Journal
JOURNAL OF NEUROPHYSIOLOGY
Volume 97, Issue 3, Pages 1931-1940Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/jn.00933.2006
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- NINDS NIH HHS [NS-044163] Funding Source: Medline
- BLRD VA [I01 BX000386] Funding Source: Medline
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Pyramidal neurons from layers II/III of somatosensory and motor cortex express multiple Kv1 alpha-subunits and a current sensitive to block by alpha-dendrotoxin ( alpha-DTX). We examined functional roles of native Kv1 channels in these cells using current-clamp recordings in brain slices and current- and voltage-clamp recordings in dissociated cells. alpha-DTX caused a significant negative shift in voltage threshold for action potentials ( APs) and reduced rheobase. Correspondingly, a ramp-voltage protocol revealed that the alpha-DTX-sensitive current activated at subthreshold voltages. AP width at threshold increased with successive APs during repetitive firing. The steady-state threshold width for a given firing rate was similar in control and alpha-DTX, despite an initially broader AP in alpha-DTX. AP voltage threshold increased similarly during a train of spikes under control conditions and in the presence of alpha-DTX. alpha-DTX had no effect on input resistance or resting membrane potential and modest effects on the amplitude or width of a single AP. Accordingly, experiments using AP waveforms ( APWs) as voltage protocols revealed that alpha-DTX-sensitive current peaked late during the AP repolarization phase. Application of alpha-DTX increased the rate of firing to intracellular current injection and increased gain ( multiplicative effects), but did not alter spike-frequency adaptation. Consistent with these findings, voltage-clamp experiments revealed that the proportion of outward current sensitive to alpha-DTX was highest during the interval between two APWs, reflecting slow deactivation kinetics at -50 mV. Finally, alpha-DTX did not alter the selectivity of pyramidal neurons for DC versus time-varying stimuli.
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