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Sagawa T, Sagawa K, Kelly JE, Tsushima RG, Wasserstrom JA. Activation of cardiac ryanodine receptors by cardiac glycosides. Am J Physiol Heart Circ Physiol 2002; 282:H1118-26. [PMID: 11834511 DOI: 10.1152/ajpheart.00700.2001] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This study investigated the effects of cardiac glycosides on single-channel activity of the cardiac sarcoplasmic reticulum (SR) Ca2+ release channels or ryanodine receptor (RyR2) channels and how this action might contribute to their inotropic and/or toxic actions. Heavy SR vesicles isolated from canine left ventricle were fused with artificial planar lipid bilayers to measure single RyR2 channel activity. Digoxin and actodigin increased single-channel activity at low concentrations normally associated with therapeutic plasma levels, yielding a 50% of maximal effect of approximately 0.2 nM for each agent. Channel activation by glycosides did not require MgATP and occurred only when digoxin was applied to the cytoplasmic side of the channel. Similar results were obtained in human RyR2 channels; however, neither the crude skeletal nor the purified cardiac channel was activated by glycosides. Channel activation was dependent on [Ca2+] on the luminal side of the bilayer with maximal stimulation occurring between 0.3 and 10 mM. Rat RyR2 channels were activated by digoxin only at 1 microM, consistent with the lower sensitivity to glycosides in rat heart. These results suggest a model in which RyR2 channel activation by digoxin occurs only when luminal [Ca2+] was increased above 300 microM (in the physiological range). Consequently, increasing SR load (by Na+ pump inhibition) serves to amplify SR release by promoting direct RyR2 channel activation via a luminal Ca2+-sensitive mechanism. This high-affinity effect of glycosides could contribute to increased SR Ca2+ release and might play a role in the inotropic and/or toxic actions of glycosides in vivo.
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Affiliation(s)
- Toshio Sagawa
- Cardiology Division, Department of Medicine, Northwestern University Medical School, Chicago, Illinois 60611, USA
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52
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Wang J, Velotta JB, McDonough AA, Farley RA. All human Na(+)-K(+)-ATPase alpha-subunit isoforms have a similar affinity for cardiac glycosides. Am J Physiol Cell Physiol 2001; 281:C1336-43. [PMID: 11546672 DOI: 10.1152/ajpcell.2001.281.4.c1336] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Three alpha-subunit isoforms of the sodium pump, which is the receptor for cardiac glycosides, are expressed in human heart. The aim of this study was to determine whether these isoforms have distinct affinities for the cardiac glycoside ouabain. Equilibrium ouabain binding to membranes from a panel of different human tissues and cell lines derived from human tissues was compared by an F statistic to determine whether a single population of binding sites or two populations of sites with different affinities would better fit the data. For all tissues, the single-site model fit the data as well as the two-site model. The mean equilibrium dissociation constant (K(d)) for all samples calculated using the single-site model was 18 +/- 6 nM (mean +/- SD). No difference in K(d) was found between nonfailing and failing human heart samples, although the maximum number of binding sites in failing heart was only approximately 50% of the number of sites in nonfailing heart. Measurement of association rate constants and dissociation rate constants confirmed that the binding affinities of the different human alpha-isoforms are similar to each other, although calculated K(d) values were lower than those determined by equilibrium binding. These results indicate both that the affinity of all human alpha-subunit isoforms for ouabain is similar and that the increased sensitivity of failing human heart to cardiac glycosides is probably due to a reduction in the number of pumps in the heart rather than to a selective inhibition of a subset of pumps with different affinities for the drugs.
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Affiliation(s)
- J Wang
- Department of Physiology and Biophysics, University of Southern California Keck School of Medicine, Los Angeles, California 90089-9142, USA
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53
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Abstract
Like several other ion transporters, the Na(+)-K(+) pump of animal cells is electrogenic. The pump generates the pump current I(p). Under physiological conditions, I(p) is an outward current. It can be measured by electrophysiological methods. These methods permit the study of characteristics of the Na(+)-K(+) pump in its physiological environment, i.e., in the cell membrane. The cell membrane, across which a potential gradient exists, separates the cytosol and extracellular medium, which have distinctly different ionic compositions. The introduction of the patch-clamp techniques and the enzymatic isolation of cells have facilitated the investigation of I(p) in single cardiac myocytes. This review summarizes and discusses the results obtained from I(p) measurements in isolated cardiac cells. These results offer new exciting insights into the voltage and ionic dependence of the Na(+)-K(+) pump activity, its effect on membrane potential, and its modulation by hormones, transmitters, and drugs. They are fundamental for our current understanding of Na(+)-K(+) pumping in electrically excitable cells.
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Affiliation(s)
- H G Glitsch
- Arbeitsgruppe Muskelphysiologie, Fakultät für Biologie, Ruhr-Universität Bochum, Bochum, Germany
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54
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Jäger H, Wozniak G, Akintürk IH, Hehrlein FW, Scheiner-Bobis G. Expression of sodium pump isoforms and other sodium or calcium ion transporters in the heart of hypertensive patients. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1513:149-59. [PMID: 11470086 DOI: 10.1016/s0005-2736(01)00347-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
The sodium pump (Na(+),K(+)-ATPase; EC 3.6.1.37) of animal cell membranes is the enzyme responsible for the maintenance of membrane potential, for the function of secondary active transporters, and for osmoregulation of the cell. Since inhibition of the enzyme by cardiac glycosides results in increased contractility of the heart muscle and increased blood pressure, we were interested in whether there is a correlation between hypertension and expression of the various isoforms of the sodium pump. In addition, we also examined the expression of the isoforms of the sarcoplasmic and plasma membrane Ca(2+)-ATPase, the Na(+)/Ca(2+)- and Na(+)/H(+)-exchangers, and Na(+) channel and Ca(2+) channel isoforms. Total mRNA was isolated from 50 mg tissue from the right atrium of hypertensive and normotensive patients who were undergoing cardiac surgery. After reverse transcription and subsequent amplification of ion transporter-specific cDNA fragments by polymerase chain reaction (PCR) in the presence of [alpha-(32)P]dCTP, quantification of the amplified fragments was carried out by the Phosphorimager technique. The data obtained show that the alphal subunit mRNA is expressed similarly in normotensive and hypertensive patients. The amount of alpha2 subunit mRNA, however, is increased 5-fold in hypertensive patients. In the same group, the amount of alpha3 isoform is also significantly increased, although not as dramatically as the alpha2 isoform. Besides the Na(+),K(+)-ATPase isoforms, a significant increase in the expression of mRNA for the Na(+)/Ca(2+)-exchanger and the plasma membrane Ca(2+)-ATPase isoforms was detected. It is possible that the observed changes in mRNA expression for these ion transporters reflect compensatory mechanisms to overcome a defective Na(+) and Ca(2+) metabolism in the tissues of hypertensive patients or reflect defects directly involved in the cause of hypertension. The expression of mRNA for all other transporters investigated was unaltered.
