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Glitsch MD. Recent advances in acid sensing by G protein coupled receptors. Pflugers Arch 2024; 476:445-455. [PMID: 38340167 PMCID: PMC11006784 DOI: 10.1007/s00424-024-02919-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2023] [Revised: 01/30/2024] [Accepted: 01/30/2024] [Indexed: 02/12/2024]
Abstract
Changes in extracellular proton concentrations occur in a variety of tissues over a range of timescales under physiological conditions and also accompany virtually all pathologies, notably cancers, stroke, inflammation and trauma. Proton-activated, G protein coupled receptors are already partially active at physiological extracellular proton concentrations and their activity increases with rising proton concentrations. Their ability to monitor and report changes in extracellular proton concentrations and hence extracellular pH appears to be involved in a variety of processes, and it is likely to mirror and in some cases promote disease progression. Unsurprisingly, therefore, these pH-sensing receptors (pHR) receive increasing attention from researchers working in an expanding range of research areas, from cellular neurophysiology to systemic inflammatory processes. This review is looking at progress made in the field of pHRs over the past few years and also highlights outstanding issues.
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Affiliation(s)
- Maike D Glitsch
- Medical School Hamburg, Am Sandtorkai 1, 20457, Hamburg, Germany.
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2
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Zhang Z, Bao YY, Zhou SH. Pump Proton and Laryngeal H +/K + ATPases. Int J Gen Med 2020; 13:1509-1514. [PMID: 33363399 PMCID: PMC7754099 DOI: 10.2147/ijgm.s284952] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2020] [Accepted: 11/20/2020] [Indexed: 12/14/2022] Open
Abstract
Purpose The presence of extra-gastric H+/K+ ATPases may explain the clinically significant effect of proton pump inhibitor (PPI) pharmacotherapy in patients with chronic laryngitis related to laryngopharyngeal reflux disease (LPRD) but without gastroesophageal reflux disease (GERD) symptoms. Given the need for a better understanding of GERD and LPRD, we review the various proton pumps with respect to their classification, function, and distribution. We then consider the potential role of the laryngeal H+/K+ ATPase pump in LPRD. Methods We searched databases of PubMed, EMBASE, and Web of Science to achieve related published before September 15, 2020. Results There were only seven English-literatures meeting inclusive criteria about laryngeal H+/K+ ATPases. Some studies provide convincing evidence of a laryngeal H+/K+ ATPase in normal laryngeal tissues but also suggest the potential role of the proton pump in the abnormal mucus secretion frequently seen in patients with chronic laryngitis. Conclusion A laryngeal H+/K+ ATPase expresses in normal laryngeal tissues. These findings question the current understanding of GERD and LPRD.
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Affiliation(s)
- Zhe Zhang
- Department of Otolaryngology, Peoples Hospital of Yuyao City, Yuyao 315400, Zhejiang, People's Republic of China
| | - Yang-Yang Bao
- Department of Otolaryngology, The First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, Zhejiang 310003, People's Republic of China
| | - Shui-Hong Zhou
- Department of Otolaryngology, The First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, Zhejiang 310003, People's Republic of China
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Wesson DE, Buysse JM, Bushinsky DA. Mechanisms of Metabolic Acidosis-Induced Kidney Injury in Chronic Kidney Disease. J Am Soc Nephrol 2020; 31:469-482. [PMID: 31988269 DOI: 10.1681/asn.2019070677] [Citation(s) in RCA: 107] [Impact Index Per Article: 26.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Retrospective analyses and single-center prospective studies identify chronic metabolic acidosis as an independent and modifiable risk factor for progression of CKD. In patients with CKD, untreated chronic metabolic acidosis often leads to an accelerated reduction in GFR. Mechanisms responsible for this reduction include adaptive responses that increase acid excretion but lead to a decline in kidney function. Metabolic acidosis in CKD stimulates production of intrakidney paracrine hormones including angiotensin II, aldosterone, and endothelin-1 (ET-1) that mediate the immediate benefit of increased kidney acid excretion, but their chronic upregulation promotes inflammation and fibrosis. Chronic metabolic acidosis also stimulates ammoniagenesis that increases acid excretion but also leads to ammonia-induced complement activation and deposition of C3 and C5b-9 that can cause tubule-interstitial damage, further worsening disease progression. These effects, along with acid accumulation in kidney tissue, combine to accelerate progression of kidney disease. Treatment of chronic metabolic acidosis attenuates these adaptive responses; reduces levels of angiotensin II, aldosterone, and ET-1; reduces ammoniagenesis; and diminishes inflammation and fibrosis that may lead to slowing of CKD progression.
