Light and electron microscope analysis of lectin binding to adult rat liver in situ

A comprehensive mapping of lectin receptors on adult rat liver in situ was performed at light and ultrastructural levels by using 12 biotin-labeled lectins and an avidin-biotin-peroxidase complex. In addition, concanavalin A conjugated directly to peroxidase was utilized to study intracellular membrane glycoconjugates. To achieve optimal preservation of these membrane sugar moieties, several fixatives and fixation procedures were evaluated. A periodate-lysin-paraformaldehyde combination provided the best compromise between preservation of ultrastructural details and lectin-binding reactivity. Hepatocyte cell surfaces reacted intensely with concanavalin A, Lens culinaris agglutinin, and Pisum sativum agglutinin (all specific for alpha-D-mannosyl and alpha-D-glucosyl groups) as well as Ricinus communis agglutinin type I (specific for alpha or beta-D-galactose) and wheat germ agglutinin (specific for neuraminic acid and beta-NAc-glucosaminyl groups). In addition, R. communis agglutinin and wheat germ agglutinin exhibited an extremely strong reactivity for bile canaliculi which surpassed the binding of concanavalin A, L. culinaris agglutinin, and P. sativum to these structures. Phaseolus vulgaris agglutinin (specific for beta-D-galactose-glucosyl-NAc and D-mannosyl groups), which exhibited a moderate binding to hepatocyte plasma membranes, reacted more strongly with the endothelium of sinusoids and portal vessels. Although all six of these lectins plus Bandeiraea simplicifolia stained Kupffer cells, B. simplicifolia lectin (an alpha-D-galactosyl marker) was unique in showing a strong reactivity for only this cell type. The avidin-biotin-peroxidase procedure is a sensitive method for detection of sugar moieties on cell surfaces of rat liver at both light and electron microscopic levels. In this study, the procedure was used to localize differential binding of lectins to several anatomical structures of the organ, and furthermore, we were able to map preferential localizations of carbohydrate residues in the glycocalyx of the rat hepatocyte in situ.