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Maiorov SA, Kairat BK, Berezhnov AV, Zinchenko VP, Gaidin SG, Kosenkov AM. Peculiarities of ion homeostasis in neurons containing calcium-permeable AMPA receptors. Arch Biochem Biophys 2024; 754:109951. [PMID: 38452968 DOI: 10.1016/j.abb.2024.109951] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2023] [Revised: 02/16/2024] [Accepted: 02/28/2024] [Indexed: 03/09/2024]
Abstract
Glutamate excitotoxicity accompanies numerous brain pathologies, including traumatic brain injury, ischemic stroke, and epilepsy. Disturbances of the ion homeostasis, mitochondria dysfunction, and further cell death are considered the main detrimental consequences of excitotoxicity. It is well known that neurons demonstrate different vulnerability to pathological exposures. In this regard, neurons containing calcium-permeable AMPA receptors (CP-AMPARs) may show higher susceptibility to excitotoxicity due to an additional pathway of Ca2+ influx. Here, we demonstrate that neurons containing CP-AMPARs are characterized by the higher amplitude of the glutamate-induced elevation of intracellular Ca2+ concentration ([Ca2+]i) and slower restoration of [Ca2+]i level compared to non-CP-AMPA neurons. Moreover, we have found that NASPM, an antagonist of CP-AMPARs, significantly decreases the amplitude of the [Ca2+]i elevation induced by glutamate or selective AMPARs agonist, 5-fluorowillardiine. In contrast, the antagonists of NMDARs or KARs affect insignificantly. We have also described some peculiarities of Na+, K+, and H+ intracellular dynamics in neurons containing CP-AMPARs. In particular, the amplitude of [Na+]i elevation was lower compared to non-CP-AMPA neurons, whereas the amplitude of [K+]i decrease was higher. We have shown the significant inverse correlation between [K+]i and [Ca2+]i and between intracellular pH and [Na+]i in CP-AMPARs-containing and non-CP-AMPA neurons upon glutamate excitotoxicity. Our data indicate that CP-AMPARs-mediated Ca2+ influx and slow removal of Ca2+ from the cytosol may underlie the vulnerability of the CP-AMPARs-containing neurons to glutamate excitotoxicity. Further studies of the mechanisms mediating the disturbances in ion homeostasis are crucial for developing new approaches for protecting these neurons at brain pathologies.
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Affiliation(s)
- Sergei A Maiorov
- Federal Research Center "Pushchino Scientific Center for Biological Research of the Russian Academy of Sciences", Institute of Cell Biophysics of the Russian Academy of Sciences, 142290, Pushchino, Russia
| | | | - Alexey V Berezhnov
- Federal Research Center "Pushchino Scientific Center for Biological Research of the Russian Academy of Sciences", Institute of Cell Biophysics of the Russian Academy of Sciences, 142290, Pushchino, Russia
| | - Valery P Zinchenko
- Federal Research Center "Pushchino Scientific Center for Biological Research of the Russian Academy of Sciences", Institute of Cell Biophysics of the Russian Academy of Sciences, 142290, Pushchino, Russia
| | - Sergei G Gaidin
- Federal Research Center "Pushchino Scientific Center for Biological Research of the Russian Academy of Sciences", Institute of Cell Biophysics of the Russian Academy of Sciences, 142290, Pushchino, Russia.
| | - Artem M Kosenkov
- Federal Research Center "Pushchino Scientific Center for Biological Research of the Russian Academy of Sciences", Institute of Cell Biophysics of the Russian Academy of Sciences, 142290, Pushchino, Russia.
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Maex R. Energy optimisation predicts the capacity of ion buffering in the brain. BIOLOGICAL CYBERNETICS 2023; 117:467-484. [PMID: 38103053 DOI: 10.1007/s00422-023-00980-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2023] [Accepted: 11/23/2023] [Indexed: 12/17/2023]
Abstract
Neurons store energy in the ionic concentration gradients they build across their cell membrane. The amount of energy stored, and hence the work the ions can do by mixing, can be enhanced by the presence of ion buffers in extra- and intracellular space. Buffers act as sources and sinks of ions, however, and unless the buffering capacities for different ion species obey certain relationships, a complete mixing of the ions may be impeded by the physical conditions of charge neutrality and isotonicity. From these conditions, buffering capacities were calculated that enabled each ion species to mix completely. In all valid buffer distributions, the [Formula: see text] ions were buffered most, with a capacity exceeding that of [Formula: see text] and [Formula: see text] buffering by at least an order of magnitude. The similar magnitude of the (oppositely directed) [Formula: see text] and [Formula: see text] gradients made extracellular space behave as a [Formula: see text]-[Formula: see text] exchanger. Anions such as [Formula: see text] were buffered least. The great capacity of the extra- and intracellular [Formula: see text] buffers caused a large influx of [Formula: see text] ions as is typically observed during energy deprivation. These results explain many characteristics of the physiological buffer distributions but raise the question how the brain controls the capacity of its ion buffers. It is suggested that neurons and glial cells, by their great sensitivity to gradients of charge and osmolarity, respectively, sense deviations from electro-neutral and isotonic mixing, and use these signals to tune the chemical composition, and buffering capacity, of the extra- and intracellular matrices.
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Affiliation(s)
- Reinoud Maex
- School of Physics, Engineering and Computer Science, University of Hertfordshire, College Lane, Hatfield, AL10 9AB, UK.
