Distinct expression and subcellular localization patterns of Na+/HCO3- cotransporter (SLC 4A4) variants NBCe1-A and NBCe1-B in mouse brain.

The electrogenic Na+/HCO3- cotransporter (NBCe1) has been identified as a key player for regulation of intracellular pH in several cell types. The present study was undertaken to determine expression and subcellular localization of the NH2-terminal solute carrier (SLC) 4A4 variants NBCe1-A and NBCe1-B in mouse brain using variant-specific antibodies by immunohistochemistry and immunoelectron microscopy. In addition, distribution of NBCe1 variants and activity-dependent regulation was investigated in mouse embryonic day 17.5 (E17.5) hippocampal primary cultures in vitro. The results showed NBCe1-A and NBCe1-B transcript expression in the mouse olfactory bulb, cerebral cortex, hippocampus and cerebellum. NBCe1-A was predominantly expressed in Purkinje cells, granule cells of the dentate gyrus, non-pyramidal cell bodies in cerebral cortex, and in periglomerular and mitral cells in the olfactory bulb. Pyramidal neurons in cerebral cortex and apical cell dendrites in the hippocampus were stained for both NBCe1-A and NBCe1-B. Moreover, NBCe1-B was present in Bergmann glia. At the ultrastructural level, NBCe1-B was preferentially expressed in perivascular astroglial lamellae, whereas both NBCe1 NH2-terminal variants were localized in pre- and postsynaptic compartments. Except for the olfactory bulb, NBCe1-A was always colocalized with calbindin. Treatment of E17.5 primary hippocampal cultures with KCl, showed dramatic downregulation of NBCe1-B mRNA and protein after 60 min, whereas NBCe1-A expression remained unchanged. These data demonstrate for the first time distinct cellular distribution of NBCe1 NH2-terminal variants in mouse brain. NBCe1 may be involved in neuronal modulation, and pH regulation during neuronal activity.

Activity-dependent release of transforming growth factor-beta in a neuronal network in vitro.

For neurotrophins and also for members of the transforming growth factor beta (TGF-beta) family an activity-dependent regulation of synthesis and release has been proposed. Together with the observation that the secretion of neurotransmitters is initiated by neurotrophic factors, it is reasonable to assume that they might act as retrograde modulators enhancing the efficacy and stabilization of synapses. In the present study, we have tested this hypothesis and studied the release and regulation of TGF-beta in vitro using mouse primary hippocampal neurons at embryonic day E16.5 as model. We show that neuronal activity regulates TGF-beta release and TGF-beta expression in vitro. Treatment of the cultures with KCl, 3-veratroylveracevine (veratridine), glutamate or carbamylcholine chloride (carbachol) increased the levels of secreted TGF-beta, as assessed by the MLEC/plasminogen activator inhibitor (PAI)-luciferase-assay, whereas TGF-beta release stimulated by KCl or veratridine was reduced in the presence of tetrodotoxin or 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA). In addition, application of glutamate significantly upregulated expression of TGF-beta2 and TGF-beta3 in the culture. Notably, KCl stimulation caused Smad (composite term from SMA (C. elegans) and MAD=mothers against dpp (Drosophila)) translocation into the nucleus and upregulated TGF-beta inducible early gene (Tieg1) expression, demonstrating that activity-dependent released TGF-beta may exert autocrine actions and thereby activate the TGF-beta-dependent signaling pathway. Together, these results suggest an activity-dependent release and gene transcription of TGF-beta from mouse hippocampal neurons in vitro as well as subsequent autocrine functions of the released TGF-beta within the hippocampal network.

Immunolocalization of anion exchanger AE2, Na(+)/H(+) exchangers NHE1 and NHE4, and vacuolar type H(+)-ATPase in rat pancreas.

