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Mitoflash biogenesis and its role in the autoregulation of mitochondrial proton electrochemical potential
Gaomin Feng1, Beibei Liu1, Jinghang Li1
1State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China.
Abstract:
Respiring mitochondria undergo an intermittent electrical and chemical excitation called mitochondrial flash (mitoflash), which transiently uncouples mitochondrial respiration from ATP production. How a mitoflash is generated and what specific role it plays in bioenergetics remain incompletely understood. Here, we investigate mitoflash biogenesis in isolated cardiac mitochondria by varying the respiratory states and substrate supply and by dissecting the involvement of different electron transfer chain (ETC) complexes. We find that robust mitoflash activity occurs once mitochondria are electrochemically charged by state II/IV respiration (i.e., no ATP synthesis at Complex V), regardless of the substrate entry site (Complex I, Complex II, or Complex IV). Inhibiting forward electron transfer abolishes, while blocking reverse electron transfer generally augments, mitoflash production. Switching from state II/IV to state III respiration, to allow for ATP synthesis at Complex V, markedly diminishes mitoflash activity. Intriguingly, when mitochondria are electrochemically charged by the ATPase activity of Complex V, mitoflashes are generated independently of ETC activity. These findings suggest that mitoflash biogenesis is mechanistically linked to the build up of mitochondrial electrochemical potential rather than ETC activity alone, and may functionally counteract overcharging of the mitochondria and hence serve as an autoregulator of mitochondrial proton electrochemical potential.
Insights
Mitochondrial flashes (mitoflashes) are electrical events that uncouple respiration from ATP production. Robust mitoflash activity depends on mitochondrial electrochemical potential, not solely electron transfer chain activity.
Area of Science:
- Mitochondrial physiology
- Bioenergetics
- Cellular respiration
Background:
- Mitochondria generate ATP through oxidative phosphorylation, involving the electron transfer chain (ETC) and proton motive force.
- Mitochondrial flashes (mitoflashes) are transient, uncoupling events in respiring mitochondria, but their biogenesis and function are unclear.
Purpose of the Study:
- Investigate the mechanisms of mitoflash generation in cardiac mitochondria.
- Determine the role of respiratory states, substrate supply, and ETC complexes in mitoflash biogenesis.
Main Methods:
- Studied isolated cardiac mitochondria under varying respiratory states (II, III, IV) and substrate conditions.
- Dissected the involvement of different electron transfer chain complexes using specific inhibitors.
- Analyzed mitoflash activity in relation to mitochondrial electrochemical potential and ATP synthesis.
Main Results:
- Robust mitoflash activity occurred when mitochondria were electrochemically charged (respiratory states II/IV), irrespective of substrate entry site.
- Inhibiting forward electron transfer abolished mitoflashes, while blocking reverse electron transfer augmented them.
- ATP synthesis (state III) diminished mitoflash activity; mitoflashes were generated independently of ETC activity when charged by Complex V ATPase.
Conclusions:
- Mitoflash biogenesis is linked to the buildup of mitochondrial electrochemical potential, not solely ETC activity.
- Mitoflashes may act as an autoregulator, preventing mitochondrial overcharging and maintaining proton electrochemical potential.
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