Linear kinetic analysis of membrane ion channels from low-frequency admittance determinations

In most kinetic analyses of ion channel conduction in biological membranes, transitions between channel states are assumed to be adequately described by a Markovian process. Under this assumption kinetic descriptions are also available directly by fitting linear models of the membrane driving-point function to the membrane low-frequency (1-5000 Hz) complex admittance, determined rapidly during voltage clamps of the membrane. An expression for the complex admittance of an axon membrane is obtained by linearizing the Hodgkin-Huxley equations and by Laplace transformation. Ideally, it is discussed to fit the resulting equation to complex conductance data. However, because of membrane capacitance and nonspecific leakage conductance, this cannot be done without first unfolding capacitance and leakage from the membrane complex admittance. This is done by first obtaining a membrane admittance with all ion conductances turned off.<>