Mucus secretion from single submucosal glands of pig - Stimulation by carbachol and vasoactive intestinal peptide

Secretion rates of >700 individual glands in isolated tracheal mucosa from 56 adult pigs were monitored optically. Basal secretion of 0.7 +/- 0.1 nl.min(-1) gland(-1) was observed 1-9 h post-harvest but was near zero on day 2. Secretion to carbachol (10 muM) peaked at 2-3 min and then declined to a sustained phase. Peak secretion was 12.4 +/- 1.1 nl.min(-1) gland(-1); sustained secretion was approximately one-third of peak secretion. Thapsigargin (1 muM) increased secretion from 0.1 +/- 0.05 to 0.7 +/- 0.2 nl.min(-1) gland(-1); thapsigargin did not cause contraction of the trachealis muscles. Isoproterenol and phenylephrine (10 muM each) were ineffective, but vasoactive intestinal peptide (1 muM) and forskolin (10 muM) each produced sustained secretion of 1.0 +/- 0.5 and 1.7 +/- 0.2 nl.min(-1) gland(-1), respectively. The density of actively secreting glands was 1.3/mm(2). Secretion to either carbachol or forskolin was inhibited (similar to50%) by either bumetanide or HCO(3) over bar removal and inhibited similar to90% by the combined treatments. Mucus secreted in response to carbachol or forskolin was acidic by similar to0.2 pH\units relative to the bath and remained acidic by similar to0.1 pH units after bumetanide. The strong secretory response to vasoactive intestinal peptide, the acidity of [CAMP](i)-stimulated mucus, and its inhibition by bumetanide were unexpected.