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Worcester EM, Bergsland KJ, Gillen DL, Coe FL. Evidence for increased renal tubule and parathyroid gland sensitivity to serum calcium in human idiopathic hypercalciuria. Am J Physiol Renal Physiol 2013; 305:F853-60. [PMID: 23863465 DOI: 10.1152/ajprenal.00124.2013] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Patients with idiopathic hypercalciuria (IH) have decreased renal calcium reabsorption, most marked in the postprandial state, but the mechanisms are unknown. We compared 29 subjects with IH and 17 normal subjects (N) each fed meals providing identical amounts of calcium. Urine and blood samples were collected fasting and after meals. Levels of three candidate signalers, serum calcium (SCa), insulin (I), and plasma parathyroid hormone (PTH), did not differ between IH and N either fasting or fed, but all changed with feeding, and the change in SCa was greater in IH than in N. Regression analysis of fractional excretion of calcium (FECa) was significant for PTH and SCa in IH but not N. With the use of multivariable analysis, Sca entered the model while PTH and I did not. To avoid internal correlation we decomposed FECa into its independent terms: adjusted urine calcium (UCa) and UFCa molarity. Analyses using adjusted Uca and unadjusted Uca parallel those using FECa, showing a dominant effect of SCa with no effect of PTH or I. The effect of SCa may be mediated via vitamin D receptor-stimulated increased abundance of basolateral Ca receptor, which is supported by the fact PTH levels also seem more responsive to serum Ca in IH than in N. Although our data support an effect of SCa on FECa and UCa, which is more marked in IH than in N, it can account for only a modest fraction of the meal effect, perhaps 10-20%, suggesting additional mediators are also responsible for the exaggerated postprandial hypercalciuria seen in IH.
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Affiliation(s)
- Elaine M Worcester
- Nephrology Section MC 5100, Univ. of Chicago Medicine, 5841 South Maryland Ave., Chicago, IL 60637.
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Tyler Miller R. Control of renal calcium, phosphate, electrolyte, and water excretion by the calcium-sensing receptor. Best Pract Res Clin Endocrinol Metab 2013; 27:345-58. [PMID: 23856264 DOI: 10.1016/j.beem.2013.04.009] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Through regulation of excretion, the kidney shares responsibility for the metabolic balance of calcium (Ca(2+)) with several other tissues including the GI tract and bone. The balances of Ca(2+) and phosphate (PO4), magnesium (Mg(2+)), sodium (Na(+)), potassium (K(+)), chloride (Cl(-)), and water (H2O) are linked via regulatory systems with overlapping effects and are also controlled by systems specific to each of them. Cloning of the calcium-sensing receptor (CaSR) along with the recognition that mutations in the CaSR gene are responsible for two familial syndromes characterized by abnormalities in the regulation of PTH secretion and Ca(2+) metabolism (Familial Hypocalciuric Hypercalcemia, FHH, and Autosomal Dominant Hypocalcemia, ADH) made it clear that extracellular Ca(2+) (Ca(2+)o) participates in its own regulation via a specific, receptor-mediated mechanism. Demonstration that the CaSR is expressed in the kidney as well as the parathyroid glands combined with more complete characterizations of FHH and ADH established that the effects of elevated Ca(2+) on the kidney (wasting of Na(+), K(+), Cl(-), Ca(2+), Mg(2+) and H2O) are attributable to activation of the CaSR. The advent of positive and negative allosteric modulators of the CaSR along with mouse models with global or tissue-selective deletion of the CaSR in the kidney have allowed a better understanding of the functions of the CaSR in various nephron segments. The biology of the CaSR is more complicated than originally thought and difficult to define precisely owing to the limitations of reagents such as anti-CaSR antibodies and the difficulties inherent in separating direct effects of Ca(2+) on the kidney mediated by the CaSR from associated CaSR-induced changes in PTH. Nevertheless, renal CaSRs have nephron-specific effects that contribute to regulating Ca(2+) in the circulation and urine in a manner that assures a narrow range of Ca(2+)o in the blood and avoids excessively high concentrations of Ca(2+) in the urine.
