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Just A, Mallmann RT, Grossmann S, Sleman F, Klugbauer N. Two-pore channel protein TPC1 is a determining factor for the adaptation of proximal tubular phosphate handling. Acta Physiol (Oxf) 2023; 237:e13914. [PMID: 36599408 DOI: 10.1111/apha.13914] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Revised: 10/27/2022] [Accepted: 01/02/2023] [Indexed: 01/06/2023]
Abstract
AIM Two-pore channels (TPCs) constitute a small family of cation channels expressed in endo-lysosomal compartments. TPCs have been characterized as critical elements controlling Ca2+ -mediated vesicular membrane fusion and thereby regulating endo-lysosomal vesicle trafficking. Exo- and endocytotic trafficking and lysosomal degradation are major mechanisms of adaption of epithelial transport. A prime example of highly regulated epithelial transport is the tubular system of the kidney. We therefore studied the localization of TPC protein 1 (TPC1) in the kidney and its functional role in the dynamic regulation of tubular transport. METHODS Immunohistochemistry in combination with tubular markers were used to investigate TPC1 expression in proximal and distal tubules. The excretion of phosphate and ammonium, as well as urine volume and pH were studied in vivo, in response to dynamic challenges induced by bolus injection of parathyroid hormone or acid-base transitions via consecutive infusion of NaCl, Na2 CO3 , and NH4 Cl. RESULTS In TPC1-deficient mice, the PTH-induced rise in phosphate excretion was prolonged and exaggerated, and its recovery delayed in comparison with wildtype littermates. In the acid-base transition experiment, TPC1-deficient mice showed an identical rise in phosphate excretion in response to Na2 CO3 compared with wildtypes, but a delayed NH4Cl-induced recovery. Ammonium-excretion decreased with Na2 CO3 , and increased with NH4 Cl, but without differences between genotypes. CONCLUSIONS We conclude that TPC1 is expressed subapically in the proximal but not distal tubule and plays an important role in the dynamic adaptation of proximal tubular phosphate reabsorption towards enhanced, but not reduced absorption.
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Affiliation(s)
- Armin Just
- Institut für Physiologie I, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Robert T Mallmann
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Sonja Grossmann
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Faten Sleman
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Norbert Klugbauer
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
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2
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Chaimana R, Teerapornpuntakit J, Jantarajit W, Lertsuwan K, Krungchanuchat S, Panupinthu N, Krishnamra N, Charoenphandhu N. CFTR-mediated anion secretion in parathyroid hormone-treated Caco-2 cells is associated with PKA and PI3K phosphorylation but not intracellular pH changes or Na +/K +-ATPase abundance. Biochem Biophys Rep 2021; 27:101054. [PMID: 34189282 PMCID: PMC8220001 DOI: 10.1016/j.bbrep.2021.101054] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2021] [Revised: 05/27/2021] [Accepted: 06/09/2021] [Indexed: 02/07/2023] Open
Abstract
Parathyroid hormone (PTH) has previously been shown to enhance the transepithelial secretion of Cl− and HCO3− across the intestinal epithelia including Caco-2 monolayer, but the underlying cellular mechanisms are not completely understood. Herein, we identified the major signaling pathways that possibly mediated the PTH action to its known target anion channel, i.e., cystic fibrosis transmembrane conductance regulator anion channel (CFTR). Specifically, PTH was able to induce phosphorylation of protein kinase A and phosphoinositide 3-kinase. Since the apical HCO3− efflux through CFTR often required the intracellular H+/HCO3− production and/or the Na+-dependent basolateral HCO3− uptake, the intracellular pH (pHi) balance might be disturbed, especially as a consequence of increased endogenous H+ and HCO3− production. However, measurement of pHi by a pH-sensitive dye suggested that the PTH-exposed Caco-2 cells were able to maintain normal pH despite robust HCO3− transport. In addition, although the plasma membrane Na+/K+-ATPase (NKA) is normally essential for basolateral HCO3− uptake and other transporters (e.g., NHE1), PTH did not induce insertion of new NKA molecules into the basolateral membrane as determined by membrane protein biotinylation technique. Thus, together with our previous data, we concluded that the PTH action on Caco-2 cells is dependent on PKA and PI3K with no detectable change in pHi or NKA abundance on cell membrane. Intestinal epithelial-like Caco-2 cells expressed CFTR and PTH1R. PTH increased anion transport across Caco-2 monolayer as suggested by Vt change. PTH induced phosphorylation of PKA and PI3K in Caco-2 cells. Intracellular pH was unaltered despite the presence of PTH-induced HCO3− efflux. PTH did not change Na+/K+-ATPase abundance in the plasma membrane.
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Affiliation(s)
- Rattana Chaimana
- Center of Calcium and Bone Research (COCAB), Faculty of Science, Mahidol University, Bangkok, Thailand.,Department of Physiology, Faculty of Science, Mahidol University, Bangkok, Thailand
| | - Jarinthorn Teerapornpuntakit
- Center of Calcium and Bone Research (COCAB), Faculty of Science, Mahidol University, Bangkok, Thailand.,Department of Physiology, Faculty of Medical Science, Naresuan University, Phitsanulok, Thailand
| | - Walailak Jantarajit
- Center of Calcium and Bone Research (COCAB), Faculty of Science, Mahidol University, Bangkok, Thailand.,Department of Physiology, Faculty of Science, Mahidol University, Bangkok, Thailand
| | - Kornkamon Lertsuwan
- Center of Calcium and Bone Research (COCAB), Faculty of Science, Mahidol University, Bangkok, Thailand.,Department of Biochemistry, Faculty of Science, Mahidol University, Bangkok, Thailand
| | - Saowalak Krungchanuchat
- Center of Calcium and Bone Research (COCAB), Faculty of Science, Mahidol University, Bangkok, Thailand
| | - Nattapon Panupinthu
- Center of Calcium and Bone Research (COCAB), Faculty of Science, Mahidol University, Bangkok, Thailand.,Department of Physiology, Faculty of Science, Mahidol University, Bangkok, Thailand
| | - Nateetip Krishnamra
- Center of Calcium and Bone Research (COCAB), Faculty of Science, Mahidol University, Bangkok, Thailand.,Department of Physiology, Faculty of Science, Mahidol University, Bangkok, Thailand
| | - Narattaphol Charoenphandhu
- Center of Calcium and Bone Research (COCAB), Faculty of Science, Mahidol University, Bangkok, Thailand.,Department of Physiology, Faculty of Science, Mahidol University, Bangkok, Thailand.,Institute of Molecular Biosciences, Mahidol University, Nakhon Pathom, Thailand.,The Academy of Science, The Royal Society of Thailand, Bangkok, Thailand
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3
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Thomas L, Xue J, Dominguez Rieg JA, Rieg T. Contribution of NHE3 and dietary phosphate to lithium pharmacokinetics. Eur J Pharm Sci 2018; 128:1-7. [PMID: 30419292 DOI: 10.1016/j.ejps.2018.11.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2018] [Revised: 10/09/2018] [Accepted: 11/08/2018] [Indexed: 01/13/2023]
Abstract
Lithium is one of the mainstays for the treatment of bipolar disorder despite its side effects on the endocrine, neurological, and renal systems. Experimentally, lithium has been used as a measure to determine proximal tubule reabsorption based on the assumption that lithium and sodium transport go in parallel in the proximal tubule. However, the exact mechanism by which lithium is reabsorbed remains elusive. The majority of proximal tubule sodium reabsorption is directly or indirectly mediated by the sodium-hydrogen exchanger 3 (NHE3). In addition, sodium-phosphate cotransporters have been implicated in renal lithium reabsorption. In order to better understand the role of sodium-phosphate cotransporters involved in lithium (re)absorption, we studied lithium pharmacokinetics in: i) tubule-specific NHE3 knockout mice (NHE3loxloxPax8Cre), and ii) mice challenged with low or high phosphate diets. Intravenous or oral administration of lithium did not result in differences in lithium bioavailability, half-life, maximum plasma concentrations, area under the curve, lithium clearance, or urinary lithium/creatinine ratios between control and NHE3loxloxPax8Cre mice. After one week of dietary phosphate challenges, lithium bioavailability was ~30% lower on low versus high dietary phosphate, possibly the consequence of a smaller area under the curve after oral administration. This was associated with higher apparent lithium clearance after oral administration and lower urinary lithium/creatinine ratios on low versus high dietary phosphate. Collectively, renal NHE3 does not play a role in lithium pharmacokinetics; however, dietary phosphate could have an indirect effect on lithium bioavailability and lithium disposition.
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Affiliation(s)
- Linto Thomas
- Department of Molecular Pharmacology and Physiology, University of South Florida, Tampa, FL 33612, USA
| | - Jianxiang Xue
- Department of Molecular Pharmacology and Physiology, University of South Florida, Tampa, FL 33612, USA
| | - Jessica A Dominguez Rieg
- Department of Molecular Pharmacology and Physiology, University of South Florida, Tampa, FL 33612, USA
| | - Timo Rieg
- Department of Molecular Pharmacology and Physiology, University of South Florida, Tampa, FL 33612, USA.
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4
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Long KR, Shipman KE, Rbaibi Y, Menshikova EV, Ritov VB, Eshbach ML, Jiang Y, Jackson EK, Baty CJ, Weisz OA. Proximal tubule apical endocytosis is modulated by fluid shear stress via an mTOR-dependent pathway. Mol Biol Cell 2017; 28:2508-2517. [PMID: 28720662 PMCID: PMC5597323 DOI: 10.1091/mbc.e17-04-0211] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2017] [Revised: 07/07/2017] [Accepted: 07/13/2017] [Indexed: 12/02/2022] Open
Abstract
Kidney proximal tubule cells cultured under shear stress become remarkably well differentiated and endocytic capacity is rapidly tuned in response to acute changes in shear stress. The results have implications for understanding how proximal tubule function is regulated acutely by daily variations in glomerular filtration rate. Cells lining the proximal tubule (PT) have unique membrane specializations that are required to maintain the high-capacity ion transport and endocytic functions of this nephron segment. PT cells in vivo acutely regulate ion transport in response to changes in glomerular filtration rate (GFR) to maintain glomerulotubular balance. PT cells in culture up-regulate endocytic capacity in response to acute changes in fluid shear stress (FSS); however, it is not known whether GFR modulates PT endocytosis to enable maximally efficient uptake of filtered proteins in vivo. Here, we show that cells cultured under continuous FSS develop an expanded apical endocytic pathway and increased endocytic capacity and lysosomal biogenesis. Furthermore, endocytic capacity in fully differentiated cells is rapidly modulated by changes in FSS. PT cells exposed to continuous FSS also acquired an extensive brush border and basolateral membrane invaginations resembling those observed in vivo. Culture under suboptimal levels of FSS led to intermediate phenotypes, suggesting a threshold effect. Cells exposed to FSS expressed higher levels of key proteins necessary for PT function, including ion transporters, receptors, and membrane-trafficking machinery, and increased adenine nucleotide levels. Inhibition of the mechanistic target of rapamycin (mTOR) using rapamycin prevented the increase in cellular energy levels, lysosomal biogenesis, and endocytic uptake, suggesting that these represent a coordinated differentiation program. In contrast, rapamycin did not prevent the FSS-induced increase in Na+/K+-ATPase levels. Our data suggest that rapid tuning of the endocytic response by changes in FSS may contribute to glomerulotubular balance in vivo. Moreover, FSS provides an essential stimulus in the differentiation of PT cells via separate pathways that up-regulate endocytosis and ion transport capacity. Variations in FSS may also contribute to the maturation of PT cells during kidney development and during repair after kidney injury.
