Discrimination between two steps in the mitochondrial permeability transition process

Area of Science:

• Mitochondrial physiology
• Biochemistry
• Cell biology

Background:

• A lag phase exists between inducers and mitochondrial permeability transition pore opening.
• Understanding this lag phase is crucial for comprehending mitochondrial function and dysfunction.

Purpose of the Study:

• To investigate the molecular events occurring during the lag phase of mitochondrial permeability transition.
• To identify the early steps preceding pore opening and membrane permeabilization.

Main Methods:

• Utilized hematoporphyrin-labeled mitochondria to monitor pore conformation via fluorescence anisotropy.
• Assessed membrane permeabilization by observing matrix swelling.
• Measured membrane depolarization to track proton permeation.

Main Results:

• Hematoporphyrin fluorescence anisotropy changes preceded membrane depolarization and matrix swelling.
• These anisotropy changes indicate sensing of the pore in a closed state.
• Acidic matrix pH and cyclosporin A inhibited the observed structural remodeling.

Conclusions:

• Mitochondrial permeability transition is a multi-step process regulated by pore component conformational changes.
• Early structural remodeling of mitochondrial domains precedes pore opening.
• Cyclosporin A and matrix pH significantly influence the transition process.