Porcine tracheal goblet cell ultrastructure: a three-dimensional reconstruction

Histamine-induced changes in rat tracheal goblet cell mucin store and mucosal edema

The pathology of chronic asthma in human and mouse is characterized by inflammation and remodeling of airway tissues. As a result of repeated inflammatory insults to the lower airways, smooth muscle thickening, mucin secretion and airway hyperreactivity may develop. In ovalbumin (OVA)-sensitized mice with repeated challenges with OVA to the lower airways, the trachea and bronchi are characterized by goblet cell hyperplasia and mucus hypersecretion from goblet cells. Previous study reports that intravenous (i.v.) application of a high dose of capsaicin releases tachykinin from capsaicin-sensitive nerves, producing acute plasma leakage and mucosal edema formation and causing depletion of mucin granules in goblet cells that results in a reduction in the number and size of Alcian blue (AB)-positive goblet cells in the rat trachea within a few minute after capsaicin application. Histamine is an important non-neural mediator of asthma from mast cells. The present study investigated whether i.v. application of a high dose of histamine (18 μmol/ml/kg) could result in these acute changes and the similar time-course changes in rat trachea. The tracheal whole mounts stained with chloroacetate esterase reagent and AB and tracheal methacrylate sections stained with AB and periodic acid-Schiff reagent were used for evaluation of histological and cellular changes. At 5 min after histamine application, mucosal leaky venules were numerous and subepithelial edema ratio (% of length of edema along the mucosal epithelial circumference of tracheal cross section) was found to be 48.2 ± 4.9, which was greater (P < 0.01) than saline-treated rats. But, the number of AB-positive goblet cells, 2,030 ± 170/mm(2) of mucosal surface epithelium, was similar to saline-treated group (P > 0.05). One day later, edema ratio remained large and the number of AB-positive goblet cells was 1,140 ± 150/mm(2) epithelium, reduced to half the number of the group at 5 min after histamine (P < 0.01). It is suggested that mucus hypersecretion occurred at this time point. At 3 or 5 days after histamine, edema ratio gradually decreased. The number of AB-positive goblet cells continued to remain small on day 3. On day 5 after histamine, the number of AB-positive goblet cells restored to the level of rat group at 5 min after histamine application. At 7 days after histamine, edema ratio returned to the level of saline-treated group. It is concluded that degranulation and thinning of tracheal goblet cells and mucus hypersecretion lagged behind histamine-induced acute plasma leakage and edema, and restoration of mucin store in goblet cells was associated with remission of mucosal edema.

Dimethylthiourea pretreatment inhibits endotoxin-induced compound exocytosis in goblet cells and plasma leakage of rat small intestine

Intravenous application of a high dose of endotoxin, also called lipopoly-saccharide (LPS), results in endotoxemia in animals, that induces production of cytokines and free radicals, systemic inflammation and mucin discharge from mucous tissues. The present study was to investigate (1) whether LPS application increased goblet cell secretion by compound exocytotic activity in mucosal villi and crypts of rat small intestine, and (2) whether hydroxyl radicals were involved in LPS-induced compound exocytosis in goblet cells and plasma leakage. Scanning electron microscopy showed that the numbers of goblet cells undergoing compound exocytosis (cavitated goblet cells) per mm(2) of ileal villus epithelium in rats 5 and 30 min after LPS (15 mg kg(-1)) were 693 +/- 196 (N = 6) and 547 +/- 213 (N = 6), respectively, which were 5.1 and 8.4 times (P < 0.05) the number of saline control. The percentage of villus cavitated goblet cell numbers, in both duodenum and ileum 5 min after LPS and in the ileum 30 min after LPS, increased significantly (P < 0.05). Pretreatment with dimethylthiourea (DMTU), a hydroxyl radical scavenger, decreased the number of cavitated goblet cells to saline control (P > 0.05). Morphometric analysis showed that the percentage of crypt epithelial area in the duodenum and ileum occupied by goblet cell mucin stores in the duodenum and ileum 30 min after LPS were 3.8 +/- 0.2% (N = 6) and 6.9 +/- 0.5 (N = 6), respectively reducing to one half the amount of control (P < 0.01). When DMTU was given prior to LPS the crypt goblet cell mucin stores and the amount of plasma leakage returned to the level of control. It is concluded that hydroxyl radicals were involved in the LPS-induced increase in compound exocytotic activity of goblet cells and the increase in plasma leakage during acute phases of inflammatory response in rat small intestine.