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Affiliation(s)
- Kimberly R Long
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Katherine E Shipman
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Youssef Rbaibi
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Elizabeth V Menshikova
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Vladimir B Ritov
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Megan L Eshbach
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Yu Jiang
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Edwin K Jackson
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Catherine J Baty
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Ora A Weisz
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
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5
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Jantarajit W, Lertsuwan K, Teerapornpuntakit J, Krishnamra N, Charoenphandhu N. CFTR-mediated anion secretion across intestinal epithelium-like Caco-2 monolayer under PTH stimulation is dependent on intermediate conductance K + channels. Am J Physiol Cell Physiol 2017; 313:C118-C129. [PMID: 28490422 DOI: 10.1152/ajpcell.00010.2017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2017] [Revised: 05/02/2017] [Accepted: 05/08/2017] [Indexed: 12/16/2022]
Abstract
Parathyroid hormone (PTH), a pleiotropic hormone that maintains mineral homeostasis, is also essential for controlling pH balance and ion transport across renal and intestinal epithelia. Optimization of luminal pH is important for absorption of trace elements, e.g., calcium and phosphorus. We have previously demonstrated that PTH rapidly stimulated electrogenic [Formula: see text] secretion in intestinal epithelial-like Caco-2 monolayers, but the underlying cellular mechanism, contributions of other ions, particularly Cl- and K+, and long-lasting responses are not completely understood. Herein, PTH and forskolin were confirmed to induce anion secretion, which peaked within 1-3 min (early phase), followed by an abrupt decay and plateau that lasted for 60 min (late phase). In both early and late phases, apical membrane capacitance was increased with a decrease in basolateral capacitance after PTH or forskolin exposure. PTH also induced a transient increase in apical conductance with a long-lasting decrease in basolateral conductance. Anion secretion in both phases was reduced under [Formula: see text]-free and/or Cl--free conditions or after exposure to carbonic anhydrase inhibitor (acetazolamide), CFTR inhibitor (CFTRinh-172), Na+/H+ exchanger (NHE)-3 inhibitor (tenapanor), or K+ channel inhibitors (BaCl2, clotrimazole, and TRAM-34; basolateral side), the latter of which suggested that PTH action was dependent on basolateral K+ recycling. Furthermore, early- and late-phase responses to PTH were diminished by inhibitors of PI3K (wortmannin and LY-294002) and PKA (PKI 14-22). In conclusion, PTH requires NHE3 and basolateral K+ channels to induce [Formula: see text] and Cl- secretion, thus explaining how PTH regulated luminal pH balance and pH-dependent absorption of trace minerals.
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Affiliation(s)
- Walailak Jantarajit
- Center of Calcium and Bone Research, Faculty of Science, Mahidol University, Bangkok, Thailand.,Department of Physiology, Faculty of Science, Mahidol University, Bangkok, Thailand
| | - Kornkamon Lertsuwan
- Department of Biochemistry, Faculty of Science, Mahidol University, Bangkok, Thailand; and
| | | | - Nateetip Krishnamra
- Center of Calcium and Bone Research, Faculty of Science, Mahidol University, Bangkok, Thailand.,Department of Physiology, Faculty of Science, Mahidol University, Bangkok, Thailand
| | - Narattaphol Charoenphandhu
- Center of Calcium and Bone Research, Faculty of Science, Mahidol University, Bangkok, Thailand; .,Department of Physiology, Faculty of Science, Mahidol University, Bangkok, Thailand.,Institute of Molecular Biosciences, Mahidol University, Nakhon Pathom, Thailand
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6
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Abstract
The H(+) concentration in human blood is kept within very narrow limits, ~40 nmol/L, 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: (i) reabsorb HCO3(-) that is filtered through the glomeruli to prevent its excretion in the urine; (ii) 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 (iii) 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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Affiliation(s)
- Ira Kurtz
- Division of Nephrology, David Geffen School of Medicine, Los Angeles, CA; Brain Research Institute, UCLA, Los Angeles, CA
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7
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Laverty G, Anttila A, Carty J, Reddy V, Yum J, Arnason SS. CFTR mediated chloride secretion in the avian renal proximal tubule. Comp Biochem Physiol A Mol Integr Physiol 2011; 161:53-60. [PMID: 21964154 DOI: 10.1016/j.cbpa.2011.09.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2010] [Revised: 09/05/2011] [Accepted: 09/07/2011] [Indexed: 01/23/2023]
Abstract
In primary cell cultures of the avian (Gallus gallus) renal proximal tubule parathyroid hormone and cAMP activation generate a Cl(-)-dependent short circuit current (I(SC)) response, consistent with net transepithelial Cl(-) secretion. In this study we investigated the expression and physiological function of the Na-K-2Cl (NKCC) transporter and CFTR chloride channel, both associated with Cl(-) secretion in a variety of tissues, in these proximal tubule cells. Using both RT-PCR and immunoblotting approaches, we showed that NKCC and CFTR are expressed, both in proximal tubule primary cultures and in a proximal tubule fraction of non-cultured (native tissue) fragments. We also used electrophysiological methods to assess the functional contribution of NKCC and CFTR to forskolin-activated I(SC) responses in filter grown cultured monolayers. Bumetanide (10 μM), a specific blocker of NKCC, inhibited forskolin activated I(SC) by about 40%, suggesting that basolateral uptake of Cl(-) is partially mediated by NKCC transport. In monolayers permeabilized on the basolateral side with nystatin, forskolin activated an apical Cl(-) conductance, manifested as bidirectional diffusion currents in the presence of oppositely directed Cl(-) gradients. Under these conditions the apical conductance appeared to show some bias towards apical-to-basolateral Cl(-) current. Two selective CFTR blockers, CFTR Inhibitor 172 and GlyH-101 (both at 20 μM) inhibited the forskolin activated diffusion currents by 38-68%, with GlyH-101 having a greater effect. These data support the conclusion that avian renal proximal tubules utilize an apical CFTR Cl(-) channel to mediate cAMP-activated Cl(-) secretion.
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Affiliation(s)
- Gary Laverty
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA.
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8
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Laohapitakworn S, Thongbunchoo J, Nakkrasae LI, Krishnamra N, Charoenphandhu N. Parathyroid hormone (PTH) rapidly enhances CFTR-mediated HCO₃⁻ secretion in intestinal epithelium-like Caco-2 monolayer: a novel ion regulatory action of PTH. Am J Physiol Cell Physiol 2011; 301:C137-49. [PMID: 21389278 DOI: 10.1152/ajpcell.00001.2011] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Besides being a Ca²-regulating hormone, parathyroid hormone (PTH) has also been shown to regulate epithelial transport of certain ions, such as Cl, HCO₃, and Na, particularly in the kidney. Although the intestinal epithelium also expressed PTH receptors, little was known regarding its mechanism in the regulation of intestinal ion transport. We investigated the ion regulatory role of PTH in intestinal epithelium-like Caco-2 monolayer by Ussing chamber technique and alternating current impedance spectroscopy. It was found that Caco-2 cells rapidly responded to PTH within 1 min by increasing apical HCO₃- secretion. CFTR served as the principal route for PTH-stimulated apical HCOV efflux, which was abolished by various CFTR inhibitors, namely, NPPB, glycine hydrazide-101 (GlyH-101), and CFTRinh-172, as well as by small interfering RNA against CFTR. Concurrently, the plasma membrane resistance was decreased with no changes in the plasma membrane capacitance or paracellular permeability. HCOV was probably supplied by basolateral uptake via the electrogenic Na⁺-HCO₃⁻ cotransporter and by methazolamide-sensitive carbonic anhydrase, while the resulting intracellular H⁺ might be extruded by both apical and basolateral Na/H exchangers. Furthermore, the PTH-stimulated HCO₃-secretion was markedly reduced by protein kinase A (PKA) inhibitor (PKI 14-22 amide) and phosphoinositide 3-kinase (PI3K) inhibitors (wortmannin and LY-294002), but not by intracellular Ca²⁺ chelator (BAPTA-AM) or protein kinase C inhibitor (GF-109203X). In conclusion, the present study provided evidence that PTH directly and rapidly stimulated apical HCO₃- secretion through CFTR in PKA- and PI3K-dependent manner, which was a novel noncalciotropic, ion regulatory action of PTH in the intestinal epithelium.
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Affiliation(s)
- Suparerk Laohapitakworn
- Consortium for Calcium and Bone Research, Faculty of Science, Mahidol University, Bangkok, Thailand
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9
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Liu J, Xie ZJ. The sodium pump and cardiotonic steroids-induced signal transduction protein kinases and calcium-signaling microdomain in regulation of transporter trafficking. Biochim Biophys Acta Mol Basis Dis 2010; 1802:1237-45. [PMID: 20144708 DOI: 10.1016/j.bbadis.2010.01.013] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2009] [Revised: 01/28/2010] [Accepted: 01/30/2010] [Indexed: 12/12/2022]
Abstract
The Na/K-ATPase was discovered as an energy transducing ion pump. A major difference between the Na/K-ATPase and other P-type ATPases is its ability to bind a group of chemicals called cardiotonic steroids (CTS). The plant-derived CTS such as digoxin are valuable drugs for the management of cardiac diseases, whereas ouabain and marinobufagenin (MBG) have been identified as a new class of endogenous hormones. Recent studies have demonstrated that the endogenous CTS are important regulators of renal Na(+) excretion and blood pressure. The Na/K-ATPase is not only an ion pump, but also an important receptor that can transduce the ligand-like effect of CTS on intracellular protein kinases and Ca(2+) signaling. Significantly, these CTS-provoked signaling events are capable of reducing the surface expression of apical NHE3 (Na/H exchanger isoform 3) and basolateral Na/K-ATPase in renal proximal tubular cells. These findings suggest that endogenous CTS may play an important role in regulation of tubular Na(+) excretion under physiological conditions; conversely, a defect at either the receptor level (Na/K-ATPase) or receptor-effector coupling would reduce the ability of renal proximal tubular cells to excrete Na(+), thus culminating/resulting in salt-sensitive hypertension.
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Affiliation(s)
- Jiang Liu
- Department of Medicine, University of Toledo College of Medicine, Toledo, OH, USA
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10
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Carraro-Lacroix LR, Malnic G, Girardi ACC. Regulation of Na+/H+ exchanger NHE3 by glucagon-like peptide 1 receptor agonist exendin-4 in renal proximal tubule cells. Am J Physiol Renal Physiol 2009; 297:F1647-55. [DOI: 10.1152/ajprenal.00082.2009] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The gut incretin hormone glucagon-like peptide 1 (GLP-1) is released in response to ingested nutrients and enhances insulin secretion. In addition to its insulinotropic properties, GLP-1 has been shown to have natriuretic actions paralleled by a diminished proton secretion. We therefore studied the role of the GLP-1 receptor agonist exendin-4 in modulating the activity of Na+/H+ exchanger NHE3 in LLC-PK1 cells. We found that NHE3-mediated Na+-dependent intracellular pH (pHi) recovery decreased ∼50% after 30-min treatment with 1 nM exendin-4. Pharmacological inhibitors and cAMP analogs that selectively activate protein kinase A (PKA) or the exchange protein directly activated by cAMP (EPAC) demonstrated that regulation of NHE3 activity by exendin-4 requires activation of both cAMP downstream effectors. This conclusion was based on the following observations: 1) the PKA antagonist H-89 completely prevented the effect of the PKA activator but only partially blocked the exendin-4-induced NHE3 inhibition; 2) the MEK1/2 inhibitor U-0126 abolished the effect of the EPAC activator but only diminished the exendin-4-induced NHE3 inhibition; 3) combination of H-89 and U-0126 fully prevented the effect of exendin-4 on NHE3; 4) no additive effect in the inhibition of NHE3 activity was observed when exendin-4, PKA, and EPAC activators were used together. Mechanistically, the inhibitory effect of exendin-4 on pHi recovery was associated with an increase of NHE3 phosphorylation. Conversely, this inhibition took place without changes in the surface expression of the transporter. We conclude that GLP-1 receptor agonists modulate sodium homeostasis in the kidney, most likely by affecting NHE3 activity.
