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Na+/H+ Exchanger (na+/h+ + exchanger)
Terms modified by Na+/H+ Exchanger Selected AbstractsRelative contribution of V-H+ATPase and NA+/H+ exchanger to bicarbonate reabsorption in proximal convoluted tubules of old ratsAGING CELL, Issue 5 2006Mariana Fiori Summary With aging, the kidney develops a progressive deterioration of several structures and functions. Proximal tubular acidification is impaired in old rats with a decrease in the activity of brush border Na+/H+ exchange and a fall of H-ion flux measured with micropuncture experiments. In the present work we evaluate the contribution of 5-N-ethyl-n-isopropyl amiloride- (EIPA) and bafilomycin-sensitive bicarbonate flux () in proximal convoluted tubules of young and aged rats. We performed micropuncture experiments inhibiting the Na+/H+ exchanger with EIPA (10,4 M) and the V-H+ATPase with bafilomycin (10,6 M). We used antibodies against the NHE3 isoform of the Na+/H+ exchanger and the subunit E of the V-H+ATPase for detecting by Western blot the abundance of these proteins in brush border membrane vesicles from proximal convoluted tubules of young and old rats. The abundance of NHE3 and the V-H+ATPase was similar in 18-month-old and 3-month-old rats. The bicarbonate flux in old rats was 30% lower than in young rats. EIPA reduced by 60% and bafilomycin by 30% in young rats; in contrast, EIPA reduced by ,40% and bafilomycin by ,50% in old rats. The inhibited by bafilomycin was the same in young and old rats: 0.62 nmol · cm,2· s,1 and 0.71 nmol · cm,2· s,1, respectively. However, the EIPA-sensitive fraction was larger in young than in old rats: 1.26 nmol · cm,2· s,1 vs. 0.85 nmol · cm,2· s,1, respectively. These results suggest that the component more affected in bicarbonate reabsorption of proximal convoluted tubules from aged rats is the Na+ -H+ exchanger, probably a NHE isoform different from NHE3. [source] Functional analysis of polar amino-acid residues in membrane associated regions of the NHE1 isoform of the mammalian Na+/H+ exchangerFEBS JOURNAL, Issue 17 2001Rakhilya Murtazina The NHE1 isoform of the Na+/H+ exchanger is a ubiquitous plasma membrane protein that regulates intracellular pH in mammalian cells. Site-specific mutagenesis was used to examine the functional role of conserved, polar amino-acid residues occurring in segments of the protein associated with the membrane. Seventeen mutant proteins were assessed by characterization of intracellular pH changes in stably transfected cells that lacked an endogenous Na+/H+ exchanger. All of the mutant proteins were targeted correctly to the plasma membrane and were expressed at similar levels. Amino-acid residues Glu262 and Asp267 were critical to Na+/H+ exchanger activity while mutation of Glu391 resulted in only a partial reduction in activity. The Glu262,Gln mutant was expressed partially as a deglycosylated protein with increased sensitivity to trypsin treatment in presence of Na+. Substitution of mutated Glu262, Asp267 and Glu391 with alternative acidic residues restored Na+/H+ exchanger activity. The Glu262,Asp mutant had a decreased affinity for Li+, but its activity for Na+ and H+ ions was unaffected. The results support the hypothesis that side-chain oxygen atoms in a few, critically placed amino acids are important in Na+/H+ exchanger activity and the acidic amino-acid residues at positions 262, 267 and 391 are good candidates for being involved in Na+ coordination by the protein. [source] Defective regulation of cholangiocyte Cl,/HCO,3 and Na+/H+ exchanger activities in primary biliary cirrhosisHEPATOLOGY, Issue 6 2002Saida Melero Primary biliary cirrhosis (PBC) is a disorder of unknown origin with autoimmune features. Recently, impaired biliary secretion of bicarbonate has been shown in patients with PBC. Here we have investigated whether bile duct epithelial cells isolated from PBC patients exhibit defects in transepithelial bicarbonate transport by analyzing the activities