The Experts below are selected from a list of 246 Experts worldwide ranked by ideXlab platform
Richard C. Gardner - One of the best experts on this subject based on the ideXlab platform.
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Residues of the yeast ALR1 protein that are critical for Magnesium uptake
Current Genetics, 2006Co-Authors: Jong-min Lee, Richard C. GardnerAbstract:Mutagenesis was used to study the function by the ALR1 (aluminium resistance) gene, which encodes the major Mg^2+ uptake system in yeast. Truncation of Alr1 showed that the N-terminal 239 amino acids and the C-terminal 53 amino acids are not essential for Magnesium uptake. Random PCR mutagenesis was undertaken of the C-terminal part of ALR1 that is homologous to the bacterial CorA Magnesium Transport family. The mutants with the most severe phenotype all had amino acid changes in a small region containing the putative transmembrane domains. Eighteen single amino acid mutants in this critical region were classified into three categories for Magnesium uptake: no, low and moderate activity. Seventeen of the 18 mutants expressed a cross-reacting band of similar size and intensity as wild-type Alr1. Conservative mutations that reduced or inactivated uptake led us to identify Ser^729, Ile^746 and Met^762 (part of the conserved GMN motif) as critical amino acid residues in Alr1. High expression of inactive mutants inhibited the capability of wild-type Alr1 to Transport Magnesium, consistent with Alr1 forming homo-oligomers. The results confirm the classification of ALR1 as a member of the CorA family of Magnesium Transport genes.
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Genes for Magnesium Transport
Current opinion in plant biology, 2003Co-Authors: Richard C. GardnerAbstract:We know very little about the regulation of Magnesium uptake and the control of Magnesium homeostasis. After years of relative neglect, however, rapid progress is now being made in understanding the molecular biology of Magnesium Transport in eukaryotes. Several new gene families have been implicated, and tools are in place for the dissection of the biochemical and biological roles played by the encoded proteins.
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A Novel Family of Magnesium Transport Genes in Arabidopsis
The Plant cell, 2001Co-Authors: Ana F. Tutone, Richard C. Gardner, Revel S.m. Drummond, Sheng LuanAbstract:Magnesium (Mg(2+)) is the most abundant divalent cation in plant cells and plays a critical role in many physiological processes. We describe the identification of a 10-member Arabidopsis gene family (AtMGT) encoding putative Mg(2+) Transport proteins. Most members of the AtMGT family are expressed in a range of Arabidopsis tissues. One member of this family, AtMGT1, functionally complemented a bacterial mutant lacking Mg(2+) Transport capability. A second member, AtMGT10, complemented a yeast mutant defective in Mg(2+) uptake and increased the cellular Mg(2+) content of starved cells threefold during a 60-min uptake period. (63)Ni tracer studies in bacteria showed that AtMGT1 has highest affinity for Mg(2+) but may also be capable of Transporting several other divalent cations, including Ni(2+), Co(2+), Fe(2+), Mn(2+), and Cu(2+). However, the concentrations required for Transport of these other cations are beyond normal physiological ranges. Both AtMGT1 and AtMGT10 are highly sensitive to Al(3+) inhibition, providing potential molecular targets for Al(3+) toxicity in plants. Using green fluorescence protein as a reporter, we localized AtMGT1 protein to the plasma membrane in Arabidopsis plants. We suggest that the AtMGT gene family encodes a Mg(2+) Transport system in higher plants.
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Magnesium Transport and Aluminium Tolerance
Plant Nutrition — Molecular Biology and Genetics, 1999Co-Authors: Kathy M. Fowler, Colin Whiti Macdiarmid, Keith Richards, Richard C. GardnerAbstract:Aluminium toxicity is a major factor limiting crop productivity internationally. Under acidic soil conditions, Al is converted from insoluble forms into soluble Al. The ion is toxic to plants and causes an immediate cessation of root growth. The mechanism of this inhibition has not been clearly established, despite a plethora of suggestions (reviewed by Kochian, 1995).
