The effects of indomethacin and prostaglandins E2 and F2 alpha on canine tracheal mucus generation

Morphological characterization of brush cells in the rat trachea

Brush cells have recently been classified as solitary chemosensory cells. However, tracheal brush cells have not been morphologically and immunohistochemically characterized yet. In the present study, the morphological and immunohistochemical characteristics of tracheal brush cells were analyzed using immunohistochemistry and scanning, and transmission electron microscopies. Brush cells in the tracheal epithelium were barrel-like or columnar in shape and were immunoreactive for villin. Scanning and transmission electron microscopies revealed densely arranged thick microvilli on the apical surface of tracheal brush cells and tubular membranous elements and/or vesicular formations in the supranuclear region. A morphometrical analysis of tracheal whole-mount preparations showed that the density of brush cells was greater in the cranial third and the mucosa on the annular ligament. Double immunofluorescence revealed that the morphology of villin-immunoreactive brush cells was distinct from other non-ciliated cells in the tracheal epithelium, i.e., MUC5AC-immunoreactive mucous cells, SNAP25-immunoreactive neuroendocrine cells, and GNAT3-immunoreactive solitary chemosensory cells. On the other hand, tracheal brush cells were immunoreactive for the marker proteins for intestinal brush cells, CK18, DCLK1, and Cox1; however, these antibodies also recognized cells other than brush cells. Furthermore, immunoreactivity for PKD2L1, a cation channel subunit, was detected in brush cells. The present results demonstrated that tracheal brush cells are independent cell types. These brush cells may be activated by acid and the secretion of prostaglandins. In conclusion, the present study revealed that tracheal brush cells are independent cell types based on the morphological and immunohistochemical characteristics.

Airway Gland Structure and Function

Submucosal glands contribute to airway surface liquid (ASL), a film that protects all airway surfaces. Glandular mucus comprises electrolytes, water, the gel-forming mucin MUC5B, and hundreds of different proteins with diverse protective functions. Gland volume per unit area of mucosal surface correlates positively with impaction rate of inhaled particles. In human main bronchi, the volume of the glands is ∼ 50 times that of surface goblet cells, but the glands diminish in size and frequency distally. ASL and its trapped particles are removed from the airways by mucociliary transport. Airway glands have a tubuloacinar structure, with a single terminal duct, a nonciliated collecting duct, then branching secretory tubules lined with mucous cells and ending in serous acini. They allow for a massive increase in numbers of mucus-producing cells without replacing surface ciliated cells. Active secretion of Cl(-) and HCO3 (-) by serous cells produces most of the fluid of gland secretions. Glands are densely innervated by tonically active, mutually excitatory airway intrinsic neurons. Most gland mucus is secreted constitutively in vivo, with large, transient increases produced by emergency reflex drive from the vagus. Elevations of [cAMP]i and [Ca(2+)]i coordinate electrolyte and macromolecular secretion and probably occur together for baseline activity in vivo, with cholinergic elevation of [Ca(2+)]i being mainly responsive for transient increases in secretion. Altered submucosal gland function contributes to the pathology of all obstructive diseases, but is an early stage of pathogenesis only in cystic fibrosis.

Extracellular sodium is required for methacholine-induced secretion of mucus glycoconjugates from canine tracheal explants

Extracellular sodium is known to influence secretion by certain secretory cells, possibly by mobilizing calcium from cellular stores or by altering intracellular pH via regulation of a Na(+)-H+ antiport system. Using canine tracheal explants, we determined whether agents which alter sodium fluxes are capable of modulating basal or cholinergically-induced secretion of mucus glycoconjugates. Methacholine, a cholinergic agonist, increased mucus secretion from explants incubated in the presence or absence of calcium, but had no effect on secretion when incubated in sodium-deficient media, indicating (a) that cholinergically-induced secretion can be mediated by mobilization of cellular calcium and (b) that extracellular sodium was required for this stimulatory effect. Several agents which increase intracellular sodium were tested for their effect on mucus secretion. Ouabain, a sodium pump inhibitor, and veratridine, a sodium channel activator, did not significantly affect control or methacholine-induced secretion; gramicidin, a sodium ionophore, also had no effect on basal release. Tetrodotoxin, a sodium channel inhibitor, was also without effect on basal or methacholine-stimulated mucus release. Agents which alter intracellular pH were also examined for their effects on basal or methacholine-induced glycoconjugate secretion. Amiloride, which decreases intracellular pH by inhibiting Na(+)-H+ exchange, produced a 19 per cent increase in basal secretion (not statistically significant), but had no effect on methacholine-induced secretion. An agent, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), which decreases intracellular pH by inhibiting HCO3(-)-Cl- exchange, elicited decreases in both basal and methacholine-induced secretion, but the inhibition did not reach statistical significance.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of endogenous and exogenous prostaglandins on glycoprotein synthesis and secretion in isolated rabbit gastric mucosa

