On the State of Calcium Ions in Isolated Rat Liver Mitochondria. IV. Prevention of Phosphate-Induced Mitochondrial Destruction by Ruthenium Red-Insensitive Calcium Release

Ruthenium red prevented the spontaneous calcium release and the accompanying mitochondrial destruction occurring in calcium-loaded mitochondria in the presence of phosphate. Under these conditions delta pH and membrane potential delta psi were preserved and the ruthenium red-induced calcium efflux was low and at a constant rate. On prolonged incubation with calcium prior to addition of ruthenium red increasingly more mitochondrial calcium developed into a pool rapidly dischargeable by ruthenium red. This development was accompanied by stimulation of respiration which was, however, not abolished by ruthenium red as could have been expected if it had been caused by calcium cycling. Calcium therefore altered mitochondria by a different mechanism than by cycling across the inner membrane.