Immunolocalization of carbonic anhydrase isozymes in rat and mouse salivary and exorbital lacrimal glands

The First Transcriptomic Atlas of the Adult Lacrimal Gland Reveals Epithelial Complexity and Identifies Novel Progenitor Cells in Mice

The lacrimal gland (LG) secretes aqueous tears. Previous studies have provided insights into the cell lineage relationships during tissue morphogenesis. However, little is known about the cell types composing the adult LG and their progenitors. Using scRNAseq, we established the first comprehensive cell atlas of the adult mouse LG to investigate the cell hierarchy, its secretory repertoire, and the sex differences. Our analysis uncovered the complexity of the stromal landscape. Epithelium subclustering revealed myoepithelial cells, acinar subsets, and two novel acinar subpopulations: Tfrchi and Car6hi cells. The ductal compartment contained Wfdc2+ multilayered ducts and an Ltf+ cluster formed by luminal and intercalated duct cells. Kit+ progenitors were identified as: Krt14+ basal ductal cells, Aldh1a1+ cells of Ltf+ ducts, and Sox10+ cells of the Car6hi acinar and Ltf+ epithelial clusters. Lineage tracing experiments revealed that the Sox10+ adult populations contribute to the myoepithelial, acinar, and ductal lineages. Using scRNAseq data, we found that the postnatally developing LG epithelium harbored key features of putative adult progenitors. Finally, we showed that acinar cells produce most of the sex-biased lipocalins and secretoglobins detected in mouse tears. Our study provides a wealth of new data on LG maintenance and identifies the cellular origin of sex-biased tear components.

Immunohistochemical localization of carbonic anhydrase IV in the human parotid gland

Carbonic anhydrases (CAs) catalyze the hydration and dehydration of carbon dioxide. They are important for regulating ions, fluid and acid-base balance in many tissues. The location of CAs by cell type is important for understanding their roles in these functions. CAs II and VI have been demonstrated using immunohistochemistry (IHC) in the serous acinar cells of human salivary glands and ducts of rat salivary glands. CA IV has been localized by IHC to the ducts of rat salivary glands. CA IV also is present in human parotid glands as shown by real time-polymerase chain reaction (RT-PCR), but this method does not show the distribution of the CA isozymes by cell type. We investigated the cell-specific distribution of CA IV in the human parotid gland. Sections from five formalin fixed, paraffin embedded specimens of human parotid gland were subjected to IHC for CA IV using a commercial antibody. Moderate to strong reactions were found in the cell membranes and cytoplasm of the intercalated, striated and excretory ducts and capillaries, and reactions in the acini were limited to faint areas in some cells. These results indicate that CA IV participates in the regulation of bicarbonate/carbon dioxide fluxes in the ductal system of the human parotid gland.

Carbonic anhydrases in the mouse harderian gland

The harderian gland is located within the orbit of the eye of most terrestrial vertebrates. It is especially noticeable in rodents, in which it synthesises lipids, porphyrins, and indoles. Various functions have been ascribed to the harderian gland, such as lubrication of the eyes, a site of immune response, and a source of growth factors. Carbonic anhydrases (CAs) are zinc-containing metalloenzymes that catalyse the reaction CO₂ + H₂O <--> H+ + HCO₃. They are involved in the adjustment of pH in the secretions of different glands. Thirteen enzymatically active isozymes have been described in the mammalian α-CA family. Here, we first investigated the mRNA expression of all 13 active CAs in the mouse harderian gland by quantitative real-time PCR. Nine CA mRNAs were detectable in the gland. Car5b and Car13 showed the highest signals. Car4, Car6, and Car12 showed moderate expression levels, whereas Car2, Car3, Car7, and Car15 mRNAs were barely within the detection limits. Immunohistochemical staining was performed to study the expression of Car2, Car4, Car5b, Car12, and Car13 at the protein level. The epithelial cells were intensively stained for CAVB, whereas only weak signal was detected for CAXIII. Positive signals for CAIV and CAXII were observed in the capillary endothelial cells and the basolateral plasma membrane of the epithelial cells, respectively. This study provides an expression profile of all CAs in the mouse harderian gland. These results should improve our understanding of the distribution of CA isozymes and their potential roles in the function of harderian gland. The high expression of mitochondrial CAVB at both mRNA and protein levels suggests a role in lipid synthesis, a key physiological process of the harderian gland.

