Alterations in biochemical activity of the cardiac mitochondria from rats treated with a high dose of vitamin D3

We previously demonstrated the functional damage in the aorta isolated from the rat treated with a high dose of vitamin D3(60th General Meeting of Jap. Pharmacol. Society). The present study was designed to elucidate pathophysiological changes in biochemical activity of the cardiac mitochondria from rats treated with a high dose of vitamin D3. Rats were treated with 500,000 units/kg p.o. for three consecutive days and sacrificed at 5th day. The cardiac mitochondria were isolated by a modified method of Sordahl. The mitochondrial calcium content of vitamin D3-treated rats was about 3-times higher than the control. Mitochondrial calcium binding and uptake activity of vitamin D-treated rats were substantially similar to the control. Calcium-stimulated, magnesium-dependent ATPase activity of the mitochondria from vitamin D-treated rat was significantly lower than the control(about 50 % decrease), whereas the magnesium-dependent ATPase was not altered by the treatment. Several indices for oxidative phosphorylating ability of the mitochondria were markedly declined by the treatment(38 to 66 % decrease). The results suggest a crucial damage in cardiac mitochondrial function by the accumulation of excessive calcium in cardiac cells induced by vitamin D3 -treatment.