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MacAulay N. Molecular mechanisms of K + clearance and extracellular space shrinkage-Glia cells as the stars. Glia 2020; 68:2192-2211. [PMID: 32181522 DOI: 10.1002/glia.23824] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2020] [Revised: 02/28/2020] [Accepted: 03/04/2020] [Indexed: 12/17/2022]
Abstract
Neuronal signaling in the central nervous system (CNS) associates with release of K+ into the extracellular space resulting in transient increases in [K+ ]o . This elevated K+ is swiftly removed, in part, via uptake by neighboring glia cells. This process occurs in parallel to the [K+ ]o elevation and glia cells thus act as K+ sinks during the neuronal activity, while releasing it at the termination of the pulse. The molecular transport mechanisms governing this glial K+ absorption remain a point of debate. Passive distribution of K+ via Kir4.1-mediated spatial buffering of K+ has become a favorite within the glial field, although evidence for a quantitatively significant contribution from this ion channel to K+ clearance from the extracellular space is sparse. The Na+ /K+ -ATPase, but not the Na+ /K+ /Cl- cotransporter, NKCC1, shapes the activity-evoked K+ transient. The different isoform combinations of the Na+ /K+ -ATPase expressed in glia cells and neurons display different kinetic characteristics and are thereby distinctly geared toward their temporal and quantitative contribution to K+ clearance. The glia cell swelling occurring with the K+ transient was long assumed to be directly associated with K+ uptake and/or AQP4, although accumulating evidence suggests that they are not. Rather, activation of bicarbonate- and lactate transporters appear to lead to glial cell swelling via the activity-evoked alkaline transient, K+ -mediated glial depolarization, and metabolic demand. This review covers evidence, or lack thereof, accumulated over the last half century on the molecular mechanisms supporting activity-evoked K+ and extracellular space dynamics.
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Affiliation(s)
- Nanna MacAulay
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark
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2
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Potassium dynamics and seizures: Why is potassium ictogenic? Epilepsy Res 2018; 143:50-59. [DOI: 10.1016/j.eplepsyres.2018.04.005] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Revised: 03/26/2018] [Accepted: 04/07/2018] [Indexed: 01/01/2023]
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Abstract
Microtubules, constituted by end-to-end negatively charged α- and β-tubulin dimers, are long, hollow, pseudohelical cylinders with internal and external diameters of about 16 and 26 nm, respectively, and widely exist in cell cytoplasm, neuron axons, and dendrites. Although their structural functions in physiological processes, such as cell mitosis, cell motility, and motor protein transport, have been widely accepted, their role in neuron activity remains attractively elusive. Here we show a new function of microtubules: they can generate instant response to a calcium pulse because of their specific permeability for ions. Our comprehensive simulations from all-atom molecular dynamics to potential of mean force and continuum modeling reveal that K+ and Na+ ions can permeate through the nanopores in the microtubule wall easily, while Ca2+ ions are blocked by the wall with a much higher free energy barrier. These cations are adsorbed to the surfaces of the wall with affinity decreasing in the sequence Ca2+, Na+, and K+. As a result, when the concentration of Ca2+ ions increases outside the microtubule during neuronal excitation, K+ and Na+ ions will be driven into the microtubule, triggering subsequent axial ion redistribution within the microtubule. The results shed light on the possibility of the ion-permeable microtubules being involved in neural signal processing.
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Affiliation(s)
- Chun Shen
- State Key Laboratory of Mechanics and Control of Mechanical Structure and Key Laboratory for Intelligent Nano Materials and Devices of the Ministry of Education, and Institute of Nanoscience , Nanjing University of Aeronautics and Astronautics , Nanjing 210016 , China
| | - Wanlin Guo
- State Key Laboratory of Mechanics and Control of Mechanical Structure and Key Laboratory for Intelligent Nano Materials and Devices of the Ministry of Education, and Institute of Nanoscience , Nanjing University of Aeronautics and Astronautics , Nanjing 210016 , China
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DiNuzzo M, Giove F, Maraviglia B, Mangia S. Computational Flux Balance Analysis Predicts that Stimulation of Energy Metabolism in Astrocytes and their Metabolic Interactions with Neurons Depend on Uptake of K + Rather than Glutamate. Neurochem Res 2016; 42:202-216. [PMID: 27628293 PMCID: PMC5283516 DOI: 10.1007/s11064-016-2048-0] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2016] [Revised: 08/22/2016] [Accepted: 08/24/2016] [Indexed: 12/04/2022]
Abstract
Brain activity involves essential functional and metabolic interactions between neurons and astrocytes. The importance of astrocytic functions to neuronal signaling is supported by many experiments reporting high rates of energy consumption and oxidative metabolism in these glial cells. In the brain, almost all energy is consumed by the Na+/K+ ATPase, which hydrolyzes 1 ATP to move 3 Na+ outside and 2 K+ inside the cells. Astrocytes are commonly thought to be primarily involved in transmitter glutamate cycling, a mechanism that however only accounts for few % of brain energy utilization. In order to examine the participation of astrocytic energy metabolism in brain ion homeostasis, here we attempted to devise a simple stoichiometric relation linking glutamatergic neurotransmission to Na+ and K+ ionic currents. To this end, we took into account ion pumps and voltage/ligand-gated channels using the stoichiometry derived from available energy budget for neocortical signaling and incorporated this stoichiometric relation into a computational metabolic model of neuron-astrocyte interactions. We aimed at reproducing the experimental observations about rates of metabolic pathways obtained by 13C-NMR spectroscopy in rodent brain. When simulated data matched experiments as well as biophysical calculations, the stoichiometry for voltage/ligand-gated Na+ and K+ fluxes generated by neuronal activity was close to a 1:1 relationship, and specifically 63/58 Na+/K+ ions per glutamate released. We found that astrocytes are stimulated by the extracellular K+ exiting neurons in excess of the 3/2 Na+/K+ ratio underlying Na+/K+ ATPase-catalyzed reaction. Analysis of correlations between neuronal and astrocytic processes indicated that astrocytic K+ uptake, but not astrocytic Na+-coupled glutamate uptake, is instrumental for the establishment of neuron-astrocytic metabolic partnership. Our results emphasize the importance of K+ in stimulating the activation of astrocytes, which is relevant to the understanding of brain activity and energy metabolism at the cellular level.
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Affiliation(s)
- Mauro DiNuzzo
- Center for Basic and Translational Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, 24.2.40, 2200, Copenhagen N, Denmark.
| | - Federico Giove
- Museo Storico della Fisica e Centro Studi e Ricerche "Enrico Fermi", Rome, Italy.,Fondazione Santa Lucia IRCCS, Rome, Italy
| | - Bruno Maraviglia
- Museo Storico della Fisica e Centro Studi e Ricerche "Enrico Fermi", Rome, Italy.,Fondazione Santa Lucia IRCCS, Rome, Italy
| | - Silvia Mangia
- Center for Magnetic Resonance Research, Department of Radiology, Univeristy of Minnesota, Minneapolis, MN, USA
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Renuka M, Vijayakumar N, Ramakrishnan A. Chrysin, a flavonoid attenuates histological changes of hyperammonemic rats: A dose dependent study. Biomed Pharmacother 2016; 82:345-54. [DOI: 10.1016/j.biopha.2016.05.013] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2016] [Revised: 05/10/2016] [Accepted: 05/10/2016] [Indexed: 01/12/2023] Open
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6
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Hertz L, Song D, Xu J, Peng L, Gibbs ME. Role of the Astrocytic Na(+), K(+)-ATPase in K(+) Homeostasis in Brain: K(+) Uptake, Signaling Pathways and Substrate Utilization. Neurochem Res 2015; 40:2505-16. [PMID: 25555706 DOI: 10.1007/s11064-014-1505-x] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2014] [Revised: 12/01/2014] [Accepted: 12/19/2014] [Indexed: 01/13/2023]
Abstract
This paper describes the roles of the astrocytic Na(+), K(+)-ATPase for K(+) homeostasis in brain. After neuronal excitation it alone mediates initial cellular re-accumulation of moderately increased extracellular K(+). At higher K(+) concentrations it is assisted by the Na(+), K(+), 2Cl(-) transporter NKCC1, which is Na(+), K(+)-ATPase-dependent, since it is driven by Na(+), K(+)-ATPase-created ion gradients. Besides stimulation by high K(+), NKCC1 is activated by extracellular hypertonicity. Intense excitation is followed by extracellular K(+) undershoot which is decreased by furosemide, an NKCC1 inhibitor. The powerful astrocytic Na(+), K(+)-ATPase accumulates excess extracellular K(+), since it is stimulated by above-normal extracellular K(+) concentrations. Subsequently K(+) is released via Kir4.1 channels (with no concomitant Na(+) transport) for re-uptake by the neuronal Na(+), K(+)-ATPase which is in-sensitive to increased extracellular K(+), but stimulated by intracellular Na(+) increase. Operation of the astrocytic Na(+), K(+)-ATPase depends upon Na(+), K(+)-ATPase/ouabain-mediated signaling and K(+)-stimulated glycogenolysis, needed in these non-excitable cells for passive uptake of extracellular Na(+), co-stimulating the intracellular Na(+)-sensitive site. A gradual, spatially dispersed release of astrocytically accumulated K(+) will therefore not re-activate the astrocytic Na(+), K(+)-ATPase. The extracellular K(+) undershoot is probably due to extracellular hypertonicity, created by a 3:2 ratio between Na(+), K(+)-ATPase-mediated Na(+) efflux and K(+) influx and subsequent NKCC1-mediated volume regulation. The astrocytic Na(+), K(+)-ATPase is also stimulated by β1-adrenergic signaling, which further stimulates hypertonicity-activation of NKCC1. Brain ischemia leads to massive extracellular K(+) increase and Ca(2+) decrease. A requirement of Na(+), K(+)-ATPase signaling for extracellular Ca(2+) makes K(+) uptake (and brain edema) selectively dependent upon β1-adrenergic signaling and inhibitable by its antagonists.