Spontaneous remission of edema and regranulation of goblet cells in rat tracheae after capsaicin-induced acute inflammation

Previous studies have investigated the short-term effect of capsaicin on edema formation and goblet-cell secretion in the trachea. The present study sought to investigate the long-term effect of a high dose of capsaicin (90 micro g/ml/kg), administered intravenously, on changes in the formation of endothelial gaps among venular endothelial cells, mucosal tissue edema and the secretory activity of goblet cells, including the number and size of goblet cells, and the mucus score and secretory ratio of goblet-cell mucus secretion in the trachea of rats. The tracheal whole mounts with silver staining, those stained with chloroacetate esterase reagent and Alcian blue and tracheal tissue sections stained with Alcian blue and periodic acid-Schiff reagent were used for evaluation. Formation of endothelial gaps occurred a few min after administration of capsaicin, and gaps almost closed within 12 min after capsaicin injection. Five min after capsaicin, the leaky blood vessels were numerous and the subepithelial edema ratio (% of length of edema along the inner circumference of tracheal cross section) was found to be 57.8+/-3.0% ( n=6). The number of Alcian blue-positive goblet cells (1,090+/-220 per mm(2) of mucosal surface) was reduced to half the number of goblet cells in the vehicle-treated rats (2,200+/-230). The mucus score of goblet cell secretion was not changed. The secretory ratio was greatly increased. One day after capsaicin, the edema ratio remained large and the number of Alcian blue-positive goblet cells was also small. The mucus score was also not changed. The secretory ratio was still large. On day 3, the edema ratio remained large, but the number of Alcian blue-positive goblet cells was increased to the level of the controls. The mucus score and secretory ratio returned to the control level. On day 5, the edema ratio was greatly decreased, but it was still significantly larger than that of the controls. The mucus score and secretory ratio remained at the baseline level. Seven days after capsaicin, the edema ratio was similar to the controls. The number of goblet cells was even larger than controls. It is concluded that capsaicin-induced acute inflammation in the rat trachea involves formation of endothelial gaps, extensive plasma extravasation and edema formation, and depletion of goblet-cell secretory granules. Spontaneous gradual remission of edema was accompanied by regranulation of goblet cells with gradual mucogenesis for several days.

Secretion of mucous granules and other membrane-bound structures: a look beyond exocytosis

The substances that animals secrete at epithelial surfaces include not only small molecules and ions delivered by exocytosis, but also a wide variety of materials in membrane-bound form. The latter include mucous granules of pulmonate molluscs, milk fat globules, and products of apocrine and holocrine secretion. Contents include hydrophobic entities (e.g., lipids, hydrocarbons), protective substances (e.g., mucus), and potentially injurious substances (e.g., digestive enzymes, toxins). In some cases vesicles or granules perform significant functions through enzymatic or other properties of the membrane itself (e.g., mammalian prostasome). Much work is still needed to elucidate the ways in which cells release membrane-bound products and how these products are deployed. The current concentration of research effort on exocytosis as a secretory modus should not divert attention from the remarkable versatility of epithelial cells that are capable of utilizing a variety of ways besides exocytosis to transfer materials and information to the external environment.

Relationship of secretory granule content and proliferative intensity in the secretory compartment of the hamster bronchial epithelium

We have previously shown that normal hamster airway epithelial secretory cells have a lower proliferative intensity than basal cells, but because of their high frequency are a major contributor to cell renewal (Am. J. Respir. Cell Mol. Biol. 1990; 2:51-58). In the present experiment, the relation between proliferative intensity and secretory granule content in bronchial epithelial cells is studied. [3H]thymidine (2 microCi/g wt) was given intraperitoneally, 1 h before killing, to 5 hamsters treated 21 days earlier with intratracheal saline and to six hamsters in which secretory cell metaplasia had been induced by intratracheal treatment with 300 micrograms of human neutrophil elastase given 21 days earlier. Light microscopic autoradiograms were prepared from 2-microns-thick Epon sections of left intrapulmonary hilar bronchi. Cells were categorized as basal, ciliated, secretory, or indeterminate. Secretory cells were classified as either: S1, with 0 to 4 granules; S2, with > or = 5 granules with intervening cytoplasm; or S3, with abundant granules and no apparent supranuclear cytoplasm. Proliferative intensity was defined by the categorical labeling index (LIc) at 1 h after [3H]thymidine injection. LIc was determined by the number of labeled cells in a category as the percent of labeled and unlabeled cells of that category. LIc of each of the cell categories were similar in the elastase and saline groups. LIc was highest for basal cells, reflecting their proliferative intensity, and lowest for ciliated cells. In the saline group, LIc of S1 (0.25%) was significantly higher compared with S2 (0.13%); S3 cells were rare (0.2%) and none were labeled.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional difference in airway epithelial response to neutrophil elastase: tracheal secretory cells discharge and recover in hamsters that develop bronchial secretory-cell metaplasia

