Calcium-Activated Potassium Channels in Insect Pacemaker Neurons as Unexpected Target Site for the Novel Fumigant Dimethyl Disulfide

• Published in: The Journal of pharmacology and experimental therapeutics 2008-01, Vol.324 (1), p.149-159
• Main Authors: Gautier, Hélène, Auger, Jacques, Legros, Christian, Lapied, Bruno
• Format: Article
• Language: English
• Subjects: Action Potentials - drug effects; Animals; Calcium - physiology; Cockroaches - physiology; Disulfides - toxicity; Ecotoxicology; In Vitro Techniques; Insecticides - toxicity; Life Sciences; Male; Neurons - drug effects; Neurons - physiology; Oligonucleotides, Antisense - pharmacology; Potassium Channels, Calcium-Activated - drug effects; Potassium Channels, Calcium-Activated - genetics; Potassium Channels, Calcium-Activated - physiology; Toxicology
• ISSN: 0022-3565; 1521-0103
• DOI: 10.1124/jpet.107.128694

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 μM), 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 [Ca2+]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 [Ca2+]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)γ], we demonstrated that TRPγ initiated calcium influx. By contrast, ω-conotoxin GVIA (an inhibitor of N-type high-voltage-activated calcium channels), did not affect the DMDS-induced [Ca2+]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 [Ca2+]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.