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

Loss of Cdc42 in Exocrine Acini Decreases Saliva Secretion but Increases Tear Secretion-A Potential Model of Exocrine Gland Senescence

Cdc42 is a small GTPase essential for the cell cycle, morphogenesis, and cell adhesion, and it is involved in the polarity of epithelial cells. However, the functional roles of Cdc42 in exocrine glands, such as the maintenance of acini and water secretion, are not yet well understood. In this study, we generated acinar-cell-specific Cdc42 conditional knockout (Cdc42cKO) mice to assess their maintenance of acinar cells and physiological functions in the salivary glands (SGs) and lacrimal glands (LGs). Our data revealed that the loss of Cdc42 altered the luminal structures to bulging structures and induced acinar cell apoptosis in both the parotid glands (PGs) and LGs of Cdc42cKO mice. Interestingly, saliva secretion in response to pilocarpine stimulation was decreased in the Cdc42cKO group, whereas tear secretion was increased. Consistent with the water secretion results, protein expression of the water channel AQP5 in acinar cells was also decreased in the PGs but conversely increased in the LGs. Moreover, the changes that increased AQP5 expression in LGs occurred in the acinar cells rather than the duct cells. The present study demonstrates that Cdc42 is involved in the structural and survival maintenance of acinar cells in SGs and LGs. On the other hand, depletion of Cdc42 caused the opposite physiological phenomena between PGs and LGs.

A Mathematical Model of Salivary Gland Duct Cells

Saliva is produced in two stages in the salivary glands: the secretion of primary saliva by the acinus and the modification of saliva composition to final saliva by the intercalated and striated ducts. In order to understand the saliva modification process, we develop a mathematical model for the salivary gland duct. The model utilises the realistic 3D structure of the duct reconstructed from an image stack of gland tissue. Immunostaining results show that TMEM16A and aquaporin are expressed in the intercalated duct cells and that ENaC is not. Based on this, the model predicts that the intercalated duct does not absorb Na\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^+$$\end{document}+ and Cl\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^-$$\end{document}- like the striated duct but secretes a small amount of water instead. The input to the duct model is the time-dependent primary saliva generated by an acinar cell model. Our duct model produces final saliva output that agrees with the experimental measurements at various stimulation levels. It also shows realistic biological features such as duct cell volume, cellular concentrations and membrane potentials. Simplification of the model by omission of all detailed 3D structures of the duct makes a negligible difference to the final saliva output. This shows that saliva production is not sensitive to structural variation of the duct.

New saliva secretion model based on the expression of Na+-K+ pump and K+ channels in the apical membrane of parotid acinar cells

The plasma membrane of parotid acinar cells is functionally divided into apical and basolateral regions. According to the current model, fluid secretion is driven by transepithelial ion gradient, which facilitates water movement by osmosis into the acinar lumen from the interstitium. The osmotic gradient is created by the apical Cl^- efflux and the subsequent paracellular Na⁺ transport. In this model, the Na⁺-K⁺ pump is located exclusively in the basolateral membrane and has essential role in salivary secretion, since the driving force for Cl^- transport via basolateral Na⁺-K⁺-2Cl^- cotransport is generated by the Na⁺-K⁺ pump. In addition, the continuous electrochemical gradient for Cl^- flow during acinar cell stimulation is maintained by the basolateral K⁺ efflux. However, using a combination of single-cell electrophysiology and Ca²⁺-imaging, we demonstrate that photolysis of Ca²⁺ close to the apical membrane of parotid acinar cells triggered significant K⁺ current, indicating that a substantial amount of K⁺ is secreted into the lumen during stimulation. Nevertheless, the K⁺ content of the primary saliva is relatively low, suggesting that K⁺ might be reabsorbed through the apical membrane. Therefore, we investigated the localization of Na⁺-K⁺ pumps in acinar cells. We show that the pumps appear evenly distributed throughout the whole plasma membrane, including the apical pole of the cell. Based on these results, a new mathematical model of salivary fluid secretion is presented, where the pump reabsorbs K⁺ from and secretes Na⁺ to the lumen, which can partially supplement the paracellular Na⁺ pathway.

