title: Calcium-activated potassium channels in insect pacemaker neurons as unexpected target site for the novel fumigant dimethyl disulfide.
abstract: Dimethyl disulfide (DMDS), a plant-derived insecticide, is a promising fumigant as a substitute for methyl bromide. To further understand the mode of action of DMDS, we examined its effect on cockroach octopaminergic neurosecretory cells, called dorsal unpaired median (DUM) neurons, using whole-cell patch-clamp technique, calcium imaging and antisense oligonucleotide strategy. At low concentration (1 microM), DMDS modified spontaneous regular spike discharge into clear bursting activity associated with a decrease of the amplitude of the afterhyperpolarization. This effect led us to suspect alterations of calcium-activated potassium currents (IKCa) and [Ca(2+)](i) changes. We showed that DMDS reduced amplitudes of both peak transient and sustained components of the total potassium current. IKCa was confirmed as a target of DMDS by using iberiotoxin, cadmium chloride, and pSlo antisense oligonucleotide. In addition, we showed that DMDS induced [Ca(2+)](i) rise in Fura-2-loaded DUM neurons. Using calcium-free solution, and (R,S)-(3,4-dihydro-6,7-dimethoxy-isoquinoline-1-yl)-2-phenyl-N,N-di-[2-(2,3,4-trimethoxy-phenyl)ethyl]-acetamide (LOE 908) [an inhibitor of transient receptor potential (TRP)gamma], we demonstrated that TRPgamma initiated calcium influx. By contrast, omega-conotoxin GVIA (an inhibitor of N-type high-voltage-activated calcium channels), did not affect the DMDS-induced [Ca(2+)](i) rise. Finally, the participation of the calcium-induced calcium release mechanism was investigated using thapsigargin, caffeine, and ryanodine. Our study revealed that DMDS-induced elevation in [Ca(2+)](i) modulated IKCa in an unexpected bell-shaped manner via intracellular calcium. In conclusion, DMDS affects multiple targets, which could be an effective way to improve pest control efficacy of fumigation.
authors.affiliation: Unité Propre de Recherche et de l'Enseignement Supérieur, Equipe d'Accueil 2647/USC Institut National de la Recherche Agronomique, Université d'Angers, Unité de Formation et de Recherche Sciences, Angers cedex, France.
authors.forename: Hélène
authors.initials: H
authors.lastname: Gautier
authors.forename: Jacques
authors.initials: J
authors.lastname: Auger
authors.forename: Christian
authors.initials: C
authors.lastname: Legros
authors.forename: Bruno
authors.initials: B
authors.lastname: Lapied
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000502:physiology; D003058:Cockroaches / Q000502:physiology*; D004220:Disulfides / Q000633:toxicity*; D066298:In Vitro Techniques; D007306:Insecticides / Q000633:toxicity*; D008297:Male; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D024681:Potassium Channels, Calcium-Activated / Q000187:drug effects* / Q000235:genetics / Q000502:physiology
chemical_list: D004220:Disulfides; D007306:Insecticides; D016376:Oligonucleotides, Antisense; D024681:Potassium Channels, Calcium-Activated; C021181:dimethyl disulfide; D002118:Calcium