Depolarization of plasma membrane of rat brain synaptosomes at extra- and intracellular acidification

To elucidate whether a decrease in pH_o and pH_i has the same effect on presynaptic plasma membrane depolarization, we compared the effects of 1 mM of amiloride which decreased pH_i down to 6.65 and incubation medium acidification down to pH^o 7.0 and 6.0 on DiSC3(5) dye fluorescence. Measurements were performed with and without the mitochondrial toxins: rotenone (10 μM) + oligomycin (5 μg/mL). In the presence of toxins the change in DiSC3(5) fluorescence was specific for plasma membrane potential. In the second case, DiSC3(5) signal represented the total potential of mitochondria and plasma membrane. It was shown that decreasing of pHo works both in the presence of mitochondrial toxins and also in their absence. Amiloride is able to increase DiSC3(5) fluorescence only in the presence of the mixture of rotenone + oligomycin. Therefore, unlike the mitochondrial potential, the plasma membrane potential is sensitive to a decrease in pH_i and pH_o.