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Hertz L, Chen Y. Importance of astrocytes for potassium ion (K+) homeostasis in brain and glial effects of K+ and its transporters on learning. Neurosci Biobehav Rev 2016; 71:484-505. [DOI: 10.1016/j.neubiorev.2016.09.018] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2016] [Revised: 08/12/2016] [Accepted: 09/23/2016] [Indexed: 10/20/2022]
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Abstract
Reconstitution of P-type ATPases in unilamellar liposomes is a useful technique to study functional properties of these active ion transporters. Experiments with such liposomes provide an easy access to substrate-binding affinities of the ion pumps as well as to the lipid and temperature dependence of the pump current. Here, we describe two reconstitution methods by dialysis and the use of potential-sensitive fluorescence dyes to study transport properties of two P-type ATPases, the Na,K-ATPase from rabbit kidney and the K(+)-transporting KdpFABC complex from E. coli. Several techniques are introduced how the measured fluorescence signals may be analyzed to gain information on properties of the ion pumps.
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Affiliation(s)
- Hans-Jürgen Apell
- Department of Biology, University of Konstanz, 635, Universitätsstr. 10, Konstanz, 78464, Germany.
| | - Bojana Damnjanovic
- Department of Biology, University of Konstanz, 635, Universitätsstr. 10, Konstanz, 78464, Germany
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Hertz L, Gerkau NJ, Xu J, Durry S, Song D, Rose CR, Peng L. Roles of astrocytic Na+,K+-ATPase and glycogenolysis for K+homeostasis in mammalian brain. J Neurosci Res 2014; 93:1019-30. [DOI: 10.1002/jnr.23499] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2014] [Revised: 08/29/2014] [Accepted: 09/22/2014] [Indexed: 01/25/2023]
Affiliation(s)
- Leif Hertz
- Laboratory of Brain Metabolic Diseases; Institute of Metabolic Disease Research and Drug Development; China Medical University; Shenyang People's Republic of China
| | - Niklas J. Gerkau
- Institute of Neurobiology, Faculty of Mathematics and Natural Sciences; Heinrich Heine University Düsseldorf; Düsseldorf Germany
| | - Junnan Xu
- Laboratory of Brain Metabolic Diseases; Institute of Metabolic Disease Research and Drug Development; China Medical University; Shenyang People's Republic of China
| | - Simone Durry
- Institute of Neurobiology, Faculty of Mathematics and Natural Sciences; Heinrich Heine University Düsseldorf; Düsseldorf Germany
| | - Dan Song
- Laboratory of Brain Metabolic Diseases; Institute of Metabolic Disease Research and Drug Development; China Medical University; Shenyang People's Republic of China
| | - Christine R. Rose
- Institute of Neurobiology, Faculty of Mathematics and Natural Sciences; Heinrich Heine University Düsseldorf; Düsseldorf Germany
| | - Liang Peng
- Laboratory of Brain Metabolic Diseases; Institute of Metabolic Disease Research and Drug Development; China Medical University; Shenyang People's Republic of China
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Hertz L, Xu J, Chen Y, Gibbs ME, Du T, Hertz L, Xu J, Chen Y, Gibbs ME, Du T. Antagonists of the Vasopressin V1 Receptor and of the β(1)-Adrenoceptor Inhibit Cytotoxic Brain Edema in Stroke by Effects on Astrocytes - but the Mechanisms Differ. Curr Neuropharmacol 2014; 12:308-23. [PMID: 25342939 PMCID: PMC4207071 DOI: 10.2174/1570159x12666140828222723] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2014] [Revised: 06/13/2014] [Accepted: 06/20/2014] [Indexed: 01/16/2023] Open
Abstract
Brain edema is a serious complication in ischemic stroke because even relatively small changes in brain volume can compromise cerebral blood flow or result in compression of vital brain structures on account of the fixed volume of the rigid skull. Literature data indicate that administration of either antagonists of the V1 vasopressin (AVP) receptor or the β1-adrenergic receptor are able to reduce edema or infarct size when administered after the onset of ischemia, a key advantage for possible clinical use. The present review discusses possible mechanisms, focusing on the role of NKCC1, an astrocytic cotransporter of Na(+), K(+), 2Cl(-) and water and its activation by highly increased extracellular K(+) concentrations in the development of cytotoxic cell swelling. However, it also mentions that due to a 3/2 ratio between Na(+) release and K(+) uptake by the Na(+),K(+)-ATPase driving NKCC1 brain extracellular fluid can become hypertonic, which may facilitate water entry across the blood-brain barrier, essential for development of edema. It shows that brain edema does not develop until during reperfusion, which can be explained by lack of metabolic energy during ischemia. V1 antagonists are likely to protect against cytotoxic edema formation by inhibiting AVP enhancement of NKCC1-mediated uptake of ions and water, whereas β1-adrenergic antagonists prevent edema formation because β1-adrenergic stimulation alone is responsible for stimulation of the Na(+),K(+)-ATPase driving NKCC1, first and foremost due to decrease in extracellular Ca(2+) concentration. Inhibition of NKCC1 also has adverse effects, e.g. on memory and the treatment should probably be of shortest possible duration.
