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Stevanović KS, Čepkenović B, Križak S, Pajić T, Todorović NV, Živić MŽ. ATP modulation of osmotically activated anionic current in the membrane of Phycomyces blakesleeanus sporangiophore. Sci Rep 2023; 13:11897. [PMID: 37488205 PMCID: PMC10366193 DOI: 10.1038/s41598-023-39021-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Accepted: 07/19/2023] [Indexed: 07/26/2023] Open
Abstract
Ion channels are vital components of filamentous fungi signaling in communication with their environment. We exploited the ability of the apical region of growing sporangiophores of Phycomyces blakesleeanus to form membrane-enveloped cytoplasmic droplets (CDs), to examine ion currents in the filamentous fungi native plasma membrane. In hypoosmotic conditions, the dominant current in the CDs is ORIC, an osmotically activated, anionic, outwardly rectified, fast inactivating instantaneous current that we have previously characterized. Here, we examined the effect of ATP on ORIC. We show that CDs contain active mitochondria, and that respiration inhibition by azide accelerates ORIC inactivation. ATP, added intracellularly, reduced ORIC run-down and shifted the voltage dependence of inactivation toward depolarized potentials, in a manner that did not require hydrolysis. Notably, ATP led to slowing down of ORIC inactivation, as evidenced by an increased time constant of inactivation, τin, and slower decline of τin during prolonged recordings. Flavonoids (genistein and quercetin) had the effect on ORIC opposite to ATP, acting as current inhibitors, possibly by disrupting the stabilizing effect of ATP on ORIC. The integration of osmotic sensing with ATP dependence of the anionic current, typical of vertebrate cells, is described here for the first time in filamentous fungi.
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Affiliation(s)
- Katarina S Stevanović
- Faculty of Biology, Institute of Physiology and Biochemistry, University of Belgrade, Studentski Trg 16, Belgrade, 11158, Serbia
| | - Bogdana Čepkenović
- Faculty of Biology, Institute of Physiology and Biochemistry, University of Belgrade, Studentski Trg 16, Belgrade, 11158, Serbia
| | - Strahinja Križak
- Institute of Multidisciplinary Research, University of Belgrade, Kneza Višeslava 1, Belgrade, 11030, Serbia
| | - Tanja Pajić
- Faculty of Biology, Institute of Physiology and Biochemistry, University of Belgrade, Studentski Trg 16, Belgrade, 11158, Serbia
| | - Nataša V Todorović
- Institute for Biological Research "Siniša Stanković", University of Belgrade, National Institute of the Republic of Serbia, Bulevar Despota Stefana 142, Belgrade, 11000, Serbia.
| | - Miroslav Ž Živić
- Faculty of Biology, Institute of Physiology and Biochemistry, University of Belgrade, Studentski Trg 16, Belgrade, 11158, Serbia
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Chen YJ, Cheng FC, Chen CJ, Su HL, Sheu ML, Sheehan J, Pan HC. Down-Regulated Expression of Magnesium Transporter Genes Following a High Magnesium Diet Attenuates Sciatic Nerve Crush Injury. Neurosurgery 2020; 84:965-976. [PMID: 29672725 DOI: 10.1093/neuros/nyy120] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2017] [Accepted: 03/10/2018] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND Magnesium supplementation has potential for use in nerve regeneration. The expression of some magnesium transporter genes is reflective of the intracellular magnesium levels. OBJECTIVE To assess the expression of various magnesium transporter genes as they relate to neurological alterations in a sciatic nerve injury model. METHODS Sciatic nerve injury was induced in rats, which were then fed either basal or high magnesium diets. Magnesium concentrations and 5 magnesium transporter genes (SLC41A1, MAGT1, CNNM2, TRPM6, and TRPM7) were measured in the tissue samples. RESULTS The high magnesium diet attenuated cytoskeletal loss in a dose-dependent manner in isolated nerve explants. The high magnesium diet augmented nerve regeneration and led to the restoration of nerve structure, increased S-100, and neurofilaments. This increased regeneration was consistent with the improvement of neurobehavioral and electrophysiological assessment. The denervated muscle morphology was restored with the high magnesium diet, and that was also highly correlated with the increased expression of desmin and acetylcholine receptors in denervated muscle. The plasma magnesium levels were significantly elevated after the animals consumed a high magnesium diet and were reciprocally related to the down-regulation of CNNM2, MagT1, and SCL41A1 in the blood monocytes, nerves, and muscle tissues of the nerve crush injury model. CONCLUSION The increased plasma magnesium levels after consuming a high magnesium diet were highly correlated with the down-regulation of magnesium transporter genes in monocytes, nerves, and muscle tissues after sciatic nerve crush injury. The study findings suggest that there are beneficial effects of administering magnesium after a nerve injury.
