Intracellular bicarbonate of skeletal muscle under different metabolic states.

Intracellular bicarbonate of single muscle fibers in vivo was measured by a direct electrometric method simultaneously with the membrane PD in rats under seven different metabolic states. From the measured intracellular bicarbonate values and the PCO2, the bicarbonate equilibrium potential and the intracellular pH were calculated. The mean intracellular [HCO3-] under normal control conditions was 10.3 +/- 0.7 mM (SE). The intracellular bicarbonate fell significantly in both chronic metabolic acidosis and chronic K+ depletion. In contrast, intracellular bicarbonate was elevated in chronic metabolic alkalosis, K+ loading, and Na+ depletion. Taking intracellular pH as an index of the acid-base status of cells, we find that whereas the calculated cell pH decreased along with the cell bicarbonate in both chronic metabolic acidosis and K+ depletion, cell pH increased along with the bicarbonate only in chronic metabolic alkalosis. Cell pH was unchanged in both chronic K+ loading and Na+ depletion.