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Affiliation(s)
- Luciene R. Carraro-Lacroix
- Department of Physiology and Biophysics, Institute of Biomedical Sciences
- Department of Physiology, Federal University of São Paulo, São Paulo, Brazil
| | - Gerhard Malnic
- Department of Physiology and Biophysics, Institute of Biomedical Sciences
| | - Adriana C. C. Girardi
- Department of Physiology and Biophysics, Institute of Biomedical Sciences
- Heart Institute (InCor), Medical School, University of São Paulo, and
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11
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Fiori M, Gras EG, Amorena C. Decreased NHE8 isoform expression and defective acidification in proximal convoluted tubules of senile rats. AGE (DORDRECHT, NETHERLANDS) 2009; 31:77-84. [PMID: 19234771 PMCID: PMC2645991 DOI: 10.1007/s11357-008-9083-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2008] [Accepted: 12/18/2008] [Indexed: 05/27/2023]
Abstract
We have previously found that aged rats show decreased proximal acidification without changes in NHE3 or V-H(+) ATPase expression in brush border membrane vesicles. However, we did not identify any mechanism underlying these observations. The aim of the present work was to evaluate some of the regulatory systems of proximal acidification that could be affected by aging. We measured plasma concentrations of parathyroid hormone (PTH) and the amount of cAMP in the renal cortex of young and old Wistar rats. PTH plasma concentration was increased in old rats, whereas, although it showed a tendency to increase, the cAMP content in the renal cortex of old rats was not significantly different compared with the cortex of young rats. We measured the abundance of NHE8 isoforms of the Na(+)/H(+) exchanger in brush border membrane vesicles from proximal convoluted tubules (PCT) of young and old rats by western blot analysis. We performed RT-PCR experiments in renal cortex homogenates from both experimental groups to evaluate mRNA expression of NHE3, NHE8 and H(+)ATPase. In senile rats, we detected a decreased abundance (at both gene expression and protein level) of the NHE8 isoform. These results could explain previous observations in which proximal tubule acidification appears affected in aged rats through a decrease in the activity of ethylisopropyl amiloride (EIPA)- and Bafilomycin-sensitive components, without changes in the NHE3 and V-H(+)ATPase abundance in the apical membrane of the PCT.
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Affiliation(s)
- Mariana Fiori
- CESyMA, Escuela de Ciencia y Tecnología, Universidad Nacional de Gral, San Martín, Av. Gral Paz 5445, 1650 San Martín, Argentina
| | - Eduardo García Gras
- CESyMA, Escuela de Ciencia y Tecnología, Universidad Nacional de Gral, San Martín, Av. Gral Paz 5445, 1650 San Martín, Argentina
| | - Carlos Amorena
- CESyMA, Escuela de Ciencia y Tecnología, Universidad Nacional de Gral, San Martín, Av. Gral Paz 5445, 1650 San Martín, Argentina
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Yang X, Huang HC, Yin H, Alpern RJ, Preisig PA. RhoA required for acid-induced stress fiber formation and trafficking and activation of NHE3. Am J Physiol Renal Physiol 2007; 293:F1054-64. [PMID: 17686951 DOI: 10.1152/ajprenal.00295.2007] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Exposure to an acid load increases apical membrane Na+/H+ antiporter (NHE3) activity, a process that involves exocytic trafficking of the transporter to the apical membrane. We have previously shown that an intact microfilament structure is required for this exocytic process (Yang X, Amemiya M, Peng Y, Moe OW, Preisig PA, Alpern RJ. Am J Physiol Cell Physiol 279: C410–C419, 2000). The present studies demonstrate that acid-induced stress fiber formation is required for stimulation of NHE3 activity. Formation of stress fibers is associated with acid-induced tyrosine phosphorylation and increases in protein abundance of two focal adhesion proteins, p125FAK and paxillin. The Rho kinase inhibitor Y27632 completely blocks acid-induced stress fiber formation and the increases in apical membrane NHE3 abundance and activity, but it has no effect on acid-induced tyrosine phosphorylation of p125FAK or paxillin. Herbimycin A completely blocks acid-induced tyrosine phosphorylation of p125FAK and paxillin but only partially blocks stress fiber formation and NHE3 activation. These studies demonstrate that Rho kinase mediates acid-induced stress fiber formation, which is required for NHE3 exocytosis, and increases in NHE3 activity. Acid-induced tyrosine phosphorylation of the focal adhesion proteins p125FAK and paxillin is not Rho kinase dependent. Thus these two acid-mediated effects are associated, yet independent processes.
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Affiliation(s)
- Xiaojing Yang
- Department of Internal Medicine, University of Texas Southwestern Medical School, Dallas, Texas, USA
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13
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Kocinsky HS, Dynia DW, Wang T, Aronson PS. NHE3 phosphorylation at serines 552 and 605 does not directly affect NHE3 activity. Am J Physiol Renal Physiol 2007; 293:F212-8. [PMID: 17409282 DOI: 10.1152/ajprenal.00042.2007] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Direct phosphorylation of sodium hydrogen exchanger type 3 (NHE3) is a well-established physiological phenomenon; however, the exact role of NHE3 phosphorylation in its regulation remains unclear. The objective of this study was to evaluate whether NHE3 phosphorylation at serines 552 and 605 is physiologically regulated in vivo and, if so, whether changes in phosphorylation at these sites are tightly coupled to changes in transport activity. To this end, we directly compared PKA-induced NHE3 inhibition with site-specific changes in NHE3 phosphorylation in vivo and in vitro. In vivo, PKA was activated using an intravenous infusion of parathyroid hormone in Sprague-Dawley rats. In vitro, PKA was activated directly in opossum kidney (OKP) cells using forskolin and IBMX. NHE3 activity was assayed in microvillar membrane vesicles in the rat model and by 22Na uptake in the OKP cell model. In both cases, NHE3 phosphorylation at serines 552 and 605 was determined using previously characterized monoclonal phosphospecific antibodies directed to these sites. In vivo, we found dramatic changes in NHE3 phosphorylation at serines 552 and 605 with PKA activation but no corresponding alteration in NHE3 activity. This dissociation between NHE3 phosphorylation and activity was further verified in OKP cells in which phosphorylation clearly preceded transport inhibition. We conclude that although phosphorylation of NHE3 at serines 552 and 605 is regulated by PKA both in vivo and in vitro, phosphorylation of these sites does not directly alter Na+/H+ exchange activity.
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Affiliation(s)
- Hetal S Kocinsky
- Dept. of Pediatrics, Yale University, New Haven, CT 06520-8064, USA.
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14
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Okamoto N, Aruga S, Tomita K, Takeuchi T, Kitamura T. Chronic acid ingestion promotes renal stone formation in rats treated with vitamin D3. Int J Urol 2007; 14:60-6. [PMID: 17199862 DOI: 10.1111/j.1442-2042.2006.01658.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
OBJECTIVE Although hypercalciuria, a well-established adverse effect of vitamin D3, can be a risk factor of renal stone formation, the risk of nephrolithiasis has not been well defined. The consumption of a diet high in acid precursors is often cited as a risk factor for the development of calcium-based kidney stones. In the present study, we investigated the effect of chronic acid ingestion on kidney stone formation in rats treated with calcitriol (1-25[OH]2 D3). METHODS Control rats (C-C), calcitriol-treated rats (C-V; three treatments of 0.5 microg of calcitriol per week) and acid-ingested (water containing 0.21 mol/L NH4Cl), calcitriol-treated (three treatments of 0.5 microg of calcitriol per week) rats (A-V) were fed in metabolic cages. After 1 month, urine, blood, kidney and bone samples were analyzed. RESULTS The A-V rats exhibited elevated serum calcium concentrations, urinary calcium and phosphate excretion, urinary type I collagen cross-linked N-peptide (NTx)/creatinine values, mRNA expression of osteopontin in the kidney, and renal calcium contents as well as decreased bone mineral densities, compared with the C-C and C-V rats. Urinary citrate excretion was lower and NaDC-1 mRNA expression in the kidney was higher in the A-V rats than in the C-C and C-V rats. Calcium phosphate kidney stones were found in the A-V rats. CONCLUSIONS The ingestion of NH4Cl, an acid precursor, promotes calcium phosphate kidney stone formation in calcitriol-treated rats. The chronic intake of a diet rich in acid precursors may be a risk factor for the development of kidney stones in subjects who are being treated with calcitriol.
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15
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Honegger KJ, Capuano P, Winter C, Bacic D, Stange G, Wagner CA, Biber J, Murer H, Hernando N. Regulation of sodium-proton exchanger isoform 3 (NHE3) by PKA and exchange protein directly activated by cAMP (EPAC). Proc Natl Acad Sci U S A 2006; 103:803-8. [PMID: 16407144 PMCID: PMC1334627 DOI: 10.1073/pnas.0503562103] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The Na(+)/H(+) exchanger 3 (NHE3) is expressed in the brush border membrane (BBM) of proximal tubules (PT). Its activity is down-regulated on increases in intracellular cAMP levels. The aim of this study was to investigate the contribution of the protein kinase A (PKA) and the exchange protein directly activated by cAMP (EPAC) dependent pathways in the regulation of NHE3 by adenosine 3',5'-cyclic monophosphate (cAMP). Opossum kidney cells and murine kidney slices were treated with cAMP analogs, which selectively activate either PKA or EPAC. Activation of either pathway resulted in an inhibition of NHE3 activity. The EPAC-induced effect was independent of PKA as indicated by the lack of activation of the kinase and the insensitivity to the PKA inhibitor H89. Both PKA and EPAC inhibited NHE3 activity without inducing changes in the expression of the transporter in BBM. Activation of PKA, but not of EPAC, led to an increase of NHE3 phosphorylation. In contrast, activation of PKA, but not of EPAC, inhibited renal type IIa Na(+)-coupled inorganic phosphate cotransporter (NaPi-IIa), another Na-dependent transporter expressed in proximal BBM. PKA, but not EPAC, induced the retrieval of NaPi-IIa from BBM. Our results suggest that EPAC activation may represent a previously unrecognized mechanism involved in the cAMP regulation of NHE3, whereas regulation of NaPi-IIa is mediated by PKA but not by EPAC.
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Affiliation(s)
- Katharina J Honegger
- Institute of Physiology, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
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16
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Leong PKK, Yang LE, Landon CS, McDonough AA, Yip KP. Phenol injury-induced hypertension stimulates proximal tubule Na+/H+ exchanger activity. Am J Physiol Renal Physiol 2006; 290:F1543-50. [PMID: 16390865 DOI: 10.1152/ajprenal.00392.2005] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Injection of 50 microl 10% phenol into rat renal cortex activates renal sympathetic nerve activity which provokes acute hypertension that persists for weeks. We have previously shown with membrane fractionation that phenol injury caused a redistribution of the main proximal tubule (PT) apical transporter NHE3 (Na+/H+ exchanger isoform 3) to low density membranes enriched in apical microvilli. The aim of this study was to determine whether phenol injury increases PT apical Na+/H+ exchanger (NHE) activity. NHE activity was measured in vivo as the initial rate of change in intracellular pH (dpH(i)/dt) during luminal Na+ removal in PT preloaded with the pH-sensitive fluorescence dye BCECF. Injection of 50 microl 10% phenol increased blood pressure from 113 +/- 5.2 to 130 +/- 4.6 mmHg without changing glomerular filtration rate or urine output. NHE activity increased 2.6-fold by 70 min after phenol injury. The increase of NHE activity was accompanied with an increase of tubular reabsorption. Total NHE activity/NHE3 protein in cortical brush-border membrane (BBM) vesicles, measured by acridine orange quench and immunoblot, respectively, was unchanged by phenol injury. In conclusion, acute phenol injury provokes coincident increases in PT apical NHE activity, redistribution of NHE3 into low density apical membranes, and hypertension. The increase in NHE activity may contribute to the lack of pressure-diuresis and the maintenance of chronic hypertension in this model.