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3
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Enhanced Ca 2+ Entry Sustains the Activation of Akt in Glucose Deprived SH-SY5Y Cells. Int J Mol Sci 2022; 23:ijms23031386. [PMID: 35163310 PMCID: PMC8835965 DOI: 10.3390/ijms23031386] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Revised: 01/23/2022] [Accepted: 01/24/2022] [Indexed: 12/27/2022] Open
Abstract
The two crucial cellular insults that take place during cerebral ischemia are the loss of oxygen and loss of glucose, which can both activate a cascade of events leading to neuronal death. In addition, the toxic overactivation of neuronal excitatory receptors, leading to Ca2+ overload, may contribute to ischemic neuronal injury. Brain ischemia can be simulated in vitro by oxygen/glucose deprivation, which can be reversible by the re-establishment of physiological conditions. Accordingly, we examined the effects of glucose deprivation on the PI3K/Akt survival signaling pathway and its crosstalk with HIF-1α and Ca2+ homeostasis in SH-SY5Y human neuroblastoma cells. It was found that glucose withdrawal decreased HIF-1α protein levels even in the presence of the ischemia-mimicking CoCl2. On the contrary, and despite neuronal death, we identified a strong activation of the master pro-survival kinase Akt, a finding that was also confirmed by the increased phosphorylation of GSK3, a direct target of p-Akt. Remarkably, the elevated Ca2+ influx recorded was found to promptly trigger the activation of Akt, while a re-addition of glucose resulted in rapid restoration of both Ca2+ entry and p-Akt levels, highlighting the plasticity of neurons to respond to ischemic challenges and the important role of glucose homeostasis for multiple neurological disorders.
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Caspofungin induces the release of Ca 2+ ions from internal stores by activating ryanodine receptor-dependent pathways in human tracheal epithelial cells. Sci Rep 2020; 10:11723. [PMID: 32678179 PMCID: PMC7367263 DOI: 10.1038/s41598-020-68626-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Accepted: 06/25/2020] [Indexed: 11/09/2022] Open
Abstract
The antimycotic drug caspofungin is known to alter the cell function of cardiomyocytes and the cilia-bearing cells of the tracheal epithelium. The objective of this study was to investigate the homeostasis of intracellular Ca2+ concentration ([Ca2+]i) after exposure to caspofungin in isolated human tracheal epithelial cells. The [Ca2+]i was measured using the ratiometric fluoroprobe FURA-2 AM. We recorded two groups of epithelial cells with distinct responses to caspofungin exposure, which demonstrated either a rapid transient rise in [Ca2+]i or a sustained elevation of [Ca2+]i. Both patterns of Ca2+ kinetics were still observed when an influx of transmembraneous Ca2+ ions was pharmacologically inhibited. Furthermore, in extracellular buffer solutions without Ca2+ ions, caspofungin exposure still evoked this characteristic rise in [Ca2+]i. To shed light on the origin of the Ca2+ ions responsible for the elevation in [Ca2+]i we investigated the possible intracellular storage of Ca2+ ions. The depletion of mitochondrial Ca2+ stores using 25 µM 2,4-dinitrophenol (DNP) did not prevent the caspofungin-induced rise in [Ca2+]i, which was rapid and transient. However, the application of caffeine (30 mM) to discharge Ca2+ ions that were presumably stored in the endoplasmic reticulum (ER) prior to caspofungin exposure completely inhibited the caspofungin-induced changes in [Ca2+]i levels. When the ER-bound IP3 receptors were blocked by 2-APB (40 µM), we observed a delayed transient rise in [Ca2+]i as a response to the caspofungin. Inhibition of the ryanodine receptors (RyR) using 40 µM ryanodine completely prevented the caspofungin-induced elevation of [Ca2+]i. In summary, caspofungin has been shown to trigger an increase in [Ca2+]i independent from extracellular Ca2+ ions by liberating the Ca2+ ions stored in the ER, mainly via a RyR pathway.
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Rimkute L, Kraujalis T, Snipas M, Palacios-Prado N, Jotautis V, Skeberdis VA, Bukauskas FF. Modulation of Connexin-36 Gap Junction Channels by Intracellular pH and Magnesium Ions. Front Physiol 2018; 9:362. [PMID: 29706896 PMCID: PMC5906587 DOI: 10.3389/fphys.2018.00362] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2018] [Accepted: 03/23/2018] [Indexed: 11/13/2022] Open
Abstract
Connexin-36 (Cx36) protein forms gap junction (GJ) channels in pancreatic beta cells and is also the main Cx isoform forming electrical synapses in the adult mammalian brain. Cx36 GJs can be regulated by intracellular pH (pHi) and cytosolic magnesium ion concentration ([Mg2+]i), which can vary significantly under various physiological and pathological conditions. However, the combined effect and relationship of these two factors over Cx36-dependent coupling have not been previously studied in detail. Our experimental results in HeLa cells expressing Cx36 show that changes in both pHi and [Mg2+]i affect junctional conductance (gj) in an interdependent manner; in other words, intracellular acidification cause increase or decay in gj depending on whether [Mg2+]i is high or low, respectively, and intracellular alkalization cause reduction in gj independently of [Mg2+]i. Our experimental and modelling data support the hypothesis that Cx36 GJ channels contain two separate gating mechanisms, and both are differentially sensitive to changes in pHi and [Mg2+]i. Using recombinant Cx36 we found that two glutamate residues in the N-terminus could be partly responsible for the observed interrelated effect of pHi and [Mg2+]i. Mutation of glutamate at position 8 attenuated the stimulatory effect of intracellular acidification at high [Mg2+]i, while mutation at position 12 and double mutation at both positions reversed stimulatory effect to inhibition. Moreover, Cx36*E8Q lost the initial increase of gj at low [Mg2+]i and double mutation lost the sensitivity to high [Mg2+]i. These results suggest that E8 and E12 are involved in regulation of Cx36 GJ channels by Mg2+ and H+ ions.
