Characterization of a novel tyramine-gated chloride channel from Haemonchus contortus

Tyramine (TA), a trace amine, is becoming accepted as a main stream neurotransmitter in invertebrates. Recent evidence indicates that part of the function of TA in nematodes involves a novel receptor (Cel-LGC-55) from the ligand-gated chloride channel class of ionotropic receptors. However, the role of TA or its receptors in the biology of nematode parasites is limited. Haemonchus contortus is a deadly parasitic worm which causes significant economic burden in the production of small ruminants in many parts of the world. In this study, we have cloned and characterized a novel LGCC from H. contortus which we have named Hco-LGC-55. This receptor subunit is a clear orthologue of Cel-LGC-55 and is able to form a homomeric chloride channel that is gated by tyramine, dopamine and octopamine. Semi-quantitative reverse transcription-polymerase chain reaction (sqRT-PCR) shows that this subunit is expressed in all life-cycle stages of the worm, but appears to have reduced mRNA expression in the adult male.

An oocyte expressing Hco-LGC-55 was washed with 10 μM of the following molecules in the following order: tyramine (TA), octopamine (OA), serotonin (5-HT), acetylcholine (Ach) and dopamine (DA). Robust currents were observed with the application of TA and DA, with TA producing the largest response.20