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The Journal of Neurophysiology Vol. 85 No. 1 January 2001, pp. 472-475
Copyright ©2001 by the American Physiological Society
RAPID COMMUNICATION
Departments of Physiology and Physical Medicine and Rehabilitation, Northwestern University Medical School, Chicago, Illinois 60611
Lee, R. H. and
C. J. Heckman.
Essential Role of a Fast Persistent Inward Current in Action
Potential Initiation and Control of Rhythmic Firing. J. Neurophysiol. 85: 472-475, 2001. In spinal
motoneurons in an in vivo preparation, we investigated the relationship
between a fast persistent inward current located in or near the soma
and the capacity of these cells to fire rhythmically. The fast
persistent current could be markedly reduced by prolonged
depolarization. Modest reductions resulted in profound changes in the
slope of the frequency-current relationship. At greater reduction
levels, rhythmic firing failed and could not be restored by increasing
injected current. However, fully formed spikes still occurred in a
slow, uncoordinated fashion, suggesting that the fast inactivating
Na+ currents that generate the spike itself
remained unchanged. Consequently, the fast persistent inward current,
which may be primarily generated by persistent
Na+ channels, appears to be essential for
initiation of spikes during rhythmic firing. Additionally, it appears
that the fast persistent current plays a major role in setting the
frequency-current gain.
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