Tissue-factor coagulant activity of cultured human endothelial and smooth muscle cells and fibroblasts

The tissue-factor (thromboplastic) activity of cultured human endothelial cells and fibroblasts is low at time of transfer into fresh medium but increases 3–10 fold. Endothelial cells reach peak activity (400 U/10(5) cells) 5–8 hr after subculture. Activity in fibroblast cultures peaks (3000–12,000 U/10(5) cells) 7–12 hr after subculture. After attaining maximum activity, endothelial and fibroblast tissue- factor content decreases in a time course similar to other cells studied in this laboratory, approaching basal levels by 24–50 hr after subculture. If medium over fibroblasts is changed every 12 hr, activity can be sustained at the peak level for an additional day but cannot be maintained at a high level indefinitely. The kinetics of expression of smooth muscle cell tissue factor are markedly different from other cell types. There is always a pronounced lag (30 hr or more) before the activity increases, and then, in most cases, there is no subsequent decline in activity even though the cells are not refed or restimulated. The activity of each of these cell types is cryptic but becomes available after freeze-thaw disruption of cells.