Endocytosis of native and cationized ferritin by intralobular duct cells of the rat parotid gland

Summary The ability of the intralobular ducts of the rat parotid gland to take up protein from the lumen was examined after retrograde infusion of native and cationized ferritin. At high concentrations (3–10 mg/ml), cells of both intercalated- and striated ducts avidly internalized the tracers. No differences were noted in the mode of uptake or fate of native or cationized ferritin. Large, apical ferritin-containing vacuoles up to 5 m in size were present in cells of the intercalated ducts after infusion for 15 min. Small, smooth-surfaced spherical or flattened vesicles and tubules containing ferritin were also observed, often in association with the large vacuoles. Ferritin uptake increased with increasing infusion time, up to 1 h. Uptake by the striated ducts was less consistent than by the intercalated ducts, and occurred mainly in small vesicles and tubules. Secondary lysosomes became labeled with ferritin in both cell types. Ferritin was not observed in the Golgi saccules, nor was it discharged from the cells at the basolateral surfaces. At low concentrations (0.3–1 mg/ml), uptake was reduced, especially by cells of intercalated ducts, and differences were noted in the behavior of the two tracers. Cationized ferritin was internalized mainly into vesicles and tubules of cells of striated ducts; little uptake of native ferritin occurred at low concentrations. These results demonstrate that the ductal cells of the salivary glands are capable of luminal endocytosis of foreign proteins. They also suggest that in addition to modifying the primary saliva by electrolyte reabsorption and secretion, and secretion of various glycoproteins, the ductal cells are able to reabsorb proteins secreted by the acinar cells.     

Expression of transforming growth factor beta 1 in the submandibular gland of the rat

We employed immunocytochemical and in situ hybridization techniques to study the expression of transforming growth factor beta 1 (TGF-beta 1) in rat submandibular gland. Immunoreactivity for TGF-beta 1 was observed in the cells of granular convoluted tubules (GCTs), striated ducts, and excretory ducts, whereas it was absent in the intercalated ducts and secretory acini in both male and female rats. Immunoelectron microscopy revealed the ultrastructural localization of TGF-beta 1 in the secretory granules of GCT cells. On the other hand, signals for rat TGF-beta 1 mRNA were abundant in the GCT and striated duct cells but were lacking in the excretory duct cells. These results provided evidence for the production of TGF-beta 1 in the GCTs and striated ducts of rat submandibular gland.     

Histomorphometrical study of the submandibular gland ductal system in the rat

The duct system of murine submandibular gland is composed, in contrast with other mammals, by four types of ducts, among which the granular duct is unique for rodents. The granular duct shows a typical secretory structure with a clear intersex morphological diversity on which we carried out a morphometrical study in order to determine the relative area of each duct in rats in comparison with the rest of ducts and the whole gland. Our results, in both sexes, show that the duct with the broadest surface is the granular duct, followed by the excretory, striated and the intercalated ducts. In addition, we found a significant intersex difference between the relative surface of the granular and the excretory ducts, being bigger in males than in females. Finally, in both sexes, there is a greater variation in the data related to the excretory ducts than to the other ducts.     

Glycoprotein secretion in the mouse submandibular gland as revealed by radioautography after L-3H-fucose injection

Summary Glycoprotein secretion in the mouse submandibular gland was investigated by light microscope radioautography of semi-thin sections after the administration of L-³H-fucose. The incorporation of the precursor in the acini was negligible. ³H-fucose was taken up in the paranuclear region of the cells lining the intercalated, secretory, striated and excretory ducts. This labeling pattern was interpreted as addition of the precursor to glycoproteins within the Golgi apparatus. Incorporation in the intercalated duct was restricted to the cells with fine cytoplasmic granules. The glycoproteins synthesized by the intercalated and secretory ducts were transported to the saliva by the secretion granules. It is assumed that the glycoproteins synthesized in the striated and excretory ducts are plasma membrane glycoproteins which seem to renew continuously. Quantitation of the radioautographs supplied data concerning the incorporation of ³H-fucose into newly synthesized glycoproteins as well as the renewal of the labeled macromolecules in each duct.     

