Blood-nerve barrier: distribution of anionic sites on the endothelial plasma membrane and basal lamina

The distribution of anionic sites on the cell membranes and basal laminae of vascular endothelial cells in the rat sciatic nerve was investigated using cationic ferritin (CF) and cationic colloidal gold (CCG). Nerves fixed by perfusion followed by immersion were chopped into 400 microns thick slices and incubated in CF or embedded in LR White resin for staining with CCG. Using electron microscopy, the distribution of these tracers was investigated. The results indicated that microdomains of various charge densities exist. Diaphragms of caveolae and transendothelial channels, and luminal endothelial processes are highly anionic, the basal laminae of endothelial cells and pericytes and luminal membranes are medium and abluminal membranes least anionic. Inter-endothelial tight junctions were unlabelled and not penetrated by CF. These structures are thought to represent charge and size filters that control permeability of the vasa nervorum. The distribution of these charge-size filters is discussed in terms of the blood-nerve barrier, a physiological property present in the endo- but absent in the peri- and epineurial vessels.