A-Type Voltage-Gated K Currents Influence Firing Properties of Isolectin B4-Positive but Not -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 B 4 (IB 4)-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 IB 4-positive than IB 4-negative neurons. Also, 4-aminopyridine (4-AP) produced a significantly greater reduction in Kv currents in IB 4-positive than IB 4-negative neurons. In contrast, IB 4-negative neurons exhibited a larger proportion of tetraethylammonium-sensitive Kv currents. Furthermore, IB 4-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 IB 4-positive but not IB 4-negative neurons. Additionally, IB 4-positive neurons are immunoreactive to Kv1.4 but not Kv1.1 and Kv1.2 subunits. Collectively, this study provides new information that 4-AP-sensitive A-type Kv currents are mainly present in IB 4-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 contribute to the distinct electrophysiological properties of IB 4-positive and-negative DRG neurons.