Diversity of expression of the sensory neuron-specific TTX-resistant voltage-gated sodium ion channels SNS and SNS2

The differential distribution of two tetrodotoxin resistant (TTXr) voltage- gated sodium channels SNS (PN3) and SNS2 (NaN) in rat primary sensory neuro ns has been investigated. Both channels are sensory neuron specific with SN S2 restricted entirely to those small dorsal root ganglion (DRG) cells with unmyelinated axons (C-fibers). SNS, in contrast, is expressed both in smal l C-fiber DRG cells and in 10% of cells with myelinated axons (A-fibers). A ll SNS expressing A-fiber cells are Trk-A positive and many express the van illoid-like receptor VRL1. About half of C-fiber DRG neurons express either SNS or SNS2, and in most, the channels are colocalized. SNS and SNS2 are f ound both in NGF-responsive and GDNF-responsive C-fibers and many of these cells also express the capsaicin receptor VR1. A very small proportion of s mall DRG cells express either only SNS or only SNS2. At least four differen t classes of A- and C-fiber one neurons exist, therefore, with respect to e xpression of these sodium channels.