Figure 3.

TRPA1 is activated by weak acids that acidify the cell cytosol. (A) Changes in emission from the pH-sensitive fluorescent probe carboxy-DFFDA in HEK-293 cells in response to acetic acid at varying concentrations (0, 0.5, 2, 10, and 100 mM at pH 5) and pH (10 mM; pH 5, 6, and 7) and to a panel of carboxylic acids (10 or 100 mM; pH 5). A representative experiment is shown on the left. (B) Proposed model for how acetic acid might activate TRPA1. (C) Currents evoked in HEK-293 cells expressing TRPA1 (peak magnitude at + 80 mV) in response to acetic acid at varying concentrations and pH, and to other carboxylic acids as indicated. Same color scheme as in A. Data for 0 and 10 mM of acetic acid, pH 5, were reproduced from Fig. 2 B. Representative traces of current activation by 100 mM of lactic acid (LA), pH 5, and 10 mM PA, pH 5, are shown on the left. Inset shows the structures of the acids. (D) The magnitude of the TRPA1 current plotted as a function of the change in fluorescence of the pH-sensitive dye carboxy-DFFDA. Colors correspond to the scheme in A and B. The correlation between the change in fluorescence and the magnitude of the TRPA1 current suggests that intracellular pH is the proximate stimulus that gates TRPA1 in response to extracellularly applied weak acids. Data are represented by the mean ± SEM.