Block of Two Subtypes of Sodium Channels in Cockroach Neurons by Indoxacarb Insecticides
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INTRODUCTION
Indoxacarb is a new broad-spectrum insecticide effective against insects belonging to at least 10 orders and well over 30 families. It exhibits low mammalian toxicity and shows no cross-resistance to carbamates, pyrethroids, spinosad, cyclodienes, benzoylureas or organophosphates (Zhao et al., 2002, Wing et al., 2004). Indoxacarb was the first commercialized Na+ channel blocking insecticide of the oxadiazine class. Indoxacarb's selective toxicity against insects is due in part to the fact that
Isolation of Cockroach Neurons
The American cockroaches, Periplaneta americana L., were purchased from Carolina Biological Supply Company (Burlington, NC), and were reared in the dark at 29 °C on rat chow (Ralston Purina Company, St. Louis, MO) and water. Neurons from three thoracic ganglia of an adult male cockroach were prepared according to a modified version of the technique of Pinnock and Sattelle (1987). Briefly, three thoracic ganglia were isolated, desheathed and incubated for 20 min in cockroach saline solution
Two Types of Na+ Currents
The cockroach thoracic ganglia contain neurons of different sizes (10–100 μm) and different shapes. Most of them are with mainly round or pyriform somata with axon remnants. Na+ currents were rarely observed in small round-shaped neurons or large neurons without axon remnants, but were reliably recorded in large pyriform neurons. This is consistent with the fact that voltage-gated Na+ channels are mainly located on the axon or the initial segment of the soma, instead of the apical pole of
Two Kinds of Na+ Currents
Voltage-gated Na+ channels in dorsal unpaired median neurons of the cockroach are located mainly on the axon and the initial segment of the soma, as shown by immunocytochemical staining (French et al., 1993, Amat et al., 1998). The physiological and pharmacological properties of the fast voltage-gated Na+ currents in both giant axons and dorsal unpaired median neurons of the cockroach were studied using voltage clamp techniques (Sattelle et al., 1979, Pelhate et al., 1979, Lapied et al., 1990,
ACKNOWLEDGEMENTS
This study was supported by National Institutes of Health grant NS14143. Samples of indoxacarb (DPX-MP062) and its metabolite, DCJW, were provided by E.I. DuPont de Nemours and Company, Newark, Delaware. The authors wish to thank Dr. Ke Dong (Michigan State University, MI) for the helpful discussion on insect sodium channels. The authors thank Nayla Hasan and Sandra Guy for technical assistances and Julia Irizarry for secretarial assistance.
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2016, Pesticide Biochemistry and PhysiologyMolecular and functional characterization of a novel sodium channel TipE-like auxiliary subunit from the American cockroach Periplaneta americana
2015, Insect Biochemistry and Molecular BiologyCitation Excerpt :Interestingly, PaTipE, PaTEH2 and PaTEH3 (unpublished data) are not expressed in DUM neurons. Since only PaTEH1 is expressed in DUM neurons in which two Nav channels have been previously characterized by patch-clamp technique (Lavialle-Defaix et al., 2006, 2010; Zhao et al., 2005), we suggest that this functional diversity is endorsed by the presence of two α-subunits, resulting from splicing or RNA editing events associated with PaTEH1. Indeed, extensive alternative splicing and RNA editions are believed to be responsible of a fine tuning of Nav channels gating properties in B. germanica and D. melanogaster (Olson et al., 2008; Song et al., 2004).
Mutations in the transmembrane helix S6 of domain IV confer cockroach sodium channel resistance to sodium channel blocker insecticides and local anesthetics
2015, Insect Biochemistry and Molecular BiologyCitation Excerpt :While DCJW is a more potent blocker of sodium channels, it is well-documented in the literature that indoxacarb exhibits a modest level of blocking effect on most mammalian sodium channel isoforms expressed in Xenopus oocytes (von Stein et al., 2013) and in mammalian neurons (Zhao et al., 2003). Indoxacarb also inhibits cockroach sodium channels in primary neurons (Zhao et al., 2005) and cockroach sodium channels expressed in Xenopus oocytes (Silver et al., 2009). The effects of indoxacarb on wild-type cockroach sodium channels from our current study are consistent with those reported in our previous study (Silver et al., 2009).
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