HUVECs were incubated with PV and acetylcholine (ACh) for 1 h, and then the culture medium was collected for NO detection with the Griess reagent. Ca2+-free medium contained 2.5 mM EGTA. BAPTA-AM chelates intracellular Ca2+. Data are expressed as the mean ± standard error of the mean (S.E.M) for more than 5 individual experiments. ** p < 0.01 indicates a significant difference from PV alone. ##p < 0.01 indicates a significant difference from ACh alone.