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N Farman

Publications and source records attributed to N Farman.

At least 55 records · Page 3Linked to original sources
PubMed1995

Synergistic action of vasopressin and aldosterone on basolateral Na(+)-K(+)-ATPase in the cortical collecting duct.

The respective effects of aldosterone and arginine vasopressin (AVP) were examined on the number of active Na(+)-K(+)-ATPase and their pumping activity in nonperfused microdissected mouse cortical collecting tubules (CCD) by measuring specific 3H-ouabain binding and ouabain-sensitive 86Rb uptake. In adrenalectomized (ADX) animals, incubation of CCD with AVP (10(-8) M for 5 min) had no effect on the number of pumps. In contrast, in ADX animals replete with aldosterone, AVP induced a approximately equal to 40% increase in the number of pumps. This was accompanied by a approximately equal to 60-65% increase in ouabain-sensitive Rb uptake. AVP effect was dose-dependent (10(-10)-10(-8) M) and was reproduced by dDAVP, forskolin and 8-Br cAMP, indicating a V2 pathway. It was inhibited by amiloride 10(-5) M, and did not occur in CCD incubated in hyperosmotic solution, suggesting that the signal was transmitted via apical sodium entry and cell swelling. Finally, the AVP-dependent increase in the number of pumps was rapid (within 5 min) and transient (< 25 min). These results demonstrate that, in the CCD, aldosterone and AVP act synergistically to increase not only the apical sodium entry but also the basolateral Na(+)-K(+)-ATPase transport capacity: AVP allows a rapid recruitment and/or activation of an aldosterone-dependent pool of latent Na(+)-K(+)-ATPase.

Aldosterone↗
PubMed1995

Aldosterone: intracellular receptors in human heart.

It has been suggested that aldosterone exerts direct effects on heart functioning, in particular by inducing cardiac fibrosis. We examined human heart tissue for the expression of aldosterone receptors (mineralocorticoid receptors, MRs) and of the MR-protecting enzyme, 11 beta hydroxysteroid dehydrogenase (11 beta HSD). In situ hybridization using cRNA probes specific for human MRs revealed the presence of mRNA encoding for MRs in cardiomyocytes. Immunohistochemistry with specific antibodies against the MR exhibited the expression of MR protein in cardiomyocytes. In contrast, intramyocardial small blood vessels showed no evidence of immunolabelling. A distinct 11 beta HSD activity, which was nicotinamide-adenine dinucleotide dependent, was also demonstrated in human cardiac tissue. These results illustrate that all the components required for a specific aldosterone effect are present in the human heart.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1995

[Distribution of amiloride-sensitive sodium channel in epithelial tissue].

Sodium transport across the apical membrane, via amiloride sensitive sodium channels, is the limiting step of sodium absorption in transporting epithelia with high intercellular electrical resistance, such as the distal parts of the colon and of the renal tubule. Several types of amiloride sensitive sodium channels have been functionally characterized: one of them (type I) with high selectivity and low conductance for sodium is under the control of aldosterone and antidiuretic hormone. This channel has been cloned (2): it is formed of three subunits, alpha, beta and gamma. The distribution of these subunits has been examined in several epitheliums at the mRNA (in situ hybridization) and protein (immunocytochemistry) levels. All three subunits are expressed in the most superficial cells of the distal colon, in principal cells of the renal distal tubule and cortical collecting duct, in striated ducts of serous acini of salivary glands, and in excretory ducts of sweat glands. Immunocytochemistry established the apical localization of the channel subunit proteins. No expression was detected in other cell types of these tissues. These results highlight the crucial role of the type I amiloride sensitive sodium channel in the control of sodium homeostasis at the level of tight, aldosterone-sensitive epitheliums. Furthermore, novel questions are opened, in view of the sodium channel being a member of a highly conserved family of mechanoreceptors, and of its implication in some human genetic diseases.

Amiloride↗
PubMed1994

Expression of 11 beta-OHSD along the nephron of mammals and humans.

