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A simple and rapid method was established to study vascular permeability by in vitroperfused endothelial cell monolayers cultured on micropore filter membrane.It can be used todetermine filtration coefficient （K

f

） to small molecules and osmotic reflection coefficient （σ） toproteins of the endothelial monolayer.Hanks’ balanced salt solution （HBSS） or 5g/L albuminin HBSS was used to perfuse the confluent endothelial monolayer at the hydrostatic pressure of2.45kPa （25cm H

2

O）.Control K

f

values were 10.1±0.75 and 3.6±0.75μl·min

-1

·cm

-2

·kPa（-1）（±

n=3） respectively for the perfusion of HBSS and albumin HBSS

suggesting that al-bumin may decrease endothelial monolayer permeability to water and small molecules.After ex-posure of endothelial monolayer to 10

-8

mol/L platelet-activating factor （PAF） for 30min

K

f

values increased to 193.1% and 133.3% respectively.Protein clearance rate (μl.min

-1

·cm

-2

)and osmotic reflection coefficient of the control endothelial monolayer were 8.0±3.22 and 0.37±0.09 respectively and those of the PAF treated endothelial monolayer 12.2±2.95μl·min

-1

·cm

-2

and 0.18±0.06

revealing increased permeability to albumin.Computer-assisted imageprocessing demonstrated that PAF treatment decreased cell area while increased cell form factorand intercellular space

suggesting that endothelial cells retracted and rounded

which may bean important mechanism of PAF-induced increase of vascular permeability.