Immunocytochemical localization of Na+/K+-ATPase and V-H+-ATPase in the salivary glands of the cockroach,Periplaneta americana

The acinous salivary glands of the cockroach (Periplaneta americana) consist of four morphologically different cell types with different functions: the peripheral cells are thought to produce the fluid component of the primary saliva, the central cells secrete the proteinaceous components, the inner acinar duct cells stabilize the acini and secrete a cuticular, intima, whereas the distal duct cells modify the primary saliva via the transport of water and electrolytes. Because there is no direct information available on the distribution of ion transporting enzymes in the salivary glands, we have mapped the distribution of two key transport enzymes, the Na⁺/K⁺-ATPase (sodium pump) and a vacuolar-type H⁺-ATPase, by immunocytochemical techniques. In the peripheral cells, the Na⁺/K⁺-ATPase is localized to the highly infolded apical membrane surface. The distal duct cells show large numbers of sodium pumps localized to the basolateral part of their plasma membrane, whereas their highly folded apical membranes have a vacuolar-type H⁺-ATPase. Our immunocytochemical data are supported by conventional electron microscopy, which shows electrondense 10-nm particles (portasomes) on the cytoplasmic surface of the infoldings of the apical membranes of the distal duct cells. The apically localized Na⁺/K⁺-ATPase in the peripheral cells is probably directly involved in the formation of the Na⁺-rich primary saliva. The latter is modified by the distal duct cells by transport mechanisms energized by the proton motive force of the apically localized V-H⁺-ATPase.     

Localization of carbonic anhydrase in identified glial cells of the leech central nervous system: application of histochemical and immunocytochemical methods

We localized the enzyme carbonic anhydrase (CA) in frozen sections of the leech (Hirudo medicinalis) central nervous system by two histochemical techniques and the indirect immunofluorescence technique. Hansson's cobalt precipitation method and the use of 1-dimethylamino-naphthalene-5-sulfonamide (DNSA) to build a fluorescent enzyme-substrate complex showed that glial cells are the sites of CA activity in the leech. Neuropil and connective glial cells surrounding the axons had strong CA activity, whereas packet glial cells, which surround neuron cell bodies, and neurons themselves remained unstained. Glial cells reacted markedly with FITC-coupled antibodies against CA isoenzyme II, but experiments with antibodies against CA isoenzyme I showed no reaction.     

Cross-reactivity of an antiserum to the α-subunit of the Na+, K+-ATPase of toad (Bufo marinus) kidney with basal and apical membranes of transporting epithelia of the rat

Summary An antibody to the 96 kD -subunit of the Na⁺, K⁺ -ATPase from Bufo marinus has been used in immunostaining rat kidney and salivary glands. Intense staining was observed on basolateral membranes of distal tubules of the kidney and striated ducts of the three major salivary glands. Less intense staining was seen on the basolateral membranes of parotid acinar cells, but no staining was seen on the acinar cells of submandibular or sublingual glands. These sites of staining have been shown, by other methods, to posses substantial Na⁺, K⁺ -ATPase, indicating that the antibody recognizes antigenic determinants of the sodium pump highly conserved in the course of evolution. In addition, staining with this antibody was observed at the apical region of cells of the proximal straight tubule and of the papillary collecting duct in the kidney. Absorption studies suggest that the apical antigenic determinants are the same or closely related to each other but are distinct from basolateral antigenic determinants.     

Localization of carbonic anhydrase in legume nodules

Extracts of the central infected zone and the surrounding cortex of nodules from Lupinus angustifolius L., Vigna unguiculata L. (Walp), Pisum sativum L., Phaseolus vulgaris L., Vicia faba L. and Medicago sativa L. contained significant activities of carbonic anhydrase (CA). Immunoassay of extracts using antisera to a putative nodule CA (Msca1) cloned from M. sativa also indicated expression in both tissue types. Quantitative confocal microscopy using laser scanning imaging and a fluorescent CA‐specific probe (5‐dimethylaminonaphthalene‐1‐sulfonamide [DNSA]) localized expression to the infected cells in the central zone tissue and a narrow band of 2–3 files of cells in the cortical tissue that corresponded to the inner cortex. In the infected cells, the enzyme activity was distributed evenly in the cytosol, but in the inner cortical cells, it was restricted to the periphery – possibly to the plasma membrane or cell wall. The functions of CA in these two tissues are considered in relation to the carbon metabolism of nodules and the participation of the inner cortex in the regulation of gaseous diffusive resistance.     

