1
|
|
2
|
Romani AMP. Cellular magnesium homeostasis. Arch Biochem Biophys 2011; 512:1-23. [PMID: 21640700 PMCID: PMC3133480 DOI: 10.1016/j.abb.2011.05.010] [Citation(s) in RCA: 354] [Impact Index Per Article: 27.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Revised: 05/16/2011] [Accepted: 05/17/2011] [Indexed: 12/12/2022]
Abstract
Magnesium, the second most abundant cellular cation after potassium, is essential to regulate numerous cellular functions and enzymes, including ion channels, metabolic cycles, and signaling pathways, as attested by more than 1000 entries in the literature. Despite significant recent progress, however, our understanding of how cells regulate Mg(2+) homeostasis and transport still remains incomplete. For example, the occurrence of major fluxes of Mg(2+) in either direction across the plasma membrane of mammalian cells following metabolic or hormonal stimuli has been extensively documented. Yet, the mechanisms ultimately responsible for magnesium extrusion across the cell membrane have not been cloned. Even less is known about the regulation in cellular organelles. The present review is aimed at providing the reader with a comprehensive and up-to-date understanding of the mechanisms enacted by eukaryotic cells to regulate cellular Mg(2+) homeostasis and how these mechanisms are altered under specific pathological conditions.
Collapse
Affiliation(s)
- Andrea M P Romani
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-4970, USA.
| |
Collapse
|
3
|
Cady EB, Iwata O, Bainbridge A, Wyatt JS, Robertson NJ. Phosphorus magnetic resonance spectroscopy 2 h after perinatal cerebral hypoxia-ischemia prognosticates outcome in the newborn piglet. J Neurochem 2008; 107:1027-35. [PMID: 18786177 DOI: 10.1111/j.1471-4159.2008.05662.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Phosphorus magnetic resonance spectroscopy ((31)P MRS) often reveals apparently normal brain metabolism in the first hours after intrapartum hypoxia-ischemia (HI) at a time when conventional clinical assessment of injury severity is problematic. We aimed to elucidate very-early, injury-severity biomarkers. Twenty-seven newborn piglets underwent cerebral HI: (31)P-MRS measures approximately 2 h after HI were compared between injury groups defined by secondary-energy-failure severity as quantified by the minimum nucleotide triphosphate (NTP) observed after 6 h. For severe and moderate injury versus baseline, [Pi]/[total exchangeable high-energy phosphate pool (EPP)] was increased (p < 0.001 and < 0.02, respectively), and [NTP]/[EPP] decreased (p < 0.03 and < 0.006, respectively): severe-injury [Pi]/[EPP] was also increased versus mild injury (p < 0.04). Mild-injury [phosphocreatine]/[EPP] was increased (p < 0.004). Severe-injury intracellular pH was alkaline versus baseline (p < 0.002). For severe and moderate injury [total Mg]/[ATP] (p < 0.0002 and < 0.02, respectively) and [free Mg] (p < 0.0001 and < 0.02, respectively) were increased versus baseline. [Pi]/[EPP], [phosphocreatine]/[Pi] and [NTP]/[EPP] correlated linearly with injury severity (p < 0.005, < 0.005 and < 0.02, respectively). Increased [Pi]/[EPP], intracellular pH and intracellular Mg approximately 2 h after intrapartum HI may prognosticate severe injury, whereas increased [phosphocreatine]/[EPP] may suggest mild damage. In vivo(31)P MRS may have potential to provide very-early prognosis in neonatal encephalopathy.
Collapse
Affiliation(s)
- Ernest B Cady
- Medical Physics & Bio-Engineering, University College London Hospitals NHS Foundation Trust, London, UK.
| | | | | | | | | |
Collapse
|
4
|
Gabriel TE, Günzel D. Quantification of Mg2+ extrusion and cytosolic Mg2+-buffering in Xenopus oocytes. Arch Biochem Biophys 2007; 458:3-15. [PMID: 16949541 DOI: 10.1016/j.abb.2006.07.007] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2006] [Revised: 05/29/2006] [Accepted: 07/13/2006] [Indexed: 11/26/2022]
Abstract
Intracellular Mg(2+) buffering and Mg(2+) extrusion were investigated in Xenopus laevis oocytes. Mg(2+) or EDTA were pressure injected and the resulting changes in the intracellular Mg(2+) concentration were measured simultaneously with Mg(2+)-selective microelectrodes. In the presence of extracellular Na(+), injected Mg(2+) was extruded from the oocytes with an estimated v(max) and K(M) of 74 pmol cm(-2)s(-1) and 1.28 mM, respectively. To investigate genuine cytosolic Mg(2+) buffering, measurements were carried out in the nominal absence of extracellular Na(+) to block Mg(2+) extrusion, and during the application of CCCP (inhibiting mitochondrial uptake). Under these conditions, Mg(2+) buffering calculated after both MgCl(2) and EDTA injections could be described by a buffer equivalent with a concentration of 9.8mM and an apparent dissociation constant, K(d-app), of 0.6mM together with an [ATP](i) of 0.9 mM with a K(d-app) 0.12 mM. Xenopus oocytes thus possess highly efficient mechanisms to maintain their intracellular Mg(2+) concentration.