The enzyme 11 beta-hydroxysteroid dehydrogenase (11 beta-OHSD) plays a major role in the protection of the mineralocorticoid receptor (MR). This cellular mechanism of aldosterone selectivity relies on the coexpression of MR and 11 beta-OHSD in the same cells. Localization of renal 11 beta-OHSD along the nephron is reviewed; comparison of data contained in different species is made; and original data is presented to show that the catalytic activity of the enzyme in tubules from human kidney is the highest in the mineralocorticoid-sensitive distal nephron.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1994

Cell-specific expression of epithelial sodium channel alpha, beta, and gamma subunits in aldosterone-responsive epithelia from the rat: localization by in situ hybridization and immunocytochemistry.

A highly selective, amiloride-sensitive, epithelial sodium channel from rat colon (rENaC), composed of three homologous subunits termed alpha, beta, and gamma rENaC, has been cloned by functional expression and was proposed to mediate electrogenic sodium reabsorption in aldosterone-responsive epithelia. To determine whether rENaC could account for sodium absorption in vivo, we studied the cellular localization of the sodium channel messenger RNA subunits by in situ hybridization and their cellular and subcellular distribution by immunocytochemistry in the kidney, colon, salivary, and sweat glands of the rat. In the kidney, we show that the three subunit mRNAs are specifically co-expressed in the renal distal convoluted tubules (DCT), connecting tubules (CNT), cortical collecting ducts (CCD), and outer medullary collecting ducts (OMCD), but not in the inner medullary collecting ducts (IMCD). We demonstrate co-localization of alpha, beta, and gamma subunit proteins in the apical membrane of a majority of cells of CCD and OMCD. Our data indicate that alpha, beta, and gamma subunit mRNAs and proteins are co-expressed in the distal nephron (excepting IMCD), a localization that correlates with the previously described physiological expression of amiloride-sensitive electrogenic sodium transport. Our data, however, suggest that another sodium transport protein mediates electrogenic amiloride-sensitive sodium reabsorption in IMCD. We also localized rENaC to the surface epithelial cells of the distal colon and to the secretory ducts of the salivary gland and sweat gland, providing further evidence consistent with the hypothesis that the highly selective, amiloride-sensitive sodium channel is physiologically expressed in aldosterone-responsive cells.

Aldosterone↗
PubMed1994

Aldosterone selectively increases Na(+)-K(+)-ATPase alpha 3-subunit mRNA expression in rat hippocampus.

In the brain, corticosteroids bind to intracellular glucocorticoid (GR) and mineralocorticoid (MR) receptors, affecting target gene transcription, and thereby altering neuronal function, including electrophysiological activity. The hippocampus very highly expresses both MR and GR; however, MR-regulated hippocampal transcripts have not yet been described. We investigated the effects of adrenalectomy +/- glucocorticoid or mineralocorticoid replacement on expression of mRNAs encoding alpha-subunit isoforms of Na(+)-K(+)-adenosinetriphosphatase, a critical transmembrane ion gradient-regulating enzyme. Aldosterone significantly increased alpha 3-subunit mRNA expression in dentate gyrus granule cells (62% increase compared with adrenalectomy) and in CA1 and CA4 hippocampal neurons (37 and 38%), but not in CA2, CA3, parietal cortex neurons, or glia. This effect was not reproduced by dexamethasone, and none of the corticosteroid manipulations altered alpha 1- or alpha 2-subunit mRNA expression at any site examined. Aldosterone-mediated upregulation of hippocampal alpha 3-subunit mRNA expression may underlie, at least in part, the specific actions of MR ligands on hippocampal function. The observation that aldosterone differentially affects alpha 3-isoform mRNA expression in distinct neuronal populations, associated with the established aldosterone modulations of alpha 1-isoform mRNA in epithelial cells, supports the presence of cell-specific factors that regulate MR-mediated transcriptional activity.

Adrenal Cortex Hormones↗
PubMed1994

Role of cell volume variations in Na(+)-K(+)-ATPase recruitment and/or activation in cortical collecting duct.

