[Study of membrane potential of Bacillus subtilis and Escherichia coli cells by the penetration ions methods]

Using the penetrating ions of tetraphenylphosphonium (TPP+) and tetraphenylborone (TPB-), the membrane potential of the Bacillus subtilis and Escherichia coli cells was shown that the TPP+ absorption by the cells is an energy-coupled process. The TPB- anions are released from the cells after addition of an energy substrate. The value of the membrane potential calculated from the distribution pattern of the penetrating ions in the cells and the incubation medium lies within the interval of --100--150 mV (intracellular negative electric potential). The value of the membrane potential strongly depends on pH of the incubation medium; our attempts to measure the membrane potential in the E. coli cells at ph 6.0 were unsuccessful; however, at pH 8.5 it was found to be equal to --100 mV. Treatment of the cells with nigericin partially prevents the decrease of the membrane potential in an acidic medium and increases the potential in neutral and alkaline media. The formation of the membrane potential is suppressed by valinomycin and gramicidine, as well as by the oxidative phosphorylation uncouplers; the inhibiting effect of valinomycin requires the presence of K+ in the incubation medium. The membrane potential of the B. subtilis cells is insensitive to the effect of cyanide in the absence of arsenate. It is concluded that the membrane potential of B. subtilis and E. coli is formed both via respiration and by hydrolysis of intracellular ATP.