THE EFFECT OF PH ON GLYCOLYSIS AND PHOSPHOFRUCTOKINASE ACTIVITY IN CULTURED-CELLS AND SYNAPTOSOMES

The effect of [H+] on the rate of glycolysis was investigated in gliom a C6 and fibroblast BHK-21 cells and in synaptosomes from rat brain. T he rates of lactate production at an extracellular pH (pH(e)) of 6.2, 7.4, and 7.8 were correlated with intracellular [ATP], [ADP], and [P-i ] ([ATP](i), [ADP](i), and [P-i](i), respectively) and, when relevant, creatine phosphate (PCr) as well as with the levels of several glycol ytic intermediates. In C6 cells cytosolic [H+] was measured simultaneo usly together with [Ca2+], [K+], [Na+], and membrane potentials. In al l three systems studied, an increase in [H+](e) suppressed whereas a f all enhanced the rate of lactate generation. Changes in pH(e) produced no simple correlation between the amount of lactate formed and altera tions either in the absolute [ATP], [ADP], [P-i], and [PCr] or their r atios but did correlate with the levels of glycolytic intermediates. H igher [fructose-1,6-bisphosphate] and [glyceraldehyde-3-phosphate] and lower [glucose-6-phosphate] and [fructose-6-phosphate] accompanied fa ster glycolytic activity, Addition of rotenone markedly enhanced glyco lysis at all pH(e) values studied. The increases were larger at higher [H+] so that the rate of lactate generation was only slightly lower a t pH 6.2 than at 7.4 or 7.8. With rotenone present, [ATP] (and where r elevant [PCr]) fell and [ADP] and [P-i] rose under all pH(e) condition s. Simultaneously [glucose-6-phosphate] and [fructose-6-phosphate] dec reased whereas [fructose-1,6-bisphosphate] and [glyceraldehyde-3-phosp hate] increased; the levels of the last two were similar at pH 6.2 and 7.4. Alterations in concentrations of cations other than H+ were smal l and unlikely to contribute to the regulation of glycolysis. It is co ncluded that (a) under intracellular conditions, in the presence of a high [ATP] and a low [ADP] and [AMP], a fall in [H+] powerfully inhibi ts phosphofructokinase; lactate production correlates with the levels of glycolytic intermediates. (b) A small decline in cellular energy st ate is sufficient to release phosphofructokinase inhibition by protons . (c) Once activated by the decrease in energy level, the steady-state glycolytic rate is dependent on other factors, such as glycolytic int ermediates and enzymes.