Experimental acidemia and muscle cell pH in chronic acidosis and renal failure

To test whether muscle intracellular pH (pHi) decreases when extracellular pH falls, 31P-nuclear magnetic resonance was utilized in rats made acidotic by infusion of HCl, gavage-feeding NH4Cl, or induction of chronic renal failure (CRF). A 2- or 4-h HCl infusion did not lower muscle pHi, even though serum bicarbonate fell to 5 mM. With chronic acidemia, blood pH was 7.15 +/- 0.01 vs. 7.38 +/- 0.02 in pair-fed controls, and muscle pHi was 7.09 +/- 0.01 and 7.14 +/- 0.02, respectively (P < 0.01). pHi in muscle of CRF rats (7.16 +/- 0.01) did not differ from sham-operated, pair-fed controls (7.19 +/- 0.01) despite a blood pH of 7.23 +/- 0.05 in CRF vs. 7.39 +/- 0.01 in controls. Because ion transport is abnormal in CRF, we examined whether recovery of pHi is impaired when muscles of six CRF and control rats were exercised to tetany by stimulation of the sciatic nerve. Neither pHi nor the recovery of pHi differed between CRF and control rats. We conclude that pHi is maintained in muscle in uremia and that signals other than changing pHi must be necessary to disrupt metabolism.