Use of lectin probes on tissues and sympathetic saliva to study the glycoproteins secreted by rat submandibular glands

Abstract

We used a panel of nine lectins to detect the glycosylation patterns of rat submandibular glycoproteins. Binding of lectins was assessed on tissue sections and on Western blots of electrophoretically separated glycoproteins from glandular extracts or sympathetic saliva. Histochemical staining of tissue sections showed that two lectins (DBA and SBA) with affinity for terminal GalNAc residues were localized specifically to acinar cells. In contrast, LTA and UEA-I (αFuc-directed) and LFA (NeuAc-directed) bound exclusively to granular tubule cells. PNA and MPA (βGal-directed), LCA (αMan- and αGlc-directed); WGA (βGlcNAc- and NeuAc-directed), and sWGA (βGlcNAc-directed) bound to both acinar and granular tubule cells. On electroblot preparations, LFA, PNA, WGA, DBA, and SBA reacted with high molecular weight acinar mucin components both in glandular extracts and in saliva. LTA, UEA-I, LFA, PNA, MPA, LCA, WGA, sWGA, and DBA bound to lower molecular weight bands on blots known to contain granular tubular proteinases. Lectin binding to acini and granular tubules was reduced in sections and in most bands from glandular extracts after sympathetic nerve stimulation. Our results show that (a) secretory glycoproteins from rat submandibular acinar cells are non-fucosylated and contain abundant αGalNAc and NeuAc and a small proportion of βGal in their oligosaccharide side chains, and (b) αFuc, NeuAc, βGal, and αGalNAc form the major carbohydrate moieties of the secretory glycoproteins from granular tubules. The results confirm the considerable potential of lectin probes for studying glycoproteins in secretions and in their cells of origin.