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Affiliation(s)
- Patrick K K Leong
- Dept. of Physiology and Biophysics, Univ. of Southern California Keck School of Medicine, Los Angeles, USA
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17
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Bobulescu IA, Dwarakanath V, Zou L, Zhang J, Baum M, Moe OW. Glucocorticoids acutely increase cell surface Na+/H+ exchanger-3 (NHE3) by activation of NHE3 exocytosis. Am J Physiol Renal Physiol 2005; 289:F685-91. [PMID: 15942046 PMCID: PMC2861571 DOI: 10.1152/ajprenal.00447.2004] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Glucocorticoids have important effects on renal function, including the modulation of renal acidification by the major proximal tubular Na(+)/H(+) exchanger, NHE3. While the chronic effect of glucocorticoids is considered to be primarily at the transcriptional level, with increases in NHE3 mRNA and protein expression driving increased transport activity, the mechanisms by which glucocorticoids activate NHE3 in an acute setting have not been investigated. Previous studies have shown that a glucocorticoid-stimulated increase in NHE3 activity can occur before any detectable change in NHE3 mRNA. The present study examines the acute effects of glucocorticoids on NHE3 using opossum kidney (OKP) cells as a cell model. In OKP cells, total NHE3 protein abundance was not changed by 3 h of treatment with dexamethasone (10(-6) M). However, the biotin-accessible fraction representing NHE3 at the apical membrane as well as Na(+)/H(+) exchange activity measured fluorimetrically using the pH-sensitive dye BCECF-AM were significantly increased. These effects were not prevented by the protein synthesis inhibitor cycloheximide. NHE3 insertion (biotinylatable NHE3 after sulfo-NHS-acetate blockade) was stimulated by dexamethasone incubation, with or without cycloheximide. The rate of NHE3 endocytic retrieval, assessed either by the avidin protection assay (early endocytosis) or by the sodium 2-mercaptoethane sulfonate (MesNa) cleavage assay (early and late endocytosis), was not affected by dexamethasone. These findings suggest that trafficking plays a key role in the acute stimulation of NHE3 by glucocorticoids, with exocytosis being the major contributor to the glucocorticoid-induced rapid increase in cell surface NHE3 protein abundance and Na(+)/H(+) exchange activity.
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Affiliation(s)
- I Alexandru Bobulescu
- Univ. of Texas Southwestern Medical Ctr., 5323 Harry Hines Blvd., Dallas, TX 75390-8856, USA
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18
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Leong PKK, Yang LE, Lin HW, Holstein-Rathlou NH, McDonough AA. Acute hypotension induced by aortic clamp vs. PTH provokes distinct proximal tubule Na+ transporter redistribution patterns. Am J Physiol Regul Integr Comp Physiol 2004; 287:R878-85. [PMID: 15205183 DOI: 10.1152/ajpregu.00180.2004] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Renal parathyroid hormone (PTH) action is often studied at high doses (100 microg PTH/kg) that lower mean arterial pressure significantly, albeit transiently, complicating interpretation of studies. Little is known about the effect of acute hypotension on proximal tubule Na(+) transporters. This study aimed to determine the effects of acute hypotension, induced by aortic clamp or by high-dose PTH (100 microg PTH/kg), on renal hemodynamics and proximal tubule Na/H exchanger isoform 3 (NHE3) and type IIa Na-P(i) cotransporter protein (NaPi2) distribution. Subcellular distribution was analyzed in renal cortical membranes fractionated on sorbitol density gradients. Aortic clamp-induced acute hypotension (from 100 +/- 3 to 78 +/- 2 mmHg) provoked a 62% decrease in urine output and a significant decrease in volume flow from the proximal tubule detected as a 66% decrease in endogenous lithium clearance. There was, however, no significant change in glomerular filtration rate (GFR) or subcellular distribution of NHE3 and NaPi2. In contrast, high-dose PTH rapidly (<2 min) decreased arterial blood pressure to 51 +/- 3 mmHg, decreased urine output, and shifted NHE3 and NaPi2 out of the low-density membranes enriched in apical markers. PTH at much lower doses (<1.4 microg.kg(-1).h(-1)) did not change blood pressure and was diuretic. In conclusion, acute hypotension per se increases proximal tubule Na(+) reabsorption without changing NHE3 or NaPi2 subcellular distribution, indicating that trafficking of transporters to the surface is not the likely mechanism; in comparison, hypotension secondary to high-dose PTH blocks the primary diuretic effect of PTH but does not inhibit the PTH-stimulated redistribution of NHE3 and NaPi2 to the base of the microvilli.
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Affiliation(s)
- Patrick K K Leong
- Dept. of Physiology and Biophysics, Univ. of Southern California Keck School of Medicine, 1333 San Pablo St., Los Angeles, CA 90089-9142, USA
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Abstract
In order to carry out their physiological functions, ion transport proteins must be targeted to the appropriate domains of cell membranes. Regulation of ion transport activity frequently involves the tightly controlled delivery of intracellular populations of transport proteins to the plasma membrane or the endocytic retrieval of transport proteins from the cell surface. Transport proteins carry signals embedded within their structures that specify their subcellular distributions and endow them with the capacity to participate in regulated membrane trafficking processes. Recently, a great deal has been learned about the biochemical nature of these signals, as well as about the cellular machinery that interprets them and acts upon their messages.
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Affiliation(s)
- Theodore R Muth
- Department of Biology, CUNY Brooklyn College, 2900 Bedford Avenue, Brooklyn, New York 11231, USA.
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20
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Bacic D, Kaissling B, McLeroy P, Zou L, Baum M, Moe OW. Dopamine acutely decreases apical membrane Na/H exchanger NHE3 protein in mouse renal proximal tubule. Kidney Int 2003; 64:2133-41. [PMID: 14633135 PMCID: PMC4114392 DOI: 10.1046/j.1523-1755.2003.00308.x] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Dopamine is a principal natriuretic hormone in mammalian Na+ homeostasis. Dopamine acutely alters glomerular filtration rate (GFR) and decreases Na+ absorption in both the proximal and distal nephron. Proximal tubule natriuresis is effected through inhibition of the apical membrane Na/H exchanger NHE3. METHODS We examined whether dopamine directly and acutely decreases apical membrane NHE3 protein using renal tissue in two in vitro systems: renal cortical slices and in vitro perfused single tubules. After incubation with dopamine, NHE3 activity was measured by 22Na flux and NHE3 antigen was measured by immunoblot in apical membrane and total cellular membranes. RESULTS Direct application of dopamine to either cortical slices or microperfused tubules acutely decreases NHE3 activity and antigen at the apical membrane of the proximal tubule. No change in total cellular NHE3 was detected. CONCLUSION One mechanism by which dopamine causes natriuresis is via direct and acute reduction of NHE3 protein at the apical membrane via changes in NHE3 protein trafficking.
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Affiliation(s)
- Desa Bacic
- Institute of Anatomy, University of Zürich, Zürich, Switzerland
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21
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Klisic J, Zhang J, Nief V, Reyes L, Moe OW, Ambühl PM. Albumin Regulates the Na+/H+Exchanger 3 in OKP Cells. J Am Soc Nephrol 2003; 14:3008-16. [PMID: 14638900 DOI: 10.1097/01.asn.0000098700.70804.d3] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
ABSTRACT. Albumin filtered by the glomerulus is reabsorbed in the proximal tubule. We have shown previously that proteinuria stimulates the proximal tubular Na+/H+exchanger 3 (NHE3) in rats. Activation of NHE3 may be a pathophysiologically important factor in the development of renal salt and water retention observed in the nephrotic syndrome. For examining whether albumin is a specific inducer of proximal tubular Na+/H+exchange and to determine the molecular mechanisms by which it regulates Na+/H+exchange, the effect of albumin on NHE3 in opossum kidney cells was studied. Albumin activated Na+/H+exchange in a time- and dose-dependent manner up to 100% in 48 h. In the early phase of stimulation (2 to 12 h), NHE3 activity was increased without changes in NHE3 protein and mRNA. At 24 h, increased NHE3 activity was accompanied by increase in cell surface NHE3 protein. The increase in surface NHE3 was associated with increased bidirectional trafficking of NHE3 protein between intracellular compartments and the cell surface. At 48 h, total cell NHE3 protein abundance and mRNA were increased as well. Whereas NHE3 translation was increased, NHE3 protein half-life remained unchanged. The effects of albumin on NHE3 protein abundance were modified by hydrocortisone in a complicated pattern. These results indicate that albumin directly regulates proximal tubular NHE3 at multiple levels.
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Affiliation(s)
- Jelena Klisic
- Department of Physiology, University of Zurich-Irchel, Zurich, Switzerland
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22
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Di Sole F, Cerull R, Babich V, Quiñones H, Gisler SM, Biber J, Murer H, Burckhardt G, Helmle-Kolb C, Moe OW. Acute regulation of Na/H exchanger NHE3 by adenosine A(1) receptors is mediated by calcineurin homologous protein. J Biol Chem 2003; 279:2962-74. [PMID: 14570899 DOI: 10.1074/jbc.m306838200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Adenosine is an autacoid that regulates renal Na(+) transport. Activation of adenosine A(1) receptor (A(1)R) by N(6)-cyclopentidyladenosine (CPA) inhibits the Na(+)/H(+) exchanger 3 (NHE3) via phospholipase C/Ca(2+)/protein kinase C (PKC) signaling pathway. Mutation of PKC phosphorylation sites on NHE3 does not affected regulation of NHE3 by CPA, but amino acid residues 462 and 552 are essential for A(1)R-dependent control of NHE3 activity. One binding partner of the NHE family is calcineurin homologous protein (CHP). We tested the role of NHE3-CHP interaction in mediating CPA-induced inhibition of NHE3 in opossum kidney (OK) and Xenopus laevis uroepithelial (A6) cells. Both native and transfected NHE3 and CHP are present in the same immuno-complex by co-immunoprecipitation. CPA (10(-6) M) increases CHP-NHE3 interaction by 30 - 60% (native and transfected proteins). Direct CHP-NHE3 interaction is evident by yeast two-hybrid assay (bait, NHE3(C terminus); prey, CHP); the minimal interacting region is localized to the juxtamembrane region of NHE3(C terminus) (amino acids 462-552 of opossum NHE3). The yeast data were confirmed in OK cells where truncated NHE3 (NHE3(delta552)) still shows CPA-stimulated CHP interaction. Overexpression of the polypeptide from the CHP binding region (NHE3(462-552)) interferes with the ability of CPA to inhibit NHE3 activity and to increase CHPNHE3(Full-length) interaction. Reduction of native CHP expression by small interference RNA abolishes the ability of CPA to inhibit NHE3 activity. We conclude that CHPNHE3 interaction is regulated by A(1)R activation and this interaction is a necessary and integral part of the signaling pathway between adenosine and NHE3.
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Affiliation(s)
- Francesca Di Sole
- Department of Internal Medicine, University of Texas Southwestern, Dallas, Texas 75390-8856, USA.
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McDonough AA, Biemesderfer D. Does membrane trafficking play a role in regulating the sodium/hydrogen exchanger isoform 3 in the proximal tubule? Curr Opin Nephrol Hypertens 2003; 12:533-41. [PMID: 12920402 DOI: 10.1097/00041552-200309000-00009] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
PURPOSE OF REVIEW The proximal tubule sodium/hydrogen exchanger continuously reabsorbs the bulk of the filtered sodium, controlling salt delivery to the distal nephron which is critical for tubuloglomerular feedback autoregulation and for fine control of salt excretion in the distal nephron. This review focuses on recent studies of the mechanisms of regulation of sodium transport in the proximal tubule, and addresses whether results from studies in proximal tubule cell lines are applicable to the proximal tubule in situ. RECENT FINDINGS Recent in-vivo studies provided evidence that sodium/hydrogen exchanger isoform 3 can move into and out of the apical microvilli accompanied by parallel changes in renal sodium transport: the exchanger is retracted from the microvilli in response to hypertension, parathyroid hormone or dopamine treatment and moved into the microvilli in response to sympathetic nervous system stimulation, puromycin aminonucleoside induced nephritic syndrome, and insulin treatment. Studies in cultured opossum kidney proximal tubule cells provided evidence for clathrin coated vesicle mediated, dynamin dependent, cytoskeleton dependent internalization of sodium/hydrogen exchanger isoform 3 from the surface to an endosomal pool in response to dopamine or parathyroid hormone. In the intact proximal tubule there is evidence for a two-step internalization process: (1) from villi to the intermicrovillar cleft region and (2) to a higher density membrane pool that may be either below the microvilli or deep in intermicrovillar clefts. Recent studies have described a significant inactive pool of the exchanger in the intermicrovillar region in vivo that may serve as a storage and recruitable pool. SUMMARY The molecular mechanisms responsible for increasing or decreasing sodium transport in the proximal tubule appear to include redistribution of sodium/hydrogen exchanger isoform 3 to or from the microvillar region. Detailed studies in cultured proximal tubule cell lines provide evidence for endocytosis and exocytosis of the exchanger dependent on cytoskeleton and clathrin coated vesicles. In vivo, the apical membrane is differentiated into discrete villar and intermicrovillar membrane domains and the intermicrovillar domain, not observed in cultured cells, may serve as a recruitable storage pool for sodium/hydrogen exchanger isoform 3.
