The effects of cationised ferritin and native ferritin upon the filtration coefficient of single frog capillaries. Evidence that proteins in the endothelial cell coat influence permeability.

To investigate whether certain macromolecules reduce capillary permeability by binding to the surface coat of endothelial cells, the effects of cationised ferritin (CF) upon the filtration coefficient (Lp) of individually perfused frog mesenteric capillaries were compared with those of native ferritin (NF). With perfusate CF concentrations between 0.1 g 100 ml-1 and 2.5 g 100 ml-1, Lp was reduced to approximately 30% of its value for the same vessel perfused with protein-free Ringer solution. Electron micrographs of the perfused capillaries revealed that over this range of perfusate concentrations. CF was concentrated uniformly in the endothelial cell coat, occupying 8.5% of its volume. Neither the effect of cationised ferritin upon Lp nor its concentration in the cell coat varied significantly over this range of perfusate concentrations. When perfusate concentration of CF was reduced to 0.01 g 100 ml-1, CF no longer reduced Lp and its concentration in the cell coat fell below 2%. Native ferritin, which is excluded from the cell coat, did not reduce Lp at a perfusate concentration of 0.1 g 100 ml-1. At a concentration of 2.5 g 100 ml-1, NF reduced Lp in a few very permeable vessels (Lp greater than 60 X 10(-3) microns sec-1 cm H2O-1) but had no significant effect on vessels with lower and more normal values of Lp. The effects of CF upon Lp can be described in terms of the Kozeny equation if a major proportion of the hydraulic resistance through the capillary wall is attributed to a fiber protein matrix.