Role of PDZK1 in membrane expression of renal brush border ion exchangers

Na-H exchanger NHE3 and Cl-anion exchanger CFEX (SLC26A6, PAT1) play principal roles in the reabsorption of Na and Cl in the proximal tubule of the mammalian kidney. The mechanisms by which NHE3 and CFEX are localized to and maintained in the brush border of the proximal tubule are largely unknown. To investigate the possible interaction of NHE3 and CFEX with the PDZ-domain-containing scaffolding protein PDZK1, we performed a series of in vitro interaction assays with GST-fusion proteins and native brush border membrane proteins. These studies demonstrated that, not only were NHE3 and CFEX capable of directly interacting with PDZK1, but that this interaction was mediated through their C-terminal PDZ-interaction sites. To determine whether PDZK1 interaction is essential for brush border localization of NHE3 and CFEX in vivo, we examined the expression of NHE3 and CFEX in kidneys of wild-type and PDZK1-null mutant mice by both Western analysis and immunocytochemistry. These studies indicated that, although brush border expression of NHE3 was unaffected by the loss of PDZK1, the expression of CFEX was markedly reduced. Finally, we assayed CFEX functional activity as Cl-oxalate exchange in brush border membrane vesicles and oxalate-stimulated volume absorption in microperfused proximal tubules. Consistent with the observed decrease in CFEX protein expression, both measures of CFEX functional activity were dramatically reduced in PDZK1-null animals. In conclusion, the scaffolding protein PDZK1 is essential for the normal expression and function of Cl-anion exchanger CFEX in the proximal tubule of the mammalian kidney.

Expression of human prostaglandin transporter in the human endometrium across the menstrual cycle

Prostaglandins (PGs) are important regulators of reproductive function. The mechanism by which PGs are transported across the biological membrane is a new emerging field of investigation. Prostaglandin transporter (PGT) has been identified as a functional PG carrier. The aim of our study was to outline the expression of PGT in the human endometrium across the menstrual cycle. Quantitative RT-PCR showed human PGT (hPGT) expression to be strong in the proliferative and early secretory phases and low in the middle to late secretory phase. Northern blot analysis revealed hPGT mRNA transcript of 4 kb in the human endometrium. A peptide-directed polyclonal antibody was generated in rabbits against the 22 amino acids forming the C terminus of hPGT. Antibody specificity was demonstrated by Western blot. Immunoblots of endogenous hPGT in the human endometrium revealed a 70-kDa protein in endometrial cells. Endometrial biopsies collected across the menstrual cycle were used to assess hPGT protein expression by immunohistochemistry. hPGT was immunolocalized to luminal, glandular epithelial, and stromal cells. Because it was observed at the mRNA level, semiquantitative analysis showed a higher protein expression in proliferative and early secretory phases than in the mid-late secretory phase. In conclusion, our study revealed that hPGT expression is modulated in epithelial and stromal cells of the human endometrium at both mRNA and protein levels during the menstrual cycle. These findings support a role for hPGT as an important new player in the regulation of PG action in the human endometrium.

[Clinicopathologic and immunohistochemical study of pulmonary epithelioid hemangioendothelioma]

OBJECTIVE

To study the clinical and pathological characteristics of pulmonary epithelioid hemangioendothelioma.

METHODS

Four cases of pulmonary epithelioid hemangioendothelioma were studied by histopathologic and immunohistochemical examination of lung biopsy specimens.

RESULTS

There were 3 female and 1 male, age 28 to 40 years. Clinically the tumor presented as multiple bilateral small nodules in the lung. Histologically, crown-like clusters of epithelioid tumor cells were obtained which filled in the alveoli locating at the periphery of the tumor nodules, while the central part of the nodules contained myxoid to hyaline matrix. The overall architecture of the lung was still preserved. Additionally, intracytoplasmic vacuoles were seen in tumor cells within which red blood cells were sometimes identified. Tumor cells generally lacked pleomorphism, mitotic activity and necrosis. They were immunohistochemically positive for CD31 and CD34. AE1/AE3 staining was positive in some cases.

CONCLUSIONS

Pulmonary epithelioid hemangioendothelioma often occurs in a middle-aged woman and represents a distinct clinical pathological entity.

