1
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Inhibition of NHE1 transport activity and gene transcription in DRG neurons in oxaliplatin-induced painful peripheral neurotoxicity. Sci Rep 2023; 13:3991. [PMID: 36894669 PMCID: PMC9998445 DOI: 10.1038/s41598-023-31095-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2022] [Accepted: 03/06/2023] [Indexed: 03/11/2023] Open
Abstract
Oxaliplatin (OHP)-induced peripheral neurotoxicity (OIPN), one of the major dose-limiting side effects of colorectal cancer treatment, is characterized by both acute and chronic syndromes. Acute exposure to low dose OHP on dorsal root ganglion (DRG) neurons is able to induce an increase in intracellular calcium and proton concentration, thus influencing ion channels activity and neuronal excitability. The Na+/H+ exchanger isoform-1 (NHE1) is a plasma membrane protein that plays a pivotal role in intracellular pH (pHi) homeostasis in many cell types, including nociceptors. Here we show that OHP has early effects on NHE1 activity in cultured mouse DRG neurons: the mean rate of pHi recovery was strongly reduced compared to vehicle-treated controls, reaching levels similar to those obtained in the presence of cariporide (Car), a specific NHE1 antagonist. The effect of OHP on NHE1 activity was sensitive to FK506, a specific calcineurin (CaN) inhibitor. Lastly, molecular analyses revealed transcriptional downregulation of NHE1 both in vitro, in mouse primary DRG neurons, and in vivo, in an OIPN rat model. Altogether, these data suggest that OHP-induced intracellular acidification of DRG neurons largely depends on CaN-mediated NHE1 inhibition, revealing new mechanisms that OHP could exert to alter neuronal excitability, and providing novel druggable targets.
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Yong MJ, Kang B, Yang U, Oh SS, Je JH. Live Streaming of a Single Cell's Life over a Local pH-Monitoring Nanowire Waveguide. NANO LETTERS 2022; 22:6375-6382. [PMID: 35877544 PMCID: PMC9372996 DOI: 10.1021/acs.nanolett.2c02185] [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] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Revised: 07/20/2022] [Indexed: 06/15/2023]
Abstract
Spatiotemporal pH monitoring of single living cells across rigid cell and organelle membranes has been challenging, despite its significance in understanding cellular heterogeneity. Here, we developed a mechanically robust yet tolerably thin nanowire waveguide that enables in situ monitoring of pH dynamics at desired cellular compartments via direct optical communication. By chemically labeling fluorescein at one end of a poly(vinylbenzyl azide) nanowire, we continuously monitored pH variations of different compartments inside a living cell, successfully observing organelle-exclusive pH homeostasis and stimuli-selective pH regulations. Importantly, it was demonstrated for the first time that, during the mammalian cell cycle, the nucleus displays pH homeostasis in interphase but a tidal pH curve in the mitotic phase, implying the existence of independent pH-regulating activities by the nuclear envelope. The rapid and accurate local pH-reporting capability of our nanowire waveguide would be highly valuable for investigating cellular behaviors under diverse biological situations in living cells.
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Affiliation(s)
- Moon-Jung Yong
- X-ray
Imaging Center and Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), 77 Cheongam-Ro, Nam-Gu, Pohang, Gyeongbuk 37673, South Korea
| | - Byunghwa Kang
- X-ray
Imaging Center and Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), 77 Cheongam-Ro, Nam-Gu, Pohang, Gyeongbuk 37673, South Korea
| | - Un Yang
- X-ray
Imaging Center and Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), 77 Cheongam-Ro, Nam-Gu, Pohang, Gyeongbuk 37673, South Korea
| | - Seung Soo Oh
- X-ray
Imaging Center and Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), 77 Cheongam-Ro, Nam-Gu, Pohang, Gyeongbuk 37673, South Korea
| | - Jung Ho Je
- X-ray
Imaging Center and Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), 77 Cheongam-Ro, Nam-Gu, Pohang, Gyeongbuk 37673, South Korea
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3
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Chung YJ, Park KC, Tokar S, Eykyn TR, Fuller W, Pavlovic D, Swietach P, Shattock MJ. Off-target effects of sodium-glucose co-transporter 2 blockers: empagliflozin does not inhibit Na+/H+ exchanger-1 or lower [Na+]i in the heart. Cardiovasc Res 2021; 117:2794-2806. [PMID: 33135077 PMCID: PMC8683707 DOI: 10.1093/cvr/cvaa323] [Citation(s) in RCA: 78] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/19/2020] [Revised: 09/28/2020] [Accepted: 11/02/2020] [Indexed: 12/17/2022] Open
Abstract
AIMS Emipagliflozin (EMPA) is a potent inhibitor of the renal sodium-glucose co-transporter 2 (SGLT2) and an effective treatment for type-2 diabetes. In patients with diabetes and heart failure, EMPA has cardioprotective effects independent of improved glycaemic control, despite SGLT2 not being expressed in the heart. A number of non-canonical mechanisms have been proposed to explain these cardiac effects, most notably an inhibitory action on cardiac Na+/H+ exchanger 1 (NHE1), causing a reduction in intracellular [Na+] ([Na+]i). However, at resting intracellular pH (pHi), NHE1 activity is very low and its pharmacological inhibition is not expected to meaningfully alter steady-state [Na+]i. We re-evaluate this putative EMPA target by measuring cardiac NHE1 activity. METHODS AND RESULTS The effect of EMPA on NHE1 activity was tested in isolated rat ventricular cardiomyocytes from measurements of pHi recovery following an ammonium pre-pulse manoeuvre, using cSNARF1 fluorescence imaging. Whereas 10 µM cariporide produced near-complete inhibition, there was no evidence for NHE1 inhibition with EMPA treatment (1, 3, 10, or 30 µM). Intracellular acidification by acetate-superfusion evoked NHE1 activity and raised [Na+]i, reported by sodium binding benzofuran isophthalate (SBFI) fluorescence, but EMPA did not ablate this rise. EMPA (10 µM) also had no significant effect on the rate of cytoplasmic [Na+]i rise upon superfusion of Na+-depleted cells with Na+-containing buffers. In Langendorff-perfused mouse, rat and guinea pig hearts, EMPA did not affect [Na+]i at baseline nor pHi recovery following acute acidosis, as measured by 23Na triple quantum filtered NMR and 31P NMR, respectively. CONCLUSIONS Our findings indicate that cardiac NHE1 activity is not inhibited by EMPA (or other SGLT2i's) and EMPA has no effect on [Na+]i over a wide range of concentrations, including the therapeutic dose. Thus, the beneficial effects of SGLT2i's in failing hearts should not be interpreted in terms of actions on myocardial NHE1 or intracellular [Na+].
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Affiliation(s)
- Yu Jin Chung
- British Heart Foundation Centre of Research Excellence, King’s College London, The Rayne Institute, St Thomas’ Hospital, Lambeth Palace Road, London SE1 7EH, UK
| | - Kyung Chan Park
- Department of Physiology, Anatomy and Genetics, Parks Road, Oxford, OX1 3PT, UK
| | - Sergiy Tokar
- British Heart Foundation Centre of Research Excellence, King’s College London, The Rayne Institute, St Thomas’ Hospital, Lambeth Palace Road, London SE1 7EH, UK
| | - Thomas R Eykyn
- British Heart Foundation Centre of Research Excellence, King’s College London, The Rayne Institute, St Thomas’ Hospital, Lambeth Palace Road, London SE1 7EH, UK
- School of Biomedical Engineering and Imaging Sciences, King’s College London, The Rayne Institute, St Thomas' Hospital, Lambeth Palace Road, London SE1 7EH, UK
| | - William Fuller
- Institute of Cardiovascular & Medical Sciences, Sir James Black Building, University of Glasgow, University Avenue, Glasgow G12 8QQ, UK
| | - Davor Pavlovic
- Institute for Cardiovascular Sciences, University of Birmingham, Wolfson Drive, Birmingham B15 2TT, UK
| | - Pawel Swietach
- Department of Physiology, Anatomy and Genetics, Parks Road, Oxford, OX1 3PT, UK
| | - Michael J Shattock
- British Heart Foundation Centre of Research Excellence, King’s College London, The Rayne Institute, St Thomas’ Hospital, Lambeth Palace Road, London SE1 7EH, UK
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4
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Wang Y, Zhao J, Cai Y, Ballard HJ. Cystic fibrosis transmembrane conductance regulator-dependent bicarbonate entry controls rat cardiomyocyte ATP release via pannexin1 through mitochondrial signalling and caspase activation. Acta Physiol (Oxf) 2020; 230:e13495. [PMID: 32386453 DOI: 10.1111/apha.13495] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2019] [Revised: 04/27/2020] [Accepted: 05/01/2020] [Indexed: 12/20/2022]
Abstract
AIM Cystic fibrosis transmembrane conductance regulator (CFTR) is expressed in the heart, but its function there is unclear. CFTR regulates an ATP release pore in many tissues, but the identity and regulatory mechanism of the pore are unknown. We investigated the role of CFTR in ATP release from primary cardiomyocytes and ventricular wall in vivo. METHODS Proteins involved in the signalling pathway for ATP release during simulated ischaemia (lactic acid treatment) were investigated using inhibitors and siRNA; colocalization was identified by coimmunofluorescence and proximity ligation assays; changes in near-membrane pH and calcium were identified with total internal reflection microscopy; in vivo ATP release was investigated using interstitial microdialysis of rat heart. RESULTS Lactic acid-induced CFTR-dependent ATP release from cultured cardiomyocytes and left ventricle in vivo. Lactic acid entry elevated near-membrane calcium, which involved Na/H- and Na/Ca-exchangers colocalized with CFTR. Calcium entry-induced CFTR activation, which involved cAMP, protein kinase A, FAK, Pyk2 and Src. Removal of extracellular bicarbonate abolished cardiomyocyte ATP release induced by lactic acid or CFTR activators. Bicarbonate stimulated cytochrome c expression, cytochrome c release and ATP release from isolated cardiomyocyte mitochondria. Pannexin 1 (Panx1) colocalized with CFTR. Lactic acid increased cardiomyocyte caspase activity: caspase inhibitors or Panx1 siRNA abolished cardiomyocyte ATP release, while pannexin inhibition abolished cardiac ATP release in vivo. CONCLUSION During simulated ischaemia, CFTR-dependent bicarbonate entry stimulated ATP and cytochrome c release from mitochondria; in the cytoplasm, cytochrome c-activated caspase 3, which in turn activated Panx1, and ATP was released through the opened Panx1 channel.
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Affiliation(s)
- Yongshun Wang
- School of Biomedical Sciences The University of Hong Kong Pokfulam Hong Kong
| | - Junjun Zhao
- School of Biomedical Sciences The University of Hong Kong Pokfulam Hong Kong
| | - Yin Cai
- Department of Anaesthesiology The University of Hong Kong Pokfulam Hong Kong
| | - Heather J. Ballard
- School of Biomedical Sciences The University of Hong Kong Pokfulam Hong Kong
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5
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Lee SP, Chao SC, Chou MF, Huang SF, Dai NT, Wu GJ, Tsai CS, Loh SH, Tsai YT. Characterization of intracellular buffering power in human induced pluripotent stem cells and the loss of pluripotency is delayed by acidic stimulation and increase of NHE1 activity. J Cell Physiol 2020; 236:1515-1528. [PMID: 32841374 DOI: 10.1002/jcp.29959] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2020] [Revised: 06/18/2020] [Accepted: 07/07/2020] [Indexed: 11/07/2022]
Abstract
The homeostasis of intracellular pH (pHi ) affects many cellular functions. Our previous study has established a functional and molecular model of the active pHi regulators in human induced pluripotent stem cells (hiPSCs). The aims of the present study were to further quantify passive pHi buffering power (β) and to investigate the effects of extracellular pH and Na+ -H+ exchanger 1 (NHE1) activity on pluripotency in hiPSCs. pHi was detected by microspectrofluorimetry with pH-sensitive dye-BCECF. Western blot, immunofluorescence staining, and flow cytometry were used to detect protein expression and pluripotency. Our study in hiPSCs showed that (a) the value of total (βtot ), intrinsic (βi ), and CO2 -dependent ( β C O 2 ) buffering power all increased while pHi increased; (b) during the spontaneous differentiation for 4 days, the β values of βtot and β C O 2 changed in a tendency of decrease, despite the absence of statistical significance; (c) an acidic cultured environment retained pluripotency and further upregulated expression and activity of NHE1 during spontaneous differentiation; (d) inhibition on NHE1 activity promoted the loss of pluripotency. In conclusion, we, for the first time, established a quantitative model of passive β during differentiation and demonstrated that maintenance of NHE1 at a higher level was of critical importance for pluripotency retention in hiPSCs.
