Histochemical localization of carbonic anhydrase in the trachea of the guinea pig

Nicotinic receptor dependent regulation of cough and other airway defensive reflexes

Nicotinic receptor activation in the airways evokes airway defensive reflexes including cough. These reflexes are the direct result of bronchopulmonary afferent nerve activation, which may occur directly, through activation of nicotinic receptors expressed on the terminals of airway sensory nerves, or indirectly, secondary to the end organ effects associated with autonomic nerve stimulation. The irritating effects of nicotine delivered topically to the airways are counterbalanced by an inhibitory effect of nicotinic receptor activation in the central nervous system. We present evidence that these nicotinic receptors are components of essential transducing and encoding mechanisms regulating airway defense.

Histochemical and ultrastructural observations of respiratory epithelium and gland in yak (Bos grunniens)

Submucous glands and epithelial mucous cells of yak (Bos grunniens) respiratory tract have been studied by a variety of histochemical methods and transmission electron microscopy for differentiating and characterizing serous and mucous cells. By light microscopy, the distribution, numbers of mucous cells, volume of mucous glands (Reid index), and the ratio of mucous cell to serous cell in the bronchial tree were measured with different staining. Histochemically, a majority of mucous cells, presented in the surface epithelium of bronchi and glands, secreted neutral and acid mucosubstances, only a few sulfated mucosubstances were present. No mucus-producing cells were observed from the terminal to respiratory bronchiolar level. Ultrastructurally, serous cells in glands of the lamina propria had two distinct forms: one type filled with many round dense secretory granules, plentiful RER and few other organelles, similar to other animals; the other type contained some oval mitochondrial and distended RER, the granules resembled the former. The mucous cells in gland were similar to that of epithelium, which containing abundant secretory granules with an eccentric core. The mucous cells of the surface epithelium differ from other animals in the structure and histochemistry of their secretory granules. Analysis of the size and distribution of the secretory granules and other organelles of serous cells suggested that differences represent different phases of a secretory cycle, not various populations of cell or granules.

Decreased soluble adenylyl cyclase activity in cystic fibrosis is related to defective apical bicarbonate exchange and affects ciliary beat frequency regulation

Human airway cilia contain soluble adenylyl cyclase (sAC) that produces cAMP upon HCO(3)(-)/CO(2) stimulation to increase ciliary beat frequency (CBF). Because apical HCO(3)(-) exchange depends on cystic fibrosis transmembrane conductance regulator (CFTR), malfunctioning CFTR might impair sAC-mediated CBF regulation in cells from patients with cystic fibrosis (CF). By Western blot, sAC isoforms are equally expressed in normal and CF airway epithelial cells, but CBF decreased more in CF than normal cells upon increased apical HCO(3)(-)/CO(2) exposure in part because of greater intracellular acidification from unbalanced CO(2) influx (estimated by 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) fluorescence). Importantly, ciliated cell-specific cAMP production (estimated by FRET fluorescence ratio changes of tagged cAMP-dependent protein kinase (PKA) subunits expressed under a ciliated cell-specific promoter) in response to increased apical HCO(3)(-)/CO(2) perfusion was higher in normal compared with CF cells. Inhibition of bicarbonate influx via CFTR (CFTR(inh)172) and inhibition of sAC (KH7) and PKA activation (H89) led to larger CBF declines in normal cells, now comparable with changes seen in CF cells. These inhibitors also reduced FRET changes in normal cells to the level of CF cells with the expected exception of H89, which does not prevent dissociation of the fluorescently tagged PKA subunits. Basolateral permeabilization and subsequent perfusion with HCO(3)(-)/CO(2) rescued CBF and FRET changes in CF cells to the level of normal cells. These results suggest that CBF regulation by sAC-produced cAMP could be impaired in CF, thereby possibly contributing to mucociliary dysfunction in this disease, at least during disease exacerbations when airway acidification is common.

Immunohistochemical demonstration of carbonic anhydrase isoenzyme VI (CA VI) expression in rat lower airways and lung

Carbonic anhydrase isoenzyme VI (CA VI), which is transported in high concentrations in saliva and milk into the alimentary tract, is an important element of mucosal protection in the upper alimentary tract. Like alimentary tract mucosa, the respiratory tract mucosa is also exposed to heavy microbial, physical, and chemical stress. The protective and renewal-promoting factors present in the surface mucus of the respiratory tract are mainly produced by the seromucous tracheobronchial glands. Here we studied the secretion of CA VI by these glands in adult and developing rats using immunohistochemical techniques. The serous acinar and duct cells of the tracheobronchial glands stained for CA VI. The presence of the enzyme also in the duct content indicates its active secretion into the surface mucus. CA VI was also visible in the secretory cells and at the base of the ciliated cells of the tracheobronchial surface epithelium. Moreover, the Clara cells of the bronchiolar surface epithelium stained for CA VI. These findings are consistent with the hypothesis that CA VI has a mucosa-protective role not only in the gastrointestinal tract but also in the respiratory tract, where CA VI may act as a pivotal pH neutralizer and growth factor.

Distribution of tracheal and laryngeal mucous glands in some rodents and the rabbit

We used scanning electron microscopy to count the number of mucous gland openings in the tracheae and lower portion of the larynges of the rat, guinea pig, hamster, mouse and rabbit. Cells of the airway surface epithelium were removed by protease digestion better to visualise the gland openings. The distribution of glands was further studied by conventional histology and by PAS/Alcian blue staining of whole mounts. In all rodent species, gland openings in the larynx occurred with a frequency of 1-2 per mm2. Mice had no gland openings in their tracheae, and hamsters, only a handful. Rat tracheae contained 126+/-42 gland openings (+/-S.D.; n = 6) at a frequency of approximately 0.6 per mm2 at the top of the trachea and approximately 0.15 per mm2 at the bottom. Guinea pig tracheae contained 153+/-90 gland openings (+/-S.D.; n = 5), with 54% being in the top 40% of the trachea. In both rat and guinea pig, tracheal glands were found in the ventral aspect between the cartilaginous rings, and were absent from the dorsal membranous portion. Gland openings in most species were simple circles of approximately 50 microm diameter. However, glands in the rat trachea generally opened obliquely into shallow (approximately 20 microm deep) oval troughs (approximately 150 x 75 microm), which had their long axes oriented from head to tail. In the rabbit, there was no evidence of tracheal or laryngeal glands histologically. However, the tracheal and laryngeal surfaces contained numerous pits (approximately 30 microm diameter) distributed evenly over and between cartilages at a frequency of approximately 4 per mm2. These may correspond to the 'nests' of goblet cells described by others.

Identification of nasal epithelial cells with carbonic anhydrase activity

Although carbonic anhydrase (CA) plays an important role in respiration, there is little information about CA in the respiratory system except for the lung. We examined the entire nasal cavity of guinea pig to identify CA activity using an enzyme-histochemical method. CA activity was detected in a group of morphologically distinct nasal epithelial cells. These cells were singly and sparsely distributed mainly in the olfactory epithelium and their number increased rostrocaudally. These cells were also detected in the apical portion of the nasal turbinate, particularly on the nasal endoturbinate, with a more complicated structure, rather than on the nasal septum and the roof of nasal cavity. Although the physiological role of these cells in unknown, based on the morphological and histochemical characteristics and the distribution of these cells, we speculated that they may represent a specialized chemoreceptors.