1
|
Di Mattia RA, Diaz-Zegarra LA, Blanco PG, Valverde CA, Gonano LA, Jaquenod De Giusti C, Portiansky EL, Vila-Petroff MG, Aiello EA, Orlowski A. The specific inhibition of the cardiac electrogenic sodium/bicarbonate cotransporter leads to cardiac hypertrophy. Life Sci 2022; 312:121219. [PMID: 36435222 DOI: 10.1016/j.lfs.2022.121219] [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: 05/17/2022] [Revised: 11/10/2022] [Accepted: 11/20/2022] [Indexed: 11/24/2022]
Abstract
Two alkalinizing mechanisms coexist in cardiac myocytes to maintain intracellular pH: sodium/bicarbonate cotransporter (electroneutral isoform NBCn1 and electrogenic isoform NBCe1) and sodium/proton exchanger (NHE1). Dysfunction of these transporters has previously been reported to be responsible for the development of cardiovascular diseases. The aim of this study was to evaluate the contribution of the downregulation of the NBCe1 to the development of cardiac hypertrophy. To specifically reduce NBCe1 expression, we cloned shRNA into a cardiotropic adeno-associated vector (AAV9-shNBCe1). After 28 days of being injected with AAV9-shNBCe1, the expression and the activity of NBCe1 in the rat heart were reduced. Strikingly, downregulation of NBCe1 causes significant hypertrophic heart growth, lengthening of the action potential in isolated myocytes, an increase in the duration of the QT interval and an increase in the frequency of Ca2+ waves without any significant changes in Ca2+ transients. An increased compensatory expression of NBCn1 and NHE1 was also observed. We conclude that reduction of NBCe1 is sufficient to induce cardiac hypertrophy and modify the electrical features of the rat heart.
Collapse
Affiliation(s)
- R A Di Mattia
- Centro de Investigaciones Cardiovasculares "Dr. Horacio Cingolani", Facultad de Ciencias Médicas, Universidad Nacional de La Plata, CONICET, La Plata, Argentina
| | - L A Diaz-Zegarra
- Centro de Investigaciones Cardiovasculares "Dr. Horacio Cingolani", Facultad de Ciencias Médicas, Universidad Nacional de La Plata, CONICET, La Plata, Argentina
| | - P G Blanco
- Centro de Fisiología Reproductiva & Métodos Complementarios de Diagnóstico (CEFIRE & MECODIAG), Facultad de Ciencias Veterinarias, Universidad Nacional de La Plata, CONICET, La Plata, Argentina
| | - C A Valverde
- Centro de Investigaciones Cardiovasculares "Dr. Horacio Cingolani", Facultad de Ciencias Médicas, Universidad Nacional de La Plata, CONICET, La Plata, Argentina
| | - L A Gonano
- Centro de Investigaciones Cardiovasculares "Dr. Horacio Cingolani", Facultad de Ciencias Médicas, Universidad Nacional de La Plata, CONICET, La Plata, Argentina
| | - C Jaquenod De Giusti
- Centro de Investigaciones Cardiovasculares "Dr. Horacio Cingolani", Facultad de Ciencias Médicas, Universidad Nacional de La Plata, CONICET, La Plata, Argentina
| | - E L Portiansky
- Laboratorio de Análisis de Imágenes, Facultad de Ciencias Veterinarias, Universidad Nacional de La Plata, CONICET, La Plata, Argentina
| | - M G Vila-Petroff
- Centro de Investigaciones Cardiovasculares "Dr. Horacio Cingolani", Facultad de Ciencias Médicas, Universidad Nacional de La Plata, CONICET, La Plata, Argentina
| | - E A Aiello
- Centro de Investigaciones Cardiovasculares "Dr. Horacio Cingolani", Facultad de Ciencias Médicas, Universidad Nacional de La Plata, CONICET, La Plata, Argentina.
| | - A Orlowski
- Centro de Investigaciones Cardiovasculares "Dr. Horacio Cingolani", Facultad de Ciencias Médicas, Universidad Nacional de La Plata, CONICET, La Plata, Argentina.
| |
Collapse
|
2
|
Di Mattía RA, Díaz Zegarra LA, Valverde CA, Blanco PG, Jaquenod De Giusti C, Portiansky EL, Aiello EA, Orlowski A. In vivo Overexpression of Electrogenic Sodium/Bicarbonate Cotransporter (NBCe1) by AAV9 Modifies the Cardiac Action Potential and the QT Interval in Mice. Front Cardiovasc Med 2022; 9:862118. [PMID: 35548416 PMCID: PMC9082548 DOI: 10.3389/fcvm.2022.862118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2022] [Accepted: 03/23/2022] [Indexed: 11/29/2022] Open
Abstract
Cardiac cells depend on specific sarcolemmal ion transporters to assure the correct intracellular pH regulation. The sodium/bicarbonate cotransporter (NBC) is one of the major alkalinizing mechanisms. In the heart two different NBC isoforms have been described: the electroneutral NBCn1 (1Na+:1HCO3-) and the electrogenic NBCe1 (1Na+:2HCO3-). NBCe1 generates an anionic repolarizing current that modulates the action potential duration (APD). In addition to regulating the pH, the NBC is a source of sodium influx. It has been postulated that NBC could play a role in the development of hypertrophy. The aim of this research was to study the contribution of NBCe1 in heart electrophysiology and in the development of heart hypertrophy in an in vivo mouse model with overexpression of NBCe1. Heart NBCe1 overexpression was achieved by a recombinant cardiotropic adeno-associated virus (AAV9) and was evidenced by western-blot and qPCR. AAV9-mCherry was used as a transduction control. NBCe1 overexpression fails to increase heart growth. Patch clamp and electrocardiogram were performed. We observed a reduction on both, ventricular myocytes APD and electrocardiogram QT interval corrected by cardiac rate, emphasizing for the first time NBCe1 relevance for the electrical activity of the heart.
Collapse
Affiliation(s)
- Romina A. Di Mattía
- Centro de Investigaciones Cardiovasculares “Dr. Horacio E. Cingolani, ” Facultad de Ciencias Médicas, Universidad Nacional de La Plata-CONICET, La Plata, Argentina
| | - Leandro A. Díaz Zegarra
- Centro de Investigaciones Cardiovasculares “Dr. Horacio E. Cingolani, ” Facultad de Ciencias Médicas, Universidad Nacional de La Plata-CONICET, La Plata, Argentina
| | - Carlos A. Valverde
- Centro de Investigaciones Cardiovasculares “Dr. Horacio E. Cingolani, ” Facultad de Ciencias Médicas, Universidad Nacional de La Plata-CONICET, La Plata, Argentina
| | - Paula G. Blanco
- Centro de Fisiología Reproductiva y Métodos Complementarios de Diagnóstico, Facultad de Ciencias Veterinarias, Universidad Nacional de La Plata-CONICET, La Plata, Argentina
| | - Carolina Jaquenod De Giusti
- Centro de Investigaciones Cardiovasculares “Dr. Horacio E. Cingolani, ” Facultad de Ciencias Médicas, Universidad Nacional de La Plata-CONICET, La Plata, Argentina
| | - Enrique L. Portiansky
- Laboratorio de Análisis de Imágenes, Facultad de Ciencias Veterinarias, Universidad Nacional de La Plata-CONICET, La Plata, Argentina
| | - Ernesto A. Aiello
- Centro de Investigaciones Cardiovasculares “Dr. Horacio E. Cingolani, ” Facultad de Ciencias Médicas, Universidad Nacional de La Plata-CONICET, La Plata, Argentina
- *Correspondence: Ernesto A. Aiello
| | - Alejandro Orlowski
- Centro de Investigaciones Cardiovasculares “Dr. Horacio E. Cingolani, ” Facultad de Ciencias Médicas, Universidad Nacional de La Plata-CONICET, La Plata, Argentina
- Alejandro Orlowski
| |
Collapse
|
3
|
The electrogenic sodium bicarbonate cotransporter and its roles in the myocardial ischemia-reperfusion induced cardiac diseases. Life Sci 2021; 270:119153. [PMID: 33539911 DOI: 10.1016/j.lfs.2021.119153] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2020] [Revised: 01/06/2021] [Accepted: 01/22/2021] [Indexed: 12/19/2022]
Abstract
Cardiac tissue ischemia/hypoxia increases glycolysis and lactic acid accumulation in cardiomyocytes, leading to intracellular metabolic acidosis. Sodium bicarbonate cotransporters (NBCs) play a vital role in modulating intracellular pH and maintaining sodium ion concentrations in cardiomyocytes. Cardiomyocytes mainly express electrogenic sodium bicarbonate cotransporter (NBCe1), which has been demonstrated to participate in myocardial ischemia/reperfusion (I/R) injury. This review outlines the structural and functional properties of NBCe1, summarizes the signaling pathways and factors that may regulate the activity of NBCe1, and reviews the roles of NBCe1 in the pathogenesis of I/R-induced cardiac diseases. Further studies revealing the regulatory mechanisms of NBCe1 activity should provide novel therapeutic targets for preventing I/R-induced cardiac diseases.
Collapse
|
4
|
Colmenares Aguilar MG, Mazzone A, Eisenman ST, Strege PR, Bernard CE, Holmes HL, Romero MF, Farrugia G, Gibbons SJ. Expression of the regulated isoform of the electrogenic Na +/HCO 3- cotransporter, NBCe1, is enriched in pacemaker interstitial cells of Cajal. Am J Physiol Gastrointest Liver Physiol 2021; 320:G93-G107. [PMID: 33112159 PMCID: PMC8112189 DOI: 10.1152/ajpgi.00255.2020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Interstitial cells of Cajal (ICCs) generate electrical slow waves, which are required for normal gastrointestinal motility. The mechanisms for generation of normal pacemaking are not fully understood. Normal gastrointestinal contractility- and electrical slow-wave activity depend on the presence of extracellular HCO3-. Previous transcriptional analysis identified enrichment of mRNA encoding the electrogenic Na+/HCO3- cotransporter (NBCe1) gene (Slc4a4) in pacemaker myenteric ICCs in mouse small intestine. We aimed to determine the distribution of NBCe1 protein in ICCs of the mouse gastrointestinal tract and to identify the transcripts of the Slc4a4 gene in mouse and human small intestinal tunica muscularis. We determined the distribution of NBCe1 immunoreactivity (NBCe1-IR) by immunofluorescent labeling in mouse and human tissues. In mice, NBCe1-IR was restricted to Kit-positive myenteric ICCs of the stomach and small intestine and submuscular ICCs of the large intestine, that is, the slow wave generating subset of ICCs. Other subtypes of ICCs were NBCe1-negative. Quantitative real-time PCR identified >500-fold enrichment of Slc4a4-207 and Slc4a4-208 transcripts ["IP3-receptor-binding protein released by IP3" (IRBIT)-regulated isoforms] in Kit-expressing cells isolated from KitcreERT2/+, Rpl22tm1.1Psam/Sj mice and from single GFP-positive ICCs from Kittm1Rosay mice. Human jejunal tunica muscularis ICCs were also NBCe1-positive, and SLC4A4-201 and SLC4A4-204 RNAs were >300-fold enriched relative to SLC4A4-202. In summary, NBCe1 protein expressed in ICCs with electrical pacemaker function is encoded by Slc4a4 gene transcripts that generate IRBIT-regulated isoforms of NBCe1. In conclusion, Na+/HCO3- cotransport through NBCe1 contributes to the generation of pacemaker activity in subsets of ICCs.NEW & NOTEWORTHY In this study, we show that the electrogenic Na+/HCO3- cotransporter, NBCe1/Slc4a4, is expressed in subtypes of interstitial cells of Cajal (ICCs) responsible for electrical slow wave generation throughout the mouse gastrointestinal tract and is absent in other types of ICCs. The transcripts of Slc4a4 expressed in mouse ICCs and human gastrointestinal smooth muscle are the regulated isoforms. This indicates a key role for HCO3- transport in generation of gastrointestinal motility patterns.
