Park J H, Brown R L, Park C R, McCully K, Cohn M, Haselgrove J, Chance B
Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232.
Proc Natl Acad Sci U S A. 1987 Dec;84(24):8976-80. doi: 10.1073/pnas.84.24.8976.
Quantitative probing of heterogeneous regions in muscle is feasible with phosphorus-31 magnetic resonance spectroscopy because of the differentiation of metabolic patterns of glycolytic and oxidative fibers. A differential recruitment of oxidative and glycolytic fibers during exercise was demonstrated in 4 of 10 untrained young men by following changes in phosphate metabolites. Concentrations of inorganic phosphate (Pi), phosphocreatine, and ATP were estimated in the wrist flexor muscles of the forearm at rest, during two cycles of three grades of exercise, and in recovery. At high work levels (40% of maximum strength), two distinct Pi peaks were observed and identified with Pi pools at pH 6.9 and pH 5.9-6.4, respectively. These could be accounted for as follows. At the lowest level of work (using 20% of maximum strength), early recruitment primarily of oxidative (type I) and possibly some intermediate (type IIA) muscle fibers occurs with relatively little net lactate production and consequently little decrease in pH. At higher work loads, however, primarily glycolytic (type IIB) muscle fibers are recruited, which have relatively high net lactate production and therefore generate a second pool of Pi at low pH. ATP depletion (35-54%) and Pi losses accompanied the reduction in ability to perform during the first exercise cycle. When the cycle of graded exercise was repeated immediately, the total Pi remained high but gave rise to only one peak at pH 6.8-7.0. These observations indicated exhaustion of glycolytic type IIB fibers, removal of lactate by high local blood flow, and sustained contractions largely by oxidative type I and IIA fibers. A functional differentiation of fiber types could also be demonstrated during recovery if exercise was stopped while two pools of Pi were still apparent. In the first 3 min of recovery, the Pi peak at pH 6.8-6.9 disappeared almost entirely, whereas the Pi peak at pH 6.0 remained unaltered, reflecting the faster recovery of oxidative type I fibers. The potential of magnetic resonance spectroscopy to characterize oxidative and glycolytic fibers, predict capacity for aerobic performance, and signal the presence of muscle pathology is discussed.
由于糖酵解纤维和氧化纤维代谢模式的差异，利用磷-31磁共振波谱对肌肉中的异质区域进行定量探测是可行的。通过跟踪磷酸盐代谢物的变化，在10名未经训练的年轻男性中有4人在运动过程中表现出氧化纤维和糖酵解纤维的差异性募集。在前臂腕屈肌中，分别在静息状态、三个运动强度等级的两个循环过程以及恢复过程中，对无机磷酸盐（Pi）、磷酸肌酸和ATP的浓度进行了估计。在高工作强度（最大力量的40%）下，观察到两个不同的Pi峰，分别与pH 6.9和pH 5.9 - 6.4的Pi池相对应。其原因如下。在最低工作强度（使用最大力量的20%）时，主要是氧化型（I型）以及可能一些中间型（IIA型）肌肉纤维早期被募集，净乳酸生成相对较少，因此pH值下降也很少。然而，在更高的工作负荷下，主要募集的是糖酵解型（IIB型）肌肉纤维，其净乳酸生成相对较高，因此在低pH值下产生了第二个Pi池。在第一个运动周期中，ATP消耗（35 - 54%）和Pi损失伴随着运动能力的下降。当立即重复分级运动周期时，总Pi仍然很高，但在pH 6.8 - 7.0处只产生一个峰。这些观察结果表明糖酵解型IIB纤维耗尽，高局部血流清除了乳酸，并且主要由氧化型I型和IIA型纤维维持收缩。如果在两个Pi池仍然明显时停止运动，在恢复过程中也可以证明纤维类型的功能差异。在恢复的前3分钟，pH 6.8 - 6.9处的Pi峰几乎完全消失，而pH 6.0处的Pi峰保持不变，这反映了氧化型I型纤维恢复得更快。本文讨论了磁共振波谱在表征氧化纤维和糖酵解纤维、预测有氧运动能力以及提示肌肉病理状况方面的潜力。