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Affiliation(s)
- Leif Hertz
- Laboratory of Brain Metabolic Diseases, Institute of Metabolic Disease Research and Drug Development, China Medical University, No. 77 Puhe Road, Shenbei District, Shenyang, 110122, People's Republic of China
| | - Dan Song
- Laboratory of Brain Metabolic Diseases, Institute of Metabolic Disease Research and Drug Development, China Medical University, No. 77 Puhe Road, Shenbei District, Shenyang, 110122, People's Republic of China
| | - Junnan Xu
- Laboratory of Brain Metabolic Diseases, Institute of Metabolic Disease Research and Drug Development, China Medical University, No. 77 Puhe Road, Shenbei District, Shenyang, 110122, People's Republic of China
| | - Liang Peng
- Laboratory of Brain Metabolic Diseases, Institute of Metabolic Disease Research and Drug Development, China Medical University, No. 77 Puhe Road, Shenbei District, Shenyang, 110122, People's Republic of China.
| | - Marie E Gibbs
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Clayton, VIC, Australia
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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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9
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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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DiNuzzo M, Mangia S, Maraviglia B, Giove F. Physiological bases of the K+ and the glutamate/GABA hypotheses of epilepsy. Epilepsy Res 2014; 108:995-1012. [PMID: 24818957 DOI: 10.1016/j.eplepsyres.2014.04.001] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2014] [Revised: 03/20/2014] [Accepted: 04/01/2014] [Indexed: 01/19/2023]
Abstract
Epilepsy is a heterogeneous family of neurological disorders that manifest as seizures, i.e. the hypersynchronous activity of large population of neurons. About 30% of epileptic patients do not respond to currently available antiepileptic drugs. Decades of intense research have elucidated the involvement of a number of possible signaling pathways, however, at present we do not have a fundamental understanding of epileptogenesis. In this paper, we review the literature on epilepsy under a wide-angle perspective, a mandatory choice that responds to the recurrent and unanswered question about what is epiphenomenal and what is causal to the disease. While focusing on the involvement of K+ and glutamate/GABA in determining neuronal hyperexcitability, emphasis is given to astrocytic contribution to epileptogenesis, and especially to loss-of-function of astrocytic glutamine synthetase following reactive astrogliosis, a hallmark of epileptic syndromes. We finally introduce the potential involvement of abnormal glycogen synthesis induced by excess glutamate in increasing susceptibility to seizures.
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Affiliation(s)
- Mauro DiNuzzo
- MARBILab, Museo storico della fisica e Centro di studi e ricerche "Enrico Fermi", Rome, Italy.
| | - Silvia Mangia
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, USA
| | - Bruno Maraviglia
- Dipartimento di Fisica, Sapienza Università di Roma, Rome, Italy; Fondazione Santa Lucia IRCCS, Rome, Italy
| | - Federico Giove
- MARBILab, Museo storico della fisica e Centro di studi e ricerche "Enrico Fermi", Rome, Italy; Dipartimento di Fisica, Sapienza Università di Roma, Rome, Italy
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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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DiNuzzo M, Mangia S, Maraviglia B, Giove F. Regulatory mechanisms for glycogenolysis and K+ uptake in brain astrocytes. Neurochem Int 2013; 63:458-64. [PMID: 23968961 DOI: 10.1016/j.neuint.2013.08.004] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2013] [Revised: 08/05/2013] [Accepted: 08/07/2013] [Indexed: 11/29/2022]
Abstract
Recent advances in brain energy metabolism support the notion that glycogen in astrocytes is necessary for the clearance of neuronally-released K(+) from the extracellular space. However, how the multiple metabolic pathways involved in K(+)-induced increase in glycogen turnover are regulated is only partly understood. Here we summarize the current knowledge about the mechanisms that control glycogen metabolism during enhanced K(+) uptake. We also describe the action of the ubiquitous Na(+)/K(+) ATPase for both ion transport and intracellular signaling cascades, and emphasize its importance in understanding the complex relation between glycogenolysis and K(+) uptake.
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Affiliation(s)
- Mauro DiNuzzo
- MARBILab, Museo storico della fisica e Centro di studi e ricerche "Enrico Fermi", Rome, Italy.
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Dinuzzo M, Mangia S, Maraviglia B, Giove F. The role of astrocytic glycogen in supporting the energetics of neuronal activity. Neurochem Res 2012; 37:2432-8. [PMID: 22614927 DOI: 10.1007/s11064-012-0802-5] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2012] [Revised: 04/16/2012] [Accepted: 05/07/2012] [Indexed: 01/07/2023]
Abstract
Energy homeostasis in the brain is maintained by oxidative metabolism of glucose, primarily to fulfil the energy demand associated with ionic movements in neurons and astrocytes. In this contribution we review the experimental evidence that grounds a specific role of glycogen metabolism in supporting the functional energetic needs of astrocytes during the removal of extracellular potassium. Based on theoretical considerations, we further discuss the hypothesis that the mobilization of glycogen in astrocytes serves the purpose to enhance the availability of glucose for neuronal glycolytic and oxidative metabolism at the onset of stimulation. Finally, we provide an evolutionary perspective for explaining the selection of glycogen as carbohydrate reserve in the energy-sensing machinery of cell metabolism.
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Affiliation(s)
- Mauro Dinuzzo
- MARBILab, Museo storico della fisica e Centro di studi e ricerche "Enrico Fermi", Rome, Italy.
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Hertz L. Astrocytic energy metabolism and glutamate formation--relevance for 13C-NMR spectroscopy and importance of cytosolic/mitochondrial trafficking. Magn Reson Imaging 2011; 29:1319-29. [PMID: 21820830 DOI: 10.1016/j.mri.2011.04.013] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2011] [Revised: 04/21/2011] [Accepted: 04/22/2011] [Indexed: 11/18/2022]
Abstract
Glutamate plays a double role in (13)C-nuclear magnetic resonance (NMR) spectroscopic determination of glucose metabolism in the brain. Bidirectional exchange between initially unlabeled glutamate and labeled α-ketoglutarate, formed from pyruvate via pyruvate dehydrogenase (PDH), indicates the rate of energy metabolism in the tricarboxylic acid (V(TCA)) cycle in neurons (V(PDH, n)) and, with additional computation, also in astrocytes (V(PDH, g)), as confirmed using the astrocyte-specific substrate [(13)C]acetate. Formation of new molecules of glutamate during increased glutamatergic activity occurs only in astrocytes by combined pyruvate carboxylase (V(PC)) and astrocytic PDH activity. V(PDH, g) accounts for ~15% of total pyruvate metabolism in the brain cortex, and V(PC) accounts for another ~10%. Since both PDH-generated and PC-generated pyruvates are needed for glutamate synthesis, ~20/25 (80%) of astrocytic pyruvate metabolism proceed via glutamate formation. Net transmitter glutamate [γ-aminobutyric acid (GABA)] formation requires transfer of newly synthesized α-ketoglutarate to the astrocytic cytosol, α-ketoglutarate transamination to glutamate, amidation to glutamine, glutamine transfer to neurons, its hydrolysis to glutamate and glutamate release (or GABA formation). Glutamate-glutamine cycling, measured as glutamine synthesis rate (V(cycle)), also transfers previously released glutamate/GABA to neurons after an initial astrocytic accumulation and measures predominantly glutamate signaling. An empirically established ~1/1 ratio between glucose metabolism and V(cycle) may reflect glucose utilization associated with oxidation/reduction processes during glutamate production, which together with associated transamination processes are balanced by subsequent glutamate oxidation after cessation of increased signaling activity. Astrocytic glutamate formation and subsequent oxidative metabolism provide large amounts of adenosine triphosphate used for accumulation from extracellular clefts of neuronally released K(+) and glutamate and for cytosolic Ca(2+) homeostasis.
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Affiliation(s)
- Leif Hertz
- Department of Clinical Pharmacology, College of Basic Medical Sciences, China Medical University, No. 92 Beier Road, Heping District, Shenyang, PR China.
