Carbon‐Dioxide Concentration and the Distribution of Monocarboxylate and H+ Ions between Intracellular and Extracellular Spaces of Hemoglobin‐Free Perfused Rat Liver

Open Access
Publisher Website
Google Scholar
Abstract
H+ movement and monocarboxylate‐monocarboxylate exchange accompanying monocarboxylate gradient equilibration in hemoglobin‐free perfused rat liver have been studied in an isopH system using different buffer systems.1. At 5–10 mM concentrations of added monocarboxylate, there is an approximately linear dependence of net H+ uptake by the liver on added monocarboxylate. Net H+ uptake at 10 mM additions is 1.5–1.6 μmol per gram liver from aromatic weak acids like benzoate or salicylate, and 0.6–0.8 μmol per gram liver for aliphatic weak acids like acetate, lactate, pyruvate, and also 5,5‐dimethyloxazolidine‐2,4‐dione.2. Practically no net H+ movement is observed with dicarboxylates like phthalate or succinate and also not with choline chloride.3. Monocarboxylate‐monocarboxylate exchange is demonstrated by preloading the hepatocytes with benzoate, lactate and pyruvate, and observation of their release upon addition of other monocarboxylates.4. Net H+ uptake increases as total CO2 in perfusate is decreased at constant extracellular pH, in accordance with an intracellular acidification by the CO2 system. This is supported by measurement of distribution of 5,5‐dimethyloxazolidine‐2,4‐dione, and by monocarboxylate release from the cells during increases of CO2 concentration.5. Intracellular pH poise is low when bicarbonate buffer is replaced by zwitterionic buffers like N‐2‐hydroxyethylpiperazine‐N′‐ethane sulfonic acid or morpholinopropane sulfonic acid, resulting in calculated intracellular alkalinization of up to 0.5 pH unit. 5,5‐Dimethyloxazolidine‐2,4‐dione as a permeant buffer system is suggested as a more suitable replacement of bicarbonate buffer than the zwitterionic buffers with respect to intracellular pH poise.