Figure 4: Proton potentiation of 2-APB-evoked currents remains in TRPV3 and TRPV1 mutants that show no response to acid alone.

(A) Whole-cell currents at −60 mV for TRPV3(L508R) expressed in HEK293 cells, showing that pH 5.5 strongly enhanced the response to 100 μM 2-APB after sensitization by repeated applications of 500 μM 2-APB. (B) Summary of relative currents elicited by 100 μM 2-APB at pH 5.5, normalized to that by the same concentration of 2-APB at pH 7.4. WT TRPV3 and linker 2–3 mutants as described in Fig. 3 were transfected into HEK293 cells individually and whole-cell recordings performed with the cells held at −60 mV. (C,D) Similar to (A) and (B), but currents were recorded from inside-out patches held at +60 mV. (E) Whole-cell currents at −60 mV for TRPV1(E600Q/T633A) expressed in HEK293 cells, showing the responses to 2-APB, capsaicin (Cap), and low pH at indicated concentrations/levels. Results revealed that pH 5.5 enhanced the currents elicited by 10 μM 2-APB but not 0.01 μM Cap. In addition, pH 5.5 alone produced no detectable current. Note that the combination of 10 μM 2-APB or 0.01 μM Cap and pH 5.5 had a steady-state response which was followed by an off response during washout. These are marked as ‘on’ and ‘off’ by arrows. (F) Summary of relative whole-cell currents of TRPV1(E600Q/T633A) evoked by 0.01 μM Cap or 10 μM 2-APB at pH 7.4 and 5.5, including both the ‘on’ and ‘off’ currents at pH 5.5. Numbers of cells are shown in parentheses. Error bars represent SEM.