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Hertz L, Lovatt D, Goldman SA, Nedergaard M. Adrenoceptors in brain: cellular gene expression and effects on astrocytic metabolism and [Ca(2+)]i. Neurochem Int 2010; 57:411-20. [PMID: 20380860 PMCID: PMC2934885 DOI: 10.1016/j.neuint.2010.03.019] [Citation(s) in RCA: 163] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2009] [Revised: 03/02/2010] [Accepted: 03/31/2010] [Indexed: 11/24/2022]
Abstract
Recent in vivo studies have established astrocytes as a major target for locus coeruleus activation (Bekar et al., 2008), renewing interest in cell culture studies on noradrenergic effects on astrocytes in primary cultures and calling for additional information about the expression of adrenoceptor subtypes on different types of brain cells. In the present communication, mRNA expression of alpha(1)-, alpha(2)- and beta-adrenergic receptors and their subtypes was determined in freshly isolated, cell marker-defined populations of astrocytes, NG2-positive cells, microglia, endothelial cells, and Thy1-positive neurons (mainly glutamatergic projection neurons) in murine cerebral cortex. Immediately after dissection of frontal, parietal and occipital cortex of 10-12-week-old transgenic mice, which combined each cell-type marker with a specific fluorescent signal, the tissue was digested, triturated and centrifuged, yielding a solution of dissociated cells of all types, which were separated by fluorescence-activated cell sorting (FACS). mRNA expression in each cell fraction was determined by microarray analysis. alpha(1A)-Receptors were unequivocally expressed in astrocytes and NG2-positive cells, but absent in other cell types, and alpha(1B)-receptors were not expressed in any cell population. Among alpha(2)-receptors only alpha(2A)-receptors were expressed, unequivocally in astrocytes and NG-positive cells, tentatively in microglia and questionably in Thy1-positive neurons and endothelial cells. beta(1)-Receptors were unequivocally expressed in astrocytes, tentatively in microglia, and questionably in neurons and endothelial cells, whereas beta(2)-adrenergic receptors showed tentative expression in neurons and astrocytes and unequivocal expression in other cell types. This distribution was supported by immunochemical data and its relevance established by previous studies in well-differentiated primary cultures of mouse astrocytes, showing that stimulation of alpha(2)-adrenoceptors increases glycogen formation and oxidative metabolism, the latter by a mechanism depending on intramitochondrial Ca(2+), whereas alpha(1)-adrenoceptor stimulation enhances glutamate uptake, and beta-adrenoceptor activation causes glycogenolysis and increased Na(+), K(+)-ATPase activity. The Ca(2+)- and cAMP-mediated association between energy-consuming and energy-yielding processes is emphasized.
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MESH Headings
- Animals
- Astrocytes/metabolism
- Brain Chemistry/genetics
- Brain Chemistry/physiology
- Calcium Signaling/physiology
- Cell Separation
- Cells, Cultured
- Flow Cytometry
- Gene Expression/physiology
- Glucose/metabolism
- Glycogen/metabolism
- Mice
- Mice, Transgenic/physiology
- Microarray Analysis
- Mitochondria/metabolism
- Oxidation-Reduction
- Pyruvic Acid/metabolism
- RNA/biosynthesis
- RNA/genetics
- Receptors, Adrenergic/biosynthesis
- Receptors, Adrenergic/genetics
- Receptors, Adrenergic, alpha-1/biosynthesis
- Receptors, Adrenergic, alpha-1/genetics
- Receptors, Adrenergic, alpha-2/biosynthesis
- Receptors, Adrenergic, alpha-2/genetics
- Receptors, Adrenergic, beta/biosynthesis
- Receptors, Adrenergic, beta/genetics
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Affiliation(s)
- Leif Hertz
- Department of Clinical Pharmacology, College of Basic Medical Sciences, China Medical University, Shenyang, P. R. China
| | - Ditte Lovatt
- Division of Glial Disease and Therapeutics, Department of Neurosurgery, University of Rochester Medical Center, Rochester, NY 14642
- Department of Neurology, University of Rochester Medical Center, Rochester, NY 14642
| | - Steven A. Goldman
- Department of Neurology, University of Rochester Medical Center, Rochester, NY 14642
| | - Maiken Nedergaard
- Division of Glial Disease and Therapeutics, Department of Neurosurgery, University of Rochester Medical Center, Rochester, NY 14642
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16
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Ouabain binding kinetics and FXYD7 expression in astrocytes and neurons in primary cultures: implications for cellular contributions to extracellular K+ homeostasis? ACTA ACUST UNITED AC 2010; 6:127-35. [PMID: 20187992 DOI: 10.1017/s1740925x10000013] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Although Na+,K+-ATPase-mediated K+ uptake into astrocytes plays a major role in re-establishing resting extracellular K+ following neuronal excitation little information is available about astrocytic Na+,K+-ATPase function, let alone mechanisms returning K+ to neurons. The catalytic units of the Na+,K+-ATPase are the astrocyte-specific α2, the neuron-specific α3 and the ubiquitously expressed α1. In the present work, Bmax and KD values for α1, α2 and α3 subunits were computed in cultured cerebro-cortical mouse astrocytes and cerebellar granule neurons by non-linear regression as high-affinity (α2, α3) and low-affinity (α1) [3H]ouabain binding sites, which stoichiometrically equal transporter sites. Cellular expression was also determined of the brain- and α1-β1 isoform-specific FDYX7, regulating Na+,K+-ATPase efficiency and K+-sensitivity. From ouabain-sensitive K+ uptake rates published by ourselves (Walz and Hertz, 1982) or others (Atterwill et al., 1985), Na+,K+-ATPase turnover was determined. Subunits α2 and α3 showed Bmax of 15-30 pmol/mg protein, with maximum turnover rates of 70-80/s. Bmax of the α1 subunit was low in neurons but very high in astrocytes (645 pmol/mg protein), where turnover rate was slow, reflecting expression of selectively expressed FXYD7, and binding was increased by K+. The role of these characteristics for K+ homeostasis are discussed.
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17
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Castro MA, Beltrán FA, Brauchi S, Concha II. A metabolic switch in brain: glucose and lactate metabolism modulation by ascorbic acid. J Neurochem 2009; 110:423-40. [PMID: 19457103 DOI: 10.1111/j.1471-4159.2009.06151.x] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
In this review, we discuss a novel function of ascorbic acid in brain energetics. It has been proposed that during glutamatergic synaptic activity neurons preferably consume lactate released from glia. The key to this energetic coupling is the metabolic activation that occurs in astrocytes by glutamate and an increase in extracellular [K(+)]. Neurons are cells well equipped to consume glucose because they express glucose transporters and glycolytic and tricarboxylic acid cycle enzymes. Moreover, neuronal cells express monocarboxylate transporters and lactate dehydrogenase isoenzyme 1, which is inhibited by pyruvate. As glycolysis produces an increase in pyruvate concentration and a decrease in NAD(+)/NADH, lactate and glucose consumption are not viable at the same time. In this context, we discuss ascorbic acid participation as a metabolic switch modulating neuronal metabolism between rest and activation periods. Ascorbic acid is highly concentrated in CNS. Glutamate stimulates ascorbic acid release from astrocytes. Ascorbic acid entry into neurons and within the cell can inhibit glucose consumption and stimulate lactate transport. For this switch to occur, an ascorbic acid flow is necessary between astrocytes and neurons, which is driven by neural activity and is part of vitamin C recycling. Here, we review the role of glucose and lactate as metabolic substrates and the modulation of neuronal metabolism by ascorbic acid.
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Affiliation(s)
- Maite A Castro
- Instituto de Bioquímica, Universidad Austral de Chile, Valdivia, Chile.
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18
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Hertz L, Peng L, Dienel GA. Energy metabolism in astrocytes: high rate of oxidative metabolism and spatiotemporal dependence on glycolysis/glycogenolysis. J Cereb Blood Flow Metab 2007; 27:219-49. [PMID: 16835632 DOI: 10.1038/sj.jcbfm.9600343] [Citation(s) in RCA: 439] [Impact Index Per Article: 25.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Astrocytic energy demand is stimulated by K(+) and glutamate uptake, signaling processes, responses to neurotransmitters, Ca(2+) fluxes, and filopodial motility. Astrocytes derive energy from glycolytic and oxidative pathways, but respiration, with its high-energy yield, provides most adenosine 5' triphosphate (ATP). The proportion of cortical oxidative metabolism attributed to astrocytes ( approximately 30%) in in vivo nuclear magnetic resonance (NMR) spectroscopic and autoradiographic studies corresponds to their volume fraction, indicating similar oxidation rates in astrocytes and neurons. Astrocyte-selective expression of pyruvate carboxylase (PC) enables synthesis of glutamate from glucose, accounting for two-thirds of astrocytic glucose degradation via combined pyruvate carboxylation and dehydrogenation. Together, glutamate synthesis and oxidation, including neurotransmitter turnover, generate almost as much energy as direct glucose oxidation. Glycolysis and glycogenolysis are essential for astrocytic responses to increasing energy demand because astrocytic filopodial and lamellipodial extensions, which account for 80% of their surface area, are too narrow to accommodate mitochondria; these processes depend on glycolysis, glycogenolysis, and probably diffusion of ATP and phosphocreatine formed via mitochondrial metabolism to satisfy their energy demands. High glycogen turnover in astrocytic processes may stimulate glucose demand and lactate production because less ATP is generated when glucose is metabolized via glycogen, thereby contributing to the decreased oxygen to glucose utilization ratio during brain activation. Generated lactate can spread from activated astrocytes via low-affinity monocarboxylate transporters and gap junctions, but its subsequent fate is unknown. Astrocytic metabolic compartmentation arises from their complex ultrastructure; astrocytes have high oxidative rates plus dependence on glycolysis and glycogenolysis, and their energetics is underestimated if based solely on glutamate cycling.
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Affiliation(s)
- Leif Hertz
- College of Basic Medical Sciences, China Medical University, Shenyang, People's Republic of China.