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Affiliation(s)
- Shiao-Pieng Lee
- Department of Dentistry, School of Dentistry, Division of Oral and Maxillofacial Surgery, Tri-Service General Hospital and National Defense Medical Center, Taipei, Taiwan
| | - Shih-Chi Chao
- Graduate Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan
| | - Mei-Fang Chou
- Department of Pharmacy Practice, Tri-Service General Hospital, Taipei, Taiwan
| | - Shu-Fu Huang
- Department of Pharmacy Practice, Tri-Service General Hospital, Taipei, Taiwan
| | - Niann-Tzyy Dai
- Department of Surgery, Division of Plastic and Reconstructive Surgery, Tri-Service General Hospital, Taipei, Taiwan
| | - Gwo-Jang Wu
- Department of Obstetrics and Gynecology, Tri-Service General Hospital, Taipei, Taiwan
| | - Chien-Sung Tsai
- Department of Surgery, Division of Cardiovascular Surgery, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan
- Department of Pharmacology, National Defense Medical Center, Taipei, Taiwan
- Institute of Pharmacy, I.M. Sechenov First Moscow State Medical University, Moscow, Russia
| | - Shih-Hurng Loh
- Graduate Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan
- Department of Pharmacy Practice, Tri-Service General Hospital, Taipei, Taiwan
- Department of Surgery, Division of Cardiovascular Surgery, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan
| | - Yi-Ting Tsai
- Department of Surgery, Division of Cardiovascular Surgery, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan
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6
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Richards MA, Simon JN, Ma R, Loonat AA, Crabtree MJ, Paterson DJ, Fahlman RP, Casadei B, Fliegel L, Swietach P. Nitric oxide modulates cardiomyocyte pH control through a biphasic effect on sodium/hydrogen exchanger-1. Cardiovasc Res 2019; 116:1958-1971. [PMID: 31742355 PMCID: PMC7567331 DOI: 10.1093/cvr/cvz311] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/22/2019] [Revised: 10/31/2019] [Accepted: 11/16/2019] [Indexed: 11/14/2022] Open
Abstract
AIMS When activated, Na+/H+ exchanger-1 (NHE1) produces some of the largest ionic fluxes in the heart. NHE1-dependent H+ extrusion and Na+ entry strongly modulate cardiac physiology through the direct effects of pH on proteins and by influencing intracellular Ca2+ handling. To attain an appropriate level of activation, cardiac NHE1 must respond to myocyte-derived cues. Among physiologically important cues is nitric oxide (NO), which regulates a myriad of cardiac functions, but its actions on NHE1 are unclear. METHODS AND RESULTS NHE1 activity was measured using pH-sensitive cSNARF1 fluorescence after acid-loading adult ventricular myocytes by an ammonium prepulse solution manoeuvre. NO signalling was manipulated by knockout of its major constitutive synthase nNOS, adenoviral nNOS gene delivery, nNOS inhibition, and application of NO-donors. NHE1 flux was found to be activated by low [NO], but inhibited at high [NO]. These responses involved cGMP-dependent signalling, rather than S-nitros(yl)ation. Stronger cGMP signals, that can inhibit phosphodiesterase enzymes, allowed [cAMP] to rise, as demonstrated by a FRET-based sensor. Inferring from the actions of membrane-permeant analogues, cGMP was determined to activate NHE1, whereas cAMP was inhibitory, which explains the biphasic regulation by NO. Activation of NHE1-dependent Na+ influx by low [NO] also increased the frequency of spontaneous Ca2+ waves, whereas high [NO] suppressed these aberrant forms of Ca2+ signalling. CONCLUSIONS Physiological levels of NO stimulation increase NHE1 activity, which boosts pH control during acid-disturbances and results in Na+-driven cellular Ca2+ loading. These responses are positively inotropic but also increase the likelihood of aberrant Ca2+ signals, and hence arrhythmia. Stronger NO signals inhibit NHE1, leading to a reversal of the aforementioned effects, ostensibly as a potential cardioprotective intervention to curtail NHE1 overdrive.
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Affiliation(s)
- Mark A Richards
- Department of Physiology, Anatomy and Genetics, Parks Road, Oxford OX1 3PT, UK
| | - Jillian N Simon
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, British Heart Foundation Centre for Research Excellence, John Radcliffe Hospital, Oxford OX3 9DU, UK
| | - Ruichong Ma
- Department of Physiology, Anatomy and Genetics, Parks Road, Oxford OX1 3PT, UK
| | - Aminah A Loonat
- Department of Physiology, Anatomy and Genetics, Parks Road, Oxford OX1 3PT, UK
| | - Mark J Crabtree
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, British Heart Foundation Centre for Research Excellence, John Radcliffe Hospital, Oxford OX3 9DU, UK
| | - David J Paterson
- Department of Physiology, Anatomy and Genetics, Parks Road, Oxford OX1 3PT, UK
| | - Richard P Fahlman
- Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Barbara Casadei
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, British Heart Foundation Centre for Research Excellence, John Radcliffe Hospital, Oxford OX3 9DU, UK
| | - Larry Fliegel
- Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Pawel Swietach
- Department of Physiology, Anatomy and Genetics, Parks Road, Oxford OX1 3PT, UK
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7
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Chao SC, Wu GJ, Huang SF, Dai NT, Huang HK, Chou MF, Tsai YT, Lee SP, Loh SH. Functional and molecular mechanism of intracellular pH regulation in human inducible pluripotent stem cells. World J Stem Cells 2018; 10:196-211. [PMID: 30613313 PMCID: PMC6306555 DOI: 10.4252/wjsc.v10.i12.196] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/17/2018] [Revised: 11/14/2018] [Accepted: 12/05/2018] [Indexed: 02/06/2023] Open
Abstract
AIM To establish a functional and molecular model of the intracellular pH (pHi) regulatory mechanism in human induced pluripotent stem cells (hiPSCs).
METHODS hiPSCs (HPS0077) were kindly provided by Dr. Dai from the Tri-Service General Hospital (IRB No. B-106-09). Changes in the pHi were detected either by microspectrofluorimetry or by a multimode reader with a pH-sensitive fluorescent probe, BCECF, and the fluorescent ratio was calibrated by the high K+/nigericin method. NH4Cl and Na-acetate prepulse techniques were used to induce rapid intracellular acidosis and alkalization, respectively. The buffering power (β) was calculated from the ΔpHi induced by perfusing different concentrations of (NH4)2SO4. Western blot techniques and immunocytochemistry staining were used to detect the protein expression of pHi regulators and pluripotency markers.
RESULTS In this study, our results indicated that (1) the steady-state pHi value was found to be 7.5 ± 0.01 (n = 20) and 7.68 ± 0.01 (n =20) in HEPES and 5% CO2/HCO3--buffered systems, respectively, which were much greater than that in normal adult cells (7.2); (2) in a CO2/HCO3--buffered system, the values of total intracellular buffering power (β) can be described by the following equation: βtot = 107.79 (pHi)2 - 1522.2 (pHi) + 5396.9 (correlation coefficient R2 = 0.85), in the estimated pHi range of 7.1-8.0; (3) the Na+/H+ exchanger (NHE) and the Na+/HCO3- cotransporter (NBC) were found to be functionally activated for acid extrusion for pHi values less than 7.5 and 7.68, respectively; (4) V-ATPase and some other unknown Na+-independent acid extruder(s) could only be functionally detected for pHi values less than 7.1; (5) the Cl-/ OH- exchanger (CHE) and the Cl-/HCO3- anion exchanger (AE) were found to be responsible for the weakening of intracellular proton loading; (6) besides the CHE and the AE, a Cl--independent acid loading mechanism was functionally identified; and (7) in hiPSCs, a strong positive correlation was observed between the loss of pluripotency and the weakening of the intracellular acid extrusion mechanism, which included a decrease in the steady-state pHi value and diminished the functional activity and protein expression of the NHE and the NBC.
CONCLUSION For the first time, we established a functional and molecular model of a pHi regulatory mechanism and demonstrated its strong positive correlation with hiPSC pluripotency.
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Affiliation(s)
- Shih-Chi Chao
- Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 11490, Taiwan
| | - Gwo-Jang Wu
- Department of Obstetrics and Gynecology, Tri-Service General Hospital, National Defense Medical Center, Taipei 11490, Taiwan
| | - Shu-Fu Huang
- Department of Pharmacy Practice, Tri-Service General Hospital, National Defense Medical Center, Taipei 11490, Taiwan
| | - Niann-Tzyy Dai
- Division of Plastic and Reconstructive Surgery, Department of Surgery, Tri-Service General Hospital, National Defense Medical Center, Taipei 11490, Taiwan
| | - Hsu-Kai Huang
- Division of Chest Surgery, Department of Surgery, Tri-Service General Hospital, National Defense Medical Center, Taipei 11490, Taiwan
| | - Mei-Fang Chou
- Department of Pharmacy Practice, Tri-Service General Hospital, National Defense Medical Center, Taipei 11490, Taiwan
| | - Yi-Ting Tsai
- Graduate Institute of Medical Sciences, National Defense Medical Center, Taipei 11490, Taiwan
- Division of Cardiovascular Surgery, Department of Surgery, Tri-Service General Hospital, National Defense Medical Center, Taipei 11490, Taiwan
| | - Shiao-Pieng Lee
- Division of Oral and Maxillofacial Surgery, Department of Dentistry, School of Dentistry, Tri-Service General Hospital and National Defense Medical Center, Taipei 11490, Taiwan
| | - Shih-Hurng Loh
- Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 11490, Taiwan
- Department of Pharmacy Practice, Tri-Service General Hospital, National Defense Medical Center, Taipei 11490, Taiwan
- Department of Pharmacology, National Defense Medical Center, Taipei 11490, Taiwan
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8
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Danes VR, Anthony J, Rayani K, Spitzer KW, Tibbits GF. pH recovery from a proton load in rat cardiomyocytes: effects of chronic exercise. Am J Physiol Heart Circ Physiol 2017; 314:H285-H292. [PMID: 29101173 DOI: 10.1152/ajpheart.00405.2017] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The ability of cardiomyocytes to recover from a proton load was examined in the hearts of exercise-trained and sedentary control rats in CO2/[Formula: see text]-free media. Acidosis was created by the NH4Cl prepulse technique, and intracellular pH (pHi) was determined using fluorescence microscopy on carboxy-SNARF-1 AM-loaded isolated cardiomyocytes. CO2-independent pHi buffering capacity (βi) was measured by incrementally reducing the extracellular NH4Cl concentration in steps of 50% from 20 to 1.25 mM. βi increased as pHi decreased in both exercise-trained and sedentary control groups. However, the magnitude of increase in βi as a function of pHi was found to be significantly ( P < 0.001) greater in the exercise-trained group compared with the sedentary control group. The rate of pHi recovery from an imposed proton load was found to not be different between the exercise-trained and control groups. The Na+/H+ exchanger-dependent H+ extrusion rate during the recovery from an imposed proton load, however, was found to be significantly greater in the exercise-trained group compared with the control group. By increasing βi and subsequently the Na+/H+ exchanger-dependent H+ extrusion rate, exercise training may provide cardiomyocytes with the ability to better handle an intracellular excess of H+ generated during hypoxia/ischemic insults and may serve in a cardioprotective role. These data may be predictive of two positive outcomes: 1) increased exercise tolerance by the heart and 2) a protective mechanism that limits the degree of myocardial acidosis and subsequent damage that accompanies ischemia-reperfusion stress. NEW & NOTEWORTHY The enhanced ability to deal with acidosis conferred by exercise training is likely to improve exercise tolerance and outcomes in response to myocardial ischemia-reperfusion injury.
