Effects Of Organophosphorus Insecticides On Phosphorylation Of Muscarinic Acetyl M2 Receptors

ObjectiveTo explore the effect of organophosphorus insecticides(OPs) on G-protein coupled receptor kinase 2—mediatedphosphorylation of m2 muscarinic receptors in vitro and tounderstand an alternative target of the OPs for human andother animals.MethodsThe acetylcholine m2 muscarinic receptors purifiedfrom rat brain by single step affinity chromatography; Invitro experiments, the purified m2 receptor was incubatedwith varying concentrations of paraoxon, chlorpyrifos oxonor the parent insecticides along with G-protein coupledreceptor kinase 2 (GRK2)and[γ-p³²] ATP. The proteins wereseparated by electrophoresis, gels were dried andautoradioprams developed. Bands containing m2 receptorwere excised and counted by liquid scintillation.ResultsChlorpyrifos oxon inhibited phosphorylation of m2muscarinic receptors by GRK2 with a median inhibition concentration (IC₅₀) of 70μmol/L. Chlorpyrifos alsoinhibited m2 receptors phosphorylation, however it was lesspotent and less efficacious than that of chlorpyrifos oxon.Interestingly, paraoxon and parathion had little effect on thereceptor phosphorylation under the same conditions.ConclusionChlorpyrifos oxon and chlopyrifos may alterGRK2—mediated regulatory pathways for m2 receptors bydirect interaction with m2 receptor. These differentialactions could contribute to differences in toxicity followingexposure to different organophosphorus toxicants.