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19
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Abstract
Astrocytes are multifunctional cells that interact with neurons and other astrocytes in signaling and metabolic functions, and their resistance to pathophysiological conditions can help restrict loss of tissue after an ischemic event provided adequate nutrients are supplied to support their requirements. Astrocytes have substantial oxidative capacity and mechanisms to upregulate glycolytic capability when respiration is impaired. An astrocytic enzyme that synthesizes a powerful activator of glycolysis is not present in neurons, endowing astrocytes with the ability to sustain ATP production under restrictive conditions. The monocarboxylic acid transporter (MCT) isoforms predominating in astrocytes are optimized to facilitate very large increases in lactate flux as lactate concentration increases within (1-3 mM) and above (>3 mM) the normal range. In sharp contrast, the major neuronal MCT serves as a barrier to increased transmembrane transport as lactate rises above 1 mM, restricting both entry and efflux. Lactate can serve as fuel during recovery from ischemia but direct evidence that lactate is oxidized by neurons (vs. astrocytes) to maintain synaptic function is lacking. Astrocytes have critical roles in regulation of ionic homeostasis and control of extracellular glutamate levels, and spreading depression associated with ischemia places high demands on energy supplies in astrocytes and contributes to metabolic exhaustion and demise. Disruption of Ca2+ homeostasis, generation of oxygen free radicals and nitric oxide, and mitochondrial depolarization contribute to astrocyte death during and after a metabolic insult. Novel pharmaceutical agents targeted to astrocytes and hyperoxic therapy that restores penumbral oxygen level during energy failure might improve postischemic outcome.
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Affiliation(s)
- Gerald A Dienel
- Department of Neurology, University of Arkansas for Medical Sciences, Little Rock, Arkansas
| | - Leif Hertz
- College of Basic Medical Sciences, China Medical University, Shenyang, People's Republic of China
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20
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Affiliation(s)
- Leif Hertz
- Hong Kong DNA Chips, Ltd., Kowloon, Hong Kong, China
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21
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Heinemann U, Buchheim K, Gabriel S, Kann O, Kovacs R, Schuchmann S. Cell death and metabolic activity during epileptiform discharges and status epilepticus in the hippocampus. PROGRESS IN BRAIN RESEARCH 2002; 135:197-210. [PMID: 12143341 DOI: 10.1016/s0079-6123(02)35019-2] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Mechanisms of seizure-induced cell death were studied in organotypic hippocampal slice cultures. These develop after withdrawal of magnesium recurrent seizure-like events (SLE), which lead to intracellular and intramitochondrial calcium accumulation. The intramitochondrial Ca accumulation seems to be involved in causing increased production of NADH, measured as NAD(P)H autofluorescence. During SLEs, depolarization of mitochondria and increased production of free radicals is indicated by fluorescence measurements with appropriate dyes. During recurrent seizures, an increased failure to produce NADH is noted while at the same time free radical production seems to increase. This increase and the decline in NADH production could be involved in transition to late recurrent discharges, a phase in which status epilepticus becomes pharmacoresistant. It also coincides with increased cell death as determined with propidium iodide fluorescence. Interestingly, some of these changes can be prevented by application of alpha-tocopherol, a free radical scavenger, which also has neuroprotective effects under our experimental conditions. The results suggest that free radical-induced mitochondrial impairment is involved in seizure-induced cell death.
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Affiliation(s)
- U Heinemann
- Johannes Müller Institute of Physiology, Charité, Humboldt University Berlin, D-10117 Berlin, Germany.
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22
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Jauch R, Windmüller O, Lehmann TN, Heinemann U, Gabriel S. Effects of barium, furosemide, ouabaine and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) on ionophoretically-induced changes in extracellular potassium concentration in hippocampal slices from rats and from patients with epilepsy. Brain Res 2002; 925:18-27. [PMID: 11755897 DOI: 10.1016/s0006-8993(01)03254-1] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Glial cells limit local K(+)-accumulation by K(+)-uptake through different mechanisms, sensitive to Ba(2+), ouabaine, furosemide, or DIDS. Since the relative contribution of these mechanisms has not yet been determined, we studied the effects of bath-applied barium (2 mM), ouabaine (9 microM), furosemide (2 mM), and DIDS (1 mM) on ionophoretically-induced rises in [K(+)](o) in the pyramidal layer of area CA1 from normal rat slices, in the presence of glutamate receptor (Glu-R) antagonists. We also investigated the effect of barium on ionophoretically-induced tetrapropylammonium (TPA(+))-signals in order to test for barium-induced changes of the extracellular space. Finally, we repeated the barium experiment on slices from human non-sclerotic and sclerotic hippocampal specimens to assess a reduced glial capability for barium-sensitive K(+)-uptake in sclerotic tissue from epilepsy patients. In normal rat slices barium augmented ionophoretically-induced rises in [K(+)](o) by approximately 120%, also in the presence of tetrodotoxin (TTX) (by approximately 150%), but did not significantly affect the TPA(+)-signal. Ouabaine also augmented the K(+)-signal, but only by 27%. Furosemide and DIDS had negligible effects. In slices from sclerotic human hippocampus an augmentation of the K(+)-signal by barium was absent. Thus barium augments ionophoretically-induced K(+)-signals to a similar extent as previously shown for stimulus-induced signals. We suggest that glial barium-sensitive K(+)-buffer mechanisms reduce fast local rises of [K(+)](o) by at least 50%. This capability of glial cells is extremely reduced in area CA1 of slices from human sclerotic hippocampal specimens.
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Affiliation(s)
- Regina Jauch
- Johannes-Müller-Institut für Physiologie, Humboldt Universität, Berlin, Germany
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23
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Hertz L, Chen Y, Spatz M. Involvement of non-neuronal brain cells in AVP-mediated regulation of water space at the cellular, organ, and whole-body level. J Neurosci Res 2000; 62:480-90. [PMID: 11070491 DOI: 10.1002/1097-4547(20001115)62:4<480::aid-jnr2>3.0.co;2-k] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Vasopressin (AVP) influences non-neuronal brain cells in cell-type specific manners: (1) it regulates water balance at the cellular level of brain parenchyma by adjusting astrocytic water permeability; (2) it contributes to the control of extracellular K(+) concentration ([K(+)](e)) in brain by stimulation of K(+) transfer from blood to brain, due to activation of an inwardly directed Na(+),K(+),Cl(-) cotransporter at the luminal membrane of capillary endothelial cells and opening of K(+) channels at their abluminal membrane; (3) it decreases formation of cerebrospinal fluid (CSF) by decreasing Cl(-) secretion into CSF by epithelial cells of the choroid plexus, probably by inhibition of Cl(-)/HCO(-)(3) exchange at their basolateral membrane; (4) it contributes to regulation of intracellular volume within the brain by regulation of water permeability in ependymal cells and subpial astrocytes; and (5) it exerts effects on specialized astrocytes in circumventricular organs, their adjacent glia limitans, and the neural pituitary, which regulate AVP release to the systemic circulation by altering the spatial relationship between neurons and their adjacent glial cells. A unified mechanism is proposed, which integrates most of the effects of AVP and may be of considerable importance for neuronal excitability and, thus, for behavior.
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Affiliation(s)
- L Hertz
- Department of Pharmacology, University of Saskatchewan, Saskatoon, Canada.
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24
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Kivi A, Lehmann TN, Kovács R, Eilers A, Jauch R, Meencke HJ, von Deimling A, Heinemann U, Gabriel S. Effects of barium on stimulus-induced rises of [K+]o in human epileptic non-sclerotic and sclerotic hippocampal area CA1. Eur J Neurosci 2000; 12:2039-48. [PMID: 10886343 DOI: 10.1046/j.1460-9568.2000.00103.x] [Citation(s) in RCA: 101] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In the hippocampus of patients with therapy-refractory temporal lobe epilepsy, glial cells of area CA1 might be less able to take up potassium ions via barium-sensitive inwardly rectifying and voltage-independent potassium channels. Using ion-selective microelectrodes we investigated the effects of barium on rises in [K+]o induced by repetitive alvear stimulation in slices from surgically removed hippocampi with and without Ammon's horn sclerosis (AHS and non-AHS). In non-AHS tissue, barium augmented rises in [K+]o by 147% and prolonged the half time of recovery by 90%. The barium effect was reversible, concentration dependent, and persisted in the presence of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), N-methyl-D-aspartate (NMDA) and gamma-aminobutyric acid [GABA(A)] receptor antagonists. In AHS tissue, barium caused a decrease in the baseline level of [K+]o. In contrast to non-AHS slices, in AHS slices with intact synaptic transmission, barium had no effect on the stimulus-induced rises of [K+]o, and the half time of recovery from the rise was less prolonged (by 57%). Under conditions of blocked synaptic transmission, barium augmented stimulus-induced rises in [K+]o, but only by 40%. In both tissues, barium significantly reduced negative slow-field potentials following repetitive stimulation but did not alter the mean population spike amplitude. The findings suggest a significant contribution of glial barium-sensitive K+-channels to K+-buffering in non-AHS tissue and an impairment of glial barium-sensitive K+-uptake in AHS tissue.
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Affiliation(s)
- A Kivi
- Johannes Müller Institut für Physiologie, Universitätsklinikum Charité, Humboldt-Universität, zu Berlin, Germany
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25
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Kala G, Kumarathasan R, Peng L, Leenen FH, Hertz L. Stimulation of Na+,K+-ATPase activity, increase in potassium uptake, and enhanced production of ouabain-like compounds in ammonia-treated mouse astrocytes. Neurochem Int 2000; 36:203-11. [PMID: 10676854 DOI: 10.1016/s0197-0186(99)00117-5] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Active potassium (K+) uptake and Na+,K+-ATPase activity were measured in primary cultures of mouse astrocytes. Both parameters were virtually unaffected by acute ammonia treatment but increased after chronic exposure to pathophysiologically relevant concentrations of ammonia (0.3 or 3 mM) for 1-4 days. The increased Na+,K+-ATPase activity after chronic treatment with ammonia was further enhanced in the acute presence of 12 mM K+. Based on these observations and literature data it was hypothesized that the direct effect of ammonia is formation of easily diffusible compound(s) with ouabain-like effect, that upregulation occurs of Na+,K+-ATPase activity and K+ uptake in response to the resulting ATPase inhibition, and that the washing procedure preceding the uptake experiments and the determination of Na+,K+-ATPase activity unmasks the upregulation. To test this hypothesis, the content of compounds with ouabain-like action was measured in media in which astrocytes had been incubated in the presence of 3 mM ammonia for 4 days and in controls to which an additional 3 mM NaCl had been added instead of ammonia. An endogenous, compound with ouabain-like activity was demonstrated both under control conditions and in the ammonia-treated cultures, and the content of this compound was increased by 50% in the ammonia-treated cultures. Preliminary experiments showed that at least part of the released ouabain-like compounds cross-react with authentic ouabain.