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Affiliation(s)
- Alicia A McDonough
- Department of Physiology, University of Southern California Keck School of Medicine, Los Angeles, California 90089-9142, USA.
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du Cheyron D, Chalumeau C, Defontaine N, Klein C, Kellermann O, Paillard M, Poggioli J. Angiotensin II stimulates NHE3 activity by exocytic insertion of the transporter: role of PI 3-kinase. Kidney Int 2003; 64:939-49. [PMID: 12911544 DOI: 10.1046/j.1523-1755.2003.00189.x] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Low-concentration angiotensin II (Ang II) stimulates Na+/H+ exchanger 3 (NHE3) activity in renal proximal tubule mainly via angiotensin II type 1 (AT1) receptors. The mechanisms that mediate the increase in NHE3 activity elicited by Ang II remain incompletely settled. METHODS To assess a potential role of NHE3 trafficking in the Ang II effect, NHE3 activity was measured by H+-driven initial rate of 22Na uptake resistant to 50 micromol/L of the Na+/H+ exchange inhibitor cariporide (HOE642), and sensitive to 300 micromol/L ethyl isopropyl amiloride (EIPA), in a model of cultured proximal tubular cells (MKCC), in which functional apical NHE3 and AT receptors are normally present. Apical expression of NHE3 protein was determined by cell surface biotinylation and immunoblotting. RESULTS Ang II (10-10 mol/L, 43 minutes) increased NHE3 activity and biotinylated NHE3 protein without any change in total amount of NHE3 protein. Both effects were suppressed by specific AT1 receptor antagonists. When 2-mercaptoethanesulphonic acid (MESNA) was used to cleave biotin from all apical proteins, intracellular biotinylated NHE3 protein remained unchanged after Ang II incubation compared to control. When sulfo-N-hydrosuccinimide (NHS)-acetate was used first to block all apical reactive sites, an increase in biotinylated NHE3 protein was observed following Ang II incubation. To evaluate the role of phosphatidylinositol 3-kinase (PI 3-kinase), the specific inhibitor wortmannin was used. It suppressed Ang II-induced increase in NHE3 activity and trafficking. Furthermore, latrunculin B, inhibitor of actin filament polymerization, prevented both Ang II stimulatory effects. CONCLUSION Ang II stimulates NHE3 activity, at least in part, by exocytic insertion of the protein into the apical membrane. This effect is mediated by PI 3-kinase and required integrity of actin cytoskeleton.
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Affiliation(s)
- Damien du Cheyron
- Institut National de la Santé et de la Recherche Médicale, Paris, France.
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25
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Wolff NA, Thies K, Kuhnke N, Reid G, Friedrich B, Lang F, Burckhardt G. Protein kinase C activation downregulates human organic anion transporter 1-mediated transport through carrier internalization. J Am Soc Nephrol 2003; 14:1959-68. [PMID: 12874449 DOI: 10.1097/01.asn.0000079040.55124.25] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Organic anion transport in intact renal proximal tubule cells in animal model systems is downregulated by treatments that activate protein kinase C (PKC). How this downregulation is achieved is not yet known. Stimulation of PKC with sn-1,2-dioctanoylglycerol resulted in strong inhibition of p-aminohippurate transport mediated by the cloned human organic anion transporter 1 (hOAT1) expressed in Xenopus oocytes and HEK293 cells, as well as hOAT1 internalization in both expression systems. The sn-1,2-dioctanoylglycerol-induced transport inhibition was partially prevented by staurosporine. It was independent of the conserved canonical PKC consensus sites in hOAT1, however, and was unaffected by agents that destabilize actin filaments or microtubules, which altered baseline hOAT1-mediated p-aminohippurate uptake activity in oocytes. It is concluded that PKC-induced hOAT1 downregulation is achieved through carrier retrieval from the cell membrane and does not involve phosphorylation of the predicted classic hOAT1 PKC consensus sites.
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Affiliation(s)
- Natascha A Wolff
- Center for Physiology and Pathophysiology, Georg August University, Göttingen, Germany.
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26
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Laverty G, McWilliams C, Sheldon A, Arnason SS. PTH stimulates a Cl(-)-dependent and EIPA-sensitive current in chick proximal tubule cells in culture. Am J Physiol Renal Physiol 2003; 284:F987-95. [PMID: 12505864 DOI: 10.1152/ajprenal.00281.2002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The electrophysiological effects of parathyroid hormone (PTH) were studied in a primary cell culture model of the chick (Gallus domesticus) proximal tubule. In this model, confluent monolayers are grown on permeable filters and exhibit vectorial transport, including glucose-stimulated current. Under short-circuit conditions, PTH, at 10(-9) M, induced a positive current [short-circuit current (I(sc))] response, with an average 2-min peak response of 14.30 +/- 1.58 microA/cm(2) over the baseline I(sc,) followed by a slow decay. The PTH response was dose dependent, with a half-maximal response at 5 x 10(-9) M and maximal response at 5 x 10(-8) M. Forskolin and dibutyryl-cAMP also stimulated I(sc), as did the phosphodiesterase inhibitor IBMX. In contrast, the phorbol ester PMA inhibited baseline I(sc). The PTH response was nearly abolished by apical addition of 100 microM EIPA, an inhibitor of Na(+)/H(+) exchangers, and partially blocked by the Cl(-) channel blockers 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB; 100 microM) and glibenclamide (300 microM). Higher doses of EIPA or NPPB alone (500 microM) were almost fully effective, with no or slight additional effects of NPPB or EIPA, respectively. The anion exchange inhibitor DIDS (100 microM) and the Na(+) channel blocker amiloride (10 microM) had no effect. Bilateral reduction of Cl(-) in the buffer, from 137 to 2.6 mM, abolished the PTH response; increasing Cl(-) concentration restored the I(sc) response, with a half-maximal effect at 50 mM. These data suggest that, in the chick proximal tubule, PTH activates both an Na(+)/H(+) exchanger and a Cl(-) channel that may be functionally linked.
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Affiliation(s)
- Gary Laverty
- Department of Biological Sciences, University of Delaware, Newark, Delaware 19716, USA.
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Leong PKK, Yang LE, Holstein-Rathlou NH, McDonough AA. Angiotensin II clamp prevents the second step in renal apical NHE3 internalization during acute hypertension. Am J Physiol Renal Physiol 2002; 283:F1142-50. [PMID: 12372791 DOI: 10.1152/ajprenal.00178.2002] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Acute hypertension inhibits proximal tubule (PT) sodium reabsorption. The resultant increase in NaCl delivery to the macula densa suppresses renin release. We tested whether the sustained pressure-induced inhibition of PT sodium reabsorption requires a renin-mediated decrease in ANG II levels. Plasma ANG II concentration of anesthesized Sprague-Dawley rats was clamped by simultaneous infusion of the ANG I-converting enzyme inhibitor captopril (12 microg/min) and ANG II (20 ng. kg(-1). min(-1)). Blood pressure was increased 50 mmHg for 20 min by arterial constriction +/- ANG II clamp or by sham operation. This acute hypertension increased urine output and endogenous Li(+) clearance, and these responses were blunted 40-50% in ANG II clamped rats. Acute hypertension provoked a rapid redistribution of Na(+)/H(+) exchanger isoform 3 (NHE3) out of apical brush-border membranes (21 +/- 4% decrease of total NHE3 abundance) to endosomal/lysosomal membranes (16 +/- 6% increase of total). In ANG II-clamped rats, acute hypertension also provoked disappearance of NHE3 from the apical membranes (27 +/- 2% decrease of total), but NHE3 was shifted to membranes enriched in intermicrovillar cleft and dense apical tubules (step 1) rather than endosomal/lysosomal membranes (step 2). This difference was independently confirmed by confocal analysis. In contrast, the pressure-induced redistribution of Na(+)-P(i) cotransporter type 2 was not altered by ANG II clamp. We conclude that the responses to acute hypertension, including diuresis and redistribution of PT NHE3 into intracellular membranes, require a responsive renin-angiotensin system and that the responses may be induced by the sustained increase in NaCl delivery to the macula densa during acute hypertension.
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Affiliation(s)
- Patrick K K Leong
- Department of Physiology and Biophysics, University of Southern California Keck School of Medicine, Los Angeles, California 90089-9142, USA
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Klisic J, Hu MC, Nief V, Reyes L, Fuster D, Moe OW, Ambühl PM. Insulin activates Na(+)/H(+) exchanger 3: biphasic response and glucocorticoid dependence. Am J Physiol Renal Physiol 2002; 283:F532-9. [PMID: 12167605 DOI: 10.1152/ajprenal.00365.2001] [Citation(s) in RCA: 135] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Insulin is an important regulator of renal salt and water excretion, and hyperinsulinemia has been implicated to play a role in hypertension. One of the target proteins of insulin action in the kidney is Na(+)/H(+) exchanger 3 (NHE3), a principal Na(+) transporter responsible for salt absorption in the mammalian proximal tubule. The molecular mechanisms involved in activation of NHE3 by insulin have not been studied so far. In opossum kidney (OK) cells, insulin increased Na(+)/H(+) exchange activity in a time- and concentration-dependent manner. This effect is due to activation of NHE3 as it persisted after pharmacological inhibition of NHE1 and NHE2. In the early phase of stimulation (2-12 h), NHE3 activity was increased without changes in NHE3 protein and mRNA. At 24 h, enhanced NHE3 activity was accompanied by an increase in total and cell surface NHE3 protein and NHE3 mRNA abundance. All the effects of insulin on NHE3 activity, protein, and mRNA were amplified in the presence of hydrocortisone. These results suggest that insulin stimulates renal tubular NHE3 activity via a biphasic mechanism involving posttranslational factors and an increase in NHE3 gene expression and the effects are dependent on the permissive action of hydrocortisone.
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Affiliation(s)
- Jelena Klisic
- Department of Physiology, University of Zurich-Irchel, CH-8057 Zurich, Switzerland
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29
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LaPointe MS, Sodhi C, Sahai A, Batlle D. Na+/H+ exchange activity and NHE-3 expression in renal tubules from the spontaneously hypertensive rat. Kidney Int 2002; 62:157-65. [PMID: 12081574 DOI: 10.1046/j.1523-1755.2002.00406.x] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND The NHE-3 isoform of the Na+/H+ antiporter, in the apical membrane of renal proximal tubule, is responsible for the bulk transport of Na+ and fluid reabsorption. Studies have reported that apical NHE-3 translocates to internal pools, thereby facilitating natriuresis when blood pressure increases abruptly. METHODS The present study examined Na+/H+ exchange activity and NHE-3 expression in renal cortical tubules from the spontaneously hypertensive rat (SHR) and WKY rats before and after the development of hypertension. SHR 4 to 6 weeks of age were pre-hypertensive, 6 to 7 weeks old had mild hypertension, and 8 to 13 weeks old had severe hypertension. Renal proximal tubules (PTs) were isolated and purified by Percoll gradient centrifugation. NHE-3 protein and mRNA levels were determined by Western and Northern blots, respectively. Apical brush border membrane vesicles (BBMV) were prepared using the MgSO4 aggregation method and Na+/H+ exchange activity assessed using the acridine orange method. RESULTS Na+/H+ exchange activity, determined as the rate of Na+-dependent intracellular pH (pHi) recovery assessed using BCECF after an acute acid load, was significantly greater in PTs from SHR than in WKY rats at all age groups (4 to 6 weeks, 0.30 +/- 0.04 vs. 0.24 +/- 0.02 pH U/30 sec, P < 0.05; 6 to 7 weeks, 0.42 +/- 0.07 vs. 0.29 +/- 0.05 pH U/30 sec, P < 0.05; and 8 to 13 weeks, 0.48 +/- 0.07 vs. 0.40 +/- 0.07 pH U/30 sec, P < 0.05). The Na+-dependent recovery in BBMV was also greater in SHR than WKY rats (1464 +/- 62 vs. 1042 +/- 79 fluorescence. U/5 sec, P < 0.001) and was unaffected by cariporide, a specific NHE-1 inhibitor. NHE-3 protein levels also were significantly higher in SHR than age-matched WKY rats at all stages during the development of hypertension (pre-hypertensive 1.8-fold; early onset hypertension twofold; established hypertension 1.5-fold; each P < 0.05). By contrast, NHE-3 mRNA levels were not different between SHR and WKY rats at each age group. CONCLUSIONS Na+/H+ exchange activity and NHE-3 protein abundance in renal proximal tubules from the SHR are increased while NHE-3 mRNA is not. A post-transcriptional event(s) best explains the increase in NHE-3 protein expression since mRNA levels were not increased. The alterations in the SHR antedate the development of hypertension and fail to decrease as blood pressure increases with age in the SHR, which likely results in inappropriate renal sodium retention in the face of a chronic rise in blood pressure.
