Diffusion potential cascade. Convenient detection of transferable membrane pores

Area of Science:

• Biophysics
• Membrane Biology
• Liposome Research

Background:

• Valinomycin creates stable potassium diffusion potentials in multilamellar liposomes.
• Gramicidin acts as a nonselective channel to collapse these potentials.

Purpose of the Study:

• To investigate the complex kinetics of gramicidin-mediated collapse of liposome membrane potential.
• To establish a method for detecting and characterizing membrane pores using voltage-sensitive dyes.

Main Methods:

• Utilized multilamellar liposomes with valinomycin-mediated K+ diffusion potentials.
• Introduced gramicidin to induce potential collapse and analyzed the kinetics.
• Employed 3,3'-diethylthiodicarbocyanine iodide [diS-C2-(5)] as a voltage-sensitive fluorescent dye.

Main Results:

• Identified key processes in potential collapse: gramicidin binding, dimerization, ion flux, and bilayer-to-bilayer propagation.
• Determined that gramicidin dissociation is rate-limiting at high concentrations, while ion flux limits at low concentrations.
• Observed voltage dependence in K+ gradient collapse at low gramicidin concentrations.

Conclusions:

• The study provides a detailed kinetic model for gramicidin-mediated membrane potential collapse in liposomes.
• Demonstrated a simple, dye-based method for detecting and characterizing membrane pores.
• Highlights the influence of liposome composition, size, and ion concentrations on the process.