Collapse
Affiliation(s)
- Thomas E Gabriel
- Institut für Neurobiologie, Heinrich-Heine-Universität, Universitätsstrasse 1, 40225 Düsseldorf, Germany
| | | |
Collapse
|
5
|
Günzel D, Kucharski LM, Kehres DG, Romero MF, Maguire ME. The MgtC virulence factor of Salmonella enterica serovar Typhimurium activates Na(+),K(+)-ATPase. J Bacteriol 2006; 188:5586-94. [PMID: 16855249 PMCID: PMC1540036 DOI: 10.1128/jb.00296-06] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The mgtC gene of Salmonella enterica serovar Typhimurium encodes a membrane protein of unknown function that is important for full virulence in the mouse. Since mgtC is part of an operon with mgtB which encodes a Mg(2+)-transporting P-type ATPase, MgtC was hypothesized to function in ion transport, possibly in Mg(2+) transport. Consequently, MgtC was expressed in Xenopus laevis oocytes, and its effect on ion transport was evaluated using ion selective electrodes. Oocytes expressing MgtC did not exhibit altered currents or membrane potentials in response to changes in extracellular H(+), Mg(2+), or Ca(2+), thus ruling out a previously postulated function as a Mg(2+)/H(+) antiporter. However, addition of extracellular K(+) markedly hyperpolarized membrane potential instead of the expected depolarization. Addition of ouabain to block the oocyte Na(+),K(+)-ATPase completely prevented hyperpolarization and restored the normal K(+)-induced depolarization response. These results suggested that the Na(+),K(+)-ATPase was constitutively activated in the presence of MgtC resulting in a membrane potential largely dependent on Na(+),K(+)-ATPase. Consistent with the involvement of Na(+),K(+)-ATPase, oocytes expressing MgtC exhibited an increased rate of (86)Rb(+) uptake and had increased intracellular free [K(+)] and decreased free [Na(+)] and ATP. The free concentrations of Mg(2+) and Ca(2+) and cytosolic pH were unchanged, although the total intracellular Ca(2+) content was slightly elevated. These results suggest that the serovar Typhimurium MgtC protein may be involved in regulating membrane potential but does not directly transport Mg(2+) or another ion.
Collapse
Affiliation(s)
- Dorothee Günzel
- Institut für klinische Physiologie, Charité-Universitätsmedizin Berlin, D-12200 Berlin, Germany
| | | | | | | | | |
Collapse
|
6
|
Romani A. Regulation of magnesium homeostasis and transport in mammalian cells. Arch Biochem Biophys 2006; 458:90-102. [PMID: 16949548 DOI: 10.1016/j.abb.2006.07.012] [Citation(s) in RCA: 181] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2006] [Accepted: 07/21/2006] [Indexed: 02/06/2023]
Abstract
Magnesium is the second most abundant cation within the cell after potassium and plays an important role in numerous biological functions. Several pieces of experimental evidence indicate that mammalian cells tightly regulate Mg(2+) content by precise control mechanisms operating at the level of Mg(2+) entry and efflux across the cell membrane, as well as at the level of intracellular Mg(2+) buffering and organelle compartmentation under resting conditions and following hormonal stimuli. This review will attempt to elucidate the mechanisms involved in hormonal-mediated Mg(2+) extrusion and accumulation, as well as the physiological implications of changes in cellular Mg(2+) content following hormonal stimuli.
Collapse
Affiliation(s)
- Andrea Romani
- Department of Physiology and Biophysics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-4970, USA.
| |
Collapse
|
7
|
The MgtC virulence factor of Salmonella enterica serovar Typhimurium activates Na(+),K(+)-ATPase. J Bacteriol 2006. [PMID: 16855249 DOI: 10.1128/jb.00296-06/format/epub] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
The mgtC gene of Salmonella enterica serovar Typhimurium encodes a membrane protein of unknown function that is important for full virulence in the mouse. Since mgtC is part of an operon with mgtB which encodes a Mg(2+)-transporting P-type ATPase, MgtC was hypothesized to function in ion transport, possibly in Mg(2+) transport. Consequently, MgtC was expressed in Xenopus laevis oocytes, and its effect on ion transport was evaluated using ion selective electrodes. Oocytes expressing MgtC did not exhibit altered currents or membrane potentials in response to changes in extracellular H(+), Mg(2+), or Ca(2+), thus ruling out a previously postulated function as a Mg(2+)/H(+) antiporter. However, addition of extracellular K(+) markedly hyperpolarized membrane potential instead of the expected depolarization. Addition of ouabain to block the oocyte Na(+),K(+)-ATPase completely prevented hyperpolarization and restored the normal K(+)-induced depolarization response. These results suggested that the Na(+),K(+)-ATPase was constitutively activated in the presence of MgtC resulting in a membrane potential largely dependent on Na(+),K(+)-ATPase. Consistent with the involvement of Na(+),K(+)-ATPase, oocytes expressing MgtC exhibited an increased rate of (86)Rb(+) uptake and had increased intracellular free [K(+)] and decreased free [Na(+)] and ATP. The free concentrations of Mg(2+) and Ca(2+) and cytosolic pH were unchanged, although the total intracellular Ca(2+) content was slightly elevated. These results suggest that the serovar Typhimurium MgtC protein may be involved in regulating membrane potential but does not directly transport Mg(2+) or another ion.
Collapse
|
8
|
Almulla HA, Bush PG, Steele MG, Ellis D, Flatman PW. Loading rat heart myocytes with Mg2+ using low-[Na+] solutions. J Physiol 2006; 575:443-54. [PMID: 16793904 PMCID: PMC1819449 DOI: 10.1113/jphysiol.2006.109850] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The objective of our study was to investigate how Mg2+ enters mammalian cardiac cells. During this work, we found evidence for a previously undescribed route for Mg2+ entry, and now provide a preliminary account of its properties. Changes in Mg2+ influx into rat ventricular myocytes were deduced from changes in intracellular ionized Mg2+ concentration ([fMg2+]i) measured from the fluorescence of mag-fura-2 loaded into isolated cells. Superfusion of myocytes at 37 degrees C with Ca2+-free solutions with both reduced [Na+] and raised [Mg2+] caused myocytes to load with Mg2+. Uptake was seen with solutions containing 5 mm Mg2+ and 95 mm Na+, and increased linearly with increasing extracellular [Mg2+] or decreasing extracellular [Na+]. It was very sensitive to temperature (Q(10) > 9, 25--37 degrees C), was observed even in myocytes with very low Na+ contents, and stopped abruptly when external [Na+] was returned to normal. Uptake was greatly reduced by imipramine or KB-R7943 if these were added when [fMg2+]i was close to the physiological level, but was unaffected if they were applied when [fMg2+]i was above 2 mm. Uptake was also reduced by depolarizing the membrane potential by increasing extracellular [K+] or voltage clamp to 0 mV. We suggest that initial Mg2+ uptake may involve several transporters, including reversed Na+-Mg2+ antiport and, depending on the exact conditions, reversed Na+-Ca2+ antiport. The ensuing rise of [fMg2+]i, in conjunction with reduced [Na+], may then activate a new Mg2+ transporter that is highly sensitive to temperature, is insensitive to imipramine or KB-R7943, but is inactivated by depolarization.
