Mucus secretion from individual submucosal glands of the ferret trachea

Abstract

Mucus secretion from individual tracheal glands in adult ferrets was studied with time-lapse optical imaging of mucus droplets under an oil layer. Density of functional glands (determined by responses to 1 μM carbachol) was 1.5 ± 0.3 per mm2 ( n = 6). Secretion rates (in pl·min−1·gland−1) were as follows: 4.1 ± 0.7 basal (unstimulated; n = 27, 669 glands), 338 ± 70 to 10 μM forskolin ( n = 8, 90 glands), 234 ± 13 to 1 μM VIP ( n = 6, 57 glands), 183 ± 92 to 10 μM isoproterenol ( n = 3, 33 glands), 978 ± 145 to 1 μM carbachol ( n = 11, 131 glands), and 1,348 ± 325 to 10 μM phenylephrine ( n = 7, 74 glands). The potency (EC50, in μM) and efficacy ( Vmax, in pl·min−1·gland−1) were 7.6 (EC50) and 338 ± 16 ( Vmax) to forskolin, 1.0 (EC50) and 479 ± 19 ( Vmax) to VIP, 0.6 (EC50) and 1,817 ± 268 ( Vmax) to carbachol, and 3.7 (EC50) and 1,801 ± 95 ( Vmax) to phenylephrine. Although carbachol and phenylephrine were equally effective secretagogues, only carbachol caused contractions of the trachealis muscle. Synergy was demonstrated between 300 nM isoproterenol and 100 nM carbachol, which, when combined, produced a secretion rate almost fourfold greater than predicted from their additive effect. The dependence of fluid secretion on Cl− and HCO3− varied depending on the mode of stimulation. Secretion stimulated by VIP or forskolin was reduced by ∼60% by blocking either anion, while carbachol-stimulated secretion was blocked 68% by bumetanide and only 32% by HEPES replacement of HCO3−. These results provide parametric data for comparison with fluid secretion from glands in ferrets lacking CFTR.