1
|
Gantsova E, Serova O, Vishnyakova P, Deyev I, Elchaninov A, Fatkhudinov T. Mechanisms and physiological relevance of acid-base exchange in functional units of the kidney. PeerJ 2024; 12:e17316. [PMID: 38699185 PMCID: PMC11064853 DOI: 10.7717/peerj.17316] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2023] [Accepted: 04/09/2024] [Indexed: 05/05/2024] Open
Abstract
This review discusses the importance of homeostasis with a particular emphasis on the acid-base (AB) balance, a crucial aspect of pH regulation in living systems. Two primary organ systems correct deviations from the standard pH balance: the respiratory system via gas exchange and the kidneys via proton/bicarbonate secretion and reabsorption. Focusing on kidney functions, we describe the complexity of renal architecture and its challenges for experimental research. We address specific roles of different nephron segments (the proximal convoluted tubule, the loop of Henle and the distal convoluted tubule) in pH homeostasis, while explaining the physiological significance of ion exchange processes maintained by the kidneys, particularly the role of bicarbonate ions (HCO3-) as an essential buffer system of the body. The review will be of interest to researchers in the fields of physiology, biochemistry and molecular biology, which builds a strong foundation and critically evaluates existing studies. Our review helps identify the gaps of knowledge by thoroughly understanding the existing literature related to kidney acid-base homeostasis.
Collapse
Affiliation(s)
- Elena Gantsova
- Avtsyn Research Institute of Human Morphology of Federal State Budgetary Scientific Institution “Petrovsky National Research Centre of Surgery”, Moscow, Russia
- Research Institute of Molecular and Cellular Medicine, Peoples’ Friendship University of Russia (RUDN University), Moscow, Russia
| | - Oxana Serova
- Shemyakin–Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russian Federation
| | - Polina Vishnyakova
- Research Institute of Molecular and Cellular Medicine, Peoples’ Friendship University of Russia (RUDN University), Moscow, Russia
- National Medical Research Center for Obstetrics, Gynecology and Perinatology Named after Academician V.I. Kulakov of Ministry of Healthcare of Russian Federation, Moscow, Russian Federation
| | - Igor Deyev
- Shemyakin–Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russian Federation
| | - Andrey Elchaninov
- Avtsyn Research Institute of Human Morphology of Federal State Budgetary Scientific Institution “Petrovsky National Research Centre of Surgery”, Moscow, Russia
- Research Institute of Molecular and Cellular Medicine, Peoples’ Friendship University of Russia (RUDN University), Moscow, Russia
| | - Timur Fatkhudinov
- Avtsyn Research Institute of Human Morphology of Federal State Budgetary Scientific Institution “Petrovsky National Research Centre of Surgery”, Moscow, Russia
- Research Institute of Molecular and Cellular Medicine, Peoples’ Friendship University of Russia (RUDN University), Moscow, Russia
| |
Collapse
|
2
|
Harris AN, Skankar M, Melanmed M, Batlle D. An Update on Kidney Ammonium Transport Along the Nephron. ADVANCES IN KIDNEY DISEASE AND HEALTH 2023; 30:189-196. [PMID: 36868733 DOI: 10.1053/j.akdh.2022.12.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/02/2022] [Accepted: 12/14/2022] [Indexed: 03/05/2023]
Abstract
Acid-base homeostasis is critical to the maintenance of normal health. The kidneys have a central role in bicarbonate generation, which occurs through the process of net acid excretion. Renal ammonia excretion is the predominant component of renal net acid excretion under basal conditions and in response to acid-base disturbances. Ammonia produced in the kidney is selectively transported into the urine or the renal vein. The amount of ammonia produced by the kidney that is excreted in the urine varies dramatically in response to physiological stimuli. Recent studies have advanced our understanding of ammonia metabolism's molecular mechanisms and regulation. Ammonia transport has been advanced by recognizing that the specific transport of NH3 and NH4+ by specific membrane proteins is critical to ammonia transport. Other studies show that proximal tubule protein, NBCe1, specifically the A variant, significantly regulates renal ammonia metabolism. This review discusses these critical aspects of the emerging features of ammonia metabolism and transport.
Collapse
Affiliation(s)
- Autumn N Harris
- Department of Small Animal Clinical Science, University of Florida College of Veterinary Medicine, Gainesville, FL; Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, FL.