Collapse
Affiliation(s)
| | - Amelia Mazzone
- 1Enteric NeuroScience Program, Division of
Gastroenterology and Hepatology, Mayo Clinic,
Rochester, Minnesota
| | - Seth T. Eisenman
- 1Enteric NeuroScience Program, Division of
Gastroenterology and Hepatology, Mayo Clinic,
Rochester, Minnesota
| | - Peter R. Strege
- 1Enteric NeuroScience Program, Division of
Gastroenterology and Hepatology, Mayo Clinic,
Rochester, Minnesota
| | - Cheryl E. Bernard
- 1Enteric NeuroScience Program, Division of
Gastroenterology and Hepatology, Mayo Clinic,
Rochester, Minnesota
| | - Heather L. Holmes
- 2Physiology and Biomedical Engineering, Nephrology and
Hypertension, Mayo Clinic College of Medicine and
Science, Rochester, Minnesota
| | - Michael F. Romero
- 2Physiology and Biomedical Engineering, Nephrology and
Hypertension, Mayo Clinic College of Medicine and
Science, Rochester, Minnesota
| | - Gianrico Farrugia
- 1Enteric NeuroScience Program, Division of
Gastroenterology and Hepatology, Mayo Clinic,
Rochester, Minnesota,3Department of Physiology and Biomedical Engineering,
Mayo Clinic, Rochester, Minnesota
| | - Simon J. Gibbons
- 1Enteric NeuroScience Program, Division of
Gastroenterology and Hepatology, Mayo Clinic,
Rochester, Minnesota
| |
Collapse
|
5
|
Medina AJ, Ibáñez AM, Diaz-Zegarra LA, Portiansky EL, Blanco PG, Pereyra EV, de Giusti VC, Aiello EA, Yeves AM, Ennis IL. Cardiac up-regulation of NBCe1 emerges as a beneficial consequence of voluntary wheel running in mice. Arch Biochem Biophys 2020; 694:108600. [PMID: 33007282 DOI: 10.1016/j.abb.2020.108600] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Revised: 09/17/2020] [Accepted: 09/23/2020] [Indexed: 11/30/2022]
Abstract
Physical training stimulates the development of physiologic cardiac hypertrophy (CH), being a key event in this process the inhibition of the Na+/H+ exchanger. However, the role of the sodium bicarbonate cotransporter (NBC) has not been explored yet under this circumstance. C57/Bl6 mice were allowed to voluntary exercise (wheel running) for five weeks. Cardiac mass was evaluated by echocardiography and histomorphometry detecting that training promoted the development of physiological CH (heart weight/tibia length ratio, mg/mm: 6.54 ± 0.20 vs 8.81 ± 0.24; interstitial collagen content, %: 3.14 ± 0.63 vs. 1.57 ± 0.27; and cross-sectional area of cardiomyocytes, μm2: 200.6 ± 8.92 vs. 281.9 ± 24.05; sedentary (Sed) and exercised (Ex) mice, respectively). The activity of the electrogenic isoform of the cardiac NBC (NBCe1) was estimated by recording intracellular pH under high potassium concentration and by measuring action potential duration (APD). NBCe1 activity was significantly increased in isolated cardiomyocytes of trained mice. Additionally, the APD was shorter and the alkalization due to high extracellular potassium-induced depolarization was greater in this group, indicating that the NBCe1 was hyperactive. These results are online with the observed myocardial up-regulation of the NBCe1 (Western Blot, %: 100 ± 13.86 vs. 202 ± 29.98; Sed vs. Ex, n = 6 each group). In addition, we detected a reduction in H2O2 production in the myocardium of trained mice. These results support that voluntary training induces the development of physiologic CH with up-regulation of the cardiac NBCe1 in mice. Furthermore, the improvement in the antioxidant capacity contributes to the beneficial cardiovascular consequences of physical training.
Collapse
Affiliation(s)
- Andrés J Medina
- Centro de Investigaciones Cardiovasculares "Dr. Horacio E, Cingolani" Facultad de Ciencias Médicas UNLP-CONICET, Argentina
| | - Alejandro M Ibáñez
- Centro de Investigaciones Cardiovasculares "Dr. Horacio E, Cingolani" Facultad de Ciencias Médicas UNLP-CONICET, Argentina
| | - Leandro A Diaz-Zegarra
- Centro de Investigaciones Cardiovasculares "Dr. Horacio E, Cingolani" Facultad de Ciencias Médicas UNLP-CONICET, Argentina
| | - Enrique L Portiansky
- Laboratorio de Análisis de Imágenes, Facultad de Ciencias Veterinarias UNLP-CONICET, Argentina
| | - Paula G Blanco
- Servicio de Cardiología, Facultad de Ciencias Veterinarias, UNLP-CONICET, Argentina
| | - Erica V Pereyra
- Centro de Investigaciones Cardiovasculares "Dr. Horacio E, Cingolani" Facultad de Ciencias Médicas UNLP-CONICET, Argentina
| | - Verónica C de Giusti
- Centro de Investigaciones Cardiovasculares "Dr. Horacio E, Cingolani" Facultad de Ciencias Médicas UNLP-CONICET, Argentina
| | - Ernesto A Aiello
- Centro de Investigaciones Cardiovasculares "Dr. Horacio E, Cingolani" Facultad de Ciencias Médicas UNLP-CONICET, Argentina
| | - Alejandra M Yeves
- Centro de Investigaciones Cardiovasculares "Dr. Horacio E, Cingolani" Facultad de Ciencias Médicas UNLP-CONICET, Argentina
| | - Irene L Ennis
- Centro de Investigaciones Cardiovasculares "Dr. Horacio E, Cingolani" Facultad de Ciencias Médicas UNLP-CONICET, Argentina.
| |
Collapse
|
6
|
Ibañez AM, Espejo MS, Zavala MR, Villa-Abrille MC, Lofeudo JM, Aiello EA, De Giusti VC. Regulation of Intracellular pH is Altered in Cardiac Myocytes of Ovariectomized Rats. J Am Heart Assoc 2019; 8:e011066. [PMID: 30917747 PMCID: PMC6509710 DOI: 10.1161/jaha.118.011066] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Background It is well known that after menopause women are exposed to a greater cardiovascular risk, but the intracellular modifications are not properly described. The sodium/proton exchanger (NHE) and the sodium/bicarbonate cotransporter (NBC) regulate the intracellular pH and, indirectly, the intracellular sodium concentration ([Na+]). There are 2 isoforms of NBC in the heart: the electrogenic (1Na+/2[Formula: see text]; NBCe1) and the electroneutral (1Na+/1[Formula: see text]; NBCn1). Because NHE and NBCn1 hyperactivity as well as the NBCe1 decreased activity have been associated with several cardiovascular pathologies, the aim of this study was to investigate the potential alterations of the alkalinizing transporters during the postmenopausal period. Methods and Results Three-month ovariectomized rats (OVX) were used. The NHE activity and protein expression are significantly increased in OVX. The NBCe1 activity is diminished, and the NBCn1 activity becomes predominant in OVX rats. p-Akt levels showed a significant diminution in OVX. Finally, NHE activity in platelets from OVX rats is also higher in comparison to sham rats, resulting in a potential biomarker of cardiovascular diseases. Conclusions Our results demonstrated for the first time that in the cardiac ventricular myocytes of OVX rats NHE and NBC isoforms are altered, probably because of the decreased level of p-Akt, compromising the ionic intracellular homeostasis.
Collapse
Affiliation(s)
- Alejandro Martín Ibañez
- 1 Centro de Investigaciones Cardiovasculares Facultad de Ciencias Médicas Universidad Nacional de La Plata-CONICET La Plata Argentina
| | - María Sofía Espejo
- 1 Centro de Investigaciones Cardiovasculares Facultad de Ciencias Médicas Universidad Nacional de La Plata-CONICET La Plata Argentina
| | - Maite Raquel Zavala
- 1 Centro de Investigaciones Cardiovasculares Facultad de Ciencias Médicas Universidad Nacional de La Plata-CONICET La Plata Argentina
| | - María Celeste Villa-Abrille
- 1 Centro de Investigaciones Cardiovasculares Facultad de Ciencias Médicas Universidad Nacional de La Plata-CONICET La Plata Argentina
| | - Juan Manuel Lofeudo
- 1 Centro de Investigaciones Cardiovasculares Facultad de Ciencias Médicas Universidad Nacional de La Plata-CONICET La Plata Argentina
| | - Ernesto Alejandro Aiello
- 1 Centro de Investigaciones Cardiovasculares Facultad de Ciencias Médicas Universidad Nacional de La Plata-CONICET La Plata Argentina
| | - Verónica Celeste De Giusti
- 1 Centro de Investigaciones Cardiovasculares Facultad de Ciencias Médicas Universidad Nacional de La Plata-CONICET La Plata Argentina
| |
Collapse
|
7
|
Aiello EA, Casey JR, Alvarez BV. Cl -/HCO 3- Exchanger slc26a6: A pH Regulator Shapes the Cardiac Action Potential. Circ Arrhythm Electrophysiol 2017; 10:CIRCEP.117.005812. [PMID: 29025770 DOI: 10.1161/circep.117.005812] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/15/2017] [Accepted: 09/19/2017] [Indexed: 11/16/2022]
Affiliation(s)
- Ernesto A Aiello
- From the Department of Biochemistry, Membrane Protein Disease Research Group, University of Alberta, Edmonton, Canada (J.R.C.); and Centro de Investigaciones Cardiovasculares CIC-CONICET, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, Argentina (E.A.A., B.V.A.)
| | - Joseph R Casey
- From the Department of Biochemistry, Membrane Protein Disease Research Group, University of Alberta, Edmonton, Canada (J.R.C.); and Centro de Investigaciones Cardiovasculares CIC-CONICET, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, Argentina (E.A.A., B.V.A.).
| | - Bernardo V Alvarez
- From the Department of Biochemistry, Membrane Protein Disease Research Group, University of Alberta, Edmonton, Canada (J.R.C.); and Centro de Investigaciones Cardiovasculares CIC-CONICET, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, Argentina (E.A.A., B.V.A.)
| |
Collapse
|
8
|
The reduced myofilament responsiveness to calcium contributes to the negative force-frequency relationship in rat cardiomyocytes: role of reactive oxygen species and p-38 map kinase. Pflugers Arch 2017; 469:1663-1673. [DOI: 10.1007/s00424-017-2058-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2017] [Accepted: 08/11/2017] [Indexed: 01/01/2023]
|
9
|
Orlowski A, De Giusti VC, Ciancio MC, Espejo MS, Aiello EA. The cardiac electrogenic sodium/bicarbonate cotransporter (NBCe1) is activated by aldosterone through the G protein-coupled receptor 30 (GPR 30). Channels (Austin) 2016; 10:428-434. [PMID: 27249584 DOI: 10.1080/19336950.2016.1195533] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The sodium/bicarbonate cotransporter (NBC) transports extracellular Na+ and HCO3- into the cytoplasm upon intracellular acidosis, restoring the acidic pHi to near neutral values. Two different NBC isoforms have been described in the heart, the electroneutral NBCn1 (1Na+:1HCO3-) and the electrogenic NBCe1 (1Na+:2HCO3-). Certain non-genomic effects of aldosterone (Ald) were due to an orphan G protein-couple receptor 30 (GPR30). We have recently demonstrated that Ald activates GPR30 in adult rat ventricular myocytes, which transactivates the epidermal growth factor receptor (EGFR) and in turn triggers a reactive oxygen species (ROS)- and PI3K/AKT-dependent pathway, leading to the stimulation of NBC. The aim of this study was to investigate the NBC isoform involved in the Ald/GPR30-induced NBC activation. Using specific NBCe1 inhibitory antibodies (a-L3) we demonstrated that Ald does not affect NBCn1 activity. Ald was able to increase NBCe1 activity recorded in isolation. Using immunofluorescence and confocal microscopy analysis we showed in this work that both NBCe1 and GPR30 are localized in t-tubules. In conclusion, we have demonstrated that NBCe1 is the NBC isoform activated by Ald in the heart.
