Oxonol VI as an optical indicator for membrane potentials in lipid vesicles

Area of Science:

• Biophysics
• Membrane Biophysics
• Lipid Bilayer Studies

Background:

• Oxonol VI is a voltage-sensitive dye used to probe membrane potential.
• Understanding dye behavior in lipid vesicles is crucial for accurate potential measurements.
• Large unilamellar dioleoylphosphatidylcholine vesicles provide a model system for these studies.

Purpose of the Study:

• To investigate the effect of membrane potential on Oxonol VI fluorescence in lipid vesicles.
• To determine the partitioning behavior of Oxonol VI between membrane and aqueous phases.
• To establish Oxonol VI as a reliable indicator for membrane potential changes.

Main Methods:

• Utilizing large unilamellar dioleoylphosphatidylcholine vesicles.
• Measuring Oxonol VI fluorescence under varying membrane potentials.
• Calibrating fluorescence changes using potassium diffusion potentials and valinomycin.
• Applying a three-capacitor model to describe dye partitioning.

Main Results:

• A significant partition equilibrium of Oxonol VI between lipid and water was observed (partition coefficient ~19,000).
• Inside-positive membrane potentials drive Oxonol VI accumulation into vesicles, increasing fluorescence.
• Voltage-dependent partitioning, not intrinsic dye fluorescence, accounts for the observed signal changes.
• Oxonol VI successfully detected membrane potential changes induced by (Na+ + K+)-ATPase activity.

Conclusions:

• Oxonol VI fluorescence is a reliable indicator of membrane potential in lipid vesicles.
• The observed fluorescence changes are primarily due to voltage-dependent partitioning of the dye.
• Oxonol VI can be used to study ion transport and membrane potential dynamics, such as those involving the (Na+ + K+)-ATPase.