The aim of this study was to examine whether cell volume variations could play a role in the previously reported Na(+)-K(+)-ATPase pump recruitment and/or activation induced by an increase in intracellular Na concentration (Nai) in cortical collecting ducts (CCD). Isolated CCD from kidneys of aldosterone-repleted mice were incubated in hyper-, hypo-, or isosmotic solutions with and without Na to modify Nai and cell volume independently. Nai, cell volume, and the number of basolateral pumps were measured using 22Na, image analysis, and specific [3H]ouabain binding, respectively. Ouabain-sensitive 86Rb uptake was also measured. In CCD with high Nai, pump recruitment and/or activation was observed only when an increase in tubular volume was associated with Na load. Pump recruitment and/or activation was also induced by cell swelling in the absence of Na load. Recruited and/or activated pumps display an affinity for ouabain and a specific activity (ouabain-sensitive Rb uptake per pump unit) similar to basal pumps. We conclude that 1) cell swelling is implied in the process of Nai-dependent pump recruitment and/or activation, 2) cell swelling can promote pump recruitment and/or activation independently of Na load, 3) basal and recruited and/or activated pumps probably correspond to the same Na(+)-K(+)-ATPase isoform.

Animals↗
PubMed1994

The mineralocorticoid receptor discriminates aldosterone from glucocorticoids independently of the 11 beta-hydroxysteroid dehydrogenase.

To investigate the mechanisms involved in the in vivo aldosterone selectivity of the mineralocorticoid receptor (MR), we studied the respective contribution of the receptor and the enzyme 11 beta-hydroxysteroid dehydrogenase (11HSD), which converts glucocorticoids into inactive metabolites. Using a cotransfection assay in CV-1 cells, aldosterone activated mouse mammary tumor virus promoter through human MR (hMR) with an ED50 of 0.01 nM. An at least 100-fold higher concentration of cortisol (F), corticosterone (B), or dexamethasone was required to obtain half-maximum transactivation, indicating a functional preference of hMR for aldosterone over glucocorticoids. The catalytic activity of 11HSD was analyzed using HPLC by measuring the tritiated metabolites produced in CV-1 and COS cells. Both cell types displayed a significant dehydrogenase activity (20 fmol/10 min.10(3) cells) inhibitable by carbenoxolone, but no detectable reductase activity. In this model, B was more rapidly metabolized than F. Carbenoxolone treatment of hMR-transfected CV-1 cells did not result in a shift of the dose-response transactivation curves of B and F toward lower concentrations, ruling out the implication of 11HSD in the aldosterone MR selectivity of these conditions. Despite similar affinity constants of aldosterone and glucocorticoids for the hMR, kinetic experiments showed that the off-rate of aldosterone from hMR was 5 times lower than that of glucocorticoids, pointing to an intrinsic discriminating property of the receptor. Therefore, we propose that in addition to 11HSD, MR plays an active role in the mechanism of aldosterone selectivity.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1994

Human skin as target for aldosterone: coexpression of mineralocorticoid receptors and 11 beta-hydroxysteroid dehydrogenase.

The expression of mineralocorticoid receptors (MR) and 11 beta-hydroxysteroid dehydrogenase (11HSD) activity has been investigated in the epidermis and appendages of the human skin. Aldosterone binds to MR and regulates sodium transport in tight epithelia. Mineralocorticoid selectivity is achieved through coexpression of MR and 11HSD, which prevents permanent MR occupancy by glucocorticoids. Some forms of hypertension may involve abnormalities of MR and/or 11HSD. However, their direct assessment in humans remains difficult in the kidney or colon. This led us to explore this system in human skin easily accessible to biopsy. In situ hybridization with specific MR complementary ribonucleic acid probes and immunohistochemistry using three different anti-MR antibodies showed that MR was expressed at both the messenger ribonucleic acid and protein levels in the keratinocytes of the epidermis, in the sweat and sebaceous glands, and in the hair follicles. A significant 11HSD activity was found in isolated sweat gland ducts (5 fmol/3-mm length.10-min incubation with 10 nmol/L corticosterone as substrate) and was very low in the epidermis. In both structures, reductase activity was 10 times lower than that of dehydrogenase. Studies on the cofactor specificity of the enzyme showed a nicotinamide-adenine-dinucleotide preference in sweat glands, contrasting with a nicotinamide-adenine-dinucleotide phosphate dependence in epidermis. Human skin appears as a new target for aldosterone because it coexpresses MR and 11HSD. Our findings present the possibility to explore the functionality of the MR system in human tissue and its implications in various physiopathological situations.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1993

Mineralocorticoid receptors in SV40-transformed tubule cell lines derived from rabbit kidney.

