Figure 2.
Menthol modulation of TRPA1 is species- and concentration-dependent as assayed by electrophysiology. A, Menthol activates hTRPA1. Left, Both menthol (250 μm) and MO (100 μm) similarly increase whole-cell currents in HEK293T cells transiently transfected with hTRPA1. Representative current traces are shown before (black), at the peak of the menthol response (green), and at the peak of the MO response (brown) after reversal of the menthol effect. Cells were challenged every 5 s with voltage ramps between −120 and +120 mV (2.8 mV/ms) from a holding potential of −50 mV (protocol shown below). The currents at −120 (red) and +120 (black) mV were measured and plotted over the entire time course of the experiment (right). Menthol and MO application is indicated by the green and brown bars, respectively. Vertical dashed lines indicate the times that either the indicated compound arrived at the bath or washout was initiated. Note that during the gap between 1100 and 1370 s, the cell was challenged with voltage step protocols (extracellular saline, 2 mm Ca2+ ES; pipette saline, 0 mm Ca2+ IS). Responses of cells tested in 0 mm Ca2+ ES were similar to those obtained in 2 mm Ca2+ ES and combined. B, Low concentrations of menthol activate mTRPA1. Left, Menthol (50 μm) increases whole-cell currents in HEK293T cells transiently transfected with mTRPA1. Representative current traces are shown before (black) and at the peak of the menthol response (green). Right, Exposure to menthol is indicated by the green bar. Note that during the gap between 220 and 380 s, the cell was challenged with voltage step protocols (extracellular saline, 0 mm Ca2+ ES; pipette saline, 0 mm Ca2+ IS). C, High concentrations of menthol block subsequent responses to MO (100 μm) applied in the presence of menthol (500 μm). Top left, Representative current traces are shown before (black), at the peak of the menthol response (green), at the peak of the MO/menthol response (brown), and at the peak of the washout response (blue). Top right, The whole-cell currents at −120 (red) and +120 (black) mV were measured and plotted over the entire time course of the experiment. The durations of exposure to menthol and MO are indicated by the green and brown bars, respectively. Bottom left, Ethanol (0.05%) had no effect on whole-cell conductance (gray trace) and 100 μm MO elicited a large response (brown trace). Bottom right, The currents at ±120 mV are shown over the course of the experiment (extracellular saline, 2 mm Ca2+ ES; pipette saline, 0 mm Ca2+ IS).