Fine structure of the silk gland in the mite Ornithocheyletia sp. (Prostigmata,Cheyletidae)

Silk spinning is widely-spread in trombidiform mites, yet scarse information is available on the morphology of their silk glands. Thus this study describes the fine structure of the prosomal silk glands in a small parasitic mite, Ornithocheyletia sp. (Cheyletidae). These are paired acinous glands incorporated into the podocephalic system, as typical of the order. Combined secretion of the coxal and silk glands is released at the tip of the gnathosoma. Data obtained show Ornithocheyletia silk gland belonging to the class 3 arthropod exocrine gland. Each gland is composed of seven pyramidal secretory cells and one ring-folded intercalary cell, rich in microtubules. The fine structure of the secretory cells points to intensive protein synthesis resulted in the presence of abundant uniform secretory granules. Fibrous content of the granules is always subdivided into several zones of two electron densities. The granules periodically discharge into the acinar cavity by means of exocytosis. The intercalary cell extends from the base of the excretory duct and contributes the wall of the acinar cavity encircling the apical margins of the secretory cells. The distal apical surface of the intercalary cell is covered with a thin cuticle resembling that of the corresponding cells in some acarine and myriapod glands. Axon endings form regular synaptic structures on the body of the intercalary cell implying nerve regulation of the gland activity.     

Peculiar salivary glands in a silk‐producing mite Bakericheyla chanayi (Cheyletidae)

This is the first ultrastructural investigation of salivary glands in the family Cheyletidae. In both sexes of Bakericheyla chanayi, paired acinous salivary glands and tubular coxal glands were shown to be united into the common podocephalic system. The secretory portion of the salivary gland includes medial and lateral lobes composed of the five and two cells, respectively, with clearly distinct ultrastructure. The cytoplasm of the cells is occupied by the secretory granules containing fine fibrous material. The fine structure of both cell types suggest a proteinaceous nature of their secretions. A single central process extending from the apical face of each secretory cell passes through the common acinar cavity to enter the conducting duct. A pair of intercalary cells at the base of the conducting duct links it with the secretory portion of the gland. Extending towards the acinar cavity, protrusions of intercalary cells alternate the apical regions of the secretory cells and form with them highly‐specialized contacts characterized by the apical network of microtubules and microfilaments. Two possible ways of secretion are suggested: 1) exocytosis into the acinar cavity and 2) direct passage via the central processes. The detection of axon profiles in the gland body suggests a neural control for the glandular cell function. In tritonymphs, neither secretion nor large lateral lobe cells were observed up to the pharate stage when the lateral lobe undergoes rapid differentiation. The arrangement of the acinous gland is compared to that of other arthropods. Its composition appears to be close to the class three of insect glands. The involvement of the lateral lobe cells in silk production is discussed. J. Morphol. 276:772–786, 2015. © 2015 Wiley Periodicals, Inc.     

Dye-coupling between cells of the salivary glands in the cockroach Periplaneta americana

Cockroaches have acinar salivary glands. The acini consist of peripheral cells specialized for electrolyte and water transport and central cells contributing proteinaceous components to the saliva. Salivary duct cells probably modify the primary saliva. The acinar cells in Nauphoeta cinerea had been shown to be electrically coupled and dye-coupled. Since intercellular communication via gap junctions between acinar cells is difficult to reconcile with previous findings that dopamine and serotonin selectively stimulate the secretion of either protein-free or protein-rich saliva in Periplaneta americana, we investigated whether dye-coupling occurs between both acinar cell types and between duct cells. We iontophoretically loaded Lucifer yellow into impaled cells and tested for dye-coupling by confocal laser scanning microscopy. We found that: (1) peripheral and central cells within an acinar lobulus of the gland in P. americana are dye-coupled; and (2) salivary duct cells are dye-coupled.     