The presence of mineralocorticoid (MR) and glucocorticoid (GR) receptors was investigated in two renal tubular cell lines, derived from primary cultures of isolated rabbit kidney cortical cells infected with the wild-type SV40 virus, which exhibit thick ascending limb (RC.SV2) and collecting tubule (RC.SV3) phenotypes (Vandewalle et al. J. Cell. Physiol. 141, 1989, 203-221). MR and GR were quantified, in cell monolayers and cell cytosolic fractions, with [3H]aldosterone, [3H]dexamethasone and [3H]RU486, an antiglucocorticoid with no affinity for MR. Cytosolic receptors from RC.SV2 and RC.SV3 cells labeled with [3H]aldosterone, [3H]dexamethasone or [3H]RU486 sedimented at approximately 8 S in a 15-40% glycerol gradient. All steroids displaced bound [3H]dexamethasone to the same extent, suggesting that dexamethasone bound to both MR and GR: under the conditions of assay, [3H]aldosterone binds exclusively to MR, and [3H]RU486 to GR. In both RC.SV2 and RC.SV3 cells, [3H]aldosterone bound to one class of high affinity sites (Kd 0.14-0.8 nM; Nmax 8 to 22 fmol/mg protein). In both cell lines, the number of high affinity binding sites for [3H]dexamethasone ranged from 9 to 18 fmol/mg protein with an affinity of 0.5-1.3 nM. Compared to renal cortex, the most striking observation was a marked decrease in [3H]dexamethasone binding in primary cultures and SV40-transformed cells. These results indicate that MR and GR are expressed in two established mammalian kidney tubular cell lines providing new models of cultured renal cells for studies on the physiological effects of corticosteroid hormones.

Aldosterone↗
PubMed1993

A putative H(+)-K(+)-ATPase is selectively expressed in surface epithelial cells of rat distal colon.

Recently, a putative distal colon H(+)-K(+)-ATPase alpha-subunit has been identified and characterized (M. S. Crowson and G. E. Shull. J. Biol. Chem. 267:13740-13748, 1992). In the present study, we report the tissue and cell expression of this putative H(+)-K(+)-ATPase. The results indicate that, first, in the gut, the putative H(+)-K(+)-ATPase alpha-subunit is restricted to the distal part of the colon and is predominantly expressed in surface epithelial cells, in marked contrast to the alpha 1-subunit of Na(+)-K(+)-ATPase that is also expressed in glands. These data suggest that the H(+)-K(+)-ATPase alpha-subunit is a potential marker for terminal differentiation of distal colon. Second, in the uterus, the putative H(+)-K(+)-ATPase is restricted to the region of the myometrium between the inner and midmuscular zone that is very rich in vascular supply and nerve cells. This striking expression suggests that the H(+)-K(+)-ATPase may not be involved in the control of pH and potassium concentration of the uterine fluid but rather in distinct functions of vascular and/or nerve cells. Third, with the use of three independent and different approaches (Northern blot analysis, ribonuclease protection assay, and in situ hybridization), we were unable to detect any significant amount of H(+)-K(+)-ATPase transcripts in kidney tissue. Our data suggest that the putative distal colon H(+)-K(+)-ATPase is probably distinct from the kidney isoform. Finally, we report the sequence of a set of degenerate oligonucleotides that are useful to clone alpha-subunits of the Na(+)-K(+)-/H(+)-K(+)-ATPase gene family in different tissues and different species.

Animals↗
PubMed1993

Rat liver 11 beta-hydroxysteroid dehydrogenase complementary deoxyribonucleic acid encodes oxoreductase activity in a mineralocorticoid-responsive toad bladder cell line.