Fine structure of the mandibular gland in volcano rabbit

The mandibular glands of 6 male and 6 female volcano rabbits were examined by means of light and transmission electron microscopy. The acinar cells of the glands were seromucous in nature, and contained faintly basophilic granules. The cells were classified into the light cells containing granules of low or moderate densities and the clear cells having polygonal granules of low density. The preacinar cells were occasionally observed at the site between acinus and intercalated duct. These cells had many weakly basophilic granules which contained fine granular materials of moderate density. The intercalated ducts were composed of light cells containing cored granules. The striated duct cells consisted of light cells and dark cells. Both of them contained a few vacuoles and vesicles, but no secretory granules. No sex-and age-related differences were observed in the mandibular gland of the volcano rabbit. The mandibular gland of the volcano rabbit was similar to the rabbit mandibular gland rather than the pika mandibular gland morphologically.     

Immunocytochemical evidence for the presence of somatostatin-like immunoreactivity in scattered cells of the duct system of the submandibular glands in the Monkey,Macaca irus

Summary Using the indirect immunofluorescent technique with anti-somatostatin serum, the distribution of scattered cells in the duct system of submandibular glands in the Monkey, Macaca irus has been assessed. In both males and females, these cells are located only in some portions of the duct system, e.g. striated ducts and excretory ducts. No immunoreactive cells were observed in the intercalated ducts or in secretory endpieces. The lymphatic node constantly adjacent to the submandibular gland did not contain immunoreactive cells. In the parotid glands, no immunoreactive cells to antisomatostatin immuneserum were ever observed     

The ultrastructure of the duct system in the rat extraorbital lacrimal gland

Summary The duct system of the rat exorbital lacrimal gland consists of intercalated ducts, interlobular ducts and excretory ducts. The morphological changes from one type of duct to the next are gradual. At the light microscopical level this consists of a change from a bilaminar epithelium in the intercalated ducts to an epithelium, consisting of approximately three layers — which may be pseudostratified — in the excretory ducts. The basal layer of the intercalated ducts consists of myoepithelial cells, whereas the inner epithelial cells may have both a secretory and an electrolyte transporting function. The interlobular duct epithelium contains many cells with deep infoldings of the basolateral plasma membranes and associated mitochondria, suggesting a similar function to the striated duct epithelium in salivary glands. Numerous basal cells in this epithelium have tentatively been interpreted as unusual myoepithelial cells. Nerve terminals have been observed in the ductal epithelium.This work was supported by the National Health and Medical Research Council of Australia. — We wish to thank Mrs. Eva Vasak for her expert technical assistance.     

Immunocytochemical evidence for the presence of somatostatin-like immunoreactivity in scattered cells of the duct system of the submandibular glands in the monkey, Macaca irus

Using the indirect immunofluorescent technique with anti-somatostatin serum, the distribution of scattered cells in the duct system of submandibular glands in the Monkey, Macaca irus has been assessed. In both males and females, these cells are located only in some portions of the duct system, e.g. striated ducts and excretory ducts. No immunoreactive cells were observed in the intercalated ducts or in secretory endpieces. The lymphatic node constantly adjacent to the submandibular gland did not contain immunoreactive cells. In the parotid glands, no immunoreactive cells to antisomatostatin immuneserum were ever observed.     

Development of secretory units of mouse submandibular gland

Summary The fine structure of the secretory units of the mouse submandibular gland was studied according to the developmental sequence. The embryonic submandibular gland consists of terminal tubules and ducts. Myoepithelium is associated only with the terminal tubules, and the cells of the primary intercalated ducts show characteristics of the young striated duct cells. The major changes shortly after birth consist of: 1) opening of the secretory lumina, 2) increasing rough ER and its altered configuration, 3) dilatation of Golgi cisternae and 4) changes in the granular structure. These findings suggest that the salivary secretion first occurs after birth, and acinar differentiation or transformation of the secretory cells of the terminal tubules is induced and profoundly affected by the commencement of the secretory activity. In the intercalated ducts this process is somehow inhibited, and the granular cells found in the adult can be considered as the remnants of the secretory cells of the terminal tubules.     

