Identification of Transmembrane Domain 5 as a Critical Molecular Determinant of Menthol Sensitivity in Mammalian TRPA1 Channels

Abstract

TRPA1 is a member of the transient receptor potential (TRP) family of ion channels and is expressed in a subset of nociceptive neurons.An increasing body of evidence suggests that TRPA1 functions as a chemical nocisensor for a variety of reactive chemicals, such as pungent natural compounds and environmental irritants. Activation of TRPA1 by reactive compounds has been demonstrated to be mediated through covalent modification of cytoplasmic cysteines located in the N terminus of the channel, rather than classical lockand-key binding. TRPA1 activity is also modulated by numerous nonreactive chemicals, but the underlying mechanism is unknown. Menthol, a natural nonreactive cooling compound, is best known as an activator of TRPM8, a related TRP ion channel required for cool thermosensation in vivo. More recently, menthol has been shown to be an activator of mouse TRPA1 at low concentrations, and a blocker, at high concentrations. Here, we show that human TRPA1 is only activated by menthol, whereas TRPA1 from nonmammalian species are insensitive to menthol. Mouse-human TRPA1 chimeras reveal the pore region [including transmembrane domain 5 (TM5) and TM6] as the critical domain determining whether menthol can act as an inhibitor. Furthermore, chimeras between Drosophila melanogaster and mammalian TRPA1 highlight specific residues within TM5 critical for menthol responsiveness. Interestingly, this TM5 region also determines the sensitivity of TRPA1 to other chemical modulators. These data suggest separable structural requirements for modulation of TRPA1 by covalent and nonreactive molecules. Whether this region is involved in binding or gating of TRPA1 channels is discussed.

Sensory Effects of Menthol and Nicotine in an E-Cigarette

“…Menthol's perceptual effects of cooling and sensory irritation have been well studied on the skin and in the mouth, 28,[37][38][39] and a recent investigation showed that menthol sniffed into the nose also produced burning and stinging as well as cooling. 40 Whereas menthol's innocuous cold sensations have been shown to depend on stimulation of the cold-sensitive receptor TRPM8, [41][42][43] its nociceptive sensations appear to arise at least in part from activation of the receptor TRPA1, 44,45 which plays an important role in pain perception, 46 including the sensitivity to painfully cold temperatures. 47 The data from experiment 1 show that when inhaled using the V2 E-cigarette, the coolness produced by 3.5% menthol was the most prominent flavor quality until the highest concentration of nicotine alone produced equal ratings of Overall Sensation.…”

Physiological, pharmacological, and behavioral evidence for a TRPA1 channel that can elicit defensive responses in the medicinal leech

“…However, 1-2 mmol l −1 menthol failed to elicit any activity in the leech lN cell (data not shown). This suggests that, similar to Drosophila TRPA1 (Xiao et al, 2008), the TRPA1-like channel in the leech is insensitive to menthol.…”

The Transient Receptor Potential Channel TRPM8 Is Inhibited via the α2A Adrenoreceptor Signaling Pathway

“…It is worthy to note that menthol is also an agonist of the TRPA1 channel expressed in small DRG neurons (29,30). However, there are several characteristic features of the mode of menthol action on TRPA1 that could be used to discriminate between TRPM8-and TRPA1-mediated menthol responses in sensory neurons.…”