Regulation of intracellular acid-base equilibrium in rats

The extracellular pH (pHe) of unrestrained male Sprague-Dawley rats was altered by either inhalation of CO2 or infusion of sodium bicarbonate and then kept constant for at least 2 h. The intracellular pH (pHi) was then determined by the DMO (5,5-dimethyl-2,4-oxazolidinedione)-method in heart, brain, liver, spleen, and ten different skeletal muscle groups. pHi varied linearly with pHe in the heart and the parenchymal organs. pHi in skeletal muscle remained constant over a pHe range from 7.31 to 7.45 but varied linearly with pHe outside this range.

1. pHi is influenced by CO2 inhalation or bicarbonate infusion. 2. pHi may be different in different tissues at specified pHe. 3. Skeletal muscle seems to be well protected against mild extracellular acidosis. 4. Slight changes of pHe affect the pHi of the heart, brain, liver, and spleen. 5. Regulation of intra- and extracellular acid-base balance probably occurs by bicarbonate transfer between the intra- and extracellular compartments. 6. The acid-base status of the various intracellular compartments cannot be determined from blood-gas analysis.