The mineralocorticoid receptor displays equal affinity for aldosterone and corticosterone. It has been proposed that aldosterone selectivity in vivo is achieved by the conversion of corticosterone into its inactive metabolite 11-dehydrocorticosterone by 11 beta-hydroxysteroid dehydrogenase (11 beta HSD). To test this hypothesis, we transfected rat liver 11 beta HSD cDNA into TBM cells, a sodium-transporting cell line. These cells respond equally well to aldosterone and corticosterone, indicating that endogenous 11 beta HSD is expressed at low levels in TBM cells. Although exogenous rat liver 11 beta HSD was expressed at high levels in transfected cells, mineralocorticoid selectivity was not observed. By contrast, the biologically inactive 11-dehydrocorticosterone was readily converted into corticosterone, a potent agonist for sodium transport. Our results indicate that rat liver 11 beta HSD behaves predominantly as a reductase in TBM cells. Another 11 beta HSD isoform is likely to be responsible for the dehydrogenase reaction in aldosterone-responsive cells.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1993

[Recent aspects of the action of aldosterone].

As described for other steroid hormones, aldosterone action in its target cells involves the binding to intracellular receptors, which modulate the expression of some genes. Recent progress in the field involves: the molecular structure of the mineralocorticoid receptor (MR) which has been cloned; the effects of MR on transcription; the hetero-oligomeric structure of MR; its tissue-specific distribution; the identification of 11 beta-hydroxysteroid dehydrogenase as an enzyme responsible for mineralocorticoid specificity. Finally, the effects of aldosterone at the cellular and molecular level are now better known. From the precise integrative view of its action on the kidney, the recent fields of this research extend to cellular and molecular understanding of aldosterone action.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1992

Multiple patterns of 11 beta-hydroxysteroid dehydrogenase catalytic activity along the mammalian nephron.

The enzyme 11 beta-hydroxysteroid dehydrogenase (11 beta-OHSD) is thought to be a protective enzyme of the mineralocorticoid receptor (MR). We have previously demonstrated (Bonvalet et al, J Clin Invest 86:832-837, 1990) that 11 beta-OHSD is colocalized with MR along the rabbit nephron. In the present study, we examined whether 11 beta-OHSD is similarly located along the nephron of other mammals. Various tubular segments were microdissected from the mouse, rat, and rabbit nephron, and incubated for two hours at 37 degrees C in the presence of 11 nM [3H]-corticosterone (B). Thereafter, the respective amounts of B and [3H]-11dehydrocorticosterone (A) in the incubation solution were measured by HPLC. In the rabbit, the mouse and the rat, about 520 pmol/10 mm of B were transformed into A in tubular segments possessing MR, that is, the distal parts of the nephron (distal and collecting tubule). Differences appeared in the aldosterone-insensitive proximal tubule; in both the initial and final parts of this segment, 11 beta-OHSD activity was low (26 pmol/10 mm) in the rabbit and the mouse, and relatively high in the rat (328 pmol/10 mm). In the cortical part of the loop of Henle, where the presence of MR is still under discussion, 11 beta-OHSD activity was low in the mouse (70 pmol/10 mm), high in the rat (533 pmol/10 mm) and intermediate in the rabbit (227 pmol/10 mm). The comparison of these results with previous data obtained with immunohistochemical methods suggests that the proximal and distal nephron might express different isoforms of 11 beta-OHSD.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1992

Time course of sodium-induced Na(+)-K(+)-ATPase recruitment in rabbit cortical collecting tubule.

