Muscle Physiology Laboratory, Department of Kinesiology, University of Massachusetts Amherst, Amherst, Massachusetts, USA.
Human Magnetic Resonance Center, Institute for Applied Life Sciences (IALS), University of Massachusetts Amherst, Amherst, Massachusetts, USA.
NMR Biomed. 2020 Nov;33(11):e4381. doi: 10.1002/nbm.4381. Epub 2020 Aug 16.
Several methods have been developed for using P-MRS to calculate rates of oxidative ATP synthesis (ATP ) during muscular contractions based on assumptions that (1) the ATP cost of force generation (ATP ) remains constant or (2) Michaelis-Menten coupling between cytosolic ADP and ATP does not change. However, growing evidence suggests that one, or both, of these assumptions are invalid during high-intensity fatigue protocols. Consequently, there is a need to examine the validity and accuracy of traditional ATP calculation methods under these conditions. To address this gap, we measured phosphate concentrations and pH in the vastus lateralis muscle of nine young adults during four rest-contraction-recovery trials lasting 24, 60, 120, and 240 s. The initial velocity of phosphocreatine resynthesis (V ) following each trial served as the criterion measure of ATP because this method makes no assumptions of constant ATP or Michaelis-Menten coupling between changes in cytosolic ADP and ATP . Subsequently, we calculated ATP throughout the 240 s trial using several traditional calculation methods and compared estimations of ATP from each method with time-matched measurements of V . Method 1, which assumes that ATP does not change, was able to model changes in V over time, but showed poor accuracy for predicting V across a wide range of ATP values. In contrast, Michaelis-Menten methods, which assume that the relationship between changes in cytosolic ADP and ATP remains constant, were invalid because they could not model the decline in V . However, adjusting these Michaelis-Menten methods for observed changes in maximal ATP capacity (i.e., V ) permitted modeling of the decline in V and markedly improved accuracy. The results of these comprehensive analyses demonstrate that valid, accurate measurements of ATP can be obtained during high-intensity contractions by adjusting Michaelis-Menten ATP calculations for changes in V observed from baseline to post-fatigue.
已经开发出几种方法,用于使用 P-MRS 根据以下假设计算肌肉收缩过程中氧化型 ATP 合成(ATP)的速率:(1)力产生的 ATP 成本(ATP)保持不变,或(2)胞质 ADP 和 ATP 之间的米氏门控耦合不变。然而,越来越多的证据表明,在高强度疲劳方案中,这些假设中的一个或两个可能无效。因此,有必要在这些条件下检查传统 ATP 计算方法的有效性和准确性。为了解决这个差距,我们在九名年轻人的股外侧肌中测量了磷酸盐浓度和 pH 值,这些人在持续 24、60、120 和 240 秒的四个休息-收缩-恢复试验中。每次试验后磷酸肌酸再合成的初始速度(V)作为 ATP 的标准测量值,因为这种方法不假设 ATP 不变或胞质 ADP 和 ATP 变化之间的米氏门控耦合不变。随后,我们使用几种传统的计算方法在整个 240 秒的试验中计算 ATP,并将每种方法的 ATP 估计值与时间匹配的 V 测量值进行比较。假设 ATP 不变的方法 1 能够模拟 V 随时间的变化,但在预测广泛的 ATP 值范围内的 V 时准确性较差。相比之下,假设胞质 ADP 和 ATP 之间的关系保持不变的米氏门控方法无效,因为它们无法模拟 V 的下降。然而,通过调整这些米氏门控方法来观察到的最大 ATP 容量(即 V)的变化,允许模拟 V 的下降,并显著提高准确性。这些综合分析的结果表明,通过调整米氏门控 ATP 计算以适应从基线到疲劳后的 V 观察到的变化,可以在高强度收缩期间获得有效的、准确的 ATP 测量值。