Quantification of the endothelial surface glycocalyx on rat and mouse blood vessels.

The glycocalyx on the surface of endothelium lining blood vessel walls modulates vascular barrier function, cell adhesion and also serves as a mechano-sensor for blood flow. Reduction of glycocalyx has been reported in many diseases including atherosclerosis, inflammation, myocardial edema, and diabetes. The surface glycocalyx layer (SGL) is composed of proteoglycans and glycosaminoglycans, of which heparan sulfate is one of the most abundant. To quantify the SGL thickness on the microvessels of rat mesentery and mouse cremaster muscle in situ, we applied a single vessel cannulation and perfusion technique to directly inject FITC-anti-heparan sulfate into a group of microvessels for immuno-labeling the SGL. We also used anti-heparan sulfate for immuno-labeling the SGL on rat and mouse aortas ex vivo. High resolution confocal microscopy revealed that the thickness of the SGL on rat mesenteric capillaries and post-capillary venules is 0.9±0.1 μm and 1.2±0.3 μm, respectively; while the thickness of the SGL on mouse cremaster muscle capillaries and post-capillary venules is 1.5±0.1 μm and 1.5±0.2 μm, respectively. Surprisingly, there was no detectable SGL in either rat mesenteric or mouse cremaster muscle arterioles. The SGL thickness is 2.5±0.1 μm and 2.1±0.2 μm respectively, on rat and mouse aorta. In addition, we observed that the SGL is continuously and evenly distributed on the aorta wall but not on the microvessel wall.