Malonate as an Inhibitor of Cyclosporine A-Sensitive Calcium-Independent Free Oxidation in Liver Mitochondria Induced by Fatty Acids

The effect of an inhibitor of succinate dehydrogenase malonate on cyclosporin A (CsA)-sensitive stimulation of respiration by alpha,omega-tetradecanedioic (TDA) and palmitic acids was investigated in experiments on rat liver mitochondria energized by the oxidation of succinate. It was found that malonate at a concentration of 0.2 mM halved the respiration rate in the presence of 50 mu M 2,4-dinitrophenol (DNP), which causes maximal stimulation of respiration. However, malonate at this and even higher concentrations had no effect on mitochondrial respiration either in the resting state (state 2) or in the case of the twofold stimulation of mitochondrial respiration by the protonophore uncoupler FCCP. TDA at a concentration of 0.5 mM causing a twofold stimulation of mitochondrial respiration, in contrast to FCCP had no effect on Delta Psi either in the absence or in the presence of malonate at a concentration below 0.5 mM. However, malonate at a concentration as low as 0.2 mM significantly reduced the activity of TDA. It was shown that malonate in liver mitochondria with similar effectiveness inhibits both TDA activity and respiration maximally stimulated by DNP. It was found that stimulation of respiration by TDA is not associated with the induction of nonspecific permeability of the inner membrane of the part of liver mitochondrial population. The specific uncoupling activity of palmtic acid (V-U) and its specific components that characterize participation of the ATP/ADP antiporter (V-Catr), aspartate/glutamate antiporter (V-Glu), and cyclosporin-A-sensitive system (V-CsA) in the palmitic acid-induced uncoupling were estimated. It was found that malonate at a concentration of 0.2 mM significantly reduces V-U and V-CsA but does not affect V-Catr and V-Glu. Based on these results we assume that CsA-sensitive stimulation of liver mitochondrial respiration by TDA and palmitic acid without changing Delta Psi may be caused by the switching of part of the respiratory chain complexes to the mode of the maximal rate of the electron transfer occurring without the vector transport of H+ from the matrix to the intermembrane space.