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Affiliation(s)
- H Jäger
- Institut für Biochemie und Endokrinologie, Justus-Liebig-Universität Giessen, Fachbereich Veterinärmedizin, Frankfurter Strasse 100, D-35392 Giessen, Germany
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55
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Rossoni LV, Pinto VD, Vassallo DV. Effects of small doses of ouabain on the arterial blood pressure of anesthetized hypertensive and normotensive rats. Braz J Med Biol Res 2001; 34:1065-77. [PMID: 11471047 DOI: 10.1590/s0100-879x2001000800014] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Ouabain increases vascular resistance and may induce hypertension by inhibiting the Na+ pump. The effects of 0.18 and 18 microg/kg, and 1.8 mg/kg ouabain pretreatment on the phenylephrine (PHE; 0.1, 0.25 and 0.5 microg, in bolus)-evoked pressor responses were investigated using anesthetized normotensive (control and uninephrectomized) and hypertensive (1K1C and DOCA-salt treated) rats. Treatment with 18 microg/kg ouabain increased systolic and diastolic blood pressure in all groups studied. However, the magnitude of this increase was larger for the hypertensive 1K1C and DOCA-salt rats than for normotensive animals, while the pressor effect of 0.18 microg/kg ouabain was greater only in DOCA-salt rats. A very large dose (1.8 mg/kg) produced toxic effects on the normotensive control but not on uninephrectomized or 1K1C rats. Rat tail vascular beds were perfused to analyze the effects of 10 nM ouabain on the pressor response to PHE. In all animals, 10 nM ouabain increased the PHE pressor response, but this increase was larger in hypertensive DOCA-salt rats than in normotensive and 1K1C rats. Results suggested that a) increases in diastolic blood pressure induced by 18 microg/kg ouabain were larger in hypertensive than normotensive rats; b) in DOCA-salt rats, smaller ouabain doses had a stronger effect than in other groups; c) hypertensive and uninephrectomized rats were less sensitive to toxic doses of ouabain, and d) after treatment with 10 nM ouabain isolated tail vascular beds from DOCA-salt rats were more sensitive to the pressor effect of PHE than those from normotensive and 1K1C hypertensive rats. These data suggest that very small doses of ouabain, which might produce nanomolar plasma concentrations, enhance pressor reactivity in DOCA-salt hypertensive rats, supporting the idea that endogenous ouabain may contribute to the increase and maintenance of vascular tone in hypertension.
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Affiliation(s)
- L V Rossoni
- Departamento de Ciências Fisiológicas, Universidade Federal do Espírito Santo, Av. Marechal Campos 1468, 29040-095 Vitória ES, Brazil.
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56
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O'Brien SE, Apkon M, Berul CI, Patel HT, Saupe K, Spindler M, Ingwall JS, Zahler R. Phenotypical features of long Q-T syndrome in transgenic mice expressing human Na-K-ATPase alpha(3)-isoform in hearts. Am J Physiol Heart Circ Physiol 2000; 279:H2133-42. [PMID: 11045946 DOI: 10.1152/ajpheart.2000.279.5.h2133] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To understand why the adult human heart expresses three isoforms of the sodium pump, we generated transgenic mice (TGM) with 2.3- to 5. 5-fold overexpression of the human alpha(3)-isoform of Na-K-ATPase in the heart. Hearts from the TGM had increased maximal Na-K-ATPase activity and ouabain affinity compared with control hearts, even though the density of Na-K-ATPase pump sites (of all isoforms) was similar to that of control mice. In perfused hearts, contractility both at baseline and in the presence of ouabain tended to be greater in TGM than in controls. Surface electrocardiograms in anesthetized TGM had a steeper dependence of Q-T on sinus cycle length, and Q-T intervals measured during atrial pacing were significantly longer in TGM. Q-T dispersion during sinus rhythm also tended to be longer in TGM. Thus TGM overexpressing human alpha(3)-isoform have several of the phenotypical features of human long Q-T syndrome, despite the absence of previously described mutations in Na(+) or K(+) channels.
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Affiliation(s)
- S E O'Brien
- Departments of Internal Medicine and Pediatrics, Yale University School of Medicine, New Haven, Connecticut 06510, USA
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57
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Trouve P, Carre F, Belikova I, Leclercq C, Dakhli T, Soufir L, Coquard I, Ramirez-Gil J, Charlemagne D. Na(+)-K(+)-ATPase alpha(2)-isoform expression in guinea pig hearts during transition from compensation to decompensation. Am J Physiol Heart Circ Physiol 2000; 279:H1972-81. [PMID: 11009487 DOI: 10.1152/ajpheart.2000.279.4.h1972] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Disturbance in ionic gradient across sarcolemma may lead to arrhythmias. Because Na(+)-K(+)-ATPase regulates intracellular Na(+) and K(+) concentrations, and therefore intracellular Ca(2+) concentration homeostasis, our aim was to determine whether changes in the Na(+)-K(+)-ATPase alpha-isoforms in guinea pigs during transition from compensated (CLVH) to decompensated left ventricular hypertrophy (DLVH) were concomitant with arrhythmias. After 12- and 20-mo aortic stenosis, CLVH and DLVH were characterized by increased mean arterial pressure (30% and 52.7%, respectively). DLVH differed from CLVH by significantly increased end-diastolic pressure (34%), decreased sarco(endo)plasmic reticulum Ca(2+)-ATPase (-75%), and increased Na(+)/Ca(2+) exchanger (25%) mRNA levels and by the occurrence of ventricular arrhythmias. The alpha-isoform (mRNA and protein levels) was significantly lower in DLVH (2.2 +/- 0.2- and 1. 4 +/- 0.15-fold, respectively, vs. control) than in CLVH (3.5 +/- 0. 4- and 2.2 +/- 0.13-fold, respectively) and was present in sarcolemma and T tubules. Changes in the levels of alpha(1)- and alpha(3)-isoform in CLVH and DLVH appear physiologically irrelevant. We suggest that the increased level of alpha(2)-isoform in CLVH may participate in compensation, whereas its relative decrease in DLVH may enhance decompensation and arrhythmias.
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Affiliation(s)
- P Trouve
- Institut National de la Santé et de la Recherche Médicale, Unité 127, Institut Fédératif de Recherche Circulation Lariboisière, Université Denis Diderot, 75475 Paris, France
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58
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Rose AM, Qazzaz HM, Zolotarjova N, Mellett BJ, Martin AW, Valdes Jr R. Sodium Pump Isoforms in Xenotransplantation: Importance of Biochemical Compatibility. Clin Chem 2000. [DOI: 10.1093/clinchem/46.2.234] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
AbstractBackground: Xenotransplantation of pig hearts to humans could be hampered by the reportedly reduced affinity for digoxin of pig heart. We examined the hypothesis that expression of the individual α-subunit isoforms of the sodium pump [Na+,K+-ATPase (NKA)], the receptor for the plant-derived cardiac glycosides, may be responsible for this difference.Methods: We used a NKA-inhibition assay in combination with Western analysis, immunohistochemistry, and phosphorylation of the NKA α subunit to identify the distribution and expression of α isoforms in four chambers of porcine and human hearts.Results: We confirmed that tissue from porcine heart is less sensitive to digitalis (IC50 = 1740 nmol/L) when compared with human heart (IC50 = 840 nmol/L), whereas porcine cerebral cortex-mix had an affinity comparable to that of human heart (IC50 = 910 nmol/L). Our data show that porcine cerebral cortex-mix and human heart contain all three α isoforms, whereas porcine heart expresses only the α1 isoform.Conclusions: The different expressions of sodium pump isoforms in human vs porcine cardiac tissues suggests that porcine hearts may not be pharmacologically or endocrinologically compatible when used in humans. Studies of both pharmacologic and endocrinologic tissue compatibility are needed prior to selection of organs for xenotransplantation.