Decreased expression of carbonic anhydrase isozyme II, rather than of isozyme VI, in submandibular glands in long-term zinc-deficient rats

We previously reported that in rats, long-term Zn deficiency significantly reduced taste sensitivity and total carbonic anhydrase (CA) activity in the submandibular gland. We therefore investigated the effects of Zn deficiency on salivary secretion and the expressions of CA isozymes (II and VI) in the rat submandibular gland, since those isozymes are thought to be related to taste sensation and salivary secretion. Male Sprague–Dawley rats, age 4 weeks, were divided into three groups (Zn-def, low-Zn and pair-fed, that were fed a diet containing 2·2, 4·1 or 33·7 mg Zn/kg, respectively, for 42 d). Northern blot analysis indicated that Zn deficiency reduced CA II mRNA expression in the submandibular gland without reducing CA VI mRNA expression. In Western blot analysis, Zn deficiency significantly reduced CA II (erythrocyte CA) protein expression in the submandibular gland without reducing CA VI protein expression. Salivary secretion was lower in the Zn-def group than in the pair-fed group. These results suggest that decreased CA isozyme II expression underlies the decreased CA activity previously reported in the submandibular gland in Zn-def rats, and this may reduce regular salivary secretion.

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.

Fluid secretion and the Na+-K+-2Cl- cotransporter in mouse exorbital lacrimal gland

We have previously suggested that fluid flow in the mouse exorbital lacrimal gland is driven by the opening of apical Cl- and K+ channels. These ions move into the lumen of the gland and water follows by osmosis. In many tissues, the Na+-K+-2Cl- cotransporter (NKCC1) replaces the Cl- and K+ ions that move into the lumen. We hypothesize that mouse exorbital lacrimal glands would have NKCC1 co-transporters and that they would be important in fluid transport by this gland. We used immunocytochemistry to localize NKCC1-like immunoreactivity to the membranes of the acinar cells as well as to the basolateral membranes of the duct cells. We developed a method to measure tear flow and its composition from mouse glands in situ. Stimulation with the acetylcholine agonist carbachol produced a peak flow followed by a plateau. Ion concentration measurements of this stimulated fluid showed it was high in K+ and Cl-. Treatment of the gland with furosemide, a blocker of the NKCC1 cotransporter, reduced the plateau phase of fluid flow by approximately 30%. Isolated cells exposed to a hypertonic shock shrank by approximately 20% and then showed a regulatory volume increase (RVI). Both the RVI and swelling were blocked by treatment with furosemide. Cells isolated from these glands shrink by approximately 10% in the presence of carbachol. Blocking NKCC1 with furosemide reduced the amount of shrinkage by approximately 50%. These data suggest that NKCC1 plays an important role in fluid secretion by the exorbital gland of mice.

Regulation of fluid and electrolyte secretion in salivary gland acinar cells

The secretion of fluid and electrolytes by salivary gland acinar cells requires the coordinated regulation of multiple water and ion transporter and channel proteins. Notably, all the key transporter and channel proteins in this process appear to be activated, or are up-regulated, by an increase in the intracellular Ca2+ concentration ([Ca2+]i). Consequently, salivation occurs in response to agonists that generate an increase in [Ca2+]i. The mechanisms that act to modulate these increases in [Ca2+]i obviously influence the secretion of salivary fluid. Such modulation may involve effects on mechanisms of both Ca2+ release and Ca2+ entry and the resulting spatial and temporal aspects of the [Ca2+]i signal, as well as interactions with other signaling pathways in the cells. The molecular cloning of many of the transporter and regulatory molecules involved in fluid and electrolyte secretion has yielded a better understanding of this process at the cellular level. The subsequent characterization of mice with null mutations in many of these genes has demonstrated the physiological roles of individual proteins. This review focuses on recent developments in determining the molecular identification of the proteins that regulate the fluid secretion process.

Molecular comparison of apocrine released and cytoplasmic resident carbonic anhydrase II

We have previously shown that carbonic anhydrase II usually described as a cytoplasmic resident isoform (cCAH II) is secreted by the rat coagulating gland (sCAH II) via the apocrine secretion mode. To get more detailed information why CAH II is cytoplasmic resident in some organs and secreted in others we cloned and sequenced the cDNA of rat coagulating gland sCAH II. The sequence of the secretory form was found to be completely identical with the cCAH II. Therefore, a signal peptide targeting sCAH II for apocrine secretion can be excluded. Considering the fact that other apocrine secreted proteins are glycosylated, cCAH II and sCAH II were analyzed for carbohydrate substitutions. As expected for a cytoplasmic protein, no glycan modification could be identified in cCAH II. In contrast, sCAH II carried exclusively Gal, GlcNAc and Fuc residues in a molar ratio of 1:0.8:0.5. Carbohydrate linkage analyses demonstrated the presence of terminal Fuc, terminal, 3-substituted and 3,6-disubstituted Gal as well as 4-substituted and 3,4-disubstituted GlcNAc. The composition of the glycan constituents as well as deglycosylation experiments clearly proved that sCAH II carries neither conventional mammalian-type N-glycans nor mucin-type O-linked sugar chains. Lacking a signal peptide for ER translocation, glycosylation of sCAH II must occur within the cytoplasmic compartment. Further studies have to elucidate whether or not glycosylation of sCAH II is essential for the apocrine release of the protein.