The postnatal development of the submandibular gland of the mouse

Summary The postnatal development of the submandibular gland was investigated in male mice of the Swiss-Webster strain, which were killed at 1, 2, 3, 4, 5, 6, 8, 10, 12, 16 and 20 weeks of age, while the older mice had been weaned at 3 weeks of age. The mean weight of the submandibular gland increases from 9.5 mg at 1 week to 232.9 mg at 20 weeks of age, and the rate of increase is rapid between 3 and 10 weeks of age. The gland's contents of DNA, RNA and protein increase in a similar manner.The changes in the constituent cell types of the gland were studied in radioautographs prepared from Epon-embedded sections of mice given ³H-thymidine and stained with toluidine blue. At 1 week of age, the gland consists of acinar cells (36%), intercalated duct cells (26%), juxta-acinar cells (13%), striated duct cells (12%) and others. The cellular composition of the gland changes little before weaning, but the absolute number of all types of cells increases with age. Between 3 and 4 weeks, juxta-acinar cells disappear and granular convoluted tubule cells appear and increase rapidly in number with age. The rapid expansion of the population size of granular convoluted tubule cells after weaning coincides with the second peak of increased proliferative activity of intercalated duct cells, whereas all the other cell types show a progressive decrease in their proliferative activity with age. In spite of the burst in proliferative activity, there is no corresponding increase in the absolute number of intercalated duct cells. The number of striated duct cells peak at 5 weeks of age and then declines. These findings indicate that the mitoses of intercalated duct cells give rise to granular convoluted tubule cells through a stage of striated duct cells. At 20 weeks of age, the gland consists of granular convoluted tubule cells (47%), acinar cells (28%), intercalated duct cells (12%), striated duct cells (1%) and others.Supported by Public Health Service Research Grant AMDE 19753 from the National Institute of Health. The authors are indebted to Mr. I. Borcsanyi for technical assistance     

Distinct immunohistochemical expression of osteopontin in the adult rat major salivary glands

Osteopontin is a multifunctional protein secreted by epithelial cells of various tissues. Its expression in the adult rat major salivary glands has not yet been studied. We examined osteopontin expression by immunohistochemistry using a well characterized monoclonal antibody. Submandibular glands of young adult male rats (70–100 days old) showed specific expression in secretion granules of granular duct cells but also in cells of the striated ducts and excretory duct. In the major sublingual as well as the parotid gland expression was found solely in the duct system. In addition, a few interstitial-like cells exhibiting very strong immunostaining for osteopontin could be found in either organ. Expression could neither be seen in acinar cells nor in cells of the intercalated ducts. Moreover, in submandibular glands of more aged rats (6- to 7-month old) which show well developed granular convoluted tubules, there was almost exclusive expression of osteopontin in granular duct cells as well as in some interstitial-like cells, but barely in the striated/excretory duct system. Western blot analysis of the submandibular gland showed a specific band migrating at approximately 74 kDa, detectable at both age stages. Osteopontin secreted fom granular duct cells may influence the compostion of the saliva, e.g. thereby modulating pathways affecting sialolithiasis. Its expression in striated duct cells may also hint to roles such as cell–cell attachment or cell differentiation. The cell-specific expression detected in the rat major salivary glands differs in part from that reported in mice, human and monkey.Nicholas Obermüller and Nikolaus Gassler contributed equally to this work.     

Fine structure of the mandibular gland of the Djungarian hamster (Phodopus sungarus)

The mandibular gland of the Djungarian hamster was examined by light microscopy, and transmission and scanning electron microscopies. Its acinar cells reacted with periodic acid-Schiff (PAS) and were weakly stained with alcian blue (AB). There were intercellular canaliculi between the acinar cells. These cells therefore appeared to be seromucous. The acinar epithelium was composed of light cells containing various spherical secretory granules. The granular cells of the mandibular gland possessed many acidophilic granules exhibiting a positive reaction to PAS stain. They were frequently observed at the junction of the acini and intercalated ducts in all mandibular glands examined. All of these cells were light and contained secretory granules of varying size and density. The intercalated ducts consisted exclusively of light cells possessing a few round granules of high density in the apical region. The striated ducts were comprised of two portions--a secretory portion and a typical striated portion without secretory granules. The secretory portion consisted of light, dark and specifically light epithelial cells containing acidophilic granules, which exhibited a strongly positive PAS reaction. The epithelium of typically striated portions was composed of light and dark cells containing fine vacuoles in the apical region. The mandibular gland of the Djungarian hamster revealed no histological differences between sexes.     

