Charges, currents, and potentials in ionic channels of one conformation

Area of Science:

• Biophysics
• Computational Biology
• Physical Chemistry

Background:

• Ionic channels are crucial for biological processes.
• Understanding ion flux dynamics is key to cellular function.
• Existing models often simplify channel properties.

Purpose of the Study:

• To analyze ionic channel flux using Poisson-Nernst-Planck (PNP) theory.
• To model channel protein as a fixed, non-uniform distribution of permanent charge.
• To investigate the interplay of permanent, mobile, and induced charges on ion transport.

Main Methods:

• Applied PNP theory to model ion flux through a channel.
• Defined three charge types: permanent, mobile (free), and induced (polarization).
• Derived boundary conditions and solved the system for two-ion bathing solutions.

Main Results:

• The model predicts a built-in Donnan potential due to permanent charge.
• Visualized distributions of potential, ion concentration, and charge types.
• Demonstrated complex flux behaviors, including energy barriers and wells, arising from charge dynamics.
• Showed that these phenomena vary with experimental conditions, independent of channel conformation.

Conclusions:

• The PNP theory, with fixed protein charge, can explain complex ionic channel behavior.
• Mobile and induced charges significantly influence potential and energy landscapes within the channel.
• Computed energy barriers and binding phenomena are emergent properties, not assumed, offering insights into channel gating and ion selectivity.