MYCOPLASMA MEMBRANE-POTENTIALS DETERMINED BY POTENTIAL-SENSITIVE FLUORESCENT DYES

The membrane potentials of mycoplasmas were investigated by using potential-sensitive cyanine dyes. The fluorescence response results from a potential-dependent partition of the dyes between the cells and the extracellular medium. Cell hyperpolarization (inside more negative), e.g., by the addition of valinomycin, results in uptake of the dyes into the cells and, by formation of dye aggregates, in quenching of the fluorescence intensity. The magnitude of the fluorescence change upon addition of valinomycin depended on the external K+ concentration. At a defined external K+ concentration, no change in fluorescence occurred. The intracellular K+ concentration was determined by atomic absorption spectroscopy. Mycoplasma membrane potentials were calculated according to the Nernst equation. The membrane potential of both Mycoplasma mycoides subsp. capri and Mycoplasma gallisepticum was -48 mV±10%; the membrane potential of Acholeplasma laidlawii was -28 mV±20%. © 1979 Springer-Verlag New York Inc.