Fig. 3.

Acidification decreased the generation of reactive oxygen species from mitochondria. An acidic extramitochondrial environment decreased the net release of H₂O₂ from control and ischemia-damaged mitochondria in the presence of either complex I (A) or complex II substrates (B). Acidification did not alter aconitase activity in control or ischemia-damaged mitochondria, suggesting that acidification does not increase superoxide generation that is directed into mitochondrial matrix (C). However, aconitase activity was reduced by ischemia. Acidification decreased oxidative phosphorylation in digitonin permeabilized myocytes when pyruvate + malate was used as a complex I substrate, indicating that intracellular pH alters complex I activity in situ. The partial block of respiration observed on acidification from pH 7.1 to 6.8 was not significantly increased by acidification to pH 6.6 or 6.4 (D). Values are means ± SE. *P <0.05 vs. pH 7.4 or pH 7.1 (D); †P < 0.05 vs. nonischemic; n = 5 in A–C; n = 6 in D.