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Affiliation(s)
- Vennetia R Danes
- Molecular Cardiac Physiology Group, Simon Fraser University , Burnaby, British Columbia , Canada
| | - Josephine Anthony
- Molecular Cardiac Physiology Group, Simon Fraser University , Burnaby, British Columbia , Canada
| | - Kaveh Rayani
- Molecular Cardiac Physiology Group, Simon Fraser University , Burnaby, British Columbia , Canada
| | - Kenneth W Spitzer
- Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah , Salt Lake City, Utah
| | - Glen F Tibbits
- Molecular Cardiac Physiology Group, Simon Fraser University , Burnaby, British Columbia , Canada.,Cardiovascular Sciences, BC Research Institute for Children's and Women's Health , Vancouver, British Columbia , Canada
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9
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Vierock J, Grimm C, Nitzan N, Hegemann P. Molecular determinants of proton selectivity and gating in the red-light activated channelrhodopsin Chrimson. Sci Rep 2017; 7:9928. [PMID: 28855540 PMCID: PMC5577340 DOI: 10.1038/s41598-017-09600-8] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2017] [Accepted: 07/21/2017] [Indexed: 12/15/2022] Open
Abstract
Channelrhodopsins are light-gated ion channels of green algae used for the precise temporal and spatial control of transmembrane ion fluxes. The channelrhodopsin Chrimson from Chlamydomonas noctigama allows unprecedented deep tissue penetration due to peak absorption at 590 nm. We demonstrate by electrophysiological recordings and imaging techniques that Chrimson is highly proton selective causing intracellular acidification in HEK cells that is responsible for slow photocurrent decline during prolonged illumination. We localized molecular determinants of both high proton selectivity and red light activation to the extracellular pore. Whereas exchange of Glu143 only drops proton conductance and generates an operational Na-channel with 590 nm activation, exchange of Glu139 in addition increased the open state lifetime and shifted the absorption hypsochromic by 70 nm. In conjunction with Glu300 in the center and Glu124 and Glu125 at the intracellular end of the pore, Glu139 contributes to a delocalized activation gate and stabilizes by long-range interaction counterion configuration involving protonation of Glu165 that we identified as a key determinant of the large opsin shift in Chrimson.
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Affiliation(s)
- Johannes Vierock
- Institute of Biology, Experimental Biophysics, Humboldt-Universität zu Berlin, 10115, Berlin, Germany.
| | - Christiane Grimm
- Institute of Biology, Experimental Biophysics, Humboldt-Universität zu Berlin, 10115, Berlin, Germany
| | - Noam Nitzan
- Institute of Biology, Experimental Biophysics, Humboldt-Universität zu Berlin, 10115, Berlin, Germany.,Neuroscience Research Center, Charité - Universitätsmedizin Berlin, Charitéplatz 1, 10117, Berlin, Germany
| | - Peter Hegemann
- Institute of Biology, Experimental Biophysics, Humboldt-Universität zu Berlin, 10115, Berlin, Germany
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10
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Yeves AM, Caldiz CI, Aiello EA, Villa-Abrille MC, Ennis IL. Reactive oxygen species partially mediate high dose angiotensin II-induced positive inotropic effect in cat ventricular myocytes. Cardiovasc Pathol 2015; 24:236-40. [DOI: 10.1016/j.carpath.2015.01.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/25/2014] [Revised: 01/21/2015] [Accepted: 01/22/2015] [Indexed: 01/11/2023] Open
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11
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Kerr JP, Ward CW, Bloch RJ. Dysferlin at transverse tubules regulates Ca(2+) homeostasis in skeletal muscle. Front Physiol 2014; 5:89. [PMID: 24639655 PMCID: PMC3944681 DOI: 10.3389/fphys.2014.00089] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2013] [Accepted: 02/15/2014] [Indexed: 11/13/2022] Open
Abstract
The class of muscular dystrophies linked to the genetic ablation or mutation of dysferlin, including Limb Girdle Muscular Dystrophy 2B (LGMD2B) and Miyoshi Myopathy (MM), are late-onset degenerative diseases. In lieu of a genetic cure, treatments to prevent or slow the progression of dysferlinopathy are of the utmost importance. Recent advances in the study of dysferlinopathy have highlighted the necessity for the maintenance of calcium handling in altering or slowing the progression of muscular degeneration resulting from the loss of dysferlin. This review highlights new evidence for a role for dysferlin at the transverse (t-) tubule of striated muscle, where it is involved in maintaining t-tubule structure and function.
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Affiliation(s)
- Jaclyn P Kerr
- Department of Physiology, University of Maryland School of Medicine Baltimore, MD, USA
| | - Christopher W Ward
- Department of Organizational Systems and Adult Health, University of Maryland School of Nursing Baltimore, MD, USA
| | - Robert J Bloch
- Department of Physiology, University of Maryland School of Medicine Baltimore, MD, USA
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12
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Chang JC, Oude-Elferink RPJ. Role of the bicarbonate-responsive soluble adenylyl cyclase in pH sensing and metabolic regulation. Front Physiol 2014; 5:42. [PMID: 24575049 PMCID: PMC3918592 DOI: 10.3389/fphys.2014.00042] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2013] [Accepted: 01/22/2014] [Indexed: 12/18/2022] Open
Abstract
The evolutionarily conserved soluble adenylyl cyclase (sAC, adcy10) was recently identified as a unique source of cAMP in the cytoplasm and the nucleus. Its activity is regulated by bicarbonate and fine-tuned by calcium. As such, and in conjunction with carbonic anhydrase (CA), sAC constitutes an HCO(-) 3/CO(-) 2/pH sensor. In both alpha-intercalated cells of the collecting duct and the clear cells of the epididymis, sAC is expressed at significant level and involved in pH homeostasis via apical recruitment of vacuolar H(+)-ATPase (VHA) in a PKA-dependent manner. In addition to maintenance of pH homeostasis, sAC is also involved in metabolic regulation such as coupling of Krebs cycle to oxidative phosphorylation via bicarbonate/CO2 sensing. Additionally, sAC also regulates CFTR channel and plays an important role in regulation of barrier function and apoptosis. These observations suggest that sAC, via bicarbonate-sensing, plays an important role in maintaining homeostatic status of cells against fluctuations in their microenvironment.
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Affiliation(s)
- Jung-Chin Chang
- Tytgat Institute for Liver and Intestinal Research, Academic Medical Center, University of Amsterdam Amsterdam, Netherlands
| | - Ronald P J Oude-Elferink
- Tytgat Institute for Liver and Intestinal Research, Academic Medical Center, University of Amsterdam Amsterdam, Netherlands
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13
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Swietach P, Leem CH, Spitzer KW, Vaughan-Jones RD. Pumping Ca2+ up H+ gradients: a Ca2(+)-H+ exchanger without a membrane. J Physiol 2014; 592:3179-88. [PMID: 24514908 DOI: 10.1113/jphysiol.2013.265959] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Cellular processes are exquisitely sensitive to H+ and Ca2+ ions because of powerful ionic interactions with proteins. By regulating the spatial and temporal distribution of intracellular [Ca2+] and [H+], cells such as cardiac myocytes can exercise control over their biological function. A well-established paradigm in cellular physiology is that ion concentrations are regulated by specialized, membrane-embedded transporter proteins. Many of these couple the movement of two or more ionic species per transport cycle, thereby linking ion concentrations among neighbouring compartments. Here, we compare and contrast canonical membrane transport with a novel type of Ca(2+)-H+ coupling within cytoplasm, which produces uphill Ca2+ transport energized by spatial H+ ion gradients, and can result in the cytoplasmic compartmentalization of Ca2+ without requiring a partitioning membrane. The mechanism, demonstrated in mammalian myocytes, relies on diffusible cytoplasmic buffers, such as carnosine, homocarnosine and ATP, to which Ca2+ and H+ ions bind in an apparently competitive manner. These buffer molecules can actively recruit Ca2+ to acidic microdomains, in exchange for the movement of H+ ions. The resulting Ca2+ microdomains thus have the potential to regulate function locally. Spatial cytoplasmic Ca(2+)-H+ exchange (cCHX) acts like a 'pump' without a membrane and may be operational in many cell types.
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Affiliation(s)
- Pawel Swietach
- Burdon Sanderson Cardiac Science Centre, Department of Physiology, Anatomy and Genetics, Oxford, UK
| | - Chae-Hun Leem
- Department of Physiology, University of Ulsan College of Medicine, Seoul, Republic of Korea
| | - Kenneth W Spitzer
- Nora Eccles Harrison Cardiovascular Research and Training Institute, Salt Lake City, UT, USA
| | - Richard D Vaughan-Jones
- Burdon Sanderson Cardiac Science Centre, Department of Physiology, Anatomy and Genetics, Oxford, UK
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14
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Bouret Y, Argentina M, Counillon L. Capturing intracellular pH dynamics by coupling its molecular mechanisms within a fully tractable mathematical model. PLoS One 2014; 9:e85449. [PMID: 24465564 PMCID: PMC3894979 DOI: 10.1371/journal.pone.0085449] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2013] [Accepted: 11/26/2013] [Indexed: 01/30/2023] Open
Abstract
We describe the construction of a fully tractable mathematical model for intracellular pH. This work is based on coupling the kinetic equations depicting the molecular mechanisms for pumps, transporters and chemical reactions, which determine this parameter in eukaryotic cells. Thus, our system also calculates the membrane potential and the cytosolic ionic composition. Such a model required the development of a novel algebraic method that couples differential equations for slow relaxation processes to steady-state equations for fast chemical reactions. Compared to classical heuristic approaches based on fitted curves and ad hoc constants, this yields significant improvements. This model is mathematically self-consistent and allows for the first time to establish analytical solutions for steady-state pH and a reduced differential equation for pH regulation. Because of its modular structure, it can integrate any additional mechanism that will directly or indirectly affect pH. In addition, it provides mathematical clarifications for widely observed biological phenomena such as overshooting in regulatory loops. Finally, instead of including a limited set of experimental results to fit our model, we show examples of numerical calculations that are extremely consistent with the wide body of intracellular pH experimental measurements gathered by different groups in many different cellular systems.
