1
|
Khor BH, Komnenov D, Rossi NF. Impact of Dietary Fructose and High Salt Diet: Are Preclinical Studies Relevant to Asian Societies? Nutrients 2022; 14:2515. [PMID: 35745245 PMCID: PMC9227020 DOI: 10.3390/nu14122515] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2022] [Revised: 06/08/2022] [Accepted: 06/11/2022] [Indexed: 02/01/2023] Open
Abstract
Fructose consumption, especially in food additives and sugar-sweetened beverages, has gained increasing attention due to its potential association with obesity and metabolic syndrome. The relationship between fructose and a high-salt diet, leading to hypertension and other deleterious cardiovascular parameters, has also become more evident, especially in preclinical studies. However, these studies have been modeled primarily on Western diets. The purpose of this review is to evaluate the dietary habits of individuals from China, Japan, and Korea, in light of the existing preclinical studies, to assess the potential relevance of existing data to East Asian societies. This review is not intended to be exhaustive, but rather to highlight the similarities and differences that should be considered in future preclinical, clinical, and epidemiologic studies regarding the impact of dietary fructose and salt on blood pressure and cardiovascular health worldwide.
Collapse
Affiliation(s)
- Ban Hock Khor
- Faculty of Food Science and Nutrition, Universiti Malaysia Sabah, Kota Kinabalu 88400, Malaysia;
| | - Dragana Komnenov
- Department of Internal Medicine, Wayne State University, Detroit, MI 48201, USA;
| | - Noreen F. Rossi
- Department of Internal Medicine, Wayne State University, Detroit, MI 48201, USA;
- Department of Physiology, Wayne State University, Detroit, MI 48201, USA
- Division of Research, John D. Dingell VA Medical Center, Detroit, MI 38201, USA
| |
Collapse
|
2
|
Nikolovska K, Seidler UE, Stock C. The Role of Plasma Membrane Sodium/Hydrogen Exchangers in Gastrointestinal Functions: Proliferation and Differentiation, Fluid/Electrolyte Transport and Barrier Integrity. Front Physiol 2022; 13:899286. [PMID: 35665228 PMCID: PMC9159811 DOI: 10.3389/fphys.2022.899286] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2022] [Accepted: 04/19/2022] [Indexed: 12/11/2022] Open
Abstract
The five plasma membrane Na+/H+ exchanger (NHE) isoforms in the gastrointestinal tract are characterized by distinct cellular localization, tissue distribution, inhibitor sensitivities, and physiological regulation. NHE1 (Slc9a1) is ubiquitously expressed along the gastrointestinal tract in the basolateral membrane of enterocytes, but so far, an exclusive role for NHE1 in enterocyte physiology has remained elusive. NHE2 (Slc9a2) and NHE8 (Slc9a8) are apically expressed isoforms with ubiquitous distribution along the colonic crypt axis. They are involved in pHi regulation of intestinal epithelial cells. Combined use of a knockout mouse model, intestinal organoid technology, and specific inhibitors revealed previously unrecognized actions of NHE2 and NHE8 in enterocyte proliferation and differentiation. NHE3 (Slc9a3), expressed in the apical membrane of differentiated intestinal epithelial cells, functions as the predominant nutrient-independent Na+ absorptive mechanism in the gut. The new selective NHE3 inhibitor (Tenapanor) allowed discovery of novel pathophysiological and drug-targetable NHE3 functions in cystic-fibrosis associated intestinal obstructions. NHE4, expressed in the basolateral membrane of parietal cells, is essential for parietal cell integrity and acid secretory function, through its role in cell volume regulation. This review focuses on the expression, regulation and activity of the five plasma membrane Na+/H+ exchangers in the gastrointestinal tract, emphasizing their role in maintaining intestinal homeostasis, or their impact on disease pathogenesis. We point to major open questions in identifying NHE interacting partners in central cellular pathways and processes and the necessity of determining their physiological role in a system where their endogenous expression/activity is maintained, such as organoids derived from different parts of the gastrointestinal tract.
Collapse
|
3
|
Nikolovska K, Cao L, Hensel I, Di Stefano G, Seidler A, Zhou K, Qian J, Singh AK, Riederer B, Seidler U. Sodium/hydrogen-exchanger-2 modulates colonocyte lineage differentiation. Acta Physiol (Oxf) 2022; 234:e13774. [PMID: 34985202 DOI: 10.1111/apha.13774] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Revised: 10/12/2021] [Accepted: 01/01/2022] [Indexed: 12/11/2022]
Abstract
AIM The sodium/hydrogen exchanger 2 (NHE2) is an intestinal acid extruder with crypt-predominant localization and unresolved physiological significance. Our aim was to decipher its role in colonic epithelial cell proliferation, differentiation and electrolyte transport. METHODS Alterations induced by NHE2-deficiency were addressed in murine nhe2-/- and nhe2+/+ colonic crypts and colonoids, and NHE2-knockdown and control Caco2Bbe cells using pH-fluorometry, gene expression analysis and immunofluorescence. RESULTS pHi -measurements along the colonic cryptal axis revealed significantly decreased intracellular pH (pHi ) in the middle segment of nhe2-/- compared to nhe2+/+ crypts. Increased Nhe2 mRNA expression was detected in murine colonoids in the transiently amplifying/progenitor cell stage (TA/PE). Lack of Nhe2 altered the differentiation programme of colonic epithelial cells with reduced expression of absorptive lineage markers alkaline phosphatase (iAlp), Slc26a3 and transcription factor hairy and enhancer-of-split 1 (Hes1), but increased expression of secretory lineage markers Mucin 2, trefoil factor 3 (Tff3), enteroendocrine marker chromogranin A and murine atonal homolog 1 (Math1). Enterocyte differentiation was found to be pHi dependent with acidic pHi reducing, and alkaline pHi stimulating the expression of enterocyte differentiation markers in Caco2Bbe cells. A thicker mucus layer, longer crypts and an expanded brush border membrane zone of sodium/hydrogen exchanger 3 (NHE3) abundance may explain the lack of inflammation and the normal fluid absorptive rate in nhe2-/- colon. CONCLUSIONS The results suggest that NHE2 expression is activated when colonocytes emerge from the stem cell niche. Its activity increases progenitor cell pHi and thereby supports absorptive enterocyte differentiation.
Collapse
Affiliation(s)
- Katerina Nikolovska
- Department of Gastroenterology, Hepatology and Endocrinology Hannover Medical School Hannover Germany
| | - Li Cao
- Department of Gastroenterology, Hepatology and Endocrinology Hannover Medical School Hannover Germany
- Department of Gastroenterology Tongji Hospital Huazhong University Wuhan China
| | - Inga Hensel
- Department of Gastroenterology, Hepatology and Endocrinology Hannover Medical School Hannover Germany
| | - Gabriella Di Stefano
- Department of Gastroenterology, Hepatology and Endocrinology Hannover Medical School Hannover Germany
| | - Anna Elisabeth Seidler
- Department of Gastroenterology, Hepatology and Endocrinology Hannover Medical School Hannover Germany
| | - Kunyan Zhou
- Department of Gastroenterology, Hepatology and Endocrinology Hannover Medical School Hannover Germany
| | - Jiajie Qian
- Department of Gastroenterology, Hepatology and Endocrinology Hannover Medical School Hannover Germany
- Department of Transplantation and Hepatobiliary Surgery First Affiliated Hospital of Zheijang University Hangzhou China
| | - Anurag Kumar Singh
- Department of Gastroenterology, Hepatology and Endocrinology Hannover Medical School Hannover Germany
- Department of Physiological Chemistry University of Halle Halle (Saale) Germany
| | - Brigitte Riederer
- Department of Gastroenterology, Hepatology and Endocrinology Hannover Medical School Hannover Germany
| | - Ursula Seidler
- Department of Gastroenterology, Hepatology and Endocrinology Hannover Medical School Hannover Germany
| |
Collapse
|
4
|
Yee J, Rosenbaum D, Jacobs JW, Sprague SM. Small Intestinal Phosphate Absorption: Novel Therapeutic Implications. Am J Nephrol 2021; 52:522-530. [PMID: 34515051 DOI: 10.1159/000518110] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2021] [Accepted: 06/24/2021] [Indexed: 01/19/2023]
Abstract
BACKGROUND Chronic kidney disease (CKD) affects approximately 15% of adults in the USA. As CKD progresses, urinary phosphate excretion decreases and results in phosphate retention and, eventually, hyperphosphatemia. As hyperphosphatemia is associated with numerous adverse outcomes, including increased cardiovascular mortality, reduction in phosphorus concentrations is a guideline-recommended, established clinical practice. Dietary phosphate restriction, dialysis, and phosphate binders are currently the only options for phosphate management. However, many patients with hyperphosphatemia have phosphorus concentrations >5.5 mg/dL, despite treatment. SUMMARY This review pre-sents recent advances in the understanding of intestinal phosphate absorption and therapeutic implications. Dietary phosphate is absorbed in the intestine through two distinct pathways, paracellular absorption and transcellular transport. Recent evidence indicates that the paracellular route accounts for 65-80% of total phosphate absorbed. Thus, the paracellular pathway is the dominant mechanism of phosphate absorption. Tenapanor is a first-in-class, non-phosphate binder that inhibits the sodium-hydrogen exchanger 3 or solute carrier family 9 member 3 (SLC9A3) encoded by the SLC9A3 gene, and blocks paracellular phosphate absorption. Key Messages: Targeted inhibition of sodium-hydrogen exchanger 3 effectively reduces paracellular permeability of phosphate. Novel therapies that target the paracellular pathway may improve phosphate control in chronic kidney disease.
Collapse
Affiliation(s)
- Jerry Yee
- Nephrology and Hypertension, Henry Ford Hospital, Detroit, Michigan, USA
| | | | | | - Stuart M Sprague
- Division of Nephrology and Hypertension, NorthShore University Health System, Evanston, Illinois, USA
| |
Collapse
|
5
|
Zhou K, Amiri M, Salari A, Yu Y, Xu H, Seidler U, Nikolovska K. Functional characterization of the sodium/hydrogen exchanger 8 and its role in proliferation of colonic epithelial cells. Am J Physiol Cell Physiol 2021; 321:C471-C488. [PMID: 34288721 DOI: 10.1152/ajpcell.00582.2020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Intestinal NaCl, HCO3-, and fluid absorption are strongly dependent on apical Na+/H+ exchange. The intestine expresses three presumably apical sodium-hydrogen exchanger (NHE) isoforms: NHE2, NHE3, and NHE8. We addressed the role of NHE8 [solute carrier 9A8 (SLC9A8)] and its interplay with NHE2 (SLC9A2) in luminal proton extrusion during acute and chronic enterocyte acidosis and studied the differential effects of NHE8 and NHE2 on enterocyte proliferation. In contrast to NHE3, which was upregulated in differentiated versus undifferentiated colonoids, the expression of NHE2 and NHE8 remained constant during differentiation of colonoids and Caco2Bbe cells. Heterogeneously expressed Flag-tagged rat (r)Nhe8 and human (h)NHE8 translocated to the apical membrane of Caco2Bbe cells. rNhe8 and hNHE8, when expressed in NHE-deficient PS120 fibroblasts showed higher sensitivity to HOE642 compared to NHE2. Lentiviral shRNA knockdown of endogenous NHE2 in Caco2Bbe cells (C2Bbe/shNHE2) resulted in a decreased steady-state intracellular pH (pHi), an increased NHE8 mRNA expression, and augmented NHE8-mediated apical NHE activity. Lentiviral shRNA knockdown of endogenous NHE8 in Caco2Bbe cells (C2Bbe/shNHE8) resulted in a decreased steady-state pHi as well, accompanied by decreased NHE2 mRNA expression and activity, which together contributed to reduced apical NHE activity in the NHE8-knockdown cells. Chronic acidosis increased NHE8 but not NHE2 mRNA expression. Alterations in NHE2 and NHE8 expression/activity affected proliferation, with C2Bbe/shNHE2 cells having lower and C2Bbe/shNHE8 having higher proliferative capacity, accompanied by amplified ERK1/2 signaling pathway and increased EGFR expression in the latter cell line. Thus, both Na+/H+ exchangers have distinct functions during cellular homeostasis by triggering different signaling pathways to regulate cellular proliferation and pHi control.