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Affiliation(s)
- R Tyler Miller
- Department of Medicine and Nephrology, University of Texas Southwestern Medical Center and Chief of Medicine Service, VA North Texas Health System, 5323 Harry Hines Blvd, Dallas, TX 75390, USA.
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Kopic S, Geibel JP. Gastric acid, calcium absorption, and their impact on bone health. Physiol Rev 2013; 93:189-268. [PMID: 23303909 DOI: 10.1152/physrev.00015.2012] [Citation(s) in RCA: 102] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Calcium balance is essential for a multitude of physiological processes, ranging from cell signaling to maintenance of bone health. Adequate intestinal absorption of calcium is a major factor for maintaining systemic calcium homeostasis. Recent observations indicate that a reduction of gastric acidity may impair effective calcium uptake through the intestine. This article reviews the physiology of gastric acid secretion, intestinal calcium absorption, and their respective neuroendocrine regulation and explores the physiological basis of a potential link between these individual systems.
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Affiliation(s)
- Sascha Kopic
- Department of Surgery and Cellular and Molecular Physiology, Yale School of Medicine, New Haven, Connecticut, USA
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Yamamura A, Yamamura H, Guo Q, Zimnicka AM, Wan J, Ko EA, Smith KA, Pohl NM, Song S, Zeifman A, Makino A, Yuan JXJ. Dihydropyridine Ca(2+) channel blockers increase cytosolic [Ca(2+)] by activating Ca(2+)-sensing receptors in pulmonary arterial smooth muscle cells. Circ Res 2013; 112:640-50. [PMID: 23300272 DOI: 10.1161/circresaha.113.300897] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
RATIONALE An increase in cytosolic free Ca(2+) concentration ([Ca(2+)](cyt)) in pulmonary arterial smooth muscle cells (PASMC) is a major trigger for pulmonary vasoconstriction and an important stimulus for PASMC proliferation and pulmonary vascular remodeling. The dihydropyridine Ca(2+) channel blockers, such as nifedipine, have been used for treatment of idiopathic pulmonary arterial hypertension (IPAH). OBJECTIVE Our previous study demonstrated that the Ca(2+)-sensing receptor (CaSR) was upregulated and the extracellular Ca(2+)-induced increase in [Ca(2+)](cyt) was enhanced in PASMC from patients with IPAH and animals with experimental pulmonary hypertension. Here, we report that the dihydropyridines (eg, nifedipine) increase [Ca(2+)](cyt) by activating CaSR in PASMC from IPAH patients (in which CaSR is upregulated), but not in normal PASMC. METHODS AND RESULTS The nifedipine-mediated increase in [Ca(2+)](cyt) in IPAH-PASMC was concentration dependent with a half maximal effective concentration of 0.20 µmol/L. Knockdown of CaSR with siRNA in IPAH-PASMC significantly inhibited the nifedipine-induced increase in [Ca(2+)](cyt), whereas overexpression of CaSR in normal PASMC conferred the nifedipine-induced rise in [Ca(2+)](cyt). Other dihydropyridines, nicardipine and Bay K8644, had similar augmenting effects on the CaSR-mediated increase in [Ca(2+)](cyt) in IPAH-PASMC; however, the nondihydropyridine blockers, such as diltiazem and verapamil, had no effect on the CaSR-mediated rise in [Ca(2+)](cyt). CONCLUSIONS The dihydropyridine derivatives increase [Ca(2+)](cyt) by potentiating the activity of CaSR in PASMC independently of their blocking (or activating) effect on Ca(2+) channels; therefore, it is possible that the use of dihydropyridine Ca(2+) channel blockers (eg, nifedipine) to treat IPAH patients with upregulated CaSR in PASMC may exacerbate pulmonary hypertension.
