Non-linear Conductance, Rectification, and Mechanosensitive Channel Formation of Lipid Membranes

Area of Science:

• Biophysics
• Membrane Biophysics
• Physical Chemistry

Background:

• Lipid bilayers are traditionally viewed as electrical insulators.
• However, evidence suggests they possess conductive properties, exhibiting current steps and rectification similar to protein channels.
• This phenomenon, observed even in symmetric bilayers, requires further investigation.

Purpose of the Study:

• To investigate the conductive properties of lipid bilayers under varying conditions.
• To explore the mechanisms behind observed current-voltage (I-V) relationships, including rectification and discrete conduction steps.
• To determine the role of membrane asymmetry, pressure gradients, and voltage in channel formation.

Main Methods:

• Theoretical modeling of electrostrictive effects and spontaneous polarization in lipid membranes.
• Experimental measurements of I-V relations in lipid membranes formed at patch pipette tips near an aqueous surface.
• Varied experimental conditions by adjusting depth relative to the air/water surface to alter pressure gradients.
• Measurements on black lipid membranes.

Main Results:

• Observed both linear and non-linear I-V profiles in lipid membranes.
• Non-linear conduction consistently showed outward rectification.
• Identified two conductance mechanisms: a constant leak current and voltage-gated pore opening leading to channel-like steps.
• Demonstrated that channel formation is dependent on pressure gradients, indicating mechanosensitivity.
• Observed negative differential conductance (dI/dV < 0) in some non-linear I-V relations.
• Black lipid membranes showed rectification but lacked voltage offset.

Conclusions:

• Lipid bilayers possess intrinsic conductive properties, including voltage-gated and mechanosensitive channel formation.
• Electrostriction and spontaneous polarization, influenced by membrane asymmetry and pressure gradients, play key roles in these phenomena.
• The findings challenge the traditional view of lipid bilayers as purely insulating barriers.