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Biophysical Journal 73: 179-185 (1997)
© 1997 the Biophysical Society

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Tail currents in the myelinated axon of Xenopus laevis suggest a two-open-state Na channel.

F Elinder and P Arhem

Nobel Institute for Neurophysiology, Karolinska Institutet, Stockholm, Sweden.

ABSTRACT

Na tail currents in the myelinated axon of Xenopus laevis were measured at -70 mV after steps to -10 mV. The tail currents were biexponential, comprising a fast and a slow component. The time constant of the slow tail component, analyzed in the time window 0.35-0.50 ms, was independent of step duration, and had a value of 0.23 ms. The amplitude, extrapolated back to time 0, varied, however, with step duration. It reached a peak after 0.7 ms and inactivated relatively slowly (at 2.1 ms the absolute value was reduced by approximately 30%). The amplitude of the fast component, estimated by subtracting the amplitude of the slow component from the calculated total tail current amplitude, reached a peak (three times larger than that of the slow component) after 0.5 ms and inactivated relatively fast (at 2.1 ms it was reduced by approximately 65%). The results were explained by a novel Na channel model, comprising two open states bifurcating from a common closed state and with separate inactivating pathways. A voltage-regulated use of the two pathways explains a number of findings reported in the literature.




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Y.-K. The, J. Fernandes, M. O. Popa, A. K. Alekov, J. Timmer, and H. Lerche
Modeling of Single Noninactivating Na+ Channels: Evidence for Two Open and Several Fast Inactivated States
Biophys. J., May 15, 2006; 90(10): 3511 - 3522.
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Copyright © 1997 by the Biophysical Society.