We studied gastric glycoprotein synthesis and secretion in organ culture before and during cyclooxygenase inhibition and replacement with exogenous prostaglandins (16,16-dimethyl prostaglandin E2 and prostaglandin F2 alpha). Isolated rabbit antral and fundic mucosal explants incorporated [14C]N-acetylglucosamine and [3H]leucine in a linear fashion and steadily secreted labeled proteins and glycoproteins during the 24-h incubation period. On sepharose 4B, greater than 90% of the secreted protein-bound [14C]N-acetylglucosamine was found in the high molecular weight peak. Incorporation of tracer was not influenced by cyclooxygenase inhibition with indomethacin or the addition of exogenous prostaglandins. Secretion of newly formed glycoprotein, however, was significantly inhibited by indomethacin and stimulated by both tested prostaglandins in a concentration-dependent manner. 16,16-Dimethyl prostaglandin E2 caused significant stimulation in concentrations that are well in the physiologic range for endogenous prostaglandin E2, whereas prostaglandin F2 alpha stimulated in 100 times higher concentrations. We conclude that in the isolated gastric mucosa both endogenous and exogenous prostaglandins stimulate mucus secretion. For prostaglandin E2, but not prostaglandin F2 alpha, a role in the physiologic regulation of gastric mucus secretion is probable.

The effects of peptides and mediators on mucus secretion rate and smooth muscle tone in the ferret trachea

The effects of a number of peptides and mediators were measured on the secretion rate of tracheal mucus and tracheal smooth muscle tone in the ferret in vitro whole trachea. The comparison of secretion rate and smooth muscle tone, measured simultaneously in the same preparation, shows that there are wide differences in sensitivity between the two systems; there appears to be no relationship between mucus volume output and smooth muscle contraction. The comparison of mucus secretion rate and glycoprotein output in other models and species to these drugs in the same concentrations indicates that there may be mucus glycoprotein output without an increase in volume output.

A source of error in the chromatographic study of 35S-sulfate labeled mucous glycoproteins secreted by the gill epithelium of Mytilus edulis

HPLC combined with [35S]-sulfate/[3H]-glucosamine radiolabeling were employed to study the synthesis and secretion of mucous glycoproteins. The secreted radiolabeled glycoproteins were separated from the medium by precipitation with a mixture of trichloroacetic-phosphotungstic acids (TCA/PTA). The redissolved glycoproteins were chromatographed on an anion exchange protein column at varying pH of the mobile phase and fractions were collected for liquid scintillation counting. Varying the pH of the mobile phase from pH 3 to 7 resulted in a decrease of glycoprotein bound [35S] from 69.5 to 0.5% of the total recovered [35S]-sulfate with the remainder recovered as free [35S]-sulfate. The [3H]-labeled glycoprotein recovered under the uV peaks at this pH range was 99.5%. When high performance size exclusion chromatography was performed the change in mobile phase pH did not affect the 100% recovery of either [35S]-or [3H]-labels under the uV peaks. No free [35S]-sulfate was obtained when [35S]-labeled glycoproteins were separated from the medium using dialysis. These data suggest that the standard method of TCA/PTA precipitation of [35S]-labeled glycoproteins may cleave the [35S]-sulfate ester linkages to the oligosaccharide chains. The [35S]-sulfate may then rebind to the macromolecule by a relatively strong noncovalent bond. This may prove critical in anion exchange protein HPLC studies.

Cyclic nucleotides fail to affect mucus glycoconjugate secretion from canine tracheal explants

Canine tracheal explants, incubated overnight with [3H]glucosamine, elicited an enhanced secretion of ethanol-precipitated [3H]labelled glycoconjugate when challenged with methacholine, 10 microM. Neither the beta-adrenoceptor agonist isoprenaline, 10 microM, nor the phosphodiesterase inhibitor theophylline, 10 mM, had any significant effect on glycoconjugate secretion. Dibutyryl cyclic AMP, 1 mM, and dibutyryl cyclic GMP, 1 mM, alone or in combination with theophylline, 10 mM, were devoid of activity on unstimulated or methacholine-stimulated tracheal explants. The calcium ionophore A23187, 10 microM, stimulated [3H]glycoconjugate secretion from each of the tissues tested; however, the cyclic nucleotides failed to modify this response. These data indicate that the cyclic nucleotides play little, if any, role in mucus glycoconjugate secretion by the canine trachea.

The calcium dependency of mucus glycoconjugate secretion by canine tracheal explants

Canine tracheal explants, incubated overnight with [14C]-glucosamine, elicited an enhanced secretion of ethanol-precipitated 14C-labelled glycoconjugate when challenged with methacholine, 10 microM. Explants were rendered deficient in total calcium content and unresponsive to methacholine, 10 microM, by incubating them in calcium-free medium for 18 to 22 h; however, the secretory response to the cholinergic agonist was restored with the addition of calcium to the medium. A dose-response relationship resulted when explants were challenged with methacholine in nutrient medium containing varied calcium concentrations (0.45 to 7.2 mM); alterations in the calcium concentration in the absence of methacholine had no significant effect on the basal secretion of 14C-labelled glycoconjugate. The calcium-selective ionophore A23187, 10 microM, stimulated [14C]-glycoconjugate secretion and induced the most significant effect in the presence of nutrient medium containing calcium. Verapamil, 10 microM, a calcium-entry blocker failed to inhibit basal or stimulated [14C]-glycoconjugate secretion; however, the intracellular calcium antagonist TMB-8, 10 to 100 microM, inhibited methacholine-induced [14C]-glycoconjugate secretion in a dose-dependent manner. These data suggest that respiratory mucus secretion is a calcium-dependent process and that intracellular calcium is more vital than extracellular calcium in supporting this phenomenon.