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Affiliation(s)
- Andrea M Rose
- Departments of Pathology and Laboratory Medicine and
| | | | | | | | | | - Roland Valdes Jr
- Departments of Pathology and Laboratory Medicine and
- Biochemistry and Molecular Biology, University of Louisville, School of Medicine, Louisville, KY 40292
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59
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Crambert G, Hasler U, Beggah AT, Yu C, Modyanov NN, Horisberger JD, Lelièvre L, Geering K. Transport and pharmacological properties of nine different human Na, K-ATPase isozymes. J Biol Chem 2000; 275:1976-86. [PMID: 10636900 DOI: 10.1074/jbc.275.3.1976] [Citation(s) in RCA: 321] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Na,K-ATPase plays a crucial role in cellular ion homeostasis and is the pharmacological receptor for digitalis in man. Nine different human Na,K-ATPase isozymes, composed of 3 alpha and beta isoforms, were expressed in Xenopus oocytes and were analyzed for their transport and pharmacological properties. According to ouabain binding and K(+)-activated pump current measurements, all human isozymes are functional but differ in their turnover rates depending on the alpha isoform. On the other hand, variations in external K(+) activation are determined by a cooperative interaction mechanism between alpha and beta isoforms with alpha2-beta2 complexes having the lowest apparent K(+) affinity. alpha Isoforms influence the apparent internal Na(+) affinity in the order alpha1 > alpha2 > alpha3 and the voltage dependence in the order alpha2 > alpha1 > alpha3. All human Na,K-ATPase isozymes have a similar, high affinity for ouabain. However, alpha2-beta isozymes exhibit more rapid ouabain association as well as dissociation rate constants than alpha1-beta and alpha3-beta isozymes. Finally, isoform-specific differences exist in the K(+)/ouabain antagonism which may protect alpha1 but not alpha2 or alpha3 from digitalis inhibition at physiological K(+) levels. In conclusion, our study reveals several new functional characteristics of human Na,K-ATPase isozymes which help to better understand their role in ion homeostasis in different tissues and in digitalis action and toxicity.
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Affiliation(s)
- G Crambert
- Institut de Pharmacologie et de Toxicologie de l'Université, Rue du Bugnon 27, CH-1005 Lausanne, Switzerland
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60
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Gao J, Wymore R, Wymore RT, Wang Y, McKinnon D, Dixon JE, Mathias RT, Cohen IS, Baldo GJ. Isoform-specific regulation of the sodium pump by alpha- and beta-adrenergic agonists in the guinea-pig ventricle. J Physiol 1999; 516 ( Pt 2):377-83. [PMID: 10087338 PMCID: PMC2269277 DOI: 10.1111/j.1469-7793.1999.0377v.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. Guinea-pig ventricle was used in the RNase protection assays to determine which alpha-isoforms of the Na+-K+ pumps are present, and ventricular myocytes were used in whole cell patch clamp studies to investigate the actions of alpha- and beta-adrenergic agonists on Na+-K+ pump current. 2. RNase protection assays showed that two isoforms of the alpha-subunit of the Na+-K+-ATPase are present in guinea-pig ventricle. The mRNA for the alpha1-isoform comprises 82 % of the total pump message, the rest being the alpha2-isoform. 3. We have previously shown that beta-adrenergic agonists affect Na+-K+ pump current (Ip) through a protein kinase A (PKA)-dependent pathway. We now show that these beta-effects are targeted to the alpha1-isoform of the Na+-K+ pumps. 4. We have also previously shown that alpha-adrenergic agonists increase Ip through a protein kinase C (PKC)-dependent pathway. We now show that these alpha-isoform effects are targeted to the alpha2-isoform of the Na+-K+ pumps. 5. These results suggest the effects of adrenergic activation on Na+-K+ pump activity in the heart can be regionally specific, depending on which alpha-isoform of the Na+-K+ pump is expressed.
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Affiliation(s)
- J Gao
- Department of Physiology & Biophysics and Institute of Molecular Cardiology, State University of New York, Stony Brook, NY 11794-8661, USA
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61
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Petrecca K, Atanasiu R, Grinstein S, Orlowski J, Shrier A. Subcellular localization of the Na+/H+ exchanger NHE1 in rat myocardium. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 276:H709-17. [PMID: 9950874 DOI: 10.1152/ajpheart.1999.276.2.h709] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The Na+/H+ exchanger NHE1 isoform is an integral component of cardiac intracellular pH homeostasis that is critically important for myocardial contractility. To gain further insight into its physiological significance, we determined its cellular distribution in adult rat heart by using immunohistochemistry and confocal microscopy. NHE1 was localized predominantly at the intercalated disk regions in close proximity to the gap junction protein connexin 43 of atrial and ventricular muscle cells. Significant labeling of NHE1 was also observed along the transverse tubular systems, but not the lateral sarcolemmal membranes, of both cell types. In contrast, the Na+-K+-ATPase alpha1-subunit was readily labeled by a specific mouse monoclonal antibody (McK1) along the entire ventricular sarcolemma and intercalated disks and, to a lesser extent, in the transverse tubules. These results indicate that NHE1 has a distinct distribution in heart and may fulfill specialized roles by selectively regulating the pH microenvironment of pH-sensitive proteins at the intercalated disks (e.g., connexin 43) and near the cytosolic surface of sarcoplasmic reticulum cisternae (e.g., ryanodine receptor), thereby influencing impulse conduction and excitation-contraction coupling.
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Affiliation(s)
- K Petrecca
- Department of Physiology, McGill University, Montreal, Quebec, Canada H3G 1Y6
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62
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Yalcin Y, Carman D, Shao Y, Ismail-Beigi F, Klein I, Ojamaa K. Regulation of Na/K-ATPase gene expression by thyroid hormone and hyperkalemia in the heart. Thyroid 1999; 9:53-9. [PMID: 10037077 DOI: 10.1089/thy.1999.9.53] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Hypothermic hyperkalemic circulatory arrest has been widely used for myocardial protection during heart surgery. Recent data showed that administration of triiodo-L-thyronine (T3) postoperatively enhanced ventricular function. The effect of hyperkalemic arrest in conjunction with thyroid hormone on the plasma membrane enzyme sodium/potassium-adenosine triphosphatase (Na/K-ATPase), was determined in cultured neonatal rat atrial and ventricular myocytes. Exposure of ventricular myocytes to hyperkalemic medium (50 mM KCl) in the absence of T3 increased expression of the Na/K-ATPase catalytic subunit mRNAs, alpha1 and alpha3 isoforms, by 1.9- and 1.5-fold, respectively (p<0.01), which were accompanied by similar increases (1.4- and 1.8-fold) in protein content. Addition of T3 to the hyperkalemic cultures attenuated these increases in Na/K-ATPase mRNA isoforms to levels of expression observed in cells treated with T3 (10(-8) M) alone. Similarly, expression of the alpha1 mRNA isoform in atrial myocytes was increased (p<0.05) by hyperkalemic conditions, and T3 treatment attenuated this effect. In contrast, although expression of the Na/K-ATPase beta1 mRNA in both atrial and ventricular myocytes was significantly increased by hyperkalemia, addition of T3 did not prevent the hyperkalemic response, and in atrial myocytes T3 significantly increased beta1 mRNA expression 1.8-fold. These results show that expression of cardiac Na/K-ATPase is regulated by T3 and hyperkalemia in an isoform and chamber specific manner, and suggest that use of hyperkalemic cardioplegia during heart surgery may alter plasma membrane ion function.
