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

There is evidence that the endothelial cell (EC) glycocalyx is a significan t determinant of vascular permeability, acting as a charge-size filter to p ermeant molecules. We have therefore examined its oligosaccharide compositi on in 3 classes of microvessel with differing permeabilities. EC in rat bra in, retina and myocardium were labelled with a panel of lectins and subject ed to a semiquantitative analysis. Surprisingly, no substantial differences were evident for any lectin labelling between the 3 microvessel types desp ite their marked morphophysiological diversity. In particular, all showed s ubstantial sialic acid expression, with Maackia amurensis (MAA) labelling s ialic acid in an alpha 2-3 linkage to beta-galactose and Sambucus nigra (SN A) recognising sialic acid in an alpha 2-6 linkage to beta-galactose. Arach is hypogaea (PNA) binding after neuraminidase digestion indicated the prese nce of Gal beta 1-3GalNAc attached to terminal sialic acid. The results the refore show that the sequences NeuNAc alpha 2-3Gal beta 1-3GalNAc and NeuNA c alpha 2-6Gal beta 1-3GalNAc are strongly expressed in the 3 microvessel t ypes irrespective of their permeability properties. This homogeneity sugges ts that these lectin ligands may be involved in a common set of EC function s, e.g. cell:cell and cell:matrix interactions. However, we cannot rule out the possibility that glycocalyx differences may exist between vessels in t he paracellular cleft which may alter its filtration properties.