Thrombin and bradykinin initiate discrete endothelial solute permeability mechanisms.
This study documents the discrete solute permeability mechanisms associated with physiologically high concentrations of human alpha-thrombin and bradykinin stimulation of bovine pulmonary artery endothelial cell (BPAEC) monolayers using fluorescein isothiocyanate-hydroxyethyl starch macromolecules. Agonist-induced alterations of intracellular free calcium ([Ca2+]i) using fura-2 acetoxymethyl ester were also measured. BPAEC monolayers showed restricted diffusion consistent with a small-pore (approximately 150 A) radius under baseline conditions. Thrombin produced a major increase in monolayer permeability that was greatest for solute molecular radii (ae) > 100 A. This effect was associated with the exposure of the large (approximately 2,000 A) pores of the filter support by 50- to 1,050-microns2 open areas between approximately 0.5% of the adjacent endothelial cells. This heterogeneous endothelial barrier of parallel large- and small-pore transport pathways permitted solute convection with free diffusion across a few large pores to dominate the restricted diffusion of most apparently unperturbed endothelial junctions. Bradykinin produced a small, transient elevation in monolayer permeability to ae < 35 A, consistent with an increase in the number of small pores or a decrease in path length of this transport pathway. The bradykinin- and thrombin-induced peak elevations in [Ca2+]i were inversely associated with the degree of increased monolayer solute permeability, and enzymatically inhibited thrombin produced none of these effects. These data show that bradykinin and human alpha-thrombin represent two distinct classes of endothelial cell agonists that initiate discrete solute permeability mechanisms.
Schaeffer
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RC
Benjamin W. Zweifach Microcirculation Laboratories, Veterans Affairs Medical Center, Tucson, Arizona 85723.
Gong
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F
Bitrick
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MS
Smith
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TL
D000818:Animals; D001920:Bradykinin / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D002199:Capillary Permeability / Q000502:physiology*; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism; D046911:Macromolecular Substances; D008855:Microscopy, Electron, Scanning; D008955:Models, Cardiovascular; D009994:Osmolar Concentration; D013917:Thrombin / Q000502:physiology*; D013997:Time Factors
D046911:Macromolecular Substances; D013917:Thrombin; D001920:Bradykinin; D002118:Calcium