Permeability of human endothelial monolayers: effect of vasoactive agonists and cAMP

Permeability coefficients of human umbilical vein endothelial cell monolayers cultured on polycarbonate filters were determined by monitoring transendothelial albumin transport. Permeability was determined as a function of time in culture and in the presence of vasoactive agonists. Permeability decreased with increasing time in culture. All agonist experiments were performed with 15-day cultures because this time point best modeled the in vivo permeability barrier function. Permeability of endothelial monolayers decreased significantly in the presence of the stable prostacyclin analogue iloprost (6 nM), dibutyryl adenosine 3',5'-cyclic monophosphate (cAMP, 0.5 mM)-3-isobutyl-1-methylxanthine (IBMX, 0.1 mM), 8-bromo cAMP (0.5 mM)-IBMX, dibutyryl cAMP-theophylline (0.5 mM), or IBMX. A 9.6-fold increase in permeability resulting from thrombin [0.15 U/ml (1 nM)] treatment was inhibited by pretreating the monolayers with dibutyryl cAMP-IBMX, 8-bromo cAMP-IBMX, dibutyryl cAMP-theophylline, dibutyryl cAMP, IBMX, iloprost, or D-Phe-Pro-Arg-CH2-alpha-thrombin (1 nM). The thrombin-induced permeability increase was not significantly altered by pretreating monolayers with aspirin (5 microM) or indomethacin (50 microM). Inactivated forms of thrombin, diisopropylflurophosphate-alpha-thrombin (1 nM) and D-Phe-Pro-Arg-CH2-alpha-thrombin, did not significantly affect permeability. Monolayer permeability was not altered in response to bradykinin (1 microM). These results suggest a mediating role for intracellular cAMP in the permeability barrier function of endothelial monolayers.