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Affiliation(s)
- Aya Yamamura
- Department of Medicine, Section of Pulmonary, Critical Care, Sleep, and Allergy Medicine and Department of Pharmacology, Institute for Personalized Respiratory Medicine, Center for Cardiovascular Research, University of Illinois at Chicago, Chicago, IL 60612, USA
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Bonny O, Edwards A. Calcium reabsorption in the distal tubule: regulation by sodium, pH, and flow. Am J Physiol Renal Physiol 2012; 304:F585-600. [PMID: 23152295 DOI: 10.1152/ajprenal.00493.2012] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We developed a mathematical model of Ca(2+) transport along the late distal convoluted tubule (DCT2) and the connecting tubule (CNT) to investigate the mechanisms that regulate Ca(2+) reabsorption in the DCT2-CNT. The model accounts for apical Ca(2+) influx across transient receptor potential vanilloid 5 (TRPV5) channels and basolateral Ca(2+) efflux via plasma membrane Ca(2+)-ATPase pumps and type 1 Na(+)/Ca(2+) exchangers (NCX1). Model simulations reproduce experimentally observed variations in Ca(2+) uptake as a function of extracellular pH, Na(+), and Mg(2+) concentration. Our results indicate that amiloride enhances Ca(2+) reabsorption in the DCT2-CNT predominantly by increasing the driving force across NCX1, thereby stimulating Ca(2+) efflux. They also suggest that because aldosterone upregulates both apical and basolateral Na(+) transport pathways, it has a lesser impact on Ca(2+) reabsorption than amiloride. Conversely, the model predicts that full NCX1 inhibition and parathyroidectomy each augment the Ca(2+) load delivered to the collecting duct severalfold. In addition, our results suggest that regulation of TRPV5 activity by luminal pH has a small impact, per se, on transepithelial Ca(2+) fluxes; the reduction in Ca(2+) reabsorption induced by metabolic acidosis likely stems from decreases in TRPV5 expression. In contrast, elevations in luminal Ca(2+) are predicted to significantly decrease TRPV5 activity via the Ca(2+)-sensing receptor. Nevertheless, following the administration of furosemide, the calcium-sensing receptor-mediated increase in Ca(2+) reabsorption in the DCT2-CNT is calculated to be insufficient to prevent hypercalciuria. Altogether, our model predicts complex interactions between calcium and sodium reabsorption in the DCT2-CNT.
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Affiliation(s)
- Olivier Bonny
- Department of Toxicology and Pharmacology, University of Lausanne, France
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Calcium-sensing receptor gene polymorphisms in patients with calcium nephrolithiasis. Curr Opin Nephrol Hypertens 2012; 21:355-61. [PMID: 22660550 DOI: 10.1097/mnh.0b013e3283542290] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
PURPOSE OF REVIEW The calcium-sensing receptor gene (CaSR, chr. 3q13.3-21) is a candidate to explain nephrolithiasis. This review analyzes the potential role of CaSR in lithogenesis according to findings of functional and genetic studies. RECENT FINDINGS CaSR is a cation receptor located in the tubular cell plasma membrane. Its activation decreases calcium reabsorption in the ascending limb and distal convoluted tubule, but increases phosphate reabsorption in proximal tubules and decreases water and proton reabsorption in collecting ducts. Its effects in proximal tubules and collecting ducts can limit the calcium phosphate precipitation risk induced by the increase in calcium excretion. The nonconservative CaSR gene Arg990Gly polymorphism was associated with nephrolithiasis and hypercalciuria in different populations. Arg990Gly is located on exon 7 and produces a gain of the CaSR function. rs7652589 and rs1501899 were also associated with nephrolithiasis in patients with normal citrate excretion. These polymorphisms are located in the CaSR gene regulatory region and may modify CaSR gene promoter activity. SUMMARY The activating Arg990Gly polymorphism may predispose to nephrolithiasis by increasing calcium excretion. Polymorphisms at the regulatory region may predispose to nephrolithiasis by changing tubular expression of the CaSR. CaSR genotype may be a marker to identify patients prone to develop calcium nephrolithiasis.