Collapse
Affiliation(s)
- Hasan A Almulla
- Centre for Integrative Physiology, The University of Edinburgh, Hugh Robson Building, George Square, Edinburgh EH8 9XD, UK.
| | | | | | | | | |
Collapse
|
9
|
Almulla HA, Bush PG, Steele MG, Flatman PW, Ellis D. Sodium-dependent recovery of ionised magnesium concentration following magnesium load in rat heart myocytes. Pflugers Arch 2005; 451:657-67. [PMID: 16133259 DOI: 10.1007/s00424-005-1501-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2005] [Accepted: 07/21/2005] [Indexed: 11/24/2022]
Abstract
Our objectives were to investigate regulation of intracellular ionised Mg2+ concentration ([fMg2+]i) in cardiac muscle and cardiac Na+/Mg2+ antiport stoichiometry. [fMg2+]i was measured at 37 degrees C in isolated rat ventricular myocytes with mag-fura-2. Superfusion of myocytes with Na+ and Ca2+ free solutions containing 30 mM Mg2+ for 15 min more than doubled [fMg2+]i from its basal level (0.75 mM). Re-addition of Na+ caused [fMg2+]i to fall exponentially with time to basal level, the rate increasing linearly with [Na+]. Log(recovery rate) increased linearly with log([Na+]), the slope of 1.06 (95% confidence limits, 0.94-1.17) suggesting one Na+ ion is exchanged for each Mg2+. [fMg2+]i recovery was complete even if the membrane potential was depolarised to 0 mV or if superfusate [Mg2+] was increased to 3 mM. Recovery was rapid in normal Tyrode (0.3 min(-1)) with a Q10 of 2.2. It was completely inhibited by 200 microM imipramine but was unaffected by 20 microM KB-R7943 or 1 microM SEA0400, suggesting the Na+ /Ca2+ antiporter is not involved. Membrane depolarisation by increasing superfusate [K+] to 70 mM, or voltage clamp to 0 mV, increased recovery rate in Na+ containing solutions more than threefold. We conclude [fMg2+]i recovery is by Mg2+ efflux on a 1 Na+:1 Mg2+ antiport.
Collapse
Affiliation(s)
- Hasan A Almulla
- Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, The University of Edinburgh, Edinburgh, EH8 9XD, Scotland, UK
| | | | | | | | | |
Collapse
|
10
|
Günzel D, Hintz K, Durry S, Schlue WR. Mg2+-Malate Co-Transport, a Mechanism for Na+-Independent Mg2+Transport in Neurons of the LeechHirudo medicinalis. J Neurophysiol 2005; 94:441-53. [PMID: 15788520 DOI: 10.1152/jn.01221.2004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Mg2+-extrusion from Mg2+-loaded neurons of the leech, Hirudo medicinalis, is mediated mainly by Na+/Mg2+antiport. However, in a number of leech neurons, Mg2+is extruded in the nominal absence of extracellular Na+, indicating the existence of an additional, Na+-independent Mg2+transport mechanism. This mechanism was investigated using electrophysiological and microfluorimetrical techniques. The rate of Na+-independent Mg2+extrusion from Mg2+-loaded leech neurons was found to be independent of extracellular Ca2+, K+, NO3−, HCO3−, SO42−, HPO42−, and of intra- and extracellular pH. Na+-independent Mg2+extrusion was not inhibited by 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS), furosemide, ouabain, vanadate, iodoacetate, 4-amino-hippurate, or α-cyano-4-hydroxycinnamate and was not influenced by changes in the membrane potential in voltage-clamp experiments. Na+-independent Mg2+extrusion was, however, inhibited by the application of 2 mM probenecid, a blocker of organic anion transporters, suggesting that Mg2+might be co-transported with organic anions. Extracellularly, of all organic anions tested (malate, citrate, lactate, α-ketoglutarate, and 4-amino-hippurate) only high, but physiological, concentrations of malate (30 mM) had a significant inhibitory effect on Na+-independent Mg2+extrusion. Intracellularly, iontophoretically injected malate, citrate, or fura-2, but not Cl−, α-ketoglutarate, glutamate, succinate, or urate, were stimulating Na+-independent Mg2+extrusion from those neurons that initially did not extrude Mg2+in Na+-free solutions. Our data indicate that Mg2+is co-transported with organic anions, preferably with malate, the predominant extracellular anion in the leech. The proposed model implies that, under experimental conditions, malate drives Mg2+extrusion, whereas under physiological conditions, malate is actively taken up, driven by Mg2+, so that malate can be metabolized.
Collapse
Affiliation(s)
- Dorothee Günzel
- Institut für Klinische Physiologie, Heinrich-Heine-Universität Düsseldorf, Germany.