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Affiliation(s)
- Lina Rimkute
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Tadas Kraujalis
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania
- Department of Applied Informatics, Kaunas University of Technology, Kaunas, Lithuania
| | - Mindaugas Snipas
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania
- Department of Mathematical Modelling, Kaunas University of Technology, Kaunas, Lithuania
| | - Nicolas Palacios-Prado
- Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile
- Department of Physiology, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Vaidas Jotautis
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Vytenis A. Skeberdis
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania
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Abstract
Traditionally, only the 3',5'-cyclic monophosphates of adenosine and guanosine (produced by adenylyl cyclase and guanylyl cyclase, respectively) are regarded as true "second messengers" in the vascular wall, despite the presence of other cyclic nucleotides in different tissues. Among these noncanonical cyclic nucleotides, inosine 3',5'-cyclic monophosphate (cIMP) is synthesized by soluble guanylyl cyclase in porcine coronary arteries in response to hypoxia, when the enzyme is activated by endothelium-derived nitric oxide. Its production is associated with augmentation of vascular contraction mediated by stimulation of Rho kinase. Based on these findings, cIMP appears to meet most, if not all, of the criteria required for it to be accepted as a "second messenger," at least in the vascular wall.
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Budelli G, Sun Q, Ferreira J, Butler A, Santi CM, Salkoff L. SLO2 Channels Are Inhibited by All Divalent Cations That Activate SLO1 K+ Channels. J Biol Chem 2016; 291:7347-56. [PMID: 26823461 DOI: 10.1074/jbc.m115.709436] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2015] [Indexed: 11/06/2022] Open
Abstract
Two members of the family of high conductance K(+)channels SLO1 and SLO2 are both activated by intracellular cations. However, SLO1 is activated by Ca(2+)and other divalent cations, while SLO2 (Slack or SLO2.2 from rat) is activated by Na(+) Curiously though, we found that SLO2.2 is inhibited by all divalent cations that activate SLO1, with Zn(2+)being the most effective inhibitor with an IC50of ∼8 μmin contrast to Mg(2+), the least effective, with an IC50of ∼ 1.5 mm Our results suggest that divalent cations are not SLO2 pore blockers, but rather inhibit channel activity by an allosteric modification of channel gating. By site-directed mutagenesis we show that a histidine residue (His-347) downstream of S6 reduces inhibition by divalent cations. An analogous His residue present in some CNG channels is an inhibitory cation binding site. To investigate whether inhibition by divalent cations is conserved in an invertebrate SLO2 channel we cloned the SLO2 channel fromDrosophila(dSLO2) and compared its properties to those of rat SLO2.2. We found that, like rat SLO2.2, dSLO2 was also activated by Na(+)and inhibited by divalent cations. Inhibition of SLO2 channels in mammals andDrosophilaby divalent cations that have second messenger functions may reflect the physiological regulation of these channels by one or more of these ions.
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Affiliation(s)
- Gonzalo Budelli
- From the Departments of Neuroscience and National Center for Behavioral Genomics and Volen Center for Complex Systems, Department of Biology, Brandeis University, Waltham, Massachusetts 02458
| | - Qi Sun
- From the Departments of Neuroscience and
| | | | | | | | - Lawrence Salkoff
- From the Departments of Neuroscience and Department of Genetics, Washington University School of Medicine, Saint Louis, Missouri 63110 and
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8
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Palacios-Prado N, Chapuis S, Panjkovich A, Fregeac J, Nagy JI, Bukauskas FF. Molecular determinants of magnesium-dependent synaptic plasticity at electrical synapses formed by connexin36. Nat Commun 2014; 5:4667. [PMID: 25135336 PMCID: PMC4142521 DOI: 10.1038/ncomms5667] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2014] [Accepted: 07/11/2014] [Indexed: 01/28/2023] Open
Abstract
Neuronal gap junction (GJ) channels composed of connexin36 (Cx36) play an important role in neuronal synchronization and network dynamics. Here we show that Cx36-containing electrical synapses between inhibitory neurons of the thalamic reticular nucleus are bidirectionally modulated by changes in intracellular free magnesium concentration ([Mg(2+)]i). Chimeragenesis demonstrates that the first extracellular loop of Cx36 contains a Mg(2+)-sensitive domain, and site-directed mutagenesis shows that the pore-lining residue D47 is critical in determining high Mg(2+)-sensitivity. Single-channel analysis of Mg(2+)-sensitive chimeras and mutants reveals that [Mg(2+)]i controls the strength of electrical coupling mostly via gating mechanisms. In addition, asymmetric transjunctional [Mg(2+)]i induces strong instantaneous rectification, providing a novel mechanism for electrical rectification in homotypic Cx36 GJs. We suggest that Mg(2+)-dependent synaptic plasticity of Cx36-containing electrical synapses could underlie neuronal circuit reconfiguration via changes in brain energy metabolism that affects neuronal levels of intracellular ATP and [Mg(2+)]i.
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Affiliation(s)
- Nicolás Palacios-Prado
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, NY 10461, USA
- Grass Laboratory, Marine Biological Laboratory, Woods Hole, MA 02543, USA
| | - Sandrine Chapuis
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, NY 10461, USA
| | - Alejandro Panjkovich
- European Molecular Biology Laboratory, Hamburg Outstation, 22603 Hamburg, Germany
| | - Julien Fregeac
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, NY 10461, USA
| | - James I. Nagy
- Department of Physiology, University of Manitoba, Winnipeg, Manitoba R3E 0J9, Canada
| | - Feliksas F. Bukauskas
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, NY 10461, USA
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9
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Abstract
PURPOSE/AIM Changes in pH are not infrequently encountered in clinical situations and can be associated with significant effects on ion channels, mitochondria and axon function. The purpose of this paper is to study the modulatory effects of pH on the anoxic response in peripheral nerve. MATERIALS AND METHODS A total of 48 rat sciatic nerves were studied in vitro in a perfusion apparatus. Experiments were carried out at 6 pH levels from 6.0 to 7.8. RESULTS The amplitude of the nerve action potential (NAP) drops more dramatically with repetitive periods of anoxia when the pH is reduced below 6.5. In addition, velocity decreases and duration increases more with each cycle of anoxia at low pH values. Despite these effects of pH on recovery after anoxia, there was no significant effect of pH on the time course of changes during anoxia. During recovery from anoxia, the NAP recovered more slowly when the pH was lowered. CONCLUSIONS The pattern of changes in amplitude, velocity and duration suggest that they may be due to interference of high hydrogen ion concentrations with sodium and potassium channel function.
