Brefeldin A preferentially inhibits secretion of proVWF from HUVECs. (A) PhosphorImager data of VWF immunoprecipitated from medium of long-term metabolically labeled HUVECs and chased in the presence (BFA) or absence (Control) of 5 μM Brefeldin A during a 5-hour period. Mature VWF and proVWF are indicated by the closed and open arrowheads, respectively. (B,C) Quantification of the time course of appearance of radiolabeled proVWF (B) and mature VWF (C) in the medium of cells chased in the presence (▴) or absence (□) of 5 μM BFA. Data points represent means (± SD) of 6 observations. Experiments were repeated on 2 further occasions with similar results.