title: Desnitro-imidacloprid activates the extracellular signal-regulated kinase cascade via the nicotinic receptor and intracellular calcium mobilization in N1E-115 cells.
abstract: Imidacloprid (IMI) is the principal neonicotinoid (the only major new class of synthetic insecticides of the past three decades). The excellent safety profile of IMI is not shared with a metabolite, desnitro-IMI (DNIMI), which displays high toxicity to mammals associated with agonist action at the alpha4beta2 nicotinic acetylcholine receptor (nAChR) in brain. This study examines the hypothesis that IMI, DNIMI, and (-)-nicotine activate the extracellular signal-regulated kinase (ERK) cascade via primary interaction with the alpha4beta2 nAChR in mouse neuroblastoma N1E-115 cells. These three nicotinic agonists induce phosphorylation of ERK (p44/p42) in a concentration-dependent manner with an optimal incubation period of 30 min. DNIMI (1 microM)-induced ERK activation is blocked by nicotinic antagonist mecamylamine but not by alpha-bungarotoxin and muscarinic antagonist atropine. This activation is prevented by intracellular Ca(2+) chelator BAPTA-AM but not by removal of external Ca(2+) using EGTA and Ca(2+)-free medium. 2-Aminoethoxy-diphenylborate, a blocker for inositol 1,4,5-trisphosphate (IP(3))-mediated Ca(2+) release from intracellular stores, inhibits DNIMI-induced ERK activation but a high level of ryanodine (to block ryanodine receptor-mediated Ca(2+) release) does not. The inhibitor U-73122 for phospholipase C (to suppress IP(3) production) prevents ERK activation evoked by DNIMI. Inhibitors for protein kinase C (PKC) (GF109203X) and ERK kinase (PD98059) block this activation whereas an inhibitor (H-89) for cyclic AMP-dependent protein kinase does not. Thus, neonicotinoids activate the ERK cascade triggered by primary action at the alpha4beta2 nAChR with an involvement of intracellular Ca(2+) mobilization possibly mediated by IP(3). It is further suggested that intracellular Ca(2+) activates a sequential pathway from PKC to ERK.
authors.affiliation: Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy, and Management, University of California, Berkeley 94720-3112, USA.
authors.forename: Motohiro
authors.initials: M
authors.lastname: Tomizawa
authors.forename: John E
authors.initials: JE
authors.lastname: Casida
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D007093:Imidazoles / Q000494:pharmacology*; D007306:Insecticides / Q000494:pharmacology*; D020935:MAP Kinase Signaling System; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000096:biosynthesis*; D000073943:Neonicotinoids; D009447:Neuroblastoma / Q000188:drug therapy / Q000201:enzymology; D009538:Nicotine / Q000494:pharmacology; D009574:Nitro Compounds; D010944:Plants; D011978:Receptors, Nicotinic / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000201:enzymology
chemical_list: D015220:Calcium Channels; D007093:Imidazoles; D007306:Insecticides; D000073943:Neonicotinoids; D009574:Nitro Compounds; D011978:Receptors, Nicotinic; C403531:nicotinic receptor alpha4beta2; C082359:imidacloprid; D009538:Nicotine; D020928:Mitogen-Activated Protein Kinases; D002118:Calcium