| | - Mythri Skankar
- Department of Nephrology, Institute of Nephro-urology, Bengaluru, India
| | - Michal Melanmed
- Albert Einstein College of Medicine/ Montefiore Medical Center, Bronx, NY
| | - Daniel Batlle
- Northwestern University Feinberg School of Medicine, Chicago, IL
| |
Collapse
|
3
|
Maalouf NM, Poindexter JR, Adams-Huet B, Moe OW, Sakhaee K. Increased production and reduced urinary buffering of acid in uric acid stone formers is ameliorated by pioglitazone. Kidney Int 2019; 95:1262-1268. [PMID: 30795852 DOI: 10.1016/j.kint.2018.11.024] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2018] [Revised: 11/08/2018] [Accepted: 11/16/2018] [Indexed: 02/08/2023]
Abstract
Idiopathic uric acid nephrolithiasis is characterized by an overly acidic urine pH caused by the combination of increased acid production and inadequate buffering of urinary protons by ammonia. A large proportion of uric acid stone formers exhibit features of the metabolic syndrome. We previously demonstrated that thiazolidinediones improved the urinary biochemical profile in an animal model of the metabolic syndrome. In this proof-of-concept study, we examined whether the thiazolidinedione pioglitazone can also ameliorate the overly acidic urine in uric acid stone formers. Thirty-six adults with idiopathic uric acid nephrolithiasis were randomized to pioglitazone 30 mg/day or matching placebo for 24 weeks. At baseline and study end, participants underwent collection of blood and 24-hour urine in an inpatient research unit while consuming a fixed metabolic diet, followed by assessment of the ammoniagenic response to an acute oral acid load. Twenty-eight participants completed the study. Pioglitazone treatment improved features of the metabolic syndrome. Pioglitazone also reduced net acid excretion and increased urine pH (5.37 to 5.59), the proportion of net acid excreted as ammonium, and ammonium excretion in response to an acute acid load, whereas these parameters were unchanged with placebo. Treatment of patients with idiopathic uric acid nephrolithiasis with pioglitazone for 24 weeks led to a reduction in the acid load presented to the kidney and a more robust ammoniagenesis and ammonium excretion, resulting in significantly higher urine pH. Future studies should consider the impact of this targeted therapy on uric acid stone formation.
Collapse
Affiliation(s)
- Naim M Maalouf
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA; Charles and Jane Pak Center for Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - John R Poindexter
- Charles and Jane Pak Center for Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Beverley Adams-Huet
- Charles and Jane Pak Center for Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, Dallas, Texas, USA; Department of Clinical Sciences, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Orson W Moe
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA; Charles and Jane Pak Center for Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, Dallas, Texas, USA; Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Khashayar Sakhaee
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA; Charles and Jane Pak Center for Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
| |
Collapse
|
4
|
Abstract
Acid-base homeostasis is critical to maintenance of normal health. Renal ammonia excretion is the quantitatively predominant component of renal net acid excretion, both under basal conditions and in response to acid-base disturbances. Although titratable acid excretion also contributes to renal net acid excretion, the quantitative contribution of titratable acid excretion is less than that of ammonia under basal conditions and is only a minor component of the adaptive response to acid-base disturbances. In contrast to other urinary solutes, ammonia is produced in the kidney and then is selectively transported either into the urine or the renal vein. The proportion of ammonia that the kidney produces that is excreted in the urine varies dramatically in response to physiological stimuli, and only urinary ammonia excretion contributes to acid-base homeostasis. As a result, selective and regulated renal ammonia transport by renal epithelial cells is central to acid-base homeostasis. Both molecular forms of ammonia, NH3 and NH4+, are transported by specific proteins, and regulation of these transport processes determines the eventual fate of the ammonia produced. In this review, we discuss these issues, and then discuss in detail the specific proteins involved in renal epithelial cell ammonia transport.
Collapse
Affiliation(s)
- I David Weiner
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida; and Nephrology and Hypertension Section, North Florida/South Georgia Veterans Health System, Gainesville, Florida
| | - Jill W Verlander
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida; and Nephrology and Hypertension Section, North Florida/South Georgia Veterans Health System, Gainesville, Florida
| |
Collapse
|
5
|
Sakhaee K. Epidemiology and clinical pathophysiology of uric acid kidney stones. J Nephrol 2014; 27:241-5. [PMID: 24497296 DOI: 10.1007/s40620-013-0034-z] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2013] [Accepted: 08/12/2013] [Indexed: 12/21/2022]
Abstract
There is global diversity in the prevalence of uric acid (UA) nephrolithiasis. UA nephrolithiasis comprises 8-10 % of all kidney stones in the United States. However, its prevalence is higher in patients with type 2 diabetes mellitus and those with obesity. Three significant urinary abnormalities have been described as the main etiologic factors for the development of UA nephrolithiasis; low urinary pH, hyperuricosuria and low urinary volume. However, an unduly acidic urine below the ionization constant of uric acid (pKa < 5.5) increases the urinary content of undissociated uric acid and thereby uric acid precipitation. Previous studies have shown the two major pathogenic mechanisms for unduly urinary pH are increased net acid excretion (NAE) and reduced renal ammonium (NH4 (+)), with a combination resulting in overly acidic urine. The impaired ammonium excretion has been demonstrated in a steady state in 24-hour urine and also following an oral ammonium chloride (NH4Cl) challenge to amplify ammoniogenic defects in this population. Similar abnormalities have been disclosed in normal populations and also in T2DM populations without kidney stones. To date, the underlying mechanism of increased acid production, source and nature of putative organic acid anions have not been fully elucidated. One plausible mechanism is the production of organic acid by intestinal and aerobic metabolism. This may occur in obese, diabetic and uric acid stone formers due to the differences in gut microflora.
