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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 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.
Insights
Brain mitochondria respiration is inhibited by calcium ions, which bind to adenine nucleotides. This effect is reversible, with calcium efflux restoring ADP responsiveness in these crucial cellular energy producers.
Area of Science:
- Mitochondrial physiology
- Cellular respiration
- Calcium signaling
Background:
- Mitochondria are vital for cellular energy production through oxidative phosphorylation.
- Calcium ions play a significant role in cellular signaling and mitochondrial function.
- Understanding the interplay between calcium and mitochondrial respiration is key to comprehending cellular bioenergetics.
Purpose of the Study:
- To investigate the effect of calcium accumulation on brain mitochondrial respiration.
- To elucidate the mechanism by which calcium influences ADP-stimulated respiration.
Main Methods:
- Measurement of respiratory control index (RCI) and P:O ratios in brain mitochondria.
- Determination of Ca2+:O ratios and oxygen uptake rates.
- Assessment of ADP-stimulated respiration in the presence and absence of accumulated Ca2+.
Main Results:
- Brain mitochondria exhibited an RCI of 5.5 and a P:O ratio of 2.9 with glutamate plus malate.
- Accumulation of Ca2+ (50-200 nmoles/mg) reversibly inhibited ADP-stimulated State 3 respiration.
- Na+/Ca2+ exchange restored ADP responsiveness, suggesting Ca2+ complexation of adenine nucleotides.
Conclusions:
- Calcium ions can inhibit mitochondrial respiration by complexing with adenine nucleotides within the mitochondria.
- This interaction reduces the availability of ADP for the F1-ATPase, impairing energy production.
- Mitochondrial calcium handling is a critical factor modulating cellular energy metabolism.