Collapse
Affiliation(s)
- Kunyan Zhou
- Department of Gastroenterology, Hepatology and Endocrinology, Hannover Medical School, Hannover, Germany
| | - Mahdi Amiri
- Department of Gastroenterology, Hepatology and Endocrinology, Hannover Medical School, Hannover, Germany
| | - Azam Salari
- Department of Gastroenterology, Hepatology and Endocrinology, Hannover Medical School, Hannover, Germany
| | - Yan Yu
- Department of Gastroenterology, Hepatology and Endocrinology, Hannover Medical School, Hannover, Germany
| | - Hua Xu
- Department of Pediatrics, University of Arizona Health Science Center, Tucson, Arizona
| | - Ursula Seidler
- Department of Gastroenterology, Hepatology and Endocrinology, Hannover Medical School, Hannover, Germany
| | - Katerina Nikolovska
- Department of Gastroenterology, Hepatology and Endocrinology, Hannover Medical School, Hannover, Germany
| |
Collapse
|
6
|
Hu Y, Lou J, Jin Z, Yang X, Shan W, Du Q, Liao Q, Xu J, Xie R. Advances in research on the regulatory mechanism of NHE1 in tumors. Oncol Lett 2021; 21:273. [PMID: 33717270 PMCID: PMC7885159 DOI: 10.3892/ol.2021.12534] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Accepted: 12/17/2020] [Indexed: 12/11/2022] Open
Abstract
Tumors pose a major threat to human health and present with difficulties that modern medicine has yet to overcome. It has been demonstrated that the acid-base balance of the tumor microenvironment is closely associated with the dynamic balance in the human body and that it regulates several processes, such as cell proliferation and differentiation, intracellular enzyme activity, and cytoskeletal assembly and depolymerization. It has been well established that the regulation of intra- and extracellular pH depends on a series of functional ion transporters and hydrogen ion channels, such as the Na+/H+ exchanger (NHE) protein and thee Cl/HCO3- exchange protein, among which the NHE1 member of the NHE family has been attracting increasing attention in recent years, particularly in studies on the correlation between pH regulation and tumors. NHE1 is a housekeeping gene encoding a protein that is widely expressed on the surface of all plasma membranes. Due to its functional domain, which determines the pHi at its N-terminus and C-terminus, NHE1 is involved in the regulation of the cellular pH microenvironment. It has been reported in the literature that NHE1 can regulate cell volume, participate in the transmembrane transport of intracellular and extracellular ions, affect cell proliferation and apoptosis, and regulate cell behavior and cell cycle progression; however, research on the role of NHE1 in tumorigenesis and tumor development in various systems is at its early stages. The aim of the present study was to review the current research on the correlation between the NHE family proteins and various systemic tumors, in order to indicate a new direction for antitumor drug development with the pH microenvironment as the target.
Collapse
Affiliation(s)
- Yanxia Hu
- Department of Gastroenterology, Affiliated Hospital of Zunyi Medical University, Zunyi, Guizhou 563003, P.R. China
| | - Jun Lou
- Department of Gastroenterology, Affiliated Hospital of Zunyi Medical University, Zunyi, Guizhou 563003, P.R. China
| | - Zhe Jin
- Department of Gastroenterology, Affiliated Hospital of Zunyi Medical University, Zunyi, Guizhou 563003, P.R. China
| | - Xiaoxu Yang
- Department of Gastroenterology, Affiliated Hospital of Zunyi Medical University, Zunyi, Guizhou 563003, P.R. China
| | - Weixi Shan
- Department of Gastroenterology, Affiliated Hospital of Zunyi Medical University, Zunyi, Guizhou 563003, P.R. China
| | - Qian Du
- Department of Gastroenterology, Affiliated Hospital of Zunyi Medical University, Zunyi, Guizhou 563003, P.R. China
| | - Qiushi Liao
- Department of Gastroenterology, Affiliated Hospital of Zunyi Medical University, Zunyi, Guizhou 563003, P.R. China
| | - Jingyu Xu
- Department of Gastroenterology, Affiliated Hospital of Zunyi Medical University, Zunyi, Guizhou 563003, P.R. China
| | - Rui Xie
- Department of Gastroenterology, Affiliated Hospital of Zunyi Medical University, Zunyi, Guizhou 563003, P.R. China
| |
Collapse
|
7
|
Komnenov D, Levanovich PE, Rossi NF. Hypertension Associated with Fructose and High Salt: Renal and Sympathetic Mechanisms. Nutrients 2019; 11:nu11030569. [PMID: 30866441 PMCID: PMC6472002 DOI: 10.3390/nu11030569] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Revised: 02/26/2019] [Accepted: 03/04/2019] [Indexed: 02/06/2023] Open
Abstract
Hypertension is a leading cause of cardiovascular and chronic renal disease. Despite multiple important strides that have been made in our understanding of the etiology of hypertension, the mechanisms remain complex due to multiple factors, including the environment, heredity and diet. This review focuses on dietary contributions, providing evidence for the involvement of elevated fructose and salt consumption that parallels the increased incidence of hypertension worldwide. High fructose loads potentiate salt reabsorption by the kidney, leading to elevation in blood pressure. Several transporters, such as NHE3 and PAT1 are modulated in this milieu and play a crucial role in salt-sensitivity. High fructose ingestion also modulates the renin-angiotensin-aldosterone system. Recent attention has been shifted towards the contribution of the sympathetic nervous system, as clinical trials demonstrated significant reductions in blood pressure following renal sympathetic nerve ablation. New preclinical data demonstrates the activation of the renal sympathetic nerves in fructose-induced salt-sensitive hypertension, and reductions of blood pressure after renal nerve ablation. This review further demonstrates the interplay between sodium handling by the kidney, the renin-angiotensin-aldosterone system, and activation of the renal sympathetic nerves as important mechanisms in fructose and salt-induced hypertension.
Collapse
Affiliation(s)
- Dragana Komnenov
- Department of Physiology, Wayne State University, 4160 John R Street #908, Detroit, MI 48201, USA.
- Department of Internal Medicine, Wayne State University, 4160 John R Street #908, Detroit, MI 48201, USA.
| | - Peter E Levanovich
- Department of Physiology, Wayne State University, 4160 John R Street #908, Detroit, MI 48201, USA.
| | - Noreen F Rossi
- Department of Physiology, Wayne State University, 4160 John R Street #908, Detroit, MI 48201, USA.
- Department of Internal Medicine, Wayne State University, 4160 John R Street #908, Detroit, MI 48201, USA.
- John D. Dingell VA Medical Center, 4646 John R Street, Detroit, MI 48201, USA.
| |
Collapse
|
8
|
Xu H, Ghishan FK, Kiela PR. SLC9 Gene Family: Function, Expression, and Regulation. Compr Physiol 2018; 8:555-583. [PMID: 29687889 DOI: 10.1002/cphy.c170027] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The Slc9 family of Na+ /H+ exchangers (NHEs) plays a critical role in electroneutral exchange of Na+ and H+ in the mammalian intestine as well as other absorptive and secretory epithelia of digestive organs. These transport proteins contribute to the transepithelial Na+ and water absorption, intracellular pH and cellular volume regulation as well as the electrolyte, acid-base, and fluid volume homeostasis at the systemic level. They also influence the function of other membrane transport mechanisms, affect cellular proliferation and apoptosis as well as cell migration, adherence to the extracellular matrix, and tissue repair. Additionally, they modulate the extracellular milieu to facilitate other nutrient absorption and to regulate the intestinal microbial microenvironment. Na+ /H+ exchange is inhibited in selected gastrointestinal diseases, either by intrinsic factors (e.g., bile acids, inflammatory mediators) or infectious agents and associated bacterial toxins. Disrupted NHE activity may contribute not only to local and systemic electrolyte imbalance but also to the disease severity via multiple mechanisms. In this review, we describe the cation proton antiporter superfamily of Na+ /H+ exchangers with a particular emphasis on the eight SLC9A isoforms found in the digestive tract, followed by a more integrative description in their roles in each of the digestive organs. We discuss regulatory mechanisms that determine the function of Na+ /H+ exchangers as pertinent to the digestive tract, their regulation in pathological states of the digestive organs, and reciprocally, the contribution of dysregulated Na+ /H+ exchange to the disease pathogenesis and progression. © 2018 American Physiological Society. Compr Physiol 8:555-583, 2018.
Collapse
Affiliation(s)
- Hua Xu
- Department of Pediatrics, Steele Children's Research Center, University of Arizona, Tucson, Arizona, USA
| | - Fayez K Ghishan
- Department of Pediatrics, Steele Children's Research Center, University of Arizona, Tucson, Arizona, USA
| | - Pawel R Kiela
- Department of Pediatrics, Steele Children's Research Center, University of Arizona, Tucson, Arizona, USA.,Department of Immunobiology, University of Arizona, Tucson, Arizona, USA
| |
Collapse
|
9
|
Johansson S, Rosenbaum DP, Palm J, Stefansson B, Knutsson M, Lisbon EA, Hilgendorf C. Tenapanor administration and the activity of the H + -coupled transporter PepT1 in healthy volunteers. Br J Clin Pharmacol 2017; 83:2008-2014. [PMID: 28432691 PMCID: PMC5582369 DOI: 10.1111/bcp.13313] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2016] [Revised: 04/06/2017] [Accepted: 04/18/2017] [Indexed: 12/24/2022] Open
Abstract
AIM Tenapanor (RDX5791/AZD1722), an inhibitor of gastrointestinal Na+ /H+ exchanger NHE3, is being evaluated for the treatment of patients with constipation-predominant irritable bowel syndrome and the treatment of hyperphosphataemia in patients with chronic kidney disease on dialysis. By reducing intestinal H+ secretion, inhibition of NHE3 by tenapanor could indirectly affect H+ -coupled transporter activity, leading to drug-drug interactions. We investigated the effect of tenapanor on the activity of the H+ -coupled peptide transporter PepT1 via assessment of the pharmacokinetics of cefadroxil - a compound transported by PepT1 - in healthy volunteers. METHODS In this open-label, two-period crossover, phase 1 study (NCT02140281), 28 volunteers received in random order: a single dose of cefadroxil 500 mg for 1 day; and tenapanor 15 mg twice daily over 4 days followed by single doses of both cefadroxil 500 mg and tenapanor 15 mg on day 5. There was a 4-day washout between treatment periods. RESULTS Cefadroxil exposure was similar when administered alone or in combination with tenapanor {geometric least-squares mean ratios [(cefadroxil + tenapanor)/cefadroxil] (90% confidence interval): area under the concentration-time curve 93.3 (90.6-96.0)%; maximum concentration in plasma 95.9 (89.8-103)%}. Tenapanor treatment caused a softening of stool consistency and an increase in stool frequency, consistent with its expected pharmacodynamic effect. No safety concerns were identified and tenapanor was not detected in plasma. CONCLUSIONS These results suggest that tenapanor 15 mg twice daily does not have a clinically relevant impact on the activity of the H+ -coupled transporter PepT1 in humans. This may guide future research on drug-drug interactions involving NHE3 inhibitors.
