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Mitochondrial membrane potential supported by exogenous cytochrome c oxidation mimics the early stages of apoptosis
G La Piana1, E Fransvea, D Marzulli
1Department of Biochemistry and Molecular Biology, University of Bari, Italy. g.lapiana@biologia.uniba.it
Abstract:
Mitochondria isolated from rat liver, incubated with inhibitors of respiratory Complexes I and III but in the presence of added NADH as a source of reducing equivalents, generate a membrane potential, the extent of which is comparable to that supported by the oxidation of intramitochondrial respiratory substrates. A catalytic amount of exogenously added cytochrome c is required in order for this membrane potential to be observed. Such an experimental approach mimics the early stages of the apoptotic program of mammalian cells. This has been reported to be characterized by the extrusion of the bulk of intermembrane pool of cytochrome c while the mitochondria continue to preserve their membrane potential. The data obtained are consistent with the proposal that the bi-trans-membrane electron transport pathway, activated by the transfer of cytochrome c from mitochondria to the cytosolic compartment, may be directly involved in the generation of the mitochondrial membrane potential at the beginning of the cell death process.
Insights
Isolated rat liver mitochondria generate membrane potential using NADH, mimicking early apoptosis. This process requires cytochrome c and suggests its role in cell death.
Area of Science:
- Biochemistry
- Cell Biology
- Mitochondrial Function
Background:
- Mitochondria play a crucial role in cellular respiration and apoptosis.
- The mitochondrial membrane potential is vital for ATP production and cell death signaling.
- Cytochrome c release from mitochondria is a key event in apoptosis.
Purpose of the Study:
- To investigate the role of cytochrome c in maintaining mitochondrial membrane potential during early apoptosis.
- To explore the mechanism of mitochondrial membrane potential generation in the presence of respiratory inhibitors and exogenous NADH.
Main Methods:
- Isolation of mitochondria from rat liver.
- Incubation of mitochondria with inhibitors of respiratory Complexes I and III.
- Addition of NADH as a source of reducing equivalents.
- Addition of exogenous cytochrome c to observe its effect on membrane potential.
Main Results:
- Mitochondria generated a significant membrane potential when supplied with NADH, even with respiratory chain inhibitors.
- A catalytic amount of exogenous cytochrome c was essential for observing this membrane potential.
- The observed membrane potential was comparable to that generated by endogenous substrates.
- These findings mimic the early apoptotic state where mitochondria retain membrane potential despite cytochrome c extrusion.
Conclusions:
- The study supports the hypothesis that a bi-trans-membrane electron transport pathway involving cytochrome c contributes to mitochondrial membrane potential generation during early apoptosis.
- Extrusion of cytochrome c to the cytosol may activate this pathway, linking mitochondrial function to cell death initiation.