English. Phorbol ester-mediated pulmonary artery endothelial barrier dysfunction through regulation of actin cytoskeletal mechanics. Am J Physiol Lung Cell Mol Physiol 287: L153-L167, 2004. First published March 5, 2004 10.1152/ajplung.00292.2003.-The mechanisms of phorbol ester-and thrombin-mediated pulmonary artery endothelial barrier dysfunction were compared. Phorbol ester dibutyrate (PDBU) mediated slow force velocity and less force than thrombin. Taxol did not attenuate PDBU-mediated tension, while it reversed nocodazole-mediated tension. PDBU-mediated tension was not affected by acrylamide; PDBU increased cell stiffness and produced greater declines in transendothelial resistance (TER) than acrylamide. Thus PDBU caused a net increase in tension and did not unload microtubule or intermediate filaments. Microfilament remodeling, determined on the basis of immunocytochemistry and actin solubility, lacked the sensitivity and specificity to predict actindependent mechanical properties. Thrombin increased myosin light chain (MLC) kinase site-specific MLC phosphorylation, according to peptide map analysis, whereas PDBU did not increase PKC-specific MLC phosphorylation. The initial PDBU-mediated tension development temporally correlated with PDBU-mediated decline in TER and increased low-molecular-weight caldesmon (l-CaD) phosphorylation. PDBU-mediated tension development and decreases in TER were associated with a temporal loss of endothelial cell-matrix adhesion, based on a numerical model of TER. Although, on the basis of immunocytochemistry, thrombin-mediated tension was associated with actin insolubility, actin reorganization, and gap formation, these changes did not predict thrombin-mediated gap formation, based on TER and time-lapse differential interference contrast microscopy. These data suggest that PDBU may disrupt endothelial barrier function through loss of cell-matrix adhesion through l-CaD-dependent actin contraction. phorbol ester dibutyrate; porcine pulmonary artery endothelial cells; myosin light chain; low-molecular-weight caldesmon IT HAS BEEN WELL DOCUMENTED that phorbol esters directly increase endothelial permeability through loss of cell adhesion in association with remodeling of the actin cytoskeleton (2, 27). Phorbol esters represent unique edemagenic molecules that allow greater insight into how signal transduction pathways remodel endothelial cell adhesion through actin-dependent mechanical forces (2,17,27,30). The precise mechanism by which phorbol esters regulate endothelial cell adhesion through remodeling of actin-dependent mechanical forces remains poorly understood.

These data suggest that cytomegalovirus disease is not a significant risk factor for the development of primary ischemic heart disease after renal transplantation.