Sodium Channel Na_v1.6 Expression in Painful and Non-Painful Human Teeth

The human dental pulp is a rich source of pain fibers and represents a valuable model to study peripheral pain mechanisms. We are using this model to evaluate changes in sodium channel (NaCh) expression since changes are implicated in the generation of pain states. Previous studies have shown increased Na_v1.7 expression at nodes of Ranvier in painful pulp samples, yet the expression of the major nodal isoform, Na_v1.6, has not been evaluated. Objective: Quantitative evaluation of nodal Na_v1.6 expression in pulp from non-painful erupted wisdom teeth compared to painful molars with irreversible pulpitis and moderate-severe/spontaneous pain (n=10 each group). Methods: Pulpal sections from both groups were identically processed and stained with the indirect immunofluorescence method using antibodies against human-specific Na_v1.6 and caspr (paranodal protein to identify nodes of Ranvier). Confocal microscopy was used to obtain Z-stack images of coronal axon bundles in non-painful samples and of bundles surrounded by inflammatory cells in painful samples. Na_v1.6 expression was evaluated within caspr-identified nodal sites that were classified as either typical (normal morphology) or atypical (split or hemi-nodes) using ImageJ software. Results: While no differences were seen between the two groups in % of nodes with Na_v1.6, or in staining intensity or size of nodal accumulations, the density of atypical nodes was significantly increased within painful samples (37.5%±6.2% vs. 5.0%±1.3%; p<0.0001). Conclusion: The expression of Na_v1.6 in atypical clusters coincides with the increased expression of other sodium channel isoforms (e.g. Na_v1.7, Na_v1.8 ) in such sites that we have seen in other studies. We suggest that the mixture of isoforms in atypical sites may contribute to the generation of spontaneous pain associated with irreversible pulpitis.

Support: NIDCR Grant #DE015576/M.A.Henry