A three-dimensional organotypic culture of the human uterine exocervix for studying mucosal epithelial differentiation and migrating leukocytes

We report on a three-dimensional organotypic culture in vitro of explants from the human uterine exocervix. Exocervical fragments (2-3 mm3) from pre-menopausal women were cultured on sponges submerged in Dulbecco's Modified Eagle's Medium containing p-nonylphenol and 10% fetal bovine serum for up to 3 weeks and the viability and cellular responses were assayed. The fragments were analyzed by immunohistochemistry for the expression and distribution of a broad spectrum of cellular markers: p63, Ki-67, involucrin, high molecular weight cytokeratins, estrogen receptor-alpha, vimentin, CD45, and CD31. The fragments preserved their tissue architecture and cellular heterogeneity comparable to that observed in exocervical tissue in vivo. Prior to culture, the original epithelium was composed of stratified multilayered keratinocytes with integrated monocyte/dendritic-like cells in the basal and suprabasal layers. The epithelium began to exfoliate in culture and within 4 days appeared to have lost its differentiated high-zone layers of keratinocytes. After 10 days a new epithelium, slightly different from the original one, was formed; it displayed an increasing prominence of basal and suprabasal keratinocyte layers, containing infiltrating leukocytes that had probably migrated from the submucosa. The epithelium subsequently lost its organization, concomitant with a progressive involution of the stroma. Subepithelial capillaries appeared to be well maintained throughout the culture period. Aside from the maintenance of cellular heterogeneity within the fragments of exocervix, these culture systems are a valuable tool for studying the mechanisms of epithelial regeneration, and may prove to be a useful model for studying mucosal immunity.

Association of tapasin and HLA class I antigen down-regulation in primary maxillary sinus squamous cell carcinoma lesions with reduced survival of patients

PURPOSE

The purpose of this research was to assess the frequency and clinical significance of antigen processing machinery component and HLA class I antigen down-regulation in primary maxillary sinus squamous cell carcinoma (SCC) lesions.

EXPERIMENTAL DESIGN

Formalin-fixed, paraffin-embedded tumor biopsy specimens at pretreatment status from 70 Japanese patients with maxillary sinus SCC were examined for HLA class I antigen and endoplasmic reticulum chaperone molecule expression using an immunohistochemical method. Furthermore, the results of immunohistochemical staining of the lesions were correlated with their histopathological characteristics and with the clinical course of the disease.

RESULTS

Calnexin, ERp57, calreticulin, tapasin, and HLA class I antigens were down-regulated in 13, 13, 24, 69, and 78% of the 70 lesions tested, respectively. Both tapasin and HLA class I antigen expression were significantly correlated with the number of infiltrating CD3(+) T cells into tumor lesions (P < 0.01); furthermore, tapasin expression was significantly correlated with tumor differentiation (P = 0.024). Tapasin expression was correlated with that of HLA class I antigens (P < 0.01). Furthermore, tapasin and HLA class I antigen down-regulation in SCC lesions was significantly associated with reduced survival of patients (P = 0.01 and P = 0.002, respectively). Multivariate Cox proportional hazards model analysis identified HLA class I antigen down-regulation as an independent prognostic marker.

CONCLUSIONS

Tapasin expression appears to be associated with HLA class I antigen expression in primary maxillary sinus SCC lesions. Furthermore, defects in tapasin and HLA class I antigen expression in primary maxillary sinus SCC lesions may play a role in the clinical course of the disease, because these defects were associated with poor prognosis.

The NorM efflux pump of Neisseria gonorrhoeae and Neisseria meningitidis recognizes antimicrobial cationic compounds

In Neisseria gonorrhoeae and Neisseria meningitidis, we identified a gene that would encode a protein highly similar to NorM of Vibrio parahaemolyticus (Y. Morita et al., Antimicrob. Agents Chemother. 42:1778-1782, 1998). A nonpolar insertional mutation in either the gonococcal or meningococcal norM gene resulted in increased bacterial sensitivity to compounds harboring a quaternary ammonium on an aromatic ring (e.g., ethidium bromide, acriflavine hydrochloride, 2-N-methylellipticinium, and berberine). The presence of point mutations within the -35 region of a putative norM promoter or a likely ribosome binding site resulted in an increased resistance of gonococci and meningococci to the same compounds, as well as to norfloxacin and ciprofloxacin. Structure-activity relationship studies with putative NorM substrates have found that a cationic moiety is essential for NorM recognition.

