Regulation of cyclosporin A sensitive mitochondrial permeability transition by the redox state of pyridine nucleotides

The mechanisms involved in the induction of cyclosporine A sensitive mitoch ondrial swelling by oxidative stress were investigated in isolated guinea p ig liver mitochondria. The aim of our study was to investigate, if swelling is inevitably associated with the oxidation of pyridine nucleotides, and i f the oxidized pyridine nucleotides have to be hydrolysed for the induction of mitochondrial swelling. Quantitative measurement of oxidized pyridine n ucleotides was performed with HPLC. Mitochondrial swelling was recorded by monitoring the decrease in light scattering of the mitochondrial suspension . Reduction and oxidation of pyridine nucleotides were followed by monitori ng the changes of the autofluorescence signal of reduced pyridine nucleotid es, Qualitative measurement of mitochondrial membrane potential was perform ed with the fluorescence indicator rhodamine 123, Neither t-butyl hydropero xide nor the dissipation of the mitochondrial inner membrane potential with FCCP (carbonyl cyanide-p-trifluoromcthoxyphenyl hydrazone) induced the ope ning of the membrane permeability transition pore, unless an extensive oxid ation of mitochondrial pyridine nucleotides took place. Mitochondrial swell ing induced by our experimental conditions was always sensitive to cyclospo rine A and accompanied by a cyclosporine A sensitive release of inner mitoc hondrial pyridine nucleotides without pyridine nucleotide hydrolysis. Not t he cycling of calcium across the mitochondrial inner membrane but the accum ulation of calcium inside the mitochondria was a prerequisite for mitochond rial swelling. The mitochondrial membrane permeability transition is neithe r caused nor accompanied by the hydrolysis of mitochondrial pyridine: nucle otides. (C) 2001 Elsevier Science Inc. Ail rights reserved.