Chemical sensing properties of Takifugu TRPA1

Transient receptor potential ankyrin 1 (TRPA1) is one of the main sensors for noxious stimuli in animals. Recent studies on the cloning and characterization of TRPA1 channels from several organisms showed the functional diversity of TRPA1 in sensing chemicals and temperature. Nociceptive receptors have been suggested to play important roles in adaptation to the environment by and survival strategies of animals; therefore, the sensitivity of various vertebrate TRPA1s needs to be examined in more detail. Here, we focused on fish TRPA1s and investigated the chemical sensing properties of pufferfish (Takifugu) TRPA1 (pfTRPA1). We determined how mammalian TRPA1 ligands activated pfTRPA1 using a Ca-imaging technique. The results obtained indicated that the sensitivity of pfTRPA1 to known TRPA1 ligands was lower than that of mammalian TRPA1s, except for the response ability to allyl isothiocyanate. We also investigated the effects of tannic acid, a type of polyphenol, by measuring ionic currents in Xenopus oocytes in a two-electrode voltage clamp. Although mouse TRPA1 was inhibited by tannic acid, pfTRPA1 channels were enhanced by the treatment with tannic acid. Taken together, these results suggest that pfTRPA1 is not a simple sensor with a lower sensitivity to chemical stimulation, but is actually a specialized sensor with unique properties.