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Tudpor K, Laínez S, Kwakernaak AJ, Kovalevskaya NV, Verkaart S, van Genesen S, van der Kemp A, Navis G, Bindels RJM, Hoenderop JGJ. Urinary plasmin inhibits TRPV5 in nephrotic-range proteinuria. J Am Soc Nephrol 2012; 23:1824-34. [PMID: 23024298 DOI: 10.1681/asn.2011111126] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Urinary proteins that leak through the abnormal glomerulus in nephrotic syndrome may affect tubular transport by interacting with membrane transporters on the luminal side of tubular epithelial cells. Patients with nephrotic syndrome can develop nephrocalcinosis, which animal models suggest may develop from impaired transcellular Ca(2+) reabsorption via TRPV5 in the distal convoluted tubule (DCT). In nephrotic-range proteinuria, filtered plasminogen reaches the luminal side of DCT, where it is cleaved into active plasmin by urokinase. In this study, we found that plasmin purified from the urine of patients with nephrotic-range proteinuria inhibits Ca(2+) uptake in TRPV5-expressing human embryonic kidney 293 cells through the activation of protease-activated receptor-1 (PAR-1). Preincubation with a plasmin inhibitor, a PAR-1 antagonist, or a protein kinase C (PKC) inhibitor abolished the effect of plasmin on TRPV5. In addition, ablation of the PKC phosphorylation site S144 rendered TRPV5 resistant to the action of plasmin. Patch-clamp experiments showed that a decreased TRPV5 pore size and a reduced open probability accompany the plasmin-mediated reduction in Ca(2+) uptake. Furthermore, high-resolution nuclear magnetic resonance spectroscopy demonstrated specific interactions between calmodulin and residues 133-154 of the N-terminus of TRPV5 for both wild-type and phosphorylated (S144pS) peptides. In summary, PAR-1 activation by plasmin induces PKC-mediated phosphorylation of TRPV5, thereby altering calmodulin-TRPV5 binding, resulting in decreased channel activity. These results indicate that urinary plasmin could contribute to the downstream effects of proteinuria on the tubulointerstitium by negatively modulating TRPV5.
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Affiliation(s)
- Kukiat Tudpor
- Department of Physiology, Nijmegen Centre for Molecular Life Sciences, Radboud University, Nijmegen Medical Centre, Nijmegen, The Netherlands
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Breitwieser GE. Minireview: the intimate link between calcium sensing receptor trafficking and signaling: implications for disorders of calcium homeostasis. Mol Endocrinol 2012; 26:1482-95. [PMID: 22745192 DOI: 10.1210/me.2011-1370] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The calcium-sensing receptor (CaSR) regulates organismal Ca(2+) homeostasis. Dysregulation of CaSR expression or mutations in the CASR gene cause disorders of Ca(2+) homeostasis and contribute to the progression or severity of cancers and cardiovascular disease. This brief review highlights recent findings that define the CaSR life cycle, which controls the cellular abundance of CaSR and CaSR signaling. A novel mechanism, termed agonist-driven insertional signaling (ADIS), contributes to the unique hallmarks of CaSR signaling, including the high degree of cooperativity and the lack of functional desensitization. Agonist-mediated activation of plasma membrane-localized CaSR increases the rate of insertion of CaSR at the plasma membrane without altering the constitutive endocytosis rate, thereby acutely increasing the maximum signaling response. Prolonged CaSR signaling requires a large intracellular ADIS-mobilizable pool of CaSR, which is maintained by signaling-mediated increases in biosynthesis. This model provides a rational framework for characterizing the defects caused by CaSR mutations and the altered functional expression of wild-type CaSR in disease states. Mechanistic dissection of ADIS of CaSR should lead to optimized pharmacological approaches to normalize CaSR signaling in disorders of Ca(2+) homeostasis.
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Affiliation(s)
- Gerda E Breitwieser
- Weis Center for Research, Geisinger Clinic, Danville, Pennsylvania 17822-2604, USA.