Ultrastructure of the submandibular gland in the rabbit

The secretory endpieces of the rabbit submandibular gland are unusual in that they consist of seromucous acini (not demilunes) that empty into serous tubules that in turn drain into intercalated ducts. Seromucous granules consist of a moderately dense spherule in a fibrillogranular matrix. Serous granules contain a feltwork of filaments, which are liberated as a tangled skein during exocytosis. Peculiar granulated cells that have secretory granules of complex morphology are present at each end of the serous tubules. Intercalated ducts are, cytologically speaking, relatively simple, but the duct cells may contain a few oblong secretory granules. Striated ducts are typical in structure, although postfixation with ferrocyanide-reduced osmium reveals significant amounts of glycogen in the basal processes. Modified mitochondria are present in striated duct cells, but their frequency varies from rabbit to rabbit. Such mitochondria contain either an array of parallel, rigid cristae linked by intermembranous bridges, or a bundle of helical filaments within an expanded crista. Interspersed with the striated duct cells, especially near the duct origin, are some highly vacuolated cells with sparse mitochondria. Excretory ducts consisting of stratified columnar (sometimes pseudostratified) epithelium often show bleb formation of the luminal surface of the tall cells.     

Immunohistochemical localization of Na+,K+-ATPase in rodent and human salivary and lacrimal glands

The enzyme Na+,K+-ATPase was localized immunohistochemically in major salivary glands of mouse, rat, and human and in exorbital lacrimal glands of the rodents. Immunoreactive Na+,K+-ATPase was abundant in the basolateral membranes of all epithelial cells lining striated and intra- and interlobular ducts of all glands. Reactivity of intercalated ducts varied among gland type and species. Cells lining granular ducts in rodent submandibular gland showed a heterogeneous staining pattern in rat but stained homogeneously in mouse. Secretory cells varied greatly in their content of immunoreactive Na+,K+-ATPase. As with all duct cells, staining was present only at the basolateral surface and was never observed at the luminal surface of reactive secretory cells. Mucous cells failed to show any reactivity in any gland examined. Serous cells showed a gradient of immunostaining intensity ranging from strongly positive in demilunes of human sublingual gland to negative in rat submandibular gland and lacrimal glands of rats and mice. The presence of basolaterally localized Na+,K+-ATPase in most serous cells but not in mucous cells suggests that the enzyme contributes to the ion and water content of copious, low-protein serous secretions. The intense immunostaining of cells in most if not all segments of the duct system supports the idea that the ducts are involved with modification of the primary saliva, and extends this concept to include all segments of the duct system.     

The immunohistolocalization of carbonic anhydrase III in the submandibular gland of rats and hamsters

Summary Carbonic anhydrase III has been localized using the avidin-biotin-glucose oxidase complex (ABC) method in the submandibular gland of the rat and hamster. This isozyme, which is predominant in skeletal muscle, was observed in intercalated duct, striated duct and excretory duct cells in the rat submandibular glands. In contrast, only some striated duct cells in hamster submandibular glands were stained.     

Immunolocalization of centriole-associated striated rootlets in human submandibular gland cells with and without solitary cilia

Using an antibody specific to striated rootlets, we investigated the immuolocalization of striated rootlets in cells constituting human submandibular glands. Striated rootlets were positively stained in all cell types constituting acini, intercalated ducts, striated ducts, and interlobular ducts, but their shapes were different. The mean lengths of striated rootlets were 1.46 +/- 0.49, 3.15 +/- 1.35 and 3.99 +/- 1.02 microm in acinar secretory cells, myoepithelial cells, and columnar cells of the striated duct, respectively. The rootlets were the longest in columnar cells of the striated duct, in which paired centrioles were located in the apical cytoplasm away from nuclei. These findings suggest that striated rootlets play important roles in the positioning of centrioles in the cell. 2-8% of striated rootlets in myoepithelial cells were associated with solitary cilia, but they were not associated with solitary cilia in acinar cells and columnar cells of the striated duct. These observations suggest that striated rootlets may be associated with centrioles under normal physiological conditions, without formation of solitary cilia.     