Collapse
Affiliation(s)
- Khashayar Sakhaee
- Department of Internal Medicine, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, TX, 75390-8885, USA,
| |
Collapse
|
6
|
Alexander RT, Dimke H, Cordat E. Proximal tubular NHEs: sodium, protons and calcium? Am J Physiol Renal Physiol 2013; 305:F229-36. [PMID: 23761670 DOI: 10.1152/ajprenal.00065.2013] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Na⁺/H⁺ exchange activity in the apical membrane of the proximal tubule is fundamental to the reabsorption of Na⁺ and water from the filtrate. The role of this exchange process in bicarbonate reclamation and, consequently, the maintenance of acid-base homeostasis has been appreciated for at least half a century and remains a pillar of renal tubular physiology. More recently, apical Na⁺/H⁺ exchange, mediated by Na⁺/H⁺ exchanger isoform 3 (NHE3), has been implicated in proximal tubular reabsorption of Ca²⁺ and Ca²⁺ homeostasis in general. Overexpression of NHE3 increased paracellular Ca²⁺ flux in a proximal tubular cell model. Consistent with this observation, mice with genetic deletion of Nhe3 have a noticable renal Ca²⁺ leak. These mice also display decreased intestinal Ca²⁺ uptake and osteopenia. This review highlights the traditional roles of proximal tubular Na⁺/H⁺ exchange and summarizes recent novel findings implicating the predominant isoform, NHE3, in Ca²⁺ homeostasis.
Collapse
Affiliation(s)
- R Todd Alexander
- Department of Pediatrics, Edmonton Clinic Health Academy, 11405-87 Ave., University of Alberta, Edmonton, AB, Canada T6G 2R7.
| | | | | |
Collapse
|
7
|
Abstract
Renal ammonia metabolism and transport mediates a central role in acid-base homeostasis. In contrast to most renal solutes, the majority of renal ammonia excretion derives from intrarenal production, not from glomerular filtration. Renal ammoniagenesis predominantly results from glutamine metabolism, which produces 2 NH4(+) and 2 HCO3(-) for each glutamine metabolized. The proximal tubule is the primary site for ammoniagenesis, but there is evidence for ammoniagenesis by most renal epithelial cells. Ammonia produced in the kidney is either excreted into the urine or returned to the systemic circulation through the renal veins. Ammonia excreted in the urine promotes acid excretion; ammonia returned to the systemic circulation is metabolized in the liver in a HCO3(-)-consuming process, resulting in no net benefit to acid-base homeostasis. Highly regulated ammonia transport by renal epithelial cells determines the proportion of ammonia excreted in the urine versus returned to the systemic circulation. The traditional paradigm of ammonia transport involving passive NH3 diffusion, protonation in the lumen and NH4(+) trapping due to an inability to cross plasma membranes is being replaced by the recognition of limited plasma membrane NH3 permeability in combination with the presence of specific NH3-transporting and NH4(+)-transporting proteins in specific renal epithelial cells. Ammonia production and transport are regulated by a variety of factors, including extracellular pH and K(+), and by several hormones, such as mineralocorticoids, glucocorticoids and angiotensin II. This coordinated process of regulated ammonia production and transport is critical for the effective maintenance of acid-base homeostasis.
Collapse
Affiliation(s)
- I David Weiner
- Nephrology and Hypertension Section, NF/SGVHS, Gainesville, Florida, USA.
| | | |
Collapse
|
8
|
Uric Acid Nephrolithiasis: Basic and Clinical Aspects. Urolithiasis 2012. [DOI: 10.1007/978-1-4471-4387-1_18] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
|
9
|
Bobulescu IA, Dubree M, Zhang J, McLeroy P, Moe OW. Reduction of renal triglyceride accumulation: effects on proximal tubule Na+/H+ exchange and urinary acidification. Am J Physiol Renal Physiol 2009; 297:F1419-26. [PMID: 19692486 DOI: 10.1152/ajprenal.00177.2009] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
One main pathophysiological mechanism underlying the increased risk for uric acid nephrolithiasis in humans with the metabolic syndrome is the excretion of unduly acidic urine, in part because of reduced excretion of the main urinary buffer, ammonium. The Zucker diabetic fatty (ZDF) rat, an established rodent model of the metabolic syndrome, has similar urinary abnormalities, attributed in part to lower expression and activity of the principal mediator of proximal tubule ammonium excretion, brush-border membrane Na+/H+ exchanger 3 (NHE3). These defects are associated with renal tubular steatosis in ZDF rats, but the causal relationship between renal steatosis and defective urinary acidification has not been investigated in vivo. We hypothesized that reduction of renal steatosis would commensurately normalize urinary acidification parameters. We treated ZDF rats with thiazolidinediones to reduce nonadipose tissue steatosis. Four weeks of treatment reduced renal triglyceride accumulation and restored urinary acidification parameters in ZDF rats to levels comparable to their lean littermates; urinary acidification was not affected by treatment in lean rats. To further document the direct effects of fat, we showed that functional abnormalities induced by fat loading in a cell culture model of proximal tubule steatosis and lipotoxicity can be reversed by fat removal but not by thiazolidinediones alone. Together, these findings support the causative role of renal steatosis in the pathogenesis of urinary acidification defects, demonstrate reversibility upon lipid removal, and highlight a potential therapeutic strategy for renal abnormalities in the metabolic syndrome.
