Harkema S J, Meyer R A
Department of Physiology, Michigan State University, East Lansing 48824, USA.
Am J Physiol. 1997 Feb;272(2 Pt 1):C491-500. doi: 10.1152/ajpcell.1997.272.2.C491.
The relationships between oxygen consumption (Q(O2)) and calculated cytoplasmic ADP concentration ([ADP]) and the free energy of ATP hydrolysis (deltaG(ATP)) were examined in ex vivo arterially perfused cat soleus muscles during repetitive twitch stimulation under normocapnic (5% CO2) and hypercapnic (70% CO2) conditions. Hypercapnia decreased extra- and intracellular pH by over 0.5 but had no significant effect on Q(O2) or phosphocreatine (PCr)/ATP in muscles at rest. The maximum Q(O2) measured during stimulation and the rate constant for PCr recovery after stimulation both decreased during hypercapnic compared with normocapnic perfusion, but the estimated ATP/O2 was unchanged. The change in PCr and deltaG(ATP) with increasing Q(O2) was greater during hypercapnic compared with normocapnic stimulation, as expected from the decrease in maximum Q(O2). However, the relationships between Q(O2) and [ADP] and deltaG(ATP) were both shifted to the left during hypercapnia compared with normocapnia. The results show that changes in cytoplasmic adenine nucleotides and phosphate are not sufficient to explain the control of respiration in skeletal muscle. However, in the context of thermodynamic models of respiratory control, the results can be explained by increased intramitochondrial potential for ATP synthesis at low pH.
在常碳酸血症（5%二氧化碳）和高碳酸血症（70%二氧化碳）条件下，对离体动脉灌注的猫比目鱼肌进行重复抽搐刺激时，研究了氧消耗（Q(O2)）与计算出的细胞质ADP浓度（[ADP]）以及ATP水解自由能（deltaG(ATP)）之间的关系。高碳酸血症使细胞外和细胞内pH值降低超过0.5，但对静息肌肉中的Q(O2)或磷酸肌酸（PCr）/ATP没有显著影响。与常碳酸血症灌注相比，高碳酸血症期间刺激过程中测得的最大Q(O2)以及刺激后PCr恢复的速率常数均降低，但估计的ATP/O2不变。与常碳酸血症刺激相比，高碳酸血症期间随着Q(O2)增加，PCr和deltaG(ATP)的变化更大，这与最大Q(O2)的降低预期一致。然而，与常碳酸血症相比，高碳酸血症期间Q(O2)与[ADP]和deltaG(ATP)之间的关系均向左移动。结果表明，细胞质腺嘌呤核苷酸和磷酸盐的变化不足以解释骨骼肌呼吸的控制。然而，在呼吸控制的热力学模型背景下，这些结果可以通过低pH值时线粒体内ATP合成潜力的增加来解释。