of 2 ion exchangers, Cl,/HCO,3 anion exchanger 2 (AE2) and Na+/H+ exchanger (NHE) in isolated cholangiocytes. AE2 and NHE activities were studied in basal conditions and after stimulation with cyclic adenosine monophosphate (cAMP) and extracellular adenosine triphosphate (ATP), respectively. Cholangiocytes were grown from needle liver biopsies from 12 PBC patients, 8 normal controls, and 9 patients with other liver diseases. Also, intrahepatic cholangiocytes were cultured after immunomagnetic isolation from normal liver tissue (n = 6), and from recipients undergoing liver transplantation for end-stage PBC (n = 9) and other forms of liver disease (n = 8). In needle-biopsy cholangiocytes, basal AE2 activity was significantly decreased in PBC as compared with normal livers and disease controls. In addition, we observed that though cAMP increased AE2 activity in cholangiocytes from both normal and non-PBC livers, this effect was absent in PBC cholangiocytes. Similarly, though in cholangiocytes from normal and disease control livers extracellular ATP induced a marked enhancement of NHE activity, cholangiocytes from PBC patients failed to respond to purinergic stimulation. In conclusion, our findings provide functional evidence that PBC cholangiocytes exhibit a widespread failure in the regulation of carriers involved in transepithelial H+/HCO,3 transport, thus, providing a molecular basis for the impaired bicarbonate secretion in this cholestatic syndrome. [source] Modulation of Na+ transport across isolated rumen epithelium by short-chain fatty acids in hay- and concentrate-fed sheepJOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 11-12 2003S. K. Uppal Summary The effect of increasing concentrations of short-chain fatty acids [SCFA; mixture of the Na+ salts of acetic acid (62.5%), propionic acid (25.0%) and of butyric acid (12.5%)] on Na+ transport of sheep rumen epithelium was studied in vitro. The conventional Ussing chamber method was used for measuring Na+ transport rates (22Na+), short-circuit current (Isc) and tissue conductance (GT) of isolated rumen epithelium. SCFA in the buffer solution on the mucosal side caused a linear increase of Jnet Na+ from 1.14, to 1.22, 1.78 and 2.50 ,eq/cm2/h in hay-fed sheep at 0, 15, 40 and 80 mmol/l SCFA, respectively. In a second study, the effect of higher SCFA concentrations [0 (control), 80, 100 and 120 mmol/l] was investigated with epithelia from two groups of sheep. One group was subjected to hay ad libitum, whereas the other received concentrate feed (800 g/day in equal portions at 7.00 am and 3.00 pm) and hay ad libitum. Epithelia from concentrate-fed sheep again showed a significant (p < 0.05) and linear increase in Jnet Na+ at 80, 100 and 120 mmol/l. However, in hay-fed sheep, the difference in increase among 80, 100 and 120 mmol/l SCFA was not significant, indicating that, above 80 mmol/l SCFA Jms and Jnet exhibit saturation. Moreover, Na+ fluxes (Jms and Jnet) were generally higher in concentrate-fed than in hay-fed sheep at all SCFA concentrations and significant differences were observed at 100 and 120 mmol/l SCFA. The obtained results confirm the effect of SCFA on Na+ transport and are in agreement with studies regarding feeding regimes and electrolyte transport in the rumen. The important new observation is the increase of Na+ transport in concentrate-fed sheep even at high concentrations of SCFA (100 and 120 mmol/l). The enhanced activity of the Na+/H+ exchanger at these SCFA concentrations supports the assumption that the capacity for regulating the intracellular pH by extrusion of protons is increased, suggesting an adaptation in concentrate-fed sheep. This adaptation could prevent possible disturbances of epithelial functions (transport and barrier) under conditions of increased SCFA absorption. [source] Inhibitors of the Na+/H+ Exchanger Cannot Prevent Atrial Electrical Remodeling in the GoatJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 4 2004YURI BLAAUW M.D. Introduction: It has been suggested that blockade of the Na+/H+ exchanger (NHE1) can prevent atrial fibrillation (AF)-induced electrical remodeling and the development of AF. Methods and Results: AF was maintained by burst pacing in 10 chronically instrumented conscious goats. Intravenous and oral dosages of two NHE1 blockers (EMD87580 and EMD125021) resulted in plasma levels several magnitudes higher than required for effective NHE1 blockade. Shortening of atrial refractoriness immediately after 5 minutes of AF was not prevented by NHE1 blockade. In remodeled atria, increasing dosages of EMD87580 and EMD125021 did not reverse shortening of the atrial refractory period or reduce the duration of AF episodes. The cycle length during persistent AF also was not affected. Oral pretreatment with EMD87580 (8 mg/kg bid) starting 3 days before AF could not prevent electrical remodeling. After 24 and 48 hours of remodeling, the duration of AF paroxysms was 47 ± 32 seconds and 135 ± 63 seconds compared to 56 ± 17 seconds and 136 ± 52 seconds in placebo-treated animals (P > 0.8), respectively. Conclusion: In the goat model of AF, the Na+/H+ exchanger inhibitors EMD87580 and EMD125021 did not prevent or revert AF-induced electrical remodeling. This indicates that activation of the Na+/H+ exchanger is not involved in the intracellular pathways of electrical remodeling. This does not support the suggestion that blockers of the Na+/H+ exchanger may be beneficial for prevention and treatment of AF. (J Cardiovasc Electrophysiol, Vol. 15, pp. 440-446, April 2004) [source] Oxidative stress and longevity in Caenorhabditis elegans as mediated by SKN-1AGING CELL, Issue 3 2009Sang-Kyu Park Summary Oxidative stress has been hypothesized to play a role in normal aging. The response to oxidative stress is regulated by the SKN-1 transcription factor, which also is necessary for intestinal development in Caenorhabditis elegans. Almost a thousand genes including the antioxidant and heat-shock responses, as well as genes responsible for xenobiotic detoxification were induced by the oxidative stress which was found using transcriptome analysis. There were also 392 down-regulated genes including many involved in metabolic homeostasis, organismal development, and reproduction. Many of these oxidative stress-induced transcriptional changes are dependent on SKN-1 action; the induction of the heat-shock response is not. When RNAi to inhibit genes was used, most had no effect on either resistance to oxidative stress or longevity; however two SKN-1-dependent genes, nlp-7 and cup-4, that were up-regulated by oxidative stress were found to be required for resistance to oxidative stress and for normal lifespan. nlp-7 encodes a neuropeptide-like protein, expressed in neurons, while cup-4 encodes a coelomocyte-specific, ligand-gated ion channel. RNAi of nlp-7 or cup-4 increased sensitivity to oxidative stress and reduced lifespan. Among down-regulated genes, only inhibition of ent-1, a nucleoside transporter, led to increased resistance to oxidative stress; inhibition had no effect on lifespan. In contrast, RNAi of nhx-2, a Na+/H+ exchanger, extended lifespan significantly without affecting sensitivity to oxidative stress. These findings showed that a transcriptional shift from growth and maintenance towards the activation of cellular defense mechanisms was caused by the oxidative stress; many of these transcriptional alterations are SKN-1 dependent. [source] Relative contribution of V-H+ATPase and NA+/H+ exchanger to bicarbonate reabsorption in proximal convoluted tubules of old ratsAGING CELL, Issue 5 2006Mariana Fiori Summary With aging, the kidney develops a progressive deterioration of several structures and functions. Proximal tubular acidification is impaired in old rats with a decrease in the activity of brush border Na+/H+ exchange and a fall of H-ion flux measured with micropuncture experiments. In the present work we evaluate the contribution of 5-N-ethyl-n-isopropyl amiloride- (EIPA) and