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Khacho M, Tarabay M, Patten D, Khacho P, MacLaurin JG, Guadagno J, Bergeron R, Cregan SP, Harper ME, Park DS, Slack RS. Acidosis overrides oxygen deprivation to maintain mitochondrial function and cell survival. Nat Commun 2014; 5:3550. [PMID: 24686499 PMCID: PMC3988820 DOI: 10.1038/ncomms4550] [Citation(s) in RCA: 133] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2013] [Accepted: 03/05/2014] [Indexed: 02/07/2023] Open
Abstract
Sustained cellular function and viability of high-energy demanding post-mitotic cells rely on the continuous supply of ATP. The utilization of mitochondrial oxidative phosphorylation for efficient ATP generation is a function of oxygen levels. As such, oxygen deprivation, in physiological or pathological settings, has profound effects on cell metabolism and survival. Here we show that mild extracellular acidosis, a physiological consequence of anaerobic metabolism, can reprogramme the mitochondrial metabolic pathway to preserve efficient ATP production regardless of oxygen levels. Acidosis initiates a rapid and reversible homeostatic programme that restructures mitochondria, by regulating mitochondrial dynamics and cristae architecture, to reconfigure mitochondrial efficiency, maintain mitochondrial function and cell survival. Preventing mitochondrial remodelling results in mitochondrial dysfunction, fragmentation and cell death. Our findings challenge the notion that oxygen availability is a key limiting factor in oxidative metabolism and brings forth the concept that mitochondrial morphology can dictate the bioenergetic status of post-mitotic cells. In hypoxic conditions, cells depend on anaerobic respiration, which results in extracellular acidosis. Khacho et al. find that acidosis serves a protective function, enhancing mitochondrial respiratory capacity and sustaining ATP synthesis despite limited oxygen availability, by both promoting mitochondrial fusion and inhibiting fission.
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Affiliation(s)
- Mireille Khacho
- Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
| | - Michelle Tarabay
- Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
| | - David Patten
- 1] Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada [2]
| | - Pamela Khacho
- 1] Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada [2]
| | - Jason G MacLaurin
- Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
| | - Jennifer Guadagno
- Department of Physiology and Pharmacology, J. Allyn Taylor Centre for Cell Biology, Robarts Research Institute, The University of Western Ontario, London, Ontario N6A 5B7, Canada
| | - Richard Bergeron
- 1] Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada [2] Ottawa Hospital Research Institute, Ottawa, Ontario K1H 8M5, Canada
| | - Sean P Cregan
- Department of Physiology and Pharmacology, J. Allyn Taylor Centre for Cell Biology, Robarts Research Institute, The University of Western Ontario, London, Ontario N6A 5B7, Canada
| | - Mary-Ellen Harper
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
| | - David S Park
- Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
| | - Ruth S Slack
- Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
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Cytosolic calcium regulation in rat afferent vagal neurons during anoxia. Cell Calcium 2013; 54:416-27. [PMID: 24189167 DOI: 10.1016/j.ceca.2013.10.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2013] [Revised: 09/30/2013] [Accepted: 10/06/2013] [Indexed: 12/12/2022]
Abstract
Sensory neurons are able to detect tissue ischaemia and both transmit information to the brainstem as well as release local vasoactive mediators. Their ability to sense tissue ischaemia is assumed to be primarily mediated through proton sensing ion channels, lack of oxygen however may also affect sensory neuron function. In this study we investigated the effects of anoxia on isolated capsaicin sensitive neurons from rat nodose ganglion. Acute anoxia triggered a reversible increase in [Ca2+]i that was mainly due to Ca2+-efflux from FCCP sensitive stores and from caffeine and CPA sensitive ER stores. Prolonged anoxia resulted in complete depletion of ER Ca2+-stores. Mitochondria were partially depolarised by acute anoxia but mitochondrial Ca2+-uptake/buffering during voltage-gated Ca2+-influx was unaffected. The process of Ca2+-release from mitochondria and cytosolic Ca2+-clearance following Ca2+ influx was however significantly slowed. Anoxia was also found to inhibit SERCA activity and, to a lesser extent, PMCA activity. Hence, anoxia has multiple influences on [Ca2+]i homeostasis in vagal afferent neurons, including depression of ATP-driven Ca2+-pumps, modulation of the kinetics of mitochondrial Ca2+ buffering/release and Ca2+-release from, and depletion of, internal Ca2+-stores. These effects are likely to influence sensory neuronal function during ischaemia.
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12
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Levitsky DO, Takahashi M. Interplay of Ca(2+) and Mg (2+) in sodium-calcium exchanger and in other Ca(2+)-binding proteins: magnesium, watchdog that blocks each turn if able. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2013; 961:65-78. [PMID: 23224871 DOI: 10.1007/978-1-4614-4756-6_7] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Sodium-calcium exchange across plasma membrane is regulated by intracellular calcium ions. The sodium-calcium exchanger (NCX1) is activated by successive saturation of numerous Ca(2+)-binding sites located in the intracellular loop of the protein. The progressive saturation of the binding domain CBD12 by Ca(2+) results in a series of conformational changes of CBD12 as well as of entire NCX1 molecule. Like other soluble and membrane Ca(2+)-binding proteins, NCX1 can also be regulated by Mg(2+) that antagonises Ca(2+) at the level of divalent cation-binding sites. This chapter summarises data on Mg(2+) impacts in the cells. Regulatory action of Mg(2+) on intracellular Ca(2+)-dependent processes can be achieved due to changes of its cytoplasmic level, which take place in the range of [Mg(2+)](i) from 0.5 to 3 mM. Under normal conditions, these changes are ensured by activation of plasmalemmal Mg(2+) transport systems and by variations in ATP level in cytoplasm. In heart and in brain, some pathological conditions, such as hypoxia, ischemia and ischemia followed by reperfusion, are associated with an important increase in intracellular Ca(2+). The tissue damage due to Ca(2+) overload may be prevented by Mg(2+). The protective actions of Mg(2+) can be achieved due to its ability to compete with Ca(2+) for the binding sites in a number of proteins responsible for the rise in intracellular free Ca(2+), including NCX1, in case when the reverse mode of Na(+)/Ca(2+) exchange becomes predominant. Saturation of CBD12 by Mg(2+) results in important changes of NCX1 conformation. Modulating actions of Mg(2+) on the conformation of NCX1 were detected at a narrow range of Mg(2+) concentration, from 0.5 to 1 mM. These data support an idea that variations of intracellular Mg(2+) could modify transmembrane Ca(2+) movements ensured by NCX1.