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Affiliation(s)
- Ying-Ju Chen
- Department of food and nutrition, Providence University, Taichung, Taiwan
| | - Fu-Chou Cheng
- Department of Medical Research, Taichung Veterans General Hospital, Taichung, Taiwan
| | - Chun-Jung Chen
- Department of Medical Research, Taichung Veterans General Hospital, Taichung, Taiwan
| | - Hong-Lin Su
- Department of Life Sciences, Agriculture Biotechnology Center, National Chung-Hsing University, Taichung, Taiwan
| | - Meei-Ling Sheu
- Institute of Biomedical Sciences, National Chung-Hsing University, Taichung, Taiwan
| | - Jason Sheehan
- Department of Neurosurgery, University of Virginia, Charlottesville, Virginia
| | - Hung-Chuan Pan
- Department of Neurosurgery, Taichung Veterans General Hospital, Taichung, Taiwan.,Faculty of Medicine, School of Medicine, National Yang-Ming University, Taipei, Taiwan
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Wu M, Tran PN, Sheng J, Randolph AL, Wu WW. Drug potency on inhibiting late Na + current is sensitive to gating modifier and current region where drug effects were measured. J Pharmacol Toxicol Methods 2019; 100:106605. [PMID: 31255744 DOI: 10.1016/j.vascn.2019.106605] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2019] [Revised: 06/18/2019] [Accepted: 06/24/2019] [Indexed: 12/19/2022]
Abstract
INTRODUCTION Cardiac late Na+ current (INaL) contributes to ventricular action potential duration. Pathological increase in INaL is arrhythmogenic, and inhibition of INaL offers protection against ventricular repolarization disturbance. Recently, two INaL datasets generated by different laboratories that assessed current inhibition by a panel of clinical drugs as a part of the Comprehensive in vitro Proarrhythmia Assay (CiPA) initiative were published. The results revealed a surprising degree of data variability despite of the use of a standardized voltage protocol. This study investigated whether remaining procedural differences related to experimental methods and data analysis associated with these datasets can produce differences in INaL pharmacology. METHODS Whole cell voltage clamp recordings were performed on cells expressing NaV1.5 α- and β1-subunits to study: 1) the impact of gating modifiers used to augment INaL (ATX-II vs. veratridine), internal solution composition (with vs. without ATP and GTP), and recording temperature (23 °C vs 37 °C) on stability of INaL measured across the duration of a patch clamp experiment; 2) mechanisms of each gating modifier on Na+ channels; and 3) effects of six drugs (lidocaine, mexiletine, chloroquine, ranolazine, ritonavir, and verapamil) on INaL induced by either gating modifier. RESULTS Stability of INaL is affected by the choice of gating modifier, presence of nucleotides in the internal solution, and recording temperature. ATX-II and veratridine produced different changes in Na+ channel gating, inducing mechanistically distinct INaL. Drug potencies on inhibiting INaL were dependent on the choice of gating modifier and current region where drug effects were measured. DISCUSSION INaL pharmacology can be impacted by all experimental factors examined in this study. The effect of gating modifier and current region used to quantify drug inhibition alone led to 30× difference in half inhibitory concentration (IC50) for ritonavir, demonstrating that substantial difference in drug inhibition can be produced. Drug potencies on inhibiting INaL derived from different patch clamp studies may thus not be generalizable. For INaL pharmacology to be useful for in silico modeling or interpreting drug-induced changes in cardiac action potentials or ECG, standardizing INaL experimental procedures including data analysis methods is necessary to minimize data variability.