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60
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Riccardi D, Kemp PJ. The Calcium-Sensing Receptor Beyond Extracellular Calcium Homeostasis: Conception, Development, Adult Physiology, and Disease. Annu Rev Physiol 2012; 74:271-97. [DOI: 10.1146/annurev-physiol-020911-153318] [Citation(s) in RCA: 111] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Daniela Riccardi
- Division of Pathophysiology and Repair, School of Biosciences, Cardiff University, Cardiff, CF10 3AX, United Kingdom; ,
| | - Paul J. Kemp
- Division of Pathophysiology and Repair, School of Biosciences, Cardiff University, Cardiff, CF10 3AX, United Kingdom; ,
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Signaling through the extracellular calcium-sensing receptor (CaSR). ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 740:103-42. [PMID: 22453940 DOI: 10.1007/978-94-007-2888-2_5] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The extracellular calcium ([Formula: see text])-sensing receptor (CaSR) was the first GPCR identified whose principal physiological ligand is an ion, namely extracellular Ca(2+). It maintains the near constancy of [Formula: see text] that complex organisms require to ensure normal cellular function. A wealth of information has accumulated over the past two decades about the CaSR's structure and function, its role in diseases and CaSR-based therapeutics. This review briefly describes the CaSR and key features of its structure and function, then discusses the extracellular signals modulating its activity, provides an overview of the intracellular signaling pathways that it controls, and, finally, briefly describes CaSR signaling both in tissues participating in [Formula: see text] homeostasis as well as those that do not. Factors controlling CaSR signaling include various factors affecting the expression of the CaSR gene as well as modulation of its trafficking to and from the cell surface. The dimeric cell surface CaSR, in turn, links to various heterotrimeric and small molecular weight G proteins to regulate intracellular second messengers, lipid kinases, various protein kinases, and transcription factors that are part of the machinery enabling the receptor to modulate the functions of the wide variety of cells in which it is expressed. CaSR signaling is impacted by its interactions with several binding partners in addition to signaling elements per se (i.e., G proteins), including filamin-A and caveolin-1. These latter two proteins act as scaffolds that bind signaling components and other key cellular elements (e.g., the cytoskeleton). Thus CaSR signaling likely does not take place randomly throughout the cell, but is compartmentalized and organized so as to facilitate the interaction of the receptor with its various signaling pathways.
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Effect of cinacalcet on renal electrolyte handling and systemic arterial blood pressure in kidney transplant patients with persistent hyperparathyroidism. Transplantation 2011; 92:883-9. [PMID: 21876476 DOI: 10.1097/tp.0b013e31822d87e8] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
BACKGROUND The calcimimetic cinacalcet has recently been increasingly used for persistent hyperparathyroidism after renal transplantation. The present study investigated the short-term effects of cinacalcet on urinary electrolyte concentration and arterial blood pressure in kidney transplant patients with persistent hyperparathyroidism. METHODS In a prospective controlled single-center cross-over study, we examined 10 stable kidney transplant patients (mean estimated glomerular filtration rate 51±10 mL/min/1.73 m(2)) who received cinacalcet daily for persistent hyperparathyroidism. Urine specimens were collected at baseline and every 2 hr for a total study period of 6 hr after ingestion of 30 mg cinacalcet and without cinacalcet. Intact parathyroid hormone was determined at baseline and 2 hr later. Using ambulatory blood pressure measurement, arterial blood pressure was determined every 15 min. RESULTS Intact parathyroid hormone was significantly reduced with cinacalcet as compared with controls (-37±27.7% vs. -9.6±10.3%, P=0.009). With cinacalcet, urinary calcium and magnesium concentration were increased (P=0.042 and P=0.007, respectively) and differed significantly as compared with the control phase without cinacalcet. After 4 hr, an increased urinary sodium concentration was also found compared with the control phase (P=0.039). Systolic blood pressure was reduced with cinacalcet (P<0.001) and differed significantly from control phase (-13.7±9.9 mm Hg vs. -3.2±5.2 mm Hg after 2 hr, P=0.009; -18.1±10.8 mm Hg vs. -1.9±5.2 mm Hg after 4 hr, P=0.001). CONCLUSIONS In the short term, cinacalcet increases the urinary concentration of calcium, magnesium, and sodium. The observed antihypertensive effect might be beneficial in patients with a high cardiovascular risk after kidney transplantation.
