Down-regulation of Kv4.3 channels and a-type K currents in V2 trigeminal ganglion neurons of rats following oxaliplatin treatment.

Chemotherapy drugs such as oxaliplatin can increase nociceptive neuron excitability to result in neuropathic pain in orofacial and other regions in patients following chemotherapy. However, mechanisms underlying chemotherapy-induced increases of nociceptive neuron excitability are not fully understood. Kv4.3 channels are voltage-gated K channels mediating A-type K (I) currents to control neuronal excitability. In the present study, we examined Kv4.3 channel expression on trigeminal neurons that innervate orofacial regions (V2 TG neurons) of rats using immunostaining method. We showed that strong Kv4.3 immunoreactivity (Kv4.3-ir) was present mainly in small-sized V2 TG neurons. The numbers of Kv4.3-ir positive V2 TG neurons were significantly reduced in oxaliplatin-treated rats, suggesting down-regulation of Kv4.3 channel expression on V2 TG neurons by the chemotherapy drug. Patch-clamp recordings from acutely dissociated rat V2 TG neurons showed that almost all nociceptive-like V2 TG neurons displayed I currents with slow inactivation kinetics. The amplitudes of I currents were significantly reduced in these nociceptive-like V2 TG neurons of oxaliplatin-treated group. Furthermore, we found that the excitability of nociceptive-like V2 TG neurons was significantly higher in the oxaliplatin-treated group than in the control group. These findings raise a possibility that down-regulation of Kv4.3 channels and I currents in nociceptive V2 TG neurons is an underlying mechanism of oxaliplatin-induced orofacial neuropathic pain.