Protective effect of magnesium and potassium ions on the permeability of the external mitochondrial membrane.

This research explores the protective influence of magnesium and potassium ions on the permeation of external mitochondrial membrane, asserting that the membrane retains its selective permeability in isotonic and hypotonic medium, thereby keeping exogenous cytochrome c molecules from permeating, even when subjected to stress conditions.

Introduction

The study aims to extend the understanding of how the outer membrane of mitochondria (MOM) behaves in isotonic and hypotonic conditions, specifically exploring the permeability to exogenous cytochrome c (cyto-c) molecules. It also investigates the effect of magnesium and potassium ions on this process.

Methods and Observations

• In isotonic medium (250 mM sucrose), it was observed that exogenous cyto-c molecules could not permeate the MOM. As a result, these molecules could not accept electrons from the sulfite/cyto-c oxido-reductase (Sox) present in the intermembrane space.
• Even when the mitochondria were solubilized, this action continued to be blocked, indicating that the mitochondria remained impermeable to added cyto-c in an isotonic medium.
• In a significantly hypotonic medium (25 mM sucrose), interestingly, the same non-permeability persisted, despite the release of Sox and adenylate kinase into the medium.
• The study noted an increase in the succinate/exogenous cyto-c reductase activity when the osmolarity of the medium decreased but it remained unaffected by the addition of trypsin, an enzyme that breaks down proteins.

Role of Magnesium and Potassium Ions

• Magnesium and potassium ions, when present in a hypotonic medium, demonstrated a protective effect on releasing enzymes and on the reactivity of cyto-c as electron acceptor from both sulfite and succinate.
• The findings are congruent with the idea that the MOM maintains its identity and remains impermeable to exogenous cyto-c.

Conclusion

The research supports the claim, substantiated by previous studies, that in an isotonic medium, the exogenous NADH/cyto-c electron transport system is catalyzed by intact mitochondria that remain impermeable to added cyto-c. Essentially, the data strengthens the understanding that the mitochondrial external membrane can remain selectively permeable under different conditions contributing to cellular stability and function.