Effect of translocator protein (18 kDa)-ligand binding on neurotransmitter-induced salivary secretion in rat submandibular glands

Background information. TSPO (translocator protein), previously known as PBR (peripheral‐type benzodiazepine receptor), is a ubiquitous 18 kDa transmembrane protein that participates in diverse cell functions. High‐affinity TSPO ligands are best known for their ability to stimulate cholesterol transport in organs synthesizing steroids and bile salts, although they modulate other physiological functions, including cell proliferation, apoptosis and calcium‐dependent transepithelial ion secretion. In present study, we investigated the localization and function of TSPO in salivary glands. Results. Immunohistochemical analysis of TSPO in rat salivary glands revealed that TSPO and its endogenous ligand, DBI (diazepam‐binding inhibitor), were present in duct and mucous acinar cells. TSPO was localized to the mitochondria of these cells, whereas DBI was cytosolic. As expected, mitochondrial membrane preparations, which were enriched in TSPO, exhibited a high affinity for the TSPO drug ligand, ³H‐labelled PK 11195, as shown by B_max and K_d values of 10.0±0.5 pmol/mg and 4.0±1.0 nM respectively. Intravenous perfusion of PK 11195 increased the salivary flow rate that was induced by muscarinic and α‐adrenergic agonists, whereas it had no effect when administered alone. Addition of PK 11195 also increased the K⁺, Na⁺, Cl⁻ and protein content of saliva, indicating that this ligand modulated secretion by acini and duct cells. Conclusions. High‐affinity ligand binding to mitochondrial TSPO modulates neurotransmitter‐induced salivary secretion by duct and mucous acinar cells of rat submandibular glands.     

The apical Na+–HCO3− cotransporter Slc4a7 (NBCn1) does not contribute to bicarbonate transport by mouse salivary gland ducts

The HCO₃ ⁻ secretion mechanism in salivary glands is unclear but is thought to rely on the co-ordinated activity of multiple ion transport proteins including members of the Slc4 family of bicarbonate transporters. Slc4a7 was immunolocalized to the apical membrane of mouse submandibular duct cells. In contrast, Slc4a7 was not detected in acinar cells, and correspondingly, Slc4a7 disruption did not affect fluid secretion in response to cholinergic or β-adrenergic stimulation in the submandibular gland (SMG). Much of the Na ⁺-dependent intracellular pH (pH _i) regulation in SMG duct cells was insensitive to 4,4′-diisothiocyano-2,2′-stilbenedisulfonic acid, S0859, and to the removal of extracellular HCO ₃ ⁻. Consistent with these latter observations, the Slc4a7 null mutation had no impact on HCO ₃ ⁻ secretion nor on pH _i regulation in duct cells. Taken together, our results revealed that Slc4a7 targets to the apical membrane of mouse SMG duct cells where it contributes little if any to pH _i regulation or stimulated HCO ₃ ⁻ secretion.     

Comparative ultrastructure of coxal glands in unfed larvae of Leptotrombidium orientale (Schluger, 1948) (Trombiculidae) and Hydryphantes ruber (de Geer, 1778) (Hydryphantidae)

Coxal glands of unfed larvae Leptotrombidium orientale (Schluger, 1948) (Trombiculidae), a terrestrial mite parasitizing vertebrates, and Hydryphantes ruber (de Geer, 1778) (Hydryphantidae), a water mite parasitizing insects were studied using transmission electron microscopy. In both species, the coxal glands are represented by a paired tubular organ extending on the sides of the brain from the mouthparts to the frontal midgut wall and are formed of the cells arranged around the central lumen. As in other Parasitengona, the coxal glands are devoid of a proximal sacculus. The excretory duct, joining with ducts of the prosomal salivary glands constitutes the common podocephalic duct, opening into the subcheliceral space. The coxal glands of L. orientale are composed of a distal tubule with a basal labyrinth, an intermediate segment without labyrinth, and a proximal tubule bearing tight microvilli on the apical cell surface and coiled around the intermediate segment. The coxal glands of H. ruber mainly consist of the uniformly organized proximal tubule with apical microvilli of the cells lacking the basal labyrinth. This tubule shows several loops running backward and forward in a vertical plane on the side of the brain. In contrast to L. orientale , larvae of H. ruber reveal a terminal cuticular sac/bladder for accumulation of secreted fluids. Organization of the coxal glands depends on the ecological conditions of mites. Larvae of terrestrial L. orientale possess distal tubule functioning in re‐absorption of ions and water. Conversely, water mite larvae H. ruber need to evacuate of the water excess, so the filtrating proximal tubule is prominent.     

