Effects Of Sodium Channel Pesticides On DSC1 Channel And Preliminary Research On Mechanism Of Action Of Haedoxan A From Phryma Leptostachya

Voltage-gated ion channels(VGICs) play essential roles in regulating neuronal activities. Different families of VGICs play different roles in modulating these activities. The Drosophila Sodium Channel 1(DSC1) gene was identified three decades. Sequence analysis predicted that DSC1 encodes an ion channel that has more than 50% similarity to the vertebrate sodium channel protein. The DSC1 channel protein has four homologous domains each containing six membrane-spanning segments. DSC1 and its orthologs from other species contain the amino acids D, E, E, A in the loop connecting S5 and S6 of domains I, II, III, and IV, respectively, whereas voltage-gated sodium channels contain the acidic residues(D, E, K, and E) and voltage-gated calcium channels contain the acidic residues(E, E, E, and E) at the corresponding positions. The E residue in domain III is important for the selectivity of the DSC1 channel. Functional analysis of the DSC1 channel and a DSC1 ortholog from the German cockroach, BSC1, in Xenopus oocytes revealed that BSC1/DSC1 channels represent a novel family of voltage-gated cation channels with high permeability to Ca2+ and exists only in invertebrates. But the role of the DSC1 channel remains mysterious. Previous research showed that haedoxan A may act on sodium channels, but the precise site remain unknown. Therefore, this paper conducted bioassays to examine the sensitivities of w1118, parats1, DSC1-/-, and parats1:DSC1-/- flies and larvae to four typeⅠand 4 typeⅡ pyrethroid insecticides, DDT and indoxacarb and measured the effect of deltamethrin, cypermethrin and permethrin on Drosophila larval neuromuscular junction potentials and conducted bioassays to examine the sensitivities of w1118, parats1, DSC1-/-, and parats1:DSC1-/- flies to haedoxan A. The results are as follows :1 Knockout of DSC1 caused enhanced sensitivity to pyrethroids in D. melanogaster and the sequence of sensitivity were DSC1-/- > W1118 ≥ parats1:DSC1-/- > parats1, suggesting that the DSC1 channel is not a direct target of pyrethroid insecticides, but has epistatic effects on pyrethroid action on the sodium channels. The sequence of sensitivity of four strains flies to DDT were W1118 > DSC1-/- ≈ parats1:DSC1-/- >> parats1. Indoxacarb is a sodium channel blocker, W1118、DSC1-/-、parats1 and parats1:DSC1-/- exhibited similar susceptibility to it.2 The sequence of sensitivity of four strains larvae to eight pyrethroid insecticides were W1118 > DSC1-/- > parats1:DSC1-/- > parats1. Compared to W1118, the parats1 strain was more than 5 to 10-fold less sensitive to eight pyrethroids. However, the parats1:DSC1-/- double mutant was about 2-fold less sensitive to eight pyrethroids compared with w1118. Knockout DSC1 channel, the larvae are more sensitive to DDT, indicating that DSC1 channel is not the direct target of DDT.3 The intracellular electrode recording results showed that under pyrethroids treatment, compared with the control, four strains larval resting potential showed a suddenly rise and repetitive firing of mEJP and the order was DSC1-/- > W1118 > parats1:DSC1-/- > parats1. In addition, it was found the time of suddenly rise of teh resting potential and first appeared repetitive firing of mEJP for deltamethrin has a concentration-dependent manner.4 Parats1 were more sensitive to haedoxan A compared to W1118. Haedoxan A and pyrethroids insecticide were negative cross-resistance.Based on the above findings, the DSC1 channel is not a direct target of pyrethroid insecticides and DDT, but the interaction between DSC1 channels and sodium channel can reduce the affinity between pesticides or DDT and the action of the sodium channel. The DSC1 channel may be used as a novel target for the development of new insecticides. Moreover, the DSC1 family of ion channels is unique in invertebrate animals. Thus, DSC1 channel-targeted chemicals may have the advantage of being highly selective and safe to mammals. However, the interaction between pyrethroids and the DSC1 channel is not fully understood and needs further investigation.Currently, insecticides have a negative cross-resistance is not much, so haedoxan A can be used as an ideal pesticide to solve the problem of resistance. But its site of action is still not clear, may be related to sodium channel resistance mutations. The specific site of action remains to be further studied.