Human neutrophil elastase (HNE) causes secretory granule discharge and conversion of many Clara cells to mucous cells in hamster bronchi. We investigated whether the trachea responds to HNE in a similar manner because of its abundance of Clara cells. By light microscopy, the tracheal epithelium of animals exposed to a single intratracheal injection of HNE was normal at 21 days, although bronchial secretory-cell metaplasia (SCM) was present. An ultrastructural differential cell count showed no increase in the proportion of granulated secretory cells in HNE-treated animals at 8 and 21 days postinjection compared to saline or untreated controls. At 2 h, the percentage of granulated secretory cells was lower and that of granulated secretory cells was higher in HNE-treated animals than in controls. The HNE-treated animals had fewer secretory granules per cell profile and more surface undulation than controls. By 1 day, the differential cell count and number of granules per cell profile were normal. Saline did not affect the differential cell count or granule number at any time. Ultrastructural study of untreated trachea disclosed the same three types of Clara cell that are found in the bronchus, but their frequencies, with one exception, are significantly different in the two regions. We conclude that HNE acts as a secretagogue in both trachea and bronchus but that an amount of enzyme sufficient to cause bronchial SCM does not induce a similar lesion in trachea. Heterogeneity of Clara cell types in hamster airways may explain the regional variation in secretory-cell modulation by HNE.

The ultrastructure of hamster bronchial epithelium

The central intrapulmonary bronchi of adult male Syrian hamsters were examined by electron microscopy to identify the principal types and proportions of epithelial cells. A differential count of cells displaying both a basal lamina and luminal border (transepithelial cells) showed that, on average, ciliated cells constituted 63% and granule-containing (granulated) secretory cells 25% of the total. Other transepithelial cells included nongranulated secretory cells (9%), preciliated cells (1.5%), and indeterminate cells (1%). The most frequent granulated secretory cell (77% of the population) was the Clara cell. It was identified by the presence of prominent apical smooth endoplasmic reticulum and secretory granules. It was subclassified into three types based on the presence or absence of rough endoplasmic reticulum and on granule morphology. Mucous cells (little or no smooth endoplasmic reticulum but with typical mucous granules) constituted approximately 20% of the granulated secretory cells. Serous cells were very infrequent. A differential count of nucleated epithelial cells demonstrated an average of 2% basal cells (hemidesmosomes present) and 20% pseudobasal cells (hemidesmosomes absent). Neuroepithelial bodies and solitary "small-granule" cells were infrequent. Brush cells and apoptotic bodies were rarely found but are noteworthy because their occurrence in hamster airways was not demonstrated previously. These results provide a foundation for subsequent analysis of alterations of epithelial homeostasis induced by injurious agents of exogenous and endogenous origin.

Three-dimensional reconstruction and quantitative analysis of rat lung type II cells: a computer-based study

The three-dimensional structure of alveolar epithelial type II cells was imaged using a computer-based system designed for reconstruction and quantitative analysis of serially sectioned specimens. Six type II cells were reconstructed from serial ultrathin sections of lungs from two Sprague Dawley male rats and the results were compared to standard morphometric estimates of type II cell composition from five other Sprague Dawley male rats. A minor portion of the type II cell surface was in contact with the alveolar airspace while most of the cell surface was embedded in the alveolar septal interstitium. The type II cells contained multiple Golgi regions located close to the nucleus. Mitochondria formed a few branching filamentous networks extending throughout the cell. The reconstructed cells appeared to represent a homogeneous population having fractional volumes of intracellular organelles very similar to those found by morphometric techniques. The spatial distribution of secretory organelle volume suggests that the organization of this cell type reflects an ordered progression of secretory particle maturation which is consistent with earlier hypotheses of lamellar body assembly.