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Affiliation(s)
- Michael S LaPointe
- Division of Nephrology and Hypertension, Department of Medicine, Northwestern University Medical School, Searle 10-475, 303 E Chicago Avenue, Chicago, IL 60611, USA.
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30
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Di Sole F, Cerull R, Casavola V, Moe OW, Burckhardt G, Helmle-Kolb C. Molecular aspects of acute inhibition of Na(+)-H(+) exchanger NHE3 by A(2)-adenosine receptor agonists. J Physiol 2002; 541:529-43. [PMID: 12042357 PMCID: PMC2290320 DOI: 10.1113/jphysiol.2001.013438] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Adenosine regulates Na(+) homeostasis by its acute effects on renal Na(+) transport. We have shown in heterologously transfected A6/C1 cells (renal cell line from Xenopus laevis) that adenosine-induced natriuresis may be effected partly via A(2) adenosine receptor-mediated inactivation of the renal brush border membrane Na(+)-H(+) exchanger NHE3. In this study we utilized A6/C1 cells stably expressing wild-type as well as mutated forms of NHE3 to assess the molecular mechanism underlying A(2)-dependent control of NHE3 function. Cell surface biotinylation combined with immunoprecipitation revealed that NHE3 is targeted exclusively to the apical domain and that the endogenous Xenopus NHE is located entirely on the basolateral side of A6/C1 transfectants. Stimulation of A(2)-adenosine receptors located on the basolateral side for 15 min with CPA (N6-cyclopentyladenosine) acutely decreased NHE3 activity (microspectrofluorimety). This effect was mimicked by 8-bromo-cAMP and entirely blocked by pharmacological inhibition of PKA (with H89) or singular substitution of two PKA target sites (serine 552 and serine 605) on NHE3. Downregulation of NHE3 activity by CPA was attributable to a reduction of NHE3 intrinsic transport activity without change in surface NHE3 protein at 15 min. At 30 min, the decrease in transport activity was associated with a decrease in apical membrane NHE3 antigen. In conclusion, two highly conserved target serine sites on NHE3 determine NHE3 modulation upon A(2)-receptor activation and NHE3 inactivation by adenosine proceeds via two phases with distinct mechanisms.
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Affiliation(s)
- Francesca Di Sole
- Department of Physiology and Pathophysiology, Division of Vegetative Physiology and Pathophysiology, Georg-August-University of Göttingen, D-37073 Göttingen, Germany
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31
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Sabolić I, Herak-Kramberger CM, Ljubojević M, Biemesderfer D, Brown D. NHE3 and NHERF are targeted to the basolateral membrane in proximal tubules of colchicine-treated rats. Kidney Int 2002; 61:1351-64. [PMID: 11918742 DOI: 10.1046/j.1523-1755.2002.00266.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Depolymerization of microtubules in proximal tubule (PT) cells of colchicine-treated rats causes disruption of vesicle recycling and redistribution of some brush-border membrane (BBM) transporters into cytoplasmic vesicles. NHE3, an isoform of the Na+/H+ exchanger in the PT cell BBM, is acutely regulated by a variety of mechanisms, including protein trafficking and interaction with the PDZ protein, NHERF. The effects of microtubule disruption by colchicine on NHE3 trafficking in PT and the potential role of NHERF in this process have not been studied. METHODS Immunofluorescence and immunogold cytochemistry were performed on cryosections of kidney tissue, and immunoblotting of BBM isolated from the renal cortex and outer stripe of control and colchicine-treated (3.2 mg/kg, IP, a single dose 12 hours before sacrifice) rats. RESULTS In cells of the convoluted PT (S1/S2 segments) of control rats, NHE3 was located mainly in the BBM; subapical endosomes were weakly stained. In cells of the straight PT (S3 segment), NHE3 was present in the BBM and in lysosomes. In colchicine-treated rats, there was a marked redistribution of NHE3 from the BBM into intracellular vesicles and the basolateral plasma membrane in the S1/S2 segments. In the S3 segment, the abundance of BBM NHE3 was not visibly changed, but NHE3-positive intracellular organelles largely disappeared, and the antigen was detectable in the basolateral plasma membrane. The PDZ protein NHERF followed a similar pattern: in control animals, it was strong in the BBM and negative in the basolateral membrane in cells along the PT. After colchicine treatment, expression of NHERF in the basolateral membrane strongly increased in all PT segments, where it colocalized with NHE3. CONCLUSIONS The data indicate that: (a) microtubules are involved in the apical targeting of NHE3 and NHERF in renal PT cells, and (b) the parallel basolateral insertion of NHE3 and NHERF may represent an indirect targeting pathway that involves transient, microtubule-independent basolateral insertion of these proteins, followed by microtubule-dependent, vesicle-mediated transcytosis to the BBM.
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Affiliation(s)
- Ivan Sabolić
- Unit of Molecular Toxicology, Institute for Medical Research and Occupational Health, Zagreb, Croatia.
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32
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Yang L, Leong PKK, Chen JO, Patel N, Hamm-Alvarez SF, McDonough AA. Acute hypertension provokes internalization of proximal tubule NHE3 without inhibition of transport activity. Am J Physiol Renal Physiol 2002; 282:F730-40. [PMID: 11880335 DOI: 10.1152/ajprenal.00298.2001] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Acute hypertension rapidly decreases proximal tubule (PT) Na(+) reabsorption, facilitated by a redistribution of PT Na(+)/H(+) exchangers (NHE3) out of the apical brush border, increasing NaCl at the macula densa, the signal for autoregulation of renal blood flow and GFR. This study aimed to determine whether NHE3 activity per transporter decreases during acute hypertension and the time dependence of the response. Blood pressure was elevated by 50-60 mmHg in male Sprague-Dawley rats for 5 or 30 min by constricting arteries. Renal cortical membranes were fractionated by density gradient centrifugation. NHE3 transport activity was assayed as the rate of appearance of acridine orange (AO) from AO-loaded vesicles in response to an inwardly directed Na(+) gradient. After 5-min hypertension, 20% of total NHE3 protein, assayed by immunoblot, redistributed from low-density apical membranes to middensity membranes enriched in intermicrovillar cleft markers; by 30 min, a similar percentage shifted to heavier density membranes containing markers of endosomes. NHE3 activity shifted to higher density membranes along with NHE3 protein, that is, no change in activity/transporter during acute hypertension. Confocal analysis of NHE3 distribution also verified removal from apical microvilli and appearance in subapical vesicles. We conclude that the decrease in renal PT Na(+) transport during acute hypertension is mediated by removal of transport-competent NHE3 from the apical brush border to subapical and internal reserves.
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Affiliation(s)
- Li Yang
- Department of Physiology and Biophysics, University of Southern California Keck School of Medicine, Los Angeles, California 90089-9142, USA
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33
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Cavet ME, Akhter S, Murtazina R, Sanchez de Medina F, Tse CM, Donowitz M. Half-lives of plasma membrane Na(+)/H(+) exchangers NHE1-3: plasma membrane NHE2 has a rapid rate of degradation. Am J Physiol Cell Physiol 2001; 281:C2039-48. [PMID: 11698263 DOI: 10.1152/ajpcell.2001.281.6.c2039] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The Na(+)/H(+) exchangers NHE2 and NHE3 are involved in epithelial Na(+) and HCO absorption. To increase insights into the functions of NHE2 vs. NHE3, we compared their cellular processing with each other and with the housekeeping isoform NHE1. Using biotinylated exchanger, we determined that the half-life of plasma membrane NHE2 was short (3 h) compared with that of NHE1 (24 h) and NHE3 (14 h) in both PS120 fibroblasts and Caco-2 cells. NHE2 transport and plasma membrane levels were reduced by 3 h of Brefeldin A treatment, whereas NHE1 was unaffected. NHE2 was degraded by the lysosomes but not proteosomes, as demonstrated by increasing levels of endocytosed NHE2 protein after inhibition of the lysosomes, but not with proteosome inhibition. Unlike that of NHE3, basal NHE2 transport activity was not affected by phosphatidylinositol 3-kinase inhibition and did not appear to be localized in the juxtanuclear recycling endosome. Therefore, for NHE2, protein degradation and/or protein synthesis probably play important roles in its basal and regulated states. These results suggest fundamental differences in the cellular processing and trafficking of NHE2 and NHE3. These differences may underlie the specialized roles that these exchangers play in epithelial cells.
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Affiliation(s)
- M E Cavet
- Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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Murer H, Hernando N, Forster I, Biber J. Molecular aspects in the regulation of renal inorganic phosphate reabsorption: the type IIa sodium/inorganic phosphate co-transporter as the key player. Curr Opin Nephrol Hypertens 2001; 10:555-61. [PMID: 11496046 DOI: 10.1097/00041552-200109000-00002] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The type IIa sodium/inorganic phosphate co-transporter is the rate-limiting inorganic phosphate transport pathway in renal brush-border membranes, and is thus a key player in overall inorganic phosphate homeostasis. Its regulation is mostly associated with membrane retrieval/reinsertion (traffic) of the transport protein. This membrane traffic is controlled by specific 'motifs' at the level of the transporter protein and probably involves interacting proteins (e.g. for scaffolding, regulation or sorting). The intracellular signaling mechanisms (e.g. the involvement of kinases) and the involvement of the cytoskeleton are not yet understood. Hereditary alterations in renal inorganic phosphate handling can be associated with factors controlling the expression of the brush-border type IIa sodium/inorganic phosphate co-transporter.
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Affiliation(s)
- H Murer
- Institute of Physiology, University of Zurich, Switzerland.
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35
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Weinman EJ, Steplock D, Wade JB, Shenolikar S. Ezrin binding domain-deficient NHERF attenuates cAMP-mediated inhibition of Na(+)/H(+) exchange in OK cells. Am J Physiol Renal Physiol 2001; 281:F374-80. [PMID: 11457730 DOI: 10.1152/ajprenal.2001.281.2.f374] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Na(+)/H(+) exchanger regulatory factor (NHERF), an essential protein cofactor in cAMP-mediated inhibition of Na(+)/H(+) exchange transporter 3 (NHE3), facilitates the formation of a signal complex of proteins that includes NHE3, NHERF, and ezrin. This model for NHE3 regulation was developed in fibroblasts and its applicability to epithelial cells remains to be established. Opossum kidney (OK) cells were transfected with either empty vector (control), full-length mouse (m) NHERF(1-355), or a truncated mNHERF(1-325) that lacked ezrin binding and had been demonstrated in fibroblasts to bind NHE3 but not mediate its cAMP-associated inhibition. 8-Bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) at 10(-4) M inhibited Na(+)/H(+) exchange activity in control and OK cells expressing wild-type mNHERF(1-355) by >60% but by <10% in cells expressing mNHERF(1-325). NHE3 coimmunoprecipitated with mNHERF(1-325), but cAMP phosphorylation of NHE3 was impaired in cells expressing mNHERF(1-325). The inhibitory effect of hyperosmolality on NHE3 activity and the uptake of 3-O-methyl-D-glucose was the same in all three cell lines. Cell surface expression of NHE3 was not changed by cAMP in any of the cells lines. These data indicate that disruption of the NHERF-ezrin signal complex attenuates the inhibitory effect of cAMP on NHE3 activity in OK cells and provides evidence supporting the proposed model of protein kinase A regulation of NHE3 in epithelial cells.
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Affiliation(s)
- E J Weinman
- Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA.
