Scanning Microscopy


During experimental atherosclerosis, arterial endothelial cells show characteristic ultrastructural changes including the appearance of increased numbers of plasmalemmal and cytoplasmic vesicles. These structures have been shown by tracer studies to participate in the transcellular transport of low-density lipoprotein cholesterol and β-very-low-density lipoprotein cholesterol from the arterial lumen into the abluminal extracellular matrix. Although this probably represents the major lipid transport pathway, other forms of transport may exist. We document the presence of apparent lipid structures averaging approximately 300 nm in diameter at or near the luminal surface of coronary arterial endothelium of atherosclerotic miniature swine. The structures exhibited a particulate nature with subunits of a heterogenous size distribution. The appearance of the endothelial plasmalemma adjacent and subjacent to these structures suggests exocytosis. We hypothesize that this previously unreported morphology may represent an in vivo structural correlate for the lipoprotein retro-endocytosis pathway which has been recently identified using biochemical methods in smooth muscle cells and fibroblasts in vitro.

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