The production of reactive oxygen species in intact isolated nerve terminals is independent of the mitochondrial membrane potential

Dependence on mitochondrial membrane potential (DeltaPsim) of hydrogen peroxide formation of in situ mitochondria in response to inhibition of complex I or III was studied in synaptosomes. Blockage of electron flow through complex I by rotenone or that through complex III by antimycin resulted in an increase in the rate of H2O2 generation as measured with the Amplex red assay. Membrane potential of mitochondria was dissipated by either FCCP (250 nM) or DNP (50 muM) and then the rate of H2O2 production was followed. Neither of the uncouplers had a significant effect on the rate of H2O2 production induced by rotenone or antimycin. Inhibition of the F0F1-ATPase by oligomycin, which also eliminates DeltaPsim in the presence of rotenone and antimycin, respectively, was also without effect on the ROS formation induced by rotenone and only slightly reduced the antimycin-induced H2O2 production. These results indicate that ROS generation of in situ mitochondria in nerve terminals in response to inhibition of complex I or complex III is independent of DeltaPsim. In addition, we detected a significant antimycin-induced H2O2 production when the flow of electrons through complex I was inhibited by rotenone, indicating that the respiratory chain of in situ mitochondria in synaptosomes has a substantial electron influx distal from the rotenone site, which could contribute to ROS generation when the complex III is inhibited.