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Affiliation(s)
- G Kala
- Department of Pharmacology, University of Saskatchewan, Saskatoon, Canada
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26
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Abstract
Studies using primary cultures of astrocytes have made essential contributions to the understanding of astrocytic functions and neuronal-astrocytic interactions. The purposes of this article are to (i) outline principles and methodologies used in the preparation of such cultures and caveats for the interpretation of the observations made; (ii) summarize astrocytic functions in turnover of the amino acid transmitters glutamate and gamma-aminobutyric acid (GABA), in energy metabolism and in Na+,K+-ATPase-catalyzed processes and emphasize the degree to which the observations have been confirmed in intact tissue; (iii) describe regulations of astrocytic functions by transmitters and by calcium channel activity; and (iv) indicate suggestions for future functional studies using astrocytes in primary cultures and emphasize that some of the conclusions about neuronal-astrocytic interactions reached on the basis of studies in cultured cells and confirmed in intact tissue may not yet have been completely integrated into general neuroscience knowledge.
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Affiliation(s)
- L Hertz
- Department of Pharmacology, University of Saskatchewan, Saskatoon, Canada
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27
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Antonelli MC, Costa Lieste M, Mercado R, Hernández-R J. Serotonin modulation of low-affinity ouabain binding in rat brain determined by quantitative autoradiography. Neurochem Res 1998; 23:939-44. [PMID: 9690735 DOI: 10.1023/a:1021024203573] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Previous results showed that Na+/K+-ATPase may have a functional relationship with the neurotransmitter serotonin which activates the glial sodium pump in the rat brain. Both the reaction rate (V) of Na+/K+-ATPase activity and [3H]ouabain binding were significantly increased in the presence of serotonin. It is not known, however, which alpha isoform is involved in the Na+/K+-ATPase response to serotonin and its regional distribution. Quantitative autoradiography of [3H]ouabain binding to rat brain slices was employed at different [3H]ouabain concentrations in order to gain information on both the distribution and the possible isoform involved. The results showed that 1500 nM [3H]ouabain binding was sensitive to serotonin 10(-3) M and significantly increased in the following brain regions: frontal cortex, areas CA1, CA2, and CA3 of the hippocampus, presubiculum, zona incerta, caudate putamen and the amygdaloid area, confirming and extending previous results. An effect of serotonin on brain but not kidney tissue at high, 1500 nM, and the lack of effect at low, 50 nM [3H]ouabain concentrations, strongly suggests the participation of the alpha2 isoform in the response of the pump to the neurotransmitter. Glial cells showed stimulation of ouabain binding by serotonin at ouabain concentrations above 350 nM. The present results open interesting questions related to the brain regions involved and the K+ handling by the glial alpha2 isoform of the pump.
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Affiliation(s)
- M C Antonelli
- Instituto de Química y Fisicoquímica Biológicas (UBA-CONICET), Universidad de Buenos Aires, Argentina
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28
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29
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Abstract
1. We studied regulation of intracellular Na+ concentration ([Na+]i) in cultured rat hippocampal neurones using fluorescence ratio imaging of the Na+ indicator dye SBFI (sodium-binding benzofuran isophthalate). 2. In standard CO2/HCO3(-)-buffered saline with 3 mM K+, neurones had a baseline [Na+]i of 8.9 +/- 3.8 mM (mean +/- S.D.). Spontaneous, transient [Na+]i increases of 5 mM were observed in neurones on 27% of the coverslips studied. These [Na+]i increases were often synchronized among nearby neurones and were blocked reversibly by 1 microM tetrodotoxin (TTX) or by saline containing 10 mM Mg2+, suggesting that they were caused by periodic bursting activity of synaptically coupled cells. Opening of voltage-gated Na+ channels by application of 50 microM veratridine caused a TTX-sensitive [Na+]i increase of 25 mM. 3. Removing extracellular Na+ caused an exponential decline in [Na+]i to values close to zero within 10 min. Inhibition of Na+,K(+)-ATPase by removal of extracellular K+ or ouabain application evoked a [Na+]i increase of 5 mM min-1. Baseline [Na+]i was similar in the presence or absence of CO2/HCO3-; switching from CO2/HCO3(-)-free to CO2/HCO3(-)-buffered saline, however, increased [Na+]i transiently by 3 mM, indicating activation of Na(+)-dependent Cl(-)-HCO3- exchange. Inhibition of Na(+)-K(+)-2Cl- cotransport by bumetanide had no effect on [Na+]i. 4. Brief, small changes in extracellular K+ concentration ([K+]o) influenced neuronal [Na+]i only weakly. Virtually no change in [Na+]i was observed with elevation or reduction of [K+]o by 1 mM. Only 30% of cells reacted to 3 min [K+]o elevations of up to 5 mM. In contrast, long [K+]o alterations (> or = 10 min) to 6 mM or greater slowly changed steady-state [Na+]i in the majority of cells. 5. Our results indicate several differences between [Na+]i regulation in cultured hippocampal neurones and astrocytes. Baseline [Na+]i is lower in neurones compared with astrocytes and is mainly determined by Na+,K(+)-ATPase, whereas Na(+)-dependent Cl(-)-HCO3- exchange, Na(+)-HCO3- cotransport or Na(+)-K(+)-2Cl- cotransport do not play a significant role. In contrast to glial cells, [Na+]i of neurones changes only weakly with small alterations in bath [K+]o, suggesting that activity-induced [K+]o changes in the brain might not significantly influence neuronal Na+,K(+)-ATPase activity.
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Affiliation(s)
- C R Rose
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06520, USA.
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30
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Abstract
Glial cell Na,K-ATPase is suggested to participate in extracellular K+ concentration ([K+]o) control by being activated when [K+]o rises in the brain. The extent of that activation directly depends on the Na/K pump affinity to [K+]o, intracellular Na+ ([Na+]i) and, indirectly on pump cycle regulation by membrane potential (Vm). In the present investigation, these Na/K pump properties were studied with the whole-cell patch-clamp technique in cultured mouse oligodendrocytes (N20.1 cell line). N20.1 cells possess ouabain-sensitive Na/K pump current (Ip) with a maximal density of 0.5-0.6 pA/pF (estimated for conditions of Na/K pump stimulation by saturating [Na+]i, [ATP]i, [K+]o and at positive Vm). This current was half-inhibited at 83 +/- 31 microM ouabain, and half-activated by [Na+]i of 9.6 +/- 1.1 mM, by [K+]o of 2.0 +/- 0.1 mM and by membrane potential at about -65 mV. High levels of nervous activity may increase [K+]o from 3 to 12 mM which would only increase Na/K pump current by 40% due to the direct effect of [K+]o. However, elevated [K+]o would also depolarize the glial cell membrane which would indirectly activate Ip and together with the direct effect of [K+]o would increase Ip as much as 2-2.5-fold. These data suggest that glial cell Na/K pump regulation by Vm may be an important factor in determining the participation of the Na/K pump in [K+]o homeostasis in the nervous system.
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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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31
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Abstract
1. We determined the intracellular Na+ concentration ([Na+]i) and mechanisms of its regulation in cultured rat hippocampal astrocytes using fluorescence ratio imaging of the Na+ indicator SBFI-AM (acetoxymethylester of sodium-binding benzofuran isophthalate, 10 microM). Dye signal calibration within the astrocytes showed that the ratiometric dye signal changed monotonically with changes in [Na+]i from 0 to 140 nM. The K+ sensitivity of the dye was negligible; intracellular pH changes, however, slightly affected the 'Na+' signal. 2. Baseline [Na+]i was 14.6 +/- 4.9 mM (mean +/- S.D.) in CO2/HCO3(-)-containing saline with 3 mM K+. Removal of extracellular Na+ decreased [Na+]i in two phases: a rapid phase of [Na+]i reduction (0.58 +/- 0.32 mM min-1) followed by a slower phase (0.15 +/- 0.09 mM min-1). 3. Changing from CO2/HCO3(-)-free to CO2/HCO3(-)-buffered saline resulted in a transient increase in [Na+]i of approximately 5 mM, suggesting activation of inward Na(+)-HCO3- cotransport by CO2/HCO3-. During furosemide (frusemide, 1 mM) or bumetanide (50 microM) application, a slow decrease in [Na+]i of approximately 2 mM was observed, indicating a steady inward transport of Na+ via Na(+)-K(+)-2Cl- cotransport under control conditions. Tetrodotoxin (100 microM) did not influence [Na+]i in the majority of cells (85%), suggesting that influx of Na+ through voltage-gated Na+ channels contributed to baseline [Na+]i in only a small subpopulation of hippocampal astrocytes. 4. Blocking Na+, K(+)-ATPase activity with cardiac glycosides (ouabain or strophanthidin, 1 mM) or removal of extracellular K+ led to an increase in [Na+]i of about 2 and 4 mM min-1, respectively. This indicated that Na+, K(+)-ATPase activity was critical in maintaining low [Na+]i in the face of a steep electrochemical gradient, which would favour a much higher [Na+]i. 5. Elevation of extracellular K+ concentration ([K+]o) by as little as 1 mM (from 3 to 4 mM) resulted in a rapid and reversible decrease in [Na+]i. Both the slope and the amplitude of the [K+]o-induced reductions in [Na+]i were sensitive to bumetanide. A reduction of [K+]o by 1 mM increased [Na+]i by 3.0 +/- 2.3 mM. In contrast, changing extracellular Na+ concentration by 20 mM resulted in changes in [Na+]i of less than 3 mM. 6. These results implied that in hippocampal astrocytes low baseline [Na+]i is determined by the action of Na(+)-HCO3- cotransport, Na(+)-K(+)-2Cl- cotransport and Na+, K(+)-ATPase, and that both Na+, K(+)-ATPase and inward Na(+)-K(+)-2Cl cotransport are activated by small, physiologically relevant increases in [K+]o. These mechanisms are well suited to help buffer increases in [K+]o associated with neural activity.
