Fig. 4.

BmTRPA1 is a thermosensitive TRP channel. (A) BmTRPA1-expressing cells were identified using coexpressed DsRed protein (Left). Representative results are shown for Fura-2 Ca²⁺ imaging at 25.1 °C, 15.4 °C, and 43.7 °C. The pseudocolor indicates intensity of the 340/380-nm fluorescence ratio. (B) Temporal changes in the Fura-2 ratio in BmTRPA1-expressing cells (Upper) and temperature (Lower) in the presence of 2 mM extracellular Ca²⁺. The average trace (red line) ± SD is shown at the top. Ionomycin was added at 240 s (Iono, gray bar), n = 85. (C) Temporal changes in the current (Upper trace) in a BmTRPA1-expressing cell and temperature (Lower trace) during temperature-fluctuation voltage-clamp whole-cell in patch-clamp analysis. Holding potential was −60 mV throughout the experiment. (D) Representative temperature-response profile for heat-induced BmTRPA1 current, as observed in C. (E) An Arrhenius plot for the heat-induced BmTRPA1 current shows a clear flex point in temperature dependency (data in D were converted). The temperature threshold for BmTRPA1 activation was defined as the point at which the two linear-fitted lines crossed (a flex point). The Q₁₀ value was calculated for each line.