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J Neurophysiol (July 7, 2004). doi:10.1152/jn.00431.2004
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Submitted on April 27, 2004
Accepted on July 2, 2004

HIGH THRESHOLD, Kv3-LIKE POTASSIUM CURRENTS IN MAGNOCELLULAR NEUROSECRETORY NEURONS AND THEIR ROLE IN SPIKE REPOLARIZATION

Talent Shevchenko, Teruyama Ryoichi, and William E. Armstrong*

* To whom correspondence should be addressed. E-mail: warmstrong{at}utmem.edu.

We identified Kv3-like high threshold K+ currents in hypothalamic supraoptic neurons using whole-cell recordings in hypothalamic slices and in acutely dissociated neurons. Tetraethylammonium (TEA) sensitive currents (<1 mM TEA) evoked from -50 mV were characterized by a large component that inactivated in10-30 ms, and a smaller, persistent component that inactivated in 1-2 s. I/V relations in dissociated neurons revealed TEA-subtracted currents with a slope and voltage-dependence consistent with the presence of Kv3-like channels. In slices, tests with 0.01-0.7 mM TEA produced an IC50 of 200-300 nM for both fast and persistent currents. The fast transient current was similar to currents associated with the expression Kv3.4 subunits, as it was sensitive to BDS-I (100 nM). The persistent TEA-sensitive current appeared similar to those due to Kv3.1/3.2 subunits. Although qualitatively similar, oxytocin (OT) and vasopressin (VP) neurons in slices differed in the stronger presence of persistent current in VP neurons. In both cell types, the IC50 for TEA-induced spike broadening was similar to that observed for current suppression in voltage clamp. However, TEA had a larger effect on the spike width of VP compared to OT neurons. Immunochemical studies revealed a stronger expression of the Kv3.1b {alpha}-subunit in VP neurons, which may be related to the greater importance of this current type in VP spike repolarization. Because OT and VP neurons are not considered fast firing, but do exhibit frequency- and calcium-dependent spike broadening, Kv3-like currents may be important for maintaining spike width and calcium influx within acceptable limits during repetitive firing.




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