The Roles of ID, IA and IK in the Electrophysiological Functions of Small-Diameter Rat Trigeminal Ganglion Neurons

The Kv currents are divided into three different K+ currents, such as slow inactivating transient K+ current (ID), fast inactivating transient K+ current (IA) and dominant sustained K+ current (IK), in small-diameter rat trigeminal ganglion (TG) neurons. The concentration of α-DTX (an ID blocker) to evoke the maximal inhibition of IA was 0.1 μM, and this concentration caused a 20 % inhibition of IA and increased the number of action potentials. Irrespective of the presence of 0.1 μM α-DTX, the application of 0.5 mM 4-AP (an IA blocker) caused a 51 % inhibition of IA and increased the number of action potentials. The responses were associated with the decreases in the resting membrane potential (RMP) and duration of depolarization phase of action potential (DDP). The application of 2 mM tetraethylammonium (TEA, an IK blocker) produced a 55 % inhibition of IK. Irrespective of the presence of both ID and IA blockers, the IK was the predominant K+ current. The prolongation of duration of action potential was usually observed following TEA treatment, suggesting that IA and IK had independent effects regulating the intrinsic firing properties of the action potential number and timing, respectively. Furthermore, the response characteristics of action potentials in the presence of both 4-AP and TEA resemble those of TG neurons in rats following chronic constriction nerve injury of the infraorbital nerve as well as after inferior alveolar nerve section. Thus, reducing effects of both IA and IK may be useful to investigate the mechanism of allodynia.