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Affiliation(s)
- C R Rose
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06520, USA
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32
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Hajek I, Subbarao KV, Hertz L. Acute and chronic effects of potassium and noradrenaline on Na+, K+-ATPase activity in cultured mouse neurons and astrocytes. Neurochem Int 1996; 28:335-42. [PMID: 8813252 DOI: 10.1016/0197-0186(95)00081-x] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Acute and chronic effects of elevated extracellular concentrations of potassium ions ([K+]0) and/or noradrenaline were studied in homogenates of primary cultures of mouse astrocytes, from the cerebral cortex or the spinal cord, and of primary cultures of mouse cerebral cortical neurons. NA+, K+-ATPase activity in cerebral cortical astrocytes showed a Km value of 1.9 mM with confidence limits of 1.3-2.9 mM and a Vmax of 5.4 mumol/h/mg protein with confidence limits of 3.3-8.1 mumol/h/mg protein. Due to the high Km value, the activity of the enzyme was significantly increased by an increase in [K+]0 in the interval 5-12 mM. In cerebral cortical neurons, Vmax was lower (1.77 +/- 0.06 mumol/h/mg protein) but the affinity was higher (Km 0.43 +/- 0.8 mM). With these kinetics, there is no stimulation of enzyme activity when [K+]0 is increased beyond control levels. In spinal cord astrocytes, the relative effect of increasing [K+]0 above 6 mM was larger than in cerebral astrocytes but the absolute activity of the enzyme was lower. Na+, K+-ATPase activity in both types of astrocyte was stimulated by noradrenaline and its beta-adrenergic subtype agonist isoproterenol but mainly or exclusively at 6 mM [K+]0. Noradrenaline also caused a stimulation in cortical neurons, but at non-physiological K+ concentrations this stimulation was converted to an inhibition, and isoproterenol had no stimulatory effect. Chronic exposure of cerebral cortical astrocytes to elevated [K+]0 caused a decrease in Na+, K+-ATPase activity when enzyme activity in the cells was subsequently measured at normal [K+]0. During exposure to 30 mM [K+]0 this "down-regulation" took place within 10 min. Conversely, chronic exposure to reduced [K+]0 led to an increase in Na+, K+-ATPase activity. Chronic exposure to noradrenaline had no significant effect but there was a tendency towards an increase.
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Affiliation(s)
- I Hajek
- Laboratory of Cellular Neurophysiology, Czech Academy of Sciences, Prague, The Czech Republic
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33
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Hertz L, Gibbs ME, O'Dowd BS, Sedman GL, Robinson SR, Syková E, Hajek I, Hertz E, Peng L, Huang R, Ng KT. Astrocyte-neuron interaction during one-trial aversive learning in the neonate chick. Neurosci Biobehav Rev 1996; 20:537-51. [PMID: 8880738 DOI: 10.1016/0149-7634(95)00020-8] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
During two specific stages of the Gibbs-Ng model of one-trial aversive learning in the neonate chick, we have recently found unequivocal evidence for a crucial involvement of astrocytes. This evidence is metabolic (utilization of the astrocyte-specific energy store, glycogen, during normal learning and inhibition of memory formation by the astrocyte specific metabolic inhibitors, fluoroacetate and methionine sulfoximine) as well as physiological (abolition of memory formation in the presence of ethacrynic acid, an astrocyte-specific inhibitor of cellular reaccumulation of potassium ions). These findings are discussed in the present review in the framework of a more comprehensive description of metabolic and physiological neuronal-astrocytic interactions across an interstitial (extracellular) space bounded by minute processes from either cell type.
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Affiliation(s)
- L Hertz
- Department of Pharmacology, University of Saskatchewan, Saskatoon, Canada
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34
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Ratnakumari L, Audet R, Qureshi IA, Butterworth RF. Na+,K(+)-ATPase activities are increased in brain in both congenital and acquired hyperammonemic syndromes. Neurosci Lett 1995; 197:89-92. [PMID: 8552287 DOI: 10.1016/0304-3940(95)11906-d] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Activities of Na+,K(+)-ATPase were measured in brain regions of experimental animals with either congenital or acquired hyperammonemia. In the sparse-fur (spf) mutant mouse, with a genetic X-linked deficiency of ornithine transcarbamylase, an animal model of congenital hyperammonemia, Na+,K(+)-ATPase was increased in frontal cortex (by 57%, P < 0.001), cerebellum (by 61%, P < 0.001), brainstem (by 71%, P < 0.001) and striatum (by 48%, P < 0.01). Four weeks following portacaval anastomosis in the rat, Na+,K(+)-ATPase activities were increased in cerebellum and striatum (by 19%, P < 0.01) and in brainstem (by 28%, P < 0.01). Stimulation of Na+,K(+)-ATPase and the subsequent alteration of neuronal excitability could contribute to the CNS dysfunction characteristic of chronic hyperammonemic syndromes.
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Affiliation(s)
- L Ratnakumari
- Neuroscience Research Unit, Hospital Saint-Luc (University of Montreal, Quebec, Canada
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35
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Munzer J, Daly S, Jewell-Motz E, Lingrel J, Blostein R. Tissue- and isoform-specific kinetic behavior of the Na,K-ATPase. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(19)89442-5] [Citation(s) in RCA: 137] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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36
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Levenson R. Isoforms of the Na,K-ATPase: family members in search of function. Rev Physiol Biochem Pharmacol 1994; 123:1-45. [PMID: 8209135 DOI: 10.1007/bfb0030902] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- R Levenson
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510
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37
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Lopes da Silva FH, Kamphuis W, Wadman WJ. Epileptogenesis as a plastic phenomenon of the brain, a short review. ACTA NEUROLOGICA SCANDINAVICA. SUPPLEMENTUM 1992; 140:34-40. [PMID: 1332360 DOI: 10.1111/j.1600-0404.1992.tb04468.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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38
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Hertz L. Autonomic control of neuronal-astrocytic interactions, regulating metabolic activities, and ion fluxes in the CNS. Brain Res Bull 1992; 29:303-13. [PMID: 1393603 DOI: 10.1016/0361-9230(92)90061-2] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
It is generally assumed that the brain, in contrast to all other organs, is not equipped with an autonomic nervous system, regulating blood supply, and cellular activities. This may be because systemic administration of most drugs acting on monoaminergic or cholinergic receptors have little or no effect on cerebral blood flow and metabolism. However, intrathecal administration of noradrenaline does, indeed, influence both blood flow and energy metabolism in the brain. The present review focuses on effects of noradrenaline or serotonin on energy metabolism, turnover of amino acid transmitters and ion homeostasis, with special emphasis on the cellular localization. Noradrenergic agonists stimulate brain metabolism in vivo as well as many aspects of energy metabolism, Na+,K(+)-ATPase activity and uptake of transmitter amino acids in astrocytes in primary cultures, with little or no effect on corresponding preparations of neurons. Serotonin acts differently, decreasing potassium-induced release of glutamate from both neurons and astrocytes. Little is known about the effects of acetylcholine. The functional significance of these effects is discussed.