Collapse
Affiliation(s)
- Alejandro Orlowski
- a Centro de Investigaciones Cardiovasculares "Dr. Horacio Cingolani" , Facultad de Ciencias Médicas, Universidad Nacional de La Plata-CONICET , La Plata , Buenos Aires , Argentina
| | - Verónica C De Giusti
- a Centro de Investigaciones Cardiovasculares "Dr. Horacio Cingolani" , Facultad de Ciencias Médicas, Universidad Nacional de La Plata-CONICET , La Plata , Buenos Aires , Argentina
| | - María C Ciancio
- a Centro de Investigaciones Cardiovasculares "Dr. Horacio Cingolani" , Facultad de Ciencias Médicas, Universidad Nacional de La Plata-CONICET , La Plata , Buenos Aires , Argentina
| | - María S Espejo
- a Centro de Investigaciones Cardiovasculares "Dr. Horacio Cingolani" , Facultad de Ciencias Médicas, Universidad Nacional de La Plata-CONICET , La Plata , Buenos Aires , Argentina
| | - Ernesto A Aiello
- a Centro de Investigaciones Cardiovasculares "Dr. Horacio Cingolani" , Facultad de Ciencias Médicas, Universidad Nacional de La Plata-CONICET , La Plata , Buenos Aires , Argentina
| |
Collapse
|
10
|
De Giusti VC, Orlowski A, Ciancio MC, Espejo MS, Gonano LA, Caldiz CI, Vila Petroff MG, Villa-Abrille MC, Aiello EA. Aldosterone stimulates the cardiac sodium/bicarbonate cotransporter via activation of the g protein-coupled receptor gpr30. J Mol Cell Cardiol 2015; 89:260-7. [PMID: 26497404 DOI: 10.1016/j.yjmcc.2015.10.024] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/21/2015] [Revised: 10/07/2015] [Accepted: 10/20/2015] [Indexed: 12/22/2022]
Abstract
Some cardiac non-genomic effects of aldosterone (Ald) are reported to be mediated through activation of the classic mineralocorticoid receptor (MR). However, in the last years, it was proposed that activation of the novel G protein-coupled receptor GPR30 mediates certain non-genomic effects of Ald. The aim of this study was to elucidate if the sodium/bicarbonate cotransporter (NBC) is stimulated by Ald and if the activation of GPR30 mediates this effect. NBC activity was evaluated in rat cardiomyocytes perfused with HCO3(-)/CO2 solution in the continuous presence of HOE642 (sodium/hydrogen exchanger blocker) during recovery from acidosis using intracellular fluorescence measurements. Ald enhanced NBC activity (% of ΔJHCO3(-); control: 100±5.82%, n=7 vs Ald: 151.88±11.02%, n=5; P<0.05), which was prevented by G15 (GPR30 blocker, 90.53±7.81%, n=7). Further evidence for the involvement of GPR30 was provided by G1 (GPR30 agonist), which stimulated NBC (185.13±18.28%, n=6; P<0.05) and this effect was abrogated by G15 (124.19±10.96%, n=5). Ald- and G1-induced NBC stimulation was abolished by the reactive oxygen species (ROS) scavenger MPG and by the NADPH oxidase inhibitor apocynin. In addition, G15 prevented Ald- and G1-induced ROS production. Pre-incubation of myocytes with wortmannin (PI3K-AKT pathway blocker) prevented Ald- or G1-induced NBC stimulation. In summary, Ald stimulates NBC by GPR30 activation, ROS production and AKT stimulation.
Collapse
Affiliation(s)
- Verónica C De Giusti
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata-CONICET, La Plata, Argentina
| | - Alejandro Orlowski
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata-CONICET, La Plata, Argentina
| | - María C Ciancio
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata-CONICET, La Plata, Argentina
| | - María S Espejo
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata-CONICET, La Plata, Argentina
| | - Luis A Gonano
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata-CONICET, La Plata, Argentina
| | - Claudia I Caldiz
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata-CONICET, La Plata, Argentina
| | - Martín G Vila Petroff
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata-CONICET, La Plata, Argentina
| | - María C Villa-Abrille
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata-CONICET, La Plata, Argentina
| | - Ernesto A Aiello
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata-CONICET, La Plata, Argentina
| |
Collapse
|
11
|
Abstract
Cation-coupled HCO3(-) transport was initially identified in the mid-1970s when pioneering studies showed that acid extrusion from cells is stimulated by CO2/HCO3(-) and associated with Na(+) and Cl(-) movement. The first Na(+)-coupled bicarbonate transporter (NCBT) was expression-cloned in the late 1990s. There are currently five mammalian NCBTs in the SLC4-family: the electrogenic Na,HCO3-cotransporters NBCe1 and NBCe2 (SLC4A4 and SLC4A5 gene products); the electroneutral Na,HCO3-cotransporter NBCn1 (SLC4A7 gene product); the Na(+)-driven Cl,HCO3-exchanger NDCBE (SLC4A8 gene product); and NBCn2/NCBE (SLC4A10 gene product), which has been characterized as an electroneutral Na,HCO3-cotransporter or a Na(+)-driven Cl,HCO3-exchanger. Despite the similarity in amino acid sequence and predicted structure among the NCBTs of the SLC4-family, they exhibit distinct differences in ion dependency, transport function, pharmacological properties, and interactions with other proteins. In epithelia, NCBTs are involved in transcellular movement of acid-base equivalents and intracellular pH control. In nonepithelial tissues, NCBTs contribute to intracellular pH regulation; and hence, they are crucial for diverse tissue functions including neuronal discharge, sensory neuron development, performance of the heart, and vascular tone regulation. The function and expression levels of the NCBTs are generally sensitive to intracellular and systemic pH. Animal models have revealed pathophysiological roles of the transporters in disease states including metabolic acidosis, hypertension, visual defects, and epileptic seizures. Studies are being conducted to understand the physiological consequences of genetic polymorphisms in the SLC4-members, which are associated with cancer, hypertension, and drug addiction. Here, we describe the current knowledge regarding the function, structure, and regulation of the mammalian cation-coupled HCO3(-) transporters of the SLC4-family.
Collapse
Affiliation(s)
- Christian Aalkjaer
- Department of Biomedicine, and the Water and Salt Research Center, Aarhus University, Aarhus, Denmark; Department of Physiology, Emory University School of Medicine, Atlanta, USA
| | | | | | | |
Collapse
|
12
|
Thornell IM, Bevensee MO. Regulators of Slc4 bicarbonate transporter activity. Front Physiol 2015; 6:166. [PMID: 26124722 PMCID: PMC4464172 DOI: 10.3389/fphys.2015.00166] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2015] [Accepted: 05/15/2015] [Indexed: 12/11/2022] Open
Abstract
The Slc4 family of transporters is comprised of anion exchangers (AE1-4), Na+-coupled bicarbonate transporters (NCBTs) including electrogenic Na/bicarbonate cotransporters (NBCe1 and NBCe2), electroneutral Na/bicarbonate cotransporters (NBCn1 and NBCn2), and the electroneutral Na-driven Cl-bicarbonate exchanger (NDCBE), as well as a borate transporter (BTR1). These transporters regulate intracellular pH (pHi) and contribute to steady-state pHi, but are also involved in other physiological processes including CO2 carriage by red blood cells and solute secretion/reabsorption across epithelia. Acid-base transporters function as either acid extruders or acid loaders, with the Slc4 proteins moving HCO−3 either into or out of cells. According to results from both molecular and functional studies, multiple Slc4 proteins and/or associated splice variants with similar expected effects on pHi are often found in the same tissue or cell. Such apparent redundancy is likely to be physiologically important. In addition to regulating pHi, a HCO−3 transporter contributes to a cell's ability to fine tune the intracellular regulation of the cotransported/exchanged ion(s) (e.g., Na+ or Cl−). In addition, functionally similar transporters or splice variants with different regulatory profiles will optimize pH physiology and solute transport under various conditions or within subcellular domains. Such optimization will depend on activated signaling pathways and transporter expression profiles. In this review, we will summarize and discuss both well-known and more recently identified regulators of the Slc4 proteins. Some of these regulators include traditional second messengers, lipids, binding proteins, autoregulatory domains, and less conventional regulators. The material presented will provide insight into the diversity and physiological significance of multiple members within the Slc4 gene family.
Collapse
Affiliation(s)
- Ian M Thornell
- Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham Birmingham, AL, USA
| | - Mark O Bevensee
- Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham Birmingham, AL, USA ; Nephrology Research and Training Center, University of Alabama at Birmingham Birmingham, AL, USA ; Center of Glial Biology in Medicine, University of Alabama at Birmingham Birmingham, AL, USA ; Civitan International Research Center, University of Alabama at Birmingham Birmingham, AL, USA
| |
Collapse
|
13
|
Wang HS, Chen Y, Vairamani K, Shull GE. Critical role of bicarbonate and bicarbonate transporters in cardiac function. World J Biol Chem 2014; 5:334-345. [PMID: 25225601 PMCID: PMC4160527 DOI: 10.4331/wjbc.v5.i3.334] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/01/2014] [Revised: 03/06/2014] [Accepted: 05/19/2014] [Indexed: 02/05/2023] Open
Abstract
Bicarbonate is one of the major anions in mammalian tissues and extracellular fluids. Along with accompanying H+, HCO3- is generated from CO2 and H2O, either spontaneously or via the catalytic activity of carbonic anhydrase. It serves as a component of the major buffer system, thereby playing a critical role in pH homeostasis. Bicarbonate can also be utilized by a variety of ion transporters, often working in coupled systems, to transport other ions and organic substrates across cell membranes. The functions of HCO3- and HCO3--transporters in epithelial tissues have been studied extensively, but their functions in heart are less well understood. Here we review studies of the identities and physiological functions of Cl-/HCO3- exchangers and Na+/HCO3- cotransporters of the SLC4A and SLC26A families in heart. We also present RNA Seq analysis of their cardiac mRNA expression levels. These studies indicate that slc4a3 (AE3) is the major Cl-/HCO3- exchanger and plays a protective role in heart failure, and that Slc4a4 (NBCe1) is the major Na+/HCO3- cotransporter and affects action potential duration. In addition, previous studies show that HCO3- has a positive inotropic effect in the perfused heart that is largely independent of effects on intracellular Ca2+. The importance of HCO3- in the regulation of contractility is supported by experiments showing that isolated cardiomyocytes exhibit sharply enhanced contractility, with no change in Ca2+ transients, when switched from Hepes-buffered to HCO3-- buffered solutions. These studies demonstrate that HCO3- and HCO3--handling proteins play important roles in the regulation of cardiac function.
Collapse
|
14
|
De Giusti VC, Ciancio MC, Orlowski A, Aiello EA. Modulation of the cardiac sodium/bicarbonate cotransporter by the renin angiotensin aldosterone system: pathophysiological consequences. Front Physiol 2014; 4:411. [PMID: 24478712 PMCID: PMC3894460 DOI: 10.3389/fphys.2013.00411] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2013] [Accepted: 12/27/2013] [Indexed: 12/22/2022] Open
Abstract
The sodium/bicarbonate cotransporter (NBC) is one of the major alkalinizing mechanisms in the cardiomyocytes. It has been demonstrated the existence of at least two functional isoforms, one that promotes the co-influx of 1 molecule of Na+ per 1 molecule of HCO−3 (electroneutral isoform; NBCn1) and the other one that generates the co-influx of 1 molecule of Na+ per 2 molecules of HCO−3 (electrogenic isoform; NBCe1). Both isoforms are important to maintain intracellular pH (pHi) and sodium concentration ([Na+]i). In addition, NBCe1 generates an anionic repolarizing current that modulates the action potential duration (APD). The renin-angiotensin-aldosterone system (RAAS) is implicated in the modulation of almost all physiological cardiac functions and is also involved in the development and progression of cardiac diseases. It was reported that angiotensin II (Ang II) exhibits an opposite effect on NBC isoforms: it activates NBCn1 and inhibits NBCe1. The activation of NBCn1 leads to an increase in pHi and [Na+]i, which indirectly, due to the stimulation of reverse mode of the Na+/Ca2+ exchanger (NCX), conduces to an increase in the intracellular Ca2+ concentration. On the other hand, the inhibition of NBCe1 generates an APD prolongation, potentially representing a risk of arrhythmias. In the last years, the potentially altered NBC function in pathological scenarios, as cardiac hypertrophy and ischemia-reperfusion, has raised increasing interest among investigators. This review attempts to draw the attention on the relevant regulation of NBC activity by RAAS, since it modulates pHi and [Na+]i, which are involved in the development of cardiac hypertrophy, the damage produced by ischemia-reperfusion and the generation of arrhythmic events, suggesting a potential role of NBC in cardiac diseases.
