1 TRPM8 (CMR1) is a Ca 2 þ -permeable channel, which can be activated by low temperatures, menthol, eucalyptol and icilin. It belongs to the transient receptor potential (TRP) family, and therefore is related to vanilloid receptor type-1 (VR1, TRPV1). We tested whether substances which are structurally related to menthol, or which produce a cooling sensation, could activate TRPM8, and compared the responses of TRPM8 and VR1 to these ligands. 2 The effects of 70 odorants and menthol-related substances on recombinant mouse TRPM8 (mTRPM8), expressed in HEK293 cells, were examined using a FLIPR s assay. In all, 10 substances (linalool, geraniol, hydroxycitronellal, WS-3, WS-23, FrescolatMGA, FrescolatML, PMD38, CoolactP and Cooling Agent 10) were found to be agonists. 3 The EC 50 values of the agonists defined their relative potencies: icilin (0.270.1 mM)4FrescolatML (3.371.5 mM) 4 WS-3 (3.771.7 mM) (À)menthol (4.171.3 mM) frescolatMAG (4.871.1 mM) 4 cooling agent 10 (672.2 mM) (þ )menthol (14.471.3 mM) 4 PMD38 (3171.1 mM) 4 WS-23 (4477.3 mM) 4 Coolact P (66720 mM) 4 geraniol (5.971.6 mM) 4 linalool (6.772.0 mM) 4 eucalyptol (7.772.0 mM) 4 hydroxycitronellal (19.672.2 mM). 4 Known VR1 antagonists (BCTC, thio-BCTC and capsazepine) were also able to block the response of TRPM8 to menthol (IC 50 : 0.871.0, 3.571.1 and 1871.1 mM, respectively). 5 The Ca 2 þ response of hVR1-transfected HEK293 cells to the endogenous VR1 agonist Narachidonoyl-dopamine was potentiated by low pH. In contrast, menthol-and icilin-activated TRPM8 currents were suppressed by low pH. 6 In conclusion, in the present study, we identified 10 new agonists and three antagonists of TRPM8. We found that, in contrast to VR1, TRPM8 is inhibited rather than potentiated by protons.
