Combined junction pore-fiber entrance layer model for capillary permeability

In Tsay, et. al., (1989) and Weinbaum, et. al., (1992) a new three-dimensional junction-pore-matrix model was developed to examine the combined role of pores formed by small breaks in the intercellular junction strand and matrix structures in the wide parts of the cleft in the regulation of capillary permeability. In this study the junction pore model was extended to examine the effect of a thin fiber layer at the entrance of the cleft or at the endothelial surface. The matrix structure was represented by either an ordered or random array of perpendicular cylindrical fibers in the entrance region of the wide part of the cleft or a porous medium with parallel channels running perpendicular to the lumen front at the endothelial surface. Our results indicated that for frog mesentery capillaries a cleft with large junctional pores of 22×44 nm and gap spacing of 480 nm and an ordered or random fiber matrix layer can fit the measured values for solute permeability for small ions and large solutes of the size close to albumin and the values for the hydraulic conductivities with and without a fiber layer present. However, it cannot also fit the measured values of solute permeability for the intermediate size solutes of 0.5 to 2.0 nm radius. The model was then modified to increase both the size of the junctional pores to 22×150 nm, and gap spacing to 2700 nm as described in preliminary ultrastructural by Adamson and Michel (1992). The combined junctional pore-fiber entrance layer model described the permeability of all solutes larger than .5 nm, but underestimated the permeability to smaller solutes. The model has been used to direct further studies to investigate structure-function correlation in the cleft between adjacent endothelial cells.