Differential expression of tetrodotoxin-resistant sodium channels NaV1.8 and NaV1.9 in normal and inflamed rats

In an attempt to understand mechanisms underlying peripheral sensitization of primary afferent fibers, we investigated the presence of the tetrodotoxin-resistant Na+ channel subunits Na(v)1.8 (SNS) and Na(v)1.9 (SNS2) on axons in digital nerves of normal and inflamed rat hindpaws. In normal animals, 14.3% of the unmyelinated and 10.7% of the myelinated axons labeled for the Na(v)1.8 subunit. These percentages significantly increased in 48 h inflamed animals to 22.0% (1.5-fold increase) and 57.5% (6-fold increase) for unmyelinated and myelinated axons, respectively. In normal animals, Na(v)1.9 labeled 9.9% of the unmyelinated and 2.1% of the myelinated axons and following inflammation, the proportion of Na(v)1.9-labeled unmyelinated axons significantly decreased to 3.0% with no change in the proportion of labeled myelinated axons. These data indicate that Na(v)1.8 and Na(v)1.9 subunits are transported to the periphery in normal animals and are differentially regulated during inflammation. The massive increase in Na(v)1.8 expression in myelinated axons suggests that these may contribute to peripheral sensitization and inflammatory hyperalgesia. (C) 2003 Elsevier Ireland Ltd. All rights reserved.