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Affiliation(s)
- Y Yalcin
- Department of Pediatrics, North Shore University Hospital, NYU School of Medicine, Manhasset, New York 11030, USA
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63
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Baba A, Yoshikawa T, Nakamura I, Iwata M, Wainai Y, Ogawa S. Isoform-specific alterations in cardiac and erythrocyte Na+,K+-ATPase activity induced by norepinephrine. J Card Fail 1998; 4:333-41. [PMID: 9924855 DOI: 10.1016/s1071-9164(98)90239-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
BACKGROUND Myocardial Na+,K+-ATPase activities are decreased in congestive heart failure because of an increase in plasma norepinephrine levels, but it is difficult to monitor the activities in the clinical setting. METHODS AND RESULTS This study investigated whether erythrocyte Na+,K+-ATPase activity can reflect myocardial enzyme activity and whether isoform-specific alterations occur in the presence of catecholamine. Na+,K+-ATPase activity was measured by the colorimetric method by using the left ventricular myocardium and erythrocytes prepared from eight rabbits given norepinephrine for 7 days and from eight control rabbits that received saline. The protein levels of total catalytic subunit and alpha1- or alpha3-isoform of Na+,K+-ATPase were determined by Western blot analysis. Na+,K+-ATPase activity was lower in both myocardium and erythrocytes from norepinephrine-treated rabbits than control rabbits (P < .01 and P < .01, respectively). There was a close correlation in Na+,K+-ATPase activity between myocardium and erythrocytes (r = .963). Total catalytic subunit protein level was lower in myocardium from norepinephrine-treated rabbits than control rabbits, but the alpha1-isoform level was similar between the two groups. The alpha3-isoform level was lower in norepinephrine-treated rabbits than control rabbits. In erythrocytes, alpha1-isoform was lower in norepinephrine-treated rabbits than control rabbits. CONCLUSIONS Na+,K+-ATPase activity in myocardium could be reflected in erythrocyte membrane, although there was a difference in isoform-specific regulation between the two.
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Affiliation(s)
- A Baba
- Department of Medicine, Keio University School of Medicine, Tokyo, Japan
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64
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Maxwell CV, Tao QF, Seely EW, Repke JT, Graves SW. Regulation of the sodium pump in pregnancy-related tissues in preeclampsia. Am J Obstet Gynecol 1998; 179:28-34. [PMID: 9704761 DOI: 10.1016/s0002-9378(98)70247-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
OBJECTIVE This study examined the expression of the three alpha-isoforms of the sodium pump in preeclampsia. Reductions in sodium pump number and activity in smooth muscle may underlie hypertension in preeclampsia. STUDY DESIGN Northern and Western analyses were used to determine whether sodium pump alpha-isoform regulation in myometrium, placenta, and umbilical artery of women with preeclampsia differed from those with normotensive pregnancies. RESULTS Levels of alpha1 and alpha3 messenger ribonucleic acid were reduced in myometrium of women with preeclampsia compared with normotensive pregnancies, as was alpha2 messenger ribonucleic acid in preeclamptic placenta. Protein expression of the alpha-isoforms was unaltered in placenta and umbilical artery from women with preeclampsia versus those with normotensive pregnancies, but myometrial alpha2 protein levels were reduced significantly in women with preeclampsia. Moreover, myometrial alpha1 protein expression was undetectable. CONCLUSIONS Reduced smooth muscle sodium pump expression in preeclampsia may raise cell sodium, increase pressor sensitivity, or increase tone directly, which may contribute to hypertension in preeclampsia.
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Affiliation(s)
- C V Maxwell
- Endocrine-Hypertension Division, Department of Medicine, Harvard Medical School, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA
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65
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Ramírez-Gil JF, Trouvé P, Mougenot N, Carayon A, Lechat P, Charlemagne D. Modifications of myocardial Na+,K(+)-ATPase isoforms and Na+/Ca2+ exchanger in aldosterone/salt-induced hypertension in guinea pigs. Cardiovasc Res 1998; 38:451-62. [PMID: 9709406 DOI: 10.1016/s0008-6363(98)00007-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
OBJECTIVE The aim of this study was to determine whether changes in cardiac Na+,K(+)-ATPase subunits and Na+/Ca2+ exchanger expression are regulated in aldosterone-salt hypertensive guinea pigs. METHODS Guinea pigs (GP) were unilaterally nephrectomized and randomized into three groups (aldosterone-salt; control-salt; control). After 90 days of treatment, echocardiographic M-mode assessment and right carotid arterial catheterization were performed in vivo, and plasma hormones and electrolytes were measured. mRNA and protein levels were studied by Northern and Western blot analysis. RESULTS Aldosterone-salt treatment induced, (1) arterial hypertension (+40%) and LV hypertrophy (+60%) without altering LV-fractional shortening, (2) an increase in plasma norepinephrine levels (+262%) and suppression of renin activity. Northern blot analysis showed the presence of the mRNA encoding the three alpha isoforms and the beta 1 subunit of Na+,K(+)-ATPase in GP myocardium. In the aldosterone-salt group, levels of alpha 1 and beta 1 mRNAs were unchanged. alpha 2 mRNA was increased in both ventricles, whereas alpha 3 mRNA was increased in hypertrophied LV only. Furthermore, levels of the Na+/Ca2+ exchanger mRNA were decreased in both ventricles. At protein level, the two major transcripts (alpha 1 and alpha 2) were detected but alpha 3 isoform was not. Parallel changes in protein and mRNA accumulation of alpha 1 and alpha 2 isoforms were observed in hypertrophied LV. CONCLUSION These results show that alpha 1 and alpha 2 isoforms are expressed in GP heart and that they are independently regulated in aldosterone-salt hypertension. Like the alpha 1 isoform in renal tissue, alpha 2 isoform is the main target of aldosterone-salt. Reciprocal expression of the Na+/Ca2+ exchanger and Na+,K(+)-ATPase suggests an adaptational mechanism which maintains an appropriate sodium gradient and calcium concentration in hypertensive myocardium.
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Affiliation(s)
- J F Ramírez-Gil
- Laboratoire de Pharmacologie Cardiovasculaire, Service de Pharmacologie, IFR Génétique et Physiopathologie Cardiovasculaire, Hôpital Pitié-Salpêtrière, Paris, France
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66
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Liu X, Hymel LJ, Songu-Mize E. Role of Na+ and Ca2+ in stretch-induced Na(+)-K(+)-ATPase alpha-subunit regulation in aortic smooth muscle cells. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:H83-9. [PMID: 9458855 DOI: 10.1152/ajpheart.1998.274.1.h83] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
This study was designed to test the role of Na+ and Ca2+ entry in the stretch-induced Na(+)-K(+)-ATPase alpha 1- and alpha 2-isoform upregulation observed in our previous studies. We measured intracellular Na+ in cyclically stretched rat aortic smooth muscle cells, with or without gadolinium treatment, for various durations and performed Western blotting to analyze the effects of stretch and the calcium channel blocker isradipine on the expression of alpha-isoforms. Intracellular Na+ was elevated significantly after 1- and 2-h stretch, but returned to baseline after 1-, 2-, and 4-day stretch. This increase in intracellular Na+ was blocked by gadolinium. Both alpha 1- and alpha 2-isoforms were upregulated after either 2 or 4 days of cyclical stretch. Isradipine had no apparent effect on stretch-induced upregulation on either alpha-isoform, thus suggesting that Ca2+ entry through L-type channels is not involved in the stretch-induced upregulation. We therefore conclude that a transient intracellular Na+ elevation during stretch may serve as a signal to mediate the alpha 1- and alpha 2-isoform upregulation.