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Affiliation(s)
- Min Wu
- Division of Applied Regulatory Science, Office of Clinical Pharmacology, Center for Drug Evaluation and Research, The US Food and Drug Administration, 10903 New Hampshire Avenue, Silver Spring, MD 20993, United States of America
| | - Phu N Tran
- Division of Applied Regulatory Science, Office of Clinical Pharmacology, Center for Drug Evaluation and Research, The US Food and Drug Administration, 10903 New Hampshire Avenue, Silver Spring, MD 20993, United States of America
| | - Jiansong Sheng
- Division of Applied Regulatory Science, Office of Clinical Pharmacology, Center for Drug Evaluation and Research, The US Food and Drug Administration, 10903 New Hampshire Avenue, Silver Spring, MD 20993, United States of America
| | - Aaron L Randolph
- Division of Applied Regulatory Science, Office of Clinical Pharmacology, Center for Drug Evaluation and Research, The US Food and Drug Administration, 10903 New Hampshire Avenue, Silver Spring, MD 20993, United States of America
| | - Wendy W Wu
- Division of Applied Regulatory Science, Office of Clinical Pharmacology, Center for Drug Evaluation and Research, The US Food and Drug Administration, 10903 New Hampshire Avenue, Silver Spring, MD 20993, United States of America.
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Harraz OF, Longden TA, Hill-Eubanks D, Nelson MT. PIP 2 depletion promotes TRPV4 channel activity in mouse brain capillary endothelial cells. eLife 2018; 7:38689. [PMID: 30084828 PMCID: PMC6117155 DOI: 10.7554/elife.38689] [Citation(s) in RCA: 101] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2018] [Accepted: 08/06/2018] [Indexed: 01/08/2023] Open
Abstract
We recently reported that the inward-rectifier Kir2.1 channel in brain capillary endothelial cells (cECs) plays a major role in neurovascular coupling (NVC) by mediating a neuronal activity-dependent, propagating vasodilatory (hyperpolarizing) signal. We further demonstrated that Kir2.1 activity is suppressed by depletion of plasma membrane phosphatidylinositol 4,5-bisphosphate (PIP2). Whether cECs express depolarizing channels that intersect with Kir2.1-mediated signaling remains unknown. Here, we report that Ca2+/Na+-permeable TRPV4 (transient receptor potential vanilloid 4) channels are expressed in cECs and are tonically inhibited by PIP2. We further demonstrate that depletion of PIP2 by agonists, including putative NVC mediators, that promote PIP2 hydrolysis by signaling through Gq-protein-coupled receptors (GqPCRs) caused simultaneous disinhibition of TRPV4 channels and suppression of Kir2.1 channels. These findings collectively support the concept that GqPCR activation functions as a molecular switch to favor capillary TRPV4 activity over Kir2.1 signaling, an observation with potentially profound significance for the control of cerebral blood flow. Capillaries form branching networks that surround all cells of the body. They allow oxygen and nutrient exchange between blood and tissue, but this is not their only role. Capillaries in the brain form a tight barrier that prevents components carried in the blood from easily reaching the brain compartment. They also detect the activity of neurons and trigger on-demand increases in blood flow to active regions of the brain. This role, revealed only recently, depends upon ion channels on the surface of the capillary cells. Active neurons release potassium ions, which open a type of ion channel called Kir2.1 that allows potassium inside the cell to flow out. This process is repeated in neighboring capillary cells until it reaches an upstream vessel, where it causes the vessel to relax and increase the blood flow. Kir2.1 channels sit astride the membranes of capillary cells, where they can interact with other membrane molecules. One such molecule, called PIP2, plays several roles in relaying signals from the outside to the inside of cells. It also physically interacts with channels in the membrane, including Kir2.1 channels. If PIP2 levels are low, Kir2.1 channel activity decreases. Here, Harraz et al. discovered that capillary cells contain another type of ion channel, called TRPV4, which is also regulated by PIP2. But unlike Kir2.1, its activity increases when PIP2 levels drop. Moreover, TRPV4 channels allow sodium and calcium ions to flow into the cell, which has an effect opposite to that of potassium flowing out of the cell. Capillary cells also have receptor proteins called GqPCRs that are activated by chemical signals released by active neurons in the brain. GqPCRs break down PIP2, so their activity turns Kir2.1 channels off and TRPV4 channels on. This resets the system so that it is ready to respond to new signals from active neurons. GqPCRs work as molecular switches to control the balance between Kir2.1 and TRPV4 channels and turn brain blood flow up and down. GqPCRs and ion channels that depend on PIP2 can also be found in other types of cells. These findings could reveal clues about how signals are switched on and off in different cells. Understanding the role of PIP2 in signaling could also unveil what happens when signaling go wrong.