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Affiliation(s)
- Dmitri O Levitsky
- Unité de Fonctionnalité et Ingénierie des Protéines, Université de Nantes, Nantes Cedex 03, France.
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Luo J, Stewart R, Berdeaux R, Hu H. Tonic inhibition of TRPV3 by Mg2+ in mouse epidermal keratinocytes. J Invest Dermatol 2012; 132:2158-65. [PMID: 22622423 PMCID: PMC3423538 DOI: 10.1038/jid.2012.144] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The transient receptor potential vanilloid 3 channel (TRPV3) is abundantly expressed in epidermal keratinocytes and plays important roles in sensory biology and skin health. Mg2+ deficiency causes skin disorders under certain pathological conditions such as type 2 diabetes mellitus. In this study, we investigated the effect of Mg2+ on TRPV3 in primary epidermal keratinocytes. Extracellular Mg2+ ([Mg2+]o) inhibited TRPV3-mediated membrane current and calcium influx. TRPV3 activation induced a calcium signaling pathway culminating in activation of the cAMP response element binding (CREB). TRPV3 inhibition by [Mg2+]o, the TRPV3 blocker ruthenium red or TRPV3 siRNA suppressed this response. In TRPV3-expressing Chinese hamster ovary (CHO) cells, both extracellular and intracellular Mg2+ inhibited TRPV3 single-channel conductance but not open probability. Neutralization of an aspartic acid residue (D641) in the extracellular pore loop or two acidic residues (E679, E682) in the inner pore region significantly attenuated the inhibitory effect of extracellular or intracellular Mg2+ on TRPV3-mediated signaling, respectively. Our findings suggest that epidermal TRPV3 is tonically inhibited by both extracellular and intracellular Mg2+, which act on both sides of the channel pore loop. Mg2+ deficiency may promote the function of TRPV3 and contribute to the pathogenesis of skin diseases.
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Affiliation(s)
- Jialie Luo
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas 77030, USA
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14
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Effects of exogenous hydrogen sulphide on calcium signalling, background (TASK) K channel activity and mitochondrial function in chemoreceptor cells. Pflugers Arch 2012; 463:743-54. [PMID: 22419174 PMCID: PMC3323823 DOI: 10.1007/s00424-012-1089-8] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2012] [Accepted: 02/17/2012] [Indexed: 12/24/2022]
Abstract
It has been proposed that endogenous H2S mediates oxygen sensing in chemoreceptors; this study investigates the mechanisms by which H2S excites carotid body type 1 cells. H2S caused a rapid reversible increase in intracellular calcium with EC50 ≈ 6 μM. This [Ca2+]i response was abolished in Ca-free Tyrode. In perforated patch current clamp recordings, H2S depolarised type 1 cells from −59 to −35 mV; this was accompanied by a robust increase in [Ca2+]i. Voltage clamping at the resting membrane potential abolished the H2S-induced rise in [Ca2+]i. H2S inhibited background K+ current in whole cell perforated patch and reduced background K+ channel activity in cell-attached patch recordings. It is concluded that H2S excites type 1 cells through the inhibition of background (TASK) potassium channels leading to membrane depolarisation and voltage-gated Ca2+ entry. These effects mimic those of hypoxia. H2S also inhibited mitochondrial function over a similar concentration range as assessed by NADH autofluorescence and measurement of intracellular magnesium (an index of decline in MgATP). Cyanide inhibited background K channels to a similar extent to H2S and prevented H2S exerting any further influence over channel activity. These data indicate that the effects of H2S on background K channels are a consequence of inhibition of oxidative phosphorylation. Whilst this does not preclude a role for endogenous H2S in oxygen sensing via the inhibition of cytochrome oxidase, the levels of H2S required raise questions as to the viability of such a mechanism.
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Yannopoulos F, Mäkelä T, Arvola O, Haapanen H, Anttila V, Kiviluoma K, Juvonen T. Remote ischemic precondition preserves cerebral oxygen tension during hypothermic circulatory arrest. SCAND CARDIOVASC J 2012; 46:245-50. [DOI: 10.3109/14017431.2012.661874] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Abstract
In the retina, light onset hyperpolarizes photoreceptors and depolarizes ON bipolar cells at the sign inverting photoreceptor-ON bipolar cell synapse. Transmission at this synapse is mediated by a signaling cascade comprised of mGluR6, a G-protein containing G(αo), and the cation channel TRP melastatin 1 (TRPM1). This system is thought to be common to both the rod- and ON-cone-driven pathways, which control vision under scotopic and photopic conditions, respectively. In this study, we present evidence that the rod pathway is uniquely susceptible to modulation by PKCα at the rod-rod bipolar cell synapse. Decreased production of DAG (an activator of PKC) by inhibition of PIP₂ (phosphatidylinositol-4,5-bisphosphate) hydrolysis caused depression of the TRPM1 current. Conversely, addition of a DAG analog, 2-acetyl-1-oleoyl-sn-glycerol (OAG), potentiated the current in rod bipolar cells but not in ON-cone bipolar cells. The potentiating effects of OAG were absent both in mutant mice that lack PKCα expression and in wild-type mice in which enzymatic activity of PKCα was pharmacologically inhibited. In addition, we found that, like other members of the TRPM subfamily, TRPM1 current is susceptible to voltage-independent inhibition by intracellular magnesium, and that modulation by PKCα relieves this inhibition, as the potentiating effects of OAG are absent in low intracellular magnesium. We conclude that activation of PKCα initiates a modulatory mechanism at the rod-rod bipolar cell synapse whose function is to reduce inhibition of the TRPM1 current by magnesium, thereby increasing the gain of transmission at this synapse.
