A model of steady state ultrafiltration through an endothelial glycocalyx bi‐layer formed by a porous outer layer and a more selective membrane‐associated inner layer

Abstract

Ultrastructural investigations of the endothelial glycocalyx reveal a layer adjacent to the cell surface with a structure consistent with the primary ultrafilter of vascular walls. Theory predicts this inner layer can be no greater than 200–300 nm thick, a result to be reconciled with observations that red cells and large macromolecules are excluded from a region up to 1 micron or more from the cell membrane. We tested whether this apparent inconsistency might be accounted for by a model of steady state water and protein transport through a glycocalyx bi‐layer. Expressions for coupled water and albumin fluxes through the two layers were used to describe steady state ultrafiltration. The model demonstrated that albumin may accumulate at the interface between the porous layer and the selective inner layer. The osmotic pressure of accumulated albumin would significantly modify the observed permeability properties of the microvessel wall by an effective unstirred layer effect. Our results place constraints on the outer layer permeability properties. For example, with an perfusate albumin concentration of 50 mg/ml, Adamson et al ( Am. J. Physiol. 557: 889–907,2004) reported that the hydraulic conductivity measured in rat mesenteric microvessels under conditions of steady state ultrafiltration were similar to that measured before steady ultrafiltration was established. The only properties of the outer layer consistent with these observations are albumin permeability coefficients and hydraulic conductivities close to an order of magnitude larger than that of the inner layer. A high filtration coefficient for the outer layer is also consistent with estimates of the hydraulic conductance of the outer layer needed to account for red cell movement over the endothelial surface up to 1 micron thick.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.