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MESH Headings
- Animals
- Aorta/enzymology
- Aorta/physiology
- Calcium/metabolism
- Calcium Channel Blockers/pharmacology
- Calcium Channels/physiology
- Calcium Channels, L-Type
- Cells, Cultured
- Gadolinium/pharmacology
- Gene Expression Regulation, Enzymologic/drug effects
- Gene Expression Regulation, Enzymologic/physiology
- Isoenzymes/biosynthesis
- Isradipine/pharmacology
- Kinetics
- Macromolecular Substances
- Male
- Muscle, Smooth, Vascular/enzymology
- Muscle, Smooth, Vascular/physiology
- Rats
- Rats, Sprague-Dawley
- Sodium/metabolism
- Sodium-Potassium-Exchanging ATPase/biosynthesis
- Stress, Mechanical
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Affiliation(s)
- X Liu
- Department of Pharmacology and Experimental Therapeutics, Louisiana State University Medical Center, New Orleans, USA
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67
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Crambert G, Franz A, Lelievre LG. Biochemical characterization of the human renal Na+,K(+)-ATPase. Ann N Y Acad Sci 1997; 834:97-100. [PMID: 9405789 DOI: 10.1111/j.1749-6632.1997.tb52229.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- G Crambert
- Laboratoire de Pharmacologie des Transports, Ioniques Membranaires, Université Paris VII-Hall de Biotechnologie, France
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68
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Book CB, Sun X, Ng YC. Developmental changes in regulation of the Na+, K(+)-ATPase alpha 3 isoform by thyroid hormone in ferret heart. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1358:172-80. [PMID: 9332453 DOI: 10.1016/s0167-4889(97)00067-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Ferret heart expresses the alpha 1- as well as the alpha 3-isoform of the Na+, K(+)-ATPase. We have shown previously that the alpha 3 isoform is differentially upregulated during postnatal cardiac development and that in adult ferrets expression of alpha 3 is not responsive to regulation by thyroid hormone (TH). Since developmental-stage dependent effects of TH have been reported previously, the present study examined whether effects of TH on expression of the Na+, K(+)-ATPase isoforms in ferret heart is modulated during development and possible mechanisms were examined. Ferrets of different age groups were treated with TH and the relative abundance of Na+, K(+)-ATPase isoforms in ferret myocardium was determined by immunoblotting. Thyroid hormone (T3; 50 micrograms/100 g body weight on 3 alternating days, s.c.) increased protein levels of the alpha 3 isoform, but not that of alpha 1 or beta 1, in myocardium of 5-day-old and 3-week-old ferrets. By contrast, in myocardium of 6- and 8-week-old ferrets T3 failed to increase protein levels of alpha 1 and alpha 3. To determine whether elevated plasma levels of TH during development plays a role in the transition, mature ferrets were first made hypothyroid before TH treatment. In these hypothyroid ferrets expression of the alpha 3 isoform remained unresponsive to TH (T4, 0.5 mg/kg for 7 days, s.c.). The transition from TH-responsive to TH-unresponsive appears to be isoform-specific because in skeletal muscle of 8-week-old ferrets and in hypothyroid ferrets the alpha 2 isoform is upregulated by TH. Finally, there appears to be functional thyroid hormone receptors throughout development because in each age group TH effectively induced expression of alpha-MHC in the myocardium. In conclusion, these findings demonstrate that expression of alpha 3 isoform in the myocardium of newborn ferret is responsive to TH; however, the responsiveness terminates between 3- and 6-weeks of age. Neither elevated endogenous TH level nor a lack of functional thyroid hormone receptor appears to be responsible for the transition from TH-responsive to TH-unresponsive.
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Affiliation(s)
- C B Book
- Department of Pharmacology, College of Medicine, Milton S. Hershey Medical Center, Pennsylvania State University, Hershey 17033, USA
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69
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Abstract
INTRODUCTION Steady-state Na/K pump current (Ip) in adult guinea pig ventricular myocytes was studied to determine the effect on the Na/K pump of transmembrane Na leak, membrane potential, and pipette Na concentration. METHODS AND RESULTS Using conventional whole cell, patch clamp techniques, Ip was identified as either Ko-sensitive or ouabain-sensitive current when most other membrane currents were inhibited. Control experiments showed that there were no Ko-sensitive currents other than Ip under the conditions of our experiments. Ip was found to be similar to that reported by others being voltage dependent between -130 and 0 mV and having a half maximal activation by Nai of 28 mM. Ouabain sensitivity was also measured, and it was found that there were two binding sites with the high affinity site comprising 5% to 10% of the total and having an apparent affinity 1000-fold higher than the low affinity site. Apparent affinity of both sites was shifted about 10-fold (higher affinity) by increasing Nai from 10 to 85 mM. When internally perfused with 0 Na solution, Na leak through the membrane was found to be linearly related to Na/K pump activity. In contrast to prior suggestions, Ip was not correlated with series resistance when there was a large transmembrane Na gradient. CONCLUSION These data suggest that, under conditions of high transmembrane Na gradient, Na leak through the membrane plays a significant role in determining Na/K pump activity.
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Affiliation(s)
- M Dobretsov
- Department of Pharmacology and Toxicology, University of Arkansas for Medical Sciences, Little Rock 72205, USA
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70
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Van der Walt JJ, Van Rooyen JM, Kellerman T, Carmeliet EE, Verdonck F. Neurospecificity of phyto-bufadienolides is not related to differences in pump inhibition. Eur J Pharmacol 1997. [DOI: 10.1016/s0014-2999(97)89181-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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71
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Liu X, Songu-Mize E. Alterations in alpha subunit expression of cardiac Na+,K+-ATPase in spontaneously hypertensive rats: effect of antihypertensive therapy. Eur J Pharmacol 1997; 327:151-6. [PMID: 9200553 DOI: 10.1016/s0014-2999(97)89654-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The alpha-2 subunit abundance of Na+,K(+)-ATPase in the rat heart has been reported to be reduced in several induced hypertensive models. To determine whether this reduction also occurs in a genetic model of hypertension, we studied expression of the alpha subunits in left ventricles of spontaneously hypertensive rats (SHR), and normotensive Wistar-Kyoto (WKY) and Sprague-Dawley rats using Western blotting and quantitative dot-blotting analysis with monoclonal antibodies. While the alpha-1 subunit was not affected in any of the strains, a significant reduction of the alpha-2 subunit expression was noted in 19-week-old SHRs, but not in age-matched WKY and Sprague-Dawley rats, supporting the hypothesis that elevated arterial pressure may differentially downregulate the alpha-2 subunit in the rat heart. To further test this hypothesis we designed experiments in which hypertensive rats were treated with the antihypertensive agents hydralazine and nifedipine. Both agents effectively normalized the blood pressure in the SHRs with no significant effect on the blood pressure in the WKY and Sprague-Dawley rats. The alpha-2 subunit in SHRs treated with hydralazine and nifedipine showed a 63.3% (n = 6, P < 0.05, analysis of variance and Fischer's test) and a 27.4% increase, respectively, over the hypertensive SHR controls, although the reversal effect of nifedipine did not quite reach significance. The alpha-1 subunit expression was not affected by any of the drug treatments. No effect of either of the drugs on the alpha-1 or alpha-2 subunit was observed in the WKY or Sprague-Dawley rat groups. These data support our hypothesis that the alpha-2 subunit may be a pressure-sensitive isoform of the cardiac Na+,K(+)-ATPase and that high blood pressure is, directly or indirectly, responsible for the reduction of the alpha-2 subunit protein expression.
