Electron microscopic evaluation of the endothelial surface layer of glomerular capillaries

Abstract Recent data from various vascular beds suggest that a layer of mucopolysaccharides covering the endothelial cells play an important role in transport processes, among others. In this study, electron microscopy (EM) was used to explore the presence of an endothelial surface layer (ESL) in rat glomerular capillaries. We adopted various fixation and labeling techniques, as follows: (1) negatively charged lipid particles were used as a tracer that was expected to be excluded from the ESL. The density of intravascular lipid particles in flow-arrested capillaries was 89% lower in a 200-nm periendothelial area than in the rest of the luminal space ( n = 6 rats, P 200 nm) ESL not previously described; however, this finding was restricted to superficial glomerular capillaries; (5) Cupromeronic Blue cytochemistry displayed a loose proteoglycan network in fenestral openings and, occasionally, a semiordered ESL; (6) ferricyanide-reduced osmication resulted in increased numbers of fenestral diaphragms. In conclusion, this study provides novel morphological evidence to support the presence of a significant glomerular ESL.