Simultaneous monitoring of intracellular pH and proton excretion during glycolysis by Streptococcus mutans and Streptococcus sanguis: effect of low pH and fluoride

A system was developed by which 2',7'-bis(carboxyethyl)-4 or 5-carboxyfluorescein could be used to monitor intracellular pH at the same time that proton excretion was being measured. Streptococcal cells were loaded with the dye, and after the addition of glucose protons were excreted and the intracellular pH increased quickly and remained higher than the extracellular pH of 7.0. The excretion of protons stopped and the intracellular pH returned to the original level when glucose was depleted. The intracellular level of ATP remained high during glucose metabolism and decreased with the depletion of glucose. At extracellular pH of 5.5, and 5.0, the intracellular pH of fasting cells was higher than the extracellular pH value. After addition of glucose there were initial lags of proton excretion and of increases in intracellular pH at the acidic extracellular pH values. In the presence of fluoride, a lag in proton excretion and a simultaneous decrease in intracellular pH were observed, indicating a partial and transient inhibition of proton-ATPase activity.