Outer mitochondrial membrane permeability can regulate coupled respiration and cell survival.

Area of Science:

• Cellular respiration and bioenergetics
• Mitochondrial function and regulation
• Cell survival and apoptosis pathways

Background:

• Efficient exchange of ATP and ADP between the cytosol and mitochondrial matrix is crucial for coupled cellular respiration.
• Growth factor withdrawal in dependent cells disrupts metabolism via impaired ATP/ADP exchange across mitochondrial membranes.

Purpose of the Study:

• To investigate the underlying cause of impaired ATP/ADP exchange upon growth factor withdrawal.
• To elucidate the role of outer mitochondrial membrane permeability in regulating metabolic flux and cell survival.

Main Methods:

• Assessed changes in outer mitochondrial membrane permeability to metabolic anions.
• Correlated permeability changes with the conductance properties of the voltage-dependent anion channel (mitochondrial porin).
• Investigated the role of Bcl-x(L) and Bcl-2 in preventing outer membrane impermeability.
• Monitored metabolic energy accumulation (creatine phosphate) and cytochrome c release.

Main Results:

• Growth factor withdrawal leads to decreased outer mitochondrial membrane permeability, linked to voltage-dependent anion channel closure.
• This loss of permeability causes intermembrane space accumulation of creatine phosphate and can be prevented by Bcl-x(L) and Bcl-2.
• Reversible loss of outer membrane permeability upon growth factor readdition was observed.

Conclusions:

• Regulated outer mitochondrial membrane permeability is critical for maintaining mitochondrial homeostasis and cell survival.
• Persistent outer membrane impermeability triggers apoptosis through cytochrome c release.
• Findings highlight a novel regulatory mechanism in bioenergetics with implications for cell death pathways.