The frequency response of ion channel currents in a combined diffusion and barrier type model

The dynamics of ion transport through channels has been calculated using a small signal analysis method. This is applied to the equations describing the rates of ion transport through channels represented by a pair of entrance barriers in series with an interior diffusion regime. The responses to combinations of applied DC and AC electric fields, assumed to be constant in space, have been calculated and are represented as complex admittances. On examining the admittance properties, the channel is found to behave electrically as a double reactance network, which can give rise to resonance effects. A further interesting property is the limiting slope of the current amplitude at high frequencies, which is found to exhibit an f-2/3 dependence for small entrance barriers and an f-1 dependence for large entrance barriers. This points to the possibility of using noise measurements for drawing conclusions about ion transport properties through channels.