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Mutations in the extracellular domains of glutamate‐gated chloride channel α3 and β subunits from ivermectin‐resistant Cooperia oncophora affect agonist sensitivity
Author(s) -
Njue Annete I.,
Hayashi Jon,
Kinne Lyle,
Feng XiaoPeng,
Prichard Roger K.
Publication year - 2004
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.2004.02379.x
Subject(s) - homomeric , glutamate receptor , xenopus , biology , chloride channel , amino acid , sodium channel , protein subunit , microbiology and biotechnology , pharmacology , biochemistry , receptor , chemistry , gene , sodium , organic chemistry
Two full‐length glutamate‐gated chloride channel (GluCl) cDNAs, encoding GluClα3 and GluClβ subunits, were cloned from ivermectin‐susceptible (IVS) and ‐resistant (IVR) Cooperia oncophora adult worms. The IVS and IVR GluClα3 subunits differ at three amino acid positions, while the IVS and IVR GluClβ subunits differ at two amino acid positions. The aim of this study was to determine whether mutations in the IVR subunits affect agonist sensitivity. The subunits were expressed singly and in combination in Xenopus laevis oocytes. Electrophysiological whole‐cell voltage‐clamp recordings showed that mutations in the IVR GluClα3 caused a modest but significant threefold loss of sensitivity to glutamate, the natural ligand for GluCl receptors. As well, a significant decrease in sensitivity to the anthelmintics ivermectin and moxidectin was observed in the IVR GluClα3 receptor. Mutations in the IVR GluClβ subunit abolished glutamate sensitivity. Co‐expressing the IVS GluClα3 and GluClβ subunits resulted in heteromeric channels that were more sensitive to glutamate than the respective homomeric channels, demonstrating co‐assembly of the subunits. In contrast, the heteromeric IVR channels were less sensitive to glutamate than the homomeric IVR GluClα3 channels. The heteromeric IVS channels were significantly more sensitive to glutamate than the heteromeric IVR channels. Of the three amino acids distinguishing the IVS and IVR GluClα3 subunits, only one of them, L256F, accounted for the differences in response between the IVS and IVR GluClα3 homomeric channels.