Estimations of membrane potentials in Streptococcus faecalis by means of a fluorescent probe

Membrane potentials in $\text{Streptococcus faecalis (faecium)}$ were estimated by means of the fluorescent probe, 1,1′-dihexyl-2,2′-oxycarbocyanine. In the absence of D-glucose the potential was ?60 to ?70 mV for normal cells suspended in 0.09 M NaCl + 0.01 M Tris-HCl at pH 7.5. When metabolism was initiated by the addition of D-glucose the cells became hyperpolarized (internal becomes more negative). The new potential, ?130 to ?140 mV, was fully manifested 35 seconds after the glucose was added. N,N′-dicyclohexylcarbodiimide, a membrane ATPase inhibitor prevented the hyperpolarization seen upon the addition glucose. The results are consistent with the view that glycolyzing cells generate a considerasble electrical potential across the cell membrane.