Coast J R, Shanely R A, Lawler J M, Herb R A
S. A. Rasmussen Exercise Physiology Laboratory, Department of Health, Physical Education, Exercise Science and Nutrition, Northern Arizona University, Flagstaff 86011-5095, USA.
Am J Respir Crit Care Med. 1995 Nov;152(5 Pt 1):1648-52. doi: 10.1164/ajrccm.152.5.7582309.
Diaphragm fatigue occurs during heavy exercise. Acidosis leads to skeletal muscle fatigue, yet the diaphragm is not a net producer of either lactic acid or hydrogen ions. We tested the hypothesis that hydrogen ion and lactic acid concentrations similar to those seen in arterial blood at maximal exercise decrease contractility of the in vitro isolated rat diaphragm. Diaphragm strips were exposed to a control solution for 15 min and then to one of the following treatment solutions: control (C, pH = 7.4) or 10 mM lactic acid buffered to pH 7.4 (L74), pH 7.2 (L72), pH 7.1 (L71), or pH 6.8 (L68). After 15 min, the force-frequency relationship of the strip was measured. The strips were then stressed with 75 contractions at 25 Hz (250-ms train duration) at the rate of one per second and the force-frequency curve was measured after 15 min of recovery. The L74, L72, and L71 strips responded similarly to the C strips at all times and frequencies. Decrements in force associated with acidosis were only seen in L68. Within L68, we found decreases in force at stimulation frequencies < 100 Hz. These data suggest that physiologic levels of exogenous hydrogen ions are not a primary cause of in vitro diaphragm fatigue.
在剧烈运动期间会发生膈肌疲劳。酸中毒会导致骨骼肌疲劳，但膈肌既不是乳酸也不是氢离子的净产生者。我们测试了这样一个假设：与最大运动时动脉血中所见浓度相似的氢离子和乳酸浓度会降低体外分离的大鼠膈肌的收缩力。将膈肌条暴露于对照溶液15分钟，然后暴露于以下处理溶液之一：对照（C，pH = 7.4）或缓冲至pH 7.4（L74）、pH 7.2（L72）、pH 7.1（L71）或pH 6.8（L68）的10 mM乳酸。15分钟后，测量条带的力-频率关系。然后以每秒一次的速率在25 Hz（250毫秒的串刺激持续时间）下对条带施加75次收缩，并在恢复15分钟后测量力-频率曲线。L74、L72和L71条带在所有时间和频率下的反应与C条带相似。仅在L68中观察到与酸中毒相关的力的下降。在L68内，我们发现在刺激频率<100 Hz时力下降。这些数据表明，外源性氢离子的生理水平不是体外膈肌疲劳的主要原因。