| | | | | | | |
Collapse
|
11
|
Tursun P, Tashiro M, Konishi M. Modulation of Mg2+ efflux from rat ventricular myocytes studied with the fluorescent indicator furaptra. Biophys J 2005; 88:1911-24. [PMID: 15626700 PMCID: PMC1305244 DOI: 10.1529/biophysj.104.055517] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2004] [Accepted: 12/22/2004] [Indexed: 11/18/2022] Open
Abstract
The fluorescent Mg(2+) indicator furaptra (mag-fura-2) was introduced into single ventricular myocytes by incubation with its acetoxy-methyl ester form. The ratio of furaptra's fluorescence intensity at 382 and 350 nm was used to estimate the apparent cytoplasmic [Mg(2+)] ([Mg(2+)](i)). In Ca(2+)-free extracellular conditions (0.1 mM EGTA) at 25 degrees C, [Mg(2+)](i) averaged 0.842 +/- 0.019 mM. After the cells were loaded with Mg(2+) by exposure to high extracellular [Mg(2+)] ([Mg(2+)](o)), reduction of [Mg(2+)](o) to 1 mM (in the presence of extracellular Na(+)) induced a decrease in [Mg(2+)](i). The rate of decrease in [Mg(2+)](i) was higher at higher [Mg(2+)](i), whereas raising [Mg(2+)](o) slowed the decrease in [Mg(2+)](i) with 50% reduction of the rate at approximately 10 mM [Mg(2+)](o). Because a part of the furaptra molecules were likely trapped inside intracellular organelles, we assessed possible contribution of the indicator fluorescence emitted from the organelles. When the cell membranes of furaptra-loaded myocytes were permeabilized with saponin (25 microg/ml for 5 min), furaptra fluorescence intensity at 350-nm excitation decreased to 22%; thus approximately 78% of furaptra fluorescence appeared to represent cytoplasmic [Mg(2+)] ([Mg(2+)](c)), whereas the residual 22% likely represented [Mg(2+)] in organelles (primarily mitochondria as revealed by fluorescence imaging). [Mg(2+)] calibrated from the residual furaptra fluorescence ([Mg(2+)](r)) was 0.6-0.7 mM in bathing solution [Mg(2+)] (i.e., [Mg(2+)](c) of the skinned myocytes) of either 0.8 mM or 4.0 mM, suggesting that [Mg(2+)](r) was lower than and virtually insensitive to [Mg(2+)](c). We therefore corrected furaptra fluorescence signals measured in intact myocytes for this insensitive fraction of fluorescence to estimate [Mg(2+)](c). In addition, by utilizing concentration and dissociation constant values of known cytoplasmic Mg(2+) buffers, we calculated changes in total Mg concentration to obtain quantitative information on Mg(2+) flux across the cell membrane. The calculations indicate that, in the presence of extracellular Na(+), Mg(2+) efflux is markedly activated by [Mg(2+)](c) above the normal basal level (approximately 0.9 mM), with a half-maximal activation of approximately 1.9 mM [Mg(2+)](c). We conclude that [Mg(2+)](c) is tightly regulated by an Mg(2+) efflux that is dependent on extracellular [Na(+)].
Collapse
Affiliation(s)
- Pulat Tursun
- Department of Physiology, Tokyo Medical University, 6-1-1 Shinjuku-ku, Tokyo 160-8402, Japan
| | | | | |
Collapse
|
12
|
Turner RJ, Van den Heuvel C, Vink R. Amiloride Increases Neuronal Damage after Traumatic Brain Injury in Rats. J Am Coll Nutr 2004; 23:534S-537S. [PMID: 15466959 DOI: 10.1080/07315724.2004.10719397] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
OBJECTIVE It is well known that traumatic brain injury (TBI) decreases brain free magnesium (Mg) concentration, and that administration of Mg salts after TBI restores concentration of Mg in brain and improves functional outcome. In the presence of hemorrhage, administration of Mg salts exacerbates the injury process and worsens outcome. An alternative to administration of Mg salts may be to prevent cellular loss of Mg with use of amiloride, which inhibits the Na(+)/Mg(2+) exchange. METHODS In the present study, male, adult Sprague-Dawley rats were injured using the impact acceleration model of diffuse TBI and administered either 100 mols/kg i.v. amiloride, or an equal volume of 50% DMSO/saline, 30 minutes (min) after injury. RESULTS Amiloride did not improve functional outcome (motor or cognitive outcome) after TBI relative to vehicle treated controls. Histologically, treatment with amiloride significantly increased hippocampal caspase-3 expression (apoptosis), axonal swellings in the medulla and the degree of dark cell change (cell stress) in the cortex. Phosphorus NMR demonstrated that amiloride did not increase free Mg concentration after injury. CONCLUSIONS Thus, amiloride is ineffective in preventing Mg loss after TBI when administered 30 min after trauma. Moreover, by administering amiloride after the TBI-related Mg decline has already been initiated, it may exacerbate injury by, in part by inhibiting Na(+)/Mg(2+) antiport and preventing entry of Mg back into the cell, and also by inhibiting other Na(+) linked transporters.
Collapse
Affiliation(s)
- Renee J Turner
- Department of Pathology, University of Adelaide, Adelaide, SA, Australia
| | | | | |
Collapse
|
13
|
Yamaoka K, Kameyama M. Regulation of L-type Ca2+ channels in the heart: overview of recent advances. Mol Cell Biochem 2004; 253:3-13. [PMID: 14619950 DOI: 10.1023/a:1026036931170] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Regulation of L-type Ca2+ channels is complex, because many factors, such as phosphorylation, divalent cations, and proteins, specified or unspecified, have been shown to affect the channel activities. An additional complication is that these factors interact with one another to achieve final outcomes. Recent molecular technologies have helped to shed light on the mechanisms governing the activity of L-type Ca2+ channels. In this review article, three major topics concerning regulation of L-type Ca2+ channels in the heart are discussed, i.e. c-AMP dependent channel phosphorylation, role of magnesium (Mg2+), and the phenomenon of channel run-down.