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Affiliation(s)
- Yann Bouret
- Université Nice Sophia Antipolis, CNRS, LPMC, UMR 7336, Nice, France
| | - Médéric Argentina
- Université Nice Sophia Antipolis, CNRS, INLN, UMR 7335, Valbonne, France
- Institut Universitaire de France (IUF), Ministère de l’Enseignement Supérieur et de la Recherche Scientifique, Paris, France
| | - Laurent Counillon
- Université Nice Sophia Antipolis, CNRS, LP2M, FRE 3472, Nice, France
- * E-mail:
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15
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Villafuerte FC, Swietach P, Youm JB, Ford K, Cardenas R, Supuran CT, Cobden PM, Rohling M, Vaughan-Jones RD. Facilitation by intracellular carbonic anhydrase of Na+ -HCO3- co-transport but not Na+ / H+ exchange activity in the mammalian ventricular myocyte. J Physiol 2013; 592:991-1007. [PMID: 24297849 PMCID: PMC3948559 DOI: 10.1113/jphysiol.2013.265439] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Carbonic anhydrase enzymes (CAs) catalyse the reversible hydration of CO2 to H+ and HCO3- ions. This catalysis is proposed to be harnessed by acid/base transporters, to facilitate their transmembrane flux activity, either through direct protein-protein binding (a 'transport metabolon') or local functional interaction. Flux facilitation has previously been investigated by heterologous co-expression of relevant proteins in host cell lines/oocytes. Here, we examine the influence of intrinsic CA activity on membrane HCO3- or H+ transport via the native acid-extruding proteins, Na+ -HCO3- cotransport (NBC) and Na+ / H+ exchange (NHE), expressed in enzymically isolated mammalian ventricular myocytes. Effects of intracellular and extracellular (exofacial) CA (CAi and CAe) are distinguished using membrane-permeant and -impermeant pharmacological CA inhibitors, while measuring transporter activity in the intact cell using pH and Na+ fluorophores. We find that NBC, but not NHE flux is enhanced by catalytic CA activity, with facilitation being confined to CAi activity alone. Results are quantitatively consistent with a model where CAi catalyses local H+ ion delivery to the NBC protein, assisting the subsequent (uncatalysed) protonation and removal of imported HCO3- ions. In well-superfused myocytes, exofacial CA activity is superfluous, most likely because extracellular CO2/HCO3- buffer is clamped at equilibrium. The CAi insensitivity of NHE flux suggests that, in the native cell, intrinsic mobile buffer-shuttles supply sufficient intracellular H+ ions to this transporter, while intrinsic buffer access to NBC proteins is restricted. Our results demonstrate a selective CA facilitation of acid/base transporters in the ventricular myocyte, implying a specific role for the intracellular enzyme in HCO3- transport, and hence pHi regulation in the heart.
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Affiliation(s)
- Francisco C Villafuerte
- Burdon Sanderson Cardiac Science Centre, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3PT, UK.
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16
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Orlowski A, Vargas LA, Aiello EA, Álvarez BV. Elevated carbon dioxide upregulates NBCn1 Na+/HCO3(-) cotransporter in human embryonic kidney cells. Am J Physiol Renal Physiol 2013; 305:F1765-74. [PMID: 24005470 DOI: 10.1152/ajprenal.00096.2013] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The NBCn1 Na(+)/HCO3(-) cotransporter catalyzes the electroneutral movement of 1 Na(+):1 HCO3(-) into kidney cells. We characterized the intracellular pH (pHi) regulation in human embryonic kidney cells (HEK) subjected to NH4Cl prepulse acid loading, and we examined the NBCn1 expression and function in HEK cells subjected to 24-h elevated Pco2 (10-15%). After acid loading, in the presence of HCO3(-), ∼50% of the pHi recovery phase was blocked by the Na(+)/H(+) exchanger inhibitors EIPA (10-50 μM) and amiloride (1 mM) and was fully cancelled by 30 μM EIPA under nominally HCO3(-)-free conditions. In addition, in the presence of HCO3(-), pHi recovery after acid loading was completely blocked when Na(+) was omitted in the buffer. pHi recovery after acidification in HEK cells was repeated in the presence of the NBC inhibitor S0859, and the pHi recovery was inhibited by S0859 in a dose-dependent manner (Ki = 30 μM, full inhibition at 60 μM), which confirmed NBC Na(+)/HCO3(-) cotransporter activation. NBCn1 expression increased threefold after 24-h exposure of cultured HEK cells to 10% CO2 and sevenfold after exposure to 15% CO2, examined by immunoblots. Finally, exposure of HEK cells to high CO2 significantly increased the HCO3(-)-dependent recovery of pHi after acid loading. We conclude that HEK cells expressed the NBCn1 Na(+)/HCO3(-) cotransporter as the only HCO3(-)-dependent mechanism responsible for cellular alkaline loading. NBCn1, which expresses in different kidney cell types, was upregulated by 24-h high-Pco2 exposure of HEK cells, and this upregulation was accompanied by increased NBCn1-mediated HCO3(-) transport.
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Affiliation(s)
- Alejandro Orlowski
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, UNLP, Calle 60 y 120, 1900, La Plata, Argentina.
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17
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Al-Samir S, Papadopoulos S, Scheibe RJ, Meißner JD, Cartron JP, Sly WS, Alper SL, Gros G, Endeward V. Activity and distribution of intracellular carbonic anhydrase II and their effects on the transport activity of anion exchanger AE1/SLC4A1. J Physiol 2013; 591:4963-82. [PMID: 23878365 DOI: 10.1113/jphysiol.2013.251181] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
We have investigated the previously published 'metabolon hypothesis' postulating that a close association of the anion exchanger 1 (AE1) and cytosolic carbonic anhydrase II (CAII) exists that greatly increases the transport activity of AE1. We study whether there is a physical association of and direct functional interaction between CAII and AE1 in the native human red cell and in tsA201 cells coexpressing heterologous fluorescent fusion proteins CAII-CyPet and YPet-AE1. In these doubly transfected tsA201 cells, YPet-AE1 is clearly associated with the cell membrane, whereas CAII-CyPet is homogeneously distributed throughout the cell in a cytoplasmic pattern. Förster resonance energy transfer measurements fail to detect close proximity of YPet-AE1 and CAII-CyPet. The absence of an association of AE1 and CAII is supported by immunoprecipitation experiments using Flag-antibody against Flag-tagged AE1 expressed in tsA201 cells, which does not co-precipitate native CAII but co-precipitates coexpressed ankyrin. Both the CAII and the AE1 fusion proteins are fully functional in tsA201 cells as judged by CA activity and by cellular HCO3(-) permeability (P(HCO3(-))) sensitive to inhibition by 4,4-Diisothiocyano-2,2-stilbenedisulfonic acid. Expression of the non-catalytic CAII mutant V143Y leads to a drastic reduction of endogenous CAII and to a corresponding reduction of total intracellular CA activity. Overexpression of an N-terminally truncated CAII lacking the proposed site of interaction with the C-terminal cytoplasmic tail of AE1 substantially increases intracellular CA activity, as does overexpression of wild-type CAII. These variously co-transfected tsA201 cells exhibit a positive correlation between cellular P(HCO3(-)) and intracellular CA activity. The relationship reflects that expected from changes in cytoplasmic CA activity improving substrate supply to or removal from AE1, without requirement for a CAII-AE1 metabolon involving physical interaction. A functional contribution of the hypothesized CAII-AE1 metabolon to erythroid AE1-mediated HCO3(-) transport was further tested in normal red cells and red cells from CAII-deficient patients that retain substantial CA activity associated with the erythroid CAI protein lacking the proposed AE1-binding sequence. Erythroid P(HCO3(-)) was indistinguishable in these two cell types, providing no support for the proposed functional importance of the physical interaction of CAII and AE1. A theoretical model predicts that homogeneous cytoplasmic distribution of CAII is more favourable for cellular transport of HCO3(-) and CO2 than is association of CAII with the cytoplasmic surface of the plasma membrane. This is due to the fact that the relatively slow intracellular transport of H(+) makes it most efficient to place the CA in the vicinity of the haemoglobin molecules, which are homogeneously distributed over the cytoplasm.
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Affiliation(s)
- Samer Al-Samir
- G. Gros: Zentrum Physiologie, Vegetative Physiologie 4220, Medizinische Hochschule Hannover, Carl-Neuberg-Str. 1, 30625 Hannover, Germany. ; V. Endeward: Zentrum Physiologie 4220, Medizinische Hochschule Hannover, Germany.
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18
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Garciarena CD, Youm JB, Swietach P, Vaughan-Jones RD. H⁺-activated Na⁺ influx in the ventricular myocyte couples Ca²⁺-signalling to intracellular pH. J Mol Cell Cardiol 2013; 61:51-9. [PMID: 23602948 DOI: 10.1016/j.yjmcc.2013.04.008] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/28/2013] [Revised: 04/02/2013] [Accepted: 04/03/2013] [Indexed: 12/23/2022]
Abstract
Acid extrusion on Na(+)-coupled pH-regulatory proteins (pH-transporters), Na(+)/H(+) exchange (NHE1) and Na(+)-HCO3(-) co-transport (NBC), drives Na(+) influx into the ventricular myocyte. This H(+)-activated Na(+)-influx is acutely up-regulated at pHi<7.2, greatly exceeding Na(+)-efflux on the Na(+)/K(+) ATPase. It is spatially heterogeneous, due to the co-localisation of NHE1 protein (the dominant pH-transporter) with gap-junctions at intercalated discs. Overall Na(+)-influx via NBC is considerably lower, but much is co-localised with L-type Ca(2+)-channels in transverse-tubules. Through a functional coupling with Na(+)/Ca(2+) exchange (NCX), H(+)-activated Na(+)-influx increases sarcoplasmic-reticular Ca(2+)-loading and release during intracellular acidosis. This raises Ca(2+)-transient amplitude, rescuing it from direct H(+)-inhibition. Functional coupling is biochemically regulated and linked to membrane receptors, through effects on NHE1 and NBC. It requires adequate cytoplasmic Na(+)-mobility, as NHE1 and NCX are spatially separated (up to 60μm). The relevant functional NCX activity must be close to dyads, as it exerts no effect on bulk diastolic Ca(2+). H(+)-activated Na(+)-influx is up-regulated during ischaemia-reperfusion and some forms of maladaptive hypertrophy and heart failure. It is thus an attractive system for therapeutic manipulation. This article is part of a Special Issue entitled "Na(+) Regulation in Cardiac Myocytes".
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Affiliation(s)
- Carolina D Garciarena
- Burdon Sanderson Cardiac Science Centre, Department of Physiology Anatomy & Genetics, Oxford, UK
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19
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Saegusa N, Garg V, Spitzer KW. Modulation of ventricular transient outward K⁺ current by acidosis and its effects on excitation-contraction coupling. Am J Physiol Heart Circ Physiol 2013; 304:H1680-96. [PMID: 23585132 DOI: 10.1152/ajpheart.00070.2013] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The contribution of transient outward current (Ito) to changes in ventricular action potential (AP) repolarization induced by acidosis is unresolved, as is the indirect effect of these changes on calcium handling. To address this issue we measured intracellular pH (pHi), Ito, L-type calcium current (ICa,L), and calcium transients (CaTs) in rabbit ventricular myocytes. Intracellular acidosis [pHi 6.75 with extracellular pH (pHo) 7.4] reduced Ito by ~50% in myocytes with both high (epicardial) and low (papillary muscle) Ito densities, with little effect on steady-state inactivation and activation. Of the two candidate α-subunits underlying Ito, human (h)Kv4.3 and hKv1.4, only hKv4.3 current was reduced by intracellular acidosis. Extracellular acidosis (pHo 6.5) shifted Ito inactivation toward less negative potentials but had negligible effect on peak current at +60 mV when initiated from -80 mV. The effects of low pHi-induced inhibition of Ito on AP repolarization were much greater in epicardial than papillary muscle myocytes and included slowing of phase 1, attenuation of the notch, and elevation of the plateau. Low pHi increased AP duration in both cell types, with the greatest lengthening occurring in epicardial myocytes. The changes in epicardial AP repolarization induced by intracellular acidosis reduced peak ICa,L, increased net calcium influx via ICa,L, and increased CaT amplitude. In summary, in contrast to low pHo, intracellular acidosis has a marked inhibitory effect on ventricular Ito, perhaps mediated by Kv4.3. By altering the trajectory of the AP repolarization, low pHi has a significant indirect effect on calcium handling, especially evident in epicardial cells.