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Affiliation(s)
- X Liu
- Department of Pharmacology and Experimental Therapeutics, Louisiana State University Medical Center, New Orleans 70112, USA
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72
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Larsen JS, Schmidt TA, Bundgaard H, Kjeldsen K. Reduced concentration of myocardial Na+,K(+)-ATPase in human aortic valve disease as well as of Na+,K(+)- and Ca(2+)-ATPase in rodents with hypertrophy. Mol Cell Biochem 1997; 169:85-93. [PMID: 9089635 DOI: 10.1023/a:1006851411650] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Myocardial Na+,K(+)-ATPase was studied in patients with aortic valve disease, and myocardial Na+,K(+)- and Ca(2+)-ATPase were assessed in spontaneously hypertensive rats (SHR) and hereditary cardiomyopathic hamsters using methods ensuring high enzyme recovery. Na+,K(+)-ATPase was quantified by [3H]ouabain binding to intact myocardial biopsies from patients with aortic valve disease. Aortic stenosis, regurgitation and a combination hereof were compared with normal human heart and were associated with reductions of left ventricular [3H]ouabain binding site concentration (pmol/g wet weight) of 56, 46 and 60%, respectively (p < 0.01). Na+,K(+)- and Ca(2+)-ATPases were quantified by K(+)- and Ca(2+)-dependent p-nitrophenyl phosphatase (pNPPase) activity determinations in crude myocardial homogenates from SHR and hereditary cardiomyopathic hamsters. When SHR were compared to age-matched Wistar Kyoto (WKY) rats an increase in heart-body weight ratio of 75% (p < 0.001) was associated with reductions of K(+)- and Ca(2+)-dependent pNPPase activities (mumol/min/g wet weight) of 42 (p < 0.01) and 27% (p < 0.05), respectively. When hereditary cardiomyopathic hamsters were compared to age-matched Syrian hamsters an increase in heart-body weight ratio of 69% (p < 0.001) was found to be associated with reductions in K(+)- and Ca(2+)-dependent pNPPase activities of 50 (p < 0.001) and 26% (p = 0.05), respectively. The reductions in Na+,K(+)- and Ca(2+)-ATPases were selective in relation to overall protein content and were not merely the outcome of increased myocardial mass relative to Na+,K(+)- and Ca(2+)-pumps. In conclusion, myocardial hypertrophy is in patients associated with reduced Na+,K(+)-ATPase concentration and in rodents with reduced Na+,K(+)- and Ca(2+)-ATPase concentrations. This may be of importance for development of heart failure and arrhythmia in hypertrophic heart disease.
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Affiliation(s)
- J S Larsen
- Department of Medicine B, Heart Centre, Rigshospitalet, National University Hospital, Copenhagen, Denmark
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73
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74
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Zinchuk VS, Kobayashi T, Garcia del Saz E, Seguchi H. Biochemical properties and cytochemical localization of ouabain-insensitive, potassium-dependent p-nitrophenylphosphatase activity in rat atrial myocytes. J Histochem Cytochem 1997; 45:177-87. [PMID: 9016308 DOI: 10.1177/002215549704500204] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Enzyme activity that represents ouabain-insensitive, potassium-dependent p-nitrophenylphosphatase (p-NPPase) was assessed in rat atrial myocytes by biochemical and cytochemical procedures. No activity was detected in parallel experiments with ventricular myocytes. Fixed tissues were incubated in a reaction medium containing Tricine buffer, p-nitrophenylphosphate (p-NPP), KCl, MgCl2, CaCl2, CeCl3. Triton X-100, levamisole, and ouabain. Final pH was adjusted to 7.5. Biochemical studies showed that accumulation of p-nitrophenol in the medium was increased proportionally in accordance with the amount of incubated tissue. This activity was optimal with incubation at pH 7.5 and in the presence of KCl. Approximately 70% of the enzyme was inhibited by 2 mM CeCl3. Electron microscopic observations revealed reaction product (RP) at sites of ouabain-insensitive, potassium-dependent p-NPPase activity as electron-dense precipitate localized at the inner surface of the plasma membrane and at the T-tubules of atrial myocytes. Control experiments indicated that the activity was strongly inhibited by sodium orthovanadate and was repressed by omeprazole and 1,3-dicyclohexylcarbodiimide. X-ray microanalysis confirmed the presence of cerium within the cytochemical RP. The ouabain-insensitive, K-dependent p-NPPase activity detected in the present study is considered to be an isoform of a P-type, H-transporting, K-dependent adenosine triphosphatase (H,K-ATPase).
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Affiliation(s)
- V S Zinchuk
- Department of Anatomy and Cell Biology, Kochi Medical School, Japan
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75
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Slezak J, Schulze W, Stefankova Z, Okruhlicova L, Danihel L, Wallukat G. Localization of alpha 1,2,3-subunit isoforms of Na,K-ATPase in cultured neonatal and adult rat myocardium: the immunofluorescence and immunocytochemical study. Mol Cell Biochem 1996; 163-164:39-45. [PMID: 8974038 DOI: 10.1007/bf00408639] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
By indirect immunofluorescence and preembedding peroxidase-diaminobenzidine technique the localization of polyclonal and monoclonal antibodies against alpha 1, alpha 2 and alpha 3 isoforms of the Na,K-ATPase were studied in rat myocardium. The alpha 1-subunit was identified predominantly on sarcolemma of cultured myocytes, neonatal, as well as adult cardiocytes. The alpha 2 signal was localized around nuclei of cultured cardiocytes, very weak signals were seen in neonatal and more intense signal, were dispersed throughout the adult myocytes. The alpha 3-subunit immunoreactivity was weak and localized in cell processes connecting individual cultured cells, on sarcolemma and intercalated discs of neonatal cells and very weak in adult working myocytes. Cytochemically demonstrated ouabain resistant Na,K-ATPase localized in junctional sarcoplasmic reticulum may represent alpha 1 isoenzyme which is directly involved in modulation of action potential fluxes.
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Affiliation(s)
- J Slezak
- Institute for Heart Research, Slovak Academy of Sciences, Bratislava, Slovak Republic
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76
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Zheng L, Wibo M, Kolár F, Godfraind T. Calcium channels and cation transport ATPases in cardiac hypertrophy induced by aortic constriction in newborn rats. Mol Cell Biochem 1996; 163-164:23-9. [PMID: 8974036 DOI: 10.1007/bf00408637] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Cardiac enlargement due to gradual pressure overload was induced by abdominal aortic constriction in 2-day-old rats. On day 90, the functional performance of the left ventricle was assessed by acute load test (ligation of ascending aorta) in open-chest anaesthetized animals. Two subgroups, designated compensated and decompensated hypertrophy (CH and DH), were distinguished on the basis of the functional reserve of left ventricle, which was significantly impaired in DH but not in CH, and of right ventricle weight, which was markedly increased in DH but not significantly modified in CH. In total particulate fractions prepared from hypertrophied left ventricles, the levels (per g tissue) of sarcoplasmic reticulum Ca(2+)-transport systems were decreased, either slightly (by 13-16%: [3H]ryanodine binding) or moderately (by 28%: thapsigargin-sensitive Ca(2+)-ATPase activity). The number of sarcolemmal L-type Ca2+ channels ([3H]PN200-110 binding) was not modified significantly, while that of beta 1-adrenoceptors ([3H]CGP-12177 binding) was reduced, especially in the DH group (by 39%). Na+,K(+)-ATPase activity was reduced by 28% in CH and 41% in DH. [3H]Ouabain binding experiments (saturation and dissociation) indicated the existence of two high-affinity binding sites, attributable to the Na+, K(+)-ATPase alpha 3 and alpha 2 subunit isoforms; while the relatively minor alpha 3 component did not change significantly in hypertrophied ventricles, the alpha 2 component was markedly down-regulated, decreasing by 57% in CH and 82% in DH.
