K+ATP channel opening prevents succinate-dependent H2O2 generation by plant mitochondria

The role of a recently identified K+ ATP channel in preventing H2O2 formation was examined in isolated pea stem mitochondria. The succinate-dependent H2O2 formation was progressively inhibited, when mitochondria were resuspended in media containing increasing concentration of KCl (from 0.05 to 0.15M). This inhibition was linked to a partial dissipation of the transmembrane electrical potential (Δψ) induced by KCl. Conversely, the malate plus glutamate-dependent H2O2 formation was not influenced. The succinate-sustained H2O2 generation was also unaffected by nigericin (a H+/K+ exchanger), but completely prevented by valinomycin (a K+ ionophore). In addition, cyclosporin A (a K+ ATP channel opener) inhibited this H2O2 formation, while ATP (an inhibitor of the channel opening) slightly increased it. The inhibitory effect of ATP was strongly stimulated in the presence of atractylate (an inhibitor of the adenine nucleotide translocase), thus suggesting that the receptor for ATP on the K+ channel faces the intermembrane space. Finally, the succinatedependent H2O2 formation was partially prevented by phenylursine oxide (a thiol oxidant).