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Affiliation(s)
- Osama F Harraz
- Department of Pharmacology, University of Vermont, Burlington, United States
| | - Thomas A Longden
- Department of Pharmacology, University of Vermont, Burlington, United States
| | - David Hill-Eubanks
- Department of Pharmacology, University of Vermont, Burlington, United States
| | - Mark T Nelson
- Department of Pharmacology, University of Vermont, Burlington, United States.,Institute of Cardiovascular Sciences, Manchester, United Kingdom
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Huguet F, Calvez ML, Benz N, Le Hir S, Mignen O, Buscaglia P, Horgen FD, Férec C, Kerbiriou M, Trouvé P. Function and regulation of TRPM7, as well as intracellular magnesium content, are altered in cells expressing ΔF508-CFTR and G551D-CFTR. Cell Mol Life Sci 2016; 73:3351-73. [PMID: 26874684 PMCID: PMC11108291 DOI: 10.1007/s00018-016-2149-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2015] [Revised: 01/14/2016] [Accepted: 01/25/2016] [Indexed: 02/03/2023]
Abstract
Cystic fibrosis (CF), one of the most common fatal hereditary disorders, is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The CFTR gene product is a multidomain adenosine triphosphate-binding cassette (ABC) protein that functions as a chloride (Cl(-)) channel that is regulated by intracellular magnesium [Mg(2+)]i. The most common mutations in CFTR are a deletion of a phenylalanine residue at position 508 (ΔF508-CFTR, 70-80 % of CF phenotypes) and a Gly551Asp substitution (G551D-CFTR, 4-5 % of alleles), which lead to decreased or almost abolished Cl(-) channel function, respectively. Magnesium ions have to be finely regulated within cells for optimal expression and function of CFTR. Therefore, the melastatin-like transient receptor potential cation channel, subfamily M, member 7 (TRPM7), which is responsible for Mg(2+) entry, was studies and [Mg(2+)]i measured in cells stably expressing wildtype CFTR, and two mutant proteins (ΔF508-CFTR and G551D-CFTR). This study shows for the first time that [Mg(2+)]i is decreased in cells expressing ΔF508-CFTR and G551D-CFTR mutated proteins. It was also observed that the expression of the TRPM7 protein is increased; however, membrane localization was altered for both ΔF508del-CFTR and G551D-CFTR. Furthermore, both the function and regulation of the TRPM7 channel regarding Mg(2+) is decreased in the cells expressing the mutated CFTR. Ca(2+) influx via TRPM7 were also modified in cells expressing a mutated CFTR. Therefore, there appears to be a direct involvement of TRPM7 in CF physiopathology. Finally, we propose that the TRPM7 activator Naltriben is a new potentiator for G551D-CFTR as the function of this mutant increases upon activation of TRPM7 by Naltriben.
