Fig. 3.

Ca²⁺ sparks are mediated by TRPM7. Application of (A) 2-APB (100 μM) and (B) waixenicin-A (3–10 μM) inhibit TRPM7 and significantly reduce Ca²⁺ spark formation. (a) Heatmaps of Ca²⁺ sparking before (top) and after (bottom) application of inhibitors. (b) Number of Ca²⁺ hotspots per active cell (2-APB: n = 24 [pre] and n = 17 [post], p < 0.001; and waixenicin-A: n = 45 [pre] and n = 20 [post], $p\ll 0.001$; Mann–Whitney U-test, two-tailed). (c) Frequency distribution of number of hotspots per cell before and after application of inhibitors (2-APB: n = 24, p < 0.01; and waixenicin-A: n = 45, $p\ll 0.001$; McNemar's test for paired proportions, two-tailed). (d) Potent inhibition of Ca²⁺ spark activities at hotspots (indicated with arrows in a) following addition of 2-APB (see also Video 4) and waixenicin-A. Note that inhibition by waixenicin-A required preincubation for a few minutes. Data are mean ± SEM of at least 5 independent experiments. ^#p < 0.01, and **p < 0.0001.