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Xu H, Collins JF, Bai L, Kiela PR, Lynch RM, Ghishan FK. Epidermal growth factor regulation of rat NHE2 gene expression. Am J Physiol Cell Physiol 2001; 281:C504-13. [PMID: 11443049 DOI: 10.1152/ajpcell.2001.281.2.c504] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Epidermal growth factor (EGF) is involved in acute regulation of Na(+)/H(+) exchangers (NHEs), but the effect of chronic EGF administration on NHE gene expression is unknown. The present studies showed that EGF treatment increased NHE2-mediated intestinal brush-border membrane vesicle Na(+) absorption and NHE2 mRNA abundance by nearly twofold in 19-day-old rats. However, no changes were observed in renal NHE2 mRNA or intestinal and renal NHE3 mRNA abundance. To understand the mechanism of this regulation, we developed the rat intestinal epithelial (RIE) cell as an in vitro model to study the effect of EGF on NHE2 gene expression. EGF increased functional NHE2 activity and mRNA abundance in cultured RIE cells, and this stimulation could be blocked by actinomycin D (a transcriptional inhibitor). Additionally, NHE2 promoter reporter gene assays in transiently transfected RIE cells showed an almost twofold increase in promoter activity after EGF treatment. We conclude that rat NHE2 activity can be stimulated by chronic EGF treatment and that this response is at least partially mediated by gene transcription.
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Affiliation(s)
- H Xu
- Departments of Pediatrics, Steele Memorial Children's Research Center, University of Arizona Health Sciences Center, Tucson, Arizona 85724, USA.
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37
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Hu MC, Fan L, Crowder LA, Karim-Jimenez Z, Murer H, Moe OW. Dopamine acutely stimulates Na+/H+ exchanger (NHE3) endocytosis via clathrin-coated vesicles: dependence on protein kinase A-mediated NHE3 phosphorylation. J Biol Chem 2001; 276:26906-15. [PMID: 11328806 DOI: 10.1074/jbc.m011338200] [Citation(s) in RCA: 129] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Dopamine (DA) is a key hormone in mammalian sodium homeostasis. DA induces natriuresis via acute inhibition of the renal proximal tubule apical membrane Na(+)/H(+) exchanger NHE3. We examined the mechanism by which DA inhibits NHE3 in a renal cell line. DA acutely decreases surface NHE3 antigen in dose- and time-dependent fashion without altering total cellular NHE3. Although DA(1) receptor agonist alone decreases surface NHE3, simultaneous DA(2) agonist synergistically enhances the effect of DA(1). Decreased surface NHE3 antigen, caused by stimulation of NHE3 endocytosis, is dependent on intact functioning of the GTPase dynamin and involves increased binding of NHE3 to the adaptor protein AP2. DA-stimulated NHE3 endocytosis can be blocked by pharmacologic or genetic protein kinase A inhibition or by mutation of two protein kinase A target serines (Ser-560 and Ser-613) on NHE3. We conclude that one mechanism by which DA induces natriuresis is via protein kinase A-mediated phosphorylation of proximal tubule NHE3 leading to endocytosis of NHE3 via clathrin-coated vesicles.
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Affiliation(s)
- M C Hu
- Medical Service, Department of Veterans Affairs Medical Center, Dallas, Texas 75216, USA
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38
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Biemesderfer D, DeGray B, Aronson PS. Active (9.6 s) and inactive (21 s) oligomers of NHE3 in microdomains of the renal brush border. J Biol Chem 2001; 276:10161-7. [PMID: 11120742 DOI: 10.1074/jbc.m008098200] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have previously shown that Na(+)-H(+) exchanger isoform NHE3 exists as both 9.6 and 21 S (megalin-associated) oligomers in the renal brush border. To characterize the oligomeric forms of the renal brush border Na(+)-H(+) exchanger in more detail, we performed membrane fractionation studies. We found that similar amounts of NHE3 were present in microvilli and a nonmicrovillar membrane domain of high density (dense vesicles). Horseradish peroxidase-labeled endosomes were not prevalent in the dense membrane fraction. However, megalin, which localizes primarily to the intermicrovillar microdomain of the brush border, was enriched in the dense vesicles, implicating this microdomain as the likely source of these membranes. Immunolocalization of NHE3 confirmed that a major fraction of the transporter colocalized with megalin in the intermicrovillar region of the brush border. Immunoprecipitation studies demonstrated that in microvilli the majority of NHE3 was not bound to megalin, while in the dense vesicles most of the NHE3 coprecipitated with megalin. Moreover, sucrose velocity gradient centrifugation experiments revealed that most NHE3 in microvilli sedimented with an S value of 9.6, while the S value of NHE3 in dense vesicles was 21. Finally, we examined the functional state of NHE3 in both membrane fractions. As assayed by changes in acridine orange fluorescence, imposing an outwardly directed Na(+) gradient caused generation of an inside acid pH gradient in the microvilli, indicating Na(+)-H(+) exchange activity, but not in the dense vesicles. Taken together, these data demonstrate that renal brush border NHE3 exists in two oligomeric states: a 9.6 S active form present in microvilli and a 21 S, megalin-associated, inactive form in the intermicrovillar microdomain of the apical plasma membrane. Thus, regulation of renal brush border Na(+)-H(+) exchange activity may be mediated by shifting the distribution between these forms of NHE3.
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Affiliation(s)
- D Biemesderfer
- Departments of Internal Medicine and of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06520-8029, USA.
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Gisler SM, Stagljar I, Traebert M, Bacic D, Biber J, Murer H. Interaction of the type IIa Na/Pi cotransporter with PDZ proteins. J Biol Chem 2001; 276:9206-13. [PMID: 11099500 DOI: 10.1074/jbc.m008745200] [Citation(s) in RCA: 203] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The type IIa Na(+)-dependent inorganic phosphate (Na/P(i)) cotransporter is localized in the apical membrane of proximal tubular cells and is regulated by an endocytotic pathway. Because molecular processes such as apical sorting, internalization, or subsequent degradation might be assisted by associated proteins, a yeast two-hybrid screen against the C-terminal, cytosolic tail of type IIa cotransporter was designed. Most of the potential proteins found belonged to proteins with multiple PDZ modules and were either identical/related to PDZK1 or identical to NHERF-1. Yeast trap truncation assays confined the peptide-protein association to the C-terminal amino acid residues TRL of type IIa cotransporter and to single PDZ domains of each identified protein, respectively. The specificity of these interactions were confirmed in yeast by testing other apical localized transmembraneous proteins. Moreover, the type IIa protein was recovered in vitro by glutathione S-transferase-fused PDZ proteins from isolated renal brush border membranes or from type IIa-expressing oocytes. Further, these PDZ proteins are immunohistochemically detected either in the microvilli or in the subapical compartment of proximal tubular cells. Our results suggest that the type IIa Na/P(i) cotransporter interacts with various PDZ proteins that might be responsible for the apical sorting, parathyroid hormone controlled endocytosis or the lysosomal sorting of internalized type IIa cotransporter.
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Affiliation(s)
- S M Gisler
- Institute of Physiology, Veterinary Biochemistry, and Anatomy, University of Zürich-Irchel, CH-8057 Zürich, Switzerland
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40
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Chalumeau C, du Cheyron D, Defontaine N, Kellermann O, Paillard M, Poggioli J. NHE3 activity and trafficking depend on the state of actin organization in proximal tubule. Am J Physiol Renal Physiol 2001; 280:F283-90. [PMID: 11208604 DOI: 10.1152/ajprenal.2001.280.2.f283] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The present study was addressed to define the contribution of cytoskeleton elements in the kidney proximal tubule Na+/H+ exchanger 3 (NHE3) activity under basal conditions. We used luminal membrane vesicles (LMV) isolated from suspensions of rat cortical tubules pretreated with either colchicine (Colch) or cytochalasin D (Cyto D). Colch pretreatment of suspensions (200 microM for 60 min) moderately decreased LMV NHE3 activity. Cyto D pretreatment (1 microM for 60 min) elicited an increase in LMV NHE3 transport activity but did not increase Na-glucose cotransport activity. Cyto D pretreatment of suspensions did not change the apparent affinity of NHE3 for internal H+. In contrast, after Cyto D pretreatment of the suspensions, NHE3 protein abundance was increased in LMV and remained unchanged in cortical cell homogenates. The effect of Cyto D on NHE3 was further assessed with cultures of murine cortical cells. The amount of surface biotinylated NHE3 increased on Cyto D treatment, whereas NHE3 protein abundance was unchanged in cell homogenates. In conclusion, under basal conditions NHE3 activity depends on the state of actin organization possibly involved in trafficking processes between luminal membrane and intracellular compartment.
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Affiliation(s)
- C Chalumeau
- Institut National de la Santé et de la Recherche Médicale Unité 356, Institut Fédératif de Recherche 58, France
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41
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Féraille E, Doucet A. Sodium-potassium-adenosinetriphosphatase-dependent sodium transport in the kidney: hormonal control. Physiol Rev 2001; 81:345-418. [PMID: 11152761 DOI: 10.1152/physrev.2001.81.1.345] [Citation(s) in RCA: 340] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Tubular reabsorption of filtered sodium is quantitatively the main contribution of kidneys to salt and water homeostasis. The transcellular reabsorption of sodium proceeds by a two-step mechanism: Na(+)-K(+)-ATPase-energized basolateral active extrusion of sodium permits passive apical entry through various sodium transport systems. In the past 15 years, most of the renal sodium transport systems (Na(+)-K(+)-ATPase, channels, cotransporters, and exchangers) have been characterized at a molecular level. Coupled to the methods developed during the 1965-1985 decades to circumvent kidney heterogeneity and analyze sodium transport at the level of single nephron segments, cloning of the transporters allowed us to move our understanding of hormone regulation of sodium transport from a cellular to a molecular level. The main purpose of this review is to analyze how molecular events at the transporter level account for the physiological changes in tubular handling of sodium promoted by hormones. In recent years, it also became obvious that intracellular signaling pathways interacted with each other, leading to synergisms or antagonisms. A second aim of this review is therefore to analyze the integrated network of signaling pathways underlying hormone action. Given the central role of Na(+)-K(+)-ATPase in sodium reabsorption, the first part of this review focuses on its structural and functional properties, with a special mention of the specificity of Na(+)-K(+)-ATPase expressed in renal tubule. In a second part, the general mechanisms of hormone signaling are briefly introduced before a more detailed discussion of the nephron segment-specific expression of hormone receptors and signaling pathways. The three following parts integrate the molecular and physiological aspects of the hormonal regulation of sodium transport processes in three nephron segments: the proximal tubule, the thick ascending limb of Henle's loop, and the collecting duct.
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Affiliation(s)
- E Féraille
- Division of Nephrology, Geneva University Hospital, Geneva, Switzerland.
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42
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Peng Y, Amemiya M, Yang X, Fan L, Moe OW, Yin H, Preisig PA, Yanagisawa M, Alpern RJ. ET(B) receptor activation causes exocytic insertion of NHE3 in OKP cells. Am J Physiol Renal Physiol 2001; 280:F34-42. [PMID: 11133512 DOI: 10.1152/ajprenal.2001.280.1.f34] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Endothelin-1 (ET-1) activates sodium/hydrogen exchanger 3 (NHE3) in opossum kidney clone P (OKP) cells expressing ET(B) receptors. ET-1 (10(-8) M) caused a two- to threefold increase in apical membrane NHE3 (assessed by surface biotinylation), in the absence of a change in total cellular NHE3. A maximal effect was achieved within 15 min. The increase in apical NHE3 was not blocked by cytochalasin D but was blocked by latrunculin B, which also prevented the ET-1-induced increase in NHE3 activity. Endocytic internalization of NHE3, measured as protection of biotinylated NHE3 from the membrane-impermeant, sulfhydryl-reducing agent MesNa was minimal within 35 min and was not regulated by ET-1. Exocytic insertion of NHE3, measured as the appearance of biotinylated NHE3 after the blockade of reactive sites with sulfo-NHS-acetate, was increased in response to ET-1. These studies demonstrate that ET-1 induces net trafficking of NHE3 to the apical membrane that is mediated by enhanced exocytic insertion and is required for increased NHE3 activity.