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Miyaji T, Sawada K, Omote H, Moriyama Y. Divalent cation transport by vesicular nucleotide transporter. J Biol Chem 2011; 286:42881-7. [PMID: 22052906 DOI: 10.1074/jbc.m111.277269] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The vesicular nucleotide transporter (VNUT) is a secretory vesicle protein that is responsible for the vesicular storage and subsequent exocytosis of ATP (Sawada, K., Echigo, N., Juge, N., Miyaji, T., Otsuka, M., Omote, H., and Moriyama, Y. (2008) Proc. Natl. Acad. Sci. U.S.A. 105, 5683-5686). Because VNUT actively transports ATP in a membrane potential (Δψ)-dependent manner irrespective of divalent cations such as Mg(2+) and Ca(2+), VNUT recognizes free ATP as a transport substrate. However, whether or not VNUT transports chelating complexes with divalent cations remains unknown. Here, we show that proteoliposomes containing purified VNUT actively took up Mg(2+) when ATP was present, as detected by atomic absorption spectroscopy. The VNUT-containing proteoliposomes also took up radioactive Ca(2+) upon imposing Δψ (positive-inside) but not ΔpH. The Δψ-driven Ca(2+) uptake required ATP and a millimolar concentration of Cl(-), which was inhibited by Evans blue, a specific inhibitor of SLC17-type transporters. VNUT in which Arg-119 was specifically mutated to alanine, the counterpart of the essential amino acid residue of the SLC17 family, lost the ability to take up both ATP and Ca(2+). Ca(2+) uptake was also inhibited in the presence of various divalent cations such as Mg(2+). Kinetic analysis indicated that Ca(2+) or Mg(2+) did not affect the apparent affinity for ATP. RNAi of the VNUT gene in PC12 cells decreased the vesicular Mg(2+) concentration to 67.7%. These results indicate that VNUT transports both nucleotides and divalent cations probably as chelating complexes and suggest that VNUT functions as a divalent cation importer in secretory vesicles under physiological conditions.
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Affiliation(s)
- Takaaki Miyaji
- Advanced Science Research Center, Okayama University, Okayama 700-8530, Japan
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Chung S, Kim YH, Koh JY, Nam TS, Ahn DS. Intracellular acidification evoked by moderate extracellular acidosis attenuates transient receptor potential V1 (TRPV1) channel activity in rat dorsal root ganglion neurons. Exp Physiol 2011; 96:1270-81. [PMID: 21930676 DOI: 10.1113/expphysiol.2011.059444] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Transient receptor potential V1 (TRPV1) has been suggested to play an important role in detecting decreases in extracellular pH (pH(o)). Results from recent in vivo studies, however, have suggested that TRPV1 channels play less of a role in sensing a moderately acidic pH(o) (6.0 < pH < 7.0) than predicted from the in vitro experiments. A clear explanation for this discrepancy between the in vitro and in vivo data has not yet been provided. We report here that intracellular acidification induced by a moderately low pH(o) (6.4) almost completely inhibited the effect of extracellular acidosis on TRPV1 activity. In our experiments, sodium acetate (20 mm), which was used to induce intracellular acidosis, attenuated the capsaicin-evoked TRPV1 current (I(CAP)) in a reversible manner in whole-cell patch-clamp mode and shifted the concentration-response curve to the right. Likewise, the concentration-response curve was significantly shifted to the right by lowering the pH of the pipette solution from 7.2 to 6.5. In addition, application of an acidic bath solution (pH 6.4) to the intracellular side also significantly suppressed I(CAP) in inside-out patch mode. In cell-attached patch mode, the single-channel activity of i(CAP) was significantly attenuated by intracellular acidosis that was induced by a decrease in pH(o) (6.4). These results suggested that intracellular acidification induced by a low pH(o) inhibited TRPV1 activity. When studied in perforated patch mode or by acidifying the intracellular pipette solution, potentiation or activation of TRPV1 by extracellular acidosis (pH 6.4) at 37 °C was almost completely inhibited. Likewise, enhancement of neuronal excitability by a moderately acidic pH(o) (6.4) at a physiological temperature (37 °C) was attenuated by lowering the pH of the pipette solution to 6.5 or using perforated patch mode. Taken together, these results suggest that extracellular acidosis of moderate intensity may not significantly modulate TRPV1 activity in physiological conditions at which intracellular pH can be readily affected by pH(o), and this phenomenon is due to attenuation of TRPV1 channel activity by low-pH(o)-induced intracellular acidification.