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.

Immunohistochemistry of carbonic anhydrase isozymes (CA-I, II and III) in canine salivary glands: a distributional and comparative assessment

The immunohistolocalization of carbonic anhydrase isozymes (CA-I, II, III) in canine salivary glands was studied using antiserum against CA-I, II, III. In parotid glands, immunostaining intensely localized cytosolic CA-II antiserum throughout the cytoplasm of acinar secretory cells and ductal epithelial cells, especially in the striated duct region. CA-III reactivity in the glands was only seen selectively at the intercalated ductal cells. In contrast, no immunoreaction localized CA-I in the gland. In the submandibular and sublingual glands, CA-I, II, and III were all observed in the ductal segments of the glands, whereas serous demilune appeared devoid of all three cytosolic CA isozymes. In contrast, in zygomatic glands (i.e. dorsal buccal glands) all CA isozymes were observed in both serous demilune and ductal segments. In all of the salivary glands examined, no mucous acinar cells were found to be reactive for any CA.

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.

Localization of carbonic anhydrase in guinea pig Bowman's glands

We examined the histochemical localization of carbonic anhydrase (CA) in Bowman's glands by light and electron microscopy. Neither CAI nor CAII was detected immunohistochemically in the duct cells. However, by enzyme histochemistry the duct cells revealed electron-dense precipitates demonstrative of CA in the microvilli and intercellular digitations. The reaction product was also noted in small vesicles in the cytoplasm of duct cells. In cells of the acini, the well-developed short microvilli, basolateral cell membrane, and mitochondria along the basolateral membrane showed strong deposits indicating CA activity. Dense reaction product of CA was also detected in a small core within the electron-lucent granules of the secretory cells, although CAI and CAII were not detected by immunostaining in the secretory granules. Although the functional significance of CA in Bowman's glands is obscure, the enzyme may play a role in regulation of pH and ion balance in the mucous layer covering the olfactory epithelium. The presence of CA activity in the ducts suggests that these structures are not simple tubes serving as a conduit for secretory substances but participate in modifying the luminal content by secreting CA. (J Histochem Cytochem 47:1525-1531, 1999)

Bilateral dimorphism of Loewenthal's gland in young male albino rats: an ultrastructural investigation

This study represents a further contribution to our knowledge about the structure of Loewenthal's gland. There are several divergences in the available literature on the topic, concerning both the histological and ultrastructural findings. However, in these studies, the authors did not take into account the potential influence of a putative side-dependent dimorphism previously reported by us. We therefore carried out histological and electronmicroscopic observations specifically aimed at evaluating the importance of the gland shape for its structure. In particular, in male albino rats aged 70-120 days, we compared the structure of the left and right glands. Depending on the side undergoing morphological investigation, we observed differences in the acini, cells, nuclei, endoplasmic reticulum, Golgi apparatus and granular content. Apart from slight individual differences, we found that structural variations were most frequently observed in glands displaying a more evident macroscopic side-specific dimorphism. Our findings demonstrate that several conflicting data in the literature dealing with the structure of Loewenthal's glands might be explained by the morphofunctional side-dependent dimorphism of the organ.

Cytoplasmic carbonic anhydrase II of rat coagulating gland is secreted via the apocrine export mode

Two different pathways for protein secretion are described for epithelial cells of rat coagulating gland and dorsal prostate: the classical merocrine and the alternative apocrine release mode. Apocrine-secreted proteins are synthesized on cytoplasmic polyribosomes and are subsequently exported in protrusions on the apical cell surface (aposomes). In this article we report the identification and purification to homogeneity of a 29-kD protein from the secretion of rat coagulating gland. N-terminal amino acid sequence analyses revealed 100% identity to rat brain carbonic anhydrase II (CAH II). In addition, the 29-kD protein showed CAH enzyme activity. On Western blot analysis, a polyclonal anti-CAH II antibody raised in rabbit reacted specifically with the rat and human but not bovine CAH II isoforms. Immunohistochemical studies on rat coagulating gland showed strong labeling for CAH II protein in aposomes. Immunoelectron microscopy confined CAH II protein to the cytoplasm and aposomes, whereas no staining was visible in the compartments of the classical merocrine route, the endoplasmic reticulum and Golgi apparatus. The resident cytoplasmic protein lactate dehydrogenase, however, was not found in the secretion. Taken together, the morphological and biochemical data clearly indicate that cytoplasmic CAH II from rat coagulating gland is specifically selected and then secreted via the apocrine pathway.