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Affiliation(s)
- L Hertz
- Department of Pharmacology, University of Saskatchewan, Saskatoon, Canada
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39
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Grisar T, Guillaume D, Delgado-Escueta AV. Contribution of Na+,K(+)-ATPase to focal epilepsy: a brief review. Epilepsy Res 1992; 12:141-9. [PMID: 1327744 DOI: 10.1016/0920-1211(92)90034-q] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The authors review some of their experimental data on the contribution of Na(+)- and K(+)-dependent adenosine triphosphatase (Na+,K(+)-ATPase) to focal epilepsy. It has been previously demonstrated that high extracellular K+ concentration increases glial Na+,K(+)-ATPase specific activities in normal conditions while this was not observed in neuronal preparations. At this time, it was hypothesized that this molecular mechanism could play a role in removing K+ released in the extracellular space during neuronal firing. These results have therefore been investigated in acute and chronic epileptogenic lesions of cats with freeze lesion. It was demonstrated that within the primary (F) and the secondary or 'mirror' (M) focus the K+ activation of the glial Na+,K(+)-ATPase dramatically decreased compared to both control animals (C) and the perifocal (PF) non epileptogenic area. Similar results were observed in man when using specimens of anterolateral temporal neocortex obtained during temporal lobectomies in patients with intractable temporal lobe epilepsy, compared with postmortem human specimens or control brain tissues. The modifications of the level of phosphorylation of partially purified Na+,K(+)-ATPase was also investigated in the epileptic cortex in these two experimental conditions. The catalytic subunits were resolved by sodium dodecylsulfate (SDS) gel electrophoresis and their phosphorylation levels were measured in the presence of various concentrations of K+ ions which dephosphorylate the catalytic subunit. K(+)-induced dephosphorylation was decreased in primary and secondary foci of acutely lesioned cats. Those alterations, due to a decreased affinity for K+, were limited to the alpha (-) subunit. In cats with chronic lesions, the dephosphorylating step of the Na+,K+-ATPase catalytic subunit recovered to normal affinity for K+.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- T Grisar
- Laboratory of Comparative and General Biochemistry, University of Liege, Belgium
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40
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Mercado R, Hernández J. Regulatory role of a neurotransmitter (5-HT) on glial Na+/K(+)-ATPase in the rat brain. Neurochem Int 1992; 21:119-27. [PMID: 1303137 DOI: 10.1016/0197-0186(92)90074-2] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
In the present work we studied the effect of serotonin (5-HT) on the kinetics of Na+/K(+)-ATPase in subcellular preparations of the cerebral cortex from male Wistar rats using various concentrations of ATP and K+ with and without added 5-HT. Also we studied the effect of 5-HT on the enzyme in glial or neuronal preparations. The results indicated that there was a significant increase (P < 0.05) of the Vmax in the presence of 5-HT in the whole tissue preparation (homogenate) but not in the subcellular fractions, suggesting that the interaction could be preferentially with the glial pump. Further results supported that this was the case since activation by 5-HT was mainly in the glial preparations. Kinetic data and the binding of [3H]ouabain supported that the enzyme is activated by 5-HT through the exposure of more enzymatic active sites.
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Affiliation(s)
- R Mercado
- Department of Physiology, Biophysics and Neurosciences, Centro de Investigación y de Estudios, Avanzados del I.P.N., México, D.F
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41
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Mahadik SP, Bharucha VA, Stadlin A, Ortiz A, Karpiak SE. Loss and recovery of activities of alpha+ and alpha isozymes of (Na(+) + K+)-ATPase in cortical focal ischemia: GM1 ganglioside protects plasma membrane structure and function. J Neurosci Res 1992; 32:209-20. [PMID: 1328661 DOI: 10.1002/jnr.490320210] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Alterations in cellular membrane structure and the subsequent failure of its function after CNS ischemia were monitored by analyzing changes in the plasma membrane marker enzyme (Na(+) + K(+)-ATPase. The levels of two isozymes of (Na(+) + K(+)-ATPase, alpha+ and alpha, which have distinct cellular and anatomical distributions, were studied to determine if differential cellular damage occurs in primary and peri-ischemic injury areas. The efficacy of monosialoganglioside (GM1) treatment was assessed, since this glycosphingolipid has been shown to reduce ischemic injury by protecting cell membrane structure/function. Using a rat model of cortical focal ischemia, levels of both ATPase isozyme activities were assayed in total membrane fractions from primary ischemic tissue (parietal cortex) and three peri-ischemic tissue areas (frontal, occipital, and temporal cortex) at 1, 3, 5, 7, and 14 days after ischemia. No significant loss of either isozyme's activity occurred in any tissue area at 1 day after ischemia. At 5 days, in the primary ischemic area, both isozyme activity levels decreased by 70-75%. The alpha+ enzyme activity loss persisted up to 14 days, while a 17% recovery in alpha activity occurred. In the three peri-ischemic tissue areas, enzyme activity losses ranged from 42%-59% at 3 days after ischemia. A complete restoration of both isozyme activities was seen at 14 days. After three days of GM1 ganglioside treatment there was no loss of total (Na*+) + K(+)-ATPase activity in the three peri-ischemic areas, and a significantly reduced loss in the primary infarct tissue. An autoradiographic analysis of brain coronal sections using 3H-ouabain supports the enzymatic data and GM1 effects. Reductions in 3H-ouabain binding in all cortical layers at 3 days after ischemia were visualized. GM1 treatment significantly reduced these 3H-ouabain binding losses. In summary, time-dependent quantitative changes in activity levels of ATPase isozymes (alpha+ and alpha) reflect the different degree of membrane damage that occurs in primary vs. peri-ischemic tissues (e.g., irreversible vs. reversible membrane damage), and that ischemia affects cell membranes of all neural elements in a largely similar fashion. GM1 ganglioside was found to reduce plasma membrane damage in all CNS cell types.
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Affiliation(s)
- S P Mahadik
- Division of Neuroscience, New York State Psychiatric Institute, New York
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42
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Laschet J, Grisar T, Bureau M, Guillaume D. Characteristics of putrescine uptake and subsequent GABA formation in primary cultured astrocytes from normal C57BL/6J and epileptic DBA/2J mouse brain cortices. Neuroscience 1992; 48:151-7. [PMID: 1584419 DOI: 10.1016/0306-4522(92)90345-3] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Brain maturation and GABA metabolism are known to play a key role in epileptogenesis. The metabolism of the polyamines (putrescine, spermidine and spermine) is closely linked to the process of brain maturation. Putrescine has been shown to be catabolized to GABA in brain tissue and astrocytes. In order to better understand the importance of glial putrescine transport and metabolism, a model of age-dependent epilepsy was used to study the kinetic properties of [14C]putrescine uptake into cultured astrocytes from normal C57/BL and audiogenic DBA/2 newborn mice, and the subsequent GABA formation. (1) Putrescine uptake exhibited non-Michaelian allosteric kinetics with positive co-operativity (Hill factor = 2), suggesting a physiological importance of putrescine uptake by astrocytes. (2) The Vmax of putrescine uptake was significantly higher in C57/BL astrocytes than in DBA/2J, but the uptake affinity for putrescine was higher in DBA/2J than in C57/BL. (3) Higher K+ concentrations (18 mM) had little effect on putrescine uptake in either strain. (4) Ten-micromolar N-acetylputrescine, the first putrescine metabolite, stimulated putrescine uptake into astrocytes of both strains, but to a different degree: +46% in C57/BL and + 102% in DBA/2J. (5) The specific radioactivity of the GABA formed from labelled putrescine was four times higher in astrocytes from DBA/2J than from C57/BL mice. (6) The molar ratio of glutamate/GABA in the cerebral cortex of the DBA/2J mice was significantly higher during the period of audiogenic seizure susceptibility than in age-matched C57/BL mice. Our results show characteristics of putrescine uptake into astrocytes; we demonstrated distinct kinetic properties between normal and epileptic strains of mice.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- J Laschet
- Department of Neurochemistry, University of Liège, Belgium
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43
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Renkawek K, Renier WO, de Pont JJ, Vogels OJ, Gabreëls FJ. Neonatal status convulsivus, spongiform encephalopathy, and low activity of Na+/K(+)-ATPase in the brain. Epilepsia 1992; 33:58-64. [PMID: 1310285 DOI: 10.1111/j.1528-1157.1992.tb02283.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The first and second child of a family died from neonatal seizures with no detectable brain malformation, metabolic, infectious, or chromosomal etiology. Neuropathological examination of the brain of the second child who died at 11 days revealed a widespread spongy state and a selective vulnerability of the astrocytes characterized by numerous enlarged bare astrocytic nuclei and different forms of astrocyte degeneration. The glial cells were strongly positive for glial fibrillary acidic protein and vimentin immunocytochemical reaction. Cortical measurement of Na+/K(+)-ATPase revealed very low enzyme activity. We hypothesize that a defect of Na+/K(+)-ATPase of the astrocytes could be the common pathogenetic factor for the congenital status convulsivus and for the spongy state.
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Affiliation(s)
- K Renkawek
- Department of Child Neurology, University of Nijmegen, The Netherlands
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44
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Hertz L, Peng L. Effects of monoamine transmitters on neurons and astrocytes: correlation between energy metabolism and intracellular messengers. PROGRESS IN BRAIN RESEARCH 1992; 94:283-301. [PMID: 1283791 DOI: 10.1016/s0079-6123(08)61758-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- L Hertz
- Department of Pharmacology, University of Saskatchewan, Saskatoon, Canada
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45
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Watts AG, Sanchez-Watts G, Emanuel JR, Levenson R. Cell-specific expression of mRNAs encoding Na+,K(+)-ATPase alpha- and beta-subunit isoforms within the rat central nervous system. Proc Natl Acad Sci U S A 1991; 88:7425-9. [PMID: 1651505 PMCID: PMC52308 DOI: 10.1073/pnas.88.16.7425] [Citation(s) in RCA: 141] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
We have used in situ hybridization histochemistry to analyze the subcellular distribution of mRNAs encoding Na,K-ATPase alpha- and beta-subunit isoforms in the rat central nervous system. Substantial differences in the cell-specific pattern of expression were found for the genes encoding three isoforms of the alpha subunit. Transcripts of alpha 1-subunit gene were detected in virtually all cell types and structures examined. Expression of alpha 2-subunit mRNA was characteristic of glia, whereas alpha 3-subunit transcripts were predominant in neurons. Transcripts encoding the beta 1 subunit were detected in neurons, whereas beta 2-subunit mRNA expression was characteristic of glia. mRNA encoding both beta-subunit isoforms was present in choroidal epithelial cells. The distribution pattern of alpha- and beta-subunit mRNAs in structures throughout the central nervous system is consistent with the possibility of six structurally distinct Na+,K(+)-ATPase isoenzymes.