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Affiliation(s)
- Noriko Saegusa
- Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City, UT 84112, USA
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20
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Regulation of ion gradients across myocardial ischemic border zones: a biophysical modelling analysis. PLoS One 2013; 8:e60323. [PMID: 23577101 PMCID: PMC3618345 DOI: 10.1371/journal.pone.0060323] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2012] [Accepted: 02/24/2013] [Indexed: 12/19/2022] Open
Abstract
The myocardial ischemic border zone is associated with the initiation and sustenance of arrhythmias. The profile of ionic concentrations across the border zone play a significant role in determining cellular electrophysiology and conductivity, yet their spatial-temporal evolution and regulation are not well understood. To investigate the changes in ion concentrations that regulate cellular electrophysiology, a mathematical model of ion movement in the intra and extracellular space in the presence of ionic, potential and material property heterogeneities was developed. The model simulates the spatial and temporal evolution of concentrations of potassium, sodium, chloride, calcium, hydrogen and bicarbonate ions and carbon dioxide across an ischemic border zone. Ischemia was simulated by sodium-potassium pump inhibition, potassium channel activation and respiratory and metabolic acidosis. The model predicted significant disparities in the width of the border zone for each ionic species, with intracellular sodium and extracellular potassium having discordant gradients, facilitating multiple gradients in cellular properties across the border zone. Extracellular potassium was found to have the largest border zone and this was attributed to the voltage dependence of the potassium channels. The model also predicted the efflux of [Formula: see text] from the ischemic region due to electrogenic drift and diffusion within the intra and extracellular space, respectively, which contributed to [Formula: see text] depletion in the ischemic region.
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21
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Garciarena CD, Ma YL, Swietach P, Huc L, Vaughan-Jones RD. Sarcolemmal localisation of Na+/H+ exchange and Na+-HCO3- co-transport influences the spatial regulation of intracellular pH in rat ventricular myocytes. J Physiol 2013; 591:2287-306. [PMID: 23420656 DOI: 10.1113/jphysiol.2012.249664] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Membrane acid extrusion by Na(+)/H(+) exchange (NHE1) and Na(+)-HCO3(-) co-transport (NBC) is essential for maintaining a low cytoplasmic [H(+)] (∼60 nm, equivalent to an intracellular pH (pHi) of 7.2). This protects myocardial function from the high chemical reactivity of H(+) ions, universal end-products of metabolism. We show here that, in rat ventricular myocytes, fluorescent antibodies map the NBC isoforms NBCe1 and NBCn1 to lateral sarcolemma, intercalated discs and transverse tubules (t-tubules), while NHE1 is absent from t-tubules. This unexpected difference matches functional measurements of pHi regulation (using AM-loaded SNARF-1, a pH fluorophore). Thus, myocyte detubulation (by transient exposure to 1.5 m formamide) reduces global acid extrusion on NBC by 40%, without affecting NHE1. Similarly, confocal pHi imaging reveals that NBC stimulation induces spatially uniform pHi recovery from acidosis, whereas NHE1 stimulation induces pHi non-uniformity during recovery (of ∼0.1 units, for 2-3 min), particularly at the ends of the cell where intercalated discs are commonly located, and where NHE1 immunostaining is prominent. Mathematical modelling shows that this induction of local pHi microdomains is favoured by low cytoplasmic H(+) mobility and long H(+) diffusion distances, particularly to surface NHE1 transporters mediating high membrane flux. Our results provide the first evidence for a spatial localisation of [H(+)]i regulation in ventricular myocytes, suggesting that, by guarding pHi, NHE1 preferentially protects gap junctional communication at intercalated discs, while NBC locally protects t-tubular excitation-contraction coupling.
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Affiliation(s)
- Carolina D Garciarena
- Burdon Sanderson Cardiac Science Centre, Department of Physiology, Anatomy and Genetics, Oxford OX1 3PT, UK
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22
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Mustafa I, Elkamel A, Lohi A, Chen P, Elnashaie SS, Ibrahim G. Application of continuation method and bifurcation for the acetylcholine neurocycle considering partial dissociation of acetic acid. Comput Chem Eng 2012. [DOI: 10.1016/j.compchemeng.2012.07.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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23
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Martin GV, Yun Y, Conforti L. Modulation of T cell activation by localized K⁺ accumulation at the immunological synapse--a mathematical model. J Theor Biol 2012; 300:173-82. [PMID: 22285786 DOI: 10.1016/j.jtbi.2012.01.018] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2011] [Revised: 12/21/2011] [Accepted: 01/11/2012] [Indexed: 01/06/2023]
Abstract
The response of T cells to antigens (T cell activation) is marked by an increase in intracellular Ca²⁺ levels. Voltage-gated and Ca²⁺-dependent K⁺ channels control the membrane potential of human T cells and regulate Ca²⁺ influx. This regulation is dependent on proper accumulation of K⁺ channels at the immunological synapse (IS) a signaling zone that forms between a T cell and antigen presenting cell. It is believed that the IS provides a site for regulation of the activation response and that K⁺ channel inhibition occurs at the IS, but the underlying mechanisms are unknown. A mathematical model was developed to test whether K⁺ efflux through K⁺ channels leads to an accumulation of K⁺ in the IS cleft, ultimately reducing K⁺ channel function and intracellular Ca²⁺ concentration ([Ca²⁺](i)). Simulations were conducted in models of resting and activated T cell subsets, which express different levels of K⁺ channels, by varying the K⁺ diffusion constant and the spatial localization of K⁺ channels at the IS. K⁺ accumulation in the IS cleft was calculated to increase K⁺ concentration ([K⁺]) from its normal value of 5.0 mM to 5.2-10.0 mM. Including K⁺ accumulation in the model of the IS reduced calculated K⁺ current by 1-12% and consequently, reduced calculated [Ca²⁺](i) by 1-28%. Significant reductions in K⁺ current and [Ca²⁺](i) only occurred in activated T cell simulations when most K⁺ channels were centrally clustered at the IS. The results presented show that the localization of K⁺ channels at the IS can produce a rise in [K⁺] in the IS cleft and lead to a substantial decrease in K⁺ currents and [Ca²⁺](i) in activated T cells thus providing a feedback inhibitory mechanism during T cell activation.
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Affiliation(s)
- Geoffrey V Martin
- Department of Internal Medicine, 231 A. Sabin Way, Division of Nephrology, University of Cincinnati, Cincinnati, OH 45267-0585, USA
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24
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Nguyen TT, Bonanno JA. Bicarbonate, NBCe1, NHE, and carbonic anhydrase activity enhance lactate-H+ transport in bovine corneal endothelium. Invest Ophthalmol Vis Sci 2011; 52:8086-93. [PMID: 21896839 DOI: 10.1167/iovs.11-8086] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE To identify and localize the monocarboxylate transporters (MCTs) expressed in bovine corneal endothelial cells (BCEC) and to test the hypothesis that buffering contributed by HCO(3)(-), sodium bicarbonate cotransporter (NBCe1), sodium hydrogen exchanger (NHE), and carbonic anhydrase (CA) activity facilitates lactate flux. METHODS MCT1-4 expression was screened by RT-PCR, Western blot analysis, and immunofluorescence. Endogenous lactate efflux and/or pH(i) were measured in BCEC in HCO(3)(-)-free or HCO(3)(-)-rich Ringer, with and without niflumic acid (MCT inhibitor), acetazolamide (ACTZ, a CA inhibitor), 5-(N-Ethyl-N-isopropyl)amiloride (EIPA) (Na(+)/H(+) exchange blocker), disodium 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (DIDS; anion transport inhibitor), or with NBCe1-specific small interfering (si) RNA-treated cells. RESULTS MCT1, 2, and 4 are expressed in BCEC. MCT1 was localized to the lateral membrane, MCT2 was lateral and apical, while MCT4 was apical. pH(i) measurements showed significant lactate-induced cell acidification (LIA) in response to 20-second pulses of lactate. Incubation with niflumic acid significantly reduced the rate of pHi change (dpH(i)/dt) and lactate-induced cell acidification. EIPA inhibited alkalinization after lactate removal. Lactate-dependent proton flux was significantly greater in the presence of HCO(3)(-) but was reduced by ACTZ. Efflux of endogenously produced lactate was significantly faster in the presence of HCO(3)(-), was greater on the apical surface, was reduced on the apical side by ACTZ, as well as on the apical and basolateral side by NBCe1-specific siRNA, DIDS, or EIPA. CONCLUSIONS MCT1, 2, and 4 are expressed in BCEC on both the apical and basolateral membrane (BL) surfaces consistent with niflumic acid-sensitive lactate-H(+) transport. Lactate dependent proton flux can activate Na(+)/H(+) exchange and be facilitated by maximizing intracellular buffering capacity through the presence of HCO(3)(-), HCO(3)(-) transport, NHE and CA activity.
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Affiliation(s)
- Tracy T Nguyen
- School of Optometry, Indiana University, Bloomington, Indiana 47405, USA
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25
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Ajiro Y, Saegusa N, Giles WR, Stafforini DM, Spitzer KW. Platelet-activating factor stimulates sodium-hydrogen exchange in ventricular myocytes. Am J Physiol Heart Circ Physiol 2011; 301:H2395-401. [PMID: 21949111 DOI: 10.1152/ajpheart.00607.2011] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Sodium-hydrogen exchanger (NHE), the principal sarcolemmal acid extruder in ventricular myocytes, is stimulated by a variety of autocrine/paracrine factors and contributes to myocardial injury and arrhythmias during ischemia-reperfusion. Platelet-activating factor (PAF; 1-o-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is a potent proinflammatory phospholipid that is released in the heart in response to oxidative stress and promotes myocardial ischemia-reperfusion injury. PAF stimulates NHE in neutrophils and platelets, but its effect on cardiac NHE (NHE1) is unresolved. We utilized quiescent guinea pig ventricular myocytes bathed in bicarbonate-free solutions and epifluorescence to measure intracellular pH (pH(i)). Methylcarbamyl-PAF (C-PAF; 200 nM), a metabolically stable analog of PAF, significantly increased steady-state pH(i). The alkalosis was completely blocked by the NHE inhibitor, cariporide, and by sodium-free bathing solutions, indicating it was mediated by NHE activation. C-PAF also significantly increased the rate of acid extrusion induced by intracellular acidosis. The ability of C-PAF to increase steady-state pH(i) was completely blocked by the PAF receptor inhibitor WEB 2086 (10 μM), indicating the PAF receptor is required. A MEK inhibitor (PD98059; 25 μM) also completely blocked the rise in pH(i) induced by C-PAF, suggesting participation of the MAP kinase signaling cascade downstream of the PAF receptor. Inhibition of PKC with GF109203X (1 μM) and chelerythrine (2 μM) did not significantly affect the alkalosis induced by C-PAF. In summary, these results provide evidence that PAF stimulates cardiac NHE1, the effect occurs via the PAF receptor, and signal relay requires participation of the MAP kinase cascade.
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Affiliation(s)
- Yoichi Ajiro
- Nora Eccles Harrison Cardiovascular Research and Training Institute, Salt Lake City, Utah, USA
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Swietach P, Camelliti P, Hulikova A, Kohl P, Vaughan-Jones RD. Spatial regulation of intracellular pH in multicellular strands of neonatal rat cardiomyocytes. Cardiovasc Res 2009; 85:729-38. [DOI: 10.1093/cvr/cvp343] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Hunter PJ, Viceconti M. The VPH-Physiome Project: Standards and Tools for Multiscale Modeling in Clinical Applications. IEEE Rev Biomed Eng 2009. [DOI: 10.1109/rbme.2009.2036204] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Vaughan-Jones RD, Spitzer KW, Swietach P. Intracellular pH regulation in heart. J Mol Cell Cardiol 2008; 46:318-31. [PMID: 19041875 DOI: 10.1016/j.yjmcc.2008.10.024] [Citation(s) in RCA: 216] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/11/2008] [Accepted: 10/11/2008] [Indexed: 12/14/2022]
Abstract
Intracellular pH (pHi) is an important modulator of cardiac excitation and contraction, and a potent trigger of electrical arrhythmia. This review outlines the intracellular and membrane mechanisms that control pHi in the cardiac myocyte. We consider the kinetic regulation of sarcolemmal H+, OH- and HCO3- transporters by pH, and by receptor-coupled intracellular signalling systems. We also consider how activity of these pHi effector proteins is coordinated spatially in the myocardium by intracellular mobile buffer shuttles, gap junctional channels and carbonic anhydrase enzymes. Finally, we review the impact of pHi regulatory proteins on intracellular Ca2+ signalling, and their participation in clinical disorders such as myocardial ischaemia, maladaptive hypertrophy and heart failure. Such multiple effects emphasise the fundamental role that pHi regulation plays in the heart.