Cytochemical localization of carbohydrates in intercalated duct and acinar cells of mouse parotid gland

Summary The glycoconjugate composition of mouse intercalated duct and acinar cells of parotid gland has been compared. Mucins containing 1,2-glycols were demonstrated by the tannic acid-uranyl acetate technique. Hexose residues of glycoconjugates were identified using ferritin conjugated withCanavalia ensiformis agglutinin (Con A),Triticum vulgare or wheat germ agglutinin (WGA),Ricinus communis I agglutinin (RCA-I),Phaseolus vulgaris agglutinin (PHA-E) andArachis hypogaea agglutinin (PNA). Whereas qualitative and quantitative differences were observed in sugar residues of secretory granules in intercalated duct and acinar cells, apical plasmalemmae were labelled sparsely and similarly. This indicates that the glycocalyx composition of apical plasma minae in the parotid acinar and intercalated duct cells is little influenced by secretory granule composition.     

Autoradiographic localization of transported neutral amino acids in epithelia of cat submandibular and sublingual salivary glands

Summary Light-microscopic autoradiography was used to localize the cellular sites for neutral amino acid uptake in submandibular and sublingual salivary gland epithelia. The vasculature of isolated glands was perfused for 3–5 min with either L-(3-³H)serine or L-(4-³H)phenylalanine and then fixed by perfusion with buffered glutaraldehyde. In the submandibular gland the small neutral amino acid L-serine and the aromatic amino acid L-phenylalanine were localized to central acinar cells, demilunar cells and ductal cells. In the sublingual gland silver grains associated with each of these tritiated amino acids were localized to central acinar and ductal cells. Perfusion of both submandibular and sublingual glands with unlabelled L-serine (25 mM) or L-phenylalanine (30 mM) resulted in a significant decrease in the silver grain density associated with each labelled amino acid. The absence of silver grains in the lumina of acinar and ductal cells and the presence of tight junctions near the apical surface of the epithelium strongly suggest that the initial uptake of these amino acids was mediated by basolateral plasma membrane carriers.     

Duct,exocrine, and endocrine components of cultured fetal mouse pancreas

Summary Twenty to twenty-two days postcoitum mouse fetal pancreas organ bits were cultured on the dermal surface of irradiated pigskin as a substrate. The medium used for long term culture consisted of Eagle’s Minimum Essential Medium with the addition of 10% bovine serum, 0.02 U/ml insulin, 0.025 μg/ml glucagon, 3.63 μg/ml hydrocortisone, 100 μg/ml soybean trypsin inhibitor or 10⁻⁸ M atropine. When the medium lacked trypsin inhibitor or atropine but contained the three hormones, the pigskin support began to be destroyed after 2 to 4 wk in culture. Thereafter, the cultured cells could not grow and survive on the digested pigskin. When 10⁻⁶ M atropine was added to the medium, amylase secretion from cultured cells and destruction of pigskin were inhibited completely but pancreas cells could not grow or survive. In contrast, 100 μg/ml soybean trypsin inhibitor or 10⁻⁸ M atropine permitted cell growth, permitted amylase secretion from the cultured acinar cells, and prevented the destruction of pigskin. Under these conditions pancreas cells migrated or grew or both from the organ bits onto the surface of the pigskin dermis and organoid aggregations formed. Hydrocortisone was needed to permit growth for more than 2 wk. Glucagon and insulin had additive effects. Light and electron microscopic observations indicated the culture of at least five kinds of cells, i.e., duct, acinar, centroacinar, endocrine, and mesenchymal. The majority of cultured cells were duct cells and acinar cells. There were few mesenchymal cells. Mouse pancreas cells were cultured for at least 12 wk by this method. This investigation was supported by PHS Grant CA 30220 awarded by the National Cancer Institute, DHHS, Grant 1203M awarded by the Council for Tobacco Research, Inc., and Grant RD-65 (for equipment) awarded by the American Cancer Society. Nude mice were provided by Dr. Wendall M. Farrow of Life Sciences, Inc., Resource Laboratory N01, CP6-1005 of the National Cancer Institute.     

