Hypoxia induced disruption of the cardiac endothelial glycocalyx: implications for capillary permeability.

OBJECTIVE: The aim was to determine the effect of hypoxia on the ultrastructure of the endothelial glycocalyx of cardiac capillaries.
METHODS: Isolated rat hearts were perfused with oxygenated or hypoxic Krebs solution for 30 min after equilibration with oxygenated medium. They were then perfused with a cationic marker (ruthenium red, lanthanum nitrate, or cationised ferritin) to delineate the cardiac endothelial glycocalyx in the electron microscope. With ruthenium red and lanthanum, perfusions were carried out both in the presence and absence of bovine serum albumin. Ferritin perfused hearts were used to quantify changes in the glycocalyx as a result of hypoxia and to measure the cross sectional area of the endothelial cells.
RESULTS: In all the hearts perfused with well oxygenated solution, all three markers showed an even, electron dense layer on the luminal surface of the capillaries. With ruthenium red and lanthanum (but not with ferritin), the marker was occasionally observed throughout the length of the interendothelial clefts and on the albuminal surface. After 30 min hypoxic perfusion, both ruthenium red and lanthanum showed disruption and irregular clumping of the glycocalyx, with or without albumin. Ferritin, however, showed a sparse and uneven layer. Measurements of endothelial cell area showed that some cells from hypoxic hearts were swollen when compared with controls. Measurements of the percentage of luminal membrane covered by ferritin molecules showed a significant loss of glycocalyx in hypoxic hearts. There was, however, no correlation between loss of glycocalyx and endothelial cell swelling.
CONCLUSIONS: The endothelial cell glycocalyx of continuous capillaries is sensitive to changes in PO2. The disruption of this surface coat may explain the reported increase in capillary permeability in hypoxia.