FIGURE 1.
PI(4,5)P2 directly activates TRPV1 and enhances capsaicin-induced current. Macroscopic currents for TRPV1 induced by PI(4,5)P2 before (A) and after (B) the addition of 1 μm CAP obtained using inside-out patches. Current recordings were obtained in response to voltage pulses from 0 mV to 220 mV in 10 mV steps. This voltage protocol was applied for each concentration of PI(4,5)P2 before and after 1 μm of CAP in the same patch (n>4). No currents were detected in these voltage ranges in the absence of agonists. Temperature: 20 °C. C, current-voltage relationship obtained by adding the indicated PI(4,5)P2 concentration and adding capsaicin. Each point is the average of measurements on 4 patches. D, current-voltage relationship obtained by adding CAP prior to the PI(4,5)P2 addition. E, dose-response curves for TRPV1wild-type treated with PI(4,5)P2 before and after adding 1 μm CAP. EC50 values were 3.2 ± 0.2 μm and 5.6 ± 0.9 μm for respectively (nH = 1.7 and 1.5, n >4). F, allosteric model proposed for the activation of the TRPV1 channel by CAP and PI(4,5)P2. F, allosteric model for TRPV1 gating. The opening reaction is described by the equilibrium constant L and the binding of PI(4,5)P2, and CAP by the equilibrium constants Q and K, respectively. Allosteric factors F and C facilitate opening when PI(4,5)P2 and CAP, respectively bind to the channel. G, PI(4,5)P2 dose-response curves. The curves were identified by using the equation given in the figure with Q = 7 μm (Fig. 1E) and K = 0.6 μm (REF. 4) and C = 1,000 and D = 10,000.