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.

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

Tissue specimens from guinea pigs were examined using an enzyme-histochemical reaction to explore the presence of carbonic anhydrase (CA) activity in the trachea. CA activity was detected in a group of morphologically distinct epithelial cells, in goblet cells, and in glands of the tracheal mucosa. The epithelial cells showing CA activity were distributed singly and sparsely throughout the entire trachea. These cells showed a wide morphological variability and were clearly different from those forming the pseudostratified ciliated epithelium. Their number was higher in sections closer to the tracheal bifurcation than in those near the larynx. Although the nature of these cells is unknown, based on their morphological and histochemical characteristics and their distribution, they may represent a specialized chemoreceptor. To our knowledge, this is the first report of CA localized in tracheal epithelial cells.

Carbonic anhydrase isozyme VI in rat lacrimal gland

Using monoclonal antibody specific to rat carbonic anhydrase isozyme VI (CA VI), the isozyme was localized in the lacrimal gland. A minority of acini (less than 10% of the total) contained a few immunoreactive acinar cells. Enzyme histochemistry indicated that the CA VI-positive cells were the only cells possessing CA in the lacrimal acini. In the acinar cells, the reaction product for CA VI was distributed in the secretory granules and cytosol between secretory granules. Except for mitochondrial enzyme (CA V) activity, the intracellular distribution of enzyme activity was similar to that of CA VI immunoreactivity, suggesting that rat lacrimal acinar cells contain only CA VI and CA V. CA VI in the secretory granules was discharged into the acinar lumen and is considered to carry out its function on the surface of the conjunctiva and cornea. The cytosolic CA VI may function in situ and be involved in electrolyte and water secretion by the acinar cells. Polyclonal antibody to rat erythrocyte CA (CA I and CA II) stained only the interlobular ducts. In contrast, all the ductal elements exhibited CA enzyme activity. This discrepancy between immunohistochemistry and enzyme histochemistry suggests the presence of CA isozyme(s) other than CA I, CA II and CA VI in the lacrimal duct.

Expression of carbonic anhydrase isozymes II and III in developing bovine parotid gland

Two cytosolic carbonic anhydrase isozymes (CA-II and CA-III) were studied by immunohistochemistry in bovine parotid glands during fetal development. In a 3-month-old fetus of crown-rump length (CRL) 17 cm, the expression of CA-II in undifferentiated epithelial cells was observed, whereas immunostaining for CA-III remained negative. At 26 cm CRL (4-5 months old), weak expression of CA-III in large ductal epithelial cells was noted. The accumulation of secreted granules in primary acinar cells was initially observed at this stage. In a newborn calf, anti-CA-II reactivity almost disappeared from most duct segments. The time-dependent expression and distribution of the isozymes in parotid glands may reflect different biological functions of these structurally closely related isozymes. Bovine parotid acinar cells of fetuses would thus appear to possess all the cellular structures and immunohistochemical properties at 4 and 5 months of gestation. CA-II subsequently disappeared from duct segments and nearly all acinar cells in adults were present at or just after birth.

Comparative immunohistolocalization of carbonic anhydrase isozymes I, II and III in the equine and bovine digestive tract

Immunohistochemical localizations of carbonic anhydrase isozymes (CA-I, CA-II and CA-III) in equine and bovine digestive tracts were studied. In the horse, epithelial cells in both the oesophagus and non-glandular part of the stomach lacked all three isozymes. In contrast, surface epithelial and parietal cells in the glandular region of the stomach showed reactivity for CA-II. In the small intestine, absorptive columnar cells covering the villi in the duodenum were positive for CA-II. The epithelium of the jejunum and ileum lacked all three isozymes. In the large intestine, CA-II was detected in the columnar cells in the upper part of the crypt. In cattle, epithelial cells of the oesophagus showed reactions for CA-I and CA-III but not for CA-II. Although the absorptive epithelial cells of the small intestine lacked CA-I, CA-II and CA-III, those of the upper part of large intestine crypts were heavily stained for all three isozymes.