bafilomycin-sensitive bicarbonate flux () in proximal convoluted tubules of young and aged rats. We performed micropuncture experiments inhibiting the Na+/H+ exchanger with EIPA (10,4 M) and the V-H+ATPase with bafilomycin (10,6 M). We used antibodies against the NHE3 isoform of the Na+/H+ exchanger and the subunit E of the V-H+ATPase for detecting by Western blot the abundance of these proteins in brush border membrane vesicles from proximal convoluted tubules of young and old rats. The abundance of NHE3 and the V-H+ATPase was similar in 18-month-old and 3-month-old rats. The bicarbonate flux in old rats was 30% lower than in young rats. EIPA reduced by 60% and bafilomycin by 30% in young rats; in contrast, EIPA reduced by ,40% and bafilomycin by ,50% in old rats. The inhibited by bafilomycin was the same in young and old rats: 0.62 nmol · cm,2· s,1 and 0.71 nmol · cm,2· s,1, respectively. However, the EIPA-sensitive fraction was larger in young than in old rats: 1.26 nmol · cm,2· s,1 vs. 0.85 nmol · cm,2· s,1, respectively. These results suggest that the component more affected in bicarbonate reabsorption of proximal convoluted tubules from aged rats is the Na+ -H+ exchanger, probably a NHE isoform different from NHE3. [source] The gene sll0273 of the cyanobacterium Synechocystis sp. strain PCC6803 encodes a protein essential for growth at low Na+/K+ ratiosPLANT CELL & ENVIRONMENT, Issue 6 2000S. Mikkat ABSTRACT A mutant of Synechocystis sp. strain PCC6803 was obtained by random cartridge mutagenesis, which could not grow at low sodium concentrations. Genetic analyses revealed that partial deletion of the sll0273 gene, encoding a putative Na+/H+ exchanger, was responsible for this defect. Physiological characterization indicated that the sll0273 mutant exhibited an increased sensitivity towards K+, even at low concentrations, which was compensated for by enhanced concentrations of Na+. This enhanced Na+ demand could also be met by Li+. Furthermore, addition of monensin, an ionophore mediating electroneutral Na+/H+ exchange, supported growth of the mutant at unfavourable Na+/K+ ratios. Measurement of internal Na+ and K+ contents of wild-type and mutant cells revealed a decreased Na+/K+ ratio in mutant cells pre-incubated at a low external Na+/K+ ratio, while it remained at the level of the wild type after pre-incubation at a high external Na+/K+ ratio. We conclude that the Sll0273 protein is required for Na+ influx, especially at low external Na+ concentrations or low Na+/K+ ratios. This system may be part of a sodium cycle and may permit re-entry of Na+ into the cells, if nutrient/Na+ symporters are not functional or operating. [source] 5-(N -ethyl-N-isopropyl)-amiloride enhances SMN2 exon 7 inclusion and protein expression in spinal muscular atrophy cellsANNALS OF NEUROLOGY, Issue 1 2008Chung-Yee Yuo PhD Objective Spinal muscular atrophy (SMA) is a common inherited neuromuscular disorder caused by homozygous loss of function of the survival motor neuron 1 (SMN1) gene. All SMA patients carry at least one copy of a nearly identical SMN2 gene. However, a critical nucleotide change in SMN2 results in alternative splicing and exclusion of exon 7 in the majority of SMN2 messenger RNA (mRNA), thus producing a low level of functional SMN protein. Increasing SMN protein production by promoting SMN2 exon 7 inclusion could be a therapeutic approach for SMA. It has been shown that cellular pH microenvironment can modulate pre-mRNA alternative splicing in vivo. In this study, we tested whether inhibitors of the Na+/H+ exchanger can modulate the exon 7 splicing of SMN2 mRNA Methods We treated SMA lymphoid cell lines with Na+/H+ exchanger inhibitors and then measured SMN2 exon 7 splicing by reverse transcriptase polymerase chain reaction and SMN protein production by Western blotting and immunofluorescence Results We found that treatment with an Na+/H+ exchanger inhibitor, 5-(N -ethyl-N-isopropyl)-amiloride (EIPA), significantly enhances SMN2 exon 