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Affiliation(s)
- Leif Hertz
- Laboratory of Brain Metabolic Diseases, Institute of Metabolic Disease Research and Drug Development, China Medical University, P.R. China
| | - Junnan Xu
- Laboratory of Brain Metabolic Diseases, Institute of Metabolic Disease Research and Drug Development, China Medical University, P.R. China
| | - Ye Chen
- Henry M. Jackson Foundation 6720A Rockledge Dr #100, Bethesda MD 20817, USA
| | - Marie E Gibbs
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University Parkville, VIC, Australia
| | - Ting Du
- Laboratory of Brain Metabolic Diseases, Institute of Metabolic Disease Research and Drug Development, China Medical University, P.R. China
| | - Leif Hertz
- Laboratory of Brain Metabolic Diseases, Institute of Metabolic Disease Research and Drug Development, China Medical University, P.R. China
| | - Junnan Xu
- Laboratory of Brain Metabolic Diseases, Institute of Metabolic Disease Research and Drug Development, China Medical University, P.R. China
| | - Ye Chen
- Henry M. Jackson Foundation 6720A Rockledge Dr #100, Bethesda MD 20817, USA
| | - Marie E Gibbs
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University Parkville, VIC, Australia
| | - Ting Du
- Laboratory of Brain Metabolic Diseases, Institute of Metabolic Disease Research and Drug Development, China Medical University, P.R. China
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Song D, Xu J, Hertz L, Peng L. Regulatory volume increase in astrocytes exposed to hypertonic medium requires β1 -adrenergic Na(+) /K(+) -ATPase stimulation and glycogenolysis. J Neurosci Res 2014; 93:130-9. [PMID: 25124094 DOI: 10.1002/jnr.23469] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2014] [Revised: 06/16/2014] [Accepted: 07/14/2014] [Indexed: 01/30/2023]
Abstract
The cotransporter of Na(+) , K(+) , 2Cl(-) , and water, NKKC1, is activated under two conditions in the brain, exposure to highly elevated extracellular K(+) concentrations, causing astrocytic swelling, and regulatory volume increase in cells shrunk in response to exposure to hypertonic medium. NKCC1-mediated transport occurs as secondary active transport driven by Na(+) /K(+) -ATPase activity, which establishes a favorable ratio for NKCC1 operation between extracellular and intracellular products of the concentrations of Na(+) , K(+) , and Cl(-) × Cl(-) . In the adult brain, astrocytes are the main target for NKCC1 stimulation, and their Na(+) /K(+) -ATPase activity is stimulated by elevated K(+) or the β-adrenergic agonist isoproterenol. Extracellular K(+) concentration is normal during regulatory volume increase, so this study investigated whether the volume increase occurred faster in the presence of isoproterenol. Measurement of cell volume via live cell microscopic imaging fluorescence to record fluorescence intensity of calcein showed that this was the case at isoproterenol concentrations of ≥1 µM in well-differentiated mouse astrocyte cultures incubated in isotonic medium with 100 mM sucrose added. This stimulation was abolished by the β1 -adrenergic antagonist betaxolol, but not by ICI118551, a β2 -adrenergic antagonist. A large part of the β1 -adrenergic signaling pathway in astrocytes is known. Inhibitors of this pathway as well as the glycogenolysis inhibitor 1,4-dideoxy-1,4-imino-D-arabinitol hydrochloride and the NKCC1 inhibitors bumetanide and furosemide abolished stimulation by isoproterenol, and it was weakened by the Na(+) /K(+) -ATPase inhibitor ouabain. These observations are of physiological relevance because extracellular hypertonicity occurs during intense neuronal activity. This might trigger a regulatory volume increase, associated with the post-excitatory undershoot.
