Fig. 2

Gating and modulation of TRPV1 channels by 1,4-dioxane. a Representative whole-cell recordings from TRPV1-expressing HEK293 cell. The cell was exposed to varied concentrations of 1,4-dioxane or capsaicin (Cap, 1 μM), as indicated. Holding potential was −60 mV. b Summary of relative currents elicited by 1,4-dioxane or capsaicin. Currents were normalized to that evoked by 1 μM capsaicin. Numbers of cells are indicated in parentheses. c Dose-response curve of 1,4-dioxane. Fitting by Hill’s equation gave an EC₅₀ = 2.1 ± 0.03% and n_H = 3.1 ± 0.22 (n = 9). d Representative single-channel currents recorded from an outside-out patch of TRPV1-expressing HEK293 cells. Currents were evoked by 1,4-dioxane at different voltages ranging from −100 to +100 mV and were low-pass filtered at 2 kHz. e Unitary current-voltage relationships activated by 1,4-dioxane (red) or capsaicin (black), showing no significant difference. f Potentiation effects of 1,4-dioxane. Currents were evoked by capsaicin, 2-APB, acidification (pH 6.0) or 1,4-dioxane as indicated. The presence of 1,4-dioxane potentiated the responses of each stimulation. Holding potential V_h = −60 mV. g Comparison of the averaged response evoked by different agonists with or without 1% 1,4-dioxane. The labels over the bars indicate the number of recordings. h Potentiation by 1,4-dioxane of single-channel activity in outside-out patches excised from TRPV1-expressing HEK293 cells. Capsaicin, 1,4-dioxane, capsazepine, or RR were applied consecutively to the same patches as indicated. The holding potentials were +60 mV (upper) and −60 mV (lower), respectively. Co-application of 1,4-dioxane (0.5%) with 0.02 μM capsaicin resulted in more single-channel openings. i Average changes in TRPV1 open probability. The addition of 1,4-dioxane remarkably increased single-channel open probability. Inclusion of RR but not capsazepine reduced the channel openings (V_h = −60 mV, n = 7–11 cells per condition)