Characterization of the human gene for a newly discovered carbonic anhydrase, CA VII, and its localization to chromosome 16

Six carbonic anhydrase (CA) isozymes (CA I-VI) in mammals and other amniotes have been described. We have isolated an additional CA gene from a human genomic library and designated its putative product carbonic anhydrase VII (CA VII). The gene is approximately 10 kb long and contains seven exons and six introns found at positions identical to those determined for the previously described CA I, CA II, and CA III genes. The finding of a 17-bp GT-rich segment in a position 28 bp downstream of the poly(A)+ signal and the high correspondence of the 5' and 3' splice sites of the six introns with consensus junction sequences are consistent with the gene being functional. The 5' flanking regions of the CA VII gene do not contain the TATA and CAAT promoter elements usually found within 100 bp upstream of transcription initiation, but do contain a TTTAA sequence 102 nucleotides upstream of the initiation codon. The 5' region of the gene (-243 to +551) is GC-rich and contains 80 CpG dinucleotides and four possible Sp1 (GGGCGG or CCGCCC) binding sites. Northern analysis has identified the salivary gland as a major site of expression. The derived amino acid sequence of the CA VII gene is 263 amino acids long and has 50, 56, and 49% identity with human CA I, CA II, and CA III, respectively. No differences were found at any of the 39 positions that have remained invariant in all mammalian CA isozymes sequenced to date. Based on analysis of interspecific somatic cell hybrids, the human CA VII gene, CA7, was assigned to chromosome 16, with localization to the long arm at the q21-23 region by in situ hybridization. This is in contrast to the location of the CA I, CA II, and CA III gene cluster on human chromosome 8 and that of the human CA VI gene on chromosome 1.

Immunohistochemical studies of the carbonic anhydrase isozymes in the bovine placenta

Placentae from 11 cows, ranging from about 80 to 270 days gestation, were studied for immunohistochemical localization of carbonic anhydrase isozymes. CA isozymes were localized using the avidin-biotin-peroxidase complex (ABC) method in the bovine placenta. CA-II was found in the fetal trophoblastic cells with single nuclei as well as in erythrocytes of maternal and fetal blood. The percentage of positive cells for anti-CA-II in the trophoblastic cells did not change during development of gestation in the fetal bovine. CA-I and CA-III were not detected in the bovine placenta.

Carbonic anhydrase III in the salivary glands and kidney of the Japanese monkey (Macaca fuscata)

Carbonic anhydrase III (CA-III) was found in muscles of the Japanese monkey by the double immunodiffusion test and western blotting using antiserum raised against equine CA-III. Immunocytochemical localization of CA-III in the salivary glands and kidney of the monkey was studied using an avidin-biotinylated glucose oxidase complex. CA-III was found mainly in the striated duct and interlobular duct cells of the parotid glands. In the submandibular glands, striated duct, interlobular duct, and excretory duct cells were strongly stained for CA-III. In the kidney of the monkey, CA-III was localized mainly in the dark cells of the collecting duct at the medulla and in the epithelial cells of thick limb of Henle's loop.

Comparative distribution of carbonic anhydrase isozymes III and II in rodent tissues

Carbonic anhydrase (CA) III was demonstrated immunocytochemically in epithelium in some regions of salivary gland ducts, colon, bronchi, and male genital tract and in adipocytes, in addition to skeletal muscle and liver where the isozyme was previously localized. Basal cells beneath the submandibular gland's excretory ducts in guinea pig stained for CA III. Carbonic anhydrase III occurred alone in some and with CA II in other sites but was often absent from CA-II-containing types of cells. This was exemplified by CA III's abundance in CA-II-positive proximal colon and its sparsity in the CA-II-rich distal colon of the mouse. Striated ducts in guinea pig, but not mouse salivary glands, stained darker for CA and appeared accordingly to function more actively in ion transport compared with excretory ducts. Carbonic anhydrase content varied among genera in liver and pancreas and between mouse species and strains in salivary glands and kidney. Newly observed murine sites of CA II activity included Auerbach's plexus and a population of leukocytes infiltrating the lamina propria in small intestine, and several types of cells in the male genital tract. In immunoblot tests, antisera to CA III showed no cross reactivity with antisera to CA II, but those to CA II disclosed weak cross reactivity with CA III.

Tissue and species distribution of the secreted carbonic anhydrase isoenzyme

The secreted carbonic anhydrases, CA VI, are high molecular mass, oligomeric enzymes originally found in the sheep parotid gland and saliva. The enzymes have been purified from the saliva or parotid glands of several different species. All the CA VI enzymes studied have an apparent subunit Mr of about 45,000 as previously reported for the sheep enzyme. By Western analysis, CA VI from human, cow and dog cross-reacted with antibody raised against the purified sheep enzyme whereas that of the mouse did not. The N-terminal sequences of the sheep, human, cow and mouse enzymes are reported. The sheep, cow and human N-terminal sequences are similar to one another while the mouse sequence is substantially different. Nevertheless, the amino acids in the aromatic cluster I (Trp-5, Tyr-7, Trp-16 and Tyr/Phe-20) have all been conserved, as is the case with the cytoplasmic carbonic anhydrases. Eighteen tissues from the sheep have been examined for the presence of CA VI by Western analysis but it has been found only in the salivary glands. Northern analysis and hybridization histochemistry show that the mRNA for CA VI in sheep is expressed specifically in the acinar cells of the parotid and submandibular glands.

