Pharmacology of Drosophila Melanogaster TRPA1 Isoforms

Abstract

The TRPA1 cation channel functions as a broadly-tuned chemonociceptor in many species. Recent studies identified several splice variants of Drosophila TRPA1 (from dTRPA1(A) to (D)). These were reported to display distinct chemical and thermal sensitivities and distinct expression patterns. Some differences in the chemical sensitivities between insect and mammalian orthologues have also been reported. Given the usefulness of Drosophila as animal model for studying TRPA1 chemosensation in vivo, we re-evaluated the effects of three mammalian TRPA1 modulators (nicotine, citronellal and menthol) on dTRPA1 splice variants in HEK293T cells. Using intracellular Ca2+ fluorimetry and whole-cell patch-clamp, we confirmed that the electrophilic agonist allyl isothiocyanate activates all splice variants, whereas nicotine activates all variants except dTRPA1(B). Citronellal robustly activated all splice variants. The activation by nicotine and citronellal could be inhibited by the TRPA1 antagonist HC030031. On the other hand, menthol did not activate any dTRPA1 isoform. Our results demonstrate that the mammalian heterologous expression system HEK293T can be used for functional studies on insect TRPA1 channels, and that the chemosensory properties of these channels may strongly differ from those of the mammalian homologues. Our findings serve as starting point for further structure-function studies for the determination of the structural bases of chemical sensitivity in TRPA1 channels.