TY - JOUR T1 - A Single Amino Acid Substitution in the Third Transmembrane Region Has Opposite Impacts on the Selectivity of the Parasiticides Fluralaner and Ivermectin for Ligand-Gated Chloride Channels JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.117.109413 SP - mol.117.109413 AU - Yunosuke Nakata AU - Toshinori Fuse AU - Kohei Yamato AU - Miho Asahi AU - Kunimitsu Nakahira AU - Fumiyo Ozoe AU - Yoshihisa Ozoe Y1 - 2017/01/01 UR - http://molpharm.aspetjournals.org/content/early/2017/09/08/mol.117.109413.abstract N2 - Fluralaner (BravectoTM) is a recently marketed isoxazoline ectoparasiticide. This compound potently inhibits γ-aminobutyric acid (GABA)-gated chloride channels (GABACls) and less potently glutamate-gated chloride channels (GluCls) in insects. The mechanism underlying this selectivity is unknown. Therefore, we sought to identify the amino acid residue(s) causing the low potency of fluralaner toward GluCls. We examined the fluralaner sensitivity of mutant housefly (Musca domestica) GluCls in which amino acid residues in the transmembrane subunit interface (TSI) were replaced with the positionally equivalent amino acids of Musca GABACls. Of these amino acids, substitution of an amino acid (Leu315) in the third transmembrane region (TM3) with an aromatic amino acid dramatically enhanced the potency of fluralaner in the GluCls. In stark contrast to the enhancement of fluralaner potency, this mutation eliminated the activation of currents and the potentiation but not the antagonism of glutamate responses that are otherwise all elicited by the macrolide parasiticide ivermectin (IVM). Our findings indicate that the amino acid Leu315 in Musca GluCls plays significant roles in determining the selectivity of fluralaner and IVM for these channels. Given the high sequence similarity of TM3, this may hold true more widely for the GluCls and GABACls of other insect species. ER -