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J Neurophysiol 85: 472-475, 2001;
0022-3077/01 $5.00
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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

Essential Role of a Fast Persistent Inward Current in Action Potential Initiation and Control of Rhythmic Firing

R. H. Lee and C. J. Heckman

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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