Localization of the tetrodotoxin-resistant sodium channel NaN in nociceptors.

Tetrodotoxin-resistant sodium currents contribute to the somal and axonal sodium currents of small diameter primary sensory neurons, many of which are nociceptive. NaN is a recently described tetrodotoxin-resistant sodium channel expressed preferentially in IB4-labeled dorsal root ganglion (DRG) neurons. We employed an antibody raised to a NaN specific peptide to show that NaN is preferentially localized along axons of IB4-positive unmyelinated fibers in the sciatic nerve and in axon terminals in the cornea. NaN immunoreactivity was also found at some nodes of Ranvier of thinly myelinated axons of the sciatic nerve, where it was juxtaposed to Kv1.2 potassium channel immunoreactivity. This distribution of NaN is consistent with a role for NaN sodium channels in nociceptive transmission.