Mucin release from rabbit tracheal epithelium in response to sera from normal and cystic fibrosis subjects

We have developed an assay for the release of mucous glyco-proteins secreted by rabbit tracheal mucosa to study the mucus- stimulating properties of cystic fibrosis (CF) serum. Glycoproteins are labeled to equilibrium with both [³⁵]-sulfate and [³H]-ghicosa- mine. The relative secretory rate (RSR) of these glycoproteins is assessed after incubation with 50% (v/v) CF and control sera. Serum from all sources significantly increased the RSR for incubation times ranging from 10 min to 4 h. CF serum produced a significantly greater RSR than control serum after 10 min exposure, but not after longer exposure intervals. After 10 min, RSR for [³⁵SC₄]-glycoproteins was 3.6 ± 0.2 in the presence of sera from healthy individuals, and 2.3 ± 0.4 in the presence of sera from control patients with lung disease. Heterozygote RSR values were usually higher than control values, but not different than CF homozygote values. The CF serum activity was reduced by freezing and thawing. Increasing the calcium content of incubation medium did not alter serum effects. Calcium inophore A23187 did not mimic CF serum activity. High molecular weight and albumin, but not IgG, fractions from Sephadex G-200 chromatography of CF and control sera generally contained high levels of mucin-release activity. No chromatographic pattern of activity was distinctive for CF. Speculation: Serum contains multiple substances, which promote the release of mucins from airways surface epithelium. Cystic fibrosis serum contains additional mucin-release activity, which does not appear to reside in a single serum component. This activity may be related to hypersecretion of mucus in people with cystic fibrosis.