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Affiliation(s)
- L Zheng
- Laboratoire de Pharmacologie, Université Catholique de Louvain, Brussels, Belgium
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77
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Wang J, Schwinger RH, Frank K, Müller-Ehmsen J, Martin-Vasallo P, Pressley TA, Xiang A, Erdmann E, McDonough AA. Regional expression of sodium pump subunits isoforms and Na+-Ca++ exchanger in the human heart. J Clin Invest 1996; 98:1650-8. [PMID: 8833915 PMCID: PMC507599 DOI: 10.1172/jci118960] [Citation(s) in RCA: 76] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Cardiac glycosides exert a positive inotropic effect by inhibiting sodium pump (Na,K-ATPase) activity, decreasing the driving force for Na+-Ca++ exchange, and increasing cellular content and release of Ca++ during depolarization. Since the inotropic response will be a function of the level of expression of sodium pumps, which are alpha(beta) heterodimers, and of Na+-Ca++ exchangers, this study aimed to determine the regional pattern of expression of these transporters in the heart. Immunoblot assays of homogenate from atria, ventricles, and septa of 14 nonfailing human hearts established expression of Na,K-ATPase alpha1, alpha2, alpha3, beta1, and Na+-Ca++ exchangers in all regions. Na,K-ATPase beta2 expression is negligible, indicating that the human cardiac glycoside receptors are alpha1beta1, alpha2beta1, and alpha3beta1. alpha3, beta1, sodium pump activity, and Na+-Ca++ exchanger levels were 30-50% lower in atria compared to ventricles and/or septum; differences between ventricles and septum were insignificant. Functionally, the EC50 of the sodium channel activator BDF 9148 to increase force of contraction was lower in atria than ventricle muscle strips (0.36 vs. 1.54 microM). These results define the distribution of the cardiac glycoside receptor isoforms in the human heart and they demonstrate that atria have fewer sodium pumps, fewer Na+-Ca++ exchangers, and enhanced sensitivity to inotropic stimulation compared to ventricles.
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Affiliation(s)
- J Wang
- Department of Physiology and Biophysics, University of Southern California School of Medicine, Los Angeles 90033, USA
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78
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Arystarkhova E, Sweadner KJ. Isoform-specific monoclonal antibodies to Na,K-ATPase alpha subunits. Evidence for a tissue-specific post-translational modification of the alpha subunit. J Biol Chem 1996; 271:23407-17. [PMID: 8798546 DOI: 10.1074/jbc.271.38.23407] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Monoclonal antibodies to isoforms of the Na,K-ATPase have become important tools in the study of the enzyme's distribution, physiological roles, and gene regulation, and when their epitopes are defined, they are useful in the study of enzyme structure as well. Evidence is presented that the alpha3-specific antibody McBX3 recognizes an unusual epitope that is not present on alpha3 in the heart. The epitope, which is also found in kidney alpha1 from some species, was mapped to a site on the large intracellular loop near the ATP binding site. DNA sequencing of reverse transcribed-PCR products encompassing the corresponding regions from alpha3 from brain (where McBX3 recognizes alpha3) and heart demonstrated that the tissue difference in epitope is not due to alternative splicing of the mRNA. Instead, hydroxylamine sensitivity indicated that the antibody recognizes a post-translational modification. The epitope for a new antibody for alpha3, XVIF9-G10, was mapped to a site near the N terminus, a location analogous to the sites for the well-characterized antibodies McK1 (alpha1) and McB2 (alpha2). The antibody XVIF9-G10 reacted with the alpha3 of the heart as well as that of the brain; however, McBX3 and XVIF9-G10 both stained the same cellular structures in sections of the rat retina. A new alpha1-specific antibody, 6F, was characterized and mapped to another site near the N terminus; this antibody has broader species specificity than the other well-characterized alpha1 antibody, McK1.
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Affiliation(s)
- E Arystarkhova
- Laboratory of Membrane Biology, Neuroscience Center, Massachusetts General Hospital, Charlestown, Massachusetts 02129, USA
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79
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Zahler R, Gilmore-Hebert M, Sun W, Benz EJ. Na, K-ATPase isoform gene expression in normal and hypertrophied dog heart. Basic Res Cardiol 1996; 91:256-66. [PMID: 8831945 DOI: 10.1007/bf00788912] [Citation(s) in RCA: 17] [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: 02/02/2023]
Abstract
OBJECTIVES The catalytic alpha subunit of the sodium-potassium ATPase, the target of digitalis glycosides, has three isoforms; the expression of these isoforms is tissue-specific and developmentally regulated. While the effect of pressure overload on Na, K-ATPase isoform expression has been studied in rodent heart, there are no systematic data on this question in hearts of larger animals, which differ from those of rodents both in isoform composition and in glycoside sensitivity. Thus, we investigated the expression of Na, K-ATPase isoforms in normal dog heart; we also examined the effect of experimental left ventricular hypertrophy on isoform expression. METHODS hypertrophy was produced by aortic banding. Expression was assessed by quantitative Northern and Western blotting, immunofluorescence, and 3H-ouabain binding. RESULTS RNA blotting indicated that the alpha 3 isoform represented 11% of Na, K-ATPase mRNA in normal dog LV. Normal dog LV expressed alpha 1 and alpha 3 protein, but no detectable alpha 2; immunoreactive alpha 1 and alpha 3 protein were also present in Purkinje fibers. There was a statistically significant decrease in total expression of all alpha isoform mRNA's in hypertrophied dog LV, resulting in a greater proportion of alpha 1. The expression level of the alpha 3 isoform mRNA and protein was lower in hypertrophied hearts. CONCLUSIONS These results indicate a greater proportion of alpha 1 isoform pumps in experimental canine hypertrophy. Thus, shifts in NA, K-ATPase isoforms occur in pressure-overloaded heart in large animals as well as rodents.
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Affiliation(s)
- R Zahler
- Section of Cardiology, Yale University School of Medicine, New Haven, Connecticut 06510, USA
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80
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McDonough AA, Zhang Y, Shin V, Frank JS. Subcellular distribution of sodium pump isoform subunits in mammalian cardiac myocytes. THE AMERICAN JOURNAL OF PHYSIOLOGY 1996; 270:C1221-7. [PMID: 8928749 DOI: 10.1152/ajpcell.1996.270.4.c1221] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The cardiac Na+ pump (Na+ -K+ -ATPase) provides the driving force for the Na+/Ca2+ exchanger, a determinant of intracellular Ca2+ stores. Three Na+ pump alpha-catalytic subunit isoforms are expressed in human heart, alpha1 and alpha2 are expressed in rat heart, and only alpha1 is expressed in guinea pig heart. The objective of this study was to determine whether there are isoform-specific patterns of expression in the transverse tubules (T tubules) vs. the peripheral sarcolemma. In adult rat cardiomyocytes, anti-alpha1-specific antibodies labeled the T tubules more intensely than the peripheral sarcolemma, in which labeling was patchy, the same pattern reported for distribution of the Na+/Ca2+ exchanger (J. S. Frank, G. Mottino, D. Reid, R. S. Molday, and K. D. Philipson, J. Cell Biol. 117: 337-345, 1992), whereas anti-alpha2- and anti-beta1-antibodies uniformly labeled T tubules and peripheral sarcolemma. In guinea pig cardiomyocytes, an anti-alpha-antibody against an extracellular epitope evenly labeled the peripheral sarcolemma and T tubules, and immunogold labeling demonstrated coincidence of alpha-subunits and intramembranous particles in sarcolemma. In summary, Na+ pumps are located in both peripheral sarcolemma and T tubules of cardiomyocytes expressing either multiple or single Na+ pump isoforms.