Collapse
Affiliation(s)
- Verónica C De Giusti
- Facultad de Ciencias Médicas, Centro de Investigaciones Cardiovasculares, Universidad Nacional de La Plata, CONICET-La Plata La Plata, Argentina
| | - María C Ciancio
- Facultad de Ciencias Médicas, Centro de Investigaciones Cardiovasculares, Universidad Nacional de La Plata, CONICET-La Plata La Plata, Argentina
| | - Alejandro Orlowski
- Facultad de Ciencias Médicas, Centro de Investigaciones Cardiovasculares, Universidad Nacional de La Plata, CONICET-La Plata La Plata, Argentina
| | - Ernesto A Aiello
- Facultad de Ciencias Médicas, Centro de Investigaciones Cardiovasculares, Universidad Nacional de La Plata, CONICET-La Plata La Plata, Argentina
| |
Collapse
|
15
|
Abstract
Carbonic anhydrases (CAs) have not only been identified as ubiquitous enzymes catalyzing the fast reversible hydration of carbon dioxide to generate or consume protons and bicarbonate, but also as intra- and extracellular proteins, which facilitate transport function of many acid/base transporting membrane proteins, coined 'transport metabolon'. Functional interaction between CAs and acid/base transporters, such as chloride/bicarbonate exchanger (AE), sodium-bicarbonate cotransporter (NBC) and sodium/hydrogen exchanger (NHE) has been shown to require both catalytic CA activity as well as direct binding of the enzyme to specific sites on the transporter. In contrast, functional interaction between different CA isoforms and lactate-proton-cotransporting monocarboxylate transporters (MCT) has been found to be isoform-specific and independent of CA catalytic activity, but seems to require an intramolecular proton shuttle within the enzyme. In this chapter, we review the various types of interactions between acid/base-coupled membrane carriers and different CA isoforms, as studied in vitro, in intact Xenopus oocytes, and in various mammalian cell types. Furthermore, we discuss recent findings that indicate the significance of these 'transport metabolons' for normal cell functions.
Collapse
|
16
|
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.
Collapse
Affiliation(s)
- Francisco C Villafuerte
- Burdon Sanderson Cardiac Science Centre, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3PT, UK.
| | | | | | | | | | | | | | | | | |
Collapse
|
17
|
Orlowski A, Ciancio MC, Caldiz CI, De Giusti VC, Aiello EA. Reduced sarcolemmal expression and function of the NBCe1 isoform of the Na⁺-HCO₃⁻ cotransporter in hypertrophied cardiomyocytes of spontaneously hypertensive rats: role of the renin-angiotensin system. Cardiovasc Res 2013; 101:211-9. [PMID: 24253522 DOI: 10.1093/cvr/cvt255] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
AIMS Electroneutral (NBCn1) and electrogenic (NBCe1) isoforms of the Na(+)-HCO3(-) cotransporter (NBC) coexist in the heart. We studied the expression and function of these isoforms in hearts of Wistar and spontaneously hypertensive rats (SHR), elucidating the direct implication of the renin-angiotensin system in the NBC regulation. METHODS AND RESULTS We used myocytes from Wistar, SHR, losartan-treated SHR (Los-SHR), and Angiotensin II (Ang II)-induced cardiac hypertrophy. We found an overexpression of NBCe1 and NBCn1 proteins in SHR that was prevented in Los-SHR. Hyperkalaemic-induced pHi alkalization was used to study selective activation of NBCe1. Despite the increase in NBCe1 expression, its activity was lower in SHR than in Wistar or Los-SHR. Similar results were found in Ang II-induced hypertrophy. A specific inhibitory antibody against NBCe1 allowed the discrimination between NBCe1 and NBCn1 activity. Whereas in SHR most of the pHi recovery was due to NBCn1 stimulation, in Wistar and Los-SHR the activity of both isoforms was equitable, suggesting that the deteriorated cardiac NBCe1 function observed in SHR is compensated by an enhanced activity of NBCn1. Using the biotin method, we observed greater level of internalized NBCe1 protein in SHR than in the non-hypertophic groups, while with immunofluorescence we localized the protein in endosomes near the nucleus only in SHR. CONCLUSIONS We conclude that Ang II is responsible for the impairment of the NBCe1 in hypertrophied hearts. This is due to retained transporter protein units in early endosomes. Moreover, NBCn1 activity seems to be increased in the hypertrophic myocardium of SHR, compensating impaired function of NBCe1.
Collapse
Affiliation(s)
- Alejandro Orlowski
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata-CONICET, Calle 60 y 120, 1900 La Plata, Argentina
| | | | | | | | | |
Collapse
|
18
|
Aiello EA, De Giusti VC. Regulation of the cardiac sodium/bicarbonate cotransporter by angiotensin II: potential Contribution to structural, ionic and electrophysiological myocardial remodelling. Curr Cardiol Rev 2013; 9:24-32. [PMID: 23116057 PMCID: PMC3584305 DOI: 10.2174/157340313805076340] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/27/2012] [Revised: 08/15/2012] [Accepted: 09/13/2012] [Indexed: 12/15/2022] Open
Abstract
The sodium/ bicarbonate cotransporter (NBC) is, with the Na+/H+ exchanger (NHE), an important alkalinizing mechanism that maintains cellular intracellular pH (pHi). In the heart exists at least three isoforms of NBC, one that promotes the co-influx of 1 molecule of Na+ per 1molecule of HCO3-(electroneutral isoform; nNBC) and two others that generates the co-influx of 1 molecule of Na+ per 2 molecules of HCO3- (electrogenic isoforms; eNBC). In addition, the eNBC generates an anionic repolarizing current that modulate the cardiac action potential (CAP), adding to such isoforms the relevance to modulate the electrophysiological function of the heart. Angiotensin II (Ang II) is one of the main hormones that regulate cardiac physiology. The alkalinizing mechanisms (NHE and NBC) are stimulated by Ang II, increasing pHi and intracellular Na+ concentration, which indirectly, due to the stimulation of the Na+/Ca2+ exchanger (NCX) operating in the reverse form, leads to an increase in the intracellular Ca2+ concentration. Interestingly, it has been shown that Ang II exhibits an opposite effect on NBC isoforms: it activates the nNBC and inhibits the eNBC. This inhibition generates a CAP prolongation, which could directly increase the intracellular Ca2+ concentration. The regulation of the intracellular Na+ and Ca2+ concentrations is crucial for the cardiac cellular physiology, but these ions are also involved in the development of cardiac hypertrophy and the damage produced by ischemia-reperfusion, suggesting a potential role of NBC in cardiac diseases.
Collapse
Affiliation(s)
- Ernesto Alejandro Aiello
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, Calle 60 y 120, 1900, La Plata, Argentina.
| | | |
Collapse
|
19
|
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".
Collapse
Affiliation(s)
- Carolina D Garciarena
- Burdon Sanderson Cardiac Science Centre, Department of Physiology Anatomy & Genetics, Oxford, UK
| | | | | | | |
Collapse
|
20
|
Parker MD, Boron WF. The divergence, actions, roles, and relatives of sodium-coupled bicarbonate transporters. Physiol Rev 2013; 93:803-959. [PMID: 23589833 PMCID: PMC3768104 DOI: 10.1152/physrev.00023.2012] [Citation(s) in RCA: 197] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The mammalian Slc4 (Solute carrier 4) family of transporters is a functionally diverse group of 10 multi-spanning membrane proteins that includes three Cl-HCO3 exchangers (AE1-3), five Na(+)-coupled HCO3(-) transporters (NCBTs), and two other unusual members (AE4, BTR1). In this review, we mainly focus on the five mammalian NCBTs-NBCe1, NBCe2, NBCn1, NDCBE, and NBCn2. Each plays a specialized role in maintaining intracellular pH and, by contributing to the movement of HCO3(-) across epithelia, in maintaining whole-body pH and otherwise contributing to epithelial transport. Disruptions involving NCBT genes are linked to blindness, deafness, proximal renal tubular acidosis, mental retardation, and epilepsy. We also review AE1-3, AE4, and BTR1, addressing their relevance to the study of NCBTs. This review draws together recent advances in our understanding of the phylogenetic origins and physiological relevance of NCBTs and their progenitors. Underlying these advances is progress in such diverse disciplines as physiology, molecular biology, genetics, immunocytochemistry, proteomics, and structural biology. This review highlights the key similarities and differences between individual NCBTs and the genes that encode them and also clarifies the sometimes confusing NCBT nomenclature.
Collapse
Affiliation(s)
- Mark D Parker
- Dept. of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Ave., Cleveland, OH 44106-4970, USA.
| | | |
Collapse
|
21
|
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.
Collapse
Affiliation(s)
- Carolina D Garciarena
- Burdon Sanderson Cardiac Science Centre, Department of Physiology, Anatomy and Genetics, Oxford OX1 3PT, UK
| | | | | | | | | |
Collapse
|
22
|
Orlowski A, De Giusti VC, Morgan PE, Aiello EA, Álvarez BV. Binding of carbonic anhydrase IX to extracellular loop 4 of the NBCe1 Na+/HCO3− cotransporter enhances NBCe1-mediated HCO3− influx in the rat heart. Am J Physiol Cell Physiol 2012; 303:C69-80. [DOI: 10.1152/ajpcell.00431.2011] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Na+/HCO3− cotransporter (NBC)e1 catalyze the electrogenic movement of 1 Na+:2 HCO3− into cardiomyocytes cytosol. NBC proteins associate with carbonic anhydrases (CA), CAII, and CAIV, forming a HCO3− transport metabolon. Herein, we examined the physical/functional interaction of NBCe1 and transmembrane CAIX in cardiac muscle. NBCe1 and CAIX physical association was examined by coimmunoprecipitation, using rat ventricular lysates. NBCe1 coimmunoprecipitated with anti-CAIX antibody, indicating NBCe1 and CAIX interaction in the myocardium. Glutathione- S-transferase (GST) pull-down assays with predicted extracellular loops (EC) of NBCe1 revealed that NBCe1-EC4 mediated interaction with CAIX. Functional NBCe1/CAIX interaction was examined using fluorescence measurements of BCECF in rat cardiomyocytes to monitor cytosolic pH. NBCe1 transport activity was evaluated after membrane depolarization with high extracellular K+ in the presence or absence of the CA inhibitors, benzolamide (BZ; 100 μM) or 6-ethoxyzolamide (ETZ; 100 μM) (* P < 0.05). This depolarization protocol produced an intracellular pH (pHi) increase of 0.17 ± 0.01 ( n = 11), which was inhibited by BZ (0.11 ± 0.02; n = 7) or ETZ (0.06 ± 0.01; n = 6). NBCe1 activity was also measured by changes of pHi in NBCe1-transfected human embryonic kidney 293 cells subjected to acid loads. Cotransfection of CAIX with NBCe1 increased the rate of pHi recovery (in mM/min) by about fourfold (12.1 ± 0.8; n = 9) compared with cells expressing NBCe1 alone (3.1 ± 0.5; n = 7), which was inhibited by BZ (7.5 ± 0.3; n = 9). We demonstrated that CAIX forms a complex with EC4 of NBCe1, which activates NBCe1-mediated HCO3− influx in the myocardium. CAIX and NBCe1 have been linked to tumorigenesis and cardiac cell growth, respectively. Thus inhibition of CA activity might be useful to prevent activation of NBCe1 under these pathological conditions.
Collapse
Affiliation(s)
- Alejandro Orlowski
- Centro de Investigaciones Cardiovasculares, CONICET-Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata, Argentina
| | - Verónica C. De Giusti
- Centro de Investigaciones Cardiovasculares, CONICET-Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata, Argentina
| | - Patricio E. Morgan
- Centro de Investigaciones Cardiovasculares, CONICET-Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata, Argentina
| | - Ernesto A. Aiello
- Centro de Investigaciones Cardiovasculares, CONICET-Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata, Argentina
| | - Bernardo V. Álvarez
- Centro de Investigaciones Cardiovasculares, CONICET-Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata, Argentina
| |
Collapse
|
23
|
De Giusti VC, Orlowski A, Villa-Abrille MC, de Cingolani GEC, Casey JR, Alvarez BV, Aiello EA. Antibodies against the cardiac sodium/bicarbonate co-transporter (NBCe1) as pharmacological tools. Br J Pharmacol 2012; 164:1976-89. [PMID: 21595652 DOI: 10.1111/j.1476-5381.2011.01496.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
BACKGROUND AND PURPOSE Na(+) /HCO(3) (-) co-transport (NBC) regulates intracellular pH (pH(i) ) in the heart. We have studied the electrogenic NBC isoform NBCe1 by examining the effect of functional antibodies to this protein. EXPERIMENTAL APPROACH We generated two antibodies against putative extracellular loop domains 3 (a-L3) and 4 (a-L4) of NBCe1 which recognized NBCe1 on immunoblots and immunostaining experiments. pH(i) was monitored using epi-fluorescence measurements in cat ventricular myocytes. Transport activity of total NBC and of NBCe1 in isolation were evaluated after an ammonium ion-induced acidosis (expressed as H(+) flux, J(H) , in mmol·L(-1) min(-1) at pH(i) 6.8) and during membrane depolarization with high extracellular potassium (potassium pulse, expressed as ΔpH(i) ) respectively. KEY RESULTS The potassium pulse produced a pH(i) increase of 0.18 ± 0.006 (n= 5), which was reduced by the a-L3 antibody (0.016 ± 0.019). The a-L-3 also decreased J(H) by 50%. Surprisingly, during the potassium pulse, a-L4 induced a higher pH(i) increase than control,(0.25 ± 0.018) whereas the recovery of pH(i) from acidosis was faster (J(H) was almost double the control value). In perforated-patch experiments, a-L3 prolonged and a-L4 shortened action potential duration, consistent with blockade and stimulation of NBCe1-carried anionic current respectively. CONCLUSIONS AND IMPLICATIONS Both antibodies recognized NBCe1, but they had opposing effects on the function of this transporter, as the a-L3 was inhibitory and the a-L4 was excitatory. These antibodies could be valuable in studies on the pathophysiology of NBCe1 in cardiac tissue, opening a path for their potential clinical use.
