Figure 2.

Acetic acid activates TRPA1 but not TRPV1. Whole cell currents evoked in response to acids from untransfected HEK-293 cells or HEK-293 cells transfected with YFP-rTRPA1 or rTRPV1 as indicated. (A) 10 mM of acetic acid (HOAc) titrated to pH 5, but not 10 mM MES, pH 5, or 10 mM HEPES, pH 5, activated a large, outwardly rectifying current in TRPA1-expressing cells (right). Current–voltage relationship obtained from ramp depolarization (1V/s) at the time indicated shows reversal of the current near 0 mV and mild outward rectification. Small currents were evoked in untransfected cells in response to pH 5.0 solution buffered with MES, HEPES, or acetic acid (left). (B) Average data from experiments as in A show that the activation of TRPA1 by acetic acid is conserved in humans and rodents. Significance (compared with activation of untransfected cells by acetic acid) was determined with the one-tailed Student’s t test (n = 4–7). Representative traces for responses from mouse or human transfected cells are shown on the right. (C) 10 mM MES, pH 5.0, activated a large TRPV1 current, which was inhibited by subsequent application of 10 mM of acetic acid, pH 5. (D) Average data (n = 10) from experiments as in C, where current decay was measured during two 10-s windows immediately before and after acetic acid application. Significance was determined by the Wilcoxon signed-rank test. Average data are represented by the mean ± SEM. *, P < 0.05; **, P < 0.01; ***, P < 0.001.