Sodium channel Nav1.8 immunoreactivity in human dental pulp

METHODS: Human tooth pulp was extracted from teeth harvested from a total of twenty-two patients (fourteen without dental pain, eight patients with dental pain). Using specific immunogens for Nav1.8 (K107 Coward et al, 2000)) - we studied Nav1.8 - immunoreactivity in relation to the neuronal marker neurofilament (clone 2F11, Dako Cambridge UK) in human dental pulp.

RESULTS: Large numbers of nerve fibres within tooth pulp were immunoreactive for neurofilament. A subset of these fibres were immunoreactive for Nav1.8, with a significant difference on image analysis between non-painful and painful groups (median (range) Nav1.8 to Neurofilament % area ratio, non-painful 0.059 (0.006- 0.24) and painful 0.265 (0.13-0.5); the Nav1.8 to neurofilament % area ratio was significantly elevated in the painful pulps compared with the non painful samples (P = 0.0019, Mann Whitney test).

DISCUSSION Here we describe, for the first time, the immunolocalisation of the voltage-gated sodium channel Nav1.8 in painful and painless human dental pulp. Our studies confirmed the presence of large numbers of small and larger calibre nerve fibres that were strongly immunoreactive to the neuronal marker neurofilament, similar to previous reports (Maeda et al., 1986). The most intense Nav1.8- immunoreactivity was observed in very fine fibres, which may represent the small diameter nociceptors.

CONCLUSION: The regulation and pathophysiological role of Nav1.8 sodium channels deserves further investigation in trigeminal nerve pathological states.