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Affiliation(s)
- Dan Song
- Laboratory of Brain Metabolic Diseases, Institute of Metabolic Disease Research and Drug Development, China Medical University, Shenyang, People's Repbulic of China
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Hertz L, Xu J, Song D, Yan E, Gu L, Peng L. Astrocytic and neuronal accumulation of elevated extracellular K(+) with a 2/3 K(+)/Na(+) flux ratio-consequences for energy metabolism, osmolarity and higher brain function. Front Comput Neurosci 2013; 7:114. [PMID: 23986689 PMCID: PMC3749512 DOI: 10.3389/fncom.2013.00114] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2013] [Accepted: 07/26/2013] [Indexed: 12/22/2022] Open
Abstract
Brain excitation increases neuronal Na+ concentration by 2 major mechanisms: (i) Na+ influx caused by glutamatergic synaptic activity; and (ii) action-potential-mediated depolarization by Na+ influx followed by repolarizating K+ efflux, increasing extracellular K+ concentration. This review deals mainly with the latter and it concludes that clearance of extracellular K+ is initially mainly effectuated by Na+,K+-ATPase-mediated K+ uptake into astrocytes, at K+ concentrations above ~10 mM aided by uptake of Na+,K+ and 2 Cl− by the cotransporter NKCC1. Since operation of the astrocytic Na+,K+-ATPase requires K+-dependent glycogenolysis for stimulation of the intracellular ATPase site, it ceases after normalization of extracellular K+ concentration. This allows K+ release via the inward rectifying K+ channel Kir4.1, perhaps after trans-astrocytic connexin- and/or pannexin-mediated K+ transfer, which would be a key candidate for determination by synchronization-based computational analysis and may have signaling effects. Spatially dispersed K+ release would have little effect on extracellular K+ concentration and allow K+ accumulation by the less powerful neuronal Na+,K+-ATPase, which is not stimulated by increases in extracellular K+. Since the Na+,K+-ATPase exchanges 3 Na+ with 2 K+, it creates extracellular hypertonicity and cell shrinkage. Hypertonicity stimulates NKCC1, which, aided by β-adrenergic stimulation of the Na+,K+-ATPase, causes regulatory volume increase, furosemide-inhibited undershoot in [K+]e and perhaps facilitation of the termination of slow neuronal hyperpolarization (sAHP), with behavioral consequences. The ion transport processes involved minimize ionic disequilibria caused by the asymmetric Na+,K+-ATPase fluxes.
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Affiliation(s)
- Leif Hertz
- Department of Clinical Pharmacology, China Medical University Shenyang, China
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Literature Alerts. J Microencapsul 2008. [DOI: 10.3109/02652049009028430] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Apell HJ. Structure-function relationship in P-type ATPases--a biophysical approach. Rev Physiol Biochem Pharmacol 2004; 150:1-35. [PMID: 12811587 DOI: 10.1007/s10254-003-0018-9] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
P-type ATPases are a large family of membrane proteins that perform active ion transport across biological membranes. In these proteins the energy-providing ATP hydrolysis is coupled to ion-transport that builds up or maintains the electrochemical potential gradients of one or two ion species across the membrane. P-type ATPases are found in virtually all eukaryotic cells and also in bacteria, and they are transporters of a broad variety of ions. So far, a crystal structure with atomic resolution is available only for one species, the SR Ca-ATPase. However, biochemical and biophysical studies provide an abundance of details on the function of this class of ion pumps. The aim of this review is to summarize the results of preferentially biophysical investigations of the three best-studied ion pumps, the Na,K-ATPase, the gastric H,K-ATPase, and the SR Ca-ATPase, and to compare functional properties to recent structural insights with the aim of contributing to the understanding of their structure-function relationship.
