Extracellular BzATP triggers microvesicle shedding, dendrite retraction, and cell shrinkage in human DCs. Immature monocyte-derived DCs seeded on a glass coverslip at a concentration of 10⁵/mL were treated with BzATP at 37°C in standard saline solution (A-B); Ca²⁺-free, 500-μM EGTA–supplemented saline solution (C); or sucrose solution (D-E) and stimulated with either 30 (A) or 200 μM BzATP (B-D). Images were acquired at 5-second intervals with the Nikon Eclipse T-300 microscopy setup described in “Materials and methods,” under “Microscopic analysis.” Bar = 10 μm. In panel E, DCs were placed in culture flasks (see “Materials and methods”) and stimulated with BzATP (200 μM) or ATP (3 mM) in sucrose saline solution (□); in Ca²⁺-free, 500-μM EGTA–containing sucrose saline solution (▪); or in the absence of extracellular Ca²⁺, after incubation of the cells for 30 minutes in the presence of 5 μM BAPTA/am (⊡). Black arrows in A, C, and D indicate shed microvesicles. Data are averages ± SE of 3 experiments performed with cells from 3 different donors.