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Affiliation(s)
- A A McDonough
- Department of Physiology and Biophysics, University of Southern California School of Medicine, Los Angeles 90033, USA
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81
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Zahler R, Sun W, Ardito T, Kashgarian M. Na-K-ATPase alpha-isoform expression in heart and vascular endothelia: cellular and developmental regulation. THE AMERICAN JOURNAL OF PHYSIOLOGY 1996; 270:C361-71. [PMID: 8772464 DOI: 10.1152/ajpcell.1996.270.1.c361] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The Na pump (Na-K-ATPase) is important for regulation of membrane potential and transport in smooth muscle and heart. The alpha (catalytic)-subunit of this pump has three isoforms: alpha 1 is ubiquitous, but alpha 2 and alpha 3 are mainly localized to excitable tissue. Physiological differences between isoforms are not completely understood, but alpha 3 pumps appear to have a lower affinity for intracellular Na and a higher ouabain affinity than alpha 1 pumps. The alpha 2-and alpha 3-isoform mRNAs are expressed at high levels in the normal adult rat cardiac conduction system. Although alpha 1 and alpha 3 are both globally expressed in neonatal rat myocardia, there is a switch in the myocardial isoform pattern from alpha 3 to alpha 2 after birth. There are also important species differences in cardiac isoform patterns. Furthermore, changes in Na-K-ATPase isoforms in heart and vascular tissue have been reported in association with hypertension, but little is known about isoform expression in normal endothelia. We therefore studied the cellular distribution of Na pump protein isoforms in neonatal and adult myocardia and endothelia. Immunohistochemical analysis of rat tissues showed that the alpha 1-isoform was expressed throughout atrial and ventricular myocardium, with alpha 1 the only isoform detectable in the adult t tubule system. Although alpha 2 was also present in ventricular myocytes, the signal was markedly stronger in conduction tissue and papillary muscle. In hearts from neonatal rats, the alpha 3-isoform predominated in the cardiac conduction system, whereas alpha 2 was not detectable in any structure except vascular endothelium. In tissues and in cell lines representing a variety of species and vessel sizes, endothelia of large vessels expressed primarily alpha 1, whereas alpha 2 could be detected in endothelia of small vessels in rat heart. No evidence of alpha 3 expression in endothelium was found. Thus the complex spatial and developmental regulation of Na pump isoform expression in cardiovascular tissues may provide additional correlates to distinct physiological roles of these transporters.
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Affiliation(s)
- R Zahler
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06510, USA
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82
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Repke KR, Sweadner KJ, Weiland J, Megges R, Schön R. In search of ideal inotropic steroids: recent progress. PROGRESS IN DRUG RESEARCH. FORTSCHRITTE DER ARZNEIMITTELFORSCHUNG. PROGRES DES RECHERCHES PHARMACEUTIQUES 1996; 47:9-52. [PMID: 8961763 DOI: 10.1007/978-3-0348-8998-8_1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- K R Repke
- Max Delbrück Center of Molecular Medicine, Berlin-Buch, Germany
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83
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Repke KR, Weiland J, Megges R, Schön R. Modeling of the three-dimensional structure of the digitalis intercalating matrix in Na+/K(+)-ATPase protodimer. JOURNAL OF ENZYME INHIBITION 1996; 10:147-57. [PMID: 8835940 DOI: 10.3109/14756369609030308] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Based on the knowledge that the digitalis receptor site in Na+/K(+)-ATPase is the interface between two interacting alpha-subunits of the protodimer (alpha beta)2, the present review makes an approach towards modeling the three-dimensional structure of the digitalis intercalating matrix by exploiting the information on: the primary structure and predicted membrane topology of the catalytic alpha-subunit; the determinants of the secondary, tertiary and quaternary structure of the membrane-spanning protein domains; the impact of mutational amino acid substitutions on the affinity of digitalis compounds, and the structural characteristics in potent representatives. The designed model proves its validity by allowing quantitative interpretations of the contributions of distinct amino acid side chains to the special bondings of the three structural elements of digitalis compounds.
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Affiliation(s)
- K R Repke
- Max Delbrück Center for Molecular Medicine, Berlin-Buch, Germany
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84
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Magyar CE, Wang J, Azuma KK, McDonough AA. Reciprocal regulation of cardiac Na-K-ATPase and Na/Ca exchanger: hypertension, thyroid hormone, development. THE AMERICAN JOURNAL OF PHYSIOLOGY 1995; 269:C675-82. [PMID: 7573397 DOI: 10.1152/ajpcell.1995.269.3.c675] [Citation(s) in RCA: 56] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Inhibiting cardiac Na pump activity decreases the driving force for the Na/Ca exchanger transport that increases cellular Ca stores and contractility. Decreased abundance of Na pumps would be expected to have the same effect as decreased activity unless there was reciprocal regulation of Na/Ca exchanger expression to oppose the effects of depressed Na pump activity on intracellular Ca stores. The aim of this study was to test the hypothesis that cardiac Na/Ca exchanger abundance is regulated in a reciprocal fashion to Na-K-ATPase abundance in a number of models known to have altered Na-K-ATPase abundance. In renovascular hypertension, cardiac ventricular Na-K-ATPase alpha 1-levels are unaltered, alpha 2-isoform subunit mRNA and protein levels decrease to 0.76 +/- 0.06 and 0.56 +/- 0.07 of control, respectively, and the Na/Ca exchanger protein (not mRNA) increased 1.35 +/- 0.11-fold. In the transition from hypothyroid to hyperthyroid cardiac alpha 1 doubles, alpha 2-protein increases 8.83 +/- 1.06-fold, and the Na/Ca exchanger protein decreases to 0.64 +/- 0.11. A similar pattern was seen during cardiac development in the preweaning rat heart. Treatment with the antiarrhythymic amiodarone has no effect on alpha 1, decreases alpha 2-protein expression to 0.51 +/- 0.08 of control, and increases exchanger expression 1.42 +/- 0.16-fold. In conclusion, the reciprocal regulation of the Na/Ca exchanger and of Na-K-ATPase alpha 2-expression provides evidence for a homeostatic mechanism that would oppose the changes in cellular Ca stores driven by the changes in Na-K-ATPase activity.
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Affiliation(s)
- C E Magyar
- Department of Physiology and Biophysics, University of Southern California School of Medicine, Los Angeles 90033, USA
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85
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Hermans AN, Glitsch HG, Verdonck F. The antagonistic effect of K+o and dihydro-ouabain on the Na+ pump current of single rat and guinea-pig cardiac cells. J Physiol 1995; 484 ( Pt 3):617-28. [PMID: 7623280 PMCID: PMC1157948 DOI: 10.1113/jphysiol.1995.sp020691] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
1. The antagonistic effect of extracellular potassium ions (K+o) and dihydro-ouabain (DHO) on the Na(+)-K+ pump current (Ip) was studied in isolated ventricular cells. 2. The myocytes were isolated from rats and guinea-pigs, two species with different sensitivity towards cardiac glycosides. Ip measurements were performed at 32-34 degrees C by means of whole-cell recording. The membrane potential was held at -20 mV throughout. 3. The DHO concentration ([DHO]) required for half-maximal Ip inhibition (apparent KD value, KD') amounted to 2.4 x 10(-3) and 1.4 x 10(-5) M for rat and guinea-pig myocytes, respectively, at 5.4 mM K+o. 4. The data suggest one-to-one binding of DHO to the Na(+)-K+ pump and a smaller association rate constant, as well as a larger dissociation rate constant, for binding of DHO in the rat cells. 5. Ip activation by K+o was nearly identical in myocytes of both species and was measured to be half-maximal at approximately 1 mM K+o. Half-maximal Ip activation by K+o remained essentially unchanged, but Ip decreased in media containing [DHO] near the respective KD' at 5.4 mM K+o. 6. The concentration-response curve of Ip inhibition by DHO was shifted to higher [DHO] at higher [K+]o. KD' increased correspondingly. The slope of the curve was unaffected. 7. Ip and KD' displayed a similar dependence on [K+]o. 8. KD' was larger in Na(+)-free than in Na(+)-containing media under conditions in which the activation of Ip by K+o was nearly the same. 9. It is concluded that the antagonism between K+o and DHO, with regard to the activation of Ip, is non-competitive. A possible mechanism of the antagonism is discussed. The mechanism implies binding of K+o and DHO to different conformational states of the Na(+)-K+ pump which are temporarily exposed to the external face of the sarcolemma in the pump cycle. The DHO-bound states do not participate in the generation of Ip.
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Affiliation(s)
- A N Hermans
- Interdisciplinary Research Centre, Catholic University of Leuven, Kortrijk, Belgium
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