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Abstract
Compelling evidence of a cell surface receptor sensitive to extracellular calcium was observed as early as the 1980s and was finally realized in 1993 when the calcium-sensing receptor (CaR) was cloned from bovine parathyroid tissue. Initial studies relating to the CaR focused on its key role in extracellular calcium homeostasis, but as the amount of information about the receptor grew it became evident that it was involved in many biological processes unrelated to calcium homeostasis. The CaR responds to a diverse array of stimuli extending well beyond that merely of calcium, and these stimuli can lead to the initiation of a wide variety of intracellular signaling pathways that in turn are able to regulate a diverse range of biological processes. It has been through the examination of the molecular characteristics of the CaR that we now have an understanding of how this single receptor is able to convert extracellular messages into specific cellular responses. Recent CaR-related reviews have focused on specific aspects of the receptor, generally in the context of the CaR's role in physiology and pathophysiology. This review will provide a comprehensive exploration of the different aspects of the receptor, including its structure, stimuli, signalling, interacting protein partners, and tissue expression patterns, and will relate their impact on the functionality of the CaR from a molecular perspective.
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Affiliation(s)
- Aaron L Magno
- Department of Endocrinology and Diabetes, First Floor, C Block, Sir Charles Gairdner Hospital, Hospital Avenue, Nedlands 6009, Western Australia, Australia
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Abstract
We recommend changing the name of the milk-alkali syndrome to the calcium-alkali syndrome, because the new terminology better reflects the shifting epidemiology and understanding of this disorder. The calcium-alkali syndrome is now the third most common cause of hospital admission for hypercalcemia, and those at greatest risk are postmenopausal or pregnant women. The incidence of the calcium-alkali syndrome is growing in large part as a result of the widespread use of over-the-counter calcium and vitamin D supplements. Advertising for treatment or prevention of osteoporosis has long encouraged this use. Intricate mechanisms mediating the calcium-alkali syndrome depend on interplay among intestine, kidney, and bone. New insights regarding its pathogenesis focus on the key role of calcium-sensing receptors and TRPV5 channels in the modulation of renal calcium excretion. Restoring extracellular blood volume, increasing GFR and calcium excretion, and discontinuing calcium supplementation provide best treatment.
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Affiliation(s)
- Ami M Patel
- Renal-Electrolyte and Hypertension Division, Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
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Gaffney-Stomberg E, Sun BH, Cucchi CE, Simpson CA, Gundberg C, Kerstetter JE, Insogna KL. The effect of dietary protein on intestinal calcium absorption in rats. Endocrinology 2010; 151:1071-8. [PMID: 20147526 PMCID: PMC2840679 DOI: 10.1210/en.2009-0744] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Increasing dietary protein intake in humans acutely increases urinary calcium. Isotopic absorption studies have indicated that, at least in the short term, this is primarily due to increased intestinal Ca absorption. To explore the mechanisms underlying dietary protein's effect on intestinal Ca absorption, female Sprague Dawley rats were fed a control (20%), low (5%), or high (40%) protein diet for 7 d, and Ca balance was measured during d 4-7. On d 7, duodenal mucosa was harvested and brush border membrane vesicles (BBMVs) were prepared to evaluate Ca uptake. By d 7, urinary calcium was more than 2-fold higher in the 40% protein group compared with control (4.2 mg/d vs. 1.7 mg/d; P < 0.05). Rats consuming the 40% protein diet both absorbed and retained more Ca compared with the 5% protein group (absorption: 48.5% vs. 34.1% and retention: 45.8% vs. 33.7%, respectively; P < 0.01). Ca uptake was increased in BBMVs prepared from rats consuming the high-protein diet. Maximum velocity (V(max)) was higher in the BBMVs prepared from the high-protein group compared with those from the low-protein group (90 vs. 36 nmol Ca/mg protein x min, P < 0.001; 95% CI: 46-2486 and 14-55, respectively). The Michaelis Menten constant (K(m)) was unchanged (2.2 mm vs. 1.8 mm, respectively; P = 0.19). We conclude that in rats, as in humans, acute increases in protein intake result in hypercalciuria due to augmented intestinal Ca absorption. BBMV Ca uptake studies suggest that higher protein intake improves Ca absorption, at least in part, by increasing transcellular Ca uptake.
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Affiliation(s)
- Erin Gaffney-Stomberg
- Department of Allied Health Sciences, University of Connecticut, Storrs, Connecticut 06269, USA.