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Affiliation(s)
- F Huguet
- Inserm, UMR1078, 46, rue Félix le Dantec, CS 51819, 29218, Brest Cedex 2, France
- Faculté de Médecine et des sciences de la santé, Université de Bretagne Occidentale, Brest, 29200, France
| | - M L Calvez
- Inserm, UMR1078, 46, rue Félix le Dantec, CS 51819, 29218, Brest Cedex 2, France
- Faculté de Médecine et des sciences de la santé, Université de Bretagne Occidentale, Brest, 29200, France
- Association G. Saleun, Brest, 29218, France
| | - N Benz
- Inserm, UMR1078, 46, rue Félix le Dantec, CS 51819, 29218, Brest Cedex 2, France
- Association G. Saleun, Brest, 29218, France
| | - S Le Hir
- Inserm, UMR1078, 46, rue Félix le Dantec, CS 51819, 29218, Brest Cedex 2, France
- Laboratoire de Génétique Moléculaire, Hôpital Morvan, C.H.U. Brest, Brest, 29200, France
| | - O Mignen
- Inserm, UMR1078, 46, rue Félix le Dantec, CS 51819, 29218, Brest Cedex 2, France
- Faculté de Médecine et des sciences de la santé, Université de Bretagne Occidentale, Brest, 29200, France
| | - P Buscaglia
- Inserm, UMR1078, 46, rue Félix le Dantec, CS 51819, 29218, Brest Cedex 2, France
- Faculté de Médecine et des sciences de la santé, Université de Bretagne Occidentale, Brest, 29200, France
| | - F D Horgen
- Laboratory of Marine Biological Chemistry, Department of Natural Sciences, Hawaii Pacific University, Kaneohe, HI, 96744, USA
| | - C Férec
- Inserm, UMR1078, 46, rue Félix le Dantec, CS 51819, 29218, Brest Cedex 2, France.
- Faculté de Médecine et des sciences de la santé, Université de Bretagne Occidentale, Brest, 29200, France.
- Laboratoire de Génétique Moléculaire, Hôpital Morvan, C.H.U. Brest, Brest, 29200, France.
- Etablissement Français du Sang - Bretagne, Brest, 29200, France.
| | - M Kerbiriou
- Inserm, UMR1078, 46, rue Félix le Dantec, CS 51819, 29218, Brest Cedex 2, France
- Faculté de Médecine et des sciences de la santé, Université de Bretagne Occidentale, Brest, 29200, France
| | - P Trouvé
- Inserm, UMR1078, 46, rue Félix le Dantec, CS 51819, 29218, Brest Cedex 2, France.
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Abstract
The physiological and clinical relevance of Mg(2+) has evolved over the last decades. The molecular identification of multiple Mg(2+) transporters (Acdp2, MagT1, Mrs2, Paracellin-1, SLC41A1, SLC41A2, TRPM6 and TRPM7) and their biophysical characterization in recent years has improved our understanding of Mg(2+) homeostasis regulation and has provided a basis for investigating the role of Mg(2+) in the immune system. Deletions and mutations of Mg(2+) transporters produce severe phenotypes with more systemic symptoms than those seen with Ca(2+) channel deletions, which tend to be more specific and less profound. Deficiency of the Mg(2+) permeable ion channels TRPM6 or TRPM7 in mice is lethal at embryonic day 12.5 or at day 6.5, respectively, and, even more surprisingly, chicken DT40 B cells lacking TRPM7 die after 24-48 h. Recent progress made in Mg(2+) research has helped to define underlying mechanisms of two hereditary diseases, human Hypomagnesemia (TRPM6 deletion) and X-chromosomal immunodeficiency (MagT1 deletion), and has revealed a potential new role for Mg(2+) as a second messenger. Future elucidation of human Mg(2+) transporters (Mrs2, SLC41A1, SLC41A2, TRPM7) expressed in immunocytes, beyond MagT1 and TRPM6, will widen our knowledge about the potential role of Mg(2+) in the activation of the immune response.