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Affiliation(s)
- Donald E Wesson
- Baylor Scott & White Health and Wellness Center, Dallas, Texas; .,Department of Internal Medicine, Texas A&M College of Medicine, Bryan, Texas
| | | | - David A Bushinsky
- Division of Nephrology, University of Rochester School of Medicine, Rochester, New York
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The Role of the Primary Cilium in Sensing Extracellular pH. Cells 2019; 8:cells8070704. [PMID: 31336778 PMCID: PMC6679169 DOI: 10.3390/cells8070704] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2019] [Revised: 07/08/2019] [Accepted: 07/09/2019] [Indexed: 12/12/2022] Open
Abstract
Biosensors on the membrane of the vascular endothelium are responsible for sensing mechanical and chemical signals in the blood. Transduction of these stimuli into intracellular signaling cascades regulate cellular processes including ion transport, gene expression, cell proliferation, and/or cell death. The primary cilium is a well-known biosensor of shear stress but its role in sensing extracellular pH change has never been examined. As a cellular extension into the immediate microenvironment, the cilium could be a prospective sensor for changes in pH and regulator of acid response in cells. We aim to test our hypothesis that the primary cilium plays the role of an acid sensor in cells using vascular endothelial and embryonic fibroblast cells as in vitro models. We measure changes in cellular pH using pH-sensitive 2',7'-biscarboxyethy1-5,6-carboxyfluorescein acetoxy-methylester (BCECF) fluorescence and mitogen-activated protein kinase (MAPK) activity to quantify responses to both extracellular pH (pHo) and intracellular pH (pHi) changes. Our studies show that changes in pHo affect pHi in both wild-type and cilia-less Tg737 cells and that the kinetics of the pHi response are similar in both cells. Acidic pHo or pHi was observed to change the length of primary cilia in wild-type cells while the cilia in Tg737 remained absent. Vascular endothelial cells respond to acidic pH through activation of ERK1/2 and p38-mediated signaling pathways. The cilia-less Tg737 cells exhibit delayed responsiveness to pHo dependent and independent pHi acidification as depicted in the phosphorylation profile of ERK1/2 and p38. Otherwise, intracellular pH homeostatic response to acidic pHo is similar between wild-type and Tg737 cells, indicating that the primary cilia may not be the sole sensor for physiological pH changes. These endothelial cells respond to pH changes with a predominantly K+-dependent pHi recovery mechanism, regardless of ciliary presence or absence.