Collapse
Affiliation(s)
- Kaoru Yamaoka
- Department of Physiology, School of Medicine, Hiroshima University, Minami-Ku, Hiroshima, Japan.
| | | |
Collapse
|
14
|
Muller A, Gunzel D, Schlue WR. Activation of AMPA/kainate receptors but not acetylcholine receptors causes Mg2+ influx into Retzius neurones of the leech Hirudo medicinalis. ACTA ACUST UNITED AC 2004; 122:727-39. [PMID: 14638932 PMCID: PMC2229594 DOI: 10.1085/jgp.200308851] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In Retzius neurones of the medicinal leech, Hirudo medicinalis, kainate activates ionotropic glutamate receptors classified as AMPA/kainate receptors. Activation of the AMPA/kainate receptor-coupled cation channels evokes a marked depolarization, intracellular acidification, and increases in the intracellular concentrations of Na+ ([Na+]i) and Ca2+. Qualitatively similar changes are observed upon the application of carbachol, an activator of acetylcholine receptor-coupled cation channels. Using multibarrelled ion-selective microelectrodes it was demonstrated that kainate, but not carbachol, caused additional increases in the intracellular free Mg2+ concentration ([Mg2+]i). Experiments were designed to investigate whether this kainate-induced [Mg2+]i increase was due to a direct Mg2+ influx through the AMPA/kainate receptor-coupled cation channels or a secondary effect due to the depolarization or the ionic changes. It was found that: (a) Similar [Mg2+]i increases were evoked by the application of glutamate or aspartate. (b) All kainate-induced effects were inhibited by the glutamatergic antagonist DNQX. (c) The magnitude of the [Mg2+]i increases depended on the extracellular Mg2+ concentration. (d) A reduction of the extracellular Ca2+ concentration increased kainate-induced [Mg2+]i increases, excluding possible Ca2+ interference at the Mg2+-selective microelectrode or at intracellular buffer sites. (e) Neither depolarizations evoked by the application of 30 mM K+, nor [Na+]i increases induced by the inhibition of the Na+/K+ ATPase caused comparable [Mg2+]i increases. (f) Inhibitors of voltage-dependent Ca2+ channels did not affect the kainate-induced [Mg2+]i increases. Moreover, previous experiments had already shown that intracellular acidification evoked by the application of 20 mM propionate did not cause changes in [Mg2+]i. The results indicate that kainate-induced [Mg2+]i increases in leech Retzius neurones are due to an influx of extracellular Mg2+ through the AMPA/kainate receptor-coupled cation channel. Mg2+ may thus act as an intracellular signal to distinguish between glutamatergic and cholinergic activation of leech Retzius neurones.
Collapse
Affiliation(s)
- Anja Muller
- Institut für Neurobiologie, Heinrich-Heine-Universität Düsseldorf, Germany
| | | | | |
Collapse
|
15
|
Gee JB, Corbett RJT, Perlman J, Laptook AR. The effects of systemic magnesium sulfate infusion on brain magnesium concentrations and energy state during hypoxia-ischemia in newborn miniswine. Pediatr Res 2004; 55:93-100. [PMID: 14561783 DOI: 10.1203/01.pdr.0000099771.39629.e5] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The mechanism of neuroprotection associated with systemically administered magnesium remains unclear. This investigation examined the acute effects of systemically administered MgSO4 on brain extracellular ([Mg]ecf) and intracellular ([Mg]i) fluid Mg concentrations, specific brain phosphorylated metabolites, and brain intracellular pH. Miniswine were studied with P-31 magnetic resonance spectra, to derive [Mg]i, and brain microdialysis probes, to measure [Mg]ecf. Animals were infused with MgSO4 (n = 5, 275 mg/kg over 30 min followed by 100 mg/kg over 30 min, designated MgHI) or Na2SO4 (n = 5, designated NaHI), and both groups underwent hypoxia-ischemia (HI) over the last 15 min of the infusions. Groups differed in plasma [Mg] at the completion of HI (9.1 +/- 1.5 versus 1.1 +/- 0.6 mM for MgHI and NaHI, respectively, p < 0.05). MgHI had elevations of [Mg]ecf (0.23 +/- 0.11 and 0.40 +/- 0.14 mM at control and completion of HI, respectively), and [Mg]ecf was unchanged for NaHI (p < 0.05 versus MgHI). At the completion of HI, MgHI had greater decreases in nucleoside triphosphate (NTP) (48 +/- 6% of control), and more brain acidosis after HI (6.01 +/- 0.07) compared with NaHI (NTP, 70 +/- 3% of control; brain pH, 6.51 +/- 0.14, both p < 0.05 versus MgHI). [Mg]i increased to elevated values during HI in both MgHI and NaHI (p < 0.05 versus control of each group) and remained higher in MgHI over the next 25 min (p < 0.05 versus NaHI). There were inverse correlations during HI between [Mg]i and brain NTP (r2 = 0.73 and 0.59 for MgHI and NaHI, respectively), and brain acidosis (r2 = 0.85 and 0.85 for MgHI and NaHI, respectively) in each group. These findings indicate complex effects of Mg on the brain. Elevation of [Mg]ecf may be beneficial with regards to excitatory neurotransmitters. However, greater disturbance of brain NTP concentration, more acidosis, and the increase in [Mg]i may offset any benefit. The results warrant further investigation using indicators of neuronal injury to determine whether Mg supplementation provides neuroprotection.
Collapse
Affiliation(s)
- Jerry B Gee
- Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas, TX 75390-9063, USA.
| | | | | | | |
Collapse
|
16
|
Günzel D, Zimmermann F, Durry S, Schlue WR. Apparent intracellular Mg2+ buffering in neurons of the leech Hirudo medicinalis. Biophys J 2001; 80:1298-310. [PMID: 11222292 PMCID: PMC1301323 DOI: 10.1016/s0006-3495(01)76104-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
The apparent intracellular Mg2+ buffering, or muffling (sum of processes that damp changes in the free intracellular Mg2+ concentration, [Mg2+](i), e.g., buffering, extrusion, and sequestration), was investigated in Retzius neurons of the leech Hirudo medicinalis by iontophoretic injection of H+, OH-, or Mg2+. Simultaneously, changes in intracellular pH and the intracellular Mg2+, Na+, or K+ concentration were recorded with triple-barreled ion-selective microelectrodes. Cell volume changes were monitored measuring the tetramethylammonium (TMA) concentration in TMA-loaded neurons. Control measurements were carried out in electrolyte droplets (diameter 100-200 microm) placed on a silver wire under paraffin oil. Droplets with or without ATP, the presumed major intracellular Mg2+ buffer, were used to quantify the pH dependence of Mg2+ buffering and to determine the transport index of Mg2+ during iontophoretic injection. The observed pH dependence of [Mg2+](i) corresponded to what would be expected from Mg2+ buffering through ATP. The quantity of Mg2+ muffling, however, was considerably larger than what would be expected if ATP were the sole Mg2+ buffer. From the decrease in Mg2+ muffling in the nominal absence of extracellular Na+ it was estimated that almost 50% of the ATP-independent muffling is due to the action of Na+/Mg2+ antiport.