We have studied the expression and localization of several H(+) and HCO(3)(-) transporters, whose presence in the rat pancreas is still unclear. The Cl(-)/HCO(3)(-) exchanger AE2, the Na(+)/H(+) exchangers NHE1 and NHE4, and the 31-kD and 70-kD vacuolar H(+)-ATPase (V-ATPase) subunits were detected by immunoblotting and immunocytochemical techniques. Immunoblotting of plasma membranes with transporter-specific antibodies revealed protein bands at approximately 160 kD for AE2, at approximately 90 kD and approximately 103 kD for NHE1 and NHE4, respectively, and at 31 kD and 70 kD for V-ATPase. NHE1 and NHE4 were further identified by amplification of isoform-specific cDNA using RT-PCR. Immunohistochemistry revealed a basolateral location of AE2, NHE1, and NHE4 in acinar cells. In ducts, NHE1 and NHE4 were basolaterally located but no AE2 expression was detected. V-ATPase was detected in zymogen granules (ZGs) by immunogold labeling, and basolaterally in duct cells by immunohistochemistry. The data indicate that NHE1 and NHE4 are co-expressed in rat pancreatic acini and ducts. Basolateral acinar AE2 could contribute to Cl(-) uptake and/or pH regulation. V-ATPase may be involved in ZG fusion/exocytosis and ductal HCO(3)(-) secretion. The molecular identity of the ductal Cl(-)/HCO(3)(-) exchanger remains unclear.

Immunolocalization of vacuolar-type H+-ATPase in rat submandibular gland and adaptive changes induced by acid-base disturbances.

Using antibodies against the 31-kD and 70-kD subunits of vacuolar type H+-ATPase (V-ATPase) and light microscopic immunocytochemistry, we have demonstrated the presence of this V-ATPase in rat submandibular gland. We have also investigated the adaptive changes of this transporter during acid-base disturbances such as acute and chronic metabolic acidosis or alkalosis. Our results show intracellularly distributed V-ATPase in striated, granular, and main excretory duct cells in controls, but no V-ATPase immunoreaction in acinar cells. Both acute and chronic metabolic acidosis caused a shift in V-ATPase away from diffuse distribution towards apical localization in striated and granular duct cells, suggesting that a V-ATPase could be involved in the regulation of acid-base homeostasis. In contrast, during acidosis the main excretory duct cells showed no changes in the V-ATPase distribution compared to controls. With acute and chronic metabolic alkalosis, no changes in the V-ATPase distribution occurred. (J Histochem Cytochem 46:91-100, 1998)

Localisation of the vacuolar proton pump (V-H+ -ATPase) and carbonic anhydrase II in the human eccrine sweat gland.

The localisation of the vacuolar proton pump (V-H+ -ATPase) and the enzyme carbonic anhydrase II (CAII) was investigated in the human eccrine sweat gland employing standard immunohistochemical techniques after antigen retrieval using microwave heat treatment and high pressure. The high-pressure antigen retrieval unmasked the presence of V-H+ -ATPase in the clear cells of the secretory coil, with a distribution similar to that previously observed for CAII. However, the dark cells were unreactive to both antibodies. In addition, heat and high-pressure antigen retrieval demonstrated the presence of CAII in the apical zone of luminal cells of the reabsorptive duct, a location not previously reported. The localisation of V-H+ -ATPase and CAII in the secretory coil clear cells suggests that the formation of HCO3- and H+ by carbonic anhydrase II and the transport of H+ by V-H+ -ATPase may play an role in sweat fluid secretion. Their presence at the apex of the duct cells indicates involvement in ductal ion reabsorption.

Expression of a sodium bicarbonate cotransporter in human parotid salivary glands.

The human parotid gland secretes much of the bicarbonate that enters the mouth. Prompted by studies of animal models, this study sought evidence for the expression of a functional Na(+)-HCO(3)(-) cotransporter (NBC) in human parotid acinar cells. Microfluorometric measurements of intracellular pH in isolated acini showed that the recovery from an acid load was achieved in part by HCO(3)(-) uptake via a Na(+)-dependent, DIDS-sensitive mechanism. By reverse transcriptase-polymerase chain reaction, a full-length NBC1 clone was obtained showing more than 99% homology with the human pancreatic isoform hpNBC1. Expressed in Xenopus oocytes, the electrogenicity of the transporter was detected as an inwardly directed, Na(+)- and HCO(3)(-)-dependent flux of negative charge. Immunohistochemistry using antibodies raised to NBC1 showed strong staining of the basolateral membrane of the acinar cells. Therefore, it was concluded that a functional electrogenic Na(+)-HCO(3)(-) cotransporter is expressed in the human parotid gland, and that it contributes to pH regulation in the acinar cells and could play a significant part in salivary secretion.

Distribution of V-ATPase in rat salivary glands.

