Fig. S3. Reduction of intracellular ATP levels by mechanical stimulation in MCC13 cells.

Fig. S3. Reduction of intracellular ATP levels by mechanical stimulation in MCC13 cells. (a) Average trace of intracellular ATP ([ATP]i) in ATP Red-1-loaded MCC13 cells before and after treatment with the mitochondrial uncoupler FCCP (3 μM). (b) Summary scatter plot for (a), showing the FCCP-induced decrease in [ATP]ᵢ relative to the baseline. Each dot represents data from an independent experiment (n = 4), with responses averaged from up to 16 cells per experiment. Data are represented as mean ± SEM. Statistical significance: ***P < 0.001 vs. baseline (one-sample t-test). (c) Representative fluorescent images (top) showing [ATP]i in ATP Red 1-loaded MCC13 cells before (left), during (middle), and after (right) mechanical stimulation (white arrows; scale bar, 50 μm). The bottom panel shows the corresponding trace of [ATP]i, indicating a decrease after mechanical stimulation (red arrow). (d) Summary scatter plot for (c), showing the mechanical stimulation-induced decrease in [ATP]ᵢ relative to the baseline. Each dot represents data from an independent experiment (n = 6). Data are represented as mean ± SEM. Statistical significance: ***P < 0.001 vs. baseline (one-sample t-test). Fluorescence signals were normalized to the pre-stimulus baseline (F/F₀). FCCP was used as a positive control to confirm ATP sensitivity of the assay. Intracellular ATP was monitored in live MCC13 cells using the fluorescent ATP indicator ATP-Red 1 and quantified as normalized fluorescence (F/F₀).Supplementary figure associated with: Seo MS et al. Merkel cells release ATP in response to mechanical stimulation to mediate paracrine signalling. British Journal of Dermatology (2026). https://doi.org/10.1093/bjd/ljag067