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5
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Wang Y, de Vallière C, Imenez Silva PH, Leonardi I, Gruber S, Gerstgrasser A, Melhem H, Weber A, Leucht K, Wolfram L, Hausmann M, Krieg C, Thomasson K, Boyman O, Frey-Wagner I, Rogler G, Wagner CA. The Proton-activated Receptor GPR4 Modulates Intestinal Inflammation. J Crohns Colitis 2018; 12:355-368. [PMID: 29136128 DOI: 10.1093/ecco-jcc/jjx147] [Citation(s) in RCA: 54] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/25/2016] [Accepted: 11/02/2017] [Indexed: 12/12/2022]
Abstract
BACKGROUND AND AIMS During active inflammation, intraluminal intestinal pH is decreased in patients with inflammatory bowel disease [IBD]. Acidic pH may play a role in IBD pathophysiology. Recently, proton-sensing G-protein coupled receptors were identified, including GPR4, OGR1 [GPR68], and TDAG8 [GPR65]. We investigated whether GPR4 is involved in intestinal inflammation. METHODS The role of GPR4 was assessed in murine colitis models by chronic dextran sulphate sodium [DSS] administration and by cross-breeding into an IL-10 deficient background for development of spontaneous colitis. Colitis severity was assessed by body weight, colonoscopy, colon length, histological score, cytokine mRNA expression, and myeloperoxidase [MPO] activity. In the spontaneous Il-10-/- colitis model, the incidence of rectal prolapse and characteristics of lamina propria leukocytes [LPLs] were analysed. RESULTS Gpr4-/- mice showed reduced body weight loss and histology score after induction of chronic DSS colitis. In Gpr4-/-/Il-10-/- double knock-outs, the onset and progression of rectal prolapse were significantly delayed and mitigated compared with Gpr4+/+/Il-10-/- mice. Double knock-out mice showed lower histology scores, MPO activity, CD4+ T helper cell infiltration, IFN-γ, iNOS, MCP-1 [CCL2], CXCL1, and CXCL2 expression compared with controls. In colon, GPR4 mRNA was detected in endothelial cells, some smooth muscle cells, and some macrophages. CONCLUSIONS Absence of GPR4 ameliorates colitis in IBD animal models, indicating an important regulatory role in mucosal inflammation, thus providing a new link between tissue pH and the immune system. Therapeutic inhibition of GPR4 may be beneficial for the treatment of IBD.
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Affiliation(s)
- Yu Wang
- Department of Gastroenterology and Hepatology, University Hospital Zurich, Zurich, Switzerland.,Institute of Physiology, University of Zurich, Zurich, Switzerland
| | - Cheryl de Vallière
- Department of Gastroenterology and Hepatology, University Hospital Zurich, Zurich, Switzerland
| | | | - Irina Leonardi
- Department of Gastroenterology and Hepatology, University Hospital Zurich, Zurich, Switzerland
| | - Sven Gruber
- Department of Gastroenterology and Hepatology, University Hospital Zurich, Zurich, Switzerland.,Institute of Physiology, University of Zurich, Zurich, Switzerland
| | - Alexandra Gerstgrasser
- Department of Gastroenterology and Hepatology, University Hospital Zurich, Zurich, Switzerland
| | - Hassan Melhem
- Department of Gastroenterology and Hepatology, University Hospital Zurich, Zurich, Switzerland
| | - Achim Weber
- Institute of Surgical Pathology, University Hospital Zurich, Zurich, Switzerland
| | - Katharina Leucht
- Department of Gastroenterology and Hepatology, University Hospital Zurich, Zurich, Switzerland
| | - Lutz Wolfram
- Department of Gastroenterology and Hepatology, University Hospital Zurich, Zurich, Switzerland
| | - Martin Hausmann
- Department of Gastroenterology and Hepatology, University Hospital Zurich, Zurich, Switzerland
| | - Carsten Krieg
- Laboratory of Applied Immunobiology, University of Zurich, Zurich, Switzerland.,Institute of Experimental Immunology, University of Zurich, Zurich, Switzerland
| | - Koray Thomasson
- Laboratory of Applied Immunobiology, University of Zurich, Zurich, Switzerland
| | - Onur Boyman
- Laboratory of Applied Immunobiology, University of Zurich, Zurich, Switzerland.,Department of Immunology, University Hospital Zurich, University of Zurich, Zurich, Switzerland
| | - Isabelle Frey-Wagner
- Department of Gastroenterology and Hepatology, University Hospital Zurich, Zurich, Switzerland
| | - Gerhard Rogler
- Department of Gastroenterology and Hepatology, University Hospital Zurich, Zurich, Switzerland.,Institute of Physiology, University of Zurich, Zurich, Switzerland
| | - Carsten A Wagner
- Institute of Physiology, University of Zurich, Zurich, Switzerland
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6
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Affiliation(s)
- Thomas D DuBose
- Wake Forest School of Medicine; and Section of General Internal Medicine, Winston Salem, North Carolina
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Atkinson KF, Nauli SM. pH sensors and ion Transporters: Potential therapeutic targets for acid-base disorders. INTERNATIONAL JOURNAL OF PHARMA RESEARCH & REVIEW 2016; 5:51-58. [PMID: 29796385 PMCID: PMC5963282] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Regulation of pH is critical for physiological processes. Maintenance of acid-base homeostasis is tightly regulated by the renal and respiratory systems. However, fluctuations in extracellular pH are also sensed by other organ systems. Ion transporter activity to modify the amount of acid (H+ and CO2) and bicarbonate (HCO3-) is therefore actively maintained within the kidney and lung. This review describes acid-base disorders (acidosis and alkalosis) and highlights the importance of pH sensors and ion transporters that may be potential therapeutic targets for treatment of acid-base disorders. Specifically, the renal pH sensors proline-rich tyrosine kinase-2 (Pyk2) and G-protein coupled receptor-4 (GPR4) are discussed here.
