title: Concentration-dependent effects of GABA on insensitivity to fipronil in the A2'S mutant RDL GABA receptor from fipronil-resistant Oulema oryzae (Coleoptera: Chrysomelidae).
abstract: The beetle Oulema oryzae Kuwayama (Coleoptera: Chrysomelidae), an important pest of rice, has developed fipronil resistance in Japan. Molecular cloning and sequence analysis of O. oryzae RDL gamma-aminobutyric acid (GABA) receptor subunit (OO-RDL) genes from fipronil-susceptible and -resistant O. oryzae identified the A2'S mutation (index number for the M2 membrane-spanning region). To investigate the effect of the A2'S mutation on fipronil resistance, we stably expressed the wild-type and mutant OO-RDL homomers in Drosophila Mel-2 cells. A membrane potential assay exhibited that the IC50 values of fipronil for inhibition of the response to EC80 GABA of the wild-type and A2'S mutant OO-RDL homomers were 0.09 microM and 0.11 microM, respectively. However, the IC50 values of fipronil for inhibition of the response to EC95 GABA of the wild-type and A2'S mutant OO-RDL homomers were 0.11 microM and approximately equal to 5 microM, respectively. These results suggest that the GABA concentration is an important factor affecting fipronil resistance in O. oryzae carrying the A2'S mutation in OO-RDL.
authors.affiliation: Agrochemical Research Center, Mitsui Chemicals Agro, Inc., Mobara, Chiba 297-0017, Japan. toshifumi.nakao@mitsui-chem.co.jp
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Nakao
authors.forename: Atsuko
authors.initials: A
authors.lastname: Naoi
authors.forename: Masako
authors.initials: M
authors.lastname: Hama
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Kawahara
authors.forename: Kangetsu
authors.initials: K
authors.lastname: Hirase
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001517:Coleoptera / Q000187:drug effects / Q000235:genetics*; D004330:Drosophila; D029721:Drosophila Proteins / Q000235:genetics; D019476:Insect Proteins / Q000235:genetics*; D007305:Insecticide Resistance / Q000235:genetics*; D007306:Insecticides / Q000494:pharmacology*; D008564:Membrane Potentials; D008969:Molecular Sequence Data; D009154:Mutation; D011720:Pyrazoles / Q000494:pharmacology*; D018079:Receptors, GABA / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection
chemical_list: D029721:Drosophila Proteins; D019476:Insect Proteins; D007306:Insecticides; D011720:Pyrazoles; D018079:Receptors, GABA; C082360:fipronil