Genetic variability of glutamate-gated chloride channel genes in ivermectin-susceptible and -resistant strains ofCooperia oncophora

Abstract

The glutamate-gated chloride channels (GluCls) are members of the ligand-gated ion channel superfamily that are thought to be involved in the mode of action of ivermectin and mechanism of resistance. Using reverse-transcriptase PCR techniques, 2 full-length GluCl cDNAs, encoding GluClα3 and GluClβ subunits, were cloned fromCooperia oncophora, a nematode parasite of cattle. The two sequences show a high degree of identity to similar subunits from other nematodes. TheC. oncophoraGluClα3 subunit is most closely related to theHaemonchus contortusGluClα3B subunit, whileC. oncophoraGluClβ subunit shares high sequence identity with theH. contortusGluClβ subunit. Using single-strand conformation polymorphism, the genetic variability of these two genes was analysed in an ivermectin-susceptible isolate and an ivermectin-resistant field isolate ofC. oncophora. Statistical analysis suggested an association between theC. oncophora GluClα3gene and ivermectin resistance. No such association was seen with theGluClβ gene.