Collapse
Affiliation(s)
- Verónica C De Giusti
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata, Argentina
| | | | | | | | | | | | | |
Collapse
|
24
|
De Giusti VC, Orlowski A, Aiello EA. Angiotensin II inhibits the electrogenic Na+/HCO3- cotransport of cat cardiac myocytes. J Mol Cell Cardiol 2010; 49:812-8. [PMID: 20692267 DOI: 10.1016/j.yjmcc.2010.07.018] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/22/2010] [Revised: 07/29/2010] [Accepted: 07/30/2010] [Indexed: 01/12/2023]
Abstract
The Na(+)/HCO(3)(-) cotransporter (NBC) plays an important role in intracellular pH (pH(i)) regulation in the heart. In the myocardium co-exist the electrogenic (eNBC) and electroneutral (nNBC) isoforms of NBC. We have recently reported that angiotensin II (Ang II) stimulated total NBC activity during the recovery from intracellular acidosis through a reactive oxygen species (ROS) and ERK-dependent pathway. In the present work we focus our attention on eNBC. In order to study the activity of the eNBC in isolation, we induced a membrane potential depolarization by increasing extracellular K(+) [K(+)](o) from 4.5 to 45 mM (K(+) pulse). This experimental protocol enhanced eNBC driving force leading to intracellular alkalization (0.19 ± 0.008, n=6; data expressed as an increase of pH(i) units after 14 min of applying the K(+) pulse). This alkalization was completely abrogated by the NBC blocker S0859 (-0.004 ± 0.016*, n=5; * indicates p<0.05 vs control) but not by the Na(+)/H(+) exchanger blocker HOE642 (0.185 ± 0.04, n=4), indicating that we are exclusively measuring eNBC. The K(+) pulse induced alkalization was canceled by 100 nM Ang II (-0.008 ± 0.018*; n=5). This inhibitory effect was prevented when the myocytes were incubated with losartan (AT(1) receptor blocker, 0.18 ± 0.02; n=4) or SB202190 (p38 MAP kinase inhibitor, 0.25 ± 0.06; n=5). Neither chelerythrine (PKC inhibitor, -0.06 ± 0.04*; n=4), nor U0126 (ERK inhibitor, -0.07 ± 0.04*; n=4) nor MPG (ROS scavenger, -0.02 ± 0.05*; n=8) affected the Ang II-induced inhibition of eNBC. The inhibitory action of Ang II on eNBC was corroborated with perforated patch-clamp experiments, since no impact of the current produced by eNBC on action potential repolarization was observed in the presence of Ang II. In conclusion, we propose that Ang II, binding to AT(1) receptors, exerts an inhibitory effect on eNBC activity in a p38 kinase-dependent manner.
Collapse
Affiliation(s)
- Verónica C De Giusti
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata, Argentina
| | | | | |
Collapse
|
25
|
Boron WF, Chen L, Parker MD. Modular structure of sodium-coupled bicarbonate transporters. ACTA ACUST UNITED AC 2009; 212:1697-706. [PMID: 19448079 DOI: 10.1242/jeb.028563] [Citation(s) in RCA: 103] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Mammalian genomes contain 10 SLC4 genes that, between them, encode three Cl-HCO(3) exchangers, five Na(+)-coupled HCO(3) transporters (NCBTs), one reported borate transporter, and what is reported to be a fourth Cl-HCO(3) exchanger. The NCBTs are expressed throughout the body and play important roles in maintaining intracellular and whole-body pH, as well as contributing to transepithelial transport processes. The importance of NCBTs is underscored by the genetic association of dysfunctional NCBT genes with blindness, deafness, epilepsy, hypertension and metal retardation. Key to understanding the action and regulation of NCBTs is an appreciation of the diversity of NCBT gene products. The transmembrane domains of human NCBT paralogs are 50-84% identical to each other at the amino acid level, and are capable of a diverse range of actions, including electrogenic Na/HCO(3) cotransport (i.e. NBCe1 and NBCe2) and electroneutral Na/HCO(3) cotransport (i.e. NBCn1 and NBCn2), as well as Na(+)-dependent Cl-HCO(3) exchange (i.e. NDCBE). Furthermore, by the use of alternative promoters and alternative-splicing events, individual SLC4 genes have the potential to generate multiple splice variants (as many as 16 in the case of NBCn1), each of which could have unique temporal and spatial patterns of distribution, unitary transporter activity (i.e. flux mediated by one molecule), array of protein-binding partners, and complement of regulatory stimuli. In the first section of this review, we summarize our present knowledge of the function and distribution of mammalian NCBTs and their multiple variants. In the second section of this review we consider the molecular consequences of NCBT variation.
Collapse
Affiliation(s)
- Walter F Boron
- Department of Physiology, Case Western Reserve University Medical School, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | | | | |
Collapse
|
26
|
Role of reactive oxygen species (ROS) in angiotensin II-induced stimulation of the cardiac Na+/HCO3- cotransport. J Mol Cell Cardiol 2009; 47:716-22. [PMID: 19646989 DOI: 10.1016/j.yjmcc.2009.07.023] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/08/2009] [Revised: 07/15/2009] [Accepted: 07/21/2009] [Indexed: 01/12/2023]
Abstract
The sarcolemmal Na+/HCO3- cotransporter (NBC) plays an important role in intracellular pH (pH(i)) regulation in the heart. In the present work we studied, in isolated cat ventricular myocytes, the role of Angiotensin II (Ang II) and reactive oxygen species (ROS) production as potential activators of the NBC. pH(i) was measured in single cells in a medium with HCO3- using the fluorescent pH indicator BCECF. The NH4+ pulse method was used to induce an intracellular acid load and the acid efflux (JH) in the presence of the Na+/H+ exchanger blocker HOE642 (10 microM) was calculated as indicator of NBC activity. The following JH data are presented at pH(i) of 6.8 (* and # indicate p<0.05 after ANOVA vs. control and Ang II, respectively). The basal JH (1.03+/-0.12 mM/min, n=11) was significantly increased in the presence of 100 nM Ang II (1.70+/-0.15 mM/min, n=8*). This effect of Ang II was abolished when we added to the extracellular solution 2 mM MPG (ROS scavenger; 0.80+/-0.08 mM/min, n=11#), 300 microM apocynin (NADPH oxidase blocker; 0.80+/-0.13 mM/min, n=6#), 500 microM 5-hydroxidecanoate (mitochondrial ATP dependent K+ channel, mK(ATP), blocker; 0.97+/-0.21 mM/min, n=9#), or the inhibitor of the MAP kinase ERK pathway U0126 (10 microM; 0.56+/-0.18 mM/min, n=6#). We also determined the phosphorylation of ERK during the first min of acidosis and we detected that Ang II significantly enhanced the ERK phosphorylation levels, an effect that was cancelled by scavenging ROS with MPG. In conclusion, we propose that Ang II enhances the production of ROS through the activation of the NADPH oxidase, which in turn triggers mK(ATP) opening and mitochondrial ROS production ("ROS-induced ROS-release mechanism"). Finally, these mitochondrial ROS stimulate the ERK pathway, leading to the activation of the NBC.
Collapse
|
27
|
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.
Collapse
Affiliation(s)
- Richard D Vaughan-Jones
- Burdon Sanderson Cardiac Science Centre, Department of Physiology, Anatomy and Genetics, Oxford, Parks Road, OX1 3PT, UK.
| | | | | |
Collapse
|
28
|
Ch'en FFT, Villafuerte FC, Swietach P, Cobden PM, Vaughan-Jones RD. S0859, an N-cyanosulphonamide inhibitor of sodium-bicarbonate cotransport in the heart. Br J Pharmacol 2008; 153:972-82. [PMID: 18204485 DOI: 10.1038/sj.bjp.0707667] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
BACKGROUND AND PURPOSE Intracellular pH (pH(i)) in heart is regulated by sarcolemmal H(+)-equivalent transporters such as Na(+)-H(+) exchange (NHE) and Na(+)-HCO(3) (-) cotransport (NBC). Inhibition of NBC influences pH(i) and can be cardioprotective in animal models of post-ischaemic reperfusion. Apart from a rabbit polyclonal NBC-antibody, a selective NBC inhibitor compound has not been studied. Compound S0859 (C(29)H(24)ClN(3)O(3)S) is a putative NBC inhibitor. Here, we provide the drug's chemical structure, test its potency and selectivity in ventricular cells and assess its suitability for experiments on cardiac contraction. EXPERIMENTAL APPROACH pH(i) recovery from intracellular acidosis was monitored using pH-epifluorescence (SNARF-fluorophore) in guinea pig, rat and rabbit isolated ventricular myocytes. Electrically evoked cell shortening (contraction) was measured optically. With CO(2)/HCO(3) (-)-buffered superfusates containing 30 muM cariporide (to inhibit NHE), pH(i) recovery is mediated by NBC. KEY RESULTS S0859, an N-cyanosulphonamide compound, reversibly inhibited NBC-mediated pH(i) recovery (K (i)=1.7 microM, full inhibition at approximately 30 microM). In HEPES-buffered superfusates, NHE-mediated pH(i) recovery was unaffected by 30 microM S0859. With CO(2)/HCO(3) (-) buffer, pH(i) recovery from intracellular alkalosis (mediated by Cl(-)/HCO(3) (-) and Cl(-)/OH(-) exchange) was also unaffected. Selective NBC-inhibition was not due to action on carbonic anhydrase (CA) enzymes, as 100 microM acetazolamide (a membrane-permeant CA-inhibitor) had no significant effect on NBC activity. pH(i) recovery from acidosis was associated with increased contractile-amplitude. The time course of recovery of pH(i) and contraction was slowed by S0859, confirming that NBC is a significant controller of contractility during acidosis. CONCLUSIONS AND IMPLICATIONS Compound S0859 is a selective, high-affinity generic NBC inhibitor, potentially important for probing the transporter's functional role in heart and other tissues.
Collapse
Affiliation(s)
- F F-T Ch'en
- Burdon Sanderson Cardiac Science Centre, Department of Physiology, Anatomy and Genetics, Division of Medical Sciences, Oxford University, Oxford, UK
| | | | | | | | | |
Collapse
|
29
|
Piermarini PM, Choi I, Boron WF. Cloning and characterization of an electrogenic Na/HCO3− cotransporter from the squid giant fiber lobe. Am J Physiol Cell Physiol 2007; 292:C2032-45. [PMID: 17267543 DOI: 10.1152/ajpcell.00544.2006] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The squid giant axon is a classic model system for understanding both excitable membranes and ion transport. To date, a Na+-driven Cl-HCO3− exchanger, sqNDCBE—related to the SLC4 superfamily and cloned from giant fiber lobe cDNA—is the only HCO3−-transporting protein cloned and characterized from a squid. The goal of our study was to clone and characterize another SLC4-like cDNA. We used degenerate PCR to obtain a partial cDNA clone (squid fiber clone 3, SF3), which we extended in both the 5′ and 3′ directions to obtain the full-length open-reading frame. The predicted amino-acid sequence of SF3 is similar to sqNDCBE, and a phylogenetic analysis of the membrane domains indicates that SF3 clusters with electroneutral Na+-coupled SLC4 transporters. However, when we measure pHi and membrane potential—or use two-electrode voltage clamping to measure currents—on Xenopus oocytes expressing SF3, the oocytes exhibit the characteristics of an electrogenic Na/HCO3− cotransporter, NBCe. That is, exposure to extracellular CO2/HCO3− not only causes a fall in pHi, followed by a robust recovery, but also causes a rapid hyperpolarization. The current-voltage relationship is also characteristic of an electrogenic NBC. The pHi recovery and current require HCO3− and Na+, and are blocked by DIDS. Furthermore, neither K+ nor Li+ can fully replace Na+ in supporting the pHi recovery. Extracellular Cl− is not necessary for the transporter to operate. Therefore, SF3 is an NBCe, representing the first NBCe characterized from an invertebrate.