Induction of Sca-1 in the duct cells of the mouse submandibular gland by obstruction of the main excretory duct

The effect of ligation of the main excretory duct (MED) of the mouse submandibular gland (SMG) on the expression of Sca-1, a stem cell antigen, was examined by Western blotting and immunohistochemistry. By Western blotting, the expression of Sca-1 with a molecular weight of 18 kDa was identified in the normal gland. At 1 day post-ligation, the expression level of Sca-1 was strongly increased in the experimental gland and weakly in the contralateral gland, and such expression in both glands decreased at 6 days. By immunohistochemistry, Sca-1 was detected weakly in the apical membrane of excretory duct (ED) cells of the SMG under the normal condition. By duct ligation, Sca-1 became expressed strongly in most cells of the two major duct systems, i.e., the striated duct (SD) and granular convoluted tubules (GCT), but was not detected in the acinar (Ac) cells. By fluorescence-activated cell sorter (FACS) analysis, the number of side population (SP) cells in this gland was found to be increased by ligation. These results imply that Sca-1-positive cells may have a role in the duct cell proliferation in the regeneration step elicited by MED ligation-induced injury.

Channels and transporters in salivary glands

According to the two-stage hypothesis, primary saliva, a NaCl-rich plasma-like isotonic fluid is secreted by salivary acinar cells and its ionic composition becomes modified in the duct system. The ducts secrete K(+) and HCO (3) (-) and reabsorb Na(+) and Cl(-) without any water movement, thus establishing a hypotonic final saliva. Salivary secretion depends on the coordinated action of several channels and transporters localized in the apical and basolateral membrane of acinar and duct cells. Early functional studies in perfused glands, followed by the molecular cloning of several transport proteins and the subsequent analysis of mutant mice, have greatly contributed to our understanding of salivary fluid and the electrolyte secretion process. With a few exceptions, most of the key channels and transporters involved in salivary secretion have now been identified and characterized. However, the picture that has emerged from all these studies is one of a complex molecular network characterized by redundancy for several transport proteins, compensatory mechanisms, and adaptive changes in health and disease. Current research is directed to the molecular interactions between the determinants and the ways in which they are regulated by extracellular signals and intracellular mediators. This review focuses on the functionally and molecularly best-characterized channels and transporters that are considered to be involved in transepithelial fluid and electrolyte transport in salivary glands.

Functional and molecular characterization of the fluid secretion mechanism in human parotid acinar cells

The strategies available for treating salivary gland hypofunction are limited because relatively little is known about the secretion process in humans. An initial microarray screen detected ion transport proteins generally accepted to be critically involved in salivation. We tested for the activity of some of these proteins, as well as for specific cell properties required to support fluid secretion. The resting membrane potential of human acinar cells was near -51 mV, while the intracellular [Cl-] was approximately 62 mM, about fourfold higher than expected if Cl ions were passively distributed. Active Cl- uptake mechanisms included a bumetanide-sensitive Na+ -K+ -2Cl- cotransporter and paired DIDS-sensitive Cl-/HCO3- and EIPA-sensitive Na+/H+ exchangers that correlated with expression of NKCC1, AE2, and NHE1 transcripts, respectively. Intracellular Ca2+ stimulated a niflumic acid-sensitive Cl- current with properties similar to the Ca2+ -gated Cl channel BEST2. In addition, intracellular Ca2+ stimulated a paxilline-sensitive and voltage-dependent, large-conductance K channel and a clotrimazole-sensitive, intermediate-conductance K channel, consistent with the detection of transcripts for KCNMA1 and KCNN4, respectively. Our results demonstrate that the ion transport mechanisms in human parotid glands are equivalent to those in the mouse, confirming that animal models provide valuable systems for testing therapies to prevent salivary gland dysfunction.