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Affiliation(s)
- H-J Apell
- Department of Biology, University of Konstanz, Fach M635, 78457 Konstanz, Germany.
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Gropp T, Cornelius F, Fendler K. K+-dependence of electrogenic transport by the NaK-ATPase. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1368:184-200. [PMID: 9459597 DOI: 10.1016/s0005-2736(97)00162-4] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Charge translocation by the NaK-ATPase from shark rectal gland was measured by adsorption of proteoliposomes to a planar lipid membrane. The proteoliposomes were prepared by reconstitution of purified NaK-ATPase into liposomes consisting of E. coli lipids. The protein was activated by applying an ATP concentration jump produced by photolysis of a protected derivative of ATP, caged ATP. K+ titrations were used to study the effect of K+ on the charge translocation kinetics of the protein. The time-dependent currents obtained after activation of the enzyme with caged ATP were analyzed with a simplified Albers-Post model (E1 (k1)-->E1ATP (k2)-->E2P (k3)-->E1) taking into account the capacitive coupling of the protein to the measuring system. The results of the K+ titrations show a strong dependence of the rate constant k3 on the K+ concentration at the extracellular side of the protein, indicating the K+ activated dephosphorylation reaction. In contrast, k1 and k2 remained constant. The K+ dependence of the rate k3 could be well described with a K+ binding model with two equivalent binding sites (E2P + 2K+ <==> E2P(K) + K+ <==> E2 P(2K)) followed by a rate limiting reaction (E2P(2K) --> E1(2K)). The half saturating K+ concentration K3,0.5 and the microscopic dissociation constant K3 for the K+ dependence of k3 were 4.5mM and 1.9mM respectively. At saturating K+ concentration the rate constant k3 was approximately 100 s(-1). The relative amount of net charge transported during the Na+ and the K+ dependent reactions could be determined from the experiments. Our results suggest electroneutral K+ translocation and do not support electrogenic K+ binding in an extracellular access channel. This is compatible with a model where 2 negative charges are cotransported with 3Na+ and 2K+ ions. Error analysis gives an upper limit of 20% charge transported during K+ translocation or during electrogenic K+ binding in a presumptive access channel compared to Na+ translocation.
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Affiliation(s)
- T Gropp
- Max-Plank-Institut für Biophysik, Frankfurt, Germany
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Friedrich T, Nagel G. Comparison of Na+/K(+)-ATPase pump currents activated by ATP concentration or voltage jumps. Biophys J 1997; 73:186-94. [PMID: 9199783 PMCID: PMC1180920 DOI: 10.1016/s0006-3495(97)78059-7] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Using the giant patch technique, we combined two fast relaxation methods on excised patches from guinea pig cardiomyocytes to compare the rate constants of the involved reaction steps. Experiments were done in the absence of intra- or extracellular K+. Fast ATP concentration jumps were generated by photolysis of caged ATP at pH 6.3 with laser flash irradiation at a wavelength of 308 nm and 10 ns duration, as described previously. Transient outward currents with a fast rising phase, followed by a slower decay and a small stationary current, were obtained. Voltage pulses were applied to the same patch in the presence or absence of intracellular ATP. Subtraction of the voltage jump-induced currents in the absence of ATP from those taken in the presence of ATP yielded monoexponential transient current signals, which were dependent on external Na+ but did not differ between intracellular pH (pHi) values 6.3 or 7.4. Rate constants showed a characteristic voltage dependence, i.e., saturating at positive potentials (approximately 200 s-1, 24 degrees C) and exponentially rising with increasing negative potentials. Rate constants of the fast component from transient currents obtained after an ATP concentration jump agree well with rate constants from currents obtained after a voltage jump to zero or positive potentials (pHi 6.3), and the two exhibit the same activation energy of approximately 80 kJ.mol-1. For a given membrane patch, the amount of charge that is moved across the plasma membrane is roughly the same for each of the two relaxation techniques.
