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Functional Roles of Kv1 Channels in Neocortical Pyramidal Neurons

¹Department of Anatomy and Neurobiology, University of Tennessee, Memphis, Tennessee; and ²Departments of Neurology and Physiology and Biophysics, University of Washington, Veterans Administration Puget Sound Health Care System, Seattle Washington

Submitted 1 September 2006; accepted in final form 9 January 2007

Pyramidal neurons from layers II/III of somatosensory and motor cortex express multiple Kv1 -subunits and a current sensitive to block by -dendrotoxin (-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. -DTX caused a significant negative shift in voltage threshold for action potentials (APs) and reduced rheobase. Correspondingly, a ramp-voltage protocol revealed that the -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 -DTX, despite an initially broader AP in -DTX. AP voltage threshold increased similarly during a train of spikes under control conditions and in the presence of -DTX. -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 -DTX–sensitive current peaked late during the AP repolarization phase. Application of -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 -DTX was highest during the interval between two APWs, reflecting slow deactivation kinetics at –50 mV. Finally, -DTX did not alter the selectivity of pyramidal neurons for DC versus time-varying stimuli.