Radioprotective effect of heat shock protein 25 on submandibular glands of rats

Irradiation (IR) is a fundamental treatment modality for head and neck malignancies. However, a significant drawback of IR treatment is irreversible damage of salivary gland in the IR field. In the present study, we investigated whether heat shock protein (HSP) 25 could be used as a radioprotective molecule for radiation-induced salivary gland damage in rats. HSP25 as well as inducible HSP70 (HSP70i) that were delivered to the salivary gland via an adenoviral vector significantly ameliorated radiation-induced salivary fluid loss. Radiation-induced apoptosis, caspase-3 activation, and poly(ADP-ribose) polymerase cleavage in acinar cells, granular convoluted cells, and intercalated ductal cells were also inhibited by HSP25 or HSP70i transfer. The alteration of salivary contents, including amylase, protein, Ca+, Cl-, and Na+, was also attenuated by HSP25 transfer. Histological analysis revealed almost no radiation-induced damage in salivary gland when HSP25 was transferred. Aquaporin 5 expression in salivary gland was inhibited by radiation; and HSP25 transfer to salivary gland prevented this alteration. The protective effect of HSP70i on radiation-induced salivary gland damage was less or delayed than that of HSP25. These results indicate that HSP25 is a good candidate molecule to protect salivary gland from the toxicity of IR.

Recovery of rat submandibular salivary gland function following removal of obstruction: a sialometrical and sialochemical study

Functional recovery of the rat submandibular gland following ligation of the main excretory duct was examined. Rat submandibular glands were ligated for 1, 4 and 8 weeks using a micro-clip with a plastic tube. Micro-clips were removed and glands were allowed to recover for periods of 8, 16 and 24 weeks. Submandibular glands were stimulated with autonomimetic drugs (methacholine and isoprenaline) and salivas were collected from atrophic or de-ligated and contralateral control glands. Glands recovered almost full size (92% of control gland) following 24 weeks of de-ligation. Saliva volume secreted by ligated/de-ligated (RSM) and control (LSM) glands were similar with different doses of agonists. Protein output expressed per gram of tissue wet weight was similar from both ligated/de-ligated and control glands with all doses of agonist. Sodium and chloride levels were higher from de-ligated glands than contralateral control glands. Protein electrophoresis showed similar profiles of salivary proteins in all samples with some minor differences. Acinar cells in de-ligated glands showed a normal morphology, as indicated by light microscopy, whilst granular ductal cells were fewer and contained fewer secretory granules. Sodium potassium ATPase staining of striated ducts in de-ligated glands was similar to that of control glands. It can be concluded that rat submandibular glands can regenerate following severe atrophy and secrete normal amounts of saliva containing broadly a full profile of secretory proteins. In contrast to acinar cells, ductal cells appear not to recover full function.

Interlobular excretory ducts of mammalian salivary glands: structural and histochemical review

In the major salivary glands of mammals, excretory ducts (EDs) succeed striated ducts. They are for the most part interlobular in position, although their proximal portions sometimes are on the periphery of a lobule, where they occasionally retain some of the structural features of striated ducts. Based on a survey of a broad range of mammalian species and glands, the predominant tissue type that composes EDs is pseudostratified epithelium. In some species, there is a progression of epithelial types: the proximal EDs are composed of simple cuboidal or columnar epithelium that, in the excurrent direction, usually gives way to the pseudostratified variety. Secretory granules are visible in the apical cytoplasm of the principal cells of the EDs of only a few species, but histochemistry has shown the presence of a variety of glycoproteins in these cells in a spectrum of species. Moreover, the latter methodology has revealed the presence of a variety of oxidative, acid hydrolytic, and transport enzymes in the EDs, showing that, rather than simply acting as a conduit for saliva, these ducts play a metabolically active role in gland function. It is difficult to describe a "typical" mammalian ED because it can vary along its length and interspecific variation does not follow a phylogenetic pattern. Moreover, in contrast to intercalated and striated ducts, ED cellular features do not exhibit a relationship to diet.

