Stimulated release of Ang-2 stored in Weibel-Palade bodies. (A) Western blot analysis of myc-tagged Ang-2 in the supernatant of retrovirally transduced HUVECs identifies ionomycin, thapsigargin, and PMA as inducers of Ang-2 release. The Ca²⁺ channel blocker nifedipine inhibits the PMA-induced release of Ang-2. (B) Cytochemical analysis demonstrates ionomycin, thapsigargin, and PMA as regulators of Ang-2 release in HUVECs. (C) Stimulation of HDMVECs with histamine or thrombin induces Ang-2 release. Original magnification × 20 (B-C).