Collapse
Affiliation(s)
- I Alexandru Bobulescu
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390-8856, USA
| | | | | | | | | |
Collapse
|
10
|
Kim HY. Renal handling of ammonium and Acid base regulation. Electrolyte Blood Press 2009; 7:9-13. [PMID: 21468179 PMCID: PMC3041479 DOI: 10.5049/ebp.2009.7.1.9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2009] [Accepted: 05/27/2009] [Indexed: 11/05/2022] Open
Abstract
Renal ammonium metabolism is the primary component of net acid excretion and thereby is critical for acid-base homeostasis. Briefly, ammonium is produced from glutamine in the proximal tubule in a series of biochemical reactions that result in equimolar bicarbonate. Ammonium is predominantly secreted into the luminal fluid via the apical Na+/H+ exchanger, NHE3. The thick ascending limb of the loop of Henle reabsorbs luminal ammonium, predominantly by transport of NH4+ by the apical Na+/K+/2Cl- cotransporter, BSC1/NKCC2. This process results in renal interstitial ammonium accumulation. Finally, the collecting duct secretes ammonium from the renal interstitium into the luminal fluid. Although in past ammonium was believed to move across epithelia entirely by passive diffusion, an increasing number of studies demonstrated that specific proteins contribute to renal ammonium transport. Recent studies have yielded important new insights into the mechanisms of renal ammonium transport. In this review, we will discuss renal handling of ammonium, with particular emphasis on the transporters involved in this process.
Collapse
Affiliation(s)
- Hye-Young Kim
- Department of Internal Medicine, Chungbuk National University College of Medicine, Cheongju, Korea
| |
Collapse
|
11
|
Bobulescu IA, Moe OW. Luminal Na(+)/H (+) exchange in the proximal tubule. Pflugers Arch 2009; 458:5-21. [PMID: 18853182 PMCID: PMC2878283 DOI: 10.1007/s00424-008-0595-1] [Citation(s) in RCA: 93] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2008] [Accepted: 09/26/2008] [Indexed: 12/11/2022]
Abstract
The proximal tubule is critical for whole-organism volume and acid-base homeostasis by reabsorbing filtered water, NaCl, bicarbonate, and citrate, as well as by excreting acid in the form of hydrogen and ammonium ions and producing new bicarbonate in the process. Filtered organic solutes such as amino acids, oligopeptides, and proteins are also retrieved by the proximal tubule. Luminal membrane Na(+)/H(+) exchangers either directly mediate or indirectly contribute to each of these processes. Na(+)/H(+) exchangers are a family of secondary active transporters with diverse tissue and subcellular distributions. Two isoforms, NHE3 and NHE8, are expressed at the luminal membrane of the proximal tubule. NHE3 is the prevalent isoform in adults, is the most extensively studied, and is tightly regulated by a large number of agonists and physiological conditions acting via partially defined molecular mechanisms. Comparatively little is known about NHE8, which is highly expressed at the lumen of the neonatal proximal tubule and is mostly intracellular in adults. This article discusses the physiology of proximal Na(+)/H(+) exchange, the multiple mechanisms of NHE3 regulation, and the reciprocal relationship between NHE3 and NHE8 at the lumen of the proximal tubule.
Collapse
Affiliation(s)
- I. Alexandru Bobulescu
- Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8856, USA
- Charles and Jane Pak Center for Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8856, USA
| | - Orson W. Moe
- Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8856, USA,
- Charles and Jane Pak Center for Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8856, USA
- Department of Physiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8856, USA
| |
Collapse
|
12
|
Bobulescu IA, Dubree M, Zhang J, McLeroy P, Moe OW. Effect of renal lipid accumulation on proximal tubule Na+/H+ exchange and ammonium secretion. Am J Physiol Renal Physiol 2008; 294:F1315-22. [PMID: 18417539 DOI: 10.1152/ajprenal.00550.2007] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Patients with metabolic syndrome have increased risk of uric acid nephrolithiasis due to lower urinary pH and impaired ammonium excretion. The pathophysiology underlying these urinary changes is unknown. We used two animal models and a cell culture model to study whether the alteration in renal acidification is associated with renal fat infiltration (steatosis). Compared with pair-fed lean control rats, Zucker diabetic fatty rats have higher renal triglyceride content, decreased urinary ammonium and pH, and lower levels of brush border membrane Na(+)/H(+) exchanger-3 (NHE3), a major mediator of ammonium excretion. High-fat feeding in Sprague-Dawley rats results in transient lowering of urinary ammonium and pH, with all parameters returning to normal when the animals resumed eating normal chow. This is consistent with an absence of diet-induced renal steatosis in these animals. To examine the direct effect of fat accumulation, we incubated opossum kidney (OKP) cells with a mixture of long-chain fatty acids and found accumulation of intracellular lipids with concomitant dose-dependent decrease in NHE3 activity, surface biotin-accessible NHE3 protein, and ammonium secretion. A lower dose of fatty acids that leads to intracellular lipid accumulation but does not change baseline NHE3 is sufficient to abolish the stimulation of NHE3 by insulin and to partially block the stimulation of NHE3 by glucocorticoid hormones; acid regulation of NHE3 in lipid-loaded OKP cells is not affected. These findings suggest that renal steatosis decreases ammonium secretion in the proximal tubule, in part by reducing NHE3 activity and by impairing the regulation of NHE3 by specific agonists.