Primary culture of polarized human salivary epithelial cells for use in developing an artificial salivary gland

Therapeutic irradiation for head and neck cancer, and the autoimmune disease Sjogren's syndrome, lead to loss of salivary parenchyma. They are the two main causes of irreversible salivary gland hypofunction. Such patients cannot produce adequate levels of saliva, leading to considerable morbidity. We are working to develop an artificial salivary gland for such patients. A major problem in this endeavor has been the difficulty in obtaining a suitable autologous cellular component. This article describes a method of culturing and expanding primary salivary cells obtained from human submandibular glands (huSMGs) that is serum free and yields cells that are epithelial in nature. These include morphological (light and transmission electron microscopy [TEM]), protein expression (immunologically positive for ZO-1, claudin-1, and E-cadherin), and functional evidence. Under confocal microscopy, huSMG cells show polarization and appropriately localize tight junction proteins. TEM micrographs show an absence of dense core granules, but confirm the presence of tight and intermediate junctions and desmosomes between the cells. Functional assays showed that huSMG cells have high transepithelial electrical resistance and low rates of paracellular fluid movement. Additionally, huSMG cells show a normal karyotype without any morphological or numerical abnormalities, and most closely resemble striated and excretory duct cells in appearance. We conclude that this culture method for obtaining autologous human salivary cells should be useful in developing an artificial salivary gland.

Immunolocalization of AQP-5 in rat parotid and submandibular salivary glands after stimulation or inhibition of secretion in vivo

In vitro studies of cultured salivary gland cells and gland slices have indicated that there may be regulated translocation of aquaporin (AQP)-5 between the apical plasma membrane and intracellular compartments of the secretory cells. However, it remains unknown whether AQP-5 in salivary glands is subject to regulated trafficking in vivo. To examine this possibility, we have investigated the subcellular localization of AQP-5 in rat parotid and submandibular glands fixed in vivo under conditions of stimulated or inhibited salivary secretion. Immunofluorescence and immunoelectron microscopy was used to determine the subcellular distribution of AQP-5 in control conditions following the stimulation of secretion with pilocarpine (a muscarinic agonist) or epinephrine (an alpha-adrenoceptor agonist) or during inhibition of basal secretion with atropine (a muscarinic antagonist) or phentolamine (an alpha-adrenoceptor antagonist). Under control conditions, >90% of AQP-5 was associated with the apical plasma membrane of acinar and intercalated duct cells, with only rare gold particles associated with intracellular membrane domains. Pilocarpine treatment dramatically increased saliva production but had no discernible effect on AQP-5 distribution. However, the increased salivary secretion was associated with luminal dilation and the appearance of a markedly punctate AQP-5 labeling pattern due to clustering of AQP-5 at the microvilli (especially evident in the parotid gland) after 10 min of drug injection. No changes in the subcellular localization of AQP-5 were seen in response to epinephrine, atropine, or phentolamine treatment compared with control tissues. Thus AQP-5 is localized predominantly in the apical plasma membrane under control conditions, and neither the onset nor the cessation of secretion is associated in vivo with any significant short-term translocation of AQP-5 between intracellular structures and the apical plasma membrane.