Mouse carbonic anhydrase III: nucleotide sequence and expression studies

A cDNA for the mouse carbonic anhydrase, CAIII, has been isolated from a lambda gt11 expression library. The cloned cDNA contains all of the coding region (777 bp) and both 5' untranslated (86-bp) and 3' untranslated (217-bp) sequences. The coding sequence shows 87% homology at the nucleotide level and 91% homology, when amino acid residues are compared, with human CAIII. Protein and mRNA analyses show that CAIII is present at low levels in cultured myoblasts and is abundant in adult skeletal muscle and in liver. The marked sex-related differences in CAIII distribution, described for rat liver, are not seen in the mouse. Restriction fragment length polymorphisms using TaqI and PstI are described which distinguish between Mus spretus and Mus musculus domesticus.

Immunocytochemical localization of carbonic anhydrase isozyme III in equine thymus

Sections of equine thymus were examined for the presence of carbonic anhydrase (CA) isozymes by an immunohistochemical method. Carbonic anhydrase III, a major enzyme of skeletal muscle, was localized in some of the epithelial-reticular cells of the equine thymus. This finding suggests the presence of a new type of cell in the thymic cortex. The concentration of CA-III in the thymus was 17 micrograms/g wet tissue. CA-I and CA-II were not found in equine thymus.

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

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.

Evidence for an anion exchanger in the mouse lacrimal gland acinar cell membrane

Anion exchange transport in the mouse lacrimal gland acinar cell membrane was studied by measuring the intracellular H+ (pHi) and Cl- (aCli) activities with double-barreled ion-selective microelectrodes. In a HCO3- -free solution of pH 7.4 (HEPES/Tris buffered), pHi was 7.25 and aCli was 33 mM. By an exposure to a HCO3- (25 mM HCO3-/5% CO2, pH 7.4) solution for 15 min, aCli was decreased to 25 mM, and pHi was transiently decreased to about 7.05 within 1 min, then slowly relaxed to 7.18 in 15 min. Intracellular HCO3- concentration [HCO3-]i, calculated by the Henderson-Hasselbalch's equation, was 11 mM at 1 min after the exposure and then slowly increased to 15 mM. Readmission of the HCO3(-)-free solution reversed the changes in aCli and pHi. The intracellular buffering power was about 40 mM/pH. An addition of DIDS (0.2 mM) significantly inhibited the rates of change in aCli, pHi, and [HCO3-]i caused by admission/withdrawal of the HCO3- solution and decreased the buffer value. Replacement of all Cl- with gluconate in the HCO3- solution increased pHi, and readmission of Cl- decreased pHi. The rates of these changes in pHi were reduced by DIDS by 32-45% but not by amiloride (0.3 mM). In the HCO3- solution, a stimulation of intracellular HCO3- production by exposing the tissue to 25 mM NH4+ increased aCli significantly. While in the HCO3(-)-free solution or in the HCO3- solution containing DIDS, exposure to NH4+ had little effect on aCli.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of aldosterone and ADH on intracellular electrolytes in the toad urinary bladder epithelium

Quantitative electron microprobe analysis was employed to compare the effects of aldosterone and ADH on the intracellular electrolyte concentrations in the toad urinary bladder epithelium. The measurements were performed on thin freeze-dried cryosections utilizing energy dispersive x-ray microanalysis. After aldosterone, a statistically significant increase in the intracellular Na concentration was detectable in 8 out of 9 experiments. The mean Na concentration of granular cells increased from 8.9 +/- 1.3 to 13.2 +/- 2.2 mmol/kg wet wt. A significantly larger Na increase was observed after an equivalent stimulation of transepithelial Na transport by ADH. On average, the Na concentration in granular cells increased from 12.0 +/- 2.3 to 31.4 +/- 9.3 mmol/kg wet wt (5 experiments). We conclude from these results that aldosterone, in addition to its stimulatory effect on the apical Na influx, also exerts a stimulatory effect on the Na pump. Based on a significant reduction in the Cl concentration of granular cells, we discuss the possibility that the stimulation of the pump is mediated by an aldosterone-induced alkalinization. Similar though less pronounced concentration changes were observed in basal cells, suggesting that this cell type also participates in transepithelial Na transport. Measurements in mitochondria-rich cells provided no consistent results.

