Interaction of calcium with mitochondria isolated from Ehrlich ascites tumour cells

Calcium ions are accumulated by intact mitochondria isolated from Ehrlich ascites tumour cells in a buffered system supplemented with ATP or succinate. In the ATP-supplemented system, the tumour mitochondria, in contrast to rat liver mitochondria, retain the accumulated Ca²⁺, do not exhibit a marked “irreversible” ATPase and do not swell. In the succinate-supplemented system, added Ca²⁺ stimulates respiration in either the absence or presence of added inorganic phosphate. Whereas respiration by rat liver mitochondria, measured in the presence of added phosphate, remains continuously activated after the addition of only a small amount of Ca²⁺, that by the tumour mitochondria can be stimulated by several successive additions of 100 μM Ca²⁺ and at all times exhibit appreciable activation ratios.