Non-stationary fluctuation analysis of the Na current in myelinated nerve fibers of Xenopus laevis: experiments and stochastic simulations.
Na current fluctuations under voltage-clamp conditions during pulse steps in the potential range from -65 to -30 mV were measured in myelinated nerve fibers of Xenopus laevis. The covariance functions for four consecutive 1 ms intervals were calculated. The time courses of the covariance functions were well fitted with monoexponential functions with time constants between 0.5 and 3 ms, larger at the end of the pulse and larger at more positive potentials. To analyze the underlying channel kinetics we simulated current fluctuations at a step to -35 mV of eight published Na channel models and calculated corresponding covariance functions. None of the models did explain the experimental fluctuation results. We therefore developed a new Na channel model that satisfactorily described the results. Features that distinguished this model from the other tested ones were a slower deactivation rate, and an inactivation transition directly from a closed state.
Elinder
F
F
Department of Neuroscience, The Nobel Institute for Neurophysiology, Karolinska Institutet, SE-171 77 Stockholm, Sweden.
Frankenhaeuser
B
B
Arhem
P
P
D000818:Animals; D007700:Kinetics; D008954:Models, Biological; D009412:Nerve Fibers / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000378:metabolism*; D014982:Xenopus laevis
D015222:Sodium Channels; D012964:Sodium