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Affiliation(s)
- Seungsoo Chung
- Brain Korea 21 Project for Medical Science, Yonsei University College of Medicine, Seodaemun-gu, Seoul 120-752, Republic of Korea
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Omote H, Miyaji T, Juge N, Moriyama Y. Vesicular Neurotransmitter Transporter: Bioenergetics and Regulation of Glutamate Transport. Biochemistry 2011; 50:5558-65. [DOI: 10.1021/bi200567k] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- Hiroshi Omote
- Department of Membrane Biochemistry, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama 700-8530, Japan
| | - Takaaki Miyaji
- Advanced Science Research Center, Okayama University, Okayama 700-8530, Japan
| | - Narinobu Juge
- Department of Membrane Biochemistry, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama 700-8530, Japan
| | - Yoshinori Moriyama
- Department of Membrane Biochemistry, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama 700-8530, Japan
- Advanced Science Research Center, Okayama University, Okayama 700-8530, Japan
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Acid-evoked Ca2+ signalling in rat sensory neurones: effects of anoxia and aglycaemia. Pflugers Arch 2010; 459:159-81. [PMID: 19806360 PMCID: PMC2765625 DOI: 10.1007/s00424-009-0715-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2008] [Revised: 07/30/2009] [Accepted: 08/14/2009] [Indexed: 12/11/2022]
Abstract
Ischaemia excites sensory neurones (generating pain) and promotes calcitonin gene-related peptide release from nerve endings. Acidosis is thought to play a key role in mediating excitation via the activation of proton-sensitive cation channels. In this study, we investigated the effects of acidosis upon Ca2+ signalling in sensory neurones from rat dorsal root ganglia. Both hypercapnic (pHo 6.8) and metabolic–hypercapnic (pHo 6.2) acidosis caused a biphasic increase in cytosolic calcium concentration ([Ca2+]i). This comprised a brief Ca2+ transient (half-time approximately 30 s) caused by Ca2+ influx followed by a sustained rise in [Ca2+]i due to Ca2+ release from caffeine and cyclopiazonic acid-sensitive internal stores. Acid-evoked Ca2+ influx was unaffected by voltage-gated Ca2+-channel inhibition with nickel and acid sensing ion channel (ASIC) inhibition with amiloride but was blocked by inhibition of transient receptor potential vanilloid receptors (TRPV1) with (E)-3-(4-t-butylphenyl)-N-(2,3-dihydrobenzo[b][1,4] dioxin-6-yl)acrylamide (AMG 9810; 1 μM) and N-(4-tertiarybutylphenyl)-4-(3-cholorphyridin-2-yl) tetrahydropryazine-1(2H)-carbox-amide (BCTC; 1 μM). Combining acidosis with anoxia and aglycaemia increased the amplitude of both phases of Ca2+ elevation and prolonged the Ca2+ transient. The Ca2+ transient evoked by combined acidosis, aglycaemia and anoxia was also substantially blocked by AMG 9810 and BCTC and, to a lesser extent, by amiloride. In summary, the principle mechanisms mediating increase in [Ca2+]i in response to acidosis are a brief Ca2+ influx through TRPV1 followed by sustained Ca2+ release from internal stores. These effects are potentiated by anoxia and aglycaemia, conditions also prevalent in ischaemia. The effects of anoxia and aglycaemia are suggested to be largely due to the inhibition of Ca2+-clearance mechanisms and possible increase in the role of ASICs.
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Margaryan G, Mladinic M, Mattioli C, Nistri A. Extracellular magnesium enhances the damage to locomotor networks produced by metabolic perturbation mimicking spinal injury in the neonatal rat spinal cord in vitro. Neuroscience 2009; 163:669-82. [DOI: 10.1016/j.neuroscience.2009.07.005] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2009] [Revised: 07/01/2009] [Accepted: 07/05/2009] [Indexed: 11/16/2022]
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Metabolic inhibition strongly inhibits Na+-dependent Mg2+ efflux in rat ventricular myocytes. Biophys J 2009; 96:4941-50. [PMID: 19527653 DOI: 10.1016/j.bpj.2009.02.013] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2008] [Revised: 01/22/2009] [Accepted: 02/02/2009] [Indexed: 10/20/2022] Open
Abstract
We measured intracellular Mg2+ concentration ([Mg2+]i) in rat ventricular myocytes using the fluorescent indicator furaptra (25 degrees C). In normally energized cells loaded with Mg2+, the introduction of extracellular Na+ induced a rapid decrease in [Mg2+]i: the initial rate of decrease in [Mg2+]i (initial Delta[Mg2+]i/Deltat) is thought to represent the rate of Na+-dependent Mg2+ efflux (putative Na+/Mg2+ exchange). To determine whether Mg2+ efflux depends directly on energy derived from cellular metabolism, in addition to the transmembrane Na+ gradient, we estimated the initial Delta[Mg2+]i/Deltat after metabolic inhibition. In the absence of extracellular Na+ and Ca2+, treatment of the cells with 1 microM carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone, an uncoupler of mitochondria, caused a large increase in [Mg2+]i from approximately 0.9 mM to approximately 2.5 mM in a period of 5-8 min (probably because of breakdown of MgATP and release of Mg2+) and cell shortening to approximately 50% of the initial length (probably because of formation of rigor cross-bridges). Similar increases in [Mg2+]i and cell shortening were observed after application of 5 mM potassium cyanide (KCN) (an inhibitor of respiration) for > or = 90 min. The initial Delta[Mg2+]i/Deltat was diminished, on average, by 90% in carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone-treated cells and 92% in KCN-treated cells. When the cells were treated with 5 mM KCN for shorter times (59-85 min), a significant decrease in the initial Delta[Mg2+]i/Deltat (on average by 59%) was observed with only a slight shortening of the cell length. Intracellular Na+ concentration ([Na+]i) estimated with a Na+ indicator sodium-binding benzofuran isophthalate was, on average, 5.0-10.5 mM during the time required for the initial Delta[Mg2+]i/Deltat measurements, which is well below the [Na+]i level for half inhibition of the Mg2+ efflux (approximately 40 mM). Normalization of intracellular pH using 10 microM nigericin, a H+ ionophore, did not reverse the inhibition of the Mg2+ efflux. From these results, it seems likely that a decrease in ATP below the threshold of rigor cross-bridge formation (approximately 0.4 mM estimated indirectly in the this study), rather than elevation of [Na+]i or intracellular acidosis, inhibits the Mg2+ efflux, suggesting the absolute necessity of ATP for the Na+/Mg2+ exchange.