7 inclusion and SMN protein production in SMA cells. In addition, EIPA increases the number of nuclear gems in SMA cells. We further explored the underlying mechanism, and our results suggest that EIPA may promote SMN2 exon 7 inclusion through upregulation of the splicing factor SRp20 in the nucleus Interpretation Our finding that EIPA, an inhibitor of the Na+/H+ exchanger, can increase SMN protein expression in SMA cells provides a new direction for the development of drugs for SMA treatment. However, further translational studies are needed to determine whether this finding is applicable for SMA treatment or just a proof of cellular pH effect on SMN splicing. Ann Neurol 2007 [source] Docosahexaenoic acid and other fatty acids induce a decrease in pHi in Jurkat T-cellsBRITISH JOURNAL OF PHARMACOLOGY, Issue 7 2003Virginie Aires Docosahexaenoic acid (DHA) induced rapid (t1/2=33 s) and dose-dependent decreases in pHi in BCECF-loaded human (Jurkat) T-cells. Addition of 5-(N,N -dimethyl)-amiloride, an inhibitor of Na+/H+ exchanger, prolonged DHA-induced acidification as a function of time, indicating that the exchanger is implicated in pHi recovery. Other fatty acids like oleic acid, arachidonic acid, eicosapentaenoic acid, but not palmitic acid, also induced a fall in pHi in these cells. To assess the role of calcium in the DHA-induced acidification, we conducted experiments in Ca2+ -free (0% Ca2+) and Ca2+ -containing (100% Ca2+) buffer. We observed that there was no difference in the degree of DHA-induced transient acidification in both the experimental conditions, though pHi recovery was faster in 0% Ca2+ medium than that in 100% Ca2+ medium. In the presence of BAPTA, a calcium chelator, a rapid recovery of DHA-induced acidosis was observed. Furthermore, addition of CaCl2 into 0% Ca2+ medium curtailed DHA-evoked rapid pHi recovery. In 0% Ca2+ medium, containing BAPTA, DHA did not evoke increases in [Ca2+]i, though this fatty acid still induced a rapid acidification in these cells. These observations suggest that calcium is implicated in the long-lasting DHA-induced acidosis. DHA-induced rapid acidification may be due to its deprotonation in the plasma membrane (flip-flop model), as suggested by the following observations: (1) DHA with a ,COOH group induced intracellular acidification, but this fatty acid with a ,COOCH3 group failed to do so, and (2) DHA, but not propionic acid, -induced acidification was completely reversed by addition of fatty acid-free bovine serum albumin in these cells. These results suggest that DHA induces acidosis via deprotonation and Ca2+ mobilization in human T-cells. British Journal of Pharmacology (2003) 140, 1217,1226. doi:10.1038/sj.bjp.0705563 [source] Pharmacological profile of SL 59.1227, a novel inhibitor of the sodium/hydrogen exchangerBRITISH JOURNAL OF PHARMACOLOGY, Issue 6 2000Janine Lorrain The NHE1 isoform of the Na+/H+ exchanger plays an important role in the regulation of intracellular pH and in cardiac cell injury caused by ischaemia and reperfusion. SL 59.1227 is a novel imidazolypiperidine Na+/H+ antiport inhibitor which is structurally unrelated to previously described acylguanidine inhibitors such as cariporide. Recovery of pHi following an intracellular acid load was measured in CCL39-derived PS120 variant cells, selectively expressing either NHE1 or NHE2 isoforms of the Na+/H+ exchanger. pHi recovery was potently and selectively slowed by SL 59.1227 in NHE1-expressing cells (IC50 3.3±1.3 nM) versus NHE2-expressing cells (2.3±1.0 ,M). The respective IC50 values for cariporide were 103±28 nM (NHE1) and 73±46 ,M (NHE2). In anaesthetized rats following left coronary artery occlusion (7 min) and reperfusion (10 min) SL 59.1227 (10,100 ,g kg,1 min,1 i.v.) inhibited ischaemia-mediated ventricular tachycardia (71,100%) and reperfusion-induced ventricular fibrillation (75,87%) and prevented mortality. Bolus i.v. administration of SL 59.1227 (1 mg kg,1) produced anti-arrhythmic effects when administered