SK prevents EC apoptosis. (A) DAPI stain performed on ECs^SK and ECs^EV in culture medium supplemented with 20% FCS (HUVE medium; HM) or SF medium. (B) Quantification of 5 consecutive microscopic fields to a total cell count of 100 from 2 separate experiments. Bars represent SEM. *P less than .001 compared with ECs^EV under SF conditions. (C) Caspase-3 activity in ECs^SK and ECs^EV in 5 separate endothelial cell lines measured under basal culture conditions (HM) or (D) after 24 hours of serum deprivation. Panel E shows the pooled data from the 5 endothelial cell lines. Bars represent 95% confidence intervals. *P less than .05 for ECs^SK under basal or serum-free conditions compared with corresponding ECs^EV, normalized to 100.