Collapse
Affiliation(s)
- Susanne Johansson
- Quantitative Clinical Pharmacology, Innovative Medicines and Early Development Biotech Unit, AstraZeneca, Mölndal, Sweden
| | | | - Johan Palm
- Product Development, Pharmaceutical Technology & Development, Operations, AstraZeneca, Mölndal, Sweden
| | - Bergur Stefansson
- Cardiovascular Metabolic Diseases, Global Medicines Development, AstraZeneca, Mölndal, Sweden
| | - Mikael Knutsson
- Biometrics & Information Sciences, Global Medicines Development, AstraZeneca, Mölndal, Sweden
| | | | - Constanze Hilgendorf
- Drug Metabolism and Pharmacokinetics, Cardiovascular and Metabolic Diseases, Innovative Medicines and Early Development Biotech Unit, AstraZeneca, Mölndal, Sweden
| |
Collapse
|
10
|
Soleiman AA, Thameem F, Khan I. Mechanism of down regulation of Na-H exchanger-2 in experimental colitis. PLoS One 2017; 12:e0176767. [PMID: 28493993 PMCID: PMC5426621 DOI: 10.1371/journal.pone.0176767] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2016] [Accepted: 04/17/2017] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND The Na-H exchanger [NHE] performs an electroneutral uptake of NaCl and water from the lumen of the gastrointestinal tract. There are several distinct NHE isoforms, some of which show an altered expression in the inflammatory bowel diseases (IBD). In this study, we examined a role of NHE-2 in experimental colitis. METHODS Colitis was induced in male Sprague-Dawley rats by intra-rectal administration of trinitrobenzenesulphonic acid (TNBS). On day 6 post-TNBS, the animals were sacrificed, colonic and ileal segments were taken out, cleaned with phosphate buffered saline and used in this study. RESULTS There was a significant decrease in the level of NHE-2 protein as measured by ECL western blot analysis and confocal immunofluorescence microscopy. The levels of NHE-2 mRNA and heteronuclear RNA measured by an end-point RT-PCR and a real time PCR were also decreased significantly in the inflamed colon. However, there was no change in the level of NHE-2 protein in response to in vitro TNF-α treatment of uninflamed rat colonic segment. These changes were selective and localized to the colon as actin, an internal control, remained unchanged. Confocal immunofluorescence microscopy revealed co-localization of NHE-2 and NHE-3 in the brush borders of colonic epithelial cells. Inflamed colon showed a significant increase in myeloperoxidase activity and colon hypertrophy. In addition, there was a significant decrease in body weight and goblet cells' mucin staining in the TNBS treated colon. These changes were not conspicuous in the non-inflamed ileum. CONCLUSIONS These findings demonstrate suppression of NHE-2 expression on the brush borders in the colonic epithelial cells which is regulated transcriptionally. However a role of TNF-α in the regulation of NHE-2 is discounted in the present model of colitis. This decrease in the NHE-2 expression will lead to a loss of electrolyte and water uptake thus contributing to the symptoms associated with IBD.
Collapse
Affiliation(s)
- Amal Ali Soleiman
- Department of Biochemistry, Faculty of Medicine, Kuwait University, Jabriya, Kuwait
| | - Farook Thameem
- Department of Biochemistry, Faculty of Medicine, Kuwait University, Jabriya, Kuwait
| | - Islam Khan
- Department of Biochemistry, Faculty of Medicine, Kuwait University, Jabriya, Kuwait
- * E-mail:
| |
Collapse
|
11
|
Shawki A, Engevik MA, Kim RS, Knight PB, Baik RA, Anthony SR, Worrell RT, Shull GE, Mackenzie B. Intestinal brush-border Na+/H+ exchanger-3 drives H+-coupled iron absorption in the mouse. Am J Physiol Gastrointest Liver Physiol 2016; 311:G423-30. [PMID: 27390324 PMCID: PMC5076011 DOI: 10.1152/ajpgi.00167.2016] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/26/2016] [Accepted: 06/29/2016] [Indexed: 01/31/2023]
Abstract
Divalent metal-ion transporter-1 (DMT1), the principal mechanism by which nonheme iron is taken up at the intestinal brush border, is energized by the H(+)-electrochemical potential gradient. The provenance of the H(+) gradient in vivo is unknown, so we have explored a role for brush-border Na(+)/H(+) exchanger (NHE) isoforms by examining iron homeostasis and intestinal iron handling in mice lacking NHE2 or NHE3. We observed modestly depleted liver iron stores in NHE2-null (NHE2(-/-)) mice stressed on a low-iron diet but no change in hematological or blood iron variables or the expression of genes associated with iron metabolism compared with wild-type mice. Ablation of NHE3 strongly depleted liver iron stores, regardless of diet. We observed decreases in blood iron variables but no overt anemia in NHE3-null (NHE3(-/-)) mice on a low-iron diet. Intestinal expression of DMT1, the apical surface ferrireductase cytochrome b reductase-1, and the basolateral iron exporter ferroportin was upregulated in NHE3(-/-) mice, and expression of liver Hamp1 (hepcidin) was suppressed compared with wild-type mice. Absorption of (59)Fe from an oral dose was substantially impaired in NHE3(-/-) compared with wild-type mice. Our data point to an important role for NHE3 in generating the H(+) gradient that drives DMT1-mediated iron uptake at the intestinal brush border.
Collapse
Affiliation(s)
- Ali Shawki
- Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, Cincinnati, Ohio; Systems Biology and Physiology Program, University of Cincinnati College of Medicine, Cincinnati, Ohio; and
| | - Melinda A Engevik
- Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, Cincinnati, Ohio; Systems Biology and Physiology Program, University of Cincinnati College of Medicine, Cincinnati, Ohio; and
| | - Robert S Kim
- Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, Cincinnati, Ohio
| | - Patrick B Knight
- Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, Cincinnati, Ohio
| | - Rusty A Baik
- Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, Cincinnati, Ohio
| | - Sarah R Anthony
- Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, Cincinnati, Ohio
| | - Roger T Worrell
- Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, Cincinnati, Ohio; Systems Biology and Physiology Program, University of Cincinnati College of Medicine, Cincinnati, Ohio; and
| | - Gary E Shull
- Systems Biology and Physiology Program, University of Cincinnati College of Medicine, Cincinnati, Ohio; and Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio
| | - Bryan Mackenzie
- Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, Cincinnati, Ohio; Systems Biology and Physiology Program, University of Cincinnati College of Medicine, Cincinnati, Ohio; and
| |
Collapse
|
12
|
Grant CN, Mojica SG, Sala FG, Hill JR, Levin DE, Speer AL, Barthel ER, Shimada H, Zachos NC, Grikscheit TC. Human and mouse tissue-engineered small intestine both demonstrate digestive and absorptive function. Am J Physiol Gastrointest Liver Physiol 2015; 308:G664-77. [PMID: 25573173 PMCID: PMC4398842 DOI: 10.1152/ajpgi.00111.2014] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/25/2014] [Accepted: 12/19/2014] [Indexed: 01/31/2023]
Abstract
Short bowel syndrome (SBS) is a devastating condition in which insufficient small intestinal surface area results in malnutrition and dependence on intravenous parenteral nutrition. There is an increasing incidence of SBS, particularly in premature babies and newborns with congenital intestinal anomalies. Tissue-engineered small intestine (TESI) offers a therapeutic alternative to the current standard treatment, intestinal transplantation, and has the potential to solve its biggest challenges, namely donor shortage and life-long immunosuppression. We have previously demonstrated that TESI can be generated from mouse and human small intestine and histologically replicates key components of native intestine. We hypothesized that TESI also recapitulates native small intestine function. Organoid units were generated from mouse or human donor intestine and implanted into genetically identical or immunodeficient host mice. After 4 wk, TESI was harvested and either fixed and paraffin embedded or immediately subjected to assays to illustrate function. We demonstrated that both mouse and human tissue-engineered small intestine grew into an appropriately polarized sphere of intact epithelium facing a lumen, contiguous with supporting mesenchyme, muscle, and stem/progenitor cells. The epithelium demonstrated major ultrastructural components, including tight junctions and microvilli, transporters, and functional brush-border and digestive enzymes. This study demonstrates that tissue-engineered small intestine possesses a well-differentiated epithelium with intact ion transporters/channels, functional brush-border enzymes, and similar ultrastructural components to native tissue, including progenitor cells, whether derived from mouse or human cells.
Collapse
Affiliation(s)
- Christa N. Grant
- 1Developmental Biology and Regenerative Medicine Program, Saban Research Institute, Children's Hospital Los Angeles, Los Angeles, California; ,2Division of Pediatric Surgery, Children's Hospital Los Angeles, USC Keck School of Medicine, Los Angeles, California;
| | - Salvador Garcia Mojica
- 1Developmental Biology and Regenerative Medicine Program, Saban Research Institute, Children's Hospital Los Angeles, Los Angeles, California;
| | - Frederic G. Sala
- 1Developmental Biology and Regenerative Medicine Program, Saban Research Institute, Children's Hospital Los Angeles, Los Angeles, California;
| | - J. Ryan Hill
- 1Developmental Biology and Regenerative Medicine Program, Saban Research Institute, Children's Hospital Los Angeles, Los Angeles, California;
| | - Daniel E. Levin
- 1Developmental Biology and Regenerative Medicine Program, Saban Research Institute, Children's Hospital Los Angeles, Los Angeles, California; ,2Division of Pediatric Surgery, Children's Hospital Los Angeles, USC Keck School of Medicine, Los Angeles, California;
| | - Allison L. Speer
- 1Developmental Biology and Regenerative Medicine Program, Saban Research Institute, Children's Hospital Los Angeles, Los Angeles, California; ,2Division of Pediatric Surgery, Children's Hospital Los Angeles, USC Keck School of Medicine, Los Angeles, California;
| | - Erik R. Barthel
- 1Developmental Biology and Regenerative Medicine Program, Saban Research Institute, Children's Hospital Los Angeles, Los Angeles, California; ,2Division of Pediatric Surgery, Children's Hospital Los Angeles, USC Keck School of Medicine, Los Angeles, California;
| | - Hiroyuki Shimada
- 4Department of Pathology, Children's Hospital Los Angeles, USC Keck School of Medicine, Los Angeles, California
| | - Nicholas C. Zachos
- 3Department of Medicine, Division of Gastroenterology and Hepatology, Johns Hopkins University School of Medicine, Baltimore, Maryland;
| | - Tracy C. Grikscheit
- 1Developmental Biology and Regenerative Medicine Program, Saban Research Institute, Children's Hospital Los Angeles, Los Angeles, California; ,2Division of Pediatric Surgery, Children's Hospital Los Angeles, USC Keck School of Medicine, Los Angeles, California;
| |
Collapse
|
13
|
Bachmann O, Seidler U. News from the end of the gut--how the highly segmental pattern of colonic HCO₃⁻ transport relates to absorptive function and mucosal integrity. Biol Pharm Bull 2011; 34:794-802. [PMID: 21628874 DOI: 10.1248/bpb.34.794] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A number of transport mechanisms in the colonic epithelium contribute to HCO₃⁻ movement across the apical and basolateral membranes, but this ion has been largely regarded as a by-product of the transport functions it is involved in, such as NaCl or short chain fatty acid (SCFA) absorption. However, emerging data points to several specific roles of HCO₃⁻ for colonic epithelial physiology, including pH control in the colonic surface microenvironment, which is important for transport and immune functions, as well as the secretion and the rheological properties of the mucus gel. Furthermore, recent studies have demonstrated that colonic HCO₃⁻ transporters are expressed in a highly segmental as well as species-specific manner. This review summarizes recently gathered information on the functional anatomy of the colon, the roles of HCO₃⁻ in the colonic epithelium, colonic mucosal integrity, and the expression and function of HCO₃⁻ transporting mechanisms in health and disease.
Collapse
Affiliation(s)
- Oliver Bachmann
- Department of Gastroenterology, Hepatology, and Endocrinology, Hannover Medical School, Hannover, Germany
| | | |
Collapse
|
14
|
Abstract
The epithelial apical membrane Na+/H+ exchangers [NHE (sodium hydrogen exchanger)2 and NHE3] and Cl-/HCO3- exchangers [DRA (down-regulated in adenoma) and PAT-1 (putative anion transporter 1)] are key luminal membrane transporters involved in electroneutral NaCl absorption in the mammalian intestine. During the last decade, there has been a surge of studies focusing on the short-term regulation of these electrolyte transporters, particularly for NHE3 regulation. However, the long-term regulation of the electrolyte transporters, involving transcriptional mechanisms and transcription factors that govern their basal regulation or dysregulation in diseased states, has only now started to unfold with the cloning and characterization of their gene promoters. The present review provides a detailed analysis of the core promoters of NHE2, NHE3, DRA and PAT-1 and outlines the transcription factors involved in their basal regulation as well as in response to both physiological (butyrate, protein kinases and probiotics) and pathophysiological (cytokines and high levels of serotonin) stimuli. The information available on the transcriptional regulation of the recently identified NHE8 isoform is also highlighted. Therefore the present review bridges a gap in our knowledge of the transcriptional mechanisms underlying the alterations in the gene expression of intestinal epithelial luminal membrane Na+ and Cl- transporters involved in electroneutral NaCl absorption. An understanding of the mechanisms of the modulation of gene expression of these transporters is important for a better assessment of the pathophysiology of diarrhoea associated with inflammatory and infectious diseases and may aid in designing better management protocols.