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Affiliation(s)
- Richard D Vaughan-Jones
- Burdon Sanderson Cardiac Science Centre, Department of Physiology, Anatomy and Genetics, Oxford, Parks Road, OX1 3PT, UK.
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Melkikh AV, Sutormina MI. Model of active transport of ions in cardiac cell. J Theor Biol 2008; 252:247-54. [PMID: 18353373 DOI: 10.1016/j.jtbi.2008.02.006] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2007] [Revised: 02/04/2008] [Accepted: 02/05/2008] [Indexed: 10/22/2022]
Abstract
A model of the active transport of ions in a cardiac muscle cell, which takes into account the active transport of Na(+), K(+), Ca(2+), Mg(2+), HCO(3)(-) and Cl(-) ions, has been constructed. The model allows independent calculations of the resting potential at the biomembrane and concentrations of basic ions (sodium, potassium, chlorine, magnesium and calcium) in a cell. For the analysis of transport processes in cardiac cell hierarchical algorithm "one ion-one transport system" was offered. The dependence of the resting potential on concentrations of the ions outside a cell has been established. It was shown, that ions of calcium and magnesium, despite their rather small concentration, play an essential role in maintenance of resting potential in cardiac cell. The calculated internal concentrations of ions are in good agreement with the corresponding experimental values.
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Affiliation(s)
- A V Melkikh
- Molecular Physics Chair, Ural State Technical University, 19 Mira Street, Yekaterinburg, Russia.
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Measuring and modeling chloride-hydroxyl exchange in the Guinea-pig ventricular myocyte. Biophys J 2007; 94:2385-403. [PMID: 18055536 DOI: 10.1529/biophysj.107.118885] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Protons are powerful modulators of cardiac function. Their intracellular concentration is regulated by sarcolemmal ion transporters that export or import H+-ions (or their ionic equivalent: HCO3-, OH-). One such transporter, which imports H+-equivalents, is a putative Cl-/OH- exchanger (CHE). A strong candidate for CHE is SLC26A6 protein, a product of the SLC26A gene family of anion transporters, which has been detected in murine heart. SLC26A6 protein is suggested to be an electrogenic 1Cl-/2OH-(2HCO3-) exchanger. Unfortunately, there is insufficient characterization of cardiac CHE against which the properties of heterologously expressed SLC26A6 can be matched. We therefore investigated the proton, Cl-, and voltage dependence of CHE activity in guinea-pig ventricular myocytes, using voltage-clamp, intracellular pH fluorescence, and mathematical modeling techniques. We find that CHE activity is tightly regulated by intracellular and extracellular pH, is voltage-insensitive over a wide range (+/-80 mV), and displays substrate dependence suggestive of electroneutral 1Cl-/1OH- exchange. These properties exclude electrogenic SLC26A6 as sole contributor to CHE. Either the SLC26A6 product in heart is electroneutral, or CHE comprises at least two transporters with oppositely balanced voltage sensitivity. Alternatively, CHE may comprise an H+-Cl- coinflux system, which cannot be distinguished kinetically from an exchanger. Irrespective of ionic mechanism, CHE's pH sensitivity helps to define resting intracellular pH, and hence basal function in the heart.
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Abstract
H(+) ions are powerful modulators of cardiac function, liberated during metabolic activity. Among their physiological effects is a chemical gating of cell-to-cell communication, caused by H(+)-mediated closure of connexin (Cx) channels at gap junctions. This protects surrounding tissue from the damaging effects of local intracellular acidosis. Cx proteins (largely Cx-43 in ventricle) form multimeric pores between cells, permitting translocation of ions and other solutes up to approximately 1 kDa. The channels are essential for electrical and metabolic coordination of a tissue. Here we demonstrate that, contrary to expectation, H(+) ions can induce an increase of gap-junctional permeability. This occurs during modest intracellular acid loads in myocyte pairs isolated from mammalian ventricle. We show that the increase in permeability allows a local rise of [H(+)](i) to dissipate into neighboring myocytes, thereby providing a mechanism for spatially regulating intracellular pH (pH(i)). During larger acid loads, the increased permeability is overridden by a more familiar H(+)-dependent inhibition (H(+) inactivation). This restricts cell-to-cell H(+) movement, while allowing sarcolemmal H(+) transporters such as Na(+)/H(+) exchange, to extrude the acid from the cell. The H(+) sensitivity of Cx channels therefore defines whether junctional or sarcolemmal mechanisms are selected locally for the removal of an acid load. The bell-shaped pH dependence of permeability suggests that, in addition to H(+) inactivation, an H(+) activation process regulates the ensemble of Cx channels open at the junction. As well as promoting spatial pH(i) regulation, H(+) activation of junctional permeability may link increased metabolic activity to improved myocardial coupling, the better to meet mechanical demand.
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Affiliation(s)
- Pawel Swietach
- The Burdon Sanderson Cardiac Science Centre, Department of Physiology, Anatomy and Genetics, University of Oxford, UK
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Yamamoto T, Shirayama T, Sakatani T, Takahashi T, Tanaka H, Takamatsu T, Spitzer KW, Matsubara H. Enhanced activity of ventricular Na+-HCO3- cotransport in pressure overload hypertrophy. Am J Physiol Heart Circ Physiol 2007; 293:H1254-64. [PMID: 17416604 DOI: 10.1152/ajpheart.00964.2006] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The Na(+)-HCO(3)(-) cotransporter (NBC) plays a key role in intracellular pH (pH(i)) regulation in normal ventricular muscle. However, the state of NBC in nonischemic hypertrophied hearts is unresolved. In this study, we examined functional and molecular properties of NBC in adult rat ventricular myocytes. The cells were enzymatically isolated from both normal and hypertrophied hearts. Ventricular hypertrophy was induced by pressure overload created by suprarenal abdominal aortic constriction of 50% for 7 wk. pH(i) was measured in single cells using the fluorescent pH indicator 2',7'-bis(2-carboxyethyl)5-(6)carboxyfluorescein. Real-time PCR analysis was used to quantitatively assess expression of NBC-encoding mRNA, including SLC4A4 (encoding electrogenic NBC, NBCe1) and SLC4A7 (electroneutral NBC, NBCn1). Our results demonstrate that: 1) mRNA levels of both the electrogenic NBCe1 (SLC4A4) and electroneutral NBCn1 (SLC4A7) forms of NBC were increased by aortic constriction, 2) the onset of NBC upregulation occurred within 3 days after constriction, 3) normal and hypertrophied ventricles displayed regional differences in NBC expression, 4) acid extrusion via NBC (J(NBC)) was increased significantly in hypertrophied myocytes, 5) although acid extrusion via Na(+)/H(+) exchange was also increased in hypertrophied myocytes, the relative enhancement of J(NBC) was larger, 6) membrane depolarization markedly increased J(NBC) in hypertrophied myocytes, and 7) losartan, an ANG II AT(1) receptor antagonist, significantly attenuated the upregulation of both NBCs induced by 3 wk of aortic constriction. Enhanced NBC activity during hypertrophic development provides a mechanism for intracellular Na(+) overload, which may render the ventricles more vulnerable to Ca(2+) overload during ischemia-reperfusion.
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MESH Headings
- Angiotensin II Type 1 Receptor Blockers/pharmacology
- Animals
- Aorta, Abdominal/surgery
- Disease Models, Animal
- Heart Ventricles/metabolism
- Hydrogen-Ion Concentration
- Hypertension/complications
- Hypertension/genetics
- Hypertension/metabolism
- Hypertrophy, Left Ventricular/etiology
- Hypertrophy, Left Ventricular/genetics
- Hypertrophy, Left Ventricular/metabolism
- Ligation
- Losartan/pharmacology
- Male
- Membrane Potentials
- Myocytes, Cardiac/drug effects
- Myocytes, Cardiac/metabolism
- RNA, Messenger/metabolism
- Rats
- Rats, Wistar
- Sodium-Bicarbonate Symporters/genetics
- Sodium-Bicarbonate Symporters/metabolism
- Sodium-Potassium-Exchanging ATPase/metabolism
- Time Factors
- Transcription, Genetic/drug effects
- Up-Regulation
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Affiliation(s)
- Taku Yamamoto
- Department of Cardiology and Vascular Regenerative Medicine, Kyoto Prefectural University of Medicine, Kawaramachi-Hirokoji, Kamigyo-ku, Kyoto 602-8566, Japan.
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Kemi OJ, Arbo I, Høydal MA, Loennechen JP, Wisløff U, Smith GL, Ellingsen Ø. Reduced pH and contractility in failing rat cardiomyocytes. Acta Physiol (Oxf) 2006; 188:185-93. [PMID: 17054658 DOI: 10.1111/j.1748-1716.2006.01621.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
AIM To determine whether reduced cardiomyocyte contractility in heart failure is associated with reduced intracellular pH (pH(i)). Involvement of the Na(+)/H(+) exchanger and the H(+)/K(+) ATPase were investigated with specific blockers. METHODS Myocardial infarction and subsequent heart failure in Sprague-Dawley rats were induced by chronic occlusion of the left coronary artery. 6 weeks post-ligation, contractility (cell shortening) and pH(i) (BCECF fluorescence) were recorded in freshly dissociated cardiomyocytes during 2-10 Hz electrical stimulation, with or without either Na(+)/H(+) exchanger or H(+)/K(+) ATPase inhibition. RESULTS Elevated end-diastolic and reduced peak systolic pressures confirmed heart failure. Increased heart weights (20-30%; P < or = 0.01) and cardiomyocyte lengths and widths (22-25%; P < or = 0.01) confirmed substantial cardiac hypertrophy. In myocytes isolated from sham operated rats, a positive staircase response occurred with stimulation rates from 2 to 7 Hz; further increases in stimulation rate up to 10 Hz reduced contractility. In contrast, pH(i) fell progressively over the entire stimulation range. In failing myocytes, pH(i) was consistently 0.07 pH units lower and contractility 40% lower (P < or = 0.01) than sham control values; the shape of the contractility staircase remained similar to controls. At all stimulation frequencies, Na(+)/H(+) exchanger inhibition reduced pH(i) by 0.05 pH units (P < or = 0.01) and contractility by 22% (P < or = 0.05) in cardiomyocytes from the heart failure group. A significantly smaller decrease of pH(i) and reduction in contractility was observed after inhibition of Na(+)/H(+) exchanger (10 micro m HOE694) in sham myocytes. H(+)/K(+) ATPase inhibition (100 micro m SCH28080) had no effect on pH(i). CONCLUSION Reduced pH(i) is accompanied by reduced cardiomyocyte contractility in isolated myocytes from post-MI heart failure. The data suggest compensatory Na(+)/H(+) exchanger activation in heart failure, whereas H(+)/K(+) ATPase does not appear to contribute significantly to pH(i) maintenance.
