Influence of acid loading, extracellular pH and uremia on intracellular pH in muscle

Our previous work has shown that chronic metabolic acidosis can induce changes in protein and amino acid metabolism in muscle. The relationship of these metabolic responses to changes in muscle pH is unknown. To examine the role that acute acidosis might have on intracellular pH in rats, we evaluated the influence an acute infusion of HCl had on intracellular pH using 31P-NMR. Male rats fed 22% protein and weighing between 150 and 170 g were infused with 150 mM HCl (4 mmol/kg) over a 2- or 4-hour period. Baseline blood pH was 7.36 and dropped to 7.04 at the end of the infusion. Despite this, no changes in intracellular pH were seen. In contrast, we found that chronic acid loading (4 mmol NH4Cl/100 g/day for 5 days) produces a small change in muscle pH (0.05 pH units, p < 0.05). Chronic uremia did not change resting muscle pH despite a decrease in extracellular pH to 7.23 even though metabolic changes are well documented.

(1) An acute acid load does not alter intracellular pH while chronic metabolic acidosis does reduce intracellular pH. (2) The lack of an acute change in intracellular pH suggests that intracellular buffering capacity changes over time.