Cytologic findings of epithelioid angiosarcoma of the thyroid. A case report

BACKGROUND

Angiosarcoma of the thyroid is a rare and aggressive tumor and occurs mainly in patients from central Europe, especially the alpine region. The fine needle aspiration findings of a keratin-positive epithelioid angiosarcoma of the thyroid occurring in a nonmountainous area in South America is described.

CASE

A 65-year-old male from São Paulo, Brazil, presented with a mass in the anterior part of the neck with progressive enlargement for three months. The cytologic findings on the fine needle aspirate were a cellular smear composed of single cells and small clusters of neoplastic cells, oval and round. Cell borders were indistinct, and the cytoplasm was vacuolated. The nuclei were eccentrically located, with irregular nuclear membranes; single, prominent nucleoli; and a coarse chromatin pattern. Features suggestive of intracytoplasmic lumens were identified. Open surgical biopsy demonstrated a tumor infiltrating the thyroid gland and composed of large, round, atypical epithelioid cells lining vascular spaces. These neoplastic cells were immunoreactive for AE1:AE3, CK7, vimentin, CD31 and factor VIII.

CONCLUSION

Epithelioid angiosarcoma should be considered in the differential diagnosis of epithelioid neoplasms of the thyroid. An immunohistochemical panel should include vascular markers even in the presence of immunoreactivity for epithelial markers.

Intratubular embryonal carcinoma

Although intratubular embryonal carcinoma has been described adjacent to invasive embryonal carcinoma, to our knowledge it has not been reported as an isolated finding. We present in this report the histologic and immunohistochemical findings of 2 cases of intratubular embryonal carcinoma. One case was exclusively intratubular embryonal carcinoma without an invasive component in the same testis. A malignant mixed germ cell tumor in the contralateral testis had been previously excised. The second case is predominantly composed of intratubular embryonal carcinoma adjacent to a malignant mixed germ cell tumor. In one case, the intratubular embryonal carcinoma was immunoreactive for CD30, AE1/AE3, cytokeratin 7 focally, and p53. It was negative for cytokeratin 20, p21, and alpha-fetoprotein. These findings are strongly supportive of the opinion that intratubular embryonal carcinoma is the precursor of invasive embryonal carcinoma.

Molecular cloning of SLC26A7, a novel member of the SLC26 sulfate/anion transporter family, from high endothelial venules and kidney

A unique characteristic of endothelial cells from high endothelial venules (HEVEC) in lymphoid organs and chronically inflamed tissues is their capacity to incorporate large amounts of sulfate into sialomucin-type counter-receptors for the lymphocyte homing receptor L-selectin. We have previously shown that HEVEC express two functional classes of sulfate transporters: sodium/sulfate cotransporters and sulfate/anion exchangers. Here, we report the molecular cloning from human HEVEC of a 2.9-kb cDNA encoding SLC26A7, a novel member of the SLC26 (solute carrier 26) sulfate/anion exchanger family. SLC26A7 exhibits 30% identity with three known sulfate transporters from the SLC26 family: SLC26A2 (also known as DTDST), SLC26A1 (also known as SAT1), and SLC26A3 (also known as DRA). Northern blot analysis revealed specific expression of SLC26A7 mRNA in kidney. Alternative splicing and polyadenylation of SLC26A7 pre-mRNA in kidney suggest the existence of two protein isoforms, SLC26A7.1 and SLC26A7.2, differing in their carboxy termini.

Immunohistochemical localization of H-K-ATPase alpha(2c)-subunit in rabbit kidney