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Rigaud M, Gemes G, Weyker PD, Cruikshank JM, Kawano T, Wu HE, Hogan QH. Axotomy depletes intracellular calcium stores in primary sensory neurons. Anesthesiology 2009; 111:381-92. [PMID: 19602958 PMCID: PMC2891519 DOI: 10.1097/aln.0b013e3181ae6212] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
BACKGROUND The cellular mechanisms of neuropathic pain are inadequately understood. Previous investigations have revealed disrupted Ca signaling in primary sensory neurons after injury. The authors examined the effect of injury on intracellular Ca stores of the endoplasmic reticulum, which critically regulate the Ca signal and neuronal function. METHODS Intracellular Ca levels were measured with Fura-2 or mag-Fura-2 microfluorometry in axotomized fifth lumbar (L5) dorsal root ganglion neurons and adjacent L4 neurons isolated from hyperalgesic rats after L5 spinal nerve ligation, compared to neurons from control animals. RESULTS Endoplasmic reticulum Ca stores released by the ryanodine-receptor agonist caffeine decreased by 46% in axotomized small neurons. This effect persisted in Ca-free bath solution, which removes the contribution of store-operated membrane Ca channels, and after blockade of the mitochondrial, sarco-endoplasmic Ca-ATPase and the plasma membrane Ca ATPase pathways. Ca released by the sarco-endoplasmic Ca-ATPase blocker thapsigargin and by the Ca-ionophore ionomycin was also diminished by 25% and 41%, respectively. In contrast to control neurons, Ca stores in axotomized neurons were not expanded by neuronal activation by K depolarization, and the proportionate rate of refilling by sarco-endoplasmic Ca-ATPase was normal. Luminal Ca concentration was also reduced by 38% in axotomized neurons in permeabilized neurons. The adjacent neurons of the L4 dorsal root ganglia showed modest and inconsistent changes after L5 spinal nerve ligation. CONCLUSIONS Painful nerve injury leads to diminished releasable endoplasmic reticulum Ca stores and a reduced luminal Ca concentration. Depletion of Ca stores may contribute to the pathogenesis of neuropathic pain.
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Affiliation(s)
- Marcel Rigaud
- Research Fellow, Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, Wisconsin
- Resident, Department of Anesthesiology, Medical University of Graz, Graz, Austria
| | - Geza Gemes
- Research Fellow, Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, Wisconsin
- Resident, Department of Anesthesiology, Medical University of Graz, Graz, Austria
| | - Paul D. Weyker
- Medical Student, University of Wisconsin, Madison, Wisconsin
| | - James M. Cruikshank
- Research Assistant, Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, Wisconsin
| | - Takashi Kawano
- Research Fellow, Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, Wisconsin
| | - Hsiang-En Wu
- Assistant Professor, Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, Wisconsin
| | - Quinn H. Hogan
- Professor, Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, Wisconsin
- Anesthesiologist, Zablocki VA Medical Center, Milwaukee, Wisconsin
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Effect of cytosolic Mg2+ on mitochondrial Ca2+ signaling. Pflugers Arch 2008; 457:941-54. [PMID: 18629534 DOI: 10.1007/s00424-008-0551-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2008] [Accepted: 06/25/2008] [Indexed: 12/20/2022]
Abstract
Cytosolic Ca2+ signals are followed by mitochondrial Ca2+ uptake, which, in turn, modifies several biological processes. Mg2+ is known to inhibit Ca2+ uptake by isolated mitochondria, but its significance in intact cells has not been elucidated. In HEK293T cells, activation of purinergic receptors with extracellular ATP caused cytosolic Ca2+ signals associated with parallel changes in cytosolic [Mg2+]. Neither signals were affected by omitting bivalent cations from the extracellular medium. The effect of store-operated Ca2+ influx on cytosolic Mg2+ concentration ([Mg2+]c) was negligible. Uncaged Ca2+ displaced Mg2+ from cytosolic binding sites, but for an equivalent Ca2+ signal, the change in [Mg2+] was significantly smaller than that measured after adding extracellular ATP. Inositol 1,4,5-trisphosphate mobilized Ca2+ and Mg2+ from internal stores in permeabilized cells. The increase of [Mg2+] in the range that occurred in ATP-stimulated cells inhibited mitochondrial Ca2+ uptake in permeabilized cells without affecting mitochondrial Ca2+ efflux. Therefore, the Mg2+ signal generated by Ca2+ mobilizing agonists may attenuate mitochondrial Ca2+ uptake.
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Henrich M, Buckler KJ. Effects of anoxia and aglycemia on cytosolic calcium regulation in rat sensory neurons. J Neurophysiol 2008; 100:456-73. [PMID: 18417627 PMCID: PMC2493471 DOI: 10.1152/jn.01380.2007] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Nociceptive neurons play an important role in ischemia by sensing and transmitting information to the CNS and by secreting peptides and nitric oxide, which can have local effects. While these responses are probably primarily mediated by acid sensing channels, other events occurring in ischemia may also influence neuron function. In this study, we have investigated the effects of anoxia and anoxic aglycemia on Ca2+ regulation in sensory neurons from rat dorsal root ganglia. Anoxia increased [Ca2+]i by evoking Ca2+ release from two distinct internal stores one sensitive to carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone (FCCP) and one sensitive to caffeine, cyclopiazonic acid (CPA), and ryanodine [assumed to be the endoplasmic reticulum (ER)]. Anoxia also promoted progressive decline in ER Ca2+ content. Despite partially depolarizing mitochondria, anoxia had relatively little effect on mitochondrial Ca2+ uptake when neurons were depolarized but substantially delayed mitochondrial Ca2+ release and subsequent Ca2+ clearance from the cytosol on repolarization. Anoxia also reduced both sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) activity and Ca2+ extrusion [probably via plasma membrane Ca2+-ATPase (PMCA)]. Thus anoxia has multiple effects on [Ca2+]i homeostasis in sensory neurons involving internal stores, mitochondrial buffering, and Ca2+ pumps. Under conditions of anoxic aglycemia, there was a biphasic and more profound elevation of [Ca2+]i, which was associated with complete ER Ca2+ store emptying and progressive, and eventually complete, inhibition of Ca2+ clearance by PMCA and SERCA. These data clearly show that loss of oxygen, and exhaustion of glycolytic substrates, can profoundly affect many aspects of cell Ca2+ regulation, and this may play an important role in modulating neuronal responses to ischemia.
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Affiliation(s)
- Michael Henrich
- Department of Physiology, Anatomy and Genetics, Oxford, United Kingdom
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