Differential distribution of sialic acid in exocrine pancreas and parotid gland

The sialic acid-specific lectin limulin (LPA, from Limulus polyphemus hemolymph) was used for the investigation of the distribution of accessible sialoglycoconjugates on the surface of cells from rat and rabbit parotid gland and exocrine pancreas. Fluorescence microscopy with rhodamine-conjugated LPA on fresh-frozen and fixed-frozen sections of the parotid gland revealed lectin binding sites on acinar and ductular epithelial cells. The staining was localized only at the periphery of the acini and ducts and was absent from the apical and lateral surface of epithelial cells. This staining pattern contrasted with that found in epithelial cells of acini and ducts in exocrine pancreas, where the luminal surface was intensely labeled by the fluorescent lectin. The luminal content of ductular tract and acini in parotid gland and pancreas was devoid of lectin-reactive sialoglycoconjugates. Connective tissue surrounding ducts and blood vessels bound the lectin heavily in both glands. These results outline that cells with similar structure and function, but constituents of different exocrine glands, exhibit differential distribution of sialoglycoconjugates on their corresponding plasmalemmal domains.