BRADYKININ-INDUCED AND THROMBIN-INDUCED INCREASES IN ENDOTHELIAL PERMEABILITY OCCUR INDEPENDENTLY OF PHOSPHOLIPASE-C BUT REQUIRE PROTEIN-KINASE-C ACTIVATION

We determined whether activation of phosphatidylinositol-specific phos pholipase C (PI-PLC) and a subsequent increase in cytosolic calcium co ncentration ([Ca2+](i)) was an obligatory signaling event mediating th e increase in transendothelial permeability induced by bradykinin (BK) and alpha-thrombin (alpha-T). Both BK and alpha-T (each at a concentr ation range of 0.01-1 mu M) caused dose-dependent increases in transen dothelial I-125-albumin permeability in cultured bovine pulmonary arte ry endothelial cell monolayers. Both agonists also produced a rise in inositol (1,4,5)-trisphosphate [Ins(1,4,5)P-3] by 10 sec that was foll owed by a prolonged increase in [Ca2+](i). Pretreatment of endothelial cells with the PLC inhibitor, 1-(6-((17 5(10)-trien-17-yl)amino)hexyl )-1H-pyrrole-2,5-dion [(U73122) at 10 mu M for 15 min], prevented the increases in lns(1,4,5)P-3 and [Ca2+](i) induced by both BK and alpha- T. However, inhibition of PLC with U73122 or another PLC inhibitor, ne omycin, did not prevent the increase in endothelial permeability induc ed by either agonist. In contrast, depletion of cellular protein kinas e C (PKC) with phorbol-12-myristate 13-acetate (0.01 mu M for 20 hr) i ncreased both BK-and alpha-T-induced phosphoinositide turnover but inh ibited the agonist-induced increase in permeability. A PKC inhibitor, staurosporine (5 mu M) likewise inhibited the BK-induced increase in e ndothelial cell permeability to albumin. We conclude that increases in endothelial permeability induced by the inflammatory mediators, BK an d thrombin, can occur independently of PLC activation and increased [C a2+](i) but that a PKC-dependent pathway is required for the permeabil ity response. (C) 1997 Wiley-Liss, Inc.