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Affiliation(s)
- Kimberly F Atkinson
- Department of Biomedical & Pharmaceutical Sciences, Chapman University, Irvine, CA, USA
| | - Surya M Nauli
- Department of Biomedical & Pharmaceutical Sciences, Chapman University, Irvine, CA, USA
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Sun X, Stephens L, DuBose TD, Petrovic S. Adaptation by the collecting duct to an exogenous acid load is blunted by deletion of the proton-sensing receptor GPR4. Am J Physiol Renal Physiol 2015; 309:F120-36. [DOI: 10.1152/ajprenal.00507.2014] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2014] [Accepted: 05/05/2015] [Indexed: 12/14/2022] Open
Abstract
We previously reported that the deletion of the pH sensor GPR4 causes a non-gap metabolic acidosis and defective net acid excretion (NAE) in the GPR4 knockout mouse (GPR4−/−) (Sun X, Yang LV, Tiegs BC, Arend LJ, McGraw DW, Penn RB, and Petrovic S. J Am Soc Nephrol 21: 1745–1755, 2010). Since the major regulatory site of NAE in the kidney is the collecting duct (CD), we examined acid-base transport proteins in intercalated cells (ICs) of the CD and found comparable mRNA expression of kidney anion exchanger 1 (kAE1), pendrin, and the a4 subunit of H+-ATPase in GPR4−/− vs. +/+. However, NH4Cl loading elicited adaptive doubling of AE1 mRNA in GPR4+/+, but a 50% less pronounced response in GPR4−/−. In GPR4+/+, NH4Cl loading evoked a cellular response characterized by an increase in AE1-labeled and a decrease in pendrin-labeled ICs similar to what was reported in rabbits and rats. This response did not occur in GPR4−/−. Microperfusion experiments demonstrated that the activity of the basolateral Cl−/HCO3− exchanger, kAE1, in CDs isolated from GPR4−/− failed to increase with NH4Cl loading, in contrast to the increase observed in GPR4+/+. Therefore, the deficiency of GPR4 blunted, but did not eliminate the adaptive response to an acid load, suggesting a compensatory response from other pH/CO2/bicarbonate sensors. Indeed, the expression of the calcium-sensing receptor (CaSR) was nearly doubled in GPR4−/− kidneys, in the absence of apparent disturbances of Ca2+ homeostasis. In summary, the expression and activity of the key transport proteins in GPR4−/− mice are consistent with spontaneous metabolic acidosis, but the adaptive response to a superimposed exogenous acid load is blunted and might be partially compensated for by CaSR.
