Measurement of Channel Permeability and Conductance

Permeability and conductivity are the main experimental observables of membrane channels. Creative Bioarray is committed to developing a variety of experimental strategies and calculations to help our clients determine the permeability and conductance to quantify the rate of solute crossing the channel, helping to connect molecular dynamics (MD) simulations and experiments quantitatively.

Background

The cell membrane forms a barrier that separates the inside of the cell from the outside and prevents most hydrophilic molecules from passing through. Channels, a large class of transporter proteins, form pores in the membrane that allow specific molecules to pass through. Permeability and conductivity are the main transport properties of membrane channels, and these two phenomenological parameters are commonly used to describe the permeation of ions through the channels. Permeability is often used as a measure of how easily an ion can pass through an open channel across a membrane and can reflect the nature of the interaction of a particular test ion with the channel. Conductance determines the ion current at an applied transmembrane voltage. These two analyses can provide very different but complementary information on the permeation process. Given the available atomic structure of many membrane channels, a variety of all-atom MD simulation methods have been established to calculate their permeability or conductance.

Fig. 1 Snapshots (rendered in VMD⁵³) of the tagged ion and water molecules in CNT1, K⁺ taken from a transition path formed by forward/backward trajectories. (Zhou, 2019)

Our Services

We offer our clients services for measuring and calculating the permeability and conductance of ion channels. Our services include but are not limited to:

• For membrane channels with fast transport kinetics (e.g. membrane channels with large pores), we obtain permeability (conductance) and crossing events directly from straightforward MD simulations at equilibrium or electrochemical potential.
• For channels with small permeabilities or low solute concentrations, capturing spontaneous permeation events would require excessively long simulations. We usually calculate a single solute-free energy profile first, and then further estimate the permeability based on the profile.
• Measurement of ion selectivity.
• Measurement of ion flux. We use appropriate radioisotopes or labeled compounds to measure ion flux or perform measurements under "zero trans" conditions. The flux data we get can be converted into permeability.

Applications

Our scientific services can be applied to the research of many fields related to ion channels.

• Study on the permeation kinetic properties of ions channels
• Study on conductance/permeability relation
• Study on the thermodynamics of ions channels

As a leading service provider in the field of ion channels, Creative Bioarray provides our clients with high-quality measurements of the properties of ion channels including permeability and conductivity through all-atom molecular dynamics simulations, which help our clients to further investigate the permeation process of ions through the channels. If you are interested in our services, please contact us for more details.

Reference

1. Zhou, X.; Zhu, F. Calculating single-channel permeability and conductance from transition paths. Journal of Chemical Information and Modeling, 2019, 59(2): 777-785.