Fig. 1.

The actin cytoskeleton limits Ca²⁺-driven WPB exocytosis. (A) Rhodamine (Rh)–phalloidin labelling of HUVECs after a 20-min incubation with vehicle (0.1% DMSO) (i), or 1 µM cytochalasin D (Cyto-D) (ii). Scale bars: 10 µm. (Bi) Cumulative plots of the total number of WPB fusion events detected during ionomycin stimulation (1 µM, applied at t=0 s) of VWFpp–EGFP-expressing HUVECs pre-treated for 20 min with vehicle [0.1% DMSO, no cytochalasin D (−Cyto-D), black, n=954] or 1 µM Cyto-D (+Cyto-D; grey, n=934). Data are scaled to the mean fraction of fluorescent WPBs that underwent fusion in each condition (−Cyto-D, 61.1±2.6%, n=19 cells; +Cyto-D, 71.0±3.3%, n=23 cells; mean±s.e.m.). (Bii) Summary of the mean±s.e.m. delay, maximum rate and percentage of fluorescent WPBs exocytosed in control (black, n=19) and Cyto-D-treated (grey, n=23) cells. *P=0.013, t-test. (C) Ionomycin-stimulated secretion of endogenous VWFpp in control; −Cyto-D (black) or +Cyto-D (grey) cells. Plots show data pooled from three independent experiments performed in triplicate (mean±s.e.m., n=9 replicates). *Adjusted P=0.011, ANOVA, Tukey multiple comparisons test.