Relaxation spectra of potassium channel noise from squid axon membranes.

Power density spectra of electrical fluctuations in potential and current (during voltage clamp) in the steady state, measured from electrically isolated patches of squid axon membrane, contain a noise component that is of the form [1 + (f/f(c))(2)](-1). For potential and temperature changes f(c) = (2pitau(n))(-1), where tau(n) is the Hodgkin-Huxley relaxation time for the potassium channel. These and other data strongly suggest that this noise is due to the potassium ion passage process in the membrane. Furthermore, by comparison of the values of f(c) from relaxation spectra of membrane channel noise with those from calculated (Hodgkin-Huxley equations) power spectra, it is possible to relate and compare channel models that previously could only be applied to macroscopic potassium conductance data. An initial result of this comparison suggests that a two-state (open-closed) conductance model, which is based upon a literal interpretation of the Hodgkin-Huxley equations, is not likely to be correct.