Using immunohistochemistry we have investigated the presence and cellular distribution of the 31-kDa subunit of vacuolar-type H+-ATPase (V-ATPase) in secretory endpieces and the duct system of rat major salivary glands. In all three salivary glands studied the 31-kDa subunit of V-ATPase was not expressed in secretory endpieces. In rat parotid gland V-ATPase was luminally located in main excretory and striated duct cells. In contrast, both rat submandibular and sublingual glands showed a diffuse intracellular V-ATPase distribution. The differences in V-ATPase immunolocalization in rat salivary glands probably reflect the structural heterogeneity of the different glands. The data also suggest that the duct systems of major salivary glands may modify the H+ and HCO3- concentration of the final saliva in different ways.

H+ and HCO3- transporters in human salivary ducts. An immunohistochemical study.

The presence and cellular distribution of key H+ and HCO3- transport proteins was studied in human salivary ducts. Immunofluorescence and immunoperoxidase light microscopy was applied, using specific antibodies against the NHE1 and NHE3 isoforms of the Na+/H+ exchanger, against the 31 and 70 kDa subunits of the vacuolar H+-ATPase and against the electrogenic Na+-HCO3- cotransporter. The results show basolateral NHE1 and apical NHE3 in human submandibular, parotid and sublingual duct cells. Vacuolar H+-ATPase was found predominantly in the apical membrane of parotid, submandibular and sublingual duct cells, although it was absent in certain parotid striated duct cells. The Na+-HCO3- cotransporter was predominantly expressed in the apical membrane of parotid and sublingual striated ducts, and intracellularly distributed in the distal parts of the gland tree and in submandibular ducts. The results indicate that HCO3- transport properties of salivary ducts may vary not only between gland and species, but even in different duct segments of the same gland as well.

Anatomic characteristics of the furcation and root surfaces of molar teeth and their significance in the clinical management of marginal periodontitis.

Treatment of periodontitis which involves the furcation area of molar teeth has always been a challenge. Sixty extracted human molar teeth were used for an anatomic study to clarify the possible morphologic factors which may affect the diagnosis, prognosis, and clinical management of periodontally involved teeth. Teeth were embedded in methylmethacrylate and cut in 70 microm cross sections from the cementoenamel junction to the apex. Cervical enamel projection, root and root trunk lengths, root proximities as well as depths of root concavities coronally, apically, and at the furcation roof were measured. Cervical enamel projections were observed in 30% of the teeth examined. The shortest root trunk was found at the buccal aspect of mandibular first molars, permitting furcation involvement at early stages of periodontal disease. The most apically located furcation was found at the distal site of maxillary first molars. Furcation roofs showed severe concavities and complex cementum morphology. Teeth exhibiting cervical enamel projection were found to have deeper root concavities compared to teeth without cervical enamel projection and mesial roots of mandibular molars possessed greater furcal concavities than distal roots. The presence of root concavities complicates the diagnosis of furcation involvement and restricts access of periodontal instruments, resulting in incomplete treatment. Furcation anatomy may also influence the long-term prognosis of the teeth by favoring the retention of bacterial deposits and making oral hygiene procedures almost impossible. The present study shows that knowledge of a tooth's unique anatomic characteristics is a prerequisite for effective periodontal therapy.

Molecular characterisation of pancreatic zymogen granule ion channel and regulator proteins involved in exocytosis.

In pancreatic acinar cells Ca(2+)-dependent secretagogues promote the fusion of zymogen granules (ZG) with the apical plasma membrane (PM) and exocytosis of digestive enzymes. In addition to exocytotic fusion complexes between SNARE proteins in the ZG membrane (ZGM) and the apical PM, enzyme secretion elicited by Ca(2+)-dependent secretagogues requires cytosolic Cl and K+ and is inhibited by blockers of Cl- and K+-channels. We have identified a Cl-conductance activated by ATP, and a K+-conductance (with properties similar to ATP-sensitive K+-channels), regulated by the granule matrix protein Zg-16p in the ZGM. Both conductances are inversely regulated by a 65-kD mdr1 gene product. We have also identified a novel Ca(2+)-activated anion conductance in ZGM, the Ca(2+)-sensitivity of which increases 50-fold when Cl is replaced by 1. This conductance is blocked by micromolar H2-DIDS or DTT, reminiscent of a family of epithelial Ca(2+)-activated Cl -channels (CaCC). Expression of a CaCC in exocrine pancreas has been confirmed by RT-PCR analysis, and by immunoblotting and immunogold labeling of ZG membranes. These data suggest that ion channels in the ZGM are essential elements in pancreatic exocytosis.

