Glycosylation of secretory proteins in salivary glands and saliva studied by lectin-probes

Lectin-probes were used histochemically to study glycosylation patterns in prepackaged secretory material in cat and rat submandibular glands and to assess the secretory changes induced by nerve stimulations. The same probes were also used for correlative biochemical assessments of the constituents in glandular extracts and in saliva from the same experiments, after electrophoretic separations and immobilization on nitrocellulose membranes. These studies provided a broader understanding than the use of either procedure alone. Lectin binding patterns in saliva were more complex than anticipated from the histochemistry and this probably relates to the presence of different constituents in secretory granules and a greater availability of binding sites biochemically. In cats, parasympathetic stimulation caused depletion of lectin staining in acini and to some extent in demilunes, whereas sympathetic stimulation caused depletion of lectin binding in striated ducts and reduction in demilunar size. Biochemically after SDS-PAGE of saliva similar secretory effects were observed but each nerve also evoked some secretion from the cells not showing histochemical change. In rats, sympathetic stimulation caused depletion of lectin positive granules from both acini and granular tubules. After SDS-PAGE of the saliva one zone of lectin binding 94 - 150 kD (Mr) was identified as acinar mucin. Granular tubule proteins consisting mainly of kallikreins occurred in a zone 25 - 35 kD (Mr) and lectin bindings suggested that different kallikreins may be differently glycosylated. This unexpected possibility was confirmed on slot-blot preparations of separated kallikreins, which also revealed the novel finding that some kallikreins are O-as well as N-glycosylated.