Mutations in the transmembrane helix S6 of domain IV confer cockroach sodium channel resistance to sodium channel blocker insecticides and local anesthetics

Abstract

Indoxacarb and metaflumizone are two sodium channel blocker insecticides (SCBIs). They preferably bind to and trap sodium channels in the slow-inactivated non-conducting state, a mode of action similar to that of local anesthetics (LAs). Recently, two sodium channel mutations, F1845Y (F4i15Y) and V1848I (V4i18I), in the transmembrane segment 6 of domain IV (IVS6), were identified to be associated with indoxacarb resistance in Plutella xylostella. F4i15 is known to be critical for the action of LAs on mammalian sodium channels. Previously, mutation F4i15A in a cockroach sodium channel, BgNav1-1a, has been shown to reduce the action of lidocaine, a LA, but not the action of SCBIs. In this study, we introduced mutations F4i15Y and V4i18A/I individually into the cockroach sodium channel, BgNav1-1a, and conducted functional analysis of the three mutants in Xenopus oocytes. We found that both the F4i15Y and V4i18I mutations reduced the inhibition of sodium current by indoxacarb, DCJW (an active metabolite of indoxacarb) and metaflumizone. F4i15Y and V4i18I mutations also reduced the use-dependent block of sodium current by lidocaine. In contrast, substitution V4i18A enhanced the action metaflumizone and lidocaine. These results show that both F4i15Y and V4i18I mutations may contribute to target-site resistance to SCBIs, and provide the first molecular evidence for common amino acid determinants on insect sodium channels involved in action of SCBIs and LA.