Membrane potential and surface potential in mitochondria. Binding of a cationic spin probe

Area of Science:

• Biophysics
• Mitochondrial Physiology
• Membrane Potential Studies

Background:

• Cationic spin probes are used to study membrane properties.
• Mitochondrial membrane potential is crucial for cellular energy production.
• Understanding probe interactions with mitochondria is key for accurate measurements.

Purpose of the Study:

• To investigate the interaction of the cationic spin probe Cat12 with mitochondria.
• To determine how salt concentration, pH, and ATP energization affect probe binding.
• To evaluate Cat12's suitability for measuring mitochondrial surface potential.

Main Methods:

• Electron Paramagnetic Resonance (EPR) spectroscopy was used to monitor the spin probe.
• Experiments were conducted on intact mitochondria, mitoplasts, and submitochondrial particles.
• Varying salt concentrations, pH levels, and ATP addition were employed.

Main Results:

• Mitochondrial membranes exhibit a negative surface potential (-10 to -15 mV at pH 7.0).
• ATP energization significantly reduced Cat12 signals in intact mitochondria and mitoplasts.
• ATP's effect was abolished in submitochondrial particles, indicating dependence on membrane potential.

Conclusions:

• Mitochondrial membrane potential formation drives Cat12 uptake and internal binding.
• This binding broadens the EPR signal, complicating surface potential measurements.
• Cat12 is not suitable for measuring surface potential in energized mitochondria.