The role of mitochondria in modifying the cellular ionic environment. Calcium-induced respiratory activities in mitochondria isolated from various tumour cells

Cyclic stimulation by Ca2+of respiration in mitochondria isolated from Ehrlich ascites-tumour cells occurs only when low phosphate concentrations (approx. 0.5mm) are also included in the incubation system. Under these circumstances the extra oxygen consumed is related stoicheiometrically to the amount of Ca2+taken up by the mitochondria; the values are similar to those obtained with mitochondria from rat liver in the absence of added phosphate. In contrast with liver mitochondria, up to 280nmol of Ca2+/mg of protein can be added to ascites mitochondria without causing any deleterious effect. Respiration in mitochondria isolated from the Yoshida ascites hepatoma (HA 130) and from the Morris hepatomas 5123C and 9618A is also stimulated by Ca2+in a cyclic manner. However, that in mitochondria from regenerating rat liver responds to Ca2+in the same way as those from normal rat liver. ADP-stimulated respiration in mitochondria from Ehrlich ascites tumour cells, but not from rat liver, is inhibited by low amounts of Ca2+.