DURAL MICROVESSELS - MOLECULAR-PROPERTIES OF THEIR LUMINAL ANIONIC SITES

(1) Neurogenic inflammation has been implicated in the pathogenesis of the vascular headaches of migraine and cluster headaches. (2) Dural b lood vessels are both pain-sensitive and show neurogenic plasma extrav asation. (3) Endothelial cell (EC) surface anionic sites appear to be a determinant of vascular permeability. We therefore examined the anio nic sites of dural EC to determine whether they are different from tho se of pial and parenchymal vessels. Luminal anionic sites of rat optic nerve EC were labelled with cationic colloidal gold (CCG) and cationi c ferritin (CF) and examined by electron microscopy. Employing a batte ry of enzymes, the effects of digestion of ultrathin sections on subse quent labelling with CCG was quantified using image analysis software. In addition, a gold-labelled lectin, wheat-germ agglutinin (WGA), was employed to locate specific saccharide residues. Of the enzymes with a narrow specificity, only neuraminidase substantially reduced CCG bin ding. Of the proteolytic enzymes, papain was most effective in reducin g labelling. These results show that the luminal EC anionic sites are chiefly composed of sialoglycoproteins. The labelling with biotinylate d WGA-streptavidin gold was similar to that with CCG without enzyme di gestion. This suggests that WGA is binding to N-acetylneuraminic (sial ic) acid residues and not to the neutral N-acetylglucosamine (since CC G would not label uncharged molecules). These results do not differ si gnificantly from those for pial and parenchymal EC. It is therefore li kely that factors other than anionic site molecular composition accoun t for the susceptibility of dural vessels to neurogenic plasma extrava sation. The relevance of these observations in an experimental animal model to the human clinical condition remains to be determined.