Distribution of charged sites on lymphatic endothelium.

The charge distribution on the luminal and abluminal aspects of fixed and living lymphatic endothelium was examined with particular emphasis on the endocytotic vesicular system and interendothelial junctions. Native ferritin (NF; pl = 4.5), when administered abluminally to perfused lymphatics, entered endocytotic vesicles and abluminal and luminal caveolae; NF was also found in intercellular channels, in contrast, NF when applied luminally was largely excluded from both luminal caveolae and intercellular channels. Cationic ferritin (CF; pl = 8.4) bound to the discontinuous basal lamina and to the abluminal plasma membrane, clustering preferentially around the stomata of abluminal caveolae. CF did not, however, bind to the plasma membrane of, or enter, either the vesicular system or intercellular channels, when administered abluminally. When added to the perfusion fluid CF bound to the luminal membrane and to the infundibula of intercellular channels. Ruthenium red (RR) and alcian blue (AB), both cationic stains, bound intensely to the luminal membrane and much less so to the abluminal surface, thus simulating the binding pattern of CF. Unlike CF, however, RR and AB bound to the membranes of abluminal and luminal caveolae with the same level of staining as to the plasma membrane to which they were attached. These results reflect a marked asymmetry in the membrane charge characteristics of endothelial cells.