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Yudin Y, Lukacs V, Cao C, Rohacs T. Decrease in phosphatidylinositol 4,5-bisphosphate levels mediates desensitization of the cold sensor TRPM8 channels. J Physiol 2011; 589:6007-27. [PMID: 22005680 DOI: 10.1113/jphysiol.2011.220228] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The activity of the cold- and menthol-activated transient receptor potential melastatin 8 (TRPM8) channels diminishes over time in the presence of extracellular Ca(2+), a phenomenon referred to as desensitization or adaptation. Here we show that activation of TRPM8 by cold or menthol evokes a decrease in cellular phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P(2)] levels. The decrease in PtdIns(4,5)P(2) levels was accompanied by increased inositol 1,4,5 trisphosphate (InsP(3)) production, and was inhibited by loading the cells with the Ca(2+) chelator BAPTA-AM, showing that it was the consequence of the activation of phospholipase C (PLC) by increased intracellular Ca(2+) concentrations. PtdIns(4,5)P(2) hydrolysis showed excellent temporal correlation with current desensitization in simultaneous patch clamp and fluorescence-based PtdIns(4,5)P(2) level measurements. Intracellular dialysis of PtdIns(4,5)P(2) inhibited desensitization both in native neuronal and recombinant TRPM8 channels. PtdIns(4)P, the precursor of PtdIns(4,5)P(2), did not inhibit desensitization, consistent with its minimal effect in excised patches. Omission of MgATP from the intracellular solution accelerated desensitization, and MgATP reactivated TRPM8 channels in excised patches in a phosphatidylinositol 4-kinase (PI4K)-dependent manner. PLC-independent depletion of PtdIns(4,5)P(2) using a voltage-sensitive phosphatase (ci-VSP) inhibited TRPM8 currents, and omission of ATP from the intracellular solution inhibited recovery from this inhibition. Inhibitors of PKC had no effect on the kinetics of desensitization. We conclude that Ca(2+) influx through TRPM8 activates a Ca(2+)-sensitive PLC isoform, and the resulting depletion of PtdIns(4,5)P(2) plays a major role in desensitization of both cold and menthol responses.
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Affiliation(s)
- Yevgen Yudin
- Department of Pharmacology and Physiology, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, NJ 07103, USA
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Zakharian E, Cao C, Rohacs T. Intracellular ATP supports TRPV6 activity via lipid kinases and the generation of PtdIns(4,5) P₂. FASEB J 2011; 25:3915-28. [PMID: 21810903 DOI: 10.1096/fj.11-184630] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Transient receptor potential vanilloid 6 (TRPV6) channels play an important role in Ca(2+) absorption in the intestines. Both phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P(2)] and cytoplasmic ATP have been proposed to be important for maintaining TRPV6 activity. To evaluate whether PtdIns(4,5)P(2) and ATP affect channel activity directly or indirectly, we have used a dual approach, examining channel activity in excised patches and planar lipid bilayers. In excised inside-out patch-clamp measurements, ATP reactivated the human TRPV6 channels after current rundown only in the presence of Mg(2+). The effect of MgATP was inhibited by 3 structurally different compounds that inhibit type III phosphatidylinositol 4-kinases (PI4Ks). PtdIns(4,5)P(2) also activated TRPV6 in excised patches, while its precursor PtdIns(4)P had only minimal effect. These data demonstrate that MgATP provides substrate for lipid kinases, allowing the resynthesis of PtdIns(4,5)P(2). To determine whether PtdIns(4,5)P(2) is a direct activator of TRPV6, we purified and reconstituted the channel protein in planar lipid bilayers. The reconstituted channel showed high activity in the presence of PtdIns(4,5)P(2), while PtdIns(4)P induced only minimal activity. Our data establish PtdIns(4,5)P(2) as a direct activator of TRPV6 and demonstrate that intracellular ATP regulates the channel indirectly as a substrate for type III PI4Ks.
