A-type voltage-gated K⁺ currents influence firing properties of isolectin B₄-positive but not isolectin B₄-negative primary sensory neurons

Voltage-gated K⁺ channels (Kv) in primary sensory neurons are important for regulation of neuronal excitability. The dorsal root ganglion (DRG) neurons are heterogeneous, and the types of native Kv currents in different groups of nociceptive DRG neurons are not fully known. In this study, we determined the difference in the A-type Kv current and its influence on the firing properties between isolectin B₄ (IB₄)-positive and -negative DRG neurons. Whole cell voltage- and current-clamp recordings were performed on acutely dissociated small DRG neurons of rats. The total Kv current density was significantly higher in IB₄-positive than that in IB₄-negative neurons. Also, 4-aminopyridine (4-AP) produced a significantly greater reduction in Kv currents in IB₄-positive than in IB₄-negative neurons. In contrast, IB₄-negative neurons exhibited a larger proportion of tetraethylammonium-sensitive Kv currents. Furthermore, IB₄-positive neurons showed a longer latency of firing and required a significantly larger amount of current injection to evoke action potentials. 4-AP significantly decreased the latency of firing and increased the firing frequency in IB₄-positive but not in IB₄-negative neurons. Additionally, IB₄-positive neurons are immunoreactive to Kv1.4 but not to Kv1.1 and Kv1.2 subunits. Collectively, this study provides new information that 4-AP-sensitive A-type Kv currents are mainly present in IB₄-positive DRG neurons and preferentially dampen the initiation of action potentials of this subpopulation of nociceptors. The difference in the density of A-type Kv currents contributes to the distinct electrophysiological properties of IB₄-positive and -negative DRG neurons.