Hypoxia/aglycemia increases endothelial permeability: role of second messengers and cytoskeleton

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Abstract
The effects of hypoxia/aglycemia on microvascular endothelial permeability were evaluated, and the second messenger systems and the cytoskeletal-junctional protein alterations in this response were also examined. Monolayers of human dermal microvascular endothelial cells on microcarrier beads were exposed to either thioglycolic acid (5 mM, an O2 chelator), glucose-free medium, or both stresses together. Permeability measurements were performed over a 90-min time course. Although neither hypoxia alone nor aglycemia alone increased endothelial permeability significantly, the combination of both increased significantly as early as 15 min. Intracellular Ca2+ measurements with fura 2-AM showed that hypoxia/aglycemia treatment increased Ca2+ influx. To determine the second messengers involved in increased permeability, monolayers were incubated for 30 min with the cytosolic Ca2+ scavenger 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester (TMB-8, 0.1 mM), a classical protein kinase C (PKC) blocker, Gö-6976 (10 nM), a cGMP-dependent protein kinase (PKG) antagonist, KT-5823 (0.5 μM), or the mitogen-activated protein (MAP) kinase inhibitor PD-98059 (20 μM). Hypoxia/aglycemia-mediated permeability changes were blocked by chelating cell Ca2+, PKC blockade, PKG blockade, and by inhibiting p38 MAP kinase-1. Finally, changes in the binding of junctional proteins to the cytoskeleton under the same conditions were assessed. The concentrations of occludin and pan-reactive cadherin binding to the cytoskeleton were significantly decreased by only both stresses together. However, these effects were also blocked by pretreatment with TMB-8, Gö-6976, KT-5823 (not in occludin), and PD-98059. These data suggest that hypoxia/aglycemia-mediated endothelial permeability may occur through PKC, PKG, MAP kinase, and Ca2+related to dissociation of cadherin-actin and occludin-actin junctional bonds.