Intracellular pH (pHi) was measured under differing conditions in the functionally isolated, perfused rat liver using double-barrelled recessed-tip micro-electrodes. 2. Under normal acid-base conditions mean hepatic pHi was 7.18. 3. Over the range studied, hepatic pHi was negatively and linearly related to the logarithm of perfusate PCO2. 4. Measurement of pHi together with measurement of pHe and intracellular and extracellular lactate concentrations suggested a non-equilibrium distribution of lactate and lactic acid across the hepatic cell membrane requiring an active transport process for entry of lactate to the cell. 5. Upon addition of D-fructose (10 mM) to the perfusate there was a rapid fall in pHi of between 0.2 and 0.54 units, which was substantially greater than observed in earlier similar experiments in which 31P-nuclear magnetic resonance was used to measure pHi. Reasons for this discrepancy are considered.
