Reversible depolarization of in situ mitochondria by oxidative stress parallels a decrease in NAD(P)H level in nerve terminals

Abstract

We have reported recently ( Chinopoulos et al., 1999 J. Neurochem. 73, 220–228) that mitochondrial membrane potential (ΔΨm) in isolated nerve terminals is markedly reduced by H 2O 2 in the absence of F 0F 1-ATPase working as a proton pump. Here we demonstrate that ΔΨm reduced by H 2O 2 (0.5 mM) in the presence of oligomycin (10 μM), an inhibitor of the F 0F 1-ATPase, was able to recover by the addition of catalase (2000 U). Similarly, a decrease in the NAD(P)H level due to H 2O 2 can be reversed by catalase. In addition, H 2O 2 decreased the ATP level and the [ATP]:[ADP] ratio measured in the presence of oligomycin reflecting an inhibition of glycolysis by H 2O 2, but this effect was not reversible. The effect of H 2O 2 on ΔΨm in the presence of the complex I inhibitor, rotenone, was also unaltered by addition of catalase. These results provide circumstantial evidence for a relationship between the decreased NAD(P)H level and the inability of mitochondria to maintain ΔΨm during oxidative stress.