On the ionic displacement current in lipid bilayer membranes

Area of Science:

• Biophysics
• Physical Chemistry
• Membrane Science

Background:

• The constant field approximation is widely used for modeling ion transport across membranes.
• However, its applicability to time-dependent signals requires further investigation.
• Understanding transient currents is crucial for characterizing membrane properties.

Purpose of the Study:

• To amend the constant field approximation for time-dependent signals.
• To investigate the role of ionic displacement current in ion transport.
• To analyze the effects of ion adsorption on membrane current transients.

Main Methods:

• Mathematical modeling of ion transport across a membrane with a rectangular potential profile.
• Analysis of time-dependent current and admittance after a voltage step.
• Comparison with existing theoretical frameworks (Cole, 1965; Andersen and Fuchs, 1975).

Main Results:

• The constant field approximation requires an additional ionic displacement current term for time-dependent signals.
• In the absence of adsorption, this current has a characteristic time of microseconds.
• Strong adsorption leads to a slower exponential transient, supporting the pseudostationary approximation.

Conclusions:

• The amended constant field approximation accurately describes time-dependent ion transport.
• Ionic displacement current is a key factor in short-time transients.
• Ion adsorption significantly alters transient behavior, necessitating specific modeling approaches.