Collapse
Affiliation(s)
- Peter M Piermarini
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut, USA.
| | | | | |
Collapse
|
30
|
Niederer SA, Smith NP. A mathematical model of the slow force response to stretch in rat ventricular myocytes. Biophys J 2007; 92:4030-44. [PMID: 17369410 PMCID: PMC1868992 DOI: 10.1529/biophysj.106.095463] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We developed a model of the rat ventricular myocyte at room temperature to predict the relative effects of different mechanisms on the cause of the slow increase in force in response to a step change in muscle length. We performed simulations in the presence of stretch-dependent increases in flux through the Na(+)-H(+) exchanger (NHE) and Cl(-)-HCO(3)(-) exchanger (AE), stretch-activated channels (SAC), and the stretch-dependent nitric oxide (NO) induced increased open probability of the ryanodine receptors to estimate the capacity of each mechanism to produce the slow force response (SFR). Inclusion of stretch-dependent NHE & AE, SACs, and stretch-dependent NO effects caused an increase in tension following 15 min of stretch of 0.87%, 32%, and 0%, respectively. Comparing [Ca(2+)](i) dynamics before and after stretch in the presence of combinations of the three stretch-dependent elements, which produced significant SFR values (>20%), showed that the inclusion of stretch-dependent NO effects produced [Ca(2+)](i) transients, which were not consistent with experimental results. Further simulations showed that in the presence of SACs and the absence of stretch-dependent NHE & AE inhibition of NHE attenuated the SFR, such that reduced SFR in the presence of NHE blockers does not indicate a stretch dependence of NHE. Rather, a functioning NHE is responsible for a portion of the SFR. Based on our simulations we estimate that in rat cardiac myocytes at room temperature SACs play a significant role in producing the SFR, potentially in the presence of stretch-dependent NHE & AE and that NO effects, if any, must involve more mechanisms than just increasing the open probability of ryanodine receptors.
Collapse
Affiliation(s)
- Steven A Niederer
- Bioengineering Institute, University of Auckland, Auckland, New Zealand
| | | |
Collapse
|
31
|
Villa-Abrille MC, Petroff MGV, Aiello EA. The electrogenic Na+/HCO3- cotransport modulates resting membrane potential and action potential duration in cat ventricular myocytes. J Physiol 2006; 578:819-29. [PMID: 17138608 PMCID: PMC2151338 DOI: 10.1113/jphysiol.2006.120170] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Perforated whole-cell configuration of patch clamp was used to determine the contribution of the electrogenic Na+/HCO3- cotransport (NBC) on the shape of the action potential in cat ventricular myocytes. Switching from Hepes to HCO3- buffer at constant extracellular pH (pH(o)) hyperpolarized resting membrane potential (RMP) by 2.67 +/- 0.42 mV (n = 9, P < 0.05). The duration of action potential measured at 50% of repolarization time (APD50) was 35.8 +/- 6.8% shorter in the presence of HCO3- than in its absence (n = 9, P < 0.05). The anion blocker SITS prevented and reversed the HCO3- -induced hyperpolarization and shortening of APD. In addition, no HCO3- -induced hyperpolarization and APD shortening was observed in the absence of extracellular Na+. Quasi-steady-state currents were evoked by 8 s duration voltage-clamped ramps ranging from -130 to +30 mV. A novel component of SITS-sensitive current was observed in the presence of HCO3-. The HCO3- -sensitive current reversed at -87 +/- 5 mV (n = 7), a value close to the expected reversal potential of an electrogenic Na+/HCO3- cotransport with a HCO3-:Na+ stoichiometry ratio of 2: 1. The above results allow us to conclude that the cardiac electrogenic Na+/HCO3- cotransport has a relevant influence on RMP and APD of cat ventricular cells.
Collapse
Affiliation(s)
- María C Villa-Abrille
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, 60 y 120, La Plata 1900, Argentina
| | | | | |
Collapse
|
32
|
Vaughan-Jones RD, Villafuerte FC, Swietach P, Yamamoto T, Rossini A, Spitzer KW. pH-Regulated Na(+) influx into the mammalian ventricular myocyte: the relative role of Na(+)-H(+) exchange and Na(+)-HCO Co-transport. J Cardiovasc Electrophysiol 2006; 17 Suppl 1:S134-S140. [PMID: 16686668 DOI: 10.1111/j.1540-8167.2006.00394.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
In the heart, intracellular Na(+) concentration (Na(+) (i)) is a controller of intracellular Ca(2+) signaling, and hence of key aspects of cell contractility and rhythm. Na(+) (i) will be influenced by variation in Na(+) influx. In the present work, we consider one source of Na(+) influx, sarcolemmal acid extrusion. Acid extrusion is accomplished by sarcolemmal H(+) and HCO(3) (-) transporters that import Na(+) ions while exporting H(+) or importing HCO(3) (-). The capacity of this system to import Na(+) is enormous, up to four times the maximum capacity of the Na(+)-K(+) ATPase to extrude Na(+) ions from the cell. In this review we consider the role of Na(+)-H(+) exchange (NHE) and Na(+)-HCO(3) (-)co-transport (NBC) in mediating Na(+) influx into cardiac myocytes. We consider, in particular, the role of NBC, as so little is known about Na(+) influx through this transporter. We show that both proteins mediate significant Na(+) influx and that although, in the ventricular myocyte, NBC-mediated Na(+) influx is less than through NHE, the proportions may be altered under a variety of conditions, including exposure to catecholamines, membrane depolarization, and interference with activity of the enzyme, carbonic anhydrase.
Collapse
|
33
|
Ten Hove M, Nederhoff MGJ, Van Echteld CJA. Relative contributions of Na+/H+exchange and Na+/HCO3−cotransport to ischemic Nai+overload in isolated rat hearts. Am J Physiol Heart Circ Physiol 2005; 288:H287-92. [PMID: 15319198 DOI: 10.1152/ajpheart.01102.2003] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The Na+/H+exchanger (NHE) and/or the Na+/HCO3−cotransporter (NBC) were blocked during ischemia in isolated rat hearts. Intracellular Na+concentration ([Na+]i), intracellular pH (pHi), and energy-related phosphates were measured by using simultaneous23Na and31P NMR spectroscopy. Hearts were subjected to 30 min of global ischemia and 30 min of reperfusion. Cariporide (3 μM) or HCO3−-free HEPES buffer was used, respectively, to block NHE, NBC, or both. End-ischemic [Na+]iwas 320 ± 18% of baseline in HCO3−-perfused, untreated hearts, 184 ± 6% of baseline when NHE was blocked, 253 ± 19% of baseline when NBC was blocked, and 154 ± 6% of baseline when both NHE and NBC were blocked. End-ischemic pHiwas 6.09 ± 0.06 in HCO3−-perfused, untreated hearts, 5.85 ± 0.02 when NHE was blocked, 5.81 ± 0.05 when NBC was blocked, and 5.70 ± 0.01 when both NHE and NBC were blocked. NHE blockade was cardioprotective, but NBC blockade and combined blockade were not, the latter likely due to a reduction in coronary flow, because omission of HCO3−under conditions of NHE blockade severely impaired coronary flow. Combined blockade of NHE and NBC conserved intracellular H+load during reperfusion and led to massive Na+influx when blockades were lifted. Without blockade, both NHE and NBC mediate acid-equivalent efflux in exchange for Na+influx during ischemia, NHE much more than NBC. Blockade of either one does not affect the other.
Collapse
Affiliation(s)
- Michiel Ten Hove
- Interuniversity Cardiology, Institute of the Netherlands, Utrecht, The Netherlands
| | | | | |
Collapse
|
34
|
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.
Collapse
Affiliation(s)
- Taku Yamamoto
- Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City, UT 84112, USA.
| | | | | | | | | | | |
Collapse
|
35
|
Aiello EA, Villa-Abrille MC, Escudero EM, Portiansky EL, Pérez NG, de Hurtado MCC, Cingolani HE. Myocardial hypertrophy of normotensive Wistar-Kyoto rats. Am J Physiol Heart Circ Physiol 2004; 286:H1229-35. [PMID: 14630632 DOI: 10.1152/ajpheart.00779.2003] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In our studies with spontaneously hypertensive (SHR), Wistar-Kyoto (WKY), and Wistar rats, we observed normotensive WKY rats with cardiac hypertrophy determined by a greater left ventricular (LV) mass (LVM)-to-body weight (BW) ratio (LVM/BW) than that of normotensive Wistar rats. Thus we compared the following parameters in SHR, WKY, and Wistar rats: LVM/BW, cell capacitance as index of total surface area of the myocytes, length, width, and cross-sectional area of cardiac myocytes, LV collagen volume fraction, and myocardial stiffness. The LVM/BW of WKY (2.41 ± 0.03 mg/g, n = 41) was intermediate between SHR (2.82 ± 0.04 mg/g, n = 47) and Wistar rats (1.98 ± 0.04 mg/g, n = 28). A positive correlation between blood pressure and LVM was found in SHR, whereas no such relationship was observed in WKY or Wistar rats. Cell capacitance and cross-sectional area were not significantly different in SHR and WKY rats; these values were significantly higher than those of Wistar rats. The cell length was smaller but the width was similar in WKY compared with SHR. Papillary muscles isolated from the LV of WKY and SHR were stiffer than those from Wistar rats. Consistently, a greater level of myocardial fibrosis was detected in WKY and SHR compared with Wistar rats. These findings demonstrate blood pressure-independent cardiac hypertrophy in normotensive WKY rats.
Collapse
Affiliation(s)
- Ernesto A Aiello
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, La Plata 1900, Argentina.
| | | | | | | | | | | | | |
Collapse
|
36
|
Versluis JP, Heslinga JW, Sipkema P, Westerhof N. Contractile reserve but not tension is reduced in monocrotaline-induced right ventricular hypertrophy. Am J Physiol Heart Circ Physiol 2004; 286:H979-84. [PMID: 14527938 DOI: 10.1152/ajpheart.00536.2002] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The objective of this study was to evaluate the role of right ventricular hypertrophy on developed tension (Fdev) and contractile reserve of rat papillary muscle by using a model of monocrotaline (Mct)-induced pulmonary hypertension. Calcium handling and the influence of bicarbonate ([Formula: see text]) were also addressed with the use of two different buffers ([Formula: see text] and HEPES). Wistar rats were injected with either Mct (40 mg/kg sc) or vehicle control (Con). Isometrically contracting right ventricular papillary muscles were studied at 80% of the length of maximal developed force. Contractile reserve (1 – Fdev/Fmax) was calculated from Fdev and maximal tension (Fmax). Calcium recirculation was determined with postextrasystolic potentiation. Both groups of muscles were superfused with either [Formula: see text] (Con-B and Mct-B, both n = 6) or HEPES (Con-H and Mct-H, both n = 6) buffer. With hypertrophy, contractions were slower but Fdev was not changed. However, Fmax was decreased ( P < 0.05). With [Formula: see text], Fmax decreased from 23.8 ± 6.5 mN·mm–2 in Con-B, to 13.7 ± 3.3 mN·mm–2 in Mct-B. With HEPES, it decreased from 16.3 ± 3.5 mN·mm–2 ( n = 6, Con-H) to 8.3 ± 1.6 mN·mm–2 (Mct-H). Contractile reserve during hypertrophy was therefore also decreased ( P < 0.05). With [Formula: see text], it decreased from 0.73 ± 0.03 (Con-B) to 0.55 ± 0.04 (Mct-B). With HEPES, it decreased ( P < 0.001) from 0.64 ± 0.07 (Con-H) to 0.19 ± 0.06 (Mct-H). The recirculation fraction decreased ( P < 0.05) from 0.59 ± 0.04 in Con-B to 0.44 ± 0.04 in Mct-B. We conclude that contractile reserve and recirculation fraction are impaired during hypertrophy, with a stronger effect under HEPES than [Formula: see text] superfusion.
Collapse
Affiliation(s)
- J Pieter Versluis
- Laboratory for Physiology, Institute for Cardiovascular Research, Vrije Univ. Medical Center, Van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands
| | | | | | | |
Collapse
|
37
|
Abstract
Computational models of the electrical and mechanical function of the heart are reviewed. These models attempt to explain the integrated function of the heart in terms of ventricular anatomy, the structure and material properties of myocardial tissue, the membrane ion channels, and calcium handling and myofilament mechanics of cardiac myocytes. The models have established the computational framework for linking the structure and function of cardiac cells and tissue to the integrated behavior of the intact heart, but many more aspects of physiological function, including metabolic and signal transduction pathways, need to be included before significant progress can be made in understanding many disease processes.
