to block menthol responses in AITC-sensitive neurons LETTER may be explained by the activation of TRPA1 counteracting block of TRPM8. Thus, VTN’s own published data seem to Reply to Voets et al.: Constellation argue against their reinterpretation. pharmacology is poised to answer Although we favor our original interpretation, we assert that fi VTN have overstated our scientific claims. In fact, we did not scienti c questions claim that “...TRPM8 is the sole functional cold and menthol sensor...” or that menthol is a “...specific TRPM8 agonist” Voets, Talavera, and Nilius (VTN) offer an alternative (emphasis added). Nor did we claim that the difference in cold interpretation (1) of our data (2) that focuses on menthol and menthol sensitivity between M+A+ (menthol, ATP, and responses in neurons sensitive to allyl isothiocyanate (AITC), AITC positive) neurons and M+A− (menthol positive but ATP a functional marker for transient receptor potential (TRP) and AITC negative) neurons “...is mainly due to differences A1 expression. They argue that such responses are mediated in the constellation of voltage-gated Ca2+,K+, and Na+ by TRPA1, not TRPM8. There is an ongoing controversy channels.” We stated explicitly that “...the magnitude of the surrounding the relative roles of TRPA1 and TRPM8 in cold response is mainly a function of differences in the constellations sensation. VTN argue that TRPA1 plays a primary role of ion channels expressed....” Because TRPA1 is part of the (ref. 1 and references therein), whereas others argue that constellation in M+A+ neurons, our statement is open to TRPA1 is not a cold sensor or is only a minor contributor to cold a TRPA1 contribution to cold and menthol sensitivity. We also sensation (3, 4). We did not intend to step into the middle of that stated, “The M+A+ neurons may be nociceptors that detect controversy. The focus of our article (2) was to illustrate the extreme cold with a sensation of burning pain, consistent utility of constellation pharmacology with specific physiologically with the coexpression of TRPM8 and TRPA1 in the same relevant examples. neuron” (2), thus acknowledging the potential role of TRPA1 in We agree with VTN that more selective TRP channel ligands the sensation of noxious cold. are needed. However, we continue to favor our original Russell W. Teichert1 and Baldomero M. Olivera interpretation of our data for multiple reasons. First, VTN cite Department of Biology, University of Utah, Salt Lake City, UT their own article to argue that menthol is an agonist of TRPA1 84112 (5). However, they fail to mention that only submicromolar to low-micromolar menthol concentrations activated TRPA1, 1. Voets T, Talavera K, Nilius B (2012) Transient receptor potential channel promiscuity frustrates constellation pharmacology. Proc Natl Acad Sci USA 109:E3338. whereas their own study, among others, demonstrated that high 2. Teichert RW, et al. (2012) Characterization of two neuronal subclasses through menthol concentrations (≥250 μM) did not activate TRPA1 constellation pharmacology. Proc Natl Acad Sci USA 109(31):12758–12763. 3. Bautista DM, et al. (2007) The menthol receptor TRPM8 is the principal detector of but actually blocked it (5). Because our experiments were environmental cold. Nature 448(7150):204–208. conducted with 250–500 μM menthol (2), the responses were 4. Knowlton WM, Bifolck-Fisher A, Bautista DM, McKemy DD (2010) TRPM8, but not TRPA1, is required for neural and behavioral responses to acute noxious cold likely mediated by TRPM8. Second, we and VTN (5) have temperatures and cold-mimetics in vivo. Pain 150(2):340–350. observed that only a minority of AITC-sensitive neurons are 5. Karashima Y, et al. (2007) Bimodal action of menthol on the transient receptor J Neurosci – fi – μ potential channel TRPA1. 27(37):9874 9884. menthol sensitive, which is dif cult to explain if 250 500 M 6. Meseguer V, et al. (2008) Transient receptor potential channels in sensory neurons are menthol activates TRPA1. Third, VTN state that their targets of the antimycotic agent clotrimazole. J Neurosci 28(3):576–586. reinterpretation is consistent with the observation that TRPM8 antagonists blocked menthol responses in AITC-insensitive Author contributions: R.W.T. designed research; R.W.T. performed research; R.W.T. and neurons but not in AITC-sensitive neurons (6). However, B.M.O. analyzed data; and R.W.T. and B.M.O. wrote the paper. their own article demonstrated that the TRPM8 antagonist The authors declare no conflict of interest. clotrimazole is also a TRPA1 agonist (6). Clotrimazole’s failure 1To whom correspondence should be addressed. E-mail: [email protected].

www.pnas.org/cgi/doi/10.1073/pnas.1215574109 PNAS | December 4, 2012 | vol. 109 | no. 49 | E3339 Downloaded by guest on September 24, 2021