The mechanism of lactate transport in human erythrocytes

Lactate accumulates in human erythrocytes stored at 4 degrees C in the presence of glucose. Efflux of lactate exhibits an activation energy of 22kcal/mole and is markedly stimulated with increasing medium pH. Lactate influx into erythrocytes that were depleted of intracellular lactate by incubation at 37 degrees at pH 8.0 was stimulated by decreasing medium pH. Under appropriate conditions the pH-dependent lactate flux was insensitive to 4-acet-amido-4'-isothiocyano-2,2'-disulfonic stilbene or 4,4'-diisothiocyano-2,2'-disulfonic stilbene, inhibitors of the inorganic anion channel, while, e.g., inorganic phosphate transport was fully sensitive. These experiments as well as measurements of H+ movements associated with lactate fluxes demonstrate that lactate transport takes place via a specific monocarboxylate transporter (distinct from the inorganic ion channel) by a H+-lactate symport mechanism.