DIII - DIV Linker Charge Mutations Differentially Affect Open and Closed State Fast Inactivation in Nav1.4

Fast inactivation in sodium channels occurs with channel opening, or in response to depolarization that does not open channels. Inactivation is dependent on the binding of an IFMT motif located in the DIII-DIV linker, flanked by a number of positively charged amino acid residues. We investigated the role of two loci of positive charge on the N terminal side of the IFMT motif, and three loci of charge on the C terminal side. To do this we compared the effects of charge reversing and charge substituting mutations in skeletal muscle sodium channel hNaV1.4. Inactivation from the closed state was prolonged by mutations on the N terminal side, but accelerated by mutations on the C terminal side of the inactivation particle. Open-state fast inactivation was typically prolonged with mutation. Our results suggest that these residues play an important role in the inactivation of sodium channels, and that both charge and structure contribute to these roles. This work was supported by NSF RUI 0235358 to JRG and NIH P20RR16454 to ISU from the INBRE program of the National Center for Research Resources.