Collapse
Affiliation(s)
- I Alexandru Bobulescu
- Dept. of Internal Medicine, Univ. of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-8856, USA
| | | | | | | | | |
Collapse
|
13
|
Nagami GT. Role of angiotensin II in the enhancement of ammonia production and secretion by the proximal tubule in metabolic acidosis. Am J Physiol Renal Physiol 2008; 294:F874-80. [DOI: 10.1152/ajprenal.00286.2007] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Acidosis and angiotensin II stimulate ammonia production and transport by the proximal tubule. We examined the modulatory effect of the type 1 angiotensin II receptor blocker losartan on the ability of metabolic acidosis to stimulate ammonia production and secretion by mouse S2 proximal tubule segments. Mice given NH4Cl for 7 days developed metabolic acidosis (low serum bicarbonate concentration) and increased urinary excretion of ammonia. S2 tubule segments from acidotic mice displayed higher rates of ammonia production and secretion compared with those from control mice. However, when losartan was coadministered in vivo with NH4Cl, both the acidosis-induced increase in urinary ammonia excretion and the adaptive increase in ammonia production and secretion of microperfused S2 segments were largely blocked. In renal cortical tissue, losartan blocked the acid-induced increase in brush-border membrane NHE3 expression but had no effect on the acid-induced upregulation of phosphate-dependent glutaminase or phosphoenolpyruvate carboxykinase 1 in cortical homogenates. Addition of angiotensin II to the microperfusion solution enhanced ammonia secretion and production rates in tubules from NH4Cl-treated and control mice in a losartan-inhibitable manner. These results demonstrate that a 7-day acid challenge induces an adaptive increase in ammonia production and secretion by the proximal tubule and suggest that during metabolic acidosis, angiotensin II signaling is necessary for adaptive enhancements of ammonia excretion by the kidney and ammonia production and secretion by S2 proximal tubule segments, as mediated, in part, by angiotensin receptor-dependent enhancement of NHE3 expression.
Collapse
|
14
|
Abstract
Acid-base homeostasis to a great extent relies on renal ammonia metabolism. In the past several years, seminal studies have generated important new insights into the mechanisms of renal ammonia transport. In particular, the theory that ammonia transport occurs almost exclusively through nonionic NH(3) diffusion and NH(4)(+) trapping has given way to a model postulating that a variety of proteins specifically transport NH(3) and NH(4)(+) and that this transport is critical for normal ammonia metabolism. Many of these proteins transport primarily H(+) or K(+) but also transport NH(4)(+). Nonerythroid Rh glycoproteins transport ammonia and may represent critical facilitators of ammonia transport in the kidney. This review discusses the underlying aspects of renal ammonia transport as well as specific proteins with important roles in renal ammonia transport.
Collapse
Affiliation(s)
- I. David Weiner
- Nephrology Section, North Florida/South Georgia Veterans Health System, University of Florida, Gainesville, Florida 32608
- Division of Nephrology, Hypertension and Transplantation, University of Florida, Gainesville, Florida 32608
| | - L. Lee Hamm
- Department of Medicine, Tulane University School of Medicine, New Orleans, Louisiana 70112
| |
Collapse
|
15
|
Seshadri RM, Klein JD, Kozlowski S, Sands JM, Kim YH, Han KH, Handlogten ME, Verlander JW, Weiner ID. Renal expression of the ammonia transporters, Rhbg and Rhcg, in response to chronic metabolic acidosis. Am J Physiol Renal Physiol 2005; 290:F397-408. [PMID: 16144966 DOI: 10.1152/ajprenal.00162.2005] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Chronic metabolic acidosis induces dramatic increases in net acid excretion that are predominantly due to increases in urinary ammonia excretion. The current study examines whether this increase is associated with changes in the expression of the renal ammonia transporter family members, Rh B glycoprotein (Rhbg) and Rh C glycoprotein (Rhcg). Chronic metabolic acidosis was induced in Sprague-Dawley rats by HCl ingestion for 1 wk; control animals were pair-fed. After 1 wk, metabolic acidosis had developed, and urinary ammonia excretion increased significantly. Rhcg protein expression was increased in both the outer medulla and the base of the inner medulla. Intercalated cells in the outer medullary collecting duct (OMCD) and in the inner medullary collecting duct (IMCD) in acid-loaded animals protruded into the tubule lumen and had a sharp, discrete band of apical Rhcg immunoreactivity, compared with a flatter cell profile and a broad band of apical immunolabel in control kidneys. In addition, basolateral Rhcg immunoreactivity was observed in both control and acidotic kidneys. Cortical Rhcg protein expression and immunoreactivity were not detectably altered. Rhcg mRNA expression was not significantly altered in the cortex, outer medulla, or inner medulla by chronic metabolic acidosis. Rhbg protein and mRNA expression were unchanged in the cortex, outer and inner medulla, and no changes in Rhbg immunolabel were evident in these regions. We conclude that chronic metabolic acidosis increases Rhcg protein expression in intercalated cells in the OMCD and in the IMCD, where it is likely to mediate an important role in the increased urinary ammonia excretion.
