K+ conduction phenomena applicable to the low frequency impedance of squid axon.

The observation of peaking in power spectra of K current noise in squid axon (Fishman, H.M, Moore, L.E., Poussart, D.J.M. 1975, J. Membrane Biol. 24:305) led to the calculation of low frequency K conduction feature in the impedance (admittance) which was confirmed (Fishman, H.M., Poussart, D.J.M., Moore, L.E. & Siebenga, E., 1977, J. Membrane Biol. 32:255). This paper analyzes two physical phenomena, one within and the other outside of the excitable membrane, that might account for the low frequency impedance (admittance) feature. The accumulation of potassium ions in a space outside the axon in conjunction with diffusion through the Schwann cell layer produces a low-frequency mode that is similar in some respects to that observed experimentally. Alternatively, a hypothetical inactivation process, with a voltage-dependent time constant, associated with conduction in potassium channels gives a better account of the data. Either or both of these phenomena could be involved in producing the low-frequency impedance behavior in the squid axon.