A Model Framework for Ion Channels with Selectivity Filters Based on Non-Equilibrium Thermodynamics.

Area of Science:

• Computational physics
• Biophysics
• Chemical engineering

Background:

• Understanding ion transport in nanopores is crucial for biological systems and nanotechnology.
• Existing models like Poisson-Nernst-Planck (PNP) have limitations in capturing complex phenomena.
• Finite ion size and solvation effects significantly influence ion selectivity and transport.

Purpose of the Study:

• To present a thermodynamically consistent model framework for ion transport in nanopores.
• To extend the classical PNP system by incorporating finite ion size and solvation.
• To accurately model the selectivity filter and predict experimental observations.

Main Methods:

• Developed a continuum model unifying electro-diffusion and selective ion transport.
• Treated the selectivity filter as an embedded domain with adaptable chemical properties and mobility.
• Incorporated finite ion size and solvation effects into the model framework.

Main Results:

• Achieved good agreement with experimental current-voltage (IV) characteristics for an L-type calcium ion channel.
• Successfully captured the anomalous mole fraction effect (AMFE) for varying ion concentrations.
• Demonstrated that surface charge, ion mobility, and available space influence ion currents.

Conclusions:

• Negative charges in the pore are critical for selective transport of divalent over monovalent ions.
• AMFE arises from competition and binding effects in multi-ion environments.
• The flexible model framework is applicable to diverse nanopore systems, including biological and synthetic channels.