Theoretical modeling of fluid transport through endothelial junctions.

Abstract

This paper will review some recent theoretical models of the fluid transport through an endothelial cell layer from the standpoint of hydrodynamic theories based on ultrastructural information. These theories attempt to use realistic models of the observed morphology of endothelial cell junctions and realistic estimates of the forces, pressures, and flows that can take place in narrow slits and porous media. The classical system of transendothelial pathways consisting of a small pore system, medium size pores and a few large pores for the passage of macromolecules is well supported by experimental data on filtration measured macroscopically. Excellent summaries of this theory and data are available (eg. Curry, 1984; Michel, 1984; Taylor and Granger,1984).1,2,3 However, the possible ultrastructural features of endothelial cells which correspond to the various sizes of pores continue to be refined by electron microscopic and other studies. One of the most striking developments is the demonstration that most vesicles of endothelial cells are attached to cell walls.4,5 This has led to a concept of a lesser role of vesicular transport and a greater emphasis on the filtration through the endothelial cell junctions.6,7 In these more recent theories, the classical system of pores is replaced by a system of narrow slits which realistically represent the endothelial cleft and tight junctions, some wider tortuous gaps between protein junctional strands, and transiently open junctions which are associated with the replacement phase of dying endothelial cells.8