Ranolazine selectively blocks persistent current evoked by epilepsy-associated Na _V1.1 mutations

BACKGROUND AND PURPOSE Mutations of SCN1A, the gene encoding the pore-forming subunit of the voltage-gated sodium channel Na _V1.1, have been associated with a spectrum of genetic epilepsies and a familial form of migraine. Several mutant Na _V1.1 channels exhibit increased persistent current due to incomplete inactivation and this biophysical defect may contribute to altered neuronal excitability in these disorders. Here, we investigated the ability of ranolazine to preferentially inhibit increased persistent current evoked by mutant Na _V1.1 channels.EXPERIMENTAL APPROACH Human wild-type (WT) and mutant Na _V1.1 channels were expressed heterologously in human tsA201 cells and whole-cell patch clamp recording was used to assess tonic and use-dependent ranolazine block.KEY RESULTS Ranolazine (30 μM) did not affect WT Na _V1.1 channel current density, activation or steady-state fast inactivation but did produce mild slowing of recovery from inactivation. Ranolazine blocked persistent current with 16-fold selectivity over tonic block of peak current and 3.6-fold selectivity over use-dependent block of peak current. Similar selectivity was observed for ranolazine block of increased persistent current exhibited by Na _V1.1 channel mutations representing three distinct clinical syndromes, generalized epilepsy with febrile seizures plus (R1648H, T875M), severe myoclonic epilepsy of infancy (R1648C, F1661S) and familial hemiplegic migraine type 3 (L263V, Q1489K). In vitro application of achievable brain concentrations (1, 3 μM) to cells expressing R1648H channels was sufficient to suppress channel activation during slow voltage ramps, consistent with inhibition of persistent current.CONCLUSIONS AND IMPLICATIONS Our findings support the feasibility of using selective suppression of increased persistent current as a potential new therapeutic strategy for familial neurological disorders associated with certain sodium channel mutations.