Collapse
|
15
|
Talbot C, Lytle C. Segregation of Na/H exchanger-3 and Cl/HCO3 exchanger SLC26A3 (DRA) in rodent cecum and colon. Am J Physiol Gastrointest Liver Physiol 2010; 299:G358-67. [PMID: 20466943 DOI: 10.1152/ajpgi.00151.2010] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The colon is believed to absorb NaCl via the coupled operation of apical Na/H exchanger-3 (NHE3) and Cl/HCO(3) exchanger SLC26A3 (DRA). Efficient coupling requires that NHE3 and DRA operate in close proximity within common luminal and cytosolic microenvironments. Thus we examined whether these proteins coexist along the apical margin of surface enterocytes by quantitative immunofluorescence microscopy in consecutive colon segments from nonfasted mice and rats. The cecocolonic profiles of NHE3 and DRA expression were roughly inverse; NHE3 was highest in proximal colon (PC) and negligible in distal colon, whereas DRA was absent in early PC and highest in the late midcolon, and DRA was prominent in the cecum whereas NHE3 was not. NHE3 and DRA coexisted only in the middle third of the colon. The consequences of unpaired NHE3/DRA expression on mucosal surface (subscript MS) pH and Na(+) concentration ([Na(+)]) were assessed in nonfasted rats in situ using miniature electrodes. In the cecum, where only DRA is expressed, pH(MS) was approximately 7.5, markedly higher than underlaying stool (6.3), consistent with net HCO(3)(-) secretion. In the early PC, where NHE3 is not expressed with DRA, pH(MS) was acidic (6.2), consistent with unopposed H(+) secretion. [Na(+)](MS) was approximately 60 mM in the cecum, decreased along the PC to approximately 20 mM, and declined further to approximately 10 mM distally. Cl(-) was secreted into the PC, then reabsorbed distally. Our results suggest a model in which 1) unpaired DRA activity in the cecum maintains an alkaline mucosal surface that could neutralize fermentative H(+); 2) unpaired NHE3 activity in the early PC preserves an acidic mucosal surface that could energize short-chain fatty acid absorption; and 3) coupled NHE3/DRA activities in the midcolon allow for vigorous NaCl absorption at a neutral pH(MS).
Collapse
|
16
|
Mechanisms of the regulation of the intestinal Na+/H+ exchanger NHE3. J Biomed Biotechnol 2010; 2010:238080. [PMID: 20011065 PMCID: PMC2789519 DOI: 10.1155/2010/238080] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2009] [Accepted: 09/11/2009] [Indexed: 01/25/2023] Open
Abstract
A major of Na+ absorptive process in the proximal part of intestine and kidney is electroneutral exchange of Na+ and H+ by Na+/H+ exchanger type 3 (NHE3). During the past decade, significant advance has been achieved in the mechanisms of NHE3 regulation. A bulk of the current knowledge on Na+/H+ exchanger regulation is based on heterologous expression of mammalian Na+/H+ exchangers in Na+/H+ exchanger deficient fibroblasts, renal epithelial, and intestinal epithelial cells. Based on the reductionist's approach, an understanding of NHE3 regulation has been greatly advanced. More recently, confirmations of in vitro studies have been made using animals deficient in one or more proteins but in some cases unexpected findings have emerged. The purpose of this paper is to provide a brief overview of recent progress in the regulation and functions of NHE3 present in the luminal membrane of the intestinal tract.
Collapse
|
17
|
Collins D, Winter DC, Hogan AM, Schirmer L, Baird AW, Stewart GS. Differential protein abundance and function of UT-B urea transporters in human colon. Am J Physiol Gastrointest Liver Physiol 2010; 298:G345-51. [PMID: 19926813 PMCID: PMC3774180 DOI: 10.1152/ajpgi.00405.2009] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/01/2009] [Accepted: 11/14/2009] [Indexed: 01/31/2023]
Abstract
Facilitative UT-B urea transporters enable the passage of urea across cell membranes. Gastrointestinal urea transporters are thought to play a significant role in the urea nitrogen salvaging process that occurs between mammalian hosts and their gut bacteria. This study investigated the expression of UT-B urea transporters in different segments of human colon. Immunoblot analysis showed that human colon expressed a 35-kDa glycosylated UT-B protein in the colonic mucosa. The 35-kDa UT-B transporter was predominantly located in plasma membrane-enriched samples (P < 0.001; n = 6), and its expression was greater in the ascending colon compared with the descending colon (P < 0.01; n = 3). At the cellular level, UT-B transporters were located throughout colonocytes situated in the upper portion of the colonic crypts. Bidirectional trans-epithelial urea transport was significantly greater in the ascending colon than the descending colon (P < 0.05; n = 6). In addition, the facilitative urea transporter inhibitor 1,3,dimethylurea significantly reduced urea transport in the ascending colon (P < 0.05; n = 6) but had no effect in the descending colon (NS; n = 6). These results illustrate differential protein abundance of functional UT-B protein in different sections of the human colon, strongly correlating to regions that contain the largest populations of intestinal bacteria. This study suggests an important role for UT-B urea transporters in maintaining the symbiotic relationship between humans and their gut bacteria.
Collapse
Affiliation(s)
- D Collins
- Center for Pain Research, Department of Anesthesiology, University of Pittsburgh, Pennsylvania, USA.
| | | | | | | | | | | |
Collapse
|
18
|
Choi LJ, Jenikova G, Hanson E, Spehlmann ME, Boehling NS, Kirstein SL, Bundey RA, Smith JR, Insel PA, Eckmann L. Coordinate down-regulation of adenylyl cyclase isoforms and the stimulatory G protein (G(s)) in intestinal epithelial cell differentiation. J Biol Chem 2010; 285:12504-11. [PMID: 20157112 DOI: 10.1074/jbc.m109.059741] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
The intestinal epithelium is dynamic, with proliferation of undifferentiated crypt cells balanced by terminal differentiation and cell death at the colon surface or small intestinal villus tips. Cyclic AMP, induced by agonists such as prostaglandin E(2) and vasoactive intestinal polypeptide, promotes proliferation and ion secretion and suppresses apoptosis in intestinal epithelial cells. Here, we show that cell differentiation in a model intestinal epithelium leads to attenuation of cAMP production in response to G protein-coupled receptor and receptor-independent agonists. Concomitantly, key components of the cAMP cascade, the alpha subunit of the stimulatory G protein, G(s), and adenylyl cyclase (AC) isoforms 3, 4, 6, and 7 are down-regulated. By contrast, AC1, AC2, AC8, and AC9, and the receptors for prostaglandin E(2) and vasoactive intestinal polypeptide, are not expressed or not affected by differentiation. We confirmed key findings in normal murine colon epithelium, in which the major AC isoforms and G(s)alpha are markedly down-regulated in differentiated surface cells. Suppression of AC isoforms and G(s)alpha is functionally important, because their constitutive expression completely reverses differentiation-induced cAMP attenuation. Thus, down-regulation of AC isoforms and G(s)alpha is an integral part of the intestinal epithelial differentiation program, perhaps serving to release cells from cAMP-promoted anti-apoptosis as a prerequisite for cell death upon terminal differentiation.
Collapse
Affiliation(s)
- Lillian J Choi
- Department of Medicine, University of California, San Diego, La Jolla, California 92093, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
19
|
Li H, Gilbert ER, Zhang Y, Crasta O, Emmerson D, Webb KE, Wong EA. Expression profiling of the solute carrier gene family in chicken intestine from the late embryonic to early post-hatch stages. Anim Genet 2008; 39:407-24. [PMID: 18544075 DOI: 10.1111/j.1365-2052.2008.01744.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Intestinal development during late embryogenesis and early post-hatch has a long-term influence on digestive and absorptive capacity in chickens. The objective of this research was to obtain a global view of intestinal solute carrier (SLC) gene family member expression from late embryogenesis until 2 weeks post-hatch with a focus on SLC genes involved in uptake of sugars and amino acids. Small intestine samples from male chicks were collected on embryonic days 18 (E18) and 20 (E20), day of hatch and days 1, 3, 7 and 14 post-hatch. The expression profiles of 162 SLC genes belonging to 41 SLC families were determined using Affymetrix chicken genome microarrays. The majority of SLC genes showed little or no difference in level of expression during E18-D14. A number of well-known intestinal transporters were upregulated between E18 and D14 including the amino acid transporters rBAT, y(+)LAT-2 and EAAT3, the peptide transporter PepT1 and the sugar transporters SGLT1, GLUT2 and GLUT5. The amino acid transporters CAT-1 and CAT-2 were downregulated. In addition, several glucose and amino acid transporters that are novel to our understanding of nutrient absorption in the chicken intestine were discovered through the arrays (SGLT6, SNAT1, SNAT2 and AST). These results represent a comprehensive characterization of the expression profiles of the SLC family of genes at different stages of development in the chicken intestine and lay the ground work for future nutritional studies.
Collapse
Affiliation(s)
- H Li
- Department of Animal and Poultry Sciences, Virginia Tech, Blacksburg, VA 24061-0306, USA
| | | | | | | | | | | | | |
Collapse
|
20
|
NHE1, NHE2, and NHE4 contribute to regulation of cell pH in T84 colon cancer cells. Pflugers Arch 2007; 455:799-810. [PMID: 17943310 DOI: 10.1007/s00424-007-0333-0] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2007] [Revised: 07/04/2007] [Accepted: 08/09/2007] [Indexed: 10/22/2022]
Abstract
The isoforms of the Na+/H+ exchanger present in T84 human colon cells were identified by functional and molecular methods. Cell pH was measured by fluorescence microscopy using the probe BCECF. Based on the pH recovery after an ammonium pulse and determination of buffering capacity of these cells, the rate of H+ extrusion (JH) was 3.68 mM/min. After the use of the amiloride derivative HOE-694 at 25 microM, which inhibits the isoforms NHE1 and NHE2, there remained 43% of the above transport rate, the nature of which was investigated. Evidence of the presence of NHE1, NHE2, and NHE4 was obtained by reverse transcriptase polymerase chain reaction (RT-PCR) (mRNA) and Western blot. There was no decrease of JH by the NHE3 inhibitor S3226 (1 microM) and no evidence of this isoform by RT-PCR was found. The following functional evidence for the presence of NHE4 was obtained: 25 microM EIPA abolished JH entirely, but NHE4 was not inhibited at 10 microM; substitution of Na by K increased the remainder, a property of NHE4; hypertonicity also increased this fraction of JH. Cl--dependent NHE was not detected: in 0 Cl- solutions JH was increased and not reduced. In 0 Cl- cell volume decreased significantly, which was abolished by the Cl- channel blocker NPPB, indicating that the 0 Cl- effect was because of reduction of cell volume. In conclusion, T84 human colon cells contain three isoforms of the Na+/H+ exchanger, NHE1, NHE2, and NHE4, but not the Cl-dependent NHE.
Collapse
|
21
|
Abstract
NHE3 is the brush-border (BB) Na+/H+exchanger of small intestine, colon, and renal proximal tubule which is involved in large amounts of neutral Na+absorption. NHE3 is a highly regulated transporter, being both stimulated and inhibited by signaling that mimics the postprandial state. It also undergoes downregulation in diarrheal diseases as well as changes in renal disorders. For this regulation, NHE3 exists in large, multiprotein complexes in which it associates with at least nine other proteins. This review deals with short-term regulation of NHE3 and the identity and function of its recognized interacting partners and the multiprotein complexes in which NHE3 functions.