Redistribution of carbonic anhydrase VI expression from ducts to acini during development of ovine parotid and submandibular glands

 Carbonic anhydrase VI (CA VI) is a secreted enzyme produced predominantly by serous acinar cells of submandibular and parotid glands. We have investigated the developmental pattern of CA VI production by these glands in the sheep, from fetal life to adulthood, using immunohistochemistry. Also, a specific radioimmunoassay for CA VI was used to measure changes in enzyme expression in the parotid gland postnatally. CA VI is detectable by immunohistochemistry in parotid excretory ducts from 106 days gestation (term is 145 days), in striated ducts from 138 days and in acinar cells from 1 day postnatal. The duct cell content of CA VI declined as the acinar cell population increased, a feature also of CA VI immunoreactivity in the submandibular gland. Production of CA VI by submandibular duct cells was detectable initially at 125 days gestation, and acinar production was not seen before 29 days post-natal. Apart from the differing ontogeny of CA VI production in ducts and acini of parotid and submandibular glands, there was a parallel pattern of CA VI expression during the development of these major salivary glands.With the development of the acinar tissues in the postnatal lamb, there was a dramatic increase (about 600-fold) in the level of expression of CA VI in the parotid gland between days 7 and 59 as measured by radioimmunoassay. Accepted: 19 December 1996     

An ultrastructural study of the submandibular glands of the squirrel monkey, Saimiri sciureus

In squirrel monkey (Saimiri sciureus) the position of submandibular glands in the neck, on either side of the trachea, more closely resembles that of rodents than that of other primates. The glands exhibit seromucous acini and mucous tubules with seromucous demilunes. Electron microscopy shows basal cytoplasmic folds and well-developed intercellular tissue spaces and canaliculi only in relation to seromucous cells. Greatly dilated cisternae of the granular endoplasmic reticulum and prominent Golgi membranes are characteristic of the mucous cells. The secretory granules of seromucous and mucous cells are morphologically distinct and indicate chemically different products for the two cell types. Histochemically, the seromucous cell shows the presence of acid mucosubstance as indicated by the PAS and Alcian blue techniques. Preliminary studies showed no appreciable quantity of amylase in submandibular glands. The intercalated duct cell is juxtaposed with the acinar cell or mucous tubule cell. Short luminal microvilli, prominent Golgi complexes and scant apical granules are notable features of intercalated duct cells. Four cell types compose the striated ducts, viz., granular light cells, agranular dark cells, vesiculated dark cells, and basal cells. Peripheral nerves are found in five different locations: in the connective tissue (interstitial), between adjacent myoepithelial and mucous-secreting cells, in the intercellular space between adjacent secretory cells, and between basal plications of striated ducts and between adjacent myoepithelial and intercalated duct cells.     

Heterogeneity of apical glycoconjugates in kidney collecting ducts: Further studies using simultaneous detection of lectin binding sites and immunocytochemical detection of key transport enzymes

Summary In the search for a functional role for the polarized glycoconjugates of rat collecting duct epithelial cells, the relation between binding of various lectins and expression of cellular transport enzyme profile of the cells was studied. For this purpose, principal and intercalated cells of rat kidney collecting duct were identified by morphological criteria and by their immunocytochemically determined content of (Na⁺+K⁺)-ATPase and carbonic anhydrase (CA II), respectively. VariousN-acetylgalactosamine-specific lectins such as those fromHelix pomatia andMaclura pomifera revealed heterogeneity among both principal and intercalated cells, whereas -N-acetylgalactosa nine-specific lectin fromDolichos biflorus andVicia villosa bound preferentially to principal cells. Still another lectin fromArachis hypogaea reacted with most collecting duct cells in the cortex and outer medulla, but only with a subpopulation of cells in the inner medulla. Interestingly, some lectins reacted exclusively with the apical aspect of the collecting duct epithelial cells, whereas others revealed both an apical and basolateral distribution of lectin reactive glycoconjugates. The results thus show subtle differences in the glycocalyx structure of principal and intercalated cells and differences in the intracellular polarization of glycoconjugates of these cells. Thus, lectins may be useful tools in the study of the molecular mechanisms which establish and maintain the polarized functions of principal and intercalated cells.     