Immunocytochemical demonstration of nerve growth factor and histofluorescence of catecholaminergic nerves in the salivary glands of diabetic mice

Summary Nerve growth factor (NGF) was localized in the submandibular, sublingual, and parotid salivary glands of male and female diabetic mice and their normal littermates by immunoperoxidase staining usingp-phenylenediamine-pyrocatechol as a chromogen for the cytochemical demonstration of peroxidase activity. In the normal male submandibular gland, immunoreactive NGF was localized in the apical regions of granular, intercalated and collecting duct cells, while in the normal female submandibular gland, NGF was present throughout the cytoplasm of granular duct cells. The localization of NGF in the diabetic male and female submandibular glands was similar and resembled that of the normal female. NGF immunoreactivity was also observed in the striated duct cells in the sublingual and parotid glands of all four types of mice.The sympathetic innervation of the submandibular glands of normal and diabetic mice was demonstrated using glyoxylic acid-induced histofluorescence. The pattern of sympathetic innervation and the intensity of catecholamine fluorescence was consistently different in the four types of mice. In the normal male submandibular gland the fluorescence was very intense, particularly in nerves adjacent to the granular ducts. In the normal female submandibular gland, the fluorescence was weak, while in the diabetic male and female the fluorescence was moderate.The correlation between the intensity of the immunocytochemical staining for NGF and the catecholamine fluorescence adjacent to the granular ducts suggests a trophic influence of the NGF-containing granular ducts on their sympathetic innervation.     

Immunolocalization of PTHrP in the sublingual glands of three mammals

The present study deals with immunohistochemical localization of PTHrP in sublingual glands of white mouse, bank vole, and common vole. PTHrP immunoreactivity was observed in epithelial cells of striated, interlobular and main excretory ducts of the salivary glands in all the three animal species tested. However, we found no positive reaction for PTHrP in epithelial cells of the intercalated ducts. In striated duct cells, the reaction intensity was species-dependent. In bank vole and common vole, the reaction was very strong, while in white mouse very weak. In the remaining segments of excretory ducts (interlobular and main excretory duct) we found no species-related differences in the reaction intensity or character. Myoepithelial cells surrounding ducts and mucous tubules with serous demilunes in sublingual glands were also PTHrP-negative in all the three animal species tested.     

Ultrastructure of the principal and accessory submandibular glands of the common vampire bat

The principal and accessory submandibular glands of the common vampire bat, Desmodus rotundus, were examined by electron microscopy. The secretory endpieces of the principal gland consist of serous tubules capped at their blind ends by mucous acini. The substructure of the mucous droplets and of the serous granules varies according to the mode of specimen preparation. With ferrocyanide-reduced osmium postfixation, the mucous droplets are moderately dense and homogeneous; the serous granules often have a polygonal outline and their matrix shows clefts in which bundles of wavy filaments may be present. With conventional osmium postfixation, the mucous droplets have a finely fibrillogranular matrix; the serous granules are homogeneously dense. Mucous cells additionally contain many small, dense granules that may be small peroxisomes, as well as aggregates of 10-nm cytofilaments. Intercalated duct cells are relatively unspecialized. Striated ducts are characterized by highly folded basal membranes and vertically oriented mitochondria. Luminal surfaces of all of the secretory and duct cells have numerous microvilli, culminating in a brush borderlike affair in the striated ducts. The accessory gland has secretory endpieces consisting of mucous acini with small mucous demilunes. The acinar mucous droplets contain a large dense region; the lucent portion has punctate densities. Demilune mucous droplets lack a dense region and consist of a light matrix in which fine fibrillogranular material is suspended. A ring of junctional cells, identifiable by their complex secretory granules, separates the mucous acini from the intercalated ducts. The intercalated ducts lack specialized structure. Striated ducts resemble their counterparts in the principal gland. As in the principal gland, all luminal surfaces are covered by an array of microvilli. At least some of the features of the principal and accessory submandibular glands of the vampire bat may be structural adaptations to the exigencies posed by the exclusively sanguivorous diet of these animals and its attendant extremely high intake of sodium chloride.