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Affiliation(s)
- Xuming Sun
- Department of Physiology and Pharmacology, Wake Forest School of Medicine, Winston-Salem, North Carolina
| | - Lisa Stephens
- Department of Internal Medicine, University of Cincinnati, Cincinnati, Ohio
| | - Thomas D. DuBose
- Section on Nephrology, Department of Internal Medicine, Wake Forest School of Medicine, Winston-Salem, North Carolina
| | - Snezana Petrovic
- Department of Physiology and Pharmacology, Wake Forest School of Medicine, Winston-Salem, North Carolina
- Section on Nephrology, Department of Internal Medicine, Wake Forest School of Medicine, Winston-Salem, North Carolina
- Claude D. Pepper Older Americans Independence Center, Wake Forest School of Medicine, Winston-Salem, North Carolina
- Hypertension and Vascular Research Center, Wake Forest School of Medicine, Winston-Salem, North Carolina; and
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9
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Justus CR, Yang LV. GPR4 decreases B16F10 melanoma cell spreading and regulates focal adhesion dynamics through the G13/Rho signaling pathway. Exp Cell Res 2015; 334:100-13. [PMID: 25845498 DOI: 10.1016/j.yexcr.2015.03.022] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2014] [Revised: 03/02/2015] [Accepted: 03/26/2015] [Indexed: 12/15/2022]
Abstract
The effect of acidosis, a biochemical hallmark of the tumor microenvironment, on cancer progression and metastasis is complex. Both pro- and anti-tumorigenic effects of acidosis have been reported and the acidic microenvironment has been exploited for specific delivery of drugs, imaging agents, and genetic constructs into tumors. In this study we investigate the spreading and focal adhesion of B16F10 melanoma cells that are genetically engineered to overexpress the pH-sensing G protein-coupled receptor GPR4. By using cell attachment assays we found that GPR4 overexpression delayed cell spreading and altered the spatial localization of dynamic focal adhesion complex, such as the localization of phosphorylated focal adhesion kinase (FAK) and paxillin, at acidic pH. The potential G-protein and downstream signaling pathways that are responsible for these effects were also investigated. By using the Rho inhibitor CT04 (C3 transferase), the Rho-associated kinase (ROCK) inhibitors Y27632 and thiazovivin, the myosin light chain kinase (MLCK) inhibitor staurosporine or a G12/13 inhibitory construct, cell spreading was restored whereas the inhibition and activation of the Gq and Gs pathways had little or no effect. Altogether our results indicate that through the G12/13/Rho signaling pathway GPR4 modulates focal adhesion dynamics and reduces cell spreading and membrane ruffling.
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Affiliation(s)
- Calvin R Justus
- Department of Internal Medicine, Brody School of Medicine, East Carolina University, Greenville, NC, USA
| | - Li V Yang
- Department of Internal Medicine, Brody School of Medicine, East Carolina University, Greenville, NC, USA; Department of Oncology, Brody School of Medicine, East Carolina University, Greenville, NC, USA; Department of Anatomy and Cell Biology, Brody School of Medicine, East Carolina University, Greenville, NC, USA; Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, NC, USA.
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10
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Abstract
H-K-ATPase type 2 (HKA2), also known as the "nongastric" or "colonic" H-K-ATPase, is broadly expressed, and its presence in the kidney has puzzled experts in the field of renal ion transport systems for many years. One of the most important and robust characteristics of this transporter is that it is strongly stimulated after dietary K(+) restriction. This result prompted many investigators to propose that it should play a role in allowing the kidney to efficiently retain K(+) under K(+) depletion. However, the apparent absence of a clear renal phenotype in HKA2-null mice has led to the idea that this transporter is an epiphenomenon. This review summarizes past and recent findings regarding the functional, structural and physiological characteristics of H-K-ATPase type 2. The findings discussed in this review suggest that, as in the famous story, the ugly duckling of the X-K-ATPase family is actually a swan.
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Affiliation(s)
- Gilles Crambert
- INSERM/UPMC Paris 6/CNRS, Centre de Recherche des Cordeliers Génomique, Physiologie et Physiopathologie Rénales, Equipe 3 U1138, ERL 8228, 15 rue de l'Ecole de Médecine, 75270 Paris Cedex, France.