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overexpression of the saccharomyces cerevisiae Magnesium Transport system confers resistance to aluminum ion
Journal of Biological Chemistry, 1998Co-Authors: Colin W Macdiarmid, Richard C. GardnerAbstract:Ionic aluminum (Al3+) is toxic to plants, microbes, fish, and animals, but the mechanism of its toxicity is unknown. We describe the isolation of two yeast genes (ALR1 and ALR2) which confer increased tolerance to Al3+ and Ga3+ ions when overexpressed while increasing strain sensitivity to Zn2+, Mn2+, Ni2+, Cu2+, Ca2+, and La3+ ions. The Alr proteins are homologous to theSalmonella typhimurium CorA protein, a bacterial Mg2+ and Co2+ Transport system located in the periplasmic membrane. Yeast strains lacking ALR gene activity required additional Mg2+ for growth, and expression of either ALR1 or ALR2 corrected the Mg2+-requiring phenotype. The results suggest that theALR genes encode the yeast uptake system for Mg2+ and other divalent cations. This hypothesis was supported by evidence that 57Co2+ accumulation was elevated in ALR-overexpressing strains and reduced in strains lacking ALR expression. ALRoverexpression also overcame the inhibition of Co2+ uptake by Al3+ ions. The results indicate that aluminum toxicity to yeast occurs as a consequence of reduced Mg2+ influx via the Alr proteins. The molecular identification of the yeast Mg2+ Transport system should lead to a better understanding of the regulation of Mg2+ homeostasis in eukaryote cells.
Michael E. Maguire - One of the best experts on this subject based on the ideXlab platform.
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Magnesium Transport and Magnesium Homeostasis
EcoSal Plus, 2008Co-Authors: Krisztina M. Papp-wallace, Michael E. MaguireAbstract:This review reviews the properties and regulation of the Salmonella enterica serovar Typhimurium and Escherichia coli Transporters that mediate Mg2+ influx: CorA and the Mgt P-type ATPases. In addition, potential Mg2+ regulation of transcription and translation, largely via the PhoPQ two component system, is discussed. CorA proteins are a unique class of Transporters and are widespread in the Bacteria and Archaea, with rather distant but functional homologs in eukaryotes. The Mgt Transporters are highly homologous to other P-type ATPases but are more closely related to the eukaryotic H+ and Ca2+ ATPases than to most prokaryotic ATPases. Hundreds of homologs of CorA are currently known from genomic sequencing. In contrast, only when extracellular and possibly intracellular Mg2+ levels fall significantly is the expression of mgtA and mgtB induced. Topology studies using blaM and lacZ fusions initially indicated that the Salmonella serovar Typhimurium CorA contained three transmembrane (TM) segments; however, subsequent data obtained using a variety of approaches showed that the CorA superfamily of proteins have only two TMs at the extreme C terminus. PhoP-PhoQ is a two-component system consisting of PhoQ, the sensor/receptor histidine kinase, and PhoP, the response regulator/transcriptional activator. The expression of both mgtA and mgtCB in either E. coli or Salmonella serovar Typhimurium is markedly induced in a PhoPQ-dependent manner by low concentrations of Mg2+ in the medium. phoP and phoQ form an operon with two promoters in both E. coli and Salmonella serovar Typhimurium.
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cation hexaammines are selective and potent inhibitors of the cora Magnesium Transport system
Journal of Biological Chemistry, 2000Co-Authors: Lisa M Kucharski, Wil J Lubbe, Michael E. MaguireAbstract:Abstract Cation hexaammines and related compounds are chemically stable analogs of the hydrated form of cations, particularly Mg2+. We tested the ability of several of these compounds to inhibit Transport by the CorA or MgtB Mg2+Transport systems or the PhoQ receptor kinase for Mg2+ inSalmonella typhimurium. Cobalt(III)-, ruthenium(II)-, and ruthenium(III)-hexaammines were potent inhibitors of CorA-mediated influx. Cobalt(III)- and ruthenium(III)chloropentaammines were slightly less potent inhibitors of CorA. The compounds inhibited uptake by the bacterial S. typhimurium CorA and by the archaealMethanococcus jannaschii CorA, which bear only 12% identity in the extracellular periplasmic domain. Cation hexaammines also inhibited growth of S. typhimurium strains dependent on CorA for Mg2+ uptake but not of isogenic strains carrying a second Mg2+ uptake system. In contrast, hexacyano-cobaltate(III) and ruthenate(II)- and nickel(II)hexaammine had little effect on uptake. The inhibition by the cation hexaammines was selective for CorA because none of the compounds had any effect on Transport by the MgtB P-type ATPase Mg2+ Transporter or the PhoQ Mg2+ receptor kinase. These results demonstrate that cation hexaammines are potent and highly selective inhibitors of the CorA Mg2+ Transport system and further indicate that the initial interaction of the CorA Transporter is with a fully hydrated Mg2+ cation.
