Ca2+-Stimulated Mitochondrial Reactive Oxygen Species Generation and Permeability Transition Are Inhibited by Dibucaine or Mg2+

Mitochondrial swelling and membrane protein thiol oxidation associated with mitochondrial permeability transition induced by Ca2+andt-butyl hydroperoxide or inorganic phosphate, but not 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid or phenylarsine oxide, are inhibited by the local anesthetic dibucaine. Dibucaine promotes an inhibition of the Ca2+-induced increase in mitochondrial H2O2generation measured by the oxidation of scopoletin in the presence of horseradish peroxidase. This decrease in mitochondrial H2O2generation may be attributed to the reduction of Ca2+binding to the membrane induced by dibucaine, as assessed by measuring45Ca2+binding to the mitochondrial membrane. Mg2+also inhibited Ca2+binding to the mitochondrial membrane, mitochondrial swelling, membrane protein thiol oxidation, and H2O2generation induced by Ca2+. Together, these results demonstrate that the mechanism by which dibucaine and Mg2+inhibit mitochondrial permeability transition is related to the decrease in reactive oxygen species generation induced by Ca2+-promoted alterations of inner mitochondrial membrane properties.