Uptake of defibrotide by endothelial cells. (A) SK cells were incubated with DF (4 μg/mL final concentration), labeled with Alexa 488, for the indicated period of time (from 0-4 h). (B) The addition of 10 μM adenosine receptor antagonist (8-p-sulfophenyltheophylline) to SK monolayers for 1 hour before the incubation with DF (4 h) did not interfere with SK–DF interaction. (C) For saturation assays, SK monolayers were exposed to increasing doses of DF (from 0-12 μg/mL) for 2 hours. (D) For temperature dependence assays, SK were incubated with 4 μg/mL for 2 hours at 37°C and 4°C. Results are expressed in percentage of positive cells.