Figure 3.

Schematic illustration of the endothelial surface layer in the presence of albumin (red dots), negatively charged at physiological plasma pH. The negative charges on heparan, chondroitin and dermatan sulphate glycosaminoglycan side chains of proteoglycans of the glycocalyx attract cations, especially the divalent Ca-ions, which shield the sulphate groups. Out of purely electrostatic considerations, this may provide an electrical double layer with a positively charged ‘outer’ face, to which albumin molecules will be attracted. Binding and enrichment of albumin in the glycocalyx results, a feature lacking for the artificial colloids in present day clinical use (all uncharged at physiological pH). For reasons of simplicity, Na⁺, K⁺ and Mg²⁺ ions are not included in the scheme