The rabbit kidney possesses mRNA for the H-K-ATPase alpha(1)-subunit (HKalpha(1)) and two splice variants of the H-K-ATPase alpha(2)-subunit (HKalpha(2)). The purpose of this study was to determine the specific distribution of one of these, the H-K-ATPase alpha(2c)-subunit isoform (HKalpha(2c)), in rabbit kidney by immunohistochemistry. Chicken polyclonal antibodies against a peptide based on the NH(2) terminus of HKalpha(2c) were used to detect HKalpha(2c) immunoreactivity in tissue sections. Immunohistochemical localization of HKalpha(2c) revealed intense apical immunoreactivity in a subpopulation of cells in the connecting segment, cortical collecting duct, and outer medullary collecting duct in both the outer and inner stripe. An additional population of cells exhibited a thin apical band of immunolabel. Immunohistochemical colocalization of HKalpha(2c) with carbonic anhydrase II, the Cl(-)/HCO exchanger AE1, and HKalpha(1) indicated that both type A and type B intercalated cells possessed intense apical HKalpha(2c) immunoreactivity, whereas principal cells and connecting segment cells had only a thin apical band of HKalpha(2c). Labeled cells were evident through the middle third of the inner medullary collecting duct in the majority of animals. Immunolabel was also present in papillary surface epithelial cells, cells in the cortical thick ascending limb of Henle's loop (cTAL), and the macula densa. Thus in the rabbit kidney, apical HKalpha(2c) is present and may contribute to acid secretion or potassium uptake throughout the connecting segment and collecting duct in both type A and type B intercalated cells, principal cells, and connecting segment cells, as well as in cells in papillary surface epithelium, cTAL, and macula densa.

A new member of the HCO3(-) transporter superfamily is an apical anion exchanger of beta-intercalated cells in the kidney

The kidneys play pivotal roles in acid-base homeostasis, and the acid-secreting (alpha-type) and bicarbonate-secreting (beta-type) intercalated cells in the collecting ducts are major sites for the final modulation of urinary acid secretion. Since the H(+)-ATPase and anion exchanger activities in these two types of intercalated cells exhibit opposite polarities, it has been suggested that the alpha- and beta-intercalated cells are interchangeable via a cell polarity change. Immunohistological studies, however, have failed to confirm that the apical anion exchanger of beta-intercalated cells is the band 3 protein localized to the basolateral membrane of alpha-intercalated cells. In the present study, we show the evidence that a novel member of the anion exchanger and sodium bicarbonate cotransporter superfamily is an apical anion exchanger of beta-intercalated cells. Cloned cDNA from the beta-intercalated cells shows about 30% homology with anion exchanger types 1-3, and functional expression of this protein in COS-7 cells and Xenopus oocytes showed sodium-independent and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid-insensitive anion exchanger activity. Furthermore, immunohistological studies revealed that this novel anion exchanger is present on the apical membrane of beta-intercalated cells, although some beta-intercalated cells were negative for AE4 staining. We conclude that our newly cloned transporter is an apical anion exchanger of the beta-intercalated cells, whereas our data do not exclude the possibility that there may be another form of anion exchanger in these cells.

AE anion exchangers in atrial tumor cells

Intracellular pH homeostasis and intracellular Cl(-) concentration in cardiac myocytes are regulated by anion exchange mechanisms. In physiological extracellular Cl(-) concentrations, Cl(-)/HCO(3)(-) exchange promotes intracellular acidification and Cl(-) loading sensitive to inhibition by stilbene disulfonates. We investigated the expression of AE anion exchangers in the AT-1 mouse atrial tumor cell line. Cultured AT-1 cells exhibited a substantial basal Na(+)-independent Cl(-)/HCO(3)(-) (but not Cl(-)/OH(-)) exchange activity that was inhibited by DIDS but not by dibenzamidostilbene disulfonic acid (DBDS). AT-1 cell Cl(-)/HCO(3)(-) activity was stimulated two- to threefold by extracellular ATP and ANG II. AE mRNAs detected by RT-PCR in AT-1 cells included brain AE3 (bAE3), cardiac AE3 (cAE3), AE2a, AE2b, AE2c1, AE2c2, and erythroid AE1 (eAE1), but not kidney AE1 (kAE1). Cultured AT-1 cells expressed AE2, cAE3, and bAE3 polypeptides, which were detected by immunoblot and immunocytochemistry. An AE1-like epitope was detected by immunocytochemistry but not by immunoblot. Both bAE3 and cAE3 were present in intact AT-1 tumors. Cultured AT-1 cells provide a useful system for the study of mediators and regulators of Cl(-)/HCO(3)(-) exchange activity in an atrial cell type.