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Magnesium Transport in prokaryotes.
Journal of biological inorganic chemistry : JBIC : a publication of the Society of Biological Inorganic Chemistry, 1999Co-Authors: Mary Beth C. Moncrief, Michael E. MaguireAbstract:Possessing the largest hydrated radius, the smallest ionic radius, and the highest charge density among the biologically relevant cations, Mg2+ provides an interesting problem for Transport into living cells. Transport systems for Mg2+ have been characterized primarily in Salmonella typhimurium because the well-developed genetics of Gram-negative bacteria make cloning and studying the Transporters a viable proposition. The CorA Transport system is expressed constitutively and is the major Mg2+ Transporter in Eubacteria and Archaea. It has three transmembrane domains, a uniquely large periplasmic domain, and no sequence homology to other proteins. The MgtE Mg2+ Transporter also lacks sequence homology to other proteins, and it is unclear if Mg2+ Transport is its primary function. The MgtA and MgtB Mg2+ Transporters have sequence homology to P-type ATPases. They are more closely related to the mammalian Ca2+–ATPases than to the prokaryotic P-type ATPases. MgtA and MgtB mediate Mg2+ influx with, rather than against, the Mg2+ electrochemical gradient. Unlike corA and mgtE, the mgtA and mgtC/mgtB loci are regulated, being induced by the two-component regulatory system PhoP/PhoQ. PhoQ is a Mg2+ membrane sensor kinase that phosphorylates the transcription factor PhoP under Mg2+–limiting conditions. This factor then induces transcription of mgtA and mgtCB. MgtC, which is encoded by the first gene in the mgtCB operon, has no sequence homology to any known protein and is essential for S.typhimurium virulence in mice and macrophages, but does appear to be a Mg2+ Transporter. The physiological roles of these Mg2+ Transporters and their mechanisms are not yet completely clear, but initial data indicate that Mg2+ Transporters are unique Transport systems with unusual mechanisms for mediating Mg2+ movement through the membrane.
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Microbial Magnesium Transport: unusual Transporters searching for identity
Molecular microbiology, 1998Co-Authors: Ronald L. Smith, Michael E. MaguireAbstract:Mg2+ is unique among biological cations because of its charge density and solution chemistry. This is abundantly reflected in its Transport systems, studied primarily in Salmonella typhimurium. The constitutively expressed CorA Transport system is the primary Mg2+ influx pathway for the Bacteria and the Archaea. Its structure of a large N-terminal soluble periplasmic domain with three transmembrane segments at the C-terminus is unique among membrane carriers, and its protein sequence bears no resemblance to other known proteins. The MgtE Transport system can also mediate Mg2+ uptake, but whether this is its primary function is not known. MgtE also lacks homology to other known proteins. In contrast, the MgtA and MgtB Mg2+ Transport systems of enteric bacteria are P-type ATPases by sequence homology, mediating Mg2+ influx with, rather than against, the Mg2+ electrochemical gradient. They are closely related to mammalian Ca2+-ATPases. Expression of MgtA and MgtB is under the control of the PhoPQ two-component regulatory system, important in bacterial virulence. In S. typhimurium, MgtB is encoded by a two-gene operon mgtCB; the function of the MgtC protein is unknown, and it lacks close homologues. The ligand for the PhoQ membrane sensor kinase is Mg2+ and, at decreased extracellular Mg2+ concentrations, transcription of mgtA and mgtCB are enormously induced. All three genes are also induced upon S. typhimurium invasion of epithelial or macrophage cells. Mutation of these genes has no effect on invasion efficiency, but an insertion in mgtC renders S. typhimurium essentially avirulent in the mouse. The physiological roles of the known Mg2+ Transport systems are not yet completely defined. Nonetheless, the singular sequence and apparent structure of the CorA and MgtE Transport proteins, the complex regulation of MgtA, MgtB and MgtC and their involvement in pathogenesis suggests that further study will be rewarding.