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Affiliation(s)
- Y Peng
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas 75235, USA
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43
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Wiederkehr MR, Di Sole F, Collazo R, Quiñones H, Fan L, Murer H, Helmle-Kolb C, Moe OW. Characterization of acute inhibition of Na/H exchanger NHE-3 by dopamine in opossum kidney cells. Kidney Int 2001; 59:197-209. [PMID: 11135072 DOI: 10.1046/j.1523-1755.2001.00480.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Dopamine (DA) is a principal natriuretic hormone that defends extracellular fluid volume from a Na load. Natriuresis is effected partly through inhibiting the proximal tubule Na/H exchanger NHE-3. Changes in NHE-3 phosphorylation is one mechanism by which NHE-3 activity is regulated. METHODS We used opossum kidney (OK) cells to characterize the differential and synergistic effects of DA receptor subtype-1 (DA1) and -2 (DA2) agonists and the effect of blockade of protein kinase A (PKA) or protein kinase C (PKC) on NHE-3 activity and phosphorylation. RESULTS DA and DA1 agonists inhibited NHE-3 activity, and DA1 antagonist blocked the effect of either DA or DA1 agonist. DA2 agonist alone had no effect, but DA2 antagonist reduced the DA effect on NHE-3 activity. DA1 and DA2 agonists together were more potent than DA1 alone. PKA inhibition eliminated the effect of DA1 agonist and partially blocked the effect of DA on NHE-3 activity. PKC inhibition did not block the DA effect. DA1 agonist and PKA activation phosphorylated NHE-3 on identical sites. Despite lack of effect on NHE-3 activity, DA2 agonists increased NHE-3 phosphorylation. DA-induced NHE-3 phosphorylation was distinct from DA1 and PKA but closely resembled DA2. CONCLUSION We postulate the following: (1) DA modifies NHE-3 phosphorylation by activating PKA through DA1 and by other kinases/phosphatases via DA2. (2) DA1 is sufficient to inhibit NHE-3, while DA2 is insufficient but plays a synergistic role by altering NHE-3 phosphorylation.
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MESH Headings
- 2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine/pharmacology
- Animals
- Bromocriptine/pharmacology
- Cells, Cultured
- Cyclic AMP/pharmacology
- Cyclic AMP-Dependent Protein Kinases/metabolism
- Dopamine/pharmacology
- Dopamine Agonists/pharmacology
- Dose-Response Relationship, Drug
- Kidney/cytology
- Kidney/metabolism
- Opossums
- Phosphorylation
- Protein Kinase C/metabolism
- Receptors, Dopamine D1/agonists
- Receptors, Dopamine D1/metabolism
- Receptors, Dopamine D2/agonists
- Receptors, Dopamine D2/metabolism
- Sodium-Hydrogen Exchanger 3
- Sodium-Hydrogen Exchangers/antagonists & inhibitors
- Time Factors
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Affiliation(s)
- M R Wiederkehr
- Medical Service, Department of Veteran Affairs Medical Center and Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75235-8856, USA
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44
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Collazo R, Fan L, Hu MC, Zhao H, Wiederkehr MR, Moe OW. Acute regulation of Na+/H+ exchanger NHE3 by parathyroid hormone via NHE3 phosphorylation and dynamin-dependent endocytosis. J Biol Chem 2000; 275:31601-8. [PMID: 10866993 DOI: 10.1074/jbc.m000600200] [Citation(s) in RCA: 116] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Parathyroid hormone (PTH) is a potent inhibitor of mammalian renal proximal tubule Na(+) transport via its action on the apical membrane Na(+)/H(+) exchanger NHE3. In the opossum kidney cell line, inhibition of NHE3 activity was detected from 5 to 45 min after PTH addition. Increase in NHE3 phosphorylation on multiple serines was evident after 5 min of PTH, but decrease in surface NHE3 antigen was not detectable until after 30 min of PTH. The decrease in surface NHE3 antigen was due to increased NHE3 endocytosis. When endocytic trafficking was arrested with a dominant negative dynamin mutant (K44A), the early inhibition (5 min) of NHE3 activity by PTH was not affected, whereas the late inhibition (30 min) and decreased surface NHE3 antigen induced by PTH were abrogated. We conclude that PTH acutely inhibits NHE3 activity in a biphasic fashion by NHE3 phosphorylation followed by dynamin-dependent endocytosis.
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Affiliation(s)
- R Collazo
- Medical Service, Department of Veterans Affairs Medical Center and Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75235, USA
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45
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Girardi AC, Titan SM, Malnic G, Rebouças NA. Chronic effect of parathyroid hormone on NHE3 expression in rat renal proximal tubules. Kidney Int 2000; 58:1623-31. [PMID: 11012896 DOI: 10.1046/j.1523-1755.2000.00323.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND The most abundant Na+/H+ exchanger in the apical membrane of proximal tubules is the type 3 isoform (NHE3), and its activity is acutely inhibited by parathyroid hormone (PTH). In the present study, we investigate whether changes in protein abundance as well as in mRNA levels play a significant role in the long-term modulation of NHE3 by PTH. METHODS Three groups of animals were compared: (1) HP: animals submitted to hyperparathyroidism by subcutaneous implantation of PTH pellets, providing threefold basal levels of this hormone (2.1 U. h-1); (2) control: sham-operated rats in which placebo pellets were implanted; (3) PTX: animals submitted to hypoparathyroidism by thyroparathyroidectomy followed by subcutaneous implantation of thyroxin pellets, which provided basal levels of thyroid hormone. After eight days, we measured bicarbonate reabsorption in renal proximal tubules by in vivo microperfusion. NHE3 activity was also measured in brush border membrane (BBM) vesicles by proton dependent uptake of 22Na. NHE3 expression was evaluated by Northern blot, Western blot and immunohistochemistry. RESULTS Bicarbonate reabsorption in renal proximal tubules was significantly decreased in HP rats. Na+/H+ exchange activity in isolated BBM vesicles was 6400 +/- 840, 9225 +/- 505, and 12205 +/- 690 cpm. mg-1. 15 s-1 in HP, sham, and PTX groups, respectively. BBM NHE3 protein abundance decreased 39.3 +/- 8.2% in HP rats and increased 54.6 +/- 7.8% in PTX rats. Immunohistochemistry showed that expression of NHE3 protein in apical BBM was decreased in HP rats and was increased in PTX rats. Northern blot analysis of total kidney RNA showed that the abundance of NHE3 mRNA was 20.3 +/- 1.3% decreased in HP rats and 27. 7 +/- 2.1% increased in PTX. CONCLUSIONS Our results indicate that the chronic inhibitory effect of PTH on the renal proximal tubule NHE3 is associated with changes in the expression of NHE3 mRNA levels and protein abundance.
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Affiliation(s)
- A C Girardi
- Instituto de Ciências Biomédicas, Departamento de Fisiologia e Biofísica, Universidade de São Paulo, São Paulo, Brazil
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46
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Magyar CE, Zhang Y, Holstein-Rathlou NH, McDonough AA. Proximal tubule Na transporter responses are the same during acute and chronic hypertension. Am J Physiol Renal Physiol 2000; 279:F358-69. [PMID: 10919857 DOI: 10.1152/ajprenal.2000.279.2.f358] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Acute hypertension in Sprague-Dawley rats (SD) provokes a decrease in renal proximal tubule (PT) salt and fluid reabsorption, redistribution of apical Na/H exchanger isoform 3 (NHE3) and Na-P(i) cotransporter type 2 (NaPi2) out of the brush border into higher density membranes, and inhibition of renal cortical Na-K-ATPase (NKA) activity (41). The aims of this study were to determine 1) whether an increase in arterial pressure affects distribution or activity of Na transporters in the spontaneously hypertensive rat (SHR) and 2) whether development of chronic hypertension in SHR leads to persistent adaptive changes in NHE3 and NaPi2 distribution and/or NKA activity. Renal cortex Na transporter protein density distributions and activities were compared by subcellular fractionation in 1) adult SHR with an acute increase or decrease in arterial pressure and 2) young SD (YSD) and young SHR (YSHR) vs. adult SD and SHR. In adult hypertensive SHR NHE3 was shifted to membranes of higher densities, analogous to SD with acute hypertension, and there were no further changes with a further increase or decrease in arterial pressure. There was no change in total pool size of NHE3 in cortex in YSHR vs. SHR. NHE3, NaPi2, megalin, NKA alpha-/beta-subunit, dipeptidyl peptidase IV (DPPIV), and villin distributions were the same in YSHR vs. YSD. NHE3, NaPi2, and megalin shifted to higher densities in adult SHR, but not SD, with age. Basolateral NKA and apical alkaline phosphatase activities were 40% greater in YSHR than YSD and decreased to SD levels in adults. We conclude that there are persistent changes in Na(+) transporter distributions and activity in response to chronic hypertension in SHR that mimic the responses to acute hypertension seen in SD rats and that elevated sodium pump activity per transporter in YSHR may contribute to the generation of hypertension.
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Affiliation(s)
- C E Magyar
- Department of Physiology and Biophysics, University of Southern California School of Medicine, Los Angeles 90033, USA
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47
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Yang X, Amemiya M, Peng Y, Moe OW, Preisig PA, Alpern RJ. Acid incubation causes exocytic insertion of NHE3 in OKP cells. Am J Physiol Cell Physiol 2000; 279:C410-9. [PMID: 10913008 DOI: 10.1152/ajpcell.2000.279.2.c410] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Incubation of opossum kidney clone P (OKP) cells in acid media (pH 6. 8) causes activation of Na(+)/H(+) exchanger 3 (NHE3) at 6, 12, and 24 h. OKP cell NHE3 protein abundance was increased by 45% at 24 h of acid incubation but was unaffected at 3-12 h. By contrast, apical membrane NHE3, measured by surface biotinylation, increased approximately twofold at 6, 12, and 24 h, mirroring the increase in activity. Acid incubation caused a 76% increase in exocytic insertion of NHE3 into the apical membrane but had no effect on endocytic internalization at 6 h. Latrunculin B, an inhibitor of microfilament organization, inhibited the acid-induced increases in apical membrane NHE3, exocytic insertion of NHE3, and NHE3 activity at 6 h. These studies demonstrate two mechanisms for acid-induced increases in NHE3 activity. Beginning at 6 h, there is an increase in apical membrane NHE3 that is due to stimulated exocytic insertion and is required for increased NHE3 activity. At 24 h, there is an additional increase in total cellular NHE3.
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Affiliation(s)
- X Yang
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas 75235, USA
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48
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Magyar CE, McDonough AA. Molecular mechanisms of sodium transport inhibition in proximal tubule during acute hypertension. Curr Opin Nephrol Hypertens 2000; 9:149-56. [PMID: 10757220 DOI: 10.1097/00041552-200003000-00009] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Acute hypertension provokes a rapid decrease in proximal tubule salt and water reabsorption that increases the levels of sodium chloride at the macula densa, the error signal to increase arteriolar resistance to autoregulate renal blood flow and glomerular filtration rate, and contributes to pressure natriuresis. The molecular mechanisms responsible for this critical homeostatic adjustment are beginning to be dissected: apical sodium transporters in the proximal tubule are redistributed out of the brush border to intermicrovillar and endosomal stores and sodium pump activity is inhibited. These responses are strikingly similar to the cellular responses to parathyroid hormone, and are mediated by similar signalling pathways.
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Affiliation(s)
- C E Magyar
- Department of Physiology and Biophysics, USC Keck School of Medicine, Los Angeles, CA 90089, USA
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49
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Chapter 12 Molecular physiology of mammalian epithelial Na+/H+ exchangers NHE2 and NHE3. CURRENT TOPICS IN MEMBRANES 2000. [DOI: 10.1016/s1063-5823(00)50014-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
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50
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Moe OW. Acute regulation of proximal tubule apical membrane Na/H exchanger NHE-3: role of phosphorylation, protein trafficking, and regulatory factors. J Am Soc Nephrol 1999; 10:2412-25. [PMID: 10541303 DOI: 10.1681/asn.v10112412] [Citation(s) in RCA: 98] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Affiliation(s)
- O W Moe
- Department of Veterans Affairs Medical Center and Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas 75235-8856, USA.
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