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Affiliation(s)
- O J Kemi
- Department of Circulation and Medical Imaging, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway
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Swietach P, Spitzer KW, Vaughan-Jones RD. pH-Dependence of extrinsic and intrinsic H(+)-ion mobility in the rat ventricular myocyte, investigated using flash photolysis of a caged-H(+) compound. Biophys J 2006; 92:641-53. [PMID: 17056723 PMCID: PMC1751406 DOI: 10.1529/biophysj.106.096560] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Passive H(+)-ion mobility within eukaryotic cells is low, due to H(+)-ion binding to cytoplasmic buffers. A localized intracellular acidosis can therefore persist for seconds or even minutes. Because H(+)-ions modulate so many biological processes, spatial intracellular pH (pH(i))-regulation becomes important for coordinating cellular activity. We have investigated spatial pH(i)-regulation in single and paired ventricular myocytes from rat heart by inducing a localized intracellular acid-load, while confocally imaging pH(i) using the pH-fluorophore, carboxy-SNARF-1. We present a novel method for localizing the acid-load. This involves the intracellular photolytic uncaging of H(+)-ions from a membrane-permeant acid-donor, 2-nitrobenzaldehyde. The subsequent spatial pH(i)-changes are consistent with intracellular H(+)-mobility and cell-to-cell H(+)-permeability constants measured using more conventional acid-loading techniques. We use the method to investigate the effect of reducing pH(i) on intrinsic (non-CO(2)/HCO(3)(-) buffer-dependent) and extrinsic (CO(2)/HCO(3)(-) buffer-dependent) components of H(i)(+)-mobility. We find that although both components mediate spatial regulation of pH within the cell, their ability to do so declines sharply at low pH(i). Thus acidosis severely slows intracellular H(+)-ion movement. This can result in spatial pH(i) nonuniformity, particularly during the stimulation of sarcolemmal Na(+)-H(+) exchange. Intracellular acidosis thus presents a window of vulnerability in the spatial coordination of cellular function.
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Affiliation(s)
- Pawel Swietach
- Burdon Sanderson Cardiac Science Centre, Department of Physiology, Anatomy and Genetics, Oxford University, Oxford, United Kingdom
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Plant LD, Bowers PN, Liu Q, Morgan T, Zhang T, State MW, Chen W, Kittles RA, Goldstein SAN. A common cardiac sodium channel variant associated with sudden infant death in African Americans, SCN5A S1103Y. J Clin Invest 2006; 116:430-5. [PMID: 16453024 PMCID: PMC1359045 DOI: 10.1172/jci25618] [Citation(s) in RCA: 169] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2005] [Accepted: 10/25/2005] [Indexed: 12/11/2022] Open
Abstract
Thousands die each year from sudden infant death syndrome (SIDS). Neither the cause nor basis for varied prevalence in different populations is understood. While 2 cases have been associated with mutations in type Valpha, cardiac voltage-gated sodium channels (SCN5A), the "Back to Sleep" campaign has decreased SIDS prevalence, consistent with a role for environmental influences in disease pathogenesis. Here we studied SCN5A in African Americans. Three of 133 SIDS cases were homozygous for the variant S1103Y. Among controls, 120 of 1,056 were carriers of the heterozygous genotype, which was previously associated with increased risk for arrhythmia in adults. This suggests that infants with 2 copies of S1103Y have a 24-fold increased risk for SIDS. Variant Y1103 channels were found to operate normally under baseline conditions in vitro. As risk factors for SIDS include apnea and respiratory acidosis, Y1103 and wild-type channels were subjected to lowered intracellular pH. Only Y1103 channels gained abnormal function, demonstrating late reopenings suppressible by the drug mexiletine. The variant appeared to confer susceptibility to acidosis-induced arrhythmia, a gene-environment interaction. Overall, homozygous and rare heterozygous SCN5A missense variants were found in approximately 5% of cases. If our findings are replicated, prospective genetic testing of SIDS cases and screening with counseling for at-risk families warrant consideration.
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Affiliation(s)
- Leigh D Plant
- Department of Pediatrics and Institute for Molecular Pediatric Sciences, Pritzker School of Medicine, Biological Sciences Division, University of Chicago, Chicago, Illinois 60637, USA
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Crampin EJ, Smith NP. A dynamic model of excitation-contraction coupling during acidosis in cardiac ventricular myocytes. Biophys J 2006; 90:3074-90. [PMID: 16473911 PMCID: PMC1432112 DOI: 10.1529/biophysj.105.070557] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Acidosis in cardiac myocytes is a major factor in the reduced inotropy that occurs in the ischemic heart. During acidosis, diastolic calcium concentration and the amplitude of the calcium transient increase, while the strength of contraction decreases. This has been attributed to the inhibition by protons of calcium uptake and release by the sarcoplasmic reticulum, to a rise of intracellular sodium caused by activation of sodium-hydrogen exchange, decreased calcium binding affinity to Troponin-C, and direct effects on the contractile machinery. The relative contributions and concerted action of these effects are, however, difficult to establish experimentally. We have developed a mathematical model to examine altered calcium-handling mechanisms during acidosis. Each of the alterations was incorporated into a dynamical model of pH regulation and excitation-contraction coupling to predict the time courses of key ionic species during acidosis, in particular intracellular pH, sodium and the calcium transient, and contraction. This modeling study suggests that the most significant effects are elevated sodium, inhibition of sodium-calcium exchange, and the direct interaction of protons with the contractile machinery; and shows how the experimental data on these contributions can be reconciled to understand the overall effects of acidosis in the beating heart.
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Affiliation(s)
- Edmund J Crampin
- Bioengineering Institute and Department of Engineering Science, University of Auckland, Auckland, New Zealand.
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Pantazis A, Keegan P, Postma M, Schwiening CJ. The effect of neuronal morphology and membrane-permeant weak acid and base on the dissipation of depolarization-induced pH gradients in snail neurons. Pflugers Arch 2005; 452:175-87. [PMID: 16341877 DOI: 10.1007/s00424-005-0019-4] [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: 06/22/2005] [Revised: 09/15/2005] [Accepted: 10/26/2005] [Indexed: 10/25/2022]
Abstract
Neuronal depolarization causes larger intracellular pH (pH(i)) shifts in axonal and dendritic regions than in the cell body. In this paper, we present evidence relating the time for collapse of these gradients to neuronal morphology. We have used ratiometric pH(i) measurements using 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) in whole-cell patch-clamped snail neurons to study the collapse of longitudinal pH gradients. Using depolarization to open voltage-gated proton channels, we produced alkaline pH(i) microdomains. In the absence of added mobile buffers, facilitated H(+) diffusion down the length of the axon plays a critical role in determining pH(i) microdomain lifetime, with axons of approximately 100 microm allowing pH differences to be maintained for >60 s. An application of mobile, membrane-permeant pH buffers accelerated the collapse of the alkaline-pH gradients but, even at 30 mM, was unable to abolish them. Modeling of the pH(i) dynamics showed that both the relatively weak effect of the weak acid/base on the peak size of the pH gradient and the accelerated collapse of the pH gradient could be due to the time taken for equilibration of the weak acid and base across the cell. We propose that appropriate weak acid/base mixes may provide a simple method for studying the role of local pH(i) signals without perturbing steady-state pH(i). Furthermore, an extrapolation of our in vitro data to longer and thinner neuronal structures found in the mammalian nervous system suggests that dendritic and axonal pH(i) are likely to be dominated by local pH(i)-regulating mechanisms rather than simply following the soma pH(i).
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Affiliation(s)
- A Pantazis
- Department of Anatomy, University of Cambridge, Downing Street, Cambridge CB2 3DY, UK
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Schwab A, Rossmann H, Klein M, Dieterich P, Gassner B, Neff C, Stock C, Seidler U. Functional role of Na+-HCO3- cotransport in migration of transformed renal epithelial cells. J Physiol 2005; 568:445-58. [PMID: 16037087 PMCID: PMC1474735 DOI: 10.1113/jphysiol.2005.092957] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Revised: 06/19/2005] [Accepted: 07/19/2005] [Indexed: 11/08/2022] Open
Abstract
Cell migration is crucial for immune defence, wound healing or formation of tumour metastases. It has been shown that the activity of the Na(+)-H(+) exchanger (NHE1) plays an important role in cell migration. However, so far it is unknown whether Na(+)- HCO(3)(-) cotransport (NBC), which has similar functions in the regulation of intracellular pH (pH(i)) as NHE1, is also involved in cell migration. We therefore isolated NHE-deficient Madin-Darby canine kidney (MDCK-F) cells and tested whether NBC compensates for NHE in pH(i) and cell volume regulation as well as in migration. Intracellular pH was measured with the fluorescent pH indicator 2'7'-bis(carboxyethyl)-5-carboxyfluorescein (BCECF). The expression of NBC isoforms was determined with semiquantitative PCR. Migration was monitored with time-lapse video microscopy and quantified as the displacement of the cell centre. We found that MDCK-F cells express the isoform NBC1 (SLCA4A gene product) at a much higher level than the isoform kNBC3 (SLCA4A8 gene product). This difference is even more pronounced in NHE-deficient cells so that NBC1 is likely to be the major acid extruder in these cells and the major mediator of propionate-induced cell volume increase. NHE-deficient MDCK-F cells migrate more slowly than normal MDCK-F cells. NBC activity promotes migration during an acute intracellular acid load and increases migratory speed and displacement on a short timescale (< 30 min) whereas it has no effect on the long-term behaviour of migrating MDCK-F cells. Taken together, our results show that NBC actvity, despite many functional similarities, does not have the same importance for cell migration as NHE1 activity.
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Affiliation(s)
- A Schwab
- Institute of Physiology II, Münster, Germany.
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Swietach P, Vaughan-Jones RD. Relationship between intracellular pH and proton mobility in rat and guinea-pig ventricular myocytes. J Physiol 2005; 566:793-806. [PMID: 15919716 PMCID: PMC1464772 DOI: 10.1113/jphysiol.2005.086165] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Intracellular H+ ion mobility in eukaryotic cells is low because of intracellular buffering. We have investigated whether Hi+ mobility varies with pHi. A dual microperfusion apparatus was used to expose guinea-pig or rat myocytes to small localized doses (3-5 mm) of ammonium chloride (applied in Hepes-buffered solution). Intracellular pH (pHi) was monitored confocally using the fluorescent dye, carboxy-SNARF-1. Local ammonium exposure produced a stable, longitudinal pHi gradient. Its size was fed into a look-up table (LUT) to give an estimate of the apparent intracellular proton diffusion coefficient (D(app)H). LUTs were generated using a diffusion-reaction model of Hi+ mobility based on intracellular buffer diffusion. To examine the pHi sensitivity of D(app)H, whole-cell pHi was initially displaced using a whole-cell ammonium or acetate prepulse, before locally applying the low dose of ammonium. In both rat and guinea-pig, D(app)H decreased with pHi over the range 7.5-6.5. In separate pipette-loading experiments, the intracellular diffusion coefficient for carboxy-SNARF-1 (a mobile-buffer analogue) exhibited no significant pHi dependence. The pHi sensitivity of D(app)H is thus likely to be governed by the mobile fraction of intrinsic buffering capacity. These results reinforce the buffer hypothesis of Hi+ mobility. The pHi dependence of D(app)H was used to characterize the mobile and fixed buffer components, and to estimate D(mob) (the average diffusion coefficient for intracellular mobile buffer). One consequence of a decline in Hi+ mobility at low pHi is that it will predispose the myocardium to pHi nonuniformity. The physiological relevance of this is discussed.
