In Vivo Effect of Uncoupling Agents on the Incorporation of Calcium and Strontium into Mitochondria and Other Subcellular Fractions of Rat Liver

After injection of ⁴⁵Ca⁺⁺ or ⁸⁹Sr⁺⁺ into rats, the largest part of the radioactivity in the liver cell is associated with the subcellular structures, only negligible amounts of it being found in the soluble hyaloplasm. 50 % or more of the ⁴⁵Ca⁺⁺ and ⁸⁹Sr⁺⁺ in the liver cell is recovered in the mitochondrial fraction. The specific activity of Ca⁺⁺ after injection of ⁴⁵Ca⁺⁺ is far greater in mitochondria than in microsomes. Pretreatment of the rats with uncouplers of oxidative phosphorylation markedly decreases the amount of radioactivity associated with the mitochondrial fraction. The amount of radioactivity recovered in the microsomes and in the final supernatant on the contrary increases. These effects are present only when mitochondrial oxidative phosphorylation is completely uncoupled. The Ca⁺⁺ content of mitochondria from the livers of rats pretreated with uncouplers is sharply decreased with respect to the controls. It is concluded that in the liver cells of the intact animal energy-linked movements of Ca⁺⁺ and Sr⁺⁺ take place in mitochondria.