Peripheral neuropathy in diabetes is characterized by a constellation of sensory abnormalities, including numbness, tingling, as well as exacerbated responses to painful and non-painful stimuli. Particular interest has concentrated on voltage-gated sodium (Nav) channels since they play central roles in painful forms of neuropathy in long-term diabetes. However, their possible contributions to the onset of neuropathy are still under investigation. In the current study, we aimed at elucidating the contribution of Nav channels during early hyperglycemia in sensory neurons from the Dorsal Root Ganglion (DRG). We used cultured DRG neurons, maintained in either control (5 mM glucose) or in high glucose media (25 mM) for up to 14 days, and intact DRG tissues from streptozotocin (STZ)-induced hyperglycemic mice (at 1 and 3 months after induction). To study Nav channel function we used whole-cell patch-clamp electrophysiology and biochemical analysis by Western blotting for the detection of Nav subunit expression. Our results indicate that DRG neurons maintained in high glucose showed reduced action potential firing frequency and reduced inward currents. The later was consistent with the downregulation of the tetrodotoxin sensitive (TTX-S) Nav1.3, Nav1.6, and Nav1.7 subunits in intact DRG tissues from one-month STZ-hyperglycemic mice. The Navβ2 subunit, which has been shown to regulate the cell surface expressions of TTX-S Nav channels, also shows reduced expression levels. Interestingly, after three months of STZ-induced hyperglycemia, there was a significant upregulation in the expression level of the TTX-S Nav1.7 subunit, which has been linked to painful forms of neuropathy. Taken together, our data revealed that changes in expression and function of TTX-S Nav subunits take place from the early stage of pathologic hyperglycemia. Therefore, our data suggest that Nav channel may be involved in the development of positive and negative sensory symptoms in diabetic neuropathy.
V.A. Campanucci: None. M. Bautista: None. J.T. Neapetung: None.
Natural Sciences and Engineering Research Council of Canada (RGPIN-2015-03958)