Voltage-gated Na+ channels (NaV) are essential for the generation of action potentials and for cell excitability.1 NaV channels are activated in response to depolarization and selectively allow flow of Na+ ions. To date, nine NaV α subunits have been cloned and named NaV1.1-1.9. 2-3 The NaV channels are classified into two groups according to their sensitivity to tetrodotoxin (TTX): TTX-sensitive and TTX-resistant channels.4-5 Expression of the α subunit isoform is developmentally and tissue specific.
Two TTX-resistant NaV channels are expressed in dorsal root ganglion (DRG) neurons, NaV1.8 and NaV1.9. The NaV1.8 channel (also called SNS, SCN10A and PN3) is mainly expressed in small-diameter DRG neurons.4-6 TTX-resistant channels have been suggested to play an important role in nociceptive transmission.
Recently, involvement of NaV1.8 in multiple sclerosis (MS) was suggested due to up-regulation of both, mRNA and protein, in Purkinje cells of MS patients and also in animal models.6