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Affiliation(s)
- A G Watts
- Neural Systems Laboratory, Salk Institute, La Jolla, CA 92037
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46
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Guillaume D, Grisar T, Delgado-Escueta AV, Laschet J, Bureau-Heeren M. Phosphorylation of brain (Na+,K+)-ATPase alpha catalytic subunits in normal and epileptic cerebral cortex: II. Partial seizures in human epilepsy. J Neurosci Res 1991; 29:218-24. [PMID: 1653859 DOI: 10.1002/jnr.490290212] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We examined the activity and phosphorylation level of (Na+,K+)-ATPase (E.C. 3.6.1.3) partially purified from normal and epileptic human cortices. Control patients (n = 11) were operated on for a non-epileptogenic deep brain lesion, while epileptic patients (n = 10) were operated on for temporal or frontal originating partial seizures, resistant to medications or secondary to evolutive brain tumors. No differences in the specific activity of microsomal (Na+,K+)-ATPase were observed between the two groups of patients. After partial purification of the enzyme followed by SDS-polyacrylamide gel electrophoresis, (Na+,K+)-ATPase catalytic subunit had a decreased affinity for K+ in human epileptic cortex and lost its sensitivity to phenytoin dephosphorylation. Indirect evidence suggests that those abnormalities of (Na+,K+)-ATPase in human epileptic cortex hold preferentially true for the alpha(-) enzymatic subunit. Those results indicate that, in human epileptic cortex, (Na+,K+)-ATPase and most probably its glial subtype is altered in its K+ regulation and phenytoin sensitivity and could be responsible for ictal transformation and seizure spread.
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Affiliation(s)
- D Guillaume
- Molecular Neuroscience Laboratories, Reed Neurological Research Center, University of California, Los Angeles
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47
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Schielke GP, Moises HC, Betz AL. Potassium activation of the Na,K-pump in isolated brain microvessels and synaptosomes. Brain Res 1990; 524:291-6. [PMID: 1963338 DOI: 10.1016/0006-8993(90)90703-e] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Brain capillary endothelial cells play an important role in ion homeostasis of the brain through the transendothelial transport of Na and K. Since little is known about the regulation of ion transport in these cells, we determined the effect of extracellular potassium concentration ([K]o) on the kinetics of the Na,K-pump in isolated cerebral microvessels using both K uptake and Na efflux as measures of pump activity. In addition, we studied K activation of K uptake into synaptosomes under similar conditions to compare this neuronal system to the capillary. When microvessels were preloaded with 22Na by 30 min incubation in K-free buffer, efflux of 22Na into buffer with varying [K]o was dependent on [K]o and inhibited by 7 mM ouabain. This activation of Na efflux was half maximal at 4.2 mM [K]. Ouabain-sensitive K uptake was also half maximally stimulated by a similar [K] in both Na loaded and non-loaded microvessels. In contrast, K uptake into synaptosomes was half maximal at 0.47 mM K. These results demonstrate that both active Na efflux and K uptake into microvessels in vitro are dependent on [K]o in the physiological range. In contrast, synaptosomal K uptake is near maximal at 3 mM K. This suggests that increases in brain [K]o may stimulate ion transport across the cerebral capillary, but will have little effect on Na,K-pump activity in neurons.
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Affiliation(s)
- G P Schielke
- Department of Surgery (Neurosurgery), University of Michigan, Ann Arbor 48109-0532
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48
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Laschet J, Guillaume D, Vergniolle-Burette M, Grisar T. Milacemide stimulates deficient glial Na+, K(+)-ATPase in freezing-induced epileptogenic cortex of cats. Brain Res 1990; 517:168-74. [PMID: 2165431 DOI: 10.1016/0006-8993(90)91022-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
We investigated the influence of milacemide, a glycinamide derivative with putative antiepileptic activity, on the K(+)-activation of Na+,K(+)-ATPase in bulk isolated glial cells and synaptosomes of control and epileptogenic cortex of cats with a chronic freeze lesion. In the primary and secondary epileptic foci of non-treated animals, glial Na+,K(+)-ATPase lost its physiological K(+)-activation, while the synaptosomal enzyme was unchanged. These data reproduced previous work done on the kinetic measurement of the enzymic activities. In treated animals (500 mg/kg milacemide given orally for 2 weeks after the freeze lesion), the glial enzyme showed a normal K(+)-activation in the epileptic foci. These results confirm the existence of an abnormal glial Na+,K(+)-ATPase in cold-induced focal epilepsy and suggest that the antiepileptic activity of milacemide might be secondary to an activation of glial Na+,K(+)-ATPase, contributing to antagonize ictal transformation and seizure spread.
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Affiliation(s)
- J Laschet
- Laboratory of Biochemistry, C.H.U., University of Liège, Belgium
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49
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Erecińska M, Dagani F. Relationships between the neuronal sodium/potassium pump and energy metabolism. Effects of K+, Na+, and adenosine triphosphate in isolated brain synaptosomes. J Gen Physiol 1990; 95:591-616. [PMID: 2159972 PMCID: PMC2216333 DOI: 10.1085/jgp.95.4.591] [Citation(s) in RCA: 123] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The relationships between Na/K pump activity and adenosine triphosphate (ATP) production were determined in isolated rat brain synaptosomes. The activity of the enzyme was modulated by altering [K+]e, [Na+]i, and [ATP]i while synaptosomal oxygen uptake and lactate production were measured simultaneously. KCl increased respiration and glycolysis with an apparent Km of about 1 mM which suggests that, at the [K+]e normally present in brain, 3.3-4 mM, the pump is near saturation with this cation. Depolarization with 6-40 mM KCl had negligible effect on ouabain-sensitive O2 uptake indicating that at the voltages involved the activity of the Na/K ATPase is largely independent of membrane potential. Increases in [Na+]i by addition of veratridine markedly enhanced glycoside-inhibitable respiration and lactate production. Calculations of the rates of ATP synthesis necessary to support the operation of the pump showed that greater than 90% of the energy was derived from oxidative phosphorylation. Consistent with this: (a) the ouabain-sensitive Rb/O2 ratio was close to 12 (i.e., Rb/ATP ratio of 2); (b) inhibition of mitochondrial ATP synthesis by Amytal resulted in a decrease in the glycoside-dependent rate of 86Rb uptake. Analyses of the mechanisms responsible for activation of the energy-producing pathways during enhanced Na and K movements indicate that glycolysis is predominantly stimulated by increase in activity of phosphofructokinase mediated via a rise in the concentrations of adenosine monophosphate [AMP] and inorganic phosphate [Pi] and a fall in the concentration of phosphocreatine [PCr]; the main moving force for the elevation in mitochondrial ATP generation is the decline in [ATP]/[ADP] [Pi] (or equivalent) and consequent readjustments in the ratio of the intramitochondrial pyridine nucleotides [( NAD]m/[NADH]m). Direct stimulation of pyruvate dehydrogenase by calcium appears to be of secondary importance. It is concluded that synaptosomal Na/K pump is fueled primarily by oxidative phosphorylation and that a fall in [ATP]/[ADP][Pi] is the chief factor responsible for increased energy production.
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Affiliation(s)
- M Erecińska
- Department of Pharmacology, University of Pennsylvania, Philadelphia 19104
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Deitmer JW, Szatkowski M. Membrane potential dependence of intracellular pH regulation by identified glial cells in the leech central nervous system. J Physiol 1990; 421:617-31. [PMID: 2112195 PMCID: PMC1190105 DOI: 10.1113/jphysiol.1990.sp017965] [Citation(s) in RCA: 79] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
1. We have measured the intracellular pH (pHi) and membrane potential of identified glial cells in the central nervous system of the leech, Hirudo medicinalis, using double-barrelled pH-sensitive microelectrodes. 2. When extracellular K+ concentration was increased, the glial membrane potential decreased and pHi increased; lowering the extracellular K+ concentration hyperpolarized the glial membrane and decreased pHi. These pHi changes were largely dependent upon the presence of CO2-HCO3-; in nominally CO2-HCO3(-)-free saline solution, they were 50-80% smaller. 3. The steady-state pHi of the glial cells in CO2-HCO3(-)-buffered saline solution strongly correlated with the membrane potential between -40 and -90 mV. The slope of this relationship was 60 mV/pH unit. 4. The neurotransmitter 5-hydroxytryptamine (50 microM), which hyperpolarizes the glial membrane, also produced a large, CO2-HCO3(-)-dependent decrease in pHi. The size of the pHi change depended upon the amplitude of the membrane hyperpolarization. 5. The increase in pHi produced by the membrane depolarization in 20 mM-K+ was abolished in Na(+)-free saline. Removal of external Na+ in the presence of 20 mM-K+ reversed the pHi increase. 6. The pHi increase in 20 mM-K+ was also inhibited by the stilbene 4,4-diisothiocyanostilbene-2'-disulphonic acid (DIDS, 0.5 mM). In a DIDS-poisoned preparation a small decrease of pHi was observed in 20 mM-K+ both in the presence and nominal absence of CO2-HCO3-. 7. In neurones, neither CO2-HCO3- nor 20 mM-K+ produced an intracellular alkanization. The steady-state pHi of several identified neurones was not correlated with the membrane potential. 8. We conclude that in glial cells, but not in neurones, the pHi is dependent upon the membrane potential. This membrane potential dependence is due to the activity of the electrogenic Na(+)-HCO3- co-transporter in the glial cell membrane.
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Affiliation(s)
- J W Deitmer
- Institut für Zoologie/Neurobiologie, Heinrich-Heine Universität, Düsseldorf, FRG
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