Depigmented genital extramammary Paget's disease: a possible histogenetic link to Toker's clear cells and clear cell papulosis

BACKGROUND

The histogenesis of extramammary Paget's disease (EMPD) is still controversial. Benign pagetoid cells of the nipple first described by Toker and the similar clear cells found in white maculopapules of clear cell papulosis (CCP) have been proposed to be potential precursor cells giving rise to EMPD and primary intraepidermal Paget's disease in the nipple. The observation of a rare case of depigmented EMPD provided us with a chance to examine further the interesting Toker's clear cell/CCP hypothesis.

METHODS

We performed pathologic studies, including Fontana-Masson stain and immunostaining for AE1/AE3 and S100P, on a new case of depigmented EMPD manifesting a 4 x 3 cm hypopigmented-depigmented patch on the root of the penis.

RESULTS

The lesion showed extensive intraepithelial proliferation of atypical pagetoid cells with markedly reduced epidermal melaninization but nearly normal numbers of melanocytes. The tumor cells were strongly positive for AE1/AE3 by immunostaining. Some tumor cells displayed tadpole-like morphology resembling the pagetoid cells of CCP. Such morphology was not observed in two random examples of non-depigmented genital EMPD.

CONCLUSIONS

The findings of tadpole-shaped pagetoid cells and depigmentation in the present case suggest that depigmented EMPD may be histogenetically related to CCP. Depigmented EMPD should be considered in the differential diagnosis of vitiligo, depigmented mycosis fungoides and lichen sclerosus located along the milk line.

Lack of HLA-class I antigens in human neuroblastoma cells: analysis of its relationship to TAP and tapasin expression

We studied the constitutive and the interferon (IFN)-gamma-induced expression of HLA class I antigen heavy chain, beta2-microglobulin (beta2m), TAP-1, TAP-2 and tapasin in a panel of eleven neuroblastoma cell lines. Surface expression of HLA class I antigens was low in eight out of eight neuroblastoma cell lines bearing MYC-N amplification and/or 1p deletion, while two out of three neuroblastoma cell lines lacking these genetic alterations showed normal expression. IFN-gamma treatment restored HLA class I antigen surface expression in all neuroblastoma cell lines. Eight out of 11 neuroblastoma cell lines did not express TAP-1 mRNA and three of them also lacked TAP-2 mRNA. beta2 m mRNA was barely detectable or absent in five neuroblastoma cell lines, while tapasin mRNA was always expressed. IFN-gamma upregulated the expression of HLA class I heavy chain, beta2 m, TAP-1, TAP-2 and tapasin, as detected at mRNA or protein level. Post-transcriptional events were involved in altered TAP-1 and beta2 m expression in one peculiar neuroblastoma cell line. These data indicate that multiple mechanisms play a role in the HLA class I antigen-deficient phenotype of human neuroblastoma.

Regulation of DRA and AE1 in rat colon by dietary Na depletion

Two distinct Cl/anion exchange activities (Cl/HCO(3) and Cl/OH) identified in apical membranes of rat distal colon are distributed in cell type-specific patterns. Cl/HCO(3) exchange is expressed only in surface cells, whereas Cl/OH exchange is localized in surface and crypt cells. Dietary Na depletion substantially inhibits Cl/HCO(3) but not Cl/OH exchange. We determined whether anion exchange isoforms (AE) and/or downregulated in adenoma (DRA) are expressed in and related to apical membrane anion exchanges by examining localization of AE isoform-specific and DRA mRNA expression in normal and Na-depleted rats. Amplification of AE cDNA fragments by RT-PCR with colonic mRNA as template indicates that AE1 and AE2 but not AE3 mRNAs are expressed. In situ hybridization study revealed that AE1 mRNA is expressed predominantly in surface but not crypt cells. In contrast, AE2 polypeptide is expressed in basolateral membranes and DRA protein is expressed in apical membranes of both surface and crypt cells. AE1 mRNA is only minimally present in proximal colon, and DRA mRNA abundance is similar in distal and proximal colon. Dietary Na depletion reduces AE1 mRNA abundance but did not alter DRA mRNA abundance. This indicates that AE1 encodes surface cell-specific aldosterone-regulated Cl/HCO(3) exchange, whereas DRA encodes aldosterone-insensitive Cl/OH exchange.