Collapse
Affiliation(s)
- Mark Donowitz
- Department of Medicine, GI Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
| | | |
Collapse
|
22
|
Gens JS, Dou H, Tackett L, Kong SS, Chu S, Montrose MH. Different ionic conditions prompt NHE2 and NHE3 translocation to the plasma membrane. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1768:1023-35. [PMID: 17303069 PMCID: PMC1974857 DOI: 10.1016/j.bbamem.2007.01.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2006] [Revised: 12/31/2006] [Accepted: 01/04/2007] [Indexed: 11/29/2022]
Abstract
We tested whether NHE3 and NHE2 Na(+)/H(+) exchanger isoforms were recruited to the plasma membrane (PM) in response to changes in ion homeostasis. NHE2-CFP or NHE3-CFP fusion proteins were functional Na(+)/H(+) exchangers when transiently expressed in NHE-deficient PS120 fibroblasts. Confocal morphometry of cells whose PM was labeled with FM4-64 measured the fractional amount of fusion protein at the cell surface. In resting cells, 10-20% of CFP fluorescence was at PM and stable over time. A protocol commonly used to activate the Na(+)/H(+) exchange function (NH(4)-prepulse acid load sustained in Na(+)-free medium), increased PM percentages of PM NHE3-CFP and NHE2-CFP. Separation of cellular acidification from Na(+) removal revealed that only NHE3-CFP translocated when medium Na(+) was removed, and only NHE2-CFP translocated when the cell was acidified. NHE2/NHE3 chimeric proteins demonstrate that the Na(+)-removal response element resides predominantly in the NHE3 cytoplasmic tail and is distinct from the acidification response sequence of NHE2.
Collapse
Affiliation(s)
- J. Scott Gens
- Biocomplexity Institute, Indiana University, Bloomington, Indiana, 47405
| | - Hongwei Dou
- Department of Molecular and Cellular Physiology, University of Cincinnati, Cincinnati, Ohio 45267
| | - Lixuan Tackett
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana 46202-5120
| | - Shen-Shen Kong
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana 46202-5120
| | - Shaoyou Chu
- Eli Lilly and Company, Indianapolis, Indiana, 46225
| | - Marshall H. Montrose
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana 46202-5120
- Corresponding Author: Marshall H. Montrose, Mail address: Department of Molecular and Cellular Physiology, University of Cincinnati, 231 Albert Sabin Way, Cincinnati, OH 45267, Telephone number: (513)-558-5636, FAX number: (513)-558-5738, E-mail:
| |
Collapse
|
23
|
Guan Y, Dong J, Tackett L, Meyer JW, Shull GE, Montrose MH. NHE2 is the main apical NHE in mouse colonic crypts but an alternative Na+-dependent acid extrusion mechanism is upregulated in NHE2-null mice. Am J Physiol Gastrointest Liver Physiol 2006; 291:G689-99. [PMID: 16690903 DOI: 10.1152/ajpgi.00342.2005] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The mechanism of apical Na(+)-dependent H(+) extrusion in colonic crypts is controversial. With the use of confocal microscopy of the living mouse distal colon loaded with BCECF or SNARF-5F (fluorescent pH sensors), measurements of intracellular pH (pH(i)) in epithelial cells at either the crypt base or colonic surface were reported. After cellular acidification, the addition of luminal Na(+) stimulated similar rates of pH(i) recovery in cells at the base of distal colonic crypts of wild-type or Na(+)/H(+) exchanger isoform 2 (NHE2)-null mice. In wild-type crypts, 20 microM HOE694 (NHE2 inhibitor) blocked 68-75% of the pH(i) recovery rate, whereas NHE2-null crypts were insensitive to HOE694, the NHE3-specific inhibitor S-1611 (20 microM), or the bicarbonate transport inhibitor 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS; 1 mM). A general NHE inhibitor, 5-(N-ethyl-N-isopropyl)amiloride (EIPA; 20 microM), inhibited pH(i) recovery in NHE2-null mice (46%) but less strongly than in wild-type mice (74%), suggesting both EIPA-sensitive and -insensitive compensatory mechanisms. Transepithelial Na(+) leakage followed by activation of basolateral NHE1 could confound the outcomes; however, the rates of Na(+)-dependent pH(i) recovery were independent of transepithelial leakiness to lucifer yellow and were unchanged in NHE1-null mice. NHE2 was immunolocalized on apical membranes of wild-type crypts but not NHE2-null tissue. NHE3 immunoreactivity was near the colonic surface but not at the crypt base in NHE2-null mice. Colonic surface cells from wild-type mice demonstrated S1611- and HOE694-sensitive pH(i) recovery in response to luminal sodium, confirming a functional role for both NHE3 and NHE2 at this site. We conclude that constitutive absence of NHE2 results in a compensatory increase in a Na(+)-dependent, EIPA-sensitive acid extruder distinct from NHE1, NHE3, or SITS-sensitive transporters.
Collapse
Affiliation(s)
- Yanfang Guan
- Dept. of Molecular and Cellular Physiology, Univ. of Cincinnati College of Medicine, 231 Albert Sabin Way, Medical Sciences Bldg., Cincinnati, OH 45267-0576, USA
| | | | | | | | | | | |
Collapse
|
24
|
Fujiwara Y, Higuchi K, Takashima T, Hamaguchi M, Hayakawa T, Tominaga K, Watanabe T, Oshitani N, Shimada Y, Arakawa T. Roles of epidermal growth factor and Na+/H+ exchanger-1 in esophageal epithelial defense against acid-induced injury. Am J Physiol Gastrointest Liver Physiol 2006; 290:G665-73. [PMID: 16306134 DOI: 10.1152/ajpgi.00238.2005] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Epidermal growth factor (EGF) is predominantly secreted by salivary glands and activates Na(+)/H(+) exchanger-1 (NHE-1), which regulates intracellular pH (pH(i)). We investigated the roles of EGF and NHE-1 in esophageal epithelial defense against acid using human esophageal epithelial cell lines and a rat chronic esophagitis model. Esophageal epithelial cells were incubated with acidified medium in the absence or presence of EGF. Cell viability and changes in pH(i) were measured. Chronic acid reflux esophagitis was induced in rats with and without sialoadenectomy. Esophageal lesion index, epithelial proliferation, and expression of EGF receptors and NHE-1 were examined. EGF protected esophageal epithelial cells against acid in a dose-dependent manner, and the cytoprotective effect of EGF was completely blocked by treatment with NHE-1 inhibitors. Tyrosine kinase, calmodulin, and PKC inhibitors significantly inhibited cytoprotection by EGF, whereas MEK, phosphatidylinositol 3-kinase, and PKA inhibitors had no effect. EGF significantly increased pH(i) recovery after NH(4)Cl pulse acidification, and this increase in pH(i) recovery was significantly blocked by inhibitors of calmodulin and PKC. Sialoadenectomy led to an increase in the severity of chronic esophagitis but affected neither epithelial proliferation nor expression of EGF receptors. Expression of NHE-1 mRNA was increased in esophagitis and upregulated in rats with sialoadenectomy. The increasing severity of esophagitis in rats with sialoadenectomy was prevented by exogenous administration of EGF. In conclusion, EGF protects esophageal epithelial cells against acid through NHE activation via Ca(2+)/calmodulin and the PKC pathway. Deficiency in endogenous EGF is associated with increased severity of esophagitis. EGF and NHE-1 play crucial roles in esophageal epithelial defense against acid.
Collapse
Affiliation(s)
- Yasuhiro Fujiwara
- Department of Gastroenterology, Osaka City University Graduate School of Medicine, Japan.
| | | | | | | | | | | | | | | | | | | |
Collapse
|
25
|
Rakonczay Z, Fearn A, Hegyi P, Boros I, Gray MA, Argent BE. Characterization of H + and HCO 3- transporters in CFPAC-1 human pancreatic duct cells. World J Gastroenterol 2006; 12:885-95. [PMID: 16521216 PMCID: PMC4066153 DOI: 10.3748/wjg.v12.i6.885] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
AIM: To characterize H+ and HCO3- transporters in polarized CFPAC-1 human pancreatic duct cells, which were derived from a cystic fibrosis patient with the ΔF508 CFTR mutation.
METHODS: CFPAC-1 cells were seeded at high density onto permeable supports and grown to confluence. The cells were loaded with the pH-sensitive fluorescent dye BCECF, and mounted into a perfusion chamber, which allowed the simultaneous perfusion of the basolateral and apical membranes. Transmembrane base flux was calculated from the changes in intracellular pH and the buffering capacity of the cells.
RESULTS: Our results showed differential permeability to HCO3-/CO2 at the apical and basolateral membranes of CFPAC-1 cells. Na+/HCO3- co-transporters (NBCs) and Cl-/HCO3- exchangers (AEs) were present on the basolateral membrane, and Na+/H+ exchangers (NHEs) on both the apical and basolateral membranes of the cells. Basolateral HCO3- uptake was sensitive to variations of extracellular K+ concentration, the membrane permeable carbonic anhydrase (CA) inhibitors acetazolamide (100 µmol/L) and ethoxyzolamide (100 µmol/L), and was partially inhibited by H2-DIDS (600 µmol/L). The membrane-impermeable CA inhibitor 1-N-(4-sulfamoylphenylethyl)-2,4,6-trimethylpyridine perchlorate did not have any effect on HCO3- uptake. The basolateral AE had a much higher activity than that in the apical membrane, whereas there was no such difference with the NHE under resting conditions. Also, 10 µmol/L forskolin did not significantly influence Cl-/HCO3- exchange on the apical and basolateral membranes. The administration of 250 µmol/L H2-DIDS significantly inhibited the basolateral AE. Amiloride (300 µmol/L) completely inhibited NHEs on both membranes of the cells. RT-PCR revealed the expression of pNBC1, AE2, and NHE1 mRNA.
CONCLUSION: These data suggest that apart from the lack of CFTR and apical Cl-/HCO3- exchanger activity, CFPAC-1 cells express similar H+ and HCO3- transporters to those observed in native animal tissue.
Collapse
Affiliation(s)
- Zoltan Rakonczay
- Institute for Cell and Molecular Biosciences, University of Newcastle upon Tyne, Medical School, Framlington Place, Newcastle upon Tyne NE2 4HH, United Kingdom
| | | | | | | | | | | |
Collapse
|
26
|
Kreydiyyeh SI, Markossian S, Hodeify RF. PGE2 exerts dose-dependent opposite effects on net water and chloride absorption from the rat colon. Prostaglandins Other Lipid Mediat 2006; 79:43-52. [PMID: 16516809 DOI: 10.1016/j.prostaglandins.2005.07.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2005] [Revised: 07/22/2005] [Accepted: 07/25/2005] [Indexed: 10/25/2022]
Abstract
This work investigated the effect of different doses of PGE2 on net water and Cl- absorption from the rat colon, using an in situ perfusion technique. PGE2 exerted opposite effects at different concentrations. Net water and Cl- absorption was significantly reduced at low doses with a minimum at 0.4 microg/100g BW, and significantly elevated at high doses with an observed maximal effect at 21 microg/100g BW. At low doses, PGE2 increased in superficial cells, the activity of the Na+-K+ ATPase and the protein expression of the Na+K+2Cl- cotransporter, but reduced them in crypt cells. Thus, the reduction in net water and Cl- absorption was ascribed to an increase in secretion by surface cells that masked absorptive processes. At high doses, PGE2 increased significantly the activity of the Na+-K+ ATPase in superficial cells only, and was without any effect on the protein expression of the cotransporter and the pump in both surface and crypt cells. The observed increase in net water and Cl- absorption was attributed in this case to an increase in absorptive processes with no effect on secretion.
