The Basolateral NHE1 Na+/H+ Exchanger Regulates Transepithelial <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif"><mml:msubsup><mml:mtext>HCO</mml:mtext><mml:mn>3</mml:mn><mml:mo>−</mml:mo></mml:msubsup></mml:math> Absorption through Actin Cytoskeleton Remodeling in Renal Thick Ascending Limb

Watts, Bruns A.; George, Thampi; Good, David W.

doi:10.1074/jbc.m410719200

Cited by 44 publications

(59 citation statements)

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“…Confocal Immunofluorescence Microscopy-MTALs were studied by confocal microscopy as previously described (18). MTALs were microdissected and mounted on Cell-Tak-coated coverslips at 10°C.…”

Section: Methodsmentioning

confidence: 99%

“…The tubules were then incubated overnight at 4°C with a 1:50 dilution of antiphospho-mTOR-Ser-2448 antibody, washed, and then incubated for 1 h at room temperature in Alexa 488-conjugated goat anti-rabbit secondary antibody (1:100; Invitrogen). Fluorescence staining was examined in the UTMB Optical Imaging Core using a Zeiss laser-scanning confocal microscope (LSM 510 UV META) as described (18). Tubules were imaged longitudinally, and z-axis optical sections (Ͻ0.4 m) were obtained through a plane at the center of the tubule, which provides a cross-sectional view of cells in the lateral tubule walls (18).…”

Section: Methodsmentioning

confidence: 99%

“…NHE1 modulates NHE3 activity by regulating the organization of the actin cytoskeleton (18). The rate of luminal H ϩ secretion and transepithelial HCO 3 Ϫ absorption in the MTAL thus depends on a regulatory interaction between the basolateral and apical membrane Na ϩ /H ϩ exchangers, whereby basolateral NHE1 enhances the activity of apical NHE3 (15)(16)(17)(18).…”

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confidence: 99%

“…Inhibition of NHE1 with amiloride or nerve growth factor (NGF) or by NHE1 knock-out results secondarily in inhibition of apical NHE3, thereby decreasing HCO 3 Ϫ absorption (15)(16)(17). NHE1 modulates NHE3 activity by regulating the organization of the actin cytoskeleton (18). The rate of luminal H ϩ secretion and transepithelial HCO 3 Ϫ absorption in the MTAL thus depends on a regulatory interaction between the basolateral and apical membrane Na ϩ /H ϩ exchangers, whereby basolateral NHE1 enhances the activity of apical NHE3 (15)(16)(17)(18).…”

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confidence: 99%

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Nerve Growth Factor Inhibits Na+/H+ Exchange and HCO3- Absorption through Parallel Phosphatidylinositol 3-Kinase-mTOR and ERK Pathways in Thick Ascending Limb

Good

George

Watts

2008

Journal of Biological Chemistry

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In the medullary thick ascending limb, inhibiting the basolateral NHE1 Na ؉ /H ؉ exchanger with nerve growth factor (NGF) induces actin cytoskeleton remodeling that secondarily inhibits apical NHE3 and transepithelial HCO 3 ؊ absorption. The inhibition by NGF is mediated 50% through activation of extracellular signal-regulated kinase (ERK). Here we examined the signaling pathway responsible for the remainder of the NGF-induced inhibition. Inhibition of HCO 3 ؊ absorption was reduced 45% by the phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin or LY294002 and 50% by rapamycin, a specific inhibitor of mammalian target of rapamycin (mTOR), a downstream effector of PI3K. The combination of a PI3K inhibitor plus rapamycin did not cause a further reduction in the inhibition by NGF. In contrast, the combination of a PI3K inhibitor plus the MEK/ ERK inhibitor U0126 completely eliminated inhibition by NGF. Rapamycin decreased NGF-induced inhibition of basolateral NHE1 by 45%. NGF induced a 2-fold increase in phosphorylation of Akt, a PI3K target linked to mTOR activation, and a 2.2-fold increase in the activity of p70 S6 kinase, a downstream effector of mTOR. p70 S6 kinase activation was blocked by wortmannin and rapamycin, consistent with PI3K, mTOR, and p70 S6 kinase in a linear pathway. Rapamycin-sensitive inhibition of NHE1 by NGF was associated with an increased level of phosphorylated mTOR in the basolateral membrane domain. These findings indicate that NGF inhibits HCO 3 ؊ absorption in the medullary thick ascending limb through the parallel activation of PI3K-mTOR and ERK signaling pathways, which converge to inhibit NHE1. The results identify a role for mTOR in the regulation of Na ؉ /H ؉ exchange activity and implicate NHE1 as a possible downstream effector contributing to mTOR's effects on cell growth, proliferation, survival, and tumorigenesis.The Na ϩ /H ϩ exchanger isoform NHE1 2 is expressed ubiquitously in the plasma membrane of nonpolarized cells and in the basolateral membrane of epithelial cells, where it plays essential roles in basic cell functions such as the maintenance of intracellular pH (pH i ) and cell volume (1-3). NHE1 is involved in other important cellular processes, including proliferation, survival, adhesion, migration, and tumor formation (2-7). These specialized functions involve regulation of NHE1 by a variety of receptor-mediated signaling networks as well as physical interactions of NHE1 with the actin cytoskeleton (2, 3, 5). By comparison, the role of NHE1 in epithelial function remains poorly understood. In particular, the contributions of NHE1 to transcellular acid-base transport and the possible mechanisms involved are largely undefined.The medullary thick ascending limb (MTAL) of the mammalian kidney participates in acid-base regulation by reabsorbing most of the filtered HCO 3Ϫ not reabsorbed by the proximal tubule (8, 9). Absorption of HCO 3 Ϫ by the MTAL depends on H ϩ secretion mediated by the apical membrane NHE3 Na ϩ /H ϩ exchanger (8, 10 -13) and basolateral HCO ...

