Effect of cyclosporin A and trifluoperazine on rat liver mitochondria swelling and lipid peroxidation

The effect of cyclosporin A (CsA) or trifluoperazine (TFP) on lipid peroxidation and mitochondrial swelling was determined using liver mitochondria incubated with 30 microM Ca2+ and 250 microM t-butylhydroperoxide or 5 mM inorganic phosphate (P(i)). Lipid peroxidation was not modified by either 1 microM CsA or 40 microM TFP. These compounds presented a distinct effect on mitochondrial permeability. Under oxidative conditions, CsA only showed a transient protective effect whereas TFP completely inhibited mitochondrial swelling. Conversely, CsA was very efficient when Ca2+ and P(i) were used, a condition under which TFP was unable to prevent the swelling. These data are consistent with our previous results (M.F. Nepomuceno, D.V. Macedo and L. Pereira-da-Silva (1991). Brazilian Journal of Medical and Biological Research, 24: 833-836) showing that lipid peroxidation is one among other different components of the permeabilization process. The data suggest that lipid peroxidation is independent of swelling, occurring later than swelling, presumably when the mitochondrial reductant systems are depleted. The differential effects of CsA and TFP suggest that these compounds can be used as specific probes in the elucidation of the two distinct mechanisms responsible for mitochondrial swelling

Lipoperoxidation associated with mitochondrial membrane permeabilization in the presence of Ca2+

Lipoperoxidation was investigated as a step for membrane protein thiol oxidation of rat liver mitochondria incubated in the presence of Ca2 and t-butylhydroproxide, by the determination of thiobarbituric acid reactive substances. Lipoperoxidation occured only when the incubation medium contained 125 µM t-butylhdroperoxide (t-buOOH) in the presence of Ca2+ and phosphate (Pi). No lipoperoxidation was observed when acetate replaced Pi as permeant anion, or when the oxidant was omitted, even at high Ca2 and Pi concentrations (up to 120 µMCa2+ and 5mMPi), conditions under which the mitochondria are fully permeabilized. In both cases, ADP protected efficiently against permeabilization, indicating the possible involvement of the ADP/ATP carrier in the earlier stages of the process