The tetrodotoxin-resistant (TTX-R) voltage-gated sodium channel Nav1.8 is predominantly expressed in peripheral afferent neurons, but in case of neuronal injury an ectopic and detrimental expression of Nav1.8 occurs in neurons of the CNS. In CNS neurons, Nav1.2 and Nav1.6 channels accumulate at the axon initial segment, the site of the generation of the action potential, through a direct interaction with the scaffolding protein ankyrin G (ankG). This interaction is regulated by protein kinase CK2 phosphorylation. In this study, we quantitatively analyzed the interaction between Nav1.8 and ankG. GST pull-down assay and surface plasmon resonance technology revealed that Nav1.8 strongly and constitutively interacts with ankG, in comparison to what observed for Nav1.2. An ion channel bearing the ankyrin-binding motif of Nav1.8 displaced the endogenous Nav1 accumulation at the axon initial segment of hippocampal neurons. Finally, Nav1.8 and ankG co-localized in skin nerves fibers. Altogether, these results indicate that Nav1.8 carries all the information required for its localization at ankG micro-domains. The constitutive binding of Nav1.8 with ankG could contribute to the pathological aspects of illnesses where Nav1.8 is ectopically expressed in CNS neurons.
The peripheral voltage-gated sodium channel Nav1.8 can be abnormally expressed in central nervous system (CNS) neurons in cases of neuronal injury. We here demonstrated that Nav1.8 binds strongly and constitutively to the scaffolding protein ankyrin G. This indicates that Nav1.8 concentrates at the ankyrin G micro-domains and could disturb the electrophysiological signature of CNS neurons where it is ectopicaly expressed.