Immunocytochemistry of myoepithelial cells in the salivary glands

MECs are distributed on the basal aspect of the intercalated duct and acinus of human and rat salivary glands. However, they do not occur in the acinus of rat parotid glands, and sometimes occur in the striated duct of human salivary glands. MECs, as the name implies, have structural features of both epithelial and smooth muscle cells. They contract by autonomic nervous stimulation, and are thought to assist the secretion by compressing and/or reinforcing the underlying parenchyma. MECs can be best observed by immunocytochemistry. There are three types of immunocytochemical markers of MECs in salivary glands. The first type includes smooth muscle protein markers such as alpha-SMA, SMMHC, h-caldesmon and basic calponin, and these are expressed by MECs and the mesenchymal vasculature. The second type is expressed by MECs and the duct cells and includes keratins 14, 5 and 17, alpha 1 beta 1 integrin, and metallothionein. Vimentin is the third type and, in addition to MECs, is expressed by the mesenchymal cells and some duct cells. The same three types of markers are used for studying the developing gland. Development of MECs starts after the establishment of an extensively branched system of cellular cords each of which terminates as a spherical cell mass, a terminal bud. The pluripotent stem cell generates the acinar progenitor in the terminal bud and the ductal progenitor in the cellular cord. The acinar progenitor differentiates into MECs, acinar cells and intercalated duct cells, whereas the ductal progenitor differentiates into the striated and excretory duct cells. Both in the terminal bud and in the cellular cord, the immediate precursors of all types of the epithelial cells appear to express vimentin. The first identifiable MECs are seen at the periphery of the terminal bud or the immature acinus (the direct progeny of the terminal bud) as somewhat flattened cells with a single cilium projecting toward them. They express vimentin and later alpha-SMA and basic calponin. At the next developmental stage, MECs acquire cytoplasmic microfilaments and plasmalemmal caveolae but not as much as in the mature cell. They express SMMHC and, inconsistently, K14. This protein is consistently expressed in the mature cell. K14 is expressed by duct cells, and vimentin is expressed by both mesenchymal and epithelial cells. After development, the acinar progenitor and the ductal progenitor appear to reside in the acinus/intercalated duct and the larger ducts, respectively, and to contribute to the tissue homeostasis. Under unusual conditions such as massive parenchymal destruction, the acinar progenitor contributes to the maintenance of the larger ducts that result in the occurrence of striated ducts with MECs. The acinar progenitor is the origin of salivary gland tumors containing MECs. MECs in salivary gland tumors are best identified by immunocytochemistry for alpha-SMA. There are significant numbers of cells related to luminal tumor cells in the non-luminal tumor cells that have been believed to be neoplastic MECs.

P-glycoprotein expression in human major and minor salivary glands

Sodium pump and carbonic anhydrase activity have been described in the salivary glands. However, it remains to be elucidated whether these energy sources are used for secretion, excretion or both. In addition, the differences in the function of excretion and the role of the excretory duct cells are currently unknown in salivary glands. Expression of P-glycoprotein (P-gp), which is an ATPase-binding efflux pump, was tested in normal major and minor salivary glands from humans. P-gp was distributed on the basolateral membrane of serous acinar cells in the major salivary glands and the minor salivary glands. In particular, it was found to be present on the basolateral membrane and cytoplasm of acinar demilunar cells in the anterior lingual gland. Intense expression was identified in the basolateral membrane of the striated duct cells of the major salivary glands. P-gp was distinctly positive in the basolateral and/or luminal membranes of the initial part and in the luminal membrane of the terminal part of the excretory duct cells of the major salivary glands, whereas it was positive in the luminal membranes of both the initial part and the terminal part of the excretory duct cells of the minor salivary glands. These disparate distributions between the major and the minor salivary glands suggest different physiological excretions in the striated duct. P-gp may be physiologically involved in an important part of the transporter system, not only in the acinar serous cells and the striated duct cells, but also in the excretory duct cells in the salivary glands.

Immunohistochemical localization of carbonic anhydrases I, II, and VI in the developing rat sublingual and submandibular glands

Carbonic anhydrase has been localized to the acini and ducts of mature rat salivary glands. This enzyme has been associated with ion transport, a prominent function of striated and excretory ducts in salivary glands, suggesting that it might be used as a marker of ductal differentiation. The purpose of this study was to immunohistochemically document developmental changes in carbonic anhydrase in the ducts of the rat sublingual and submandibular glands. Immunohistochemistry was performed with antibodies to human carbonic anhydrase isoenzymes I, II and VI on sections of sublingual and submandibular glands from rats at representative postnatal developmental ages. Reactions were weak in the ducts of both glands at 1 day, then progressively increased. By 42 days, reactions had the adult pattern of virtually none in the mucous or seromucous acini, moderate to strong in the striated and excretory ducts, and none to weak in the intercalated ducts. Weak to moderate reactions were observed in the granular convoluted tubules of the submandibular gland as they became recognizable at age 42 days. Reactions to carbonic anhydrase I and II antibodies also increased from none (1 day) to modest (42 days) in the demilunes of the sublingual gland. The order of reaction intensity of the antibodies was II > I > VI. When localized via these anti-human antibodies, carbonic anhydrase is a useful marker of the functional differentiation of the striated and excretory ducts of the developing rat sublingual and submandibular glands.