Characterization of the Saccharomyces cerevisiae high affinity copper transporter Ctr3

Copper is an essential nutrient required for the activity of a number of enzymes with diverse biological roles. In the bakers' yeast Saccharomyces cerevisiae, copper is transported into cells by two high affinity copper transport proteins, Ctr1 and Ctr3. Although Ctr1 and Ctr3 are functionally redundant, they bear little homology at the amino acid sequence level. In this report, we characterize Ctr3 with respect to its localization, assembly, and post-transcriptional regulation. Ctr3 is an integral membrane protein that assembles as a trimer to form a competent copper uptake permease at the plasma membrane. Whereas the CTR1 and CTR3 genes are similarly regulated at the transcriptional level in response to copper, post-transcriptional regulation of these proteins is distinct. Unlike Ctr1, the Ctr3 transporter is neither regulated at the level of protein degradation nor endocytosis as a function of elevated copper levels. Our studies suggest that Ctr3 constitutes a fundamental module found in all eukaryotic high affinity copper transporters to date, which is sufficient for copper uptake but lacks elements for post-transcriptional regulation by copper.

The function of alkaline phosphatase in the liver: regulation of intrahepatic biliary epithelium secretory activities in the rat

We studied the effects of alkaline phosphatase (AP) on the secretory processes of the rat intrahepatic biliary epithelium as well as the role of the intrahepatic biliary epithelium in the uptake and biliary secretion of exogenous AP. The effects of acute and chronic administration of AP on bile secretory parameters were investigated in vivo in normal and bile duct ligated (BDL) rats and in vitro in isolated rat bile duct units (IBDU). In vivo, acute AP administration decreased bile flow and biliary bicarbonate excretion and abolished secretin choleresis in BDL rats but not in normal rats. On the contrary, the AP inhibitor, levamisole, increased in BDL rat bile flow and biliary bicarbonate excretion. In vitro, basal and secretin-stimulated Cl(-)/HCO(3)(-) exchanger activity in IBDU was immediately inhibited by AP intraluminal microinjection (apical exposure) but only after a prolonged exposure to the basolateral pole. Levamisole increased the Cl(-)/HCO(3)(-) exchanger activity of IBDU. A significant basolateral uptake of AP occurs in IBDU with a progressive transport to the apical domain. AP chronic treatment increased AP and gamma-glutamyltranspeptidase (gamma-GT) activities in the intrahepatic bile ducts and hepatocyte canalicular pole, promoted enlargement of bile canaliculi, and decreased bile flow and biliary bicarbonate excretion. In conclusion, the intrahepatic biliary epithelium plays a role in the uptake and biliary secretion of serum AP. AP inhibits the secretory processes of the intrahepatic biliary epithelium and induces features of intrahepatic cholestasis after chronic administration. These findings indicate that AP plays an active role in down-regulating the secretory activities of the intrahepatic biliary epithelium.

Red cell Na+/Li+ countertransport and Na+/H+ exchanger isoforms in human proximal tubules

BACKGROUND

Increased activity of the Na+/Li+ countertransporter (SLC) is a well-recognized intermediate phenotype of hypertension and diabetic nephropathy and may indicate a predisposition to hypertension. Previous work has attempted to link this membrane transport marker to altered Na+ reabsorption in the proximal tubule. Since the Na+/H+ exchanger (NHE) isoforms 1 and 3 are expressed in the basolateral and apical membranes of the proximal tubule, respectively, we investigated the relationship between these transport proteins and red cell SLC to examine whether the peripheral blood transport phenotype is associated with altered levels of transport proteins in the proximal tubule.

METHODS

Proximal tubules were prepared from human nephrectomy specimens. NHE-1 and NHE-3 were detected on Western blots by specific antibodies. Red cell SLC was also measured.

RESULTS

Both NHE-1 and NHE-3 proteins were demonstrated, with molecular weights of 97 and 85 kD, respectively. SLC was very strongly correlated with the level of NHE-3 protein (r = 0.78, P < 0.001) and was negatively related to NHE-1 protein (r = -0.32). In multiple regression analysis, only NHE-3 and NHE-1 protein levels were significant predictors of red cell SLC, accounting for up to about 70% of the variance of this parameter.

CONCLUSIONS

We conclude that red cell SLC may be a marker of increased NHE-3 protein expression in the proximal tubule, which may account for the blunted pressure natriuresis and predisposition to hypertension.

