イヌTRPM8とTRPA1 のメントールに対する反応性の違い

抄録

Although menthol generally provides a pleasant cooling sensation in humans, at high concentrations it can cause discomfort and/or pain. This effect is attributable to two cation channels, TRPM8 and TRPA1, that exhibit different dose dependency in humans. Given that the dose dependency of these receptors to menthol might differ in other mammalian species, we examined the reactivity of canine TRPM8 and TRPA1 to menthol by using recombinantly expressed channels. HEK293T cells were transfected with canine TRPM8 or TRPA1 and subjected to calcium imaging. Canine TRPA1 was confirmed to be activated by the selective TRPA1 agonist allyl isothiocyanate in a dose-dependent manner, which was inhibited by the TRPA1 antagonist HC-030031. Canine TRPA1 was also activated by menthol in a dose-dependent manner, even at high concentrations (up to 3 mM), in contrast with TRPA1 in rodents, which was inhibited by a high concentration of menthol. Canine TRPA1 showed a much higher value at EC₅₀ for menthol response compared with canine TRPM8 (178.9 μM and 5.3 μM, respectively). The activation of TRPA1 by menthol was inhibited by HC-030031 but it was not inhibited by the TRPM8 antagonist RQ-00203078. Our results suggest that menthol activates TRPM8 at low concentrations and may induce a pleasant cooling sensation, whereas at high concentrations it activates TRPA1 and may cause discomfort in dogs as in humans. In addition, this mechanism is suggested to be conserved in some carnivora and primates.