Collapse
|
27
|
Abdoun K, Stumpff F, Wolf K, Martens H. Modulation of electroneutral Na transport in sheep rumen epithelium by luminal ammonia. Am J Physiol Gastrointest Liver Physiol 2005; 289:G508-20. [PMID: 15831711 DOI: 10.1152/ajpgi.00436.2004] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Ammonia is an abundant fermentation product in the forestomachs of ruminants and the intestine of other species. Uptake as NH3 or NH4+ should modulate cytosolic pH and sodium-proton exchange via Na+/H+ exchanger (NHE). Transport rates of Na+, NH4+, and NH3 across the isolated rumen epithelium were studied at various luminal ammonia concentrations and pH values using the Ussing chamber method. The patch-clamp technique was used to identify an uptake route for NH4+. The data show that luminal ammonia inhibits electroneutral Na transport at pH 7.4 and abolishes it at 30 mM (P < 0.05). In contrast, at pH 6.4, ammonia stimulates Na transport (P < 0.05). Flux data reveal that at pH 6.4, approximately 70% of ammonia is absorbed in the form of NH4+, whereas at pH 7.4, uptake of NH3 exceeds that of NH4+ by a factor of approximately four. The patch-clamp data show a quinidine-sensitive permeability for NH4+ and K+ but not Na+. Conductance was 135 +/- 12 pS in symmetrical NH(4)Cl solution (130 mM). Permeability was modulated by the concentration of permeant ions, with P(K) > P(NH4) at high and P(NH4) > P(K) at lower external concentrations. Joint application of both ions led to anomalous mole fraction effects. In conclusion, the luminal pH determines the predominant form of ammonia absorption from the rumen and the effect of ammonia on electroneutral Na transport. Protons that enter the cytosol through potassium channels in the form of NH4+ stimulate and nonionic diffusion of NH3 blocks NHE, thus contributing to sodium transport and regulation of pH.
Collapse
Affiliation(s)
- Khalid Abdoun
- Dept. of Physiology, Faculty of Veterinary Sciences, University of Khartoum, Sudan
| | | | | | | |
Collapse
|
28
|
Abstract
The sodium/hydrogen exchange (NHE) gene family plays an integral role in neutral sodium absorption in the mammalian intestine. The NHE gene family is comprised of nine members that are categorized by cellular localization (i.e., plasma membrane or intracellular). In the gastrointestinal (GI) tract of multiple species, there are resident plasma membrane isoforms including NHE1 (basolateral) and NHE2 (apical), recycling isoforms (NHE3), as well as intracellular isoforms (NHE6, 7, 9). NHE3 recycles between the endosomal compartment and the apical plasma membrane and functions in both locations. NHE3 regulation occurs during normal digestive processes and is often inhibited in diarrheal diseases. The C terminus of NHE3 binds multiple regulatory proteins to form large protein complexes that are involved in regulation of NHE3 trafficking to and from the plasma membrane, turnover number, and protein phosphorylation. NHE1 and NHE2 are not regulated by trafficking. NHE1 interacts with multiple regulatory proteins that affect phosphorylation; however, whether NHE1 exists in large multi-protein complexes is unknown. Although intestinal and colonic sodium absorption appear to involve at least NHE2 and NHE3, future studies are necessary to more accurately define their relative contributions to sodium absorption during human digestion and in pathophysiological conditions.
Collapse
Affiliation(s)
- Nicholas C Zachos
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2195, USA.
| | | | | |
Collapse
|
29
|
Narins SC, Park EH, Ramakrishnan R, Garcia FU, Diven JN, Balin BJ, Hammond CJ, Sodam BR, Smith PR, Abedin MZ. Functional characterization of Na(+)/H(+) exchangers in primary cultures of prairie dog gallbladder. J Membr Biol 2004; 197:123-34. [PMID: 15014914 DOI: 10.1007/s00232-003-0647-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2003] [Indexed: 10/26/2022]
Abstract
Gallbladder Na(+) absorption is linked to gallstone formation in prairie dogs. We previously reported Na(+)/H(+) exchanger (NHE1-3) expression in native gallbladder tissues. Here we report the functional characterization of NHE1, NHE2 and NHE3 in primary cultures of prairie dog gallbladder epithelial cells (GBECs). Immunohistochemical studies showed that GBECs grown to confluency are homogeneous epithelial cells of gastrointestinal origin. Electron microscopic analysis of GBECs demonstrated that the cells form polarized monolayers characterized by tight junctions and apical microvilli. GBECs grown on Snapwells exhibited polarity and developed transepithelial short-circuit current, I(sc), (11.6 +/- 0.5 microA. cm(-2)), potential differences, V(t) (2.1 +/- 0.2 mV), and resistance, R(t) (169 +/- 12 omega. cm(2)). NHE activity in GBECs assessed by measuring dimethylamiloride-inhibitable (22)Na(+) uptake under a H(+) gradient was the same whether grown on permeable Snapwells or plastic wells. The basal rate of (22)Na(+) uptake was 21.4 +/- 1.3 nmol x mg prot(-1) x min(-1), of which 9.5 +/- 0.7 (approximately 45%) was mediated through apically-restricted NHE. Selective inhibition with HOE-694 revealed that NHE1, NHE2 and NHE3 accounted for approximately 6%, approximately 66% and approximately 28% of GBECs' total NHE activity, respectively. GBECs exhibited saturable NHE kinetics ( V(max) 9.2 +/- 0.3 nmol x mg prot(-1) x min(-1); K(m) 11.4 +/- 1.4 m M Na(+)). Expression of NHE1, NHE2 and NHE3 mRNAs was confirmed by RT-PCR analysis. These results demonstrate that the primary cultures of GBECs exhibit Na(+) transport characteristics similar to native gallbladder tissues, suggesting that these cells can be used as a tool for studying the mechanisms of gallbladder ion transport both under physiologic conditions and during gallstone formation.
Collapse
Affiliation(s)
- S C Narins
- Department of Surgery, Drexel University College of Medicine, Philadelphia, PA, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
30
|
Hecht G, Hodges K, Gill RK, Kear F, Tyagi S, Malakooti J, Ramaswamy K, Dudeja PK. Differential regulation of Na+/H+ exchange isoform activities by enteropathogenic E. coli in human intestinal epithelial cells. Am J Physiol Gastrointest Liver Physiol 2004; 287:G370-8. [PMID: 15075254 DOI: 10.1152/ajpgi.00432.2003] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Enteropathogenic Escherichia coli (EPEC) is an important human intestinal foodborne pathogen associated with diarrhea, especially in infants and young children. Although EPEC produces characteristic attaching and effacing lesions and loss of microvilli, the pathophysiology of EPEC-associated diarrhea, particularly during early infection, remains elusive. The present studies were designed to examine the direct effects of EPEC infection on intestinal absorption via Na(+)/H(+) exchanger (NHE) isoforms. Caco-2 cells were infected with EPEC strain E2348/69 or nonpathogenic E. coli HB101 for a period of 60 to 120 min. Total NHE activity was significantly increased at 60 min, reaching approximately threefold increase after 90 min of EPEC infection. Similar findings were seen in HT-29 cells and T84 cells indicating that the response was not cell-line specific. Most surprising was the differential regulation of NHE2 and NHE3 by EPEC. Marked activation of NHE2 (300%) occurred, whereas significant inhibition ( approximately 50%) of NHE3 activity was induced. The activity of basolateral isoform NHE1 was also significantly increased in response to EPEC infection. Mutations that disrupted the type III secretion system (TTSS) ablated the effect of EPEC on the activity of both NHE2 and NHE3. These results suggest that EPEC, through a TTSS-dependent mechanism, exerts differential effects on NHE isoform activity in intestinal epithelial cells. Additionally, NHEs do not appear to play any role in EPEC-mediated inflammation, because the NHE inhibitors amiloride and 5-(N-ethyl-N-isopropyl)amiloride did not prevent EPEC-mediated IkappaBalpha degradation.
Collapse
Affiliation(s)
- Gail Hecht
- Univ. of Illinois at Chicago, Medical Research Service (600/151 Chicago Veterans Affairs Health Care System, 820 S. Damen Ave., Chicago, IL 60612, USA
| | | | | | | | | | | | | | | |
Collapse
|
31
|
Bachmann O, Riederer B, Rossmann H, Groos S, Schultheis PJ, Shull GE, Gregor M, Manns MP, Seidler U. The Na+/H+ exchanger isoform 2 is the predominant NHE isoform in murine colonic crypts and its lack causes NHE3 upregulation. Am J Physiol Gastrointest Liver Physiol 2004; 287:G125-33. [PMID: 14962844 DOI: 10.1152/ajpgi.00332.2003] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The Na(+)/H(+) exchanger isoform NHE2 is highly expressed in the intestinal tract, but its physiological role has remained obscure. The aim of this study was to define its expression, location, and regulatory properties in murine colon and to look for the compensatory changes in NHE2 (-/-) colon that allow normal histology and absorptive function. To this end, we measured murine proximal colonic surface and crypt cell NHE1, NHE2, and NHE3 expression levels, transport rates in response to acid, hyperosmolarity and cAMP in murine proximal colonic crypts, as well as changes in transcript levels and acid-activated NHE activity in NHE2 (-/-) crypts. We found that NHE2 was expressed most abundantly in crypts, NHE1 equally in crypts and surface cells, and NHE3 much stronger in surface cells. NHE2, like NHE1, was activated by low intracellular pH (pH(i)), hyperosmolarity, and cAMP, whereas NHE3 was activated only by low pH(i). Crypts isolated from NHE2 (-/-) mice displayed increased acid-activated NHE1- and NHE3-attributable Na(+)/H(+) exchange activity, no change in NHE1 expression, and NHE3 expression levels twice as high as in normal littermates. No change in cellular ultrastructure was found in NHE2 (-/-) colon. Our results demonstrate high NHE2 expression in the crypts and suggest a role for NHE2 in cryptal pH(i) and volume homeostasis.
Collapse
Affiliation(s)
- O Bachmann
- Dept. of Gastroenterology, Hepatology, and Endocrinology, Hannover Medical School, Carl-Neuberg-Strasse 1, 30623 Hannover, Germany
| | | | | | | | | | | | | | | | | |
Collapse
|
32
|
Reid AC, Mackins CJ, Seyedi N, Levi R, Silver RB. Coupling of angiotensin II AT1 receptors to neuronal NHE activity and carrier-mediated norepinephrine release in myocardial ischemia. Am J Physiol Heart Circ Physiol 2003; 286:H1448-54. [PMID: 14684374 DOI: 10.1152/ajpheart.01062.2003] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In ischemia, cardiac sympathetic nerve endings (cSNE) release excessive amounts of norepinephrine (NE) via the nonexocytotic Na(+)-dependent NE transporter (NET). NET, normally responsible for NE reuptake into cSNE, reverses in myocardial ischemia, releasing pathological amounts of NE. This carrier-mediated NE release can be triggered by elevated intracellular Na(+) levels in the axoplasm. The fact that ischemia activates the intracellular pH regulatory Na(+)/H(+) exchanger (NHE) in cSNE is pivotal in increasing intraneuronal Na(+) and thus activating carrier-mediated NE release. Angiotensin (ANG) II levels are also significantly elevated in the ischemic heart. However, the effects of ANG II on cSNE, which express the ANG II receptor, AT(1)R, are poorly understood. We hypothesized that ANG II-induced AT(1)R activation in cSNE may be positively coupled to NHE activity and thereby facilitate the pathological release of NE associated with myocardial ischemia. We tested this hypothesis in a cSNE model, human neuroblastoma cells stably transfected with rat recombinant AT(1A) receptor (SH-SY5Y-AT(1A)). SH-SY5Y-AT(1A) constitutively expresses amiloride-sensitive NHE and the NET. NHE activity was assayed in BCECF-loaded SH-SY5Y-AT(1A) as the rate of the Na(+)-dependent alkalinization in response to an acute acidosis. ANG II activation of AT(1)R markedly increased NHE activity in SH-SY5Y-AT(1A) via a Ca(2+)-dependent pathway and promoted carrier-mediated NE release. In addition, in guinea pig cSNE expressing native AT(1)R, ANG II elicited carrier-mediated NE release. In SH-SY5Y-AT(1A) and cSNE, amiloride inhibited the ANG II-mediated release of NE. Our results provide a link between AT(1)R and NHE in cSNE, which can exacerbate carrier-mediated NE release during protracted myocardial ischemia.