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The Magnesium Transport ATPases of Salmonella typhimurium
ATPases, 1996Co-Authors: Tao Tao, Michael E. MaguireAbstract:Publisher Summary Mg 2+ is one of the most abundant cations, second to potassium, and the most abundant divalent cation. This chapter provides an overview of the previous studies on Mg 2+ Transport in enteric bacteria and the Mg 2+ Transporting ATPases of Salmonella typhimurium . Mg 2+ is important for many aspects of cellular function. Structurally it is a major stabilizing factor for all biomembranes and the ribosomal translation apparatus, and it binds to nucleic acids and proteins to help maintain specific conformations. The gram negative bacterium Salmonella typhimurium is used as the model system for the study of transmembrane Mg 2+ Transport, because (1) in general, bacterial Transport systems are homologous in structure and mechanism to eukaryotic systems, (2) Salmonella typhimurium has been studied in great detail and the genetic techniques for prokaryotic systems are unmatched by any eukaryotic system, and (3) the previous studies of Mg 2+ Transport in the related bacterium, E.coli, provide background knowledge.
Pascal Houillier - One of the best experts on this subject based on the ideXlab platform.
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Performance of ion chromatography to measure picomole amounts of Magnesium in nanolitre samples.
The Journal of physiology, 2020Co-Authors: Lucile Figueres, Caroline Prot-bertoye, Luciana Morla, Elsa Ferriere, Camille Griveau, Gaelle Brideau, Stéphanie Baron, Pascal HouillierAbstract:Key points An UHPLC method to measure picomole amounts of Magnesium has been developed. The method is sensitive, specific, accurate and reproducible. The method is suitable for quantifying Magnesium Transport across intact epithelia. Abstract Magnesium is involved in many biological processes. Extracellular Magnesium homeostasis mainly depends on the renal handling of Magnesium, the study of which requires measurement of low concentrations of Magnesium in renal tubular fluid. We developed an ultra-high-performance liquid chromatography method to measure millimolar concentrations of Magnesium in nanolitre samples. Within-assay and between-assay coefficients of variation were lower than 5% and 6.6%, respectively. Measurement of Magnesium concentration was linear (r2 = 0.9998) over the range 0-4 mmol/l. Absolute bias ranged from -0.03 to 0.05 mmol/l. The lower limit of quantification was 0.2 mmol/l. Recovery was 97.5-100.3%. No significant interference with calcium, another divalent cation present in the same samples, was detected. The method was successfully applied to quantify transepithelial Magnesium Transport by medullary and cortical thick ascending limbs during ex vivo microperfusion experiments. In conclusion, ultra-high-performance liquid chromatography is suitable for measurement of picomole amounts of Magnesium in renal tubular fluid. The method allows detailed studies of transepithelial Magnesium Transport across native epithelium.
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Mechanisms and Regulation of Renal Magnesium Transport
Annual review of physiology, 2014Co-Authors: Pascal HouillierAbstract:Magnesium's most important role is in the release of chemical energy. Although most Magnesium is stored outside of the extracellular fluid compartment, the regulated value is blood Magnesium concentration. Cellular Magnesium and bone Magnesium do not play a major role in the defense of blood Magnesium concentration; the major role is played by the kidney, where the renal tubule matches the urinary Magnesium excretion and the net entry of Magnesium into the extracellular fluid. In the kidney, Magnesium is reabsorbed in the proximal tubule, the thick ascending limb of the loop of Henle, and the distal convoluted tubule. Magnesium absorption is mainly paracellular in the proximal tubule and in the thick ascending limb of the loop of Henle, whereas it is transcellular in the distal convoluted tubule. Several hormones and extracellular Magnesium itself alter the distal tubular handling of Magnesium, but the hormone(s) regulating extracellular Magnesium concentration remains unknown.