Expression of rat kidney anion exchanger 1 in type A intercalated cells in metabolic acidosis and alkalosis

By enzyme-linked in situ hybridization (ISH), direct evidence is provided that acid-secreting intercalated cells (type A IC) of both the cortical and medullary collecting ducts of the rat kidney selectively express the mRNA of the kidney splice variant of anion exchanger 1 (kAE1) and no detectable levels of the erythrocyte AE1 (eAE1) mRNA. Using single-cell quantification by microphotometry of ISH enzyme reaction, medullary type A IC were found to contain twofold higher kAE1 mRNA levels compared with cortical type A IC. These differences correspond to the higher intensity of immunostaining in medullary versus cortical type A IC. Chronic changes of acid-base status induced by addition of NH(4)Cl (acidosis) or NaHCO3 (alkalosis) to the drinking water resulted in up to 35% changes of kAE1 mRNA levels in both cortical and medullary type A IC. These experiments provide direct evidence at the cellular level of kAE1 expression in type A IC and show moderate capacity of type A IC to respond to changes of acid-base status by modulation of kAE1 mRNA levels.

Ionic selectivity of the Ca2+/H+ antiport in synaptic vesicles of sheep brain cortex

As we previously reported, synaptic vesicles isolated from sheep brain cortex contain a Ca2+/H+ antiport that permits Ca2+ accumulation inside the vesicles ( approximately 5 nmol/mg protein) at expenses of the pH gradient generated by the H+-pumping ATPase. We observed that the system associates Ca2+ influx to H+ release and operates with low affinity for Ca2+. In the present work, we found that Ca2+/H+ antiport mediates exchange of protons with other cations such as Zn2+ and Cd2+, suggesting that these cations and Ca2+ share the same transporter molecules to enter the intravesicular space. Zn2+ and Cd2+ induce H+ release in a concentration-dependent manner (fluorimetrically evaluated) and they inhibit the antiport-mediated Ca2+ uptake by the vesicles (isotopically measured). In contrast, large cations such as Ba2+ and Cs+ do not alter Ca2+ influx and they are unable to induce proton release from the vesicles. With respect to Sr2+, which has an intermediary size relatively to the other groups of cations, we found that it does not induce H+ liberation from the vesicles, but it has a concentration-dependent inhibitory effect on the Ca2+-induced H+ release and Ca2+ uptake by the vesicles. These results indicate that the cation selectivity of the synaptic vesicles Ca2+/H+ antiport is essentially determined by the size of the cation transported into the vesicles.

Non-selective voltage-activated cation channel in the human red blood cell membrane

Using the patch-clamp technique, a non-selective voltage-activated Na+ and K+ channel in the human red blood cell membrane was found. The channel operates only at positive membrane potentials from about +30 mV (inside positive) onwards. For sodium and potassium ions, similar conductances of about 21 pS were determined. Together with the recently described K+(Na+)/H+ exchanger, this channel is responsible for the increase of residual K+ and Na+ fluxes across the human red blood cell membrane when the cells are suspended in low ionic strength medium.

Rat osteoclast precursors in vivo express a vitronectin receptor and a chloride-bicarbonate exchanger

In vivo osteoclast precursors, which are mononuclear, were previously found to express TRAP (tartrate-resistant acid phosphatase) and CTR (calcitonin receptor), like multinucleated osteoclasts. In vitro, they were found to express, in addition, VNR (vitronectin receptor) and CBE (chloride-bicarbonate exchanger). In order to ascertain that osteoclast precursors in vivo express VNR and CBE like their in vitro counterparts, we used immunohistochemistry to localize these molecules in developing long bones of neonatal rats. Frozen sections of metatarsals and phalanges of 1-2 day-old rats were stained for TRAP and mineralization using histochemistry or were reacted with polyclonal antibodies specific for either the beta3 chain of the VNR or synthetic sequences of the CBE. Both mature, multinucleated osteoclasts within the forming marrow cavity of metatarsals (as shown previously) and mononuclear osteoclast precursors located outside the bony collar of the phalangeal calcified rudiment (as shown here for the first time) expressed both TRAP, VNR and CBE. These findings suggest that mononuclear osteoclast precursors express many of the phenotypical markers of multinucleated osteoclasts prior to their fusion and multinucleation which may allow them to resorb bone, as suggested by in vitro observations of pit formation by preosteoclasts cultured on resorbable substances.

