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Biophys J, August 2001, p. 895-904, Vol. 81, No. 2
Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104 USA
We present a model for the action of 4-aminopyridine
(4AP) on K channels. The model is closely based on the gating current studies of the preceding paper and has been extended to account for
ionic current data in the literature. We propose that 4AP, like
tetraethylammonium ion and other quaternary ammonium ions, enters and
leaves the channel only when the activation gate is open, a proposal
that is strongly supported by the literature. Once in the open channel,
4AP's major action is to bias the activation gate toward the closed
conformation by approximately the energy of a hydrogen bond. S4 segment
movement, as reflected in gating currents, is almost normal for a
4AP-occupied channel; only the final opening transition is affected.
The model is qualitatively the same as the one used for many years to
explain the action of quaternary ammonium ions.
Biophys J, August 2001, p. 895-904, Vol. 81, No. 2
© 2001 by the Biophysical Society 0006-3495/01/08/895/10 $2.00
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