Functional characterisation of a nicotinic acetylcholine receptor α subunit from the brown dog tick, Rhipicephalus sanguineus

Ticks and tick-borne diseases have a major impact on human and animal health worldwide. Current con- trol strategies rely heavily on the use of chemical acaricides, most of which target the CNS and with increasing resistance, new drugs are urgently needed. Nicotinic acetylcholine receptors (nAChRs) are tar- gets of highly successful insecticides. We isolated a full-length nAChR a subunit from a normalised cDNA library from the synganglion (brain) of the brown dog tick, Rhipicephalus sanguineus. Phylogenetic analysis has shown this R. sanguineus nAChR to be most similar to the insect a1 nAChR group and has been named Rsana1. Rsana1 is distributed in multiple tick tissues and is present across all life-stages. When expressed in Xenopus laevis oocytes Rsana1 failed to function as a homomer, with and without the addition of either Caenorhabditis elegans resistance-to-cholinesterase (RIC)-3 or X. laevis RIC-3. When co-expressed with chicken b2 nAChR, Rsana1 evoked concentration-dependent, inward currents in response to acetylcholine (ACh) and showed sensitivity to nicotine (100 lM) and choline (100 lM). Rsana1/b2 was insensitive to both imidacloprid (100 lM) and spinosad (100 lM). The unreliable expression of Rsana1 in vitro suggests that additional subunits or chaperone proteins may be required for more robust expression. This study enhances our understanding of nAChRs in arachnids and may provide a basis for further studies on the interaction of compounds with the tick nAChR as part of a discovery process for novel acaricides.