Recovery and half-life of Weibel-Palade body-stored endothelial cell Ang-2. (A) Ang-2–overexpressing HUVECs were stimulated with PMA for 1 hour after which the medium was changed and the recovery of intracellular Ang-2 monitored over time by Ang-2 immunocytochemistry. The recovery of the depleted Ang-2 stores is detectable within 8 hours. The monolayer is uniformly Ang-2⁺ after 24 hours. (B) The recovery of intracellular Ang-2 stores is paralleled by a transcriptional upregulation of Ang-2 mRNA, which is detectable within 4 to 6 hours on PMA challenge. (C) Ang-2 has a long half-life period. Ang-2 is still detectable after 16 hours of actinomycin D challenge in cultured HUVECs. Original magnification, × 20 (A-C).