Surface and intracellular localization of concanavalin A binding sites in rat liver cells.

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Abstract
The concanavalin [con] A-peroxidase method was used to localize surface and intracellular .alpha.-D-glucose, .alpha.-D-mannose and .beta.-D-fructose residues of polysaccharide chains in rat liver cells. In order to obtain both good preservation of cell fine structure and homogeneous penetration of the lectin, various technical parameters were studied. The best results were obtained by use of fixation by immersion in 6% paraformaldehyde-1% glutaraldehyde mixture for 4 h and then by passage in buffered glycerol before cryostat sectioning. Continuous labeling of cell surfaces was observed in the different types of liver cells (hepatocytes, endothelial, Kupffer and biliary cells). Both sinusoidal and bile canalicular microvilli and intercellular membranes of hepatocytes were labeled. Desmosomes and gap-junctions were often filled with Con A but well-fixed tight-junctions were not. The inner side of endoplasmic reticulum and of Golgi apparatus membranes was also stained when the liver cells were previously cut, but mitochondria and glycogen particles were rarely labeled. Endomembranes are probably easily accessible to Con A in sectioned cells only and this lectin fixes sugar residues of saccharides making up plasma membranes as well as those of endoplasmic reticulum and Golgi apparatus. In hepatocytes, Con A receptors could correspond to glycoproteins tightly associated with the membrane structure and/or plasma glycoproteins synthesized by these cells.

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