Pyrethroids are insecticides used since the 1970s. They are favored for their low mammalian toxicity, improved environmental stability and insecticidal potency. Voltage-gated sodium channels (VGSCs) are a known target but in vitro evidence indicates that voltage-gated calcium channels (VGCCs) are also targets. Site-directed mutagenesis of CaV2.2 (N-type), altering threonine 422 to glutamate (T422E), produces a mutant channel that acts as if permanently phosphorylated. Deltamethrin increases peak current of T422E CaV2.2 compared to its antagonistic action on wild type CaV2.2 when expressed in Xenopus oocytes. Phosphorylation of wild type CaV2.2 is evoked by the phorbol ester PMA by activating endogenous protein kinase C (PKC) in oocytes. Under steady-state conditions, deltamethrin increases transient peak current and slows deactivation kinetics of the PKC phosphorylated channel thereby increasing Ca2+ influx and neurotransmitter release. Conversely, deltamethrin treatment resulted in no effect on the deactivation kinetics of the unphosphorylated or T422E channels. Under voltage-dependent conditions, deltamethrin enhances peak current, and causes a hyperpolarizing shift in activation midpoint potential of the PKC phosphorylated channel which is consistent with enhanced Ca2+ influx. The hyperpolarizing shift of activation midpoint potential was not observed when deltamethrin was applied to the T422E mutant channels indicating that the other phosphorylation sites on CaV2.2 may be playing a role in the differential effects observed in the action of deltamethrin on the unphosphorylated channel, the T422E mutant and the PMA-activated PKC phosphorylation channel.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:theses-1847 |
| Date | 01 January 2012 |
| Creators | Alves, Anna-maria |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Masters Theses 1911 - February 2014 |
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