Immunohistochemical study of carbonic anhydrase in mixed tumours and adenomas of sweat and sebaceous glands

Immunohistochemical distribution of carbonic anhydrase II (CA) in mixed tumours and adenomas of sweat gland origin and in sebaceous adenomas was demonstrated by the PAP method. Normal sweat glands, both eccrine and apocrine, clear cells of the secretory coils, and ductal epithelial cells all showed conspicuous staining for CA, and sebaceous glands were also positive. Mixed tumours of the skin indicated strongly positive staining for CA in the luminal cells of tubular and duct-like or cystic structures, while most of the other tumour cells were negative. In solid or massive foci, CA positive cells were found scattered among the cellular mass. Sebaceous adenomas were usually moderately positive for CA throughout the tumour.

Acetylcholine-induced Na+ influx in the mouse lacrimal gland acinar cells: demonstration of multiple Na+ transport mechanisms by intracellular Na+ activity measurements

In the isolated, superfused mouse lacrimal gland, intracellular Na+ activities (aNai) of the acinar cells were directly measured with double-barreled Na+-selective microelectrodes. In the nonstimulated condition aNai was 6.5 +/- 0.5 mM and membrane potential (Vm) was -38.9 +/- 0.4 mV. Addition of 1 mM ouabain or superfusion with a K+-free solution slightly depolarized the membrane and caused a gradual increase in aNai. Stimulation with acetylcholine (ACh, 1 microM) caused a membrane hyperpolarization by about 20 mV and an increase in aNai by about 9 mM in 5 min. The presence of amiloride (0.1 mM) reduced the ACh-induced increase in aNai by approximately 50%, without affecting Vm and input resistance in both nonstimulated and ACh-stimulated conditions. Acid loading the acinar cells by an addition/withdrawal of 20 mM NH4Cl or by replacement of Tris+-buffer saline solution with HCO3-/CO2-buffered solution increased aNai by a few mM. Superfusion with a Cl(-)-free NO3- solution or 1 mM furosemide or 0.5 mM bumetanide-containing solution had little effect on the resting aNai levels, however, it reduced the ACh-induced increase in aNai by about 30%. Elimination of metabolite anions (glutamate, fumarate and pyruvate) from the superfusate reduced both the resting aNai and the ACh-induced increase in aNai. The present results suggest the presence of multiple Na+ entry mechanisms activated by ACh, namely, Na+/H+ exchange, Na-K-Cl cotransport and organic substrate-coupled Na+ transport mechanisms.

Carbonic anhydrase activity in a calcium-mobilizing epithelium of the crustacean Orchestia cavimana during molting

We investigated the involvement of the enzyme, carbonic anhydrase, in the calcification-decalcification processes occurring in the posterior caeca of the midgut of the terrestrial crustacean, Orchestia cavimana, before and after exuviation. This enzyme was ultrahistochemically localized throughout the membranes of the caecal epithelium as well as extracellularly, i.e., within pre-exuvial calcareous concretions and postexuvial calcified spherules. During the molt cycle, the pattern of carbonic anhydrase activity in the posterior caeca was correlated with the calcium content at this level. Acetazolamide treatment in vivo inhibited about 50% of the calcium uptake during both pre-exuvial secretion and postexuvial reabsorption. The role of carbonic anhydrase in this mineralizing-demineralizing epithelium is discussed and compared with that of other mechanisms involved in this calcium turnover.

Immunohistochemical observations on carbonic anhydrase I and II in human salivary glands and submandibular obstructive adenitis

Immunohistochemical identification of carbonic anhydrase I and II (CA-I, CA-II) was made in human major salivary glands and obstructive adenitis in submandibular glands. Normal salivary glands stained the strongest for CA-II in serious acinar cells and were negative in mucous cells. Moderate to strong staining for CA-I and CA-II was found in ductal segments. Submandibular glands with obstructive adenitis exhibited reduced CA-I activity in atrophic acinar cells, but not in ductal elements in the early and intermediate stages of the disorder. In the late stage of the obstructive lesion, CA staining in duct-like structures was moderate; however, almost degenerate ductal cells were negative for CA. During the progression of the degeneration in the obstructive lesion, the CA staining decreased dependent on acinar atrophy. Even after longstanding obstruction of the salivary gland, altered ductal epithelia may retain some of their functions.

