Effect of decreased pH on force and phosphocreatine in mammalian skeletal muscle

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Abstract
Phosphocreatine (PCr) and intracellular pH changes were monitored by 31P-NMR spectroscopy in isolated, arterially perfused cat biceps and soleus muscles, while the pH of the CO2–bicarbonate buffered perfusate was decreased from 7.1–7.4 to 6.4–6.7 by increasing the CO2 in the equilibrating gas from 5 to up to 70%. In biceps (fast twitch) muscles, intracellular pH decreased from 7.0 to 6.6 (30% CO2, 30 °C), peak tetanic force decreased by 8%, but the rise and relaxation times of tetani were not significantly changed. In soleus muscles, intracelluar pH decreased from 7.0 to 6.6 (30% CO2, 30 °C), peak tetanic force was unchanged, but the rise and relaxation times of tetani were increased by 27 and 112%, respectively. In both muscles greater decreases in tetanic force were observed during repetitive or ischemic stimulation, which resulted in intracelluar pH similar to that produced by hypercapnia. Contrary to previous reports, there was no significant decrease in PCr level in either muscle type with decreased intracellular pH. In the soleus at 30 °C there was a significant increase in PCr level with decreased pH.Key words: cat, biceps brachii, soleus, 31P-nuclear magnetic resonance spectroscopy, fatigue.

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