Collapse
Affiliation(s)
- D Günzel
- Institut für Neurobiologie, Heinrich-Heine-Universität Düsseldorf, D-40225 Düsseldorf, Germany.
| | | | | | | |
Collapse
|
17
|
Schweigel M, Vormann J, Martens H. Mechanisms of Mg(2+) transport in cultured ruminal epithelial cells. Am J Physiol Gastrointest Liver Physiol 2000; 278:G400-8. [PMID: 10712259 DOI: 10.1152/ajpgi.2000.278.3.g400] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Net Mg(2+) absorption from the rumen is mainly mediated by a transcellular pathway, with the greater part (62%) being electrically silent. To investigate this component of Mg(2+) transport, experiments were performed with isolated ruminal epithelial cells (REC). Using the fluorescent indicators mag-fura 2, sodium-binding benzofuran isophthalate, and 2', 7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein, we measured the intracellular free Mg(2+) concentration ([Mg(2+)](i)), the intracellular Na(+) concentration ([Na(+)](i)), and the intracellular pH (pH(i)) of REC under basal conditions, after stimulation with butyrate and HCO(-)(3), and after changing the transmembrane chemical gradients for Mg(2+), H(+), and Na(+). REC had a mean resting pH(i) of 6.83 +/- 0.1, [Mg(2+)](i) was 0.56 +/- 0. 14 mM, and [Na(+)](i) was 18.95 +/- 3.9 mM. Exposure to both HCO(-)(3) and HCO(-)(3)/butyrate led to a stimulation of Mg(2+) influx that amounted to 27.7 +/- 5 and 29 +/- 10.6 microM/min, respectively, compared with 15 +/- 1 microM/min in control solution. The increase of [Mg(2+)](i) was dependent on extracellular Mg(2+) concentration ([Mg(2+)](e)). Regulation of pH(i) has been demonstrated to be Na(+) dependent and is performed, for the most part, by a Na(+)/H(+) exchanger. The recovery of pH(i) was fully blocked in nominally Na(+)-free media, even if [Mg(2+)](e) was stepwise increased from 0 to 7.5 mM. However, an increase of [Mg(2+)](i) was observed after reversing the transmembrane Na(+) gradient. This rise in [Mg(2+)](i) was pH independent, K(+) insensitive, dependent on [Mg(2+)](e), imipramine and quinidine sensitive, and accompanied by a decrease of [Na(+)](i). The results are consistent with the existence of a Na(+)/Mg(2+) exchanger in the cell membrane of REC. The coupling between butyrate, CO(2)/HCO(-)(3), and Mg(2+) transport may be mediated by another mechanism, perhaps by cotransport of Mg(2+) and HCO(-)(3).
Collapse
Affiliation(s)
- M Schweigel
- Department of Veterinary Physiology, Free University of Berlin, 14163 Berlin, Germany.
| | | | | |
Collapse
|
18
|
Cefaratti C, Romani A, Scarpa A. Differential localization and operation of distinct Mg(2+) transporters in apical and basolateral sides of rat liver plasma membrane. J Biol Chem 2000; 275:3772-80. [PMID: 10660526 DOI: 10.1074/jbc.275.6.3772] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Upon activation of specific cell signaling, hepatocytes rapidly accumulate or release an amount of Mg(2+) equivalent to 10% of their total Mg(2+) content. Although it is widely accepted that Mg(2+) efflux is Na(+)-dependent, little is known about transporter identity and the overall regulation. Even less is known about the mechanism of cellular Mg(2+) uptake. Using sealed and right-sided rat liver plasma membrane vesicles representing either the basolateral (bLPM) or apical (aLPM) domain, it was possible to dissect three different Mg(2+) transport mechanisms based upon specific inhibition, localization within the plasma membrane, and directionality. The bLPM possesses only one Mg(2+) transporter, which is strictly Na(+)-dependent, bi-directional, and not inhibited by amiloride. The aLPM possesses two separate Mg(2+) transporters. One, similar to that in the bLPM because it strictly depends on Na(+) transport, and it can be differentiated from that of the bLPM because it is unidirectional and fully inhibited by amiloride. The second is a novel Ca(2+)/Mg(2+) exchanger that is unidirectional and inhibited by amiloride and imipramine. Hence, the bLPM transporter may be responsible for the exchange of Mg(2+) between hepatocytes and plasma, and vice versa, shown in livers upon specific metabolic stimulation, whereas the aLPM transporters can only extrude Mg(2+) into the biliary tract. The dissection of these three distinct pathways and, therefore, the opportunity to study each individually will greatly facilitate further characterization of these transporters and a better understanding of Mg(2+) homeostasis.
Collapse
Affiliation(s)
- C Cefaratti
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4970, USA
| | | | | |
Collapse
|
19
|
Günzel D, Müller A, Durry S, Schlue WR. Multi-barrelled ion-sensitive microelectrodes and their application in micro-droplets and biological systems. Electrochim Acta 1999. [DOI: 10.1016/s0013-4686(99)00084-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
|
20
|
Kilb W, Schlue WR. Mechanism of the kainate-induced intracellular acidification in leech Retzius neurons. Brain Res 1999; 824:168-82. [PMID: 10196447 DOI: 10.1016/s0006-8993(99)01212-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
We examined the effect of the glutamatergic agonist kainate on the membrane potential, the intracellular Na+ concentration ([Na+]i), the intracellular-free Ca2+ concentration, and on the intracellular pH of Retzius neurons of the medicinal leech, Hirudo medicinalis, in order to investigate the mechanism responsible for the intracellular acidification caused by glutamatergic stimulation. The recordings were made with Na+- and pH-sensitive microelectrodes and iontophoretically injected Fura-2. Bath application of kainate evoked a marked membrane depolarization, a [Na+]i increase, and an intracellular acidification. The intracellular acidification was unaffected by reversal of the electromotive force for H+, suggesting that an influx of H+ from the interstitial space does not contribute to the acidification. While the Ca2+ channel blockers La3+ and Co2+ had no effect on the kainate-induced intracellular acidification, suggesting that a Ca2+ influx via voltage-dependent Ca2+ channels was not relevant, the acidification was reduced in Ca2+-free saline solution. In Na+-free saline solution the kainate-induced intracellular acidification was absent, suggesting the involvement of Na+ influx in generating the acidification. When injected iontophoretically Na+ induced an intracellular acidification but Li+, K+, Rb+ or Cs+ did not. Furthermore, a [Na+]i increase induced by blocking the Na+/K+ pump also led to an intracellular acidification. We conclude that the [Na+]i increase is the crucial event underlying the kainate-induced intracellular acidification. Possible mechanisms linking the [Na+]i increase to the intracellular acidification are discussed.