Vacuolar-type H+ -ATPase distribution in unstimulated and acetylcholine-activated isolated human eccrine sweat glands.

The presence and cellular distribution of subunits of the V1 sector of the vacuolar-type H+ -ATPase (V-ATPase) was investigated in isolated human eccrine sweat glands. In every instance, V-ATPase was located in the cytoplasm and apical membranes of the luminal cells of the reabsorptive duct segment. In the secretory coil, both diffuse and perinuclear staining was demonstrated in the secretory cells, with additional expression at the apical and basolateral membranes and on the intercellular canaliculi. There was no detectable difference in V-ATPase expression as a result of prior application of 100 microM acetylcholine.

Cloning and immunolocalization of a rat pancreatic Na(+) bicarbonate cotransporter.

In the rat, pancreatic HCO(-)(3) secretion is believed to be mediated by duct cells with an apical Cl(-)/HCO(-)(3) exchanger acting in parallel with a cAMP-activated Cl(-) channel and protons being extruded through a basolateral Na(+)/H(+) exchanger. However, this may not be the only mechanism for HCO(-)(3) secretion by the rat pancreas. Recently, several members of electrogenic Na(+)/HCO(-)(3) cotransporters (NBC) have been cloned. Here we report the cloning of a NBC from rat pancreas (rpNBC). This rpNBC is 99% identical to the longer, more common form of NBC [pNBC; 1079 amino acids (aa); 122 kDa in human heart, pancreas, prostate, and a minor clone in kidney]. The longer NBC isoforms are identical to the rat and human kidney-specific forms (kNBC; 1035 aa; 116 kDa) at the approximately 980 C-terminal aa's and are unique (with different lengths) at the initial N-terminus. Using polyclonal antibodies to the common N- and C-termini of rat kidney NBC, a approximately 130-kDa protein band was labeled by immunoblotting of rat pancreas homogenate and was enriched in the plasma membrane fraction. Immunofluorescence and immunoperoxidase light microscopy of rat pancreatic tissue with both antibodies revealed basolateral labeling of acinar cells. Labeling of both apical and basolateral membranes was found in centroacinar cells, intra- and extralobular duct, and main duct cells. The specificity of the antibody labeling was confirmed by antibody preabsorption experiments with the fusion protein used for immunization. The data suggest that rpNBC likely plays a more important role in the transport of HCO(-)(3) by rat pancreatic acinar and duct cells than previously believed.

Immunolocalization of anion exchanger AE2 and Na(+)-HCO(-)(3) cotransporter in rat parotid and submandibular glands.

Salivary glands secrete K(+) and HCO(-)(3) and reabsorb Na(+) and Cl(-), but the identity of transporters involved in HCO(-)(3) transport remains unclear. We investigated localization of Cl(-)/HCO(-)(3) exchanger isoform AE2 and of Na(+)-HCO(-)(3) cotransporter (NBC) in rat parotid gland (PAR) and submandibular gland (SMG) by immunoblot and immunocytochemical techniques. Immunoblotting of PAR and SMG plasma membranes with specific antibodies against mouse kidney AE2 and rat kidney NBC revealed protein bands at approximately 160 and 180 kDa for AE2 and approximately 130 kDa for NBC, as expected for the AE2 full-length protein and consistent with the apparent molecular mass of NBC in several tissues other than kidney. Immunostaining of fixed PAR and SMG tissue sections revealed specific basolateral staining of PAR acinar cells for AE2 and NBC, but in SMG acinar cells only basolateral AE2 labeling was observed. No AE2 expression was detected in any ducts. Striated, intralobular, and main duct cells of both glands showed NBC expression predominantly at basolateral membranes, with some cells being apically stained. In SMG duct cells, NBC staining exhibited a gradient of distribution from basolateral localization in more proximal parts of the ductal tree to apical localization toward distal parts of the ductal tree. Both immunoblotting signals and immunostaining were abolished in preabsorption experiments with the respective antigens. Thus the mechanisms of fluid and anion secretion in salivary acinar cells may be different between PAR and SMG, and, because NBC was detected in acinar and duct cells, it may play a more important role in transport of HCO(-)(3) by rat salivary duct cells than previously believed.