Differential expression of three distinct potassium currents in the ventral cochlear nucleus

In the ventral cochlear nucleus (VCN), neurons transform information from auditory nerve fibers into a set of parallel ascending pathways, each emphasizing different aspects of the acoustic environment. Previous studies have shown that VCN neurons differ in their intrinsic electrical properties, including the K+ currents they express. In this study, we examine these K+ currents in more detail using whole cell voltage-clamp techniques on isolated VCN cells from adult guinea pigs at 22degreesC. Our results show a differential expression of three distinct K+ currents. Whereas some VCN cells express only a high-threshold delayed-rectifier-like current (I-HT), others express I-HT in combination with a fast inactivating current (I-A) and/or a slow-inactivating low-threshold current (I-LT). I-HT, I-LT, and I-A, were partially blocked by 1 mM 4-aminopyridine. In contrast, only I-LT was blocked by 10-100 nM dendrotoxin-I. A surprising finding was the wide range of levels of I-LT, suggesting I-LT is expressed as a continuum across cell types rather than modally in a particular cell type. I-A, on the other hand, appears to be expressed only in cells that show little or no I-LT, the Type I cells. Boltzmann analysis shows I-HT activates with 164 +/- 12 (SE) nS peak conductance, -14.3 +/- 0.7 mV half-activation, and 7.0 +/- 0.5 mV slope factor. Similar analysis shows I-LT activates with 171 +/- 22 nS peak conductance, -47.4 +/- 1.0 mV half-activation, and 5.8 +/- 0.3 mV slope factor.