Collapse
Affiliation(s)
- Ramanathan M Seshadri
- University of Florida College of Medicine, P. O. Box 100224, Gainesville, FL 32610-0224, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
16
|
Handlogten ME, Hong SP, Westhoff CM, Weiner ID. Apical ammonia transport by the mouse inner medullary collecting duct cell (mIMCD-3). Am J Physiol Renal Physiol 2005; 289:F347-58. [PMID: 15798090 DOI: 10.1152/ajprenal.00253.2004] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The collecting duct is the primary site of urinary ammonia secretion; the current study determines whether apical ammonia transport in the mouse inner medullary collecting duct cell (mIMCD-3) occurs via nonionic diffusion or a transporter-mediated process and, if the latter, presents the characteristics of this apical ammonia transport. We used confluent cells on permeable support membranes and examined apical uptake of the ammonia analog [14C]methylammonia ([14C]MA). mIMCD-3 cells exhibited both diffusive and saturable, transporter-mediated, nondiffusive apical [14C]MA transport. Transporter-mediated [14C]MA uptake had a Kmof 7.0 ± 1.5 mM and was competitively inhibited by ammonia with a Kiof 4.3 ± 2.0 mM. Transport activity was stimulated by both intracellular acidification and extracellular alkalinization, and it was unaltered by changes in membrane voltage, thereby functionally identifying an apical, electroneutral NH4+/H+exchange activity. Transport was bidirectional, consistent with a role in ammonia secretion. In addition, transport was not altered by Na+or K+removal, not inhibited by luminal K+, and not mediated by apical H+-K+-ATPase, Na+-K+-ATPase, or Na+/H+exchange. Finally, mIMCD-3 cells express the recently identified ammonia transporter family member Rh C glycoprotein (RhCG) at its apical membrane. These studies indicate that the renal collecting duct cell mIMCD-3 has a novel apical, electroneutral Na+- and K+-independent NH4+/H+exchange activity, possibly mediated by RhCG, that is likely to mediate important components of collecting duct ammonia secretion.
Collapse
Affiliation(s)
- Mary E Handlogten
- Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville, 32610-0224, USA
| | | | | | | |
Collapse
|
17
|
Abstract
The kidney adjusts net acid excretion to match production with exquisite precision, despite little or no change in the plasma bicarbonate concentration. The acid-sensing pathway that signals the kidney to increase acid secretion involves activation of the proto-oncogene c-Src. A new study in this issue shows that proline-rich tyrosine kinase 2 (Pyk2) is responsible for acid-induced activation of c-Src and is essential for acid sensing in renal epithelial cells. The findings implicate a broader role for Pyk2 in acid-base homeostasis in bone and other tissues beyond the kidney.
Collapse
Affiliation(s)
- Stephen L Gluck
- Division of Nephrology, UCSF, 513 Parnassus Avenue, Box 0532, San Francisco, California 94143-0532, USA.
| |
Collapse
|
18
|
Handlogten ME, Hong SP, Westhoff CM, Weiner ID. Basolateral ammonium transport by the mouse inner medullary collecting duct cell (mIMCD-3). Am J Physiol Renal Physiol 2004; 287:F628-38. [PMID: 15149971 DOI: 10.1152/ajprenal.00363.2003] [Citation(s) in RCA: 39] [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
The renal collecting duct is the primary site for the ammonia secretion necessary for acid-base homeostasis. Recent studies have identified the presence of putative ammonia transporters in the collecting duct, but whether the collecting duct has transporter-mediated ammonia transport is unknown. The purpose of this study was to examine basolateral ammonia transport in the mouse collecting duct cell (mIMCD-3). To examine mIMCD-3 basolateral ammonia transport, we used cells grown to confluence on permeable support membranes and quantified basolateral uptake of the radiolabeled ammonia analog [14C]methylammonia ([14C]MA). mIMCD-3 cell basolateral MA transport exhibited both diffusive and transporter-mediated components. Transporter-mediated uptake exhibited a Kmfor MA of 4.6 ± 0.2 mM, exceeded diffusive uptake at MA concentrations below 7.0 ± 1.8 mM, and was competitively inhibited by ammonia with a Kiof 2.1 ± 0.6 mM. Transporter-mediated uptake was not altered by inhibitors of Na+-K+-ATPase, Na+-K+-2Cl−cotransporter, K+channels or KCC proteins, by excess potassium, by extracellular sodium or potassium removal or by varying membrane potential, suggesting the presence of a novel, electroneutral ammonia-MA transport mechanism. Increasing the outwardly directed transmembrane H+gradient increased transport activity by increasing Vmax. Finally, mIMCD-3 cells express mRNA and protein for the putative ammonia transporter Rh B-glycoprotein (RhBG), and they exhibit basolateral RhBG immunoreactivity. We conclude that mIMCD-3 cells express a basolateral electroneutral NH4+/H+exchange activity that may be mediated by RhBG.
