Influence of adenosine kinase (AK) repression on endothelial barrier function in vitro. (A,B) Characterization of a HMEC-1 line with psiRNA repression of AK. PsiRNA-mediated silenced cells (HMEC-AK) or control transfected HMEC-1s (HMEC-Scr) were subjected to normoxia or hypoxia (12 hours). AK transcript was determined by real-time RT-PCR. Results are derived from 3 experiments. *Difference between normoxia and hypoxia (*P < .01). (B) Western blot analysis of AK protein. (C) Influence of extracellular adenosine on endothelial barrier function in HMEC-1 with psiRNA-repression of AK (HMEC-AK), or controls (HMEC-Scr). Indicated concentrations of adenosine were added to the apical surface and permeability to FITC-dextran was quantified. Data are expressed as mean plus or minus SD of percent control flux (*P < .01, significant differences between normoxia and hypo-xia; #P < .001, significant differences between HMEC-Scr and HMEC-AK). (D) Influence of AK inhibitor 5′-iodotubericidin (ITU, 20 μM) on adenosine-elicited barrier responses. (*P < .05, significant differences between normoxia and hypoxia; #P < .001, significant differences between treatment with ITU or control).