Figure 3: TRPM8 osmosensitivity is modulated by temperature.
From: TRPM8 is a neuronal osmosensor that regulates eye blinking in mice
(a) Time course of [Ca2+]i responses evoked by raising the osmolality from 267 mOsm kg−1 to the values shown by addition of sucrose. Solution changes at 20 s. (b) Osmolality-[Ca2+]i response relationship for mTRPM8-expressing CHO cells. EC50 value was 318±5 mOsm kg−1 (n=9). Note the absence of evoked increase in [Ca2+]i in untransfected CHO cells. (c) Activation of TRPM8 by a hyperosmotic solution (367 mOsm kg−1) in the presence of increasing concentrations of AMTB, IC50 4±0.3 μM (n=3). (d) Osmolality-response curves at 25, 29, 33 and 37 °C (curves are representative examples of nine experiments). (e) EC50 values for osmolality evoked responses in mTRPM8 CHO cells at 25, 29, 33 and 37 °C (n=9). P values represent comparison to 25 °C, **P<0.01, Kruskal–Wallis test with pairwise comparisons. (f) Temperature activation thresholds were determined by plotting the log Fura-2 (340/380) ratio against temperature. The temperature at which the log ratio begins to deviate from baseline was used as the temperature activation threshold. The graph illustrates a [Ca2+]i response evoked by a cooling ramp in a mTRPM8 CHO cell population (367 mOsm kg−1). (g) Temperature activation thresholds of mTRPM8 CHO cells at different osmolalities (n=4–5 experiments (minimum of 19 cells per experiment)). (h) Change in temperature thresholds in response to two sequential cooling ramps. First ramp in solution of 267 mOsm kg−1, second ramp at osmolalities indicated. Neurons exposed to an increase in osmolality exhibited shifts in activation thresholds to warmer temperatures (267 mOsm kg−1, n=38 neurons. 367 mOsm kg−1, n=85 neurons. 517 mOsm kg−1, n=55), P values represent comparison to 267 mOsm kg−1. **P<0.01, ***P<0.001, Kruskal–Wallis, followed by Dunn-Bonferroni’s pairwise post-hoc test. Increases in osmolality in experiments (a–h) were made by addition of sucrose.
