MOLECULAR CHARACTERIZATION OF ANIONIC SITES ON THE LUMINAL FRONT OF ENDONEURIAL CAPILLARIES IN SCIATIC-NERVE

The distribution of anionic microdomains has been described in cerebra l vessels and more recently in capillaries of peripheral nerve. Eviden ce is accumulating that these sites play a role in the barrier functio n of vascular endothelia in the PNS and CNS. The chemical nature of an ionic sites has been at least partly determined for cerebral vessels b ut not in peripheral nerve. This study reports our preliminary investi gations to determine the nature of endothelial anionic sites in sciati c nerve. The effects of digestion of ultra-thin sections of nerve with a battery of proteolytic and glycolytic enzymes (papain, trypsin, pro teinase K, hyaluronidase, heparinase, heparitinase and neuraminidase) on the distribution of anionic sites was determined using the label, c ationic colloidal gold. Papain, a proteolytic enzyme of broad specific ity, succeeded in removing the majority of cationic colloidal gold-bin ding sites on the luminal surface of vascular endothelia. In contrast trypsin and proteinase K were less effective, reflecting their narrowe r specificity. Hyaluronidase, heparinase and heparitinase did not sign ificantly affect cationic colloidal gold-labelling. However, a conside rable reduction in cationic colloidal gold-binding occurred following neuraminidase digestion. These results suggest that, as in cerebral ve ssels, sialic acid-containing glycoproteins are largely responsible fo r the negatively charged domains on the luminal membrane of endothelia l cells in peripheral nerve.