Collapse
Affiliation(s)
- Mary E Handlogten
- Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine,Gainesville, FL 32610-0224, USA
| | | | | | | |
Collapse
|
19
|
Abstract
PURPOSE OF REVIEW Renal acid-base homeostasis, to a very large extent, depends on renal ammonia production and transport. A putative ammonia transporter family of proteins has recently been identified, and at least two members of this family are expressed in the renal connecting segment and collecting duct. The purpose of this review is to discuss key features of renal ammonia metabolism and transport, with particular emphasis on the transporters involved in this process. RECENT FINDINGS The putative ammonia transporter family members, RhBG and RhCG, are expressed in the renal connecting segment and collecting duct. Basolateral RhBG is expressed by all cells in the connecting segment and cortical collecting duct, and by intercalated cells in the outer medullary and inner medullary collecting duct. Apical RhCG is expressed in the same distribution and also in the outer stripe of the outer medullary collecting duct principal cells. In all regions, the expression of RhBG and RhCG is greater in intercalated cells than in principal cells. The related protein, RhAG, appears to be an erythroid-specific protein that mediates ammonium/hydrogen ion (NH4/H) exchange. RhBG and RhCG appear to be sodium and potassium ion-independent ammonia transporters. Whether they mediate electrogenic ammonia transport or electroneutral ammonia/hydrogen ion exchange remains an active area of investigation. Finally, transport studies have identified that electroneutral ammonium/hydrogen ion exchange is present in the collecting duct. SUMMARY The Rh glycoproteins, RhBG and RhCG, appear to mediate important roles in renal ammonia transport, and therefore in acid-base homeostasis.
Collapse
Affiliation(s)
- I David Weiner
- Nephrology and Hypertension Section, North Florida/South Georgia Veterans Health System, Gainesville, Florida, USA.
| |
Collapse
|
20
|
van de Poll MCG, Soeters PB, Deutz NEP, Fearon KCH, Dejong CHC. Renal metabolism of amino acids: its role in interorgan amino acid exchange. Am J Clin Nutr 2004; 79:185-97. [PMID: 14749222 DOI: 10.1093/ajcn/79.2.185] [Citation(s) in RCA: 167] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The kidneys play a role in the synthesis and interorgan exchange of several amino acids. The quantitative importance of renal amino acid metabolism in the body is not, however, clear. We review here the role of the kidney in the interorgan exchange of amino acids, with emphasis on quantitative aspects. We reviewed relevant literature by using a computerized literature search (PubMed) and checking relevant references from the identified articles. Our own data are discussed in the context of the literature. The kidney takes up glutamine and metabolizes it to ammonia. This process is sensitive to pH and serves to maintain acid-base homeostasis and to excrete nitrogen. In this way, the metabolism of renal glutamine and ammonia is complementary to hepatic urea synthesis. Citrulline, derived from intestinal glutamine breakdown, is converted to arginine by the kidney. Renal phenylalanine uptake is followed by stoichiometric tyrosine release, and glycine uptake is accompanied by serine release. Certain administered oligopeptides (eg, glutamine dipeptides) are converted by the kidneys to their constituent components before they can be used in metabolic processes. The kidneys play an important role in the interorgan exchange of amino acids. Quantitatively, for several important amino acids, the kidneys are as important as the gut in intermediary metabolism. The kidneys may be crucial "mediators" of the beneficial effects of specialized, disease-specific feeding solutions such as those enriched in glutamine dipeptides.
Collapse
|
21
|
Nagami GT. Enhanced ammonia secretion by proximal tubules from mice receiving NH(4)Cl: role of angiotensin II. Am J Physiol Renal Physiol 2002; 282:F472-7. [PMID: 11832428 DOI: 10.1152/ajprenal.00249.2001] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Acidosis and angiotensin II (ANG II) stimulate ammonia production and transport by the proximal tubule. We examined the effect of short-term (18 h) in vivo acid loading with NH(4)Cl on ammonia production and secretion rates by mouse S2 proximal tubule segments microperfused in vitro with or without ANG II in the luminal microperfusion solution. S2 tubules from NH(4)Cl-treated mice displayed higher rates of luminal ammonia secretion compared with those from control mice. The adaptive increase in ammonia secretion in NH(4)Cl-treated mice was eliminated when losartan was coadministered in vivo with NH(4)Cl. Ammonia secretion rates from both NH(4)Cl-treated and control mice were largely inhibited by amiloride. Addition of ANG II to the microperfusion solution enhanced ammonia secretion and production rates to a greater extent in tubules from NH(4)Cl-treated mice compared with those from controls, and the stimulatory effects of ANG II were blocked by losartan. These results demonstrate that a short-term acid challenge induces an adaptive increase in ammonia secretion by the proximal tubule and suggest that ANG II plays an important role in the adaptive enhancement of ammonia secretion that is observed with short-term acid challenges.
