Lectin-Induced Mucus Release in the Urn Cell Complex of the Marine Invertebrate Sipunculus nudus (Linnaeus).

The mucociliary urn cell complex of the marine coelomate Sipunculus nudus secretes mucus 4 to 5 minutes after being exposed to Lotus tetragonolobus and Ricinus communis I agglutinins. Surface binding of both lectins is confined to the secretory area of the urn cell complex and, like the release of mucus, is inhibited by the specific saccharides L-fucose and D-galactose or by incubation in L-fucosidase and D-galactosidase. Mucus secretion may therefore be initiated by the interaction of mucus-releasing stimuli with fucosyl or galactosyl residues of specific membrane receptors.