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Affiliation(s)
- Pawel Swietach
- Burdon Sanderson Cardiac Science Centre, University Laboratory of Physiology, Oxford OX1 3PT, UK
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40
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Swietach P, Leem CH, Spitzer KW, Vaughan-Jones RD. Experimental generation and computational modeling of intracellular pH gradients in cardiac myocytes. Biophys J 2005; 88:3018-37. [PMID: 15653720 PMCID: PMC1305395 DOI: 10.1529/biophysj.104.051391] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
It is often assumed that pH(i) is spatially uniform within cells. A double-barreled microperfusion system was used to apply solutions of weak acid (acetic acid, CO(2)) or base (ammonia) to localized regions of an isolated ventricular myocyte (guinea pig). A stable, longitudinal pH(i) gradient (up to 1 pH(i) unit) was observed (using confocal imaging of SNARF-1 fluorescence). Changing the fractional exposure of the cell to weak acid/base altered the gradient, as did changing the concentration and type of weak acid/base applied. A diffusion-reaction computational model accurately simulated this behavior of pH(i). The model assumes that H(i)(+) movement occurs via diffusive shuttling on mobile buffers, with little free H(+) diffusion. The average diffusion constant for mobile buffer was estimated as 33 x 10(-7) cm(2)/s, consistent with an apparent H(i)(+) diffusion coefficient, D(H)(app), of 14.4 x 10(-7) cm(2)/s (at pH(i) 7.07), a value two orders of magnitude lower than for H(+) ions in water but similar to that estimated recently from local acid injection via a cell-attached glass micropipette. We conclude that, because H(i)(+) mobility is so low, an extracellular concentration gradient of permeant weak acid readily induces pH(i) nonuniformity. Similar concentration gradients for weak acid (e.g., CO(2)) occur across border zones during regional myocardial ischemia, raising the possibility of steep pH(i) gradients within the heart under some pathophysiological conditions.
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Affiliation(s)
- Pawel Swietach
- Burdon Sanderson Cardiac Science Centre, University Laboratory of Physiology, Oxford OX1 3PT, UK
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Yamamoto T, Swietach P, Rossini A, Loh SH, Vaughan-Jones RD, Spitzer KW. Functional diversity of electrogenic Na+-HCO3- cotransport in ventricular myocytes from rat, rabbit and guinea pig. J Physiol 2004; 562:455-75. [PMID: 15550467 PMCID: PMC1665517 DOI: 10.1113/jphysiol.2004.071068] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
The Na(+)-HCO(3)(-) cotransporter (NBC) is an important sarcolemmal acid extruder in cardiac muscle. The characteristics of NBC expressed functionally in heart are controversial, with reports suggesting electroneutral (NBCn; 1HCO(3)(-) : 1Na(+); coupling coefficient N= 1) or electrogenic forms of the transporter (NBCe; equivalent to 2HCO(3)(-) : 1Na(+); N= 2). We have used voltage-clamp and epifluorescence techniques to compare NBC activity in isolated ventricular myocytes from rabbit, rat and guinea pig. Depolarization (by voltage clamp or hyperkalaemia) reversibly increased steady-state pH(i) while hyperpolarization decreased it, effects seen only in CO(2)/HCO(3)(-)-buffered solutions, and blocked by S0859 (cardiac NBC inhibitor). Species differences in amplitude of these pH(i) changes were rat > guinea pig approximately rabbit. Tonic depolarization (-140 mV to -0 mV) accelerated NBC-mediated pH(i) recovery from an intracellular acid load. At 0 mV, NBC-mediated outward current at resting pH(i) was +0.52 +/- 0.05 pA pF(-1) (rat, n= 5), +0.26 +/- 0.05 pA pF(-1) (guinea pig, n= 5) and +0.10 +/- 0.03 pA pF(-1) (rabbit, n= 9), with reversal potentials near -100 mV, consistent with N= 2. The above results indicate a functionally active voltage-sensitive NBCe in these species. Voltage-clamp hyperpolarization negative to the reversal potential for NBCe failed, however, to terminate or reverse NBC-mediated pH(i)-recovery from an acid load although it was slowed significantly, suggesting electroneutral NBC may also be operational. NBC-mediated pH(i) recovery was associated with a rise of [Na(+)](i) at a rate approximately 25% of that mediated via NHE, and consistent with an apparent NBC stoichiometry between N= 1 and N= 2. In conclusion, NBCe in the ventricular myocyte displays considerable functional variation among the three species tested (greatest in rat, least in rabbit) and may coexist with some NBCn activity.
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Affiliation(s)
- Taku Yamamoto
- Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City, UT 84112, USA.
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Swietach P, Vaughan-Jones RD. Novel method for measuring junctional proton permeation in isolated ventricular myocyte cell pairs. Am J Physiol Heart Circ Physiol 2004; 287:H2352-63. [PMID: 15242838 DOI: 10.1152/ajpheart.00528.2004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Partial exposure of single ventricular myocytes to membrane-permeant weak acids or bases, using a dual-microperfusion technique, generates large and stable intracellular pH (pHi) gradients. In this study, we have investigated the feasibility of using the technique to estimate junctional proton permeability. This was done by recording the pHi gradient developed across the junctional region of a pair of conjoined ventricular myocytes, isolated enzymically from a guinea pig heart when one of the cells was partially exposed to acetate or ammonium. We show that under HEPES-buffered conditions, the junctional discontinuity in the pHi profile can be used to derive an apparent proton permeability coefficient (PHapp). The mean PHapp obtained was 4.45 +/- 0.21.10(-4) cm/s (n=43) at an average junctional pHi of 7.04 +/- 0.02. In the presence of the junctional inhibitor alpha-glycyrrhetinic acid, exposure of the proximal cell to weak acid or base produced no pHi change in the distal cell, confirming that distal changes were normally caused by acid-base flux through connexons assembled into junctional channels. The validity of the dual-microperfusion method was tested further by using a diffusion-permeation-reaction model for intracellular protons, designed to highlight possible errors in the estimates of PHapp. Our technique for measuring PHapp provides a useful alternative to the previous, more invasive technique of locally loading acid through a cell-attached patch pipette. The technique may provide a simple method for investigating the factors regulating cell-to-cell proton transmission.
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Affiliation(s)
- Pawel Swietach
- Burdon Sanderson Cardiac Science Centre, Univ. Laboratory of Physiology, Oxford OX1 3PT, UK
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43
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Loiselle FB, Morgan PE, Alvarez BV, Casey JR. Regulation of the human NBC3 Na+/HCO3- cotransporter by carbonic anhydrase II and PKA. Am J Physiol Cell Physiol 2004; 286:C1423-33. [PMID: 14736710 DOI: 10.1152/ajpcell.00382.2003] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Human NBC3 is an electroneutral Na(+)/HCO(3)(-) cotransporter expressed in heart, skeletal muscle, and kidney in which it plays an important role in HCO(3)(-) metabolism. Cytosolic enzyme carbonic anhydrase II (CAII) catalyzes the reaction CO(2) + H(2)O left arrow over right arrow HCO(3)(-) + H(+) in many tissues. We investigated whether NBC3, like some Cl(-)/HCO(3)(-) exchange proteins, could bind CAII and whether PKA could regulate NBC3 activity through modulation of CAII binding. CAII bound the COOH-terminal domain of NBC3 (NBC3Ct) with K(d) = 101 nM; the interaction was stronger at acid pH. Cotransfection of HEK-293 cells with NBC3 and CAII recruited CAII to the plasma membrane. Mutagenesis of consensus CAII binding sites revealed that the D1135-D1136 region of NBC3 is essential for CAII/NBC3 interaction and for optimal function, because the NBC3 D1135N/D1136N retained only 29 +/- 22% of wild-type activity. Coexpression of the functionally dominant-negative CAII mutant V143Y with NBC3 or addition of 100 microM 8-bromoadenosine to NBC3 transfected cells reduced intracellular pH (pH(i)) recovery rate by 31 +/- 3, or 38 +/- 7%, respectively, relative to untreated NBC3 transfected cells. The effects were additive, together decreasing the pH(i) recovery rate by 69 +/- 12%, suggesting that PKA reduces transport activity by a mechanism independently of CAII. Measurements of PKA-dependent phosphorylation by mass spectroscopy and labeling with [gamma-(32)P]ATP showed that NBC3Ct was not a PKA substrate. These results demonstrate that NBC3 and CAII interact to maximize the HCO(3)(-) transport rate. Although PKA decreased NBC3 transport activity, it did so independently of the NBC3/CAII interaction and did not involve phosphorylation of NBC3Ct.
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Affiliation(s)
- Frederick B Loiselle
- Canadian Institute of Health Research Membrane Protein Research Group, Department of Physiology, University of Alberta, Edmonton, Canada T6G 2H7
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Ch'en FFT, Dilworth E, Swietach P, Goddard RS, Vaughan-Jones RD. Temperature dependence of Na+-H+ exchange, Na+-HCO3- co-transport, intracellular buffering and intracellular pH in guinea-pig ventricular myocytes. J Physiol 2003; 552:715-26. [PMID: 12923205 PMCID: PMC2343456 DOI: 10.1113/jphysiol.2003.051888] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Revised: 07/24/2003] [Accepted: 08/15/2003] [Indexed: 12/14/2022] Open
Abstract
Almost all aspects of cardiac function are sensitive to modest changes of temperature. We have examined the thermal sensitivity of intracellular pH regulation in the heart. To do this we determined the temperature sensitivity of pHi, intracellular buffering capacity, and the activity of sarcolemmal acid-extrusion proteins, Na+-H+ exchange (NHE) and Na+-HCO3- co-transport (NBC) in guinea-pig isolated ventricular myocytes. pHi was recorded fluorimetrically with acetoxymethyl (AM)-loaded carboxy-SNARF-1 at either 27 or 37 degrees C. At 27 degrees C, intrinsic (non-CO2-dependent) buffering power (betai) was approximately 60% of that at 37 degrees C. Acid-extrusion (Je) through NHE was approximately 50% slower than at 37 degrees C, consistent with a Q10 of approximately 2. In 5% CO2/HCO3--buffered conditions, in the presence of 30 microM cariporide to inhibit NHE, acid extrusion via NBC was also slowed at 27 degrees C, suggestive of a comparable Q10. Resting pHi at 27 degrees C was similar in Hepes- or 5% CO2/HCO3--buffered superfusates but, in both cases, was approximately 0.1 pH units lower at 37 degrees C. The higher the starting pHi, the larger was the thermally induced fall of pHi, consistent with a mathematical model where intrinsic buffers with a low principal pKa (e.g. close to 6.0) are less temperature-sensitive than those with a higher pKa. The high temperature sensitivity of pHi regulation in mammalian cardiac cells has implications for experimental work conducted at room temperature. It also has implications for the ability of intracellular acidosis to generate intracellular Na+ and Ca2+ overload, cardiac injury and arrhythmia in the heart.
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Affiliation(s)
- Frederick F-T Ch'en
- Burdon Sanderson Cardiac Science Centre, University Laboratory of Physiology, University of Oxford, Parks Road, Oxford OX1 3PT, UK
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Abstract
Although protons can directly or indirectly gate solute permeability of the myocardial gap junction, there is little information regarding their own permeation, despite their importance in the regulation of myocardial contractility and rhythm. By pipette-loading of acid into guinea pig isolated, ventricular myocyte pairs while imaging pH(i) confocally using SNARF fluorescence, we have observed that protons permeate the junctional region. Permeation is inhibited by glycyrrhetinic acid, an agent that also increases intercellular electrical resistance, suggesting H+ permeation via gap junctions. The rate of spread of acid between cells appears to be limited by junctional permeation rather than by cytoplasmic diffusion. Mathematical analyses, combined with experiments using SNARF as a proton carrier, suggest that gap junctional H+ transmission may be accomplished physiologically by the permeation of intrinsic "proton-porter" molecules. We propose that proton flux through gap junctions will contribute to the dissipation of regional acid loads within the myocardium. This represents a mechanism for the local control of myocardial pH(i).
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Affiliation(s)
- Massimiliano Zaniboni
- Burdon Sanderson Cardiac Science Centre, University Laboratory of Physiology, Parks Road, Oxford OX1 3PT, UK
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