The Interaction of Calcium Transport and ADP Phosphorylation in Brain Mitochondria

Abstract

Brain mitochondria respiring on glutamate plus malate had a respiratory control index (RCI) for the addition of ADP of 5.5 and a P:O ratio of 2.9. These mitochondria also had a Ca²⁺ :O ratio of approximately 5.2, and the ratio of oxygen uptake in the presence of external Ca²⁺ to that in its absence was 4.0. The reversible transition of respiration to State 3 on the addition of ADP in phosphate media could be blocked by the prior accumulation of 50–200 nmoles/mg of Ca²⁺. The inhibition was reversible, and on the release of the accumulated Ca²⁺ by Na⁺/Ca²⁺ exchange, the mitochondria became responsive to ADP. The decreased response to ADP following the addition of Ca²⁺ is probably associated with Ca²⁺ ions complexing adenine nucleotides within the mitochondria, thus reducing the exchangeable pool and the amount of ADP available to the F₁-ATPase.