Figure 2. Acid potentiates 2-APB-evoked currents from the cytoplasmic side in HEK293 cells that expressed TRPV3, TRPV2 and TRPV1.

(A) 2-APB and extracellular acidification lower intracellular pH (pH_i). Effects of 2-APB (A1) and low extracellular pH (pH 5.5, A2) on pH_i, measured by BCECF, in control (open circles) and TRPV3-expressing cells (filled circles). Panel (A3) shows concentration response to 2-APB in TRPV3-expressing cells. The solid line represents a fit to the Hill Equation. (B) Representative currents at +60 mV recorded in an inside-out patch excised from a TRPV3-expressing cell. After sensitization by repeated applications of 100 μM 2-APB to the cytoplasmic side, the patch was exposed to 5 μM 2-APB at pH 7.4 and pH 5.5. Note, pH 5.5 alone also elicited a small increase in current when applied from the intracellular side. (C) Relative TRPV3 currents elicited by 5 μM 2-APB at pH 7.4 and pH 5.5 from the cytoplasmic side. (D,E) Effects of intracellular acid on 2-APB evoked TRPV2 currents in inside-out patches. Representative current trace (D) and average responses (E) show that lowering pH_i to 6.0 and 5.5 strongly enhanced the current elicited by 300 μM 2-APB. Note, pH 5.5 alone did not induce any detectable current. (F) Representative TRPV1 currents recorded from an inside-out patch stimulated with varying concentrations of capsaicin (Cap) or 2-APB at either pH 7.4 or 5.5 applied from the cytoplasmic side. Note, when applied intracellularly, pH 5.5 did not induce any measurable TRPV1 current. (G) Relative TRPV1 currents at +60 mV elicited by 0.1 μM Cap and 100 μM 2-APB at pH 7.4 and 5.5 from the cytoplasmic side. The acidic pH only potentiated the response to 2-APB but not that to Cap. Membrane patches were excised from TRPV3, TRPV2 or TRPV1-expressing HEK293 cells. Holding potential was +60 mV. Error bars represent SEM.