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Nerve Growth Factor Inhibits Na+/H+ Exchange and HCO3- Absorption through Parallel Phosphatidylinositol 3-Kinase-mTOR and ERK Pathways in Thick Ascending Limb

Good

George

Watts

2008

Journal of Biological Chemistry

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“…18 This was postulated as regulatory cross-talk between basolateral NHE1 and apical NHE3 because pharmacologic inhibition of basolateral NHE1 downregulates apical NHE3 activity. 19,20 The mechanism of this postulated cross-talk is unclear. However, 2 different mouse models lacking NHE1 have no overt disturbance of whole-body acid-base homeostasis.…”

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Na+/H+ Exchangers in Renal Regulation of Acid-Base Balance

Bobulescu

Moe

2006

Seminars in Nephrology

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The kidney plays key roles in extracellular fluid pH homeostasis by reclaiming bicarbonate (HCO 3 − ) filtered at the glomerulus and generating the consumed HCO 3 − by secreting protons (H + ) into the urine (renal acidification). Sodium-proton exchangers (NHEs) are ubiquitous transmembrane proteins mediating the countertransport of Na + and H + across lipid bilayers. In mammals, NHEs participate in the regulation of cell pH, volume, and intracellular sodium concentration, as well as in transepithelial ion transport. Five of the 10 isoforms (NHE1-4 and NHE8) are expressed at the plasma membrane of renal epithelial cells. The best-studied isoform for acid-base homeostasis is NHE3, which mediates both HCO 3 − absorption and H + excretion in the renal tubule. This article reviews some important aspects of NHEs in the kidney, with special emphasis on the role of renal NHE3 in the maintenance of acid-base balance.Keywords sodium/hydrogen exchange; renal acidification; bicarbonate absorption The free hydrogen ion (H + ) concentration in body fluids is regulated exquisitely around 40 nmol/L (pH 7.40) whereas H + flux through the body greatly exceeds this magnitude. In a 70-kg human being at a basal state, normal metabolic and dietary acid production rate is about 50 to 70 mmoles/d and respiratory volatile acid production at the basal state is around 15,000 mmoles/d, with peak production at maximal exercise reaching 200 mmoles/min. The flux of H + through the organism over 24 hours is 8 orders of magnitude greater than the total pool of free H + in total body water (<2 μmoles). This remarkable homeostatic feat is accomplished by concerted efforts of extracellular and intracellular buffers, highly efficient ventilatory responses, metabolic functions of the liver, and renal ammoniagenic and solute transport mechanisms. For excretion of nonvolatile acid and base loads, the kidney assumes the pivotal role.A filtration-reabsorption nephron bears an exorbitant burden of having to reclaim a vast amount of valuable solutes indiscriminately dispensed in the filtrate; one of which of course is the approximately 4,000 mmoles of bicarbonate (HCO 3 − ) per day. The luminal acid disequilibrium pH implies that the predominant mode of HCO 3 − absorption involves H + secretion, although a small concomitant degree of direct HCO 3 − reabsorption cannot be excluded. 1 Two points are noteworthy. First, complete reclamation of the approximately 4,000 mmoles of filtered HCO 3 − forestalls a physiologic disaster but does not lead to net acid secretion. Further elaboration of H + into the urine is necessary. Second, whether the organism is catering to the The era of phenomenologic analysis was supplemented by gene-and protein-specific reagents when the first mammalian NHE was cloned by Sardet et al. 7 The relationship between mammalian NHE genetic sequence and those from a multitude of organisms is shown in Fig 2. Na + /H + exchange across lipid bilayers and proteins that sustain this function are universal in prokaryotic, animal, and...

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Molecular Mechanisms and Regulation of Urinary Acidification

Kurtz

2014

Comprehensive Physiology

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The H+ concentration in human blood is kept within very narrow limits, ~ 40 nM, despite the fact that dietary metabolism generates acid and base loads that are added to the systemic circulation throughout the life of mammals. One of the primary functions of the kidney is to maintain the constancy of systemic acid-base chemistry. The kidney has evolved the capacity to regulate blood acidity by performing three key functions: 1) reabsorb HCO3− that is filtered through the glomeruli to prevent its excretion in the urine; 2) generate a sufficient quantity of new HCO3− to compensate for the loss of HCO3− resulting from dietary metabolic H+ loads and loss of HCO3− in the urea cycle; and 3) excrete HCO3− (or metabolizable organic anions) following a systemic base load. The ability of the kidney to perform these functions requires that various cell types throughout the nephron respond to changes in acid-base chemistry by modulating specific ion transport and/or metabolic processes in a coordinated fashion such that the urine and renal vein chemistry is altered appropriately. The purpose of the article is to provide the interested reader with a broad review of a field that began historically ~ 60 years ago with whole animal studies, and has evolved to where we are currently addressing questions related to kidney acid-base regulation at the single protein structure/function level.

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The Basolateral NHE1 Na+/H+ Exchanger Regulates Transepithelial HCO3− Absorption through Actin Cytoskeleton Remodeling in Renal Thick Ascending Limb

Cited by 44 publications

References 47 publications

Nerve Growth Factor Inhibits Na+/H+ Exchange and HCO3- Absorption through Parallel Phosphatidylinositol 3-Kinase-mTOR and ERK Pathways in Thick Ascending Limb

Nerve Growth Factor Inhibits Na+/H+ Exchange and HCO3- Absorption through Parallel Phosphatidylinositol 3-Kinase-mTOR and ERK Pathways in Thick Ascending Limb

Na+/H+ Exchangers in Renal Regulation of Acid-Base Balance

Molecular Mechanisms and Regulation of Urinary Acidification

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