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Affiliation(s)
- T Friedrich
- Johann Wolfgang Goethe-Universität Frankfurt am Main, Germany
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Apell HJ. Separation and characterization of Na+,K(+)-ATPase containing vesicles. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1196:29-37. [PMID: 7986807 DOI: 10.1016/0005-2736(94)90291-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Na+,K(+)-ATPase was reconstituted in vesicles prepared by a dialysis method. Ion-exchange chromatography was used to obtain well characterized fractions from the inhomogeneous vesicle preparation. Lipid and protein content was determined by optical methods during the elution process. It was possible to separate fractions with distinct enzymatic and transport activities. A protocol was set up, which allowed to calculate the average number of 5-IAF labeled ion pumps per vesicle in the different fractions. The dependence of the number of protein molecules per vesicle was studied as function of the initial protein concentration added to the lipid solution before dialysis. The transport activity disappears completely at very low protein concentrations (3.3 micrograms protein per mg lipid). This observation is in favor of the proposal discussed in the literature, that the heterodimer (alpha beta)2 is the transport-active form of the Na+,K(+)-ATPase. The presented method can be applied to all reconstituted vesicle preparations in which the proteins can be labeled quantitatively with a fluorescence dye.
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Riek R, Apell HJ. Investigation of reconstitution of the Na, K-ATPase in lipid vesicles. BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1148:321-30. [PMID: 8389199 DOI: 10.1016/0005-2736(93)90146-q] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Vesicles containing Na,K-ATPase were prepared by a dialysis method in buffers with various concentrations of K+ and Na+ ions. Ion-exchange chromatography has been used to separate proteoliposomes into protein-depleted and protein-rich fractions. The pumping activity of reconstituted ion pumps has been determined in the different fractions of the vesicle preparation using voltage-dependent fluorescence dyes. This method allowed to characterise vesicle fractions by a quantity which is proportional to the average number of pumps per vesicle with an active (inside-out) orientation. It could be shown that both, the amount of enzymatic active protein and the orientation of Na,K-ATPase in the vesicle lipid bilayer, is partially controlled by the Na+ and K+ concentration in the buffer during vesicle formation. High Na+ concentrations preferentially maintain the E1 conformation of the enzyme, which is less stable against denaturation during the dialysis, but displays a higher percentage of inside-out orientation of the transport-active protein. High K+ concentrations maintain the E2 conformation of the enzyme, which is stable against denaturation during the dialysis, but leads to a random orientation of the pump during dialysis.
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Kalinowski S, Figaszewski Z. A new system for bilayer lipid membrane capacitance measurements: method, apparatus and applications. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1112:57-66. [PMID: 1420270 DOI: 10.1016/0005-2736(92)90254-j] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
A new method and a new apparatus for capacitance measurements on bilayer lipid membranes are described. The membrane is charged and discharged with a constant current during the measurement. The charge-discharge cycle duration, which is proportional to the membrane capacitance, is measured. The measured time period is converted into a binary number by digital systems and then this number is either further converted into a constant capacity-proportional voltage or read out by the computer. The apparatus makes it possible to measure the capacitances of voltage-polarized membranes. Application of the apparatus to capacitance measurements of bilayer lipid membranes during their potential on the capacitance is presented. The capacitances of membranes stimulated by rectangular voltage pulses and of those stimulated by a linearly varying potential were reported.
