title: Study of the nematode putative GABA type-A receptor subunits: evidence for modulation by ivermectin.
abstract: Two alleles of the HG1 gene, which encodes a putative GABA receptor alpha/gamma subunit, were isolated from Haemonchus contortus. These two alleles were shown previously to be associated with ivermectin susceptibility (HG1A) and resistance (HG1E), respectively. Sequence analysis indicates that they differ in four amino acids. To explore the functional properties of the two alleles, a full-length cDNA encoding the beta subunit, a key functional component of the GABA receptor, was isolated from Caenorhabditis elegans (gab-1, corresponding to the GenBank locus ZC482.1) and coexpressed in Xenopus oocytes with the HG1 alleles. When gab-1 was coexpressed with either the HG1A allele or the HG1E allele in Xenopus oocytes, gamma-aminobutyric acid (GABA)-responsive channels with different sensitivity to the agonist were formed. The effects of ivermectin on the hetero-oligomeric receptors were determined. Application of ivermectin alone had no effect on the receptors. However, when coapplied with 10 micro m GABA, ivermectin potentiated the GABA-evoked current of the GAB-1/HG1A receptor, but attenuated the GABA response of the GAB-1/HG1E receptor. We demonstrated that the coexpressed HG1 and GAB-1 receptors are GABA-responsive, and provide evidence for the possible involvement of GABA receptors in the mechanism of ivermectin resistance.
authors.affiliation: Institute of Parasitology, McGill University, Quebec, Canada.
authors.forename: Xiao-Peng
authors.initials: XP
authors.lastname: Feng
authors.forename: Jon
authors.initials: J
authors.lastname: Hayashi
authors.forename: Robin N
authors.initials: RN
authors.lastname: Beech
authors.forename: Roger K
authors.initials: RK
authors.lastname: Prichard
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001667:Binding, Competitive / Q000187:drug effects; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000096:biosynthesis / Q000235:genetics*; D004351:Drug Resistance / Q000235:genetics*; D004594:Electrophysiology; D015870:Gene Expression; D006189:Haemonchus; D015801:Helminth Proteins / Q000096:biosynthesis / Q000235:genetics; D007559:Ivermectin / Q000494:pharmacology*; D008024:Ligands; D008969:Molecular Sequence Data; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D010802:Phylogeny; D021122:Protein Subunits / Q000096:biosynthesis / Q000235:genetics; D011963:Receptors, GABA-A / Q000096:biosynthesis / Q000235:genetics*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014162:Transfection; D014981:Xenopus; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
chemical_list: D029742:Caenorhabditis elegans Proteins; C469698:GAB-1 protein, C elegans; D015801:Helminth Proteins; D008024:Ligands; D021122:Protein Subunits; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; D007559:Ivermectin