Collapse
Affiliation(s)
- Alicia C Reid
- Department of Physiology and Biophysics, Cornell University, Weill Cornell Medical College, New York, NY 10021, USA
| | | | | | | | | |
Collapse
|
33
|
Granger D, Marsolais M, Burry J, Laprade R. Na+/H+ exchangers in the human eccrine sweat duct. Am J Physiol Cell Physiol 2003; 285:C1047-58. [PMID: 12839839 DOI: 10.1152/ajpcell.00581.2002] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Using an anti-NHE1 antibody, we demonstrate the presence of a Na+/H+ exchanger of isoform 1 (NHE1) in the human eccrine sweat duct. A strong staining was observed at the basolateral membrane of the outer cell layer (NHE1basal), at the junction between inner and outer cells layers (NHE1inter), and along the lateral membranes (NHE1later) of all cells of the duct. At the luminal membrane, no staining was demonstrated either for NHE1 or NHE3. To investigate Na+/H+ mediated proton transport, straight sweat duct portions were isolated and perfused in vitro under HCO3-free conditions. In the presence of basolateral 5-ethyl-N-isopropyl amiloride (EIPA), an acidification of 0.29 +/- 0.03 pH units was observed, whereas no effect was observed with luminal EIPA. Bath sodium removal generated a stronger acidification (0.41 +/- 0.09 pH units). Removal of luminal sodium (in the absence or presence of basolateral EIPA), or low luminal chloride, led to an alkalinization, presumably due to a decrease in intracellular sodium, strongly suggesting functional activity of NHE1inter. We therefore conclude that in the sweat duct, NHE1 plays a major role in intracellular pH regulation.
Collapse
Affiliation(s)
- D Granger
- Université de Montréal, GEPROM, C.P. 6128, Succursale Centre-ville, Montréal, Québec, Canada H3C 3J7
| | | | | | | |
Collapse
|
34
|
Gill RK, Saksena S, Syed IA, Tyagi S, Alrefai WA, Malakooti J, Ramaswamy K, Dudeja PK. Regulation of NHE3 by nitric oxide in Caco-2 cells. Am J Physiol Gastrointest Liver Physiol 2002; 283:G747-56. [PMID: 12181191 DOI: 10.1152/ajpgi.00294.2001] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The effect of nitric oxide (NO) on Na+/H+ exchange (NHE) activity was investigated utilizing Caco-2 cells as an experimental model. Incubation of Caco-2 cells with 10(-3) M S-nitroso-N-acetylpenicillamine (SNAP), a conventional donor of NO, for 20 min resulted in a approximately 45% dose-dependent decrease in NHE activity, as determined by assay of ethylisopropylamiloride-sensitive 22Na uptake. A similar decrease in NHE activity was observed utilizing another NO-specific donor, sodium nitroprusside. SNAP-mediated inhibition of NHE activity was not secondary to a loss of cell viability. NHE3 activity was significantly reduced by SNAP (P < 0.05), whereas NHE2 activity was essentially unaltered. The effects of SNAP were mediated by the cGMP-dependent signal transduction pathway as follows: 1) LY-83583 and 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (ODQ), specific inhibitors of soluble guanylate cyclase, blocked the inhibitory effect of SNAP on NHE; 2) 8-bromo-cGMP mimicked the effects of SNAP on NHE activity; 3) the SNAP-induced decrease in NHE activity was counteracted by a specific protein kinase G inhibitor, KT-5823 (1 microM); 4) chelerythrine chloride (2 microM) or calphostin C (200 nM), specific protein kinase C inhibitors, did not affect inhibition of NHE activity by SNAP; 5) there was no cross activation by the protein kinase A-dependent pathway, as the inhibitory effects of SNAP were not blocked by Rp-cAMPS (25 microM), a specific protein kinase A inhibitor. These data provide novel evidence that NO inhibits NHE3 activity via activation of soluble guanylate cyclase, resulting in an increase in intracellular cGMP levels and activation of protein kinase G.
Collapse
Affiliation(s)
- Ravinder K Gill
- Section of Digestive and Liver Diseases, Department of Medicine, University of Illinois at Chicago and West Side Veterans Affairs Medical Center, Chicago, Illinois 60612, USA
| | | | | | | | | | | | | | | |
Collapse
|
35
|
Németh ZH, Deitch EA, Szabó C, Haskó G. Hyperosmotic stress induces nuclear factor-kappaB activation and interleukin-8 production in human intestinal epithelial cells. THE AMERICAN JOURNAL OF PATHOLOGY 2002; 161:987-96. [PMID: 12213727 PMCID: PMC1867255 DOI: 10.1016/s0002-9440(10)64259-9] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Inflammatory bowel disease of the colon is associated with a high osmolarity of colonic contents. We hypothesized that this hyperosmolarity may contribute to colonic inflammation by stimulating the proinflammatory activity of intestinal epithelial cells (IECs). The human IEC lines HT-29 and Caco-2 were used to study the effect of hyperosmolarity on the IEC inflammatory response. Exposure of IECs to hyperosmolarity triggered expression of the proinflammatory chemokine interleukin (IL)-8 both at the secreted protein and mRNA levels. In addition, hyperosmotic stimulation induced the release of another chemokine, GRO-alpha. These effects were because of activation of the transcription factor, nuclear factor (NF)-kappaB, because hyperosmolarity stimulated both NF-kappaB DNA binding and NF-kappaB-dependent transcriptional activity. Hyperosmolarity activated both p38 and p42/44 mitogen-activated protein kinases, which effect contributed to hyperosmolarity-stimulated IL-8 production, because p38 and p42/44 inhibition prevented the hyperosmolarity-induced increase in IL-8 production. In addition, the proinflammatory effects of hyperosmolarity were, in a large part, mediated by activation of Na(+)/H(+) exchangers, because selective blockade of Na(+)/H(+) exchangers prevented the hyperosmolarity-induced IEC inflammatory response. In summary, hyperosmolarity stimulates IEC IL-8 production, which effect may contribute to the maintenance of inflammation in inflammatory bowel disease.
Collapse
Affiliation(s)
- Zoltán H Németh
- Department of Surgery, University of Medicine and Dentistry-New Jersey Medical School, Newark 07103, USA
| | | | | | | |
Collapse
|
36
|
Chu J, Chu S, Montrose MH. Apical Na+/H+ exchange near the base of mouse colonic crypts. Am J Physiol Cell Physiol 2002; 283:C358-72. [PMID: 12055105 DOI: 10.1152/ajpcell.01380.2000] [Citation(s) in RCA: 51] [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]
Abstract
Colonic crypts can absorb fluid, but the identity of the absorptive transporters remains speculative. Near the crypt base, the epithelial cells responsible for vectorial transport are relatively undifferentiated and often presumed to mediate only Cl- secretion. We have applied confocal microscopy in combination with an extracellular fluid marker [Lucifer yellow (LY)] or a pH-sensitive dye (2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein) to study mouse colonic crypt epithelial cells directly adjacent to the crypt base within an intact mucosal sheet. Measurements of intracellular pH report activation of colonocyte Na+/H+ exchange in response to luminal or serosal Na+. Studies with LY demonstrate the presence of a paracellular fluid flux, but luminal Na+ does not activate Na+/H+ exchange in the nonepithelial cells of the lamina propria, and studies with LY suggest that the fluid bathing colonocyte basolateral membranes is rapidly refreshed by serosal perfusates. The apical Na+/H+ exchange in crypt colonocytes is inhibited equivalently by luminal 20 microM ethylisopropylamiloride and 20 microM HOE-694 but is not inhibited by luminal 20 microM S-1611. Immunostaining reveals the presence of epitopes from NHE1 and NHE2, but not NHE3, in epithelial cells near the base of colonic crypts. Comparison of apical Na+/H+ exchange activity in the presence of Cl- with that in the absence of Cl- (substitution by gluconate or nitrate) revealed no evidence of the Cl--dependent Na+/H+ exchange that had been previously reported as the sole apical Na+/H+ exchange activity in the colonic crypt. Results suggest the presence of an apical Na+/H+ exchanger near the base of crypts with functional attributes similar to those of the cloned NHE2 isoform.
Collapse
Affiliation(s)
- Jingsong Chu
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana 46202-5120, USA
| | | | | |
Collapse
|
37
|
Gawenis LR, Stien X, Shull GE, Schultheis PJ, Woo AL, Walker NM, Clarke LL. Intestinal NaCl transport in NHE2 and NHE3 knockout mice. Am J Physiol Gastrointest Liver Physiol 2002; 282:G776-84. [PMID: 11960774 DOI: 10.1152/ajpgi.00297.2001] [Citation(s) in RCA: 123] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Sodium/proton exchangers [Na(+)/H(+) (NHEs)] play an important role in salt and water absorption from the intestinal tract. To investigate the contribution of the apical membrane NHEs, NHE2 and NHE3, to electroneutral NaCl absorption, we measured radioisotopic Na(+) and Cl(-) flux across isolated jejuna from wild-type [NHE(+)], NHE2 knockout [NHE2(-)], and NHE3 knockout [NHE3(-)] mice. Under basal conditions, NHE(+) and NHE2(-) jejuna had similar rates of net Na(+) (approximately 6 microeq/cm(2) x h) and Cl(-) (approximately 3 microeq/cm(2) x h) absorption. In contrast, NHE3(-) jejuna had reduced net Na(+) absorption (approximately 2 microeq/cm(2) x h) but absorbed Cl(-) at rates similar to NHE(+) and NHE2(-) jejuna. Treatment with 100 microM 5-(N-ethyl-N-isopropyl) amiloride (EIPA) completely inhibited net Na(+) and Cl(-) absorption in all genotypes. Studies of the Na(+) absorptive flux (J) indicated that J in NHE(+) jejunum was not sensitive to 1 microM EIPA, whereas J in NHE3(-) jejunum was equally sensitive to 1 and 100 microM EIPA. Treatment with forskolin/IBMX to increase intracellular cAMP (cAMP(i)) abolished net NaCl absorption and stimulated electrogenic Cl(-) secretion in all three genotypes. Quantitative RT-PCR of epithelia from NHE2(-) and NHE3(-) jejuna did not reveal differences in mRNA expression of NHE3 and NHE2, respectively, when compared with jejunal epithelia from NHE(+) siblings. We conclude that 1) NHE3 is the dominant NHE involved in small intestinal Na(+) absorption; 2) an amiloride-sensitive Na(+) transporter partially compensates for Na(+) absorption in NHE3(-) jejunum; 3) cAMP(i) stimulation abolishes net Na(+) absorption in NHE(+), NHE2(-), and NHE3(-) jejunum; and 4) electroneutral Cl(-) absorption is not directly dependent on either NHE2 or NHE3.
Collapse
Affiliation(s)
- Lara R Gawenis
- Dalton Cardiovascular Research Center and Department of Biomedical Sciences, University of Missouri-Columbia, Columbia, Missouri 65211, USA
| | | | | | | | | | | | | |
Collapse
|
38
|
Ledoussal C, Woo AL, Miller ML, Shull GE. Loss of the NHE2 Na(+)/H(+) exchanger has no apparent effect on diarrheal state of NHE3-deficient mice. Am J Physiol Gastrointest Liver Physiol 2001; 281:G1385-96. [PMID: 11705743 DOI: 10.1152/ajpgi.2001.281.6.g1385] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The expression of NHE2 and NHE3 on intestinal-brush border membranes suggests that both Na(+)/H(+) exchangers serve absorptive functions. Studies with knockout mice showed that the loss of NHE3, but not NHE2, causes diarrhea, demonstrating that NHE3 is the major absorptive exchanger and indicating that any remaining absorptive capacity contributed by NHE2 is not sufficient to compensate fully for the loss of NHE3. To test the hypothesis that NHE2 provides partial compensation for the diarrheal state of NHE3-deficient mice, we crossed doubly heterozygous mice carrying null mutations in the Nhe2 and Nhe3 genes and analyzed the phenotypes of their offspring. The additional loss of NHE2 in NHE3-deficient mice caused no apparent reduction in viability, no further impairment of systemic acid-base status or increase in aldosterone levels, and no apparent worsening of the diarrheal state. These in vivo phenotypic correlates of the absorptive defect suggest that the NaCl, HCO, and fluid absorption that is dependent on apical Na(+)/H(+) exchange is due overwhelmingly to the activity of NHE3, with little contribution from NHE2.