Video-imaging microfluorometry identifies alpha- and beta-like cell types in Madin-Darby canine kidney monolayers

On the basis of intracellular, accumulation of c-SNAFL-2, we have identified three cell subtypes in Madin-Darby canine kidney (MDCK) monolayers. Highly fluorescent cells (HFC) have a high intracellular pH (pHi, whereas cells with medium fluorescence (MFC) have low pHi when perfused with buffer containing 125 mM Cl-. HFC express a Cl-/HCO3- exchanger on the apical but not the basolateral membrane. MFC express a Cl-/HCO3- exchanger on the basolateral but not the apical membrane. We have termed these cells beta- and alpha-MDCK cells, respectively. Cells with low fluorescence (LFC) probably extrude c-SNAFL-2 through a monocarboxylate transporter, because p-4-(chloromercuri)phenylsulfonic acid (PCMBS), an inhibitor of this transporter, leads to homogeneous fluorescence.

pH dependence of Cl/HCO3 exchanger in the rat jejunal enterocyte

During bicarbonate absorption in rat jejunum, a Cl/HCO3 exchanger mediates bicarbonate extrusion across the basolateral membrane of the enterocyte. Previous studies demonstrated that anion antiport exhibits a particular behaviour: its activity is positively affected by the presence of sodium, but the cation is not translocated by the carrier protein. In view of the particular features of the jejunal Cl/HCO3 antiporter, first we performed a pharmacological characterisation of the transport protein using various Cl channels blockers. Then, since it is well known that anion exchangers play a substantial role in cell pH regulation, we investigated the possible involvement of jejunal basolateral Cl/HCO3 antiporter in intracellular pH maintenance. The sensitivity of the exchanger to pH was investigated by measuring 36Cl uptake into basolateral membrane vesicles either varying simultaneously intra- and extravesicular pH, or presetting at 7.4 external pH and varying only the internal one. Experiments were performed both in the absence and in the presence of Na. In all the tested conditions, uptake peaked at pH of about 7. 3-7.4 and then decreased, suggesting that the main function of Cl/HCO3 exchanger is related to HCO3 absorption rather than to intracellular pH control. Since pH-regulating mechanisms counteracting acidification are well known in the jejunal enterocyte, we investigated how it regulates pH after alkalinisation of the cytosol. We tested both basolateral and brush border membrane vesicles for the presence of a K/H exchanger, but we could not give evidence for its presence by means of 86Rb uptake experiments. In conclusion, the jejunal enterocyte seems to lack a mechanism counteracting cellular alkalinisation: the main purpose of pH homeostasis might be to hinder acidification of the cytosol due to influx of protons and production of acid by the metabolism.

Immunolocalization of sat-1 sulfate/oxalate/bicarbonate anion exchanger in the rat kidney

The rat liver sulfate/bicarbonate/oxalate exchanger (sat-1) transports sulfate across the canalicular membrane in exchange for either bicarbonate or oxalate. Sulfate/oxalate exchange has been detected in the proximal tubule of the kidney, where it is probably involved in the reabsorption of filtered sulfate and the secretion of oxalate and may contribute to oxalate-dependent chloride reabsorption. Screening of a renal cortex cDNA library determined that sat-1 is expressed in the rat kidney. To evaluate this anion exchanger, the sat-1 protein was expressed in Sf9 cells. Sodium-independent sulfate and oxalate uptake was enhanced 7.3-fold and 13.1-fold, respectively, in Sf9 cells expressing the sat-1 protein compared with cells infected with wild-type virus. We determined that sat-1 is glycosylated in the kidney; however, anion exchange via sat-1 is observed despite incomplete glycosylation of sat-1 in Sf9 cells. The sat-1 protein, with an added COOH-terminal 6-histidine tag, was purified on a metal affinity column and used to generate anti-sat-1 monoclonal antibodies. The sat-1 protein was localized to the basolateral membrane, but not the apical membrane, of the proximal tubule by both Western blot analysis and immunohistochemistry. These studies demonstrate that sulfate/oxalate exchange on the apical and basolateral membranes of the proximal tubule represents transport on two different anion exchangers.