Endothelial glycocalyx layer properties and its ability to limit leukocyte adhesion

The endothelial glycocalyx layer (EGL), consisting of long proteoglycans protruding from the endothelium, acts as a regulator of inflammation by preventing leukocyte engagement with adhesion molecules on the endothelial surface. The amount of resistance to adhesive events the EGL provides is the result of two properties: EGL thickness and stiffness. To determine these, we used an atomic force microscope to indent the surfaces of cultured endothelial cells with a glass bead and evaluated two different approaches for interpreting the resulting force-indentation curves. In one we treat the EGL as a molecular brush and in the other, as a thin elastic layer on an elastic half-space. The latter approach proved more robust in our hands and yielded a thickness of 110 nm and a modulus of 0.025 kPa. Neither value showed significant dependence on indentation rate.  The brush model indicated a larger layer thickness (~350 nm) but tended to result in larger uncertainties in the fitted parameters. Th...