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Riccardi D, Brown EM. Physiology and pathophysiology of the calcium-sensing receptor in the kidney. Am J Physiol Renal Physiol 2010; 298:F485-99. [PMID: 19923405 PMCID: PMC2838589 DOI: 10.1152/ajprenal.00608.2009] [Citation(s) in RCA: 227] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2009] [Accepted: 11/13/2009] [Indexed: 12/21/2022] Open
Abstract
The extracellular calcium-sensing receptor (CaSR) plays a major role in the maintenance of a physiological serum ionized calcium (Ca2+) concentration by regulating the circulating levels of parathyroid hormone. It was molecularly identified in 1993 by Brown et al. in the laboratory of Dr. Steven Hebert with an expression cloning strategy. Subsequent studies have demonstrated that the CaSR is highly expressed in the kidney, where it is capable of integrating signals deriving from the tubular fluid and/or the interstitial plasma. Additional studies elucidating inherited and acquired mutations in the CaSR gene, the existence of activating and inactivating autoantibodies, and genetic polymorphisms of the CaSR have greatly enhanced our understanding of the role of the CaSR in mineral ion metabolism. Allosteric modulators of the CaSR are the first drugs in their class to become available for clinical use and have been shown to treat successfully hyperparathyroidism secondary to advanced renal failure. In addition, preclinical and clinical studies suggest the possibility of using such compounds in various forms of hypercalcemic hyperparathyroidism, such as primary and lithium-induced hyperparathyroidism and that occurring after renal transplantation. This review addresses the role of the CaSR in kidney physiology and pathophysiology as well as current and in-the-pipeline treatments utilizing CaSR-based therapeutics.
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Affiliation(s)
- Daniela Riccardi
- School of Biosciences, Cardiff University, Cardiff, United Kingdom.
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Abstract
PURPOSE OF REVIEW Parathyroid hormone (PTH) maintains a physiological balance of calcium and phosphate concentrations by binding to its receptor on the plasma membrane of cells in bone and kidney. It signals through multiple pathways, including protein kinase A and protein kinase C, although a preference for certain pathways is apparent in each organ and function. Here, we will review the recent advancements regarding PTH signaling in bone and kidney. RECENT FINDINGS Wnt proteins have been reported as important regulators of bone metabolism in both PTH-dependent and independent pathways. Recent studies emphasize its role as a mediator of PTH signaling, as PTH treatment increased the expression of wnt4 and sfrp4 and decreased the expression of Wnt inhibitors such as Sost and sclerostin, leading to an increase in Wnt signaling. In kidney, sodium-hydrogen exchanger regulatory factor 1, originally known for its role in the retention of NaPi-IIa at the apical membrane, was shown to have multiple roles in PTH signaling, both as a mediator and regulator. SUMMARY PTH activates a number of different signaling pathways by binding to a single receptor in bone and kidney. Recent studies demonstrate the involvement of novel factors as well as additional roles for previously identified downstream factors of PTH.
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Riccardi D, Finney BA, Wilkinson WJ, Kemp PJ. Novel regulatory aspects of the extracellular Ca2+-sensing receptor, CaR. Pflugers Arch 2009; 458:1007-22. [PMID: 19484257 DOI: 10.1007/s00424-009-0681-z] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2009] [Revised: 04/30/2009] [Accepted: 05/05/2009] [Indexed: 01/15/2023]
Abstract
The capacity to sense and adapt to changes in environmental cues is of paramount importance for every living organism. From yeast to man, cells must be able to match cellular activities to growth environment and nutrient availability. Key to this process is the development of membrane-bound systems that can detect modifications in the extracellular environment and to translate these into biological responses. Evidence gathered over the last 15 years has demonstrated that many of these cell surface "sensors" belong to the G protein-coupled receptor superfamily. Crucial to our understanding of nutrient sensing in mammalian species has been the identification of the extracellular Ca(2+)/cation-sensing receptor, CaR. CaR was the first ion-sensing molecule identified in man and genetic studies in humans have revealed the importance of the CaR in mineral ion metabolism. Latter, it has become apparent that the CaR also plays an important role outside the Ca(2+) homeostatic system, as an integrator of multiple environmental signals for the regulation of many vital cellular processes, from cell-to-cell communication to secretion and cell survival/cell death. Recently, novel aspects of receptor function reveal an unexpected role for the CaR in the regulation of growth and development in utero.
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