Collapse
Affiliation(s)
- Peter J Hunter
- Bioengineering Institute, University of Auckland, New Zealand.
| | | | | |
Collapse
|
38
|
Abstract
Bicarbonate is not freely permeable to membranes. Yet, bicarbonate must be moved across membranes, as part of CO2 metabolism and to regulate cell pH. Mammalian cells ubiquitously express bicarbonate transport proteins to facilitate the transmembrane bicarbonate flux. These bicarbonate transporters, which function by different transport mechanisms, together catalyse transmembrane bicarbonate movement. Recent advances have allowed the identification of several new bicarbonate transporter genes. Bicarbonate transporters cluster into two separate families: (i) the anion exachanger (AE) family of Cl-/HCO3- exchangers is related in sequence to the NBC family of Na+/HCO3- cotransporters and the Na(+)-dependent Cl/HCO3- exchangers and (ii) some members of the SLC26a family of sulfate transporters will also transport bicarbonate but are not related in sequence to the AE/NBC family of transporters. This review summarizes our understanding of the mammalian bicarbonate transporter superfamily.
Collapse
Affiliation(s)
- Deborah Sterling
- Department of Physiology, University of Alberta, Edmonton, Canada
| | | |
Collapse
|
39
|
Vaughan-Jones RD, Spitzer KW. Role of bicarbonate in the regulation of intracellular pH in the mammalian ventricular myocyte. Biochem Cell Biol 2003; 80:579-96. [PMID: 12440699 DOI: 10.1139/o02-157] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Bicarbonate is important for pHi control in cardiac cells. It is a major part of the intracellular buffer apparatus, it is a substrate for sarcolemmal acid-equivalent transporters that regulate intracellular pH, and it contributes to the pHo sensitivity of steady-state pHi, a phenomenon that may form part of a whole-body response to acid/base disturbances. Both bicarbonate and H+/OH- transporters participate in the sarcolemmal regulation of pHi, namely Na(+)-HCO3-cotransport (NBC), Cl(-)-HCO3- exchange (i.e., anion exchange, AE), Na(+)-H+ exchange (NHE), and Cl(-)-OH- exchange (CHE). These transporters are coupled functionally through changes of pHi, while pHi is linked to [Ca2+]i through secondary changes in [Na+] mediated by NBC and NHE. Via such coupling, decreases of pHo and pHi can ultimately lead to an elevation of [Ca2+]i, thereby influencing cardiac contractility and electrical rhythm. Bicarbonate is also an essential component of an intracellular carbonic buffer shuttle that diffusively couples cytoplasmic pH to the sarcolemma and minimises the formation of intracellular pH microdomains. The importance of bicarbonate is closely linked to the activity of the enzyme carbonic anhydrase (CA). Without CA activity, intracellular bicarbonate-dependent buffering, membrane bicarbonate transport, and the carbonic shuttle are severely compromised. There is a functional partnership between CA and HCO3- transport. Based on our observations on intracellular acid mobility, we propose that one physiological role for CA is to act as a pH-coupling protein, linking bulk pH to the allosteric H+ control sites on sarcolemmal acid/base transporters.
Collapse
|
40
|
Bril A. [Ion transporters and cardiovascular diseases: pH control or modulation of intracellular calcium concentration]. Ann Cardiol Angeiol (Paris) 2003; 52:41-51. [PMID: 12710294 DOI: 10.1016/s0003-3928(02)00182-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The regulation of the intracellular pH is under tight control by several ion transport systems including the sodium-proton exchanger, the sodium-bicarbonate cotransporter and the chlore-bicarbonate anion exchanger. While the activation of the anion exchange induces a cellular acidification, both the sodium-proton exchanger and the sodium-bicarbonate cotransporter are responsible for a protection against acidosis by extruding protons or importing bicarbonate. These transporters are transmembrane proteins whose activity is regulated by several mechanisms including phosphorylation, calcium binding and which are involved in several pathophysiologic processes such as ischemia, hypertrophy and arrhythmias. Recent studies suggest that the activation of these transporters during various diseases induces an increase in intracellular calcium concentration. Therefore, inhibiting these transporters could represent novel therapeutic strategies for the treatment of cardiovascular diseases.
Collapse
Affiliation(s)
- A Bril
- Laboratoire de physiopathologie et pharmacologie cardiovasculaires expérimentales, IFR 100, facultés de médecine et pharmacie, 7, boulevard Jeanne-d'Arc, BP 87900, 21079 Dijon, France.
| |
Collapse
|
41
|
Gross E, Kurtz I. Structural determinants and significance of regulation of electrogenic Na(+)-HCO(3)(-) cotransporter stoichiometry. Am J Physiol Renal Physiol 2002; 283:F876-87. [PMID: 12372762 DOI: 10.1152/ajprenal.00148.2002] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Na(+)-HCO(3)(-) cotransporters play an important role in intracellular pH regulation and transepithelial HCO(3)(-) transport in various tissues. Of the characterized members of the HCO(3)(-) transporter superfamily, NBC1 and NBC4 proteins are known to be electrogenic. An important functional property of electrogenic Na(+)-HCO(3)(-) cotransporters is their HCO(3)(-):Na(+) coupling ratio, which sets the transporter reversal potential and determines the direction of Na(+)-HCO(3)(-) flux. Recent studies have shown that the HCO(3)(-):Na(+) transport stoichiometry of NBC1 proteins is either 2:1 or 3:1 depending on the cell type in which the transporters are expressed, indicating that the HCO(3)(-):Na(+) coupling ratio can be regulated. Mutational analysis has been very helpful in revealing the molecular mechanisms and signaling pathways that modulate the coupling ratio. These studies have demonstrated that PKA-dependent phosphorylation of the COOH terminus of NBC1 proteins alters the transport stoichiometry. This cAMP-dependent signaling pathway provides HCO(3)(-) -transporting epithelia with an efficient mechanism for modulating the direction of Na(+)-HCO(3)(-) flux through the cotransporter.
Collapse
Affiliation(s)
- Eitan Gross
- Departments of Urology and Physiology and Biophysics, Case Western Reserve University, and Veterans Affairs Medical Center, Cleveland, Ohio 44106, USA
| | | |
Collapse
|
42
|
Baetz D, Haworth RS, Avkiran M, Feuvray D. The ERK pathway regulates Na(+)-HCO(3)(-) cotransport activity in adult rat cardiomyocytes. Am J Physiol Heart Circ Physiol 2002; 283:H2102-9. [PMID: 12384488 DOI: 10.1152/ajpheart.01071.2001] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The sarcolemmal Na(+)-HCO cotransporter (NBC) is stimulated by intracellular acidification and acts as an acid extruder. We examined the role of the ERK pathway of the MAPK cascade as a potential mediator of NBC activation by intracellular acidification in the presence and absence of angiotensin II (ANG II) in adult rat ventricular myocytes. Intracellular pH (pH(i)) was recorded with the use of seminaphthorhodafluor-1. The NH method was used to induce an intracellular acid load. NBC activation was significantly decreased with the ERK inhibitors PD-98059 and U-0126. NBC activity after acidification was increased in the presence of ANG II (pH(i) range of 6.75-7.00). ANG II plus PD-123319 (AT(2) antagonist) still increased NBC activity, whereas ANG II plus losartan (AT(1) antagonist) did not affect it. ERK phosphorylation (measured by immunoblot analysis) during intracellular acidification was increased by ANG II, an effect that was abolished by losartan and U-0126. In conclusion, the MAPK(ERK)-dependent pathway facilitates the rate of pH(i) recovery from acid load through NBC activity and is involved in the AT(1) receptor-mediated stimulation of such activity by ANG II.
Collapse
Affiliation(s)
- Delphine Baetz
- Laboratoire de Physiologie Cellulaire and Centre National de la Recherche Scientifique, Hôpital Marie Lannelongue-Université Paris XI, 91405 Orsay Cedex, France
| | | | | | | |
Collapse
|
43
|
Virkki LV, Wilson DA, Vaughan-Jones RD, Boron WF. Functional characterization of human NBC4 as an electrogenic Na+-HCO cotransporter (NBCe2). Am J Physiol Cell Physiol 2002; 282:C1278-89. [PMID: 11997242 DOI: 10.1152/ajpcell.00589.2001] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have functionally characterized Na+-driven bicarbonate transporter (NBC)4, originally cloned from human heart by Pushkin et al. (Pushkin A, Abuladze N, Newman D, Lee I, Xu G, and Kurtz I. Biochem Biophys Acta 1493: 215-218, 2000). Of the four NBC4 variants currently present in GenBank, our own cloning efforts yielded only variant c. We expressed NBC4c (GenBank accession no. AF293337) in Xenopus laevis oocytes and assayed membrane potential (Vm) and pH regulatory function with microelectrodes. Exposing an NBC4c-expressing oocyte to a solution containing 5% CO2 and 33 mM HCO elicited a large hyperpolarization, indicating that the transporter is electrogenic. The initial CO2-induced decrease in intracellular pH (pH(i)) was followed by a slow recovery that was reversed by removing external Na+. Two-electrode voltage clamp of NBC4c-expressing oocytes revealed large HCO- and Na+-dependent currents. When we voltage clamped V(m) far from NBC4c's estimated reversal potential (E(rev)), the pH(i) recovery rate increased substantially. Both the currents and pH(i) recovery were blocked by 200 microM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). We estimated the transporter's HCO:Na+ stoichiometry by measuring E(rev) at different extracellular Na+ concentration ([Na+]o) values. A plot of E(rev) against log[Na+]o was linear, with a slope of 54.8 mV/log[Na+]o. This observation, as well as the absolute E(rev) values, are consistent with a 2:1 stoichiometry. In conclusion, the behavior of NBC4c, which we propose to call NBCe2-c, is similar to that of NBCe1, the first electrogenic NBC.
Collapse
Affiliation(s)
- Leila V Virkki
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06520-8026, USA.
| | | | | | | |
Collapse
|
44
|
Pandit SV, Clark RB, Giles WR, Demir SS. A mathematical model of action potential heterogeneity in adult rat left ventricular myocytes. Biophys J 2001; 81:3029-51. [PMID: 11720973 PMCID: PMC1301767 DOI: 10.1016/s0006-3495(01)75943-7] [Citation(s) in RCA: 236] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
Mathematical models were developed to reconstruct the action potentials (AP) recorded in epicardial and endocardial myocytes isolated from the adult rat left ventricle. The main goal was to obtain additional insight into the ionic mechanisms responsible for the transmural AP heterogeneity. The simulation results support the hypothesis that the smaller density and the slower reactivation kinetics of the Ca(2+)-independent transient outward K(+) current (I(t)) in the endocardial myocytes can account for the longer action potential duration (APD), and more prominent rate dependence in that cell type. The larger density of the Na(+) current (I(Na)) in the endocardial myocytes results in a faster upstroke (dV/dt(max)). This, in addition to the smaller magnitude of I(t), is responsible for the larger peak overshoot of the simulated endocardial AP. The prolonged APD in the endocardial cell also leads to an enhanced amplitude of the sustained K(+) current (I(ss)), and a larger influx of Ca(2+) ions via the L-type Ca(2+) current (I(CaL)). The latter results in an increased sarcoplasmic reticulum (SR) load, which is mainly responsible for the higher peak systolic value of the Ca(2+) transient [Ca(2+)](i), and the resultant increase in the Na(+)-Ca(2+) exchanger (I(NaCa)) activity, associated with the simulated endocardial AP. In combination, these calculations provide novel, quantitative insights into the repolarization process and its naturally occurring transmural variations in the rat left ventricle.