Gary A. Quamme - One of the best experts on this subject based on the ideXlab platform.
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Magnesium Transport in the renal distal convoluted tubule
Physical Review, 2001Co-Authors: Long-jun Dai, Gordon Ritchie, Dirk Kerstan, Hyung Sub Kang, David E C Cole, Gary A. QuammeAbstract:The distal tubule reabsorbs ∼10% of the filtered Mg2+, but this is 70–80% of that delivered from the loop of Henle. Because there is little Mg2+ reabsorption beyond the distal tubule, this segment ...
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Epithelial Magnesium Transport and regulation by the kidney.
Frontiers in bioscience : a journal and virtual library, 2000Co-Authors: Gary A. Quamme, C De RouffignacAbstract:Magnesium is the fourth most abundant cation in the body and the second most common cation in the intracellular fluid. It is the kidney that provides the most sensitive control for Magnesium balance. About a 80% of the total serum Magnesium is ultrafilterable through the glomerular membrane. In all of the mammalian species studied to date, the proximal tubule of the adult animal reabsorbs only a small fraction, 10-15%, of the filtered Magnesium. Unlike the adult proximal convoluted tubule that of young rats (aged 13-15 days) reabsorbs 50-60% of filtered Magnesium along the proximal tubule together with sodium, calcium, and water. Micropuncture experiments, in every species studied to date, indicates that a large part (approximately 60%) of the filtered Magnesium is reabsorbed in the loop of Henle. Magnesium reabsorption in the loop occurs within the cortical thick ascending limb (cTAL) by passive means driven by the transepithelial voltage through the paracellular pathway. Micropuncture experiments have clearly showed that the superficial distal tubule reabsorbs significant amounts of Magnesium. Unlike the thick ascending limb of the loop of Henle, Magnesium reabsorption in the distal tubule is transcellular and active in nature. Many hormones and nonhormonal factors influence renal Magnesium reabsorption to variable extent in the cTAL and distal tubule. Moreover, nonhormonal factors may have important implications on hormonal controls of renal Magnesium conservation. Dietary Magnesium restriction leads to renal Magnesium conservation with diminished urinary Magnesium excretion. Adaptation of Magnesium Transport with dietary Magnesium restriction occurs in both the cTAL and distal tubule. Elevation of plasma Magnesium or calcium concentration inhibits Magnesium and calcium reabsorption leading to hypermagnesiuria and hypercalciuria. The identification of an extracellular Ca2+/Mg2+ -sensing receptor located on the peritubular side of cTAL and distal tubule cells explains this phenomenon. Loop diuretics, such as furosemide and bumetanide, diminish salt absorption in the cTAL whereas the distally acting diuretics, amiloride and chlorothiazide stimulate Magnesium reabsorption within the distal convoluted tubule. Finally, metabolic acidosis, potassium depletion or phosphate restriction can diminish Magnesium reabsorption within the loop and distal tubule. Research in the 90's have greatly contributed to our understanding of renal Magnesium handling.
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Determination of epithelial Magnesium Transport with stable isotopes.