Enzyme histochemical localization of Na(+),K(+)-ATPase and NADH-DE in the developing rat parotid gland

Information on ductal differentiation in the developing rat parotid gland is sparse. Striated and excretory ducts are rich in a number of enzymes related to ion movement. The objective of this investigation was to delineate histochemically the chronology of two of these, ouabain-sensitive Na(+),K(+)-ATPase and NADH-DE, in the developing rat parotid gland. Parotid glands were excised from rats at representative ages from 20 days in utero to 42 days. Enzyme histochemistry was performed on air-dried frozen sections. For Na(+), K(+)-ATPase, some sections also were fixed in phosphate-buffered formalin. Ouabain blocked Na(+),K(+)-ATPase activity, and neither enzyme reacted without substrate. Weak Na(+),K(+)-ATPase reactions were initially seen in unfixed sections at 1 day, and increased steadily to the adult pattern of strong (concentrated basolaterally) in striated ducts and excretory ducts, respectively, and weak to modest (diffuse) in acini and intercalated ducts at 28 days. In fixed sections, localization was sharper but the reaction was somewhat reduced. NADH-DE was modest in terminal buds and ducts before birth, then progressively changed to the adult pattern of weak in acini and intercalated ducts and strong (concentrated basally and luminally) in striated and excretory ducts at 28 days. As demonstrated by enzyme histochemistry of Na(+),K(+)-ATPase and NADH-DE, differentiation of rat parotid striated ducts and excretory ducts occurs mainly between birth and 28 days. Anat Rec 256:72-77, 1999. Published 1999 Wiley-Liss, Inc.

Modulation of thyroid hormone-dependent Na+,K(+)-ATPase induction in cultured human submandibular gland cell lines, HSG cells

The hormonal regulation of Na+,K(+)-ATPase enzyme activities and induction of the alpha subunit protein of the enzyme in the human submandibular gland (HSG) were studied by use of cultured HSG cells. We treated HSG cells with thyroid hormone, androgen, mineralocorticoid, and glucocorticoid, singly or in combination. 3,5,3'-Triiodothyronine (T3), 5 alpha-dihydrotestosterone (DHT), and aldosterone (Ald) induced neither Na+,K(+)-ATPase enzyme activity nor its protein. On the other hand, dexamethasone (Dex) induced both Na+,K(+)-ATPase enzyme activity and the alpha subunit protein level to 128% of the control. The effects of Dex in combination with either T3 or DHT were similar to the effect of Dex alone. Treatment in combination with Dex and Ald increased the enzyme activity and alpha subunit protein level to 160%, synergistically. These increased Na+,K(+)-ATPase enzyme activities were shown to be dependent on their protein levels induced by the hormones. Contrary to the previous evidence that Na+,K(+)-ATPase of ducts in the salivary gland are thyroid hormone inducible, HSG cells had an insignificant response to thyroid hormone in the present study. Also, Na+,K(+)-ATPase enzyme activity and its alpha subunit protein were not induced by any kind of combined treatments with T3. Furthermore, T3 did not cause intracellular calcium mobilization in HSG cells. In view of all data taken together, we suggest that HSG cells lack the thyroid hormone receptor, which is necessary for Na+,K(+)-ATPase induction in human salivary gland.

Molecular cloning and characterization of a novel Ste20-related protein kinase enriched in neurons and transporting epithelia

A novel cDNA encoding a protein kinase (termed PASK) was isolated from rat brain. The PASK catalytic domain was most similar to Ste20-related protein kinases, showing 45.5 and 39.2% amino acid identity with human SOK1 and yeast Sps1, respectively. The amino-terminal noncatalytic domain of 71 amino acids was rich in alanine and proline and contained several proline-alanine repeats. PASK was widely expressed in rat tissues but negligible in liver and skeletal muscle. Immunohistochemical analysis revealed that PASK was localized to a distinct set of cells including neurons, adrenal glomerulosa cells, and transporting epithelia such as epithelial cells of brain choroid plexus, distal tubule and collecting duct of kidney, duct of salivary gland, and parietal cells of stomach. Subcellular fractionation showed that PASK was present in both the cytosol and the Triton X-100-insoluble cytoskeletal fraction in brain.

