An ivermectin-sensitive glutamate-gated chloride channel subunit from Dirofilaria immitis

Abstract

Dirofilaria immitis is a filarial nematode that infects dogs and causes cardiopulmonary disease. The most effective way of controlling the infection is by chemoprophylaxis, using members of the avermectin/milbemycin (A/M) class of anthelmintics, which includes ivermectin; these drugs act at invertebrate glutamate-gated chloride channels (GluCl). We have cloned two cDNAs encoding D. immitis GluCl subunits and demonstrated that at least one may be an important molecular target for the A/Ms in vivo. The subunits are orthologues of the alternatively spliced GluClα3A and α3B subunits (encoded by the avr-14 gene) previously identified in Caenorhabditis elegans and in Haemonchus contortus. Although the alternative splicing of avr-14 is conserved across the species, the processing of the mature GluClα3A mRNA differs in D. immitis compared to C. elegans and H. contortus. Two-electrode voltage clamp recordings were made from Xenopus oocytes injected with subunit-specific cRNAs. The DiGluClα3B subunit formed channels that were gated by l-glutamate (1–100 mM) and ivermectin (1 μM). Oocytes injected with DiGluClα3A cRNA failed to respond to l-glutamate. The qualitative responses obtained were consistent with the pharmacology observed for the GluClα3 subunits from C. elegans and H. contortus.