Abstracts

Rationale: Mutations in brain isoforms of voltage-gated sodium channels (VGSCs) have been identified in patients with distinct epileptic phenotypes. Most of these mutations occur in SCN1A (Nav1.1) and are associated with severe myoclonic epilepsy in infancy also known as Dravet Syndrome. Recently, mutations in SCN8A (Nav1.6) have been identified in patients with severe epileptic encephalopathy. Clinically, these patients do not respond well to classical antiepileptics and many remain refractory to treatment. Exogenous as well as endogenous cannabinoids have been shown to target VGSCs and has recently received attention for its efficacy in the treatment of childhood epilepsies. In this study, we wanted to further explore how cannabinoids modulate sodium currents from wildtype and epilepsy-associated mutant VGSCs. Methods: We examined the biophysical consequences of epilepsy-associated missense mutations in both Nav1.1 (R1648H and N1788K) and Nav1.6 (N1768D and L1331V), some of which have not been previously characterized. We used site-directed mutagenesis to introduce the missense mutations into the optimized human cDNA constructs of wildtype channels. Hek293t cells were transfected with wildtype or mutant channels using a calcium-phosphate transfection method and whole-cell patch clamp recordings were obtained in the presence and absence of 200µM Navß4 peptide in the internal solution to induce resurgent sodium currents. Results: Resurgent sodium currents are an atypical subthreshold current that is thought to influence cellular excitability and has been implicated in many disorders of excitability. We found that both mutations in Nav1.1 decreased resurgent currents while both mutations in Nav1.6 increased resurgent currents. We then examined the effects of anandamide, N-arachidonoylglycine, and cannabidiol (CBD) on transient and resurgent currents from wildtype and mutant channels. Interestingly, we found that CBD can preferentially target resurgent sodium currents over peak transient currents generated by Nav1.6. Conclusions: Targeting resurgent sodium current is a novel therapeutic strategy for the treatment of childhood epilepsies and although further studies are needed, these results support the potential use of CBD in the treatment of childhood epilepsies.