Sequence variations at I260 and A1731 contribute to persistent currents in Drosophila sodium channels

Abstract

Tetrodotoxin-sensitive persistent sodium currents, INaP, that activate at subthreshold voltages, have been detected in numerous vertebrate and invertebrate neurons. These currents are believed to be critical for regulating neuronal excitability. However, the molecular mechanism underlying INaP is controversial. In this study, we identified an INaP with a broad range of voltage dependence, from −60 mV to 20 mV, in a Drosophila sodium channel variant expressed in Xenopus oocytes. Mutational analysis revealed that two variant-specific amino acid changes, I260T in the S4–S5 linker of domain I (ILS4–S5) and A1731V in the voltage sensor S4 of domain IV (IVS4), contribute to the INaP. I260T is critical for the portion of INaP at hyperpolarized potentials. The T260-mediated INaP is likely the result of window currents flowing in the voltage range where the activation and inactivation curves overlap. A1731V is responsible for impaired inactivation and contributes to the portion of INaP at depolarized potentials. Furthermore, A1731V causes enhanced activity of two site-3 toxins which induce persistent currents by inhibiting the outward movement of IVS4, suggesting that A1731V inhibits the outward movement of IVS4. These results provided molecular evidence for the involvement of distinct mechanisms in the generation of INaP: T260 contributes to INaP via enhancement of the window current, whereas V1731 impairs fast inactivation probably by inhibiting the outward movement of IVS4.

Double sodium channel mutation, I265T/L1014F, is possibly related to pyrethroid‐resistant in Thrips palmi

“…In addition, the production of mutation has been reported in many insects. In domain Ⅰ, I260T and I265N mutations have been reported in D. melanogaster (Gao et al, 2014; Rinkevich et al, 2015). The classic positions 1014 and 918 belonged to the double binding region of pyrethroids in insect VGSC, which are currently found high levels of resistance in insect populations (Du et al, 2013; Eleftherianos et al, 2008; Miyazaki et al, 1996).…”