Collapse
Affiliation(s)
- W Kilb
- Institut für Neurobiologie, Heinrich-Heine-Universität Düsseldorf, Universitätsstr. 1, D-40225, Düsseldorf, Germany
| | | |
Collapse
|
21
|
Reynolds IJ. Intracellular calcium and magnesium: critical determinants of excitotoxicity? PROGRESS IN BRAIN RESEARCH 1999; 116:225-43. [PMID: 9932380 DOI: 10.1016/s0079-6123(08)60440-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/10/2023]
Affiliation(s)
- I J Reynolds
- Department of Pharmacology, University of Pittsburgh, PA 15261-0001, USA
| |
Collapse
|
22
|
Tessman PA, Romani A. Acute effect of EtOH on Mg2+ homeostasis in liver cells: evidence for the activation of an Na+/Mg2+ exchanger. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 275:G1106-16. [PMID: 9815041 DOI: 10.1152/ajpgi.1998.275.5.g1106] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
The acute administration of ethanol mobilizes a considerable amount of Mg2+ from perfused rat livers and isolated hepatocytes in a dose-dependent fashion in the absence of release of cellular K+ or lactate dehydrogenase (LDH) in the extracellular medium. Mg2+ extrusion becomes detectable within 2 min and reaches the maximum within 8 min after ethanol addition, declining toward the basal value thereafter irrespective of the persistence of alcohol in the perfusion system and the dose of ethanol administered. The effect is the result of a specific impairment of Mg2+ transport and/or regulatory mechanisms. In fact, Mg2+ extrusion does not occur under conditions in which 1) ethanol is replaced by an equivalent dose of DMSO, 2) amiloride or imipramine are used as inhibitors of the Na+/Mg2+ exchanger, 3) extracellular Na+ is replaced by an equimolar concentration of choline chloride, and 4) 4-methylpyrazole is used to specifically inhibit alcohol dehydrogenase and cytochrome P-4502E1. Finally, the observation that the cellular level of ATP is markedly reduced after acute ethanol administration would suggest that Mg2+ extrusion results from a decreased buffering capacity of cytosolic Mg-ATP complex.
Collapse
Affiliation(s)
- P A Tessman
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio 44106-4970, USA
| | | |
Collapse
|
23
|
Affiliation(s)
- D Bruns
- Howard Hughes Medical Institute, Boyer Center for Molecular Medicine, Yale University School of Medicine, New Haven, Connecticut 06510, USA
| |
Collapse
|
24
|
Cefaratti C, Romani A, Scarpa A. Characterization of two Mg2+ transporters in sealed plasma membrane vesicles from rat liver. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 275:C995-C1008. [PMID: 9755053 DOI: 10.1152/ajpcell.1998.275.4.c995] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The plasma membrane of mammalian cells possesses rapid Mg2+ transport mechanisms. The identity of Mg2+ transporters is unknown, and so are their properties. In this study, Mg2+ transporters were characterized using a biochemically and morphologically standardized preparation of sealed rat liver plasma membranes (LPM) whose intravesicular content could be set and controlled. The system has the advantages that it is not regulated by intracellular signaling machinery and that the intravesicular ion milieu can be designed. The results indicate that 1) LPM retain trapped intravesicular total Mg2+ with negligible leak; 2) the addition of Na+ or Ca2+ induces a concentration- and temperature-dependent efflux corresponding to 30-50% of the intravesicular Mg2+; 3) the rate of flux is very rapid (137.6 and 86.8 nmol total Mg2+ . micrometer -2 . min-1 after Na+ and Ca2+ addition, respectively); 4) coaddition of maximal concentrations of Na+ and Ca2+ induces an additive Mg2+ efflux; 5) both Na+- and Ca2+-stimulated Mg2+ effluxes are inhibited by amiloride, imipramine, or quinidine but not by vanadate or Ca2+ channel blockers; 6) extracellular Na+ or Ca2+ can stimulate Mg2+ efflux in the absence of Mg2+ gradients; and 7) Mg2+ uptake occurs in LPM loaded with Na+ but not with Ca2+, thus indicating that Na+/Mg2+ but not Ca2+/Mg2+ exchange is reversible. These data are consistent with the operation of two distinct Mg2+ transport mechanisms and provide new information on rates of Mg2+ transport, specificity of the cotransported ions, and reversibility of the transport.
Collapse
Affiliation(s)
- C Cefaratti
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4970, USA
| | | | | |
Collapse
|
25
|
Abstract
The effects of carbamate anticholinesterases, pyridostigmine and physostigmine, on the function of the nicotinic receptor (nAChR) in TE671 cells was studied, precluding their inhibition of acetylcholine hydrolysis by carbachol usage. In radioassay, the simultaneous application of carbachol and carbamates dose-dependently decreased carbachol-induced 22Na+ influx, compared with carbachol activation alone. Increasing cell preincubation in the presence of carbamates, however, potentiated influx at low concentrations in a time-dependent manner. This facilitating effect of carbamates, even at high concentrations, was significantly increased by washing out these drugs and was blocked by pretreatment with diisopropylfluorophosphate. Similar results were also obtained in whole-cell patch-clamp study. There were insignificant changes in desensitization properties during facilitation. It is thus supposed that facilitation cannot be explained by the inhibition of acetylcholine hydrolysis. These results support a previous hypothesis that acetylcholinesterase might modulate nAChR by an unknown mechanism. In addition, the clinical effects of carbamates may be partly attributed to this facilitation.