The expression of carbonic anhydrases II and IV in the human pancreatic cancer cell line (Capan 1) is associated with bicarbonate ion channels

Summary— Human pancreatic ductal cells of the Capan 1 cell line differentiate progressively during growth. After the exponential growth phase, the cells elongate and become polarized with their apical poles covered by microvilli and separated from the basolateral pole by tight junctions. In this stationary phase, they form domes, which are thought to result from the exchange of water and electrolytes. In this study, we demonstrated, using patch-clamp techniques, that HCO₃^? ions exit via the g350 high conductance anionic channel we observed recently at the Capan 1 cell surface. This g350 channel was thought to be either a Cl^?/HCO₃^? antiport or a simple HCO₃^? channel. The stilbene derivatives 4-acetamido-4 isothiocyano-2-2′-disulfonic acid (SITS) and 4,4′ diisothiocyano stilbene-2,2′ disulfonic acid (DIDS) reduced both the number of domes and the Cl^? and HCO₃^? flux through the g350 channel. Moreover, using histochemical, immunocytochemical and biochemical methods we showed that Capan 1 cells express a specific pattern of carbonic anhydrases (CA). Two types of CA were detected: the CA II isozyme mainly localized in the cytoplasm, but also found beneath the inner leaflet of the apical plasma membrane, and the CA IV isozyme localized on the outer leaflet of the apical plasma membrane and microvilli. Their molecular masses were 30 (CA II) and 55 kDa (CA IV), respectively. They were expressed continuously during the exponential growth phase, although their activity increased greatly during the stationary phase. Inhibition of dome formation by acetazolamide indicated the existence of a direct relationship between dome formation and CA. Characteristic structures with a central electron-dense core surrounded by a light halo were observed on the surface of cell membranes using histochemical and immunocytochemical methods. These structures were thought to represent a channel, corresponding possibly to CA IV. Our observations suggest that Capan 1 cells, despite their neoplasic transformation, produce HCO₃^? ions in the same way as normal human pancreatic ductal cells. Capan 1 cells in culture may therefore represent a suitable model for studying pancreatic duct HCO₃^? secretion at the cellular and molecular levels.     

Light microscopic detection of sugar residues in glycoconjugates of salivary glands and the pancreas with lectin-horseradish peroxidase conjugates. I. Mouse

Summary Mouse salivary glands and pancreases were stained with a battery of ten horseradish peroxidase-conjugated lectins. Lectin staining revealed striking differences in the structure of oligosaccharides of stored intracellular secretory glycoproteins and glycoconjugates associated with the surface of epithelial cells lining excretory ducts. The percentage of acinar cells containing terminal -N-acetylgalactosamine residues varied greatly in submandibular glands of 30 male mice, but all submandibular acinar cells contained oligosaccharides with terminal sialic acid and penultimate -galactose residues. The last named dimer was abundant in secretory glycoprotein of all mucous acinar cells in murine sublingual glands and an additional 20–50% of these cells in all glands contained terminalN-acetylglucosamine residues. In contrast, terminal -N-acetylgalactosamine was abundant in sublingual serous demilune secretions. Serous acinar cells in the exorbital lacrimal gland, posterior lingual gland, parotid gland and pancreas exhibited a staining pattern unique to each organ. In contrast, the apical cytoplasm and surface of striated duct epithelial cells in the submandibular, sublingual, parotid and exorbital lacrimal gland stained similarly. A comparison of staining with conjugated lectins reported biochemically to have very similar carbohydrate binding specificity has revealed some remarkable differences in their reactivity, suggesting different binding specificity for the same terminal sugars having different glycosidic linkages or with different penultimate sugar residues.     

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 sytem. The ducts secrete K⁺ and HCO₃^- 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.