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Fisher KD, Codina J, Petrovic S, DuBose TD. Pyk2 regulates H+-ATPase-mediated proton secretion in the outer medullary collecting duct via an ERK1/2 signaling pathway. Am J Physiol Renal Physiol 2012; 303:F1353-62. [PMID: 22811489 DOI: 10.1152/ajprenal.00008.2012] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Acid-secreting intercalated cells respond to changes in systemic pH through regulation of apical H(+) transporters. Little is known about the mechanism by which these cells sense changes in extracellular pH (pH(o)). Pyk2 is a nonreceptor tyrosine kinase activated by autophosphorylation at Tyr402 by cell-specific stimuli, including decreased pH, and is involved in the regulation of MAPK signaling pathways and transporter activity. We examined whether the Pyk2 and MAPK signaling pathway mediates the response of transport proteins to decreased pH in outer medullary collecting duct cells. Immunoblot analysis of phosphorylated Pyk2 (Tyr402), ERK1/2 (Thr202/Tyr204), and p38 (Thr180/Tyr182) was used to assay protein activation. To examine specificity of kinase activation and its effects, we used Pyk2 small interfering RNA to knockdown Pyk2 expression levels, the Src kinase inhibitor 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]-pyrimidine (PP 1) to inhibit Pyk2 phosphorylation, and the MEK inhibitor U0126 to inhibit ERK1/2 phosphorylation. The pH-sensitive fluorescent probe 2'-7'-bis(carboxyethyl)-5(6)-carboxyfluorescein-acetoxymethyl ester (BCECF-AM) was used to assay H(+) transporter activity. The activity of H(+) transporters was measured as the rate of intracellular pH (pH(i)) recovery after an NH(4)Cl prepulse. We show that Pyk2 is endogenously expressed and activated by acid pH in mouse-derived outer medullary collecting duct (mOMCD1) cells. Incubation of mOMCD1 cells in acid media [extracellular pH (pH(o)) 6.7] increased the phosphorylation of Pyk2, ERK1/2, and p38. Reduction in pH(i) induced by an NH(4)Cl prepulse also increased the phosphorylation of Pyk2, ERK1/2, and p38. Consistent with our previous studies, we found that mOMCD1 cells exhibit H(+)-ATPase and H(+),K(+)-ATPase activity. Pyk2 inhibition by Pyk2 siRNA and PP 1 prevented Pyk2 phosphorylation as well as H(+)-ATPase-mediated recovery in mOMCD1 cells. In addition, ERK1/2 inhibition by U0126 prevented acid-induced ERK1/2 phosphorylation and H(+)-ATPase-mediated pH(i) recovery but not phosphorylation of p38. We conclude that Pyk2 and ERK1/2 are required for increasing H(+)-ATPase, but not H(+),K(+)-ATPase, activity at decreased pH(i) in mOMCD1 cells.
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Affiliation(s)
- Kimberly D Fisher
- Sections on Nephrology and Molecular Medicine, Department of Internal Medicine, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157, USA
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Salhi A, Centeno G, Firsov D, Crambert G. Circadian expression of H,K-ATPase type 2 contributes to the stability of plasma K⁺ levels. FASEB J 2012; 26:2859-67. [PMID: 22459151 DOI: 10.1096/fj.11-199711] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Maintenance by the kidney of stable plasma K(+) values is crucial, as plasma K(+) controls muscle and nerve activity. Since renal K(+) excretion is regulated by the circadian clock, we aimed to identify the ion transporters involved in this process. In control mice, the renal mRNA expression of H,K-ATPase type 2 (HKA2) is 25% higher during rest compared to the activity period. Conversely, under dietary K(+) restriction, HKA2 expression is ∼40% higher during the activity period. This reversal suggests that HKA2 contributes to the circadian regulation of K(+) homeostasis. Compared to their wild-type (WT) littermates, HKA2-null mice fed a normal diet have 2-fold higher K(+) renal excretion during rest. Under K(+) restriction, their urinary K(+) loss is 40% higher during the activity period. This inability to excrete K(+) "on time" is reflected in plasma K(+) values, which vary by 12% between activity and rest periods in HKA2-null mice but remain stable in WT mice. Analysis of the circadian expression of HKA2 regulators suggests that Nrf2, but not progesterone, contributes to its rhythmicity. Therefore, HKA2 acts to maintain the circadian rhythm of urinary K(+) excretion and preserve stable plasma K(+) values throughout the day.
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Affiliation(s)
- Amel Salhi
- Université Pierre et Marie Curie Paris 6, Institut National de Santé et de Recherche Médicale (INSERM), Centre National Recherche Scientifique (CNRS) Unité Mixte de Recherche en Santé 872, Equipe 3, Laboratoire de Génomique, Physiologie et Physiopathologie Rénales ERL Paris, France
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