Endothelial glycoconjugates: a comparative lectin study of the brain, retina and myocardium

There is evidence that the endothelial cell (EC) glycocalyx is a significant determinant of vascular permeability, acting as a charge-size filter to permeant molecules. We have therefore examined its oligosaccharide composition in 3 classes of microvessel with differing permeabilities. EC in rat brain, retina and myocardium were labelled with a panel of lectins and subjected to a semiquantitative analysis. Surprisingly, no substantial differences were evident for any lectin labelling between the 3 microvessel types despite their marked morphophysiological diversity. In particular, all showed substantial sialic acid expression, with Maackia amurensis (MAA) labelling sialic acid in an alpha2-3 linkage to beta-galactose and Sambucus nigra (SNA) recognising sialic acid in an alpha2-6 linkage to beta-galactose. Arachis hypogaea (PNA) binding after neuraminidase digestion indicated the presence of Gal beta1-3GalNAc attached to terminal sialic acid. The results therefore show that the sequences NeuNAc alpha2-3Gal beta1-3GalNAc and NeuNAc alpha2-6Gal beta1-3GalNAc are strongly expressed in the 3 microvessel types irrespective of their permeability properties. This homogeneity suggests that these lectin ligands may be involved in a common set of EC functions, e.g. cell:cell and cell:matrix interactions. However, we cannot rule out the possibility that glycocalyx differences may exist between vessels in the paracellular cleft which may alter its filtration properties.