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Affiliation(s)
- Eleonora Zakharian
- University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, New Jersey 07103, USA
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9
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Rosário LM, Barbosa RM, Antunes CM, Baldeiras IE, Silva AM, Tomé AR, Santos RM. Regulation by glucose of oscillatory electrical activity and 5-HT/insulin release from single mouse pancreatic islets in absence of functional K(ATP) channels. Endocr J 2008; 55:639-50. [PMID: 18493109 DOI: 10.1507/endocrj.k07e-131] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
The glucose sensitivity of bursting electrical activity and pulsatile insulin release from pancreatic islets was determined in absence of functional K(ATP) channels. Membrane potential, [Ca(2+)](i) and 5-HT/insulin release were measured by intracellular recording, fura-2 fluorescence and 5-HT amperometry, respectively. Single mouse islets, bathed in tolbutamide or glibenclamide and high extracellular Ca(2+) (Ca(2+)(o)), displayed bursting activity and concomitant fast [Ca(2+)](i) and 5-HT/insulin oscillations. Sulphonylurea block of K(ATP) channel current was unaffected by raising Ca(2+)(o). Raising glucose or alpha-ketoisocaproic acid (KIC) concentration from 3 to 30 mM increased spiking activity and burst plateau duration. Staurosporine did not impair glucose potentiation of electrical activity, ruling out the involvement of serine/threonine kinases. Glucose enhanced both [Ca(2+)](i) and 5-HT/insulin oscillatory activity, causing a approximately 3-fold increase in overall 5-HT release rate. Cells lacking bursting activity in high Ca(2+)(o) and low glucose (or KIC) developed a pattern of intensified spiking in response to 11 mM glucose. It is concluded that beta-cells exhibit graded oscillatory electrical and secretory responses to glucose in absence of functional K(ATP) channels. This suggests that, under physiological conditions, early glucose sensing may involve other channels besides the K(ATP) channel.
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Affiliation(s)
- Luís M Rosário
- Center for Neurosciences and Cell Biology, University of Coimbra, Portugal
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10
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Ikuma M, Welsh MJ. Regulation of CFTR Cl- channel gating by ATP binding and hydrolysis. Proc Natl Acad Sci U S A 2000; 97:8675-80. [PMID: 10880569 PMCID: PMC27007 DOI: 10.1073/pnas.140220597] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2000] [Accepted: 05/15/2000] [Indexed: 11/18/2022] Open
Abstract
Opening and closing of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel is regulated by the interaction of ATP with its two cytoplasmic nucleotide-binding domains (NBD). Although ATP hydrolysis by the NBDs is required for normal gating, the influence of ATP binding versus hydrolysis on specific steps in the gating cycle remains uncertain. Earlier work showed that the absence of Mg(2+) prevents hydrolysis. We found that even in the absence of Mg(2+), ATP could support channel activity, albeit at a reduced level compared with the presence of Mg(2+). Application of ATP with a divalent cation, including the poorly hydrolyzed CaATP complex, increased the rate of opening. Moreover, in CFTR variants with mutations that disrupt hydrolysis, ATP alone opened the channel and Mg(2+) further enhanced ATP-dependent opening. These data suggest that ATP alone can open the channel and that divalent cations increase ATP binding. Consistent with this conclusion, when we mutated an aspartate thought to bind Mg(2+), divalent cations failed to increase activity compared with ATP alone. Two observations suggested that divalent cations also stabilize the open state. In wild-type CFTR, CaATP generated a long duration open state, whereas ATP alone did not. With a CFTR variant in which hydrolysis was disrupted, MgATP, but not ATP alone, produced long openings. These results suggest a gating cycle for CFTR in which ATP binding opens the channel and either hydrolysis or dissociation leads to channel closure. In addition, the data suggest that ATP binding and hydrolysis by either NBD can gate the channel.
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Affiliation(s)
- M Ikuma
- Howard Hughes Medical Institute, Departments of Internal Medicine and Physiology and Biophysics, University of Iowa College of Medicine, Iowa City, IA 52242, USA
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Harrington MA, Gunderson KL, Kopito RR. Redox reagents and divalent cations alter the kinetics of cystic fibrosis transmembrane conductance regulator channel gating. J Biol Chem 1999; 274:27536-44. [PMID: 10488089 DOI: 10.1074/jbc.274.39.27536] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Gating of the cystic fibrosis Cl(-) channel requires hydrolysis of ATP by its nucleotide binding folds, but how this process controls the kinetics of channel gating is poorly understood. In the present work we show that the kinetics of channel gating and presumably the rate of ATP hydrolysis depends on the species of divalent cation present and the oxidation state of the protein. With Ca(2+) as the dominant divalent cation instead of Mg(2+), the open burst duration of the channel is increased approximately 20