In cortical collecting tubules (CCD) of aldosterone-repleted rabbit kidney, an increase in intracellular sodium concentration (Nai) induces the recruitment and/or activation of latent Na(+)-K(+)-ATPase pumps (Blot-Chabaud et al., J. Biol. Chem. 265: 11676-11681, 1990). The present study was addressed to determine the time course of this Nai-dependent pump recruitment and to examine some of the factors possibly involved in this phenomenon. CCD from adrenalectomized rabbits complemented with aldosterone and dexamethasone were incubated at 4 degrees C either in a K(+)-free saline solution (Na(+)-loaded CCD) or in a sucrose solution (control CCD) and then rewarmed for various time periods to allow pump recruitment to occur. The number of pumps in the membrane was determined by specific [3H]ouabain binding; Nai was measured using 22Na. A rise in Nai induced a threefold increase in the number of basolateral pumps, which was fully achieved within 1-2 min. This pump recruitment was reversible within 15 min after restoration of low Nai. It was unaffected by inhibitors of cytoskeleton and Ca2+ ionophore A 23187. The blocker of the Na(+)-H+ antiporter, amiloride, did not prevent it. The protein kinase C activator, phorbol 12-myristate 13-acetate, did not induce it in the absence of Na+. We conclude that Nai is a major determinant of pump recruitment and/or activation, which occurs over a very short period of time. It may constitute a rapid adaptative response to an increase in the cell Na+ load.

Animals↗
PubMed1992

Adrenalectomy reduces alpha 1 and not beta 1 Na(+)-K(+)-ATPase mRNA expression in rat distal nephron.

The abundance of mRNA of alpha 1-, alpha 2-, alpha 3-, beta 1-, and beta 2-isoforms of Na(+)-K(+)-ATPase was examined in several renal structures of normal and adrenalectomized (ADX) rats. In situ hybridization with 35S-labeled cRNA probes was performed on kidney sections from adult rats. The number of silver grains per unit surface area was quantified over cells of the glomerulus, proximal convoluted tubules (PCT), early distal tubules (EDT), and cortical collecting ducts (CCD). In normal rat kidney, alpha 1- and beta 1-mRNA was detected in PCT, EDT, and CCD, with the following range of magnitude: EDT > CCD > PCT > glomerulus. The amount of alpha 1- and beta 1-mRNA was equivalent. A large abundance of these two mRNA species was also found in the medullary thick ascending limb of the loop of Henle. Expression of alpha 2, alpha 3, and beta 2 was very low and evenly distributed over any cell type. In ADX, a significant decrease in alpha 1-mRNA (30%) was observed in EDT and CCD, with no change in PCT. beta 1-mRNA abundance was unaffected by adrenalectomy. These results indicate that 1) in the rat kidney alpha 1- and beta 1-mRNA are coexpressed at a similar level that varies along the renal tubule according to the cell type, 2) minute expression of alpha 2-, alpha 3-, and beta 2-mRNA is present in the kidney, and 3) corticosteroid depletion reduces the expression of alpha 1- and not beta 1-mRNA in the corticosteroid-sensitive tubular cells.

Adrenalectomy↗
PubMed1992

Immunohistochemical and biochemical evidence for a cardiovascular mineralocorticoid receptor.

The presence of mineralocorticoid receptors (MRs) and their physicochemical characteristics were investigated in the heart and blood vessels of rabbits. Immunohistochemical methods using the monoclonal anti-idiotypic antibody H10E, which interacts with the steroid binding domain of MRs, revealed the presence of immunoreactive material in the heart and large blood vessels. In the heart, a positive staining was observed in myocytes and endothelial cells of atria and ventricles. In vessels, MRs were detected in the aorta and pulmonary artery. They were localized in endothelial and vascular smooth muscle cells. No staining was present in the small vascular bed, arterioles, and capillaries. In all these studies, the mineralocorticoid specificity of the staining was assessed by in situ competition experiments with aldosterone and RU486, a glucocorticoid antagonist. The presence of MRs in the heart and vessels was further demonstrated by specific aldosterone binding to one class of high affinity binding sites in the cytosol of the adrenalectomized rabbit heart (Kd, 0.25 nM; maximum MR concentration, 15-20 fmol/mg protein), whose mineralocorticoid specificity has been clearly established by competition studies. Sedimentation gradient analyses revealed that the cardiovascular MR is an 8.5S hetero-oligomer that includes the heat shock protein 90. The physicochemical characteristics of the cardiovascular MRs are virtually identical to those of the renal MRs. Altogether, our results clearly demonstrate the presence of MRs in the cardiovascular system. This supports the possibility of direct aldosterone actions in the heart and blood vessels.

Adrenalectomy↗