--oxidative capacity and contractile costs--vary among individuals in human muscle and can be measured noninvasively by 31 P NMR.
本研究确定了人体肢体肌肉收缩过程中个体间ATP使用情况以及刺激后ATP合成的差异。通过代谢应激试验评估肌肉能量学，该试验利用31P核磁共振波谱将ATP利用与合成区分开来。对8名正常受试者的正中神经和尺神经进行经皮超最大抽搐刺激（1Hz），并结合手指和腕部屈肌的缺血处理。缺血刺激期间线性磷酸肌酸（PCr）分解定义了ATP使用情况（每次抽搐的ΔPCr或近似P/抽搐），并且如三次重复测量中11%的相对标准偏差[（标准偏差/平均值）×100]所示，具有高度可重复性。有氧恢复期间单指数PCr变化的时间常数代表ATP合成速率，相对标准偏差也较低（9%）。发现个体在平均近似P/抽搐（PCr分解速率，每秒0.29 - 0.45%PCr或每次抽搐%PCr；方差分析，p < 0.001）和平均恢复时间常数（41 - 74秒；方差分析，P < 0.001）方面均存在显著差异。这个近似P/抽搐范围与屈肌报道的纤维类型范围相对应。此外，近似P/抽搐与慢肌纤维组成的代谢物标志物（Pi/ATP）呈负相关。恢复时间常数近2倍的范围与人体肌肉活检中发现的线粒体体积密度范围一致。这些结果表明，参与肌肉能量平衡的两个组成部分——氧化能力和收缩成本——在人体肌肉个体间存在差异，并且可以通过31P核磁共振进行无创测量。
