Effects of extracellular pH on lactate efflux from frog sartorius muscle

The isolated sartorius muscle of frog was stimulated under an anaerobic condition, and intracellular lactate concentration and intracellular pH was determined sequentially by 1H-nuclear magnetic resonance, and the efflux of lactate was measured by an enzymatic method on the incubation media with different pH levels. The lactate efflux was shown to increase in proportion to the concentration difference of lactate across the membrane up to 25 mmol X l H2O-1, and the permeability of the membrane to lactate increased with the increment of extracellular pH. H+ efflux was determined from pH change and the buffer capacity of incubation medium. The efflux of H+ rose approximately linearly with the efflux of lactate up to approximately 70 mumol X min-1 X l H2O-1, and the relationship then revealed a clear leveling off. From these results the efflux of lactate was analyzed in terms of a predominantly nonionic or a predominantly ionic efflux mechanism. Analysis showed that the mechanism of efflux was in both the ionic and nonionic form.