Collapse
Affiliation(s)
- S V Pandit
- Joint Graduate Program in Biomedical Engineering, The University of Memphis, Tennessee 38152-3210, USA
| | | | | | | |
Collapse
|
45
|
Salas MA, Vila-Petroff MG, Palomeque J, Aiello EA, Mattiazzi A. Positive inotropic and negative lusitropic effect of angiotensin II: intracellular mechanisms and second messengers. J Mol Cell Cardiol 2001; 33:1957-71. [PMID: 11708841 DOI: 10.1006/jmcc.2001.1460] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In the cat ventricle angiotensin II exerts a positive inotropic effect produced by an increase in intracellular calcium associated with a prolongation of relaxation. The signaling cascades involved in these effects as well as the subcellular mechanisms of the negative lusitropic effect are still not clearly defined. The present study was directed to investigate these issues in cat papillary muscles and isolated myocytes. The functional suppression of the sarcoplasmic reticulum (SR) with either 0.5 microm ryanodine or 0.5 microm ryanodine plus 1 microm thapsigargin or the preincubation of the myocytes with the specific inhibitor of the inositol 1,4,5-triphosphate (IP3) receptors [diphenylborinic acid, ethanolamine ester (2-APB), 5-50 microm] did not prevent the positive inotropic effect and the increment in Ca2+ transient produced by 1 microm angiotensin II. In contrast, protein kinase C (PKC) inhibitors, chelerythrine (20 microm) and calphostin C (1 microm) completely inhibited both, the angiotensin II-induced increase in L-type calcium current and positive inotropic effect. The prolongation of half relaxation time produced by 0.5 microm angiotensin II [207+/-15.4 msec (control) to 235+/-19.98 msec (angiotensin II), P<0.05] was completely blunted by PKC inhibition. This antirelaxant effect, which was independent of intracellular pH changes, was associated with a prolongation of the action potential duration and was preserved after either the inhibition of the SR and the SR Ca2+ ATPase (ryanodine plus thapsigargin) or of the reverse mode of the Na+/Ca2+ exchanger (KB-R7943, 5 microm). We conclude that in feline myocardium the positive inotropic and negative lusitropic effects of angiotensin II are both entirely mediated by PKC without any significant participation of the IP3 limb of the phosphatidylinositol/phospholipase C cascade. The results suggest that the antirelaxant effect of angiotensin II might be determined by the decrease in Ca2+ efflux through the Na+/Ca2+ exchanger produced by the angiotensin II-induced prolongation of the action potential duration.
Collapse
Affiliation(s)
- M A Salas
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, La Plata, 1900, Argentina
| | | | | | | | | |
Collapse
|
46
|
Bassingthwaighte JB. The modelling of a primitive 'sustainable' conservative cell. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2001; 359:1055-1072. [PMID: 21938260 PMCID: PMC3175798 DOI: 10.1098/rsta.2001.0821] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The simple sustainable or 'eternal' cell model, assuming preservation of all proteins, is designed as a building block, a primitive element upon which one can build more complete functional cell models of various types, representing various species. In the modelling we emphasize the electrophysiological aspects, in part because these are a well-developed component of cell models and because membrane potentials and their fluctuations have been generally omitted from metabolically oriented cell models in the past. Fluctuations in membrane potential deserve heightened consideration because probably all cells have negative intracellular potentials and most cells demonstrate electrical activity with vesicular extrusion, receptor occupancy, as well as with stimulated excitation resulting in regenerative depolarization. The emphasis is on the balances of mass, charge, and of chemical species while accounting for substrate uptake, metabolism and metabolite loss from the cell. By starting with a primitive representation we emphasize the conservation ideas. As more advanced models are generated they must adhere to the same basic principles as are required for the most primitive incomplete model.
Collapse
|
47
|
Aiello EA, Cingolani HE. Angiotensin II stimulates cardiac L-type Ca(2+) current by a Ca(2+)- and protein kinase C-dependent mechanism. Am J Physiol Heart Circ Physiol 2001; 280:H1528-36. [PMID: 11247763 DOI: 10.1152/ajpheart.2001.280.4.h1528] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Angiotensin II (ANG II) evokes positive inotropic responses in various species. However, the effects of this peptide on L-type Ca(2+) currents (I(Ca)) are still controversial. We report in this study that the effects of ANG II on I(Ca) differ depending on the mode of patch-clamp technique used, standard whole cell (WC) or perforated patch (PP). No significant effects of ANG II (0.5 microM) were observed when WC in cells dialyzed with high EGTA was used. However, when the intracellular milieu was preserved using PP, ANG II induced a significant 77 +/- 6% increase in I(Ca) (-2.2 +/- 0.3 in control and -3.9 +/- 0.6 pA/pF in ANG II, n = 8, P < 0.05). When WC was used in cells dialyzed with low Ca(2+) buffer capacity (EGTA 0.1 mM), ANG II was able to induce an increase in I(Ca) (-3.5 +/- 0.3 in control vs. -4.8 +/- 0.4 pA/pF in ANG II, n = 13, P < 0.05). This increase was prevented when the cells were also dialyzed with the protein kinase C (PKC) inhibitor chelerythrine (50 microM) or calphostin C (1 microM). The above results allow us to conclude that strong intracellular Ca(2+) buffering prevents the physiological actions of ANG II on cardiac I(Ca), which are also dependent on activation of PKC.
Collapse
Affiliation(s)
- E A Aiello
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata 1900, Argentina.
| | | |
Collapse
|
48
|
Petroff MG, Aiello EA, Palomeque J, Salas MA, Mattiazzi A. Subcellular mechanisms of the positive inotropic effect of angiotensin II in cat myocardium. J Physiol 2000; 529 Pt 1:189-203. [PMID: 11080261 PMCID: PMC2270170 DOI: 10.1111/j.1469-7793.2000.00189.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
1. Cat ventricular myocytes loaded with [Ca2+]i- and pHi-sensitive probes were used to examine the subcellular mechanism(s) of the Ang II-induced positive inotropic effect. Ang II (1 microM) produced parallel increases in contraction and Ca2+ transient amplitudes and a slowly developing intracellular alkalisation. Maximal increases in contraction amplitude and Ca2+ transient amplitude were 163 +/- 22 and 43 +/- 8 %, respectively, and occurred between 5 and 7 min after Ang II administration, whereas pHi increase (0.06 +/- 0.03 pH units) became significant only 15 min after the addition of Ang II. Furthermore, the inotropic effect of Ang II was preserved in the presence of Na+-H+ exchanger blockade. These results indicate that the positive inotropic effect of Ang II is independent of changes in pHi. 2. Similar increases in contractility produced by either elevating extracellular [Ca2+] or by Ang II application produced similar increases in peak systolic Ca2+ indicating that an increase in myofilament responsiveness to Ca2+ does not participate in the Ang II-induced positive inotropic effect. 3. Ang II significantly increased the L-type Ca2+ current, as assessed by using the perforated patch-clamp technique (peak current recorded at 0 mV: -1.88 +/- 0.16 pA pF-1 in control vs. -3.03 +/- 0.20 pA pF-1 after 6-8 min of administration of Ang II to the bath solution). 4. The positive inotropic effect of Ang II was not modified in the presence of either KB-R7943, a specific blocker of the Na+-Ca2+ exchanger, or ryanodine plus thapsigargin, used to block the sarcoplasmic reticulum function. 5. The above results allow us to conclude that in the cat ventricle the Ang II-induced positive inotropic effect is due to an increase in the intracellular Ca2+ transient, an enhancement of the L-type Ca2+ current being the dominant mechanism underlying this increase.
Collapse
Affiliation(s)
- M G Petroff
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Medicas, Universidad Nacional de La Plata, La Plata 1900, Argentina
| | | | | | | | | |
Collapse
|
49
|
Sciortino CM, Romero MF. Cation and voltage dependence of rat kidney electrogenic Na(+)-HCO(-)(3) cotransporter, rkNBC, expressed in oocytes. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 277:F611-23. [PMID: 10516286 DOI: 10.1152/ajprenal.1999.277.4.f611] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Recently, we reported the cloning and expression of the rat renal electrogenic Na(+)-HCO(-)(3) cotransporter (rkNBC) in Xenopus oocytes [M. F. Romero, P. Fong, U. V. Berger, M. A. Hediger, and W. F. Boron. Am. J. Physiol. 274 (Renal Physiol. 43): F425-F432, 1998]. Thus far, all NBC cDNAs are at least 95% homologous. Additionally, when expressed in oocytes the NBCs are 1) electrogenic, 2) Na(+) dependent, 3) HCO(-)(3) dependent, and 4) inhibited by stilbenes such as DIDS. The apparent HCO(-)(3):Na(+) coupling ratio ranges from 3:1 in kidney to 2:1 in pancreas and brain to 1:1 in the heart. This study investigates the cation and voltage dependence of rkNBC expressed in Xenopus oocytes to better understand NBC's apparent tissue-specific physiology. Using two-electrode voltage clamp, we studied the cation specificity, Na(+) dependence, and the current-voltage (I-V) profile of rkNBC. These experiments indicate that K(+) and choline do not stimulate HCO(-)(3)-sensitive currents via rkNBC, and Li(+) elicits only 3 +/- 2% of the total Na(+) current. The Na(+) dose response studies show that the apparent affinity of rkNBC for extracellular Na(+) ( approximately 30 mM [Na(+)](o)) is voltage and HCO(-)(3) independent, whereas the rkNBC I-V relationship is Na(+) dependent. At [Na(+)](o) v(max) (96 mM), the I-V response is approximately linear; both inward and outward Na(+)-HCO(-)(3) cotransport are observed. In contrast, only outward cotransport occurs at low [Na(+)](o) (<1 mM [Na(+)](o)). All rkNBC currents are inhibited by extracellular application of DIDS, independent of voltage and [Na(+)](o). Using ion-selective microelectrodes, we monitored intracellular pH and Na(+) activity. We then calculated intracellular [HCO(-)(3)] and, with the observed reversal potentials, calculated the stoichiometry of rkNBC over a range of [Na(+)](o) values from 10 to 96 mM at 10 and 33 mM [HCO(-)(3)](o). rkNBC stoichiometry is 2 HCO(-)(3):1 Na(+) over this entire Na(+) range at both HCO(-)(3) concentrations. Our results indicate that rkNBC is highly selective for Na(+), with transport direction and magnitude sensitive to [Na(+)](o) as well as membrane potential. Since the rkNBC protein alone in oocytes exhibits a stoichiometry of less than the 3 HCO(-)(3):1 Na(+) thought necessary for HCO(-)(3) reabsorption by the renal proximal tubule, a control mechanism or signal that alters its in vivo function is hypothesized.
Collapse
Affiliation(s)
- C M Sciortino
- Department of Physiology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4970, USA
| | | |
Collapse
|
50
|
Morgan PE, Aiello EA, Chiappe de Cingolani GE, Mattiazzi AR, Cingolani HE. Chronic administration of nifedipine induces up-regulation of functional calcium channels in rat myocardium. J Mol Cell Cardiol 1999; 31:1873-83. [PMID: 10525425 DOI: 10.1006/jmcc.1999.1019] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Previous studies from our laboratory demonstrated the up-regulation of cardiac dihydropyridine (DHP) receptors in rabbits chronically treated with nifedipine (NIFE). The goal of the present study was to further examine the functionality of this increased number of receptors by analysing different steps of excitation contraction coupling mechanism in adult rats chronically treated with NIFE (a single 10-mg oral dose/kg/day for 28 days). Ca2+ channel density was assessed by specific binding at the DHP receptors with [methyl-(3)H]PN 200-110 in rat ventricular membranes. Chronic NIFE treatment produced up-regulation of Ca2+ channels, being the maximal binding capacities 222+/-19 fmol/mg protein (n=14) and 310+/-21 fmol/mg protein (n=11) in untreated and treated animals, respectively (P<0.05). The functional consequences of this up-regulation of Ca2+ channels were determined in isolated ventricular myocytes by measuring L-type Ca2+ currents (I(Ca)) with the whole-cell configuration of patch-clamp technique and by intracellular Ca2+ (Ca2+(i)) transients estimated by the Indo-1/AM fluorescence ratio (410/482) simultaneously monitored with cell shortening. Peak I(Ca) density recorded at 0 mV was 32% greater in myocytes isolated from the treated group than in those obtained from the untreated group (-10.43+/-0.73 pA/pF (n=13) vs-7.10+/-0.59 pA/pF (n=12) P<0.05). Ca2+(i) transient amplitude and cell shortening, explored at 1 and 2 mM extracellular calcium ([Ca]0) were significantly higher in ventricular myocytes obtained fom NIFE-treated rats than in myocytes isolated from untreated animals. At 2 mM [Ca]0, the values of Ca2+(i) transient and shortening were 460+/-61 nM and 11+/-1 % of resting length (L(0)) in myocytes from treated rats (n=9) and 212+/-22 nM and 5.3+/-0.5% of L(0) in myocytes from control rats (n=6, P<0.05). The results demonstrate an up-regulation of functionally-active cardiac Ca2+ channels after NIFE treatment, and offer a possible explanation for a "withdrawal effect" at myocardial level after the suppression of the treatment with this drug.
Collapse
Affiliation(s)
- P E Morgan
- Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata, 1900, Argentina
| | | | | | | | | |
Collapse
|