Directional Ca2+ effect on stimulation of mucin secretion from chicken trachea in vitro

Chicken tracheal mucosa in vitro transported and incorporated radioactive precursors into mucins, which were secreted at a steady rate into the tracheal lumen. Secretion of mucins labelled with (35)S and (3)H after pulse-labelling of the mucosal layer with Na(2) (35)SO(4) and d-[1-(3)H]glucosamine as precursors was an energy-dependent process, as it was strongly inhibited by the action of respiratory-chain inhibitors, an uncoupler of oxidative phosphorylation, a metabolic blocker and a temperature shift from 41 degrees C to 5 degrees C. On the other hand, both cholinergic and parasympathomimetic agents considerably increased the secretion of dual-radiolabelled mucins when applied on the submucosal side of the trachea. The effect of Ca(2+) was directional, since only high submucosal (3.6 or 18mm) or low luminal (zero or 0.18mm) Ca(2+) massively enhanced the secretion of radiolabelled mucin compared with the mucin output measured under physiological Ca(2+) conditions (1.8mm). Whereas application of ionophore A23187 on either side of the trachea significantly increased mucin output, its presence in the appropriate tracheal compartment and under appropriate Ca(2+) conditions further accentuated the output of radiolabelled mucins. Addition of acetylcholine under appropriate conditions also had an additive effect on the Ca(2+)-stimulated secretion of mucins. Ca(2+) stimulation of mucin secretion appears to be dependent on the metabolic integrity of the mucosal cells. Mucins secreted in response to high submucosal and low luminal [Ca(2+)] appear to consist of a number of different types of glycoproteins, as judged from their ion-exchange-chromatographic behaviour.