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Glycoproteins produced by the tracheae of anaesthetized cats were radiolabelled biosynthetically by a pulse administration of Na2 35SO4 and [3H]glucose into the tracheal lumen. Subsequently, radiolabelled secretions were washed from the tracheal lumen. Repeated doses of pilocarpine and then ammonia vapour were given to stimulate secretion. Pilocarpine-stimulated glycoproteins, which came mainly from the submucosal glands, were particularly enriched with 35S. Ammonia-stimulated secretions, which probably came mostly from the microvillous border of the surface epithelium, contained mainly 3H radioactivity but little 35S. Two negatively-charged glycoproteins of different molecular size were identified in the secretions: the larger component was excluded on Sepharose CL-4B and it had a higher 3H 35S ratio than the smaller component which was retarded on Sepharose CL-4B. The relative amount of the smaller component decreased progressively with repeated pilocarpine stimulation and it was not detected in secretions induced by ammonia. Pilocarpine stimulation caused little alteration in carbohydrate composition of the secreted glycoproteins. In response to ammonia, glycoproteins were secreted with a high sialic acid content but quantitatively they represented a small amount of material compared with that induced by pilocarpine. These findings suggest that tracheal glycoproteins from different epithelial-cell sources have distinctive chemical compositions and that their secretions may be independently regulated. The 35S-rich high-molecular-weight glycoproteins from the submucosal glands were of the mucin-type but those derived from the microvillus border may represent a different class of airway glycoproteins from typical epithelial mucins.

1. Reduced viscosities, in water, of different types of mucin, such as fibrillar, gelatinous and soluble phase, separated from chicken tracheal secretions were measured. 2. H-bond breaking agents caused a significant decrease in the reduced viscosity of these mucins, but thiol-reagents alone did not have any effect. 3. Papain and Pronase did not cause any decrease in the reduced viscosity of these mucins. Neuraminidase decreased the reduced viscosity of soluble phase mucin by 50% by removing about 30% of its N-acetylneuraminic acid but had no effect on fibrillar and gelatinous mucins. Sulphatase neither removed any sulphate ester groups nor decreased the reduced viscosity. Due to some nonspecific intermolecular interaction, mixtures of mucins and enzymes or ovalbumin exhibited elevated reduced viscosities. 4. Ionic strength of the solutions appeared to decrease the reduced viscosity of these mucins. Increasing concentrations of Ca2+ in solutions of ionic strength of approx. 0.1 caused significant decrease in the reduced viscosity, but had no such effect in solutions of ionic strength of more than 0.1. 5. N-Acetylneuraminic acid and sulphate ester residues were 46.6 +/- 0.2, 43.4 +/- 0.6, 27.9 +/- 3.3 mg/g and 66.0 +/- 2.0, 34.2 +/- 3.3, 2.5 +/- 0.8 mg/g for fibrillar, gelatinous and soluble phase mucins, respectively. There appeared to be a good correlation between viscosity and N-acetylneuraminic acid contents among mucins of low reduced viscosities and between viscosity and sulphate ester residues among mucins of high reduced viscosities.

High submucosal Ca2+ (3.6-18 mM) significantly increased the secretion of a common high molecular weight fibrillar mucin (approx. Mr is greater than 2.10(6)) and also elicited the secretion of an additional low molecular weight component (approx. Mr 325,000). Low luminal Ca2+ (0.018 mM) also significantly increased the secretion of a common high molecular weight gelatinous mucin (approx. Mr is greater than 2.10(6)) and elicited the secretion of an additional low molecular weight component (approx. Mr 46,200). The additional low molecular weight components were more heavily sulphated (6.7 and 4.2%) than common high molecular weight mucins (2.1 and 1%). The low molecular weight components and high molecular weight mucins were secreted as aggregates which could be dissociated by EGTA. The low molecular weight components and high molecular weight mucins were different in the number of their glycoprotein constituents and in the ion-exchange chromatographic profiles and the carbohydrate and ester sulphate residue content of their acidic glycoproteins.

Reduced viscosities of fibrillar and gelatinous type mucins produced in response to high submucosal Ca2+ and low luminal Ca2+ effects were significantly higher than those of corresponding types of normal mucins. The increased reduced viscosity of experimental mucin samples was due to their aggregation with unique low molecular weight (mr 325,000 and 46,200) sulphate-rich components. The Ca2+ appeared to exert two opposing effects on viscosity properties of mucins; whereas Ca2+-dependent complexes between different types of mucins appeared to be a selective phenomenon between sulphate-rich mucins and components. Ester sulphate residue content rather than N-acetylneuraminic acid residue content of these mucins and low molecular weight components showed a very good correlation with their reduced viscosity and Ca2+-binding values.

1. The glycoprotein and glycolipid composition of isolated rabbit small-intestinal brush borders has been studied. 2. The total glycoprotein fraction contains an average 95 microgram carbohydrate per mg protein, composed of mannose, galactose, fucose, N-acetylglucosamine and N-acetylgalactosamine. Glucose is also present but sialic acid is absent. 3. The isolated glycolipids include ceramide lactoside, ceramide trihexoside and two N-acetylglucosamine-containing glycolipids. Sialic acid containing glycolipid (gangliosides) is present only in trace quantities. 4. The biosynthesis of the brush border-bound glycoproteins and glycolipids has been studied following intraperitoneal injection with D-[1-14C]glucosamine and isolation of the brush borders at intervals between 3 and 24 h. 5. The total glycoprotein fraction labels maximally 7.5 h after injection and subsequently exhibits an exponential loss of radioactivity with a half-life of 11.2 h. The labelling kinetics of one of the glucosamine-containing glycolipids is similar to that of the glycoproteins in that it labels maximally between 7.5 and 12 h, but the second glucosamine-containing glycolipid labels later at approximately 18 h. These results indicate that the glycoproteins and glycolipids are actively synthesized and degraded within the mature small intestinal enterocyte and that individual glycolipids turn over independently.