Depolarization of In Situ Mitochondria Due to Hydrogen Peroxide‐Induced Oxidative Stress in Nerve Terminals

Abstract: Mitochondrial membrane potential (Δ?m) was determined in intact isolated nerve terminals using the membrane potential‐sensitive probe JC‐1. Oxidative stress induced by H2O2 (0.1‐1 mM) caused only a minor decrease in Δ?m. When complex I of the respiratory chain was inhibited by rotenone (2 μM), Δ?m was unaltered, but on subsequent addition of H2O2, Δ?m started to decrease and collapsed during incubation with 0.5 mM H2O2 for 12 min. The ATP level and [ATP]/[ADP] ratio were greatly reduced in the simultaneous presence of rotenone and H2O2. H2O2 also induced a marked reduction in Δ?m when added after oligomycin (10 μM), an inhibitor of F0F1‐ATPase. H2O2 (0.1 or 0.5 mM) inhibited α‐ketoglutarate dehydrogenase and decreased the steady‐state NAD(P)H level in nerve terminals. It is concluded that there are at least two factors that determine Δ?m in the presence of H2O2: (a) The NADH level reduced owing to inhibition of α‐ketoglutarate dehydrogenase is insufficient to ensure an optimal rate of respiration, which is reflected in a fall of Δ?m when the F0F1‐ATPase is not functional. (b) The greatly reduced ATP level in the presence of rotenone and H2O2 prevents maintenance of Δ?m by F0F1‐ATPase. The results indicate that to maintain Δ?m in the nerve terminal during H2O2‐induced oxidative stress, both complex I and F0F1‐ATPase must be functional. Collapse of Δ?m could be a critical event in neuronal injury in ischemia or Parkinson’s disease when H2O2 is generated in excess and complex I of the respiratory chain is simultaneously impaired.