either before or during ischaemia. Cardiac infarct size was determined in anaesthetized rabbits following left coronary artery occlusion (30 min) and reperfusion (120 min). Infarct size measured as a percentage of the area at risk was 36.2±3.4% (control group) versus 15.3±3.9% (SL 59.1227 0.6 mg kg,1 i.v.). SL 59.1227 is the first example of a potent and NHE1-selective non-acylguanidine Na+/H+ exchanger inhibitor. It possesses marked cardioprotective properties. British Journal of Pharmacology (2000) 131, 1188,1194; doi:10.1038/sj.bjp.0703671 [source] Resuscitation with Na+/H+ exchanger inhibitor in traumatic haemorrhagic shock: Cardiopulmonary performance, oxygen transport and tissue inflammationCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 3 2010Dongmei Wu Summary 1. The aim of the present study was to examine the effects of inhibition of the Na+/H+ exchanger (NHE-1) on cardiopulmonary performance, oxygen carrying capacity and tissue inflammation in a pig model of traumatic haemorrhage,resuscitation. 2. In 12 instrumented anaesthetized pigs, traumatic haemorrhage was modelled by producing tibia fractures, followed by haemorrhage of 25 mL/kg for 20 min, and then a 4 mm hepatic arterial tear with surgical repair after 20 min. Animals then underwent low-volume fluid resuscitation with either Hextend (vehicle; n = 6; Hospira, Lake Forest, IL, USA) or 3 mg/kg BIIB513 (an NHE-1 inhibitor) + Hextend (n = 6). The experiment was terminated 6 h after the beginning of resuscitation. 3. Compared with vehicle-treated controls, the addition of NHE-1 inhibition with BIIB513 significantly improved the left ventricle stroke work index and attenuated increases in pulmonary arterial pressure and pulmonary vascular resistance. Furthermore, BIIB513 treatment significantly increased the oxygenated haemoglobin ratio, blood oxygen content and mixed venous blood oxygen saturation and improved blood oxygen delivery. In addition, BIIB513 treatment reduced lung tissue levels of interleukin-6 by 80%, tumour necrosis factor-, by 37% and myeloperoxidase activity by 38%. Nuclear factor-,B DNA binding activity in the lung was also slightly and significantly attenuated following BIIB513 treatment. 4. In conclusion, the present study shows that NHE-1 inhibition facilitates the response to fluid resuscitation after traumatic haemorrhage by improving cardiac function, pulmonary vascular function and oxygen carrying capacity, which results in reduced tissue inflammatory injury. [source] Na+/H+ exchangers and the regulation of volumeACTA PHYSIOLOGICA, Issue 1-2 2006R. T. Alexander Abstract The regulation of volume is fundamental to life. There exist numerous conditions that can produce perturbations of cell volume. The cell has developed mechanisms to directly counteract these perturbations so as to maintain its physiological volume. Directed influx of the major extracellular cation, sodium, serves to counteract a decreased cell volume through the subsequent osmotically coupled movement of water to the intracellular space. This process, termed regulatory volume increase is often mediated by the ubiquitous sodium/hydrogen ion exchanger, NHE1. Similarly, the maintenance of intravascular volume is essential for the maintenance of blood pressure and consequently the proper perfusion of vital organs. Numerous mechanisms exist to counterbalance alterations in intravascular volume, not the least of which is the renal absorption of sodium filtered at the glomerulus. Two-thirds of filtered sodium and water are absorbed in the renal proximal tubule, a mechanism that intimately involves the apical sodium/hydrogen ion exchanger, NHE3. This isoform is fundamental to the maintenance and regulation of intravascular volume and blood pressure. In this article, the effects of cell volume on the activity of these different isoforms, NHE1 and NHE3, will be described and the consequences of their activity on intracellular and intravascular volume will be explored. [source] | |||||||||||||