Immunohistochemical localization of carbonic anhydrase I and II in submandibular salivary glands of the mouse, rat, hamster and guinea pig

Tissues were fixed in Bouin and Carnoy solutions, and the peroxidase, anti-peroxidase (PAP) method was used. Serous acinar cells of the guinea pig were positive for carbonic anhydrase (CA), but acinar cells of rodents were negative. Granular convoluted tubule (GCT) cells of the mouse, rat and hamster had varying degrees of staining for CA isoenzyme I and II. Striated and excretory ducts from all four species were usually positive for CA. Scattered cells containing a high concentration of CA I and CA II were present in striated ducts and GCT of the hamster, GCT of the rat and striated and excretory ducts of the guinea pig.

Immunohistochemical localization of carbonic anhydrase in submandibular salivary glands of mice and hamsters treated with phenylephrine, testosterone or duct-ligation

Using the peroxidase antiperoxidase (PAP) technique, the submandibular glands (SMG) from normal mice showed positive carbonic anhydrase (CA) staining in both striated duct (SD) and granular convoluted tubule (GCT) cells, which varied from moderate to strong. In normal hamsters, the GCT showed strong focal staining. Phenylephrine in mice and hamsters resulted in a decrease in CA in GCT cells; staining was much reduced in the GCT segments of the mouse. One hour after a phenylephrine injection into testosterone-treated mice, there was no change in the staining intensity of GCT cells but an increase in cell size. Only a slight decrease in immunostaining occurred in mouse and hamster SD cells. CA staining in duct-ligated glands of mice decreased within 3 days but regenerated duct-like structures at later stages showed moderate staining.

Immunohistochemical study of carbonic anhydrase in mixed tumours from major salivary glands and skin

Immunohistochemical distribution of carbonic anhydrase isoenzyme I and II was studied in mixed tumours of major salivary glands and skin. The normal salivary glands displayed strong carbonic anhydrase activity in both ductal epithelium and serous acinar cells and the serous demilune cells in the submandibular glands, including the eccrine ducts. Pleomorphic adenoma salivary gland origin exhibited positive staining in the inner-layer of epithelial cells of tubular, duct-like and glandular structures. No enzymatic staining was noted in the outer layer of tumour cells in these structures. Spindle tumour cells or the fibroblast-like cells with long cytoplasmic processes identified in the adjacent hyalin and myxomatous stroma were rarely positive, while chondroidal and osteo-chondroidal cells were highly reactive. Mixed tumours of eccrine gland origin showed the most reactive staining cells scattered throughout neoplastic epithelium in all tissues examined. Immunohistochemical stainability was usually higher for carbonic anhydrase II than I for both normal and tumour tissues. The biological roles of the distribution profiles of carbonic anhydrase are discussed.

Carbonic anhydrase is associated with taste buds in rat tongue

A modification of Hansson's histochemical technique was used to reveal carbonic anhydrase activity in mounted cryostat sections of the circumvallate papillae from rat tongue. An intensely positive reaction was found at the level of the neck of the papilla, associated with the taste buds. Lingual glands also contained abundant carbonic anhydrase activity. The presence of carbonic anhydrase in taste buds, as well as our previous observation that it is found in a population of olfactory receptor cells, may indicate a role for the enzyme in gustative and olfactory phenomena.

Implications of the immunohistochemical localization of the carbonic anhydrase isozymes for their function in normal and pathologic cells

Histochemical knowledge of the distribution of CA and the two isozymes CA I and CA II has been reviewed here. An abundance of CA occurs most commonly in epithelial cells specializing in transport of ions and water. A mechanism is favored whereby the polarity of efflux of CA-generated protons and bicarbonate across the apical versus the basolateral plasmalemma depends not on the location of CA, which is probably in the cytosol in most sites, but rather on the transport properties of the luminal compared with the serosal region of the plasma membrane in each epithelial cell type. CA exists also in some protein-secreting, merocrine cells including serous cells of salivary and tracheobronchial glands. Available evidence supports the possibility that CA stored as a secretory product in the cytoplasmic granules is released from these cells and, thus, implies extracellular biologic activity for CA in these sites. CA exists also in abundance in various nonepithelial cells performing different and not fully defined biologic functions in these cells. Prevalence of one isozyme over another varies in different cell types. A question remains whether the significance of this variability depends on work load or other undetermined factors.

The value of inherited deficiencies of human carbonic anhydrase isozymes in understanding their cellular roles

Very little light has been shed on the role of the low-activity CA I isozyme in humans by studies on CA I-deficient individuals. On the other hand, CA II-deficient individuals exhibit abnormalities of bone, kidney and brain, implicating a functional role for the high-activity CA II isozyme in cells from these tissues and organs. It also appears that the CA II-deficient red cell is capable of normal respiratory function under unstressed conditions. In addition, there is some preliminary evidence that those organs such as the eye which primarily contain the CA II isozyme, may be able to function effectively in the absence of CA II.