Hydration Forces Dominate Surface Charge Dependent Lipid Bilayer Interactions under Physiological Conditions

Area of Science:

• Biophysics
• Surface Science
• Electrochemistry

Background:

• Lipid bilayer interactions are fundamental to cellular processes like intracellular transport.
• Surface charging, driven by ion adsorption/desorption on lipid headgroups, influences electrostatic and hydration forces between bilayers.
• Understanding these forces is key to comprehending biological functions.

Purpose of the Study:

• To directly measure lipid bilayer interactions during charge modulation.
• To quantify the influence of polarization and ion concentration on hydration and electric double layer forces.
• To elucidate the mechanisms governing bilayer interactions under physiological conditions.

Main Methods:

• Utilized a symmetrically polarized electrochemical three-mirror interferometer surface forces apparatus for direct measurement.
• Investigated concentration-dependent ion adsorption and desorption on lipid headgroups.
• Analyzed surface potential-dependent forces, including hydration and electric double layer forces.

Main Results:

• Demonstrated that exponential hydration layer interactions accurately describe surface potential-dependent forces at high salt concentrations.
• Quantified cation adsorption/desorption effects on hydration and electric double layer forces.
• Showed that inner Helmholtz charge regulation exclusively dominates electric double layers of lipid bilayers under physiological conditions.

Conclusions:

• Lipid bilayer interactions are significantly modulated by surface charge and ion concentration.
• Charge regulation via ion adsorption is a primary mechanism controlling bilayer forces in biological systems.
• These findings provide a basis for understanding how charge modulation acts as biological triggers for cellular function and signaling.