Journal of pharmacological and toxicological methods, 2000Co-Authors: Werner Stegmann, Gary A. QuammeAbstract:The inability to adequately determine Mg(2+) flux rates with radiotracer studies has stymied our efforts to understand how Magnesium is Transported by epithelial cells. To evaluate epithelial Mg(2+) Transport, a stable 25Mg isotope was used to measure Magnesium uptake into normal and Mg(2+)-depleted Madin-Darby canine kidney (MDCK) cells. 25Mg entry rates were significantly increased in Mg(2+)-depleted cells relative to those cultured in normal Magnesium media, 0.5 mM. 25Mg uptake was inhibited by external La(3+) but not Ca(2+) in both normal and Mg(2+)-depleted cells suggesting a specific entry pathway. These results with 25Mg were the same as with microfluorescence determinations using mag-fura-2. We have shown that Mg(2+) entry into epithelial cells reflects transepithelial Transport; accordingly, increased Mg(2+) uptake in Mg(2+)-depleted cells provides an important intrinsic control of renal Magnesium absorption. Furthermore, these studies indicate that cellular Mg(2+) Transport may be quantitated with the use of stable isotopes that may be successfully applied to cells other than epithelia.
Karl Peter Schlingmann - One of the best experts on this subject based on the ideXlab platform.
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A critical role of TRPM channel-kinase for human Magnesium Transport.
The Journal of Physiology, 2005Co-Authors: Karl Peter Schlingmann, Thomas GudermannAbstract:Hereditary disorders of Magnesium homeostasis comprise a heterogenous group of diseases mainly affecting the renal conservation of Magnesium. In the past few years, genetic studies in affected individuals disclosed the first molecular components of epithelial Magnesium Transport: the tight junction protein paracellin-1 (claudin-16) was discovered as a key player in paracellular Magnesium and calcium reabsorption in the thick ascending limb of Henle's loop and the γ-subunit was identified as a component of renal Na+–K+-ATPase critical for transcellular Magnesium reabsorption in the distal convoluted tubule. However, the molecular identity of proteins directly involved in cellular Magnesium Transport remained largely unknown until a series of recent studies highlighted the critical role of two members of the transient receptor potential (TRP) family, for body Magnesium homeostasis. TRPM6 and TRPM7 belong to the melastatin-related TRPM subfamily of TRP channels whose eight members exhibit a significant diversity in domain structure as well as cation selectivity and activation mechanisms. Both proteins share the unique feature of an atypical kinase domain at their C-terminus for which they have been termed ‘chanzymes’ (channels plus enzymes). Whereas electrophysiological and biochemical analyses identified TRPM7 as an important player in cellular Magnesium homeostasis, the critical role of TRPM6 for epithelial Magnesium Transport emerged from the discovery of loss-of-function mutations in patients with a severe form of hereditary hypomagnesaemia called primary hypomagnesaemia with secondary hypocalcaemia or HSH. The aim of this review is to summarize the data emerging from molecular genetic, biochemical and electrophysiological studies on these fascinating two new proteins combining ion channel and enzyme functions/properties.
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Essential role for TRPM6 in epithelial Magnesium Transport and body Magnesium homeostasis.
Pflugers Archiv : European journal of physiology, 2005Co-Authors: Vladimir Chubanov, Thomas Gudermann, Karl Peter SchlingmannAbstract:Magnesium is an important cofactor for many biological processes such as protein synthesis, nucleic acid stability and neuromuscular excitability. The extracellular Magnesium concentration is regulated tightly by the extent of intestinal absorption and renal excretion. Despite their critical role in Magnesium handling, the molecular mechanisms mediating transepithelial Transport are still not understood completely. Recently, genetic studies in patients with primary hypomagnesaemia and secondary hypocalcaemia (HSH), a combined defect of intestinal Magnesium absorption and renal Magnesium conservation, have identified “transient receptor potential (melastatin) 6” (TRPM6) as the first component involved directly in epithelial Magnesium reabsorption. TRPM7, the closest homologue of TRPM6, has a central role in Mg2+ uptake in vertebrate cells since TRPM7-deficient cells become Mg2+ deficient and are not viable. TRPM7 has been characterized functionally as a constitutively active ion channel permeable for a variety of cations including calcium and Magnesium and regulated by intracellular concentrations of Magnesium and/or Magnesium-nucleotide complexes. Both proteins share the unique feature of cation channels fused to serine/threonine kinase domains. This review summarizes recent data that has emerged from molecular genetic, biochemical and electrophysiological studies on these fascinating two new proteins and their involvement in epithelial Magnesium Transport.
