Figure 4: CaM enhances TRPA1 sensitivity and is essential for TRPA1 CDP in low Ca²⁺.

(A) Dose-response relationship between TRPA1 peak currents and carvacrol concentrations in HEK293 cells expressing TRPA1 or together with CaM mutants in nominal 0 Ca²⁺ (n = 6–10 for each curve). (B) Example TRPA1 currents evoked by carvacrol (CV, 100 μM) potentiated by Ca²⁺ (10 μM) with (red) or without CaM. (C) A typical TRPA1 current evoked by carvacrol (CV, 100 μM) was potentiated by Ba²⁺ (10 μM). (D) A summary of TRPA1 potentiation caused by 10 μM Ca²⁺ or Ba²⁺ in experiments similar to those in (B,C) in the presence of different CaM mutants. The number of experiments is given above each bar. (E) Scatter plots of Ca²⁺-induced TRPA1 potentiation fold as a function of initial TRPA1 peak currents from the same cells used in (B and D). Cells expressing TRPA1 only (black diamond) correspond to the control group in (D). (F) Schematic diagram shows the binding of Ca²⁺-CaM to the C terminus of TRPA1 and to the chimeric Tac-A1-CaMBD (top). Underneath are representative TRPA1 currents elicited by carvacrol (CV, 100 μM) potentiated by Ca²⁺ in cells co-expressing Tac (black) or Tac-A1-CaMBD (red) or perfused with W-7 (100 μM) (blue). (G) Collective results of TRPA1 potentiation induced by Ca²⁺ (10 μM, 500 μM) from experiments similar to those in (F). The number of experiments is shown above each bar. (H,I) Example (H) and summary (I) of Ca²⁺-induced potentiation of TRPA1 currents evoked by carvacrol (CV, 100 μM) in DRG neurons. AITC (100 μM, 25 s) was applied at the end. The potentiation was prevented by the CaMBD peptide (200 μM) (H,I), but not by the scrambled peptide (I). The number of experiments is indicated above each bar. All data are mean ± SEM. NS, not significant; **P < 0.01; ***P < 0.001; ^###P < 0.001 compared to bar 5.