Collapse
Affiliation(s)
- C Ledoussal
- Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati, Cincinnati, Ohio 45267, USA
| | | | | | | |
Collapse
|
39
|
Alrefai WA, Scaglione-Sewell B, Tyagi S, Wartman L, Brasitus TA, Ramaswamy K, Dudeja PK. Differential regulation of the expression of Na(+)/H(+) exchanger isoform NHE3 by PKC-alpha in Caco-2 cells. Am J Physiol Cell Physiol 2001; 281:C1551-8. [PMID: 11600418 DOI: 10.1152/ajpcell.2001.281.5.c1551] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Na(+)/H(+) exchange (NHE) activity has been shown to be regulated by various external signals and protein kinases in many tissues and cell types. A family of six NHE isoforms has been identified. Three isoforms, NHE1, NHE2, and NHE3, have been shown to be expressed in the human intestine. The present studies were designed to study regulation of these human NHE isoforms by the alpha-isoform of protein kinase C (PKC) in the Caco-2 cell line. The mRNA levels of the NHE isoforms in Caco-2 cells were initially measured by a semiquantitative RT-PCR technique in response to PKC downregulation by long-term exposure to 1 microM 12-O-tetradecanoylphorbol-13-acetate (TPA) for 24 h. PKC downregulation resulted in an approximately 60% increase in the mRNA level for NHE3, but not for NHE1 or NHE2. Utilizing dichlorobenzimidazole riboside, an agent to block the synthesis of new mRNA, we demonstrated that the increase in the NHE3 mRNA in response to downregulation of PKC was predominantly due to an increase in the rate of transcription, rather than a decrease in the NHE3 mRNA stability. Consistent with the mRNA results, our data showed that amiloride-sensitive (22)Na(+) uptake was increased after incubation of Caco-2 cells with 1 microM TPA for 24 h. To elucidate the role of PKC-alpha, an isoform downregulated by TPA, the relative abundance of NHE isoform mRNA levels and the apical NHE activity were assessed in Caco-2 cells over- and underexpressing PKC-alpha. Our results demonstrated that NHE3, but not NHE1 or NHE2, mRNA was downregulated by PKC-alpha and that apical NHE activity was higher in cells underexpressing PKC-alpha and lower in cells overexpressing PKC-alpha than in control cells. In conclusion, these data demonstrate a differential regulation of NHE3, but not NHE2 or NHE1, expression by PKC in Caco-2 cells, and this regulation appears to be predominantly due to PKC-alpha.
Collapse
Affiliation(s)
- W A Alrefai
- Section of Digestive and Liver Diseases, Department of Medicine, University of Illinois at Chicago, and Westside Veterans Affairs Medical Center, Chicago 60612, USA
| | | | | | | | | | | | | |
Collapse
|
40
|
Khan I, Thomas N, Haridas S. Expression and sub cellular localization of the sodium hydrogen exchanger isoform-1 in rat tissues: a possible functional relevance. Mol Cell Biochem 2001; 219:153-61. [PMID: 11354247 DOI: 10.1023/a:1010867631953] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
In an attempt to understand the mechanism underlying the tissue-dependent function, the expression of NHE-1 protein and its sub cellular localization was examined in the rat GI-tract and other tissues. Rat NHE-1 polyclonal antibodies were raised in rabbits using a NHE-1 fusion protein antigen. The antibodies recognized a 110 kD protein in rats and mice, but not in human or rabbit RBCs. Colon, stomach, brain, spleen and kidney expressed NHE-1 protein abundantly, whereas the skeletal muscle the least abundant. Ouabain-sensitive-K+-stimulated p-nitrophenylphosphatase (PNPPase), the partial activity of the sodium pump and alkaline phosphatase (Apase) were used as the markers of the basolateral and apical membranes. NHE-1 was detected predominantly in the PNPPase enriched membrane fractions, but was also detected in the apical membrane enriched fractions in the kidney cortex, jejunum and colon at a lower level. NHE-1 was detected in the plasma membrane enriched fractions from the skeletal muscle and ventricle. Immunofluorescence data showed a similar localization pattern of NHE-1 in the colon and kidney sections. These findings suggest that NHE-1 is localized both on the apical and basolateral membrane. In view of its similar sub cellular localization in the GI-tract and kidney, but a different level of expression, might suggest that the level of protein, but not the sub cellular distribution is important to regulate its tissue-dependent function.
Collapse
Affiliation(s)
- I Khan
- Department of Biochemistry, Faculty of Medicine, Kuwait University
| | | | | |
Collapse
|
41
|
Repishti M, Hogan DL, Pratha V, Davydova L, Donowitz M, Tse CM, Isenberg JI. Human duodenal mucosal brush border Na(+)/H(+) exchangers NHE2 and NHE3 alter net bicarbonate movement. Am J Physiol Gastrointest Liver Physiol 2001; 281:G159-63. [PMID: 11408268 DOI: 10.1152/ajpgi.2001.281.1.g159] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The proximal duodenal mucosa secretes HCO that serves to protect the epithelium from injury. In isolated human duodenal enterocytes in vitro, multiple luminal membrane proteins are involved in acid/base transport. We postulated that one or more isoforms of the Na(+)/H(+) exchanger (NHE) family is located on the apical surface of human duodenal mucosal epithelial cells and thereby contributes to duodenal mucosal HCO transport. Duodenal biopsies were obtained from human volunteers, and the presence of NHE2 and NHE3 was determined by using previously characterized polyclonal antibodies (Ab 597 for NHE2 and Ab 1381 for NHE3). In addition, proximal duodenal mucosal HCO(3)(-) transport was measured in humans in vivo in response to luminal perfusion of graded doses of amiloride; 10(-5)--10(-4) M amiloride was used to inhibit NHE2 and 10(-3) M amiloride to inhibit NHE3. Both NHE2 and NHE3 were localized principally to the brush border of duodenal villus cells. Sequential doses of amiloride resulted in significant, step-wise increases in net duodenal HCO(3)(-) output. Inhibition of NHE2 with 10(-5) M and 10(-4) M amiloride significantly increased net HCO(3)(-) output. Moreover, there was an additional, equivalent increase (P < 0.05) in duodenal HCO(3)(-) output with 10(-3) M amiloride, which inhibited NHE3. We conclude that 1) NHE2 and NHE3 are localized principally to the brush border of human duodenal villus epithelial cells; 2) sequential inhibition of NHE2 and NHE3 isoforms resulted in step-wise increases in net HCO(3)(-) output; 3) NHE2 and NHE3 participate in human duodenal villus cell HCO(3)(-) transport; and 4) the contribution of NHE-related transport events should be considered when studying duodenal HCO(3)(-) transport processes.
Collapse
Affiliation(s)
- M Repishti
- Department of Medicine, University of California at San Diego, San Diego, California 92103-8413, USA
| | | | | | | | | | | | | |
Collapse
|
42
|
Maouyo D, Chu S, Montrose MH. pH heterogeneity at intracellular and extracellular plasma membrane sites in HT29-C1 cell monolayers. Am J Physiol Cell Physiol 2000; 278:C973-81. [PMID: 10794671 DOI: 10.1152/ajpcell.2000.278.5.c973] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In the colonic mucosa, short-chain fatty acids change intracellular pH (pH(i)) and extracellular pH (pH(e)). In this report, confocal microscopy and dual-emission ratio imaging of carboxyseminaphthorhodofluor-1 were used for direct evaluation of pH(i) and pH(e) in a simple model epithelium, HT29-C1 cells. Live cell imaging along the apical-to-basal axis of filter-grown cells allowed simultaneous measurement of pH in the aqueous environment near the apical membrane, the lateral membrane, and the basal membrane. Subapical cytoplasm reported the largest changes in pH(i) after isosmotic addition of 130 mM propionate or 30 mM NH(4)Cl. In resting cells and cells with an imposed acid load, lateral membranes had pH(i) values intermediate between the relatively acidic subapical region (pH 6.3-6.9) and the relatively alkaline basal pole of the cells (pH 7.4-7.1). Transcellular pH(i) gradients were diminished or eliminated during an induced alkaline load. Propionate differentially altered pH(e) near the apical membrane, in lateral intracellular spaces between adjacent cells, and near the basal membrane. Luminal or serosal propionate caused alkalinization of the cis compartment (where propionate was added) but acidification of the trans compartment only in response to luminal propionate. Addition of NH(4)Cl produced qualitatively opposite pH(e) excursions. The microscopic values of pH(i) and pH(e) can explain a portion of the selective activation of polarized Na/H exchangers observed in HT29-C1 cells in the presence of transepithelial propionate gradients.
Collapse
Affiliation(s)
- D Maouyo
- Department of Medicine, Johns Hopkins University, Baltimore, Maryland 21205, USA
| | | | | |
Collapse
|
43
|
Khan I, Ali M. Altered expression of the Na+/H+ exchanger isoform-3 in experimental colitis: effect of garlic. Mol Cell Biochem 1999; 200:77-84. [PMID: 10569186 DOI: 10.1023/a:1006990027764] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The sodium-hydrogen exchanger isoform, NHE-3 is essential for the absorption of sodium and water from intestine. Whether this protein plays any role in inflammatory bowel disease is less understood. To address this issue, NHE-3 mRNA and protein levels were estimated in the terminal ileum and colon of the rats having colitis induced with trinitrobenzenesulphonic acid (TNBS). The effect of garlic (Allium sativum) was also evaluated on the expression of NHE-3. The animals were treated with garlic extract intraperitoneally starting 2 h before the TNBS administration until day 4 post-TNBS administration and were sacrificed on day 5. In control animals, the levels of NHE-3 in colon was higher than the ileum. As a result of colitis, the levels of NHE-3 protein and mRNA increased both in the colon and terminal ileum. Garlic treatment of the colitic animals resulted in a selective suppression of NHE-3 in the terminal ileum. Colitis caused an induction of the myeloperoxidase activity, the marker of inflammation in the colon but not in the ileum. These findings suggest that induction of NHE-3 is not primarily due to inflammation. Selective suppression of this protein in ileum by garlic may cause loss of sodium chloride and water during colitis.
Collapse
Affiliation(s)
- I Khan
- Department of Biochemistry, Faculty of Medicine, Kuwait University
| | | |
Collapse
|
44
|
Thwaites DT, Ford D, Glanville M, Simmons NL. H(+)/solute-induced intracellular acidification leads to selective activation of apical Na(+)/H(+) exchange in human intestinal epithelial cells. J Clin Invest 1999; 104:629-35. [PMID: 10487777 PMCID: PMC408543 DOI: 10.1172/jci7192] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The intestinal absorption of many nutrients and drug molecules is mediated by ion-driven transport mechanisms in the intestinal enterocyte plasma membrane. Clearly, the establishment and maintenance of the driving forces - transepithelial ion gradients - are vital for maximum nutrient absorption. The purpose of this study was to determine the nature of intracellular pH (pH(i)) regulation in response to H(+)-coupled transport at the apical membrane of human intestinal epithelial Caco-2 cells. Using isoform-specific primers, mRNA transcripts of the Na(+)/H(+) exchangers NHE1, NHE2, and NHE3 were detected by RT-PCR, and identities were confirmed by sequencing. The functional profile of Na(+)/H(+) exchange was determined by a combination of pH(i), (22)Na(+) influx, and EIPA inhibition experiments. Functional NHE1 and NHE3 activities were identified at the basolateral and apical membranes, respectively. H(+)/solute-induced acidification (using glycylsarcosine or beta-alanine) led to Na(+)-dependent, EIPA-inhibitable pH(i) recovery or EIPA-inhibitable (22)Na(+) influx at the apical membrane only. Selective activation of apical (but not basolateral) Na(+)/H(+) exchange by H(+)/solute cotransport demonstrates that coordinated activity of H(+)/solute symport with apical Na(+)/H(+) exchange optimizes the efficient absorption of nutrients and Na(+), while maintaining pH(i) and the ion gradients involved in driving transport.
Collapse
Affiliation(s)
- D T Thwaites
- Department of Physiological Sciences, Medical School, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, United Kingdom.
| | | | | | | |
Collapse
|