Collapse
Affiliation(s)
- Glenn T Nagami
- Nephrology Section, Medical and Research Services, Veterans Affairs Greater Los Angeles Healthcare System at West Los Angeles, Los Angeles 90073, USA.
| |
Collapse
|
22
|
Dejong CH, Deutz NE, Soeters PB. Ammonia and glutamine metabolism during liver insufficiency: the role of kidney and brain in interorgan nitrogen exchange. SCANDINAVIAN JOURNAL OF GASTROENTEROLOGY. SUPPLEMENT 1996; 218:61-77. [PMID: 8865453 DOI: 10.3109/00365529609094733] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
BACKGROUND During liver failure, urea synthesis capacity is impaired. In this situation the most important alternative pathway for ammonia detoxification is the formation of glutamine from ammonia and glutamate. Information is lacking about the quantitative and qualitative role of kidney and brain in ammonia detoxification during liver failure. METHODS This review is based on own experiments considered against literature data. RESULTS AND CONCLUSIONS Brain detoxifies ammonia during liver failure by ammonia uptake from the blood, glutamine synthesis and subsequent glutamine release into the blood. Although quantitatively unimportant, this may be qualitatively important, because it may influence metabolic and/or neurotransmitter glutamate concentrations. The kidney plays an important role in adaptation to hyperammonaemia by reversing the ratio of ammonia excreted in the urine versus ammonia released into the blood from 0.5 to 2. Thus, the kidney changes into an organ that netto removes ammonia from the body as opposed to the normal situation in which it adds ammonia to the body pools.
Collapse
Affiliation(s)
- C H Dejong
- Dept. of Surgery, University Hospital Maastricht, The Netherlands
| | | | | |
Collapse
|
23
|
Dejong CH, Deutz NE, Soeters PB. Metabolic adaptation of the kidney to hyperammonemia during chronic liver insufficiency in the rat. Hepatology 1993; 18:890-902. [PMID: 8406365 DOI: 10.1002/hep.1840180422] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The aim of this study was to evaluate the role of renal ammonia and glutamine metabolism in the metabolic adaptation to chronic liver insufficiency-induced hyperammonemia in the rat. To this purpose, urinary excretion, renal net exchange and tissue concentrations of ammonia and amino acids were measured in anesthetized, normal control rats that did not undergo surgery, in control rats that underwent sham surgery, in rats that underwent portacaval shunting and in rats that underwent both portacaval shunting and bile duct ligation. Rats that underwent sham surgery and portacaval shunting were pair-fed with rats that underwent portacaval shunting and biliary obstruction, to correct for anorexia in that group, and all rats that were operated on were studied 7 and 14 days after surgery. Arterial ammonia and glutamine levels were elevated in groups that underwent portacaval shunting and portacaval shunting plus biliary obstruction at all time points. At days 7 and 14, total renal ammonia production decreased in rats that underwent portacaval shunting and in rats that underwent portacaval shunting plus biliary obstruction, associated with a 50% decrease in net renal glutamine uptake and strongly diminished net ammonia release into the renal vein, which was most prominent in the group that underwent portacaval shunting plus biliary obstruction. Urinary ammonia excretion was similar in rats that underwent portacaval shunting and in those that underwent sham surgery but was increased more than 200% at days 7 and 14 in rats that underwent portacaval shunting plus biliary obstruction. In this group, in contrast to portacaval-shunted rats, the kidney appeared to be an organ of net ammonia disposal from the body. In separate experiments in unanesthetized, unrestrained rats, similar changes in urinary ammonia excretion were observed without changes in arterial pH, excluding an effect of anesthesia or pH on the obtained results. These results indicate that the kidney plays an important role in the metabolic adaptation to hyperammonemia during chronic liver insufficiency in the rat.
Collapse
Affiliation(s)
- C H Dejong
- Department of Surgery, University of Limburg, Maastricht, The Netherlands
| | | | | |
Collapse
|
24
|
Abstract
Tubulointerstitial injury is an invariant finding in the chronically diseased kidney, irrespective of the type of disease or the compartment in which the disease originates. Such histologic changes are functionally significant in that scores for such damage, rather than glomerular injury, correlate with decline of renal function. This review summarizes (1) clinical evidence attesting to tubulointerstitial changes as an index of functional impairment, (2) mechanisms by which tubulointerstitial injury impairs renal function, and (3) interactions of pathologic processes in the vascular, glomerular, tubular, and interstitial compartments that culminate in tubulointerstitial injury. This report concludes with a review of interstitial fibrosis, a pathologic process regarded as an irreversible outcome from tubulointerstitial injury.
Collapse
Affiliation(s)
- K A Nath
- Department of Medicine, University of Minnesota, Minneapolis
| |
Collapse
|