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Affiliation(s)
- S Kalinowski
- Institute of Chemistry, University of Warsaw, Białystok, Poland
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Abstract
The energy dependent exchange of cytoplasmic Na+ for extracellular K+ in mammalian cells is due to a membrane bound enzyme system, the Na,K-ATPase. The exchange sustains a gradient for Na+ into and for K+ out of the cell, and this is used as an energy source for creation of the membrane potential, for its de- and repolarisation, for regulation of cytoplasmic ionic composition and for transepithelial transport. The Na,K-ATPase consists of two membrane spanning polypeptides, an alpha-subunit of 112-kD and a beta-subunit, which is a glycoprotein of 35-kD. The catalytic properties are associated with the alpha-subunit, which has the binding domain for ATP and the cations. In the review, attention will be given to the biochemical characterization of the reaction mechanism underlying the coupling between hydrolysis of the substate ATP and transport of Na+ and K+.
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Affiliation(s)
- J C Skou
- Institute of Biophysics, University of Aarhus, Denmark
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Cornelius F. Functional reconstitution of the sodium pump. Kinetics of exchange reactions performed by reconstituted Na/K-ATPase. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1071:19-66. [PMID: 1848452 DOI: 10.1016/0304-4157(91)90011-k] [Citation(s) in RCA: 102] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- F Cornelius
- Institute of Biophysics, University of Aarhus, Denmark
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Clarke RJ. Binding and diffusion kinetics of the interaction of a hydrophobic potential-sensitive dye with lipid vesicles. Biophys Chem 1991; 39:91-106. [PMID: 2012838 DOI: 10.1016/0301-4622(91)85010-n] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The interaction of the dye oxonol V with unilamellar dioleoylphosphatidylcholine vesicles has previously been investigated using a fluorescence stopped-flow technique. It has been found that the most suitable mathematical description of the equilibrium and kinetic data is obtained by assuming the presence of saturable dye binding sites in both monolayers of the vesicle membrane and a potential-dependent diffusion across the membrane interior between these two classes of sites. A kinetic model is presented which takes into account the degree of saturation of the binding sites, the degree of fluorescence quenching within the membrane, and the production of an electrical potential gradient across the membrane interior by the binding of the negatively charged dye. The model successfully predicts the time course of the fluorescence change due to binding and diffusion over the complete range of dye and vesicle concentrations as well as the fluorescence response of the dye to changing membrane potential.
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Affiliation(s)
- R J Clarke
- School of Chemical Sciences, University of East Anglia, Norwich, U.K
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Skou JC. The fourth Datta lecture. The energy coupled exchange of Na+ for K+ across the cell membrane. The Na+, K(+)-pump. FEBS Lett 1990; 268:314-24. [PMID: 2166689 DOI: 10.1016/0014-5793(90)81278-v] [Citation(s) in RCA: 91] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- J C Skou
- Institute of Biophysics, University of Arhus, Denmark
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Apell HJ, Solioz M. Electrogenic transport by the Enterococcus hirae ATPase. BIOCHIMICA ET BIOPHYSICA ACTA 1990; 1017:221-8. [PMID: 2164846 DOI: 10.1016/0005-2728(90)90188-a] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
A transport ATPase from Enterococcus hirae was reconstituted in lipid vesicles and its electrogenic action investigated with the fluorescent dye oxonol VI as membrane potential probe. Reconstitution in bacterial and in soybean phospholipid mixtures led to transport-active vesicle preparations. Inside-out oriented ATPase molecules were activated by the addition of ATP to the extravesicular medium, generating in all experiments an intravesicularly positive potential. The extravesicular pH strongly influenced the initial pumping rate and the duration of the pumping activity. At neutral pH, transient pumping activity was observed, lasting for 1-2 min, while at pH 5.6, pumping was continuous. The transport activity was not dependent on the ionic composition of the buffer on either side of the membrane. These findings can be interpreted as the action of a proton ATPase, regulated by the cytoplasmic proton concentration and electrogenically translocating protons from the cytoplasm to the extracellular space.
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Affiliation(s)
- H J Apell
- Department of Biology, University of Konstanz, F.R.G
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