Collapse
Affiliation(s)
- J J Sung
- Department of Pharmacology, Neuroscience Research Institute, Seoul, Korea
| | | | | | | | | | | | | | | |
Collapse
|
26
|
Prudnikov IM, Tsyvkin VN. Agonist-dependent attenuation of GTPase activity of G proteins coupled to dopamine receptors in the molluscan nervous system. NEUROPHYSIOLOGY+ 1998. [DOI: 10.1007/bf02463056] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
|
27
|
Tashiro M, Konishi M. Na+ gradient-dependent Mg2+ transport in smooth muscle cells of guinea pig tenia cecum. Biophys J 1997; 73:3371-84. [PMID: 9414247 PMCID: PMC1181238 DOI: 10.1016/s0006-3495(97)78361-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Thin strips of guinea pig tenia cecum were loaded with the Mg2+ indicator furaptra, and the indicator fluorescence signals measured in Ca2+-free condition were converted to cytoplasmic-free Mg2+ concentration ([Mg2+]i). Lowering the extracellular Na+ concentration ([Na+]o) caused a reversible increase in [Mg2+]i, consistent with the inhibition of Na+ gradient-dependent extrusion of cellular Mg2+ (Na+-Mg2+ exchange). Curve-fitting analysis indicated that the relation between [Na+]o and the rate of rise in [Mg2+], had a Hill coefficient of approximately 3, a [Na+]o at the half-maximal rate of rise of approximately 30 mM, and a maximal rate of 0.16 +/- 0.01 microM/s (mean +/- SE, n = 6). Depolarization with 56 mM K+ shifted the curve slightly toward higher [Na+]o without significantly changing the maximal rate, suggesting that the Na+-Mg2+ exchange was inhibited by depolarization. The maximal rate would correspond to a flux of 0.15-0.4 pmol/cm2/s, if cytoplasmic Mg2+ buffering power (defined as the ratio of the changes in total Mg2+ and free Mg2+ concentrations) is assumed to be 2-5. Ouabain (1-5 microM) increased the intracellular Na+ concentration, as assessed with fluorescence of SBFI (sodium-binding benzofuran isophthalate, a Na+ indicator), and elevated [Mg2+]i. In ouabain-treated preparations, removal of extracellular Na+ rapidly increased [Mg2+]i, with an initial rate of rise roughly proportional to the degree of the Mg2+ load, and, probably, to the Na+ load caused by ouabain. The enhanced rate of rise in [Mg2+]i (up to approximately 1 microM/s) could be attributed to the Mg2+ influx as a result of the reversed Na+-Mg2+ exchange. Our results support the presence of a reversible and possibly electrogenic Na+-Mg2+ exchange in the smooth muscle cells of tenia cecum.
Collapse
Affiliation(s)
- M Tashiro
- Department of Physiology, The Jikei University School of Medicine, Tokyo, Japan.
| | | |
Collapse
|
28
|
Wolf FI, Di Francesco A, Covacci V, Cittadini A. Regulation of magnesium efflux from rat spleen lymphocytes. Arch Biochem Biophys 1997; 344:397-403. [PMID: 9264554 DOI: 10.1006/abbi.1997.0199] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Rat spleen lymphocytes (RSL) incubated at 37 degrees C in Mg-free medium (O-trans conditions) exibited Mg2+ efflux with apparent velocity of 0.2 nmol/mg protein/min. After 30 min, this process accounted for the mobilization of about 15% of cell total Mg2+. Half of the Mg2+ efflux depended on extracellular Na+ and was stimulated by cAMP. IFN-alpha significantly enhanced Mg2+ efflux under O-trans conditions as well as in the presence of physiological extracellular Mg2+. Pretreatment of RSL with indomethacin completely abolished IFN-alpha-induced Mg2+ efflux, suggesting a crucial role for cyclooxygenase-dependent arachidonate metabolism. On the other hand, pretreatment of RSL with the PKA inhibitor (Rp)8-Br-cAMPS prevented IFN-alpha stimulation of Mg2+ efflux, indicating the involvement of cAMP. Consistently, both IFN-alpha and exogenous PGE1 increased cAMP from 50 to 125 pmol/mg protein. Altogether these results show that IFN-alpha stimulates Mg2+ efflux by activating arachidonate metabolism and synthesis of prostaglandins. By influencing adenylcyclase activity, PGEs can eventually promote cAMP-dependent Mg2+ efflux, possibly through the activity of a Na-Mg antiport. In RSL, therefore, magnesium movements can be under the control of IFN-alpha and, perhaps, of other cytokines, suggesting the involvement of Mg2+ in cell response to receptor-mediated stimuli.
Collapse
Affiliation(s)
- F I Wolf
- Institute of General Pathology and Giovanni XXIII Cancer Research Centre, Università Cattolica del Sacro Cuore, Rome, Italy
| | | | | | | |
Collapse
|
29
|
Lohrengel M. Interface and volume effects in biological cells and electrochemical microcells. Electrochim Acta 1997. [DOI: 10.1016/s0013-4686(97)00177-1] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
|
30
|
Spichiger U, Fakler A. Potentiometric microelectrodes as sensor and detectors. Magnesium-selective electrodes as sensors, and hofmeister electrodes as detectors for histamine in capillary electrophoresis. Electrochim Acta 1997. [DOI: 10.1016/s0013-4686(97)00167-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
|
31
|
Intracellular Mg2+ is regulated by antiport in neurones of an invertebrate central nervous system. Electrochim Acta 1997. [DOI: 10.1016/s0013-4686(97)00194-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
|