title: Molecular basis of differential sensitivity of insect sodium channels to DCJW, a bioactive metabolite of the oxadiazine insecticide indoxacarb.
abstract: Indoxacarb (DPX-JW062) was recently developed as a new oxadiazine insecticide with high insecticidal activity and low mammalian toxicity. Previous studies showed that indoxacarb and its bioactive metabolite, N-decarbomethoxyllated JW062 (DCJW), block insect sodium channels in nerve preparations and isolated neurons. However, the molecular mechanism of indoxacarb/DCJW action on insect sodium channels is not well understood. In this study, we identified two cockroach sodium channel variants, BgNa(v)1-1 and BgNa(v)1-4, which differ in voltage dependence of fast and slow inactivation, and channel sensitivity to DCJW. The voltage dependence of fast inactivation and slow inactivation of BgNa(v)1-4 were shifted in the hyperpolarizing direction compared with those of BgNa(v)1-1 channels. At the holding potential of -90 mV, 20 microM of DCJW reduced the peak current of BgNa(v)1-4 by about 40%, but had no effect on BgNa(v)1-1. However, at the holding potential of -60 mV, DCJW also reduced the peak currents of BgNa(v)1-1 by about 50%. Furthermore, DCJW delayed the recovery from slow inactivation of both variants. Substitution of E1689 in segment 4 of domain four (IVS4) of BgNa(v)1-4 with a K, which is present in BgNa(v)1-1, was sufficient to shift the voltage dependence of fast and slow inactivation of BgNa(v)1-4 channels to the more depolarizing membrane potential close to that of BgNa(v)1-1 channels. The E1689K change also eliminated the DCJW inhibition of BgNa(v)1-4 at the hyperpolarizing holding potentials. These results show that the E1689K change is responsible for the difference in channel gating and sensitivity to DCJW between BgNa(v)1-4 and BgNa(v)1-1. Our results support the notion that DCJW preferably acts on the inactivated state of the sodium channel and demonstrate that K1689E is a major molecular determinant of the voltage-dependent inactivation and state-dependent action of DCJW.
authors.affiliation: Department of Entomology and Neuroscience Program, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Weizhong
authors.initials: W
authors.lastname: Song
authors.forename: Zhiqi
authors.initials: Z
authors.lastname: Liu
authors.forename: Ke
authors.initials: K
authors.lastname: Dong
mesh_terms: D000596:Amino Acids / Q000378:metabolism / Q000502:physiology; D000818:Animals; D003058:Cockroaches / Q000378:metabolism*; D004594:Electrophysiology; D007306:Insecticides / Q000378:metabolism / Q000494:pharmacology*; D015640:Ion Channel Gating / Q000187:drug effects; D007700:Kinetics; D009865:Oocytes / Q000378:metabolism; D010078:Oxazines / Q000378:metabolism / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D011994:Recombinant Proteins / Q000378:metabolism; D026941:Sodium Channel Blockers; D015222:Sodium Channels / Q000187:drug effects* / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology; D014982:Xenopus laevis
chemical_list: D000596:Amino Acids; D007306:Insecticides; C510261:N-decarbomethoxyllated JW062; D010078:Oxazines; D011994:Recombinant Proteins; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D013779:Tetrodotoxin; C401104:indoxacarb