Intercellular material in the basal and lateral folds of parotid serous cells in four species of bats

BACKGROUND

Basal folds are slender plications at the basal surface of acinar cells in the salivary glands of many mammalian species. These largely organelle-free folds increase the surface area of the basal plasmalemma manyfold and are unquestionably involved in the translocation of organic and inorganic molecules and water into the acinar cells.

METHODS

Specimens of salivary glands were obtained from over 230 species of live-trapped bats from major areas of the globe. Tissues for electron microscopy were fixed and processed by conventional means.

RESULTS

A number of the bat species examined had dense material in the intercellular spaces between basal and lateral folds of serous cells in the parotid gland. This intercellular material was particularly prominent in three species of New World bats, viz., Pteronotus parnellii, P quadridens, and Phyllostomus latifolius, and in one species of Old World bats, Chalinolobus argentatus. This dense material, which has a farinaceous texture, appears not to pass through tight junctions, so it is excluded from the lumina of intercellular canaliculi and acini. The dense material originates in the acinar cells--it is carried to the membranes of the folds via coated vesicles, which empty their dense content by exocytosis into the intercellular space. Similar dense material is present in the intercellular spaces of the basal labyrinth of striated ducts in the two species of Pteronotus. The manner in which this material accumulates in the striated duct is unclear.

CONCLUSIONS

Although the function of the intracellular dense material is undetermined, it appears to be placed strategically to influence molecular traffic into acinar cells or to modulate the paracellular pathway. From a comparative evolutionary perspective, we hypothesize that, in bats, the combination of basal folds and extracellular densities is associated with insectivory. Similar morphologies appear to be lacking in frugivorous or nectarivorous species.

Enzyme histochemical and immunohistochemical localization of carbonic anhydrase as a marker of ductal differentiation in the developing rat parotid gland

BACKGROUND

Carbonic anhydrase has been localized to the acini and ducts of mature rat parotid glands. This enzyme has been associated with ion transport, a prominent function of striated and excretory ducts in salivary glands, suggesting that it might be used as a marker of ductal differentiation. The purpose of this study was histochemically to document developmental changes in carbonic anhydrase in the ducts of the rat parotid gland.

METHODS

Parotid glands were excised from rats at representative developmental ages. Enzyme histochemistry was done on frozen sections fixed in acetone, and immunohistochemistry was performed with antibodies to human carbonic anhydrase isoenzymes I, II, and VI on paraffin sections of glands fixed in Helly's fluid.

RESULTS

Carbonic anhydrase activity was weak until age 21 days after birth, when it had increased slightly in the acini and intercalated ducts and moderately in striated and excretory ducts. The adult pattern was attained by 28 days, in which reactions were moderate to strong in the striated and excretory ducts and modest in the acini and intercalated ducts. Immunohistochemical reactions were weak until 14 days, then increased rapidly, and by 28 days approached the adult pattern of virtually none in the acini and modest to moderately strong in the striated and excretory ducts. The order of reaction intensity of the antibodies was II > I > VI.

CONCLUSIONS

Carbonic anhydrase is a useful marker of the functional differentiation of the striated and excretory ducts of the developing rat parotid gland.

Immunohistochemical identification of proteoglycans in gelatinous membranes of cat and gerbil inner ear

Proteoglycans have been identified in gelatinous membranes of adult cat and gerbil inner ears using highly specific histochemical techniques. The tectorial and otoconial membranes and cupula of both species stained strongly with high iron diamine which is specific for sulfate esters and with monoclonal antibody against keratan sulfate proteoglycan (KSPG). The cat tectorial membrane also showed strong immunoreactivity with monoclonal antibody against chondroitin sulfate proteoglycan (CSPG) but the gerbil tectorial membrane reacted only weakly with this antibody. Otoconial membranes and the cupula of both species showed little if any immunostaining with antibodies against CSPG. Supporting cells in the vestibular neurosensory epithelium and planum semilunatum cells in the ampullae of the cat stained strongly with anti-KSPG, demonstrating the origin of KSPG in the cat. These cell types failed to stain in the gerbil, however, suggesting a different mechanism of secretion or a slower rate of turnover of membraneous KSPG in the gerbil. Interdental cells of both species failed to react with either antibody, leaving the origin of tectorial membrane proteoglycans in question. The approach used here provides a highly sensitive and reliable means of assessing the contribution of specific proteoglycans to inner ear structure and function.

Rat sublingual salivary glands: secretory changes on parasympathetic or sympathetic nerve stimulation and a reappraisal of the adrenergic innervation of striated ducts

Sublingual glands were examined by light and electron microscopy after stimulating the parasympathetic nerve (5 Hz continuously) or the sympathetic nerve (50 Hz in bursts 1 s every 10 s) and compared with contralateral, unstimulated, normal glands from each animal. Parasympathetic stimulation caused secretion of mucin from the tubulo-acini and possibly a small amount of degranulation from the demilunes but no changes were detected in the striated ducts. Sympathetic stimulation, on the other hand, had no effect on the tubulo-acini or demilunes but caused a surprisingly extensive degranulation of the striated ducts plus loss of glycogen from their cells. Reassessment of the adrenergic innervation in the glands was therefore undertaken, by means of catecholamine fluorescence. This identified a regular association between adrenergic nerves and the striated ducts not only in sublingual but also in submandibular glands; features that have not previously been recognized. There was, however, only a sparse adrenergic innervation of the other parenchymal elements in the sublingual glands.

Na/K-ATPase in rabbit paranasal sinus mucosa during induced sinusitis

Sinusitis was produced in rabbits, after which animals were separated into three groups: allergic sinusitis, induced purulent sinusitis, and spontaneous purulent sinusitis. Mucosal specimens were taken from these animals and normal controls. Na/K-ATPase was localized cytochemically and its activity studied in order to define the energy metabolism of secretion. The Na/K-ATPase reaction was unable to be clearly distinguished in either the allergic sinusitis specimens or the normal mucosa. In both purulent sinusitis groups, an intensive reaction was observed in the subepithelial glands and a weak reaction was found in the goblet cells. The Na/K-ATPase activity in the purulent sinusitis groups was significantly higher than that in the normal control group. The increased Na/K-ATPase activity may be an affect of hyperactivity of the secretory cells.

Immunolocalization of Na+,K(+)-ATPase and carbonic anhydrase in the gerbil's vestibular system

The distribution of two ion transport enzymes in the vestibular system was investigated immunocytochemically. Immunostaining demonstrated abundant Na+,K(+)-ATPase in the basolateral plasmalemma of all dark cells and of cuboidal (transitional) cells bordering maculae and planum semilunatum cells bordering cristae. Na+,K(+)-ATPase was also present in nerve terminals impinging on vestibular hair cells and around nerve fibers and ganglion cells. Na+,K(+)-ATPase containing cells with fine intertwining processes were found within the perilymphatic stroma beneath maculae and cristae. These cells and interspersed nerves form a distinct, highly cellular plate that lies under neurosensory epithelium selectively. The catalytic alpha subunit of Na+,K(+)-ATPase in vestibular epithelia differs antigenically from the alpha subunit in nerves and from the alpha subunit in salivary gland and renal epithelium. Carbonic anhydrase (CA) isozyme II was localized in the apex of all supporting cells in neurosensory epithelia. In contrast, CA II immunostaining varied in vestibular dark cells showing heterogeneity in ion transport activity among these cells. Immunostaining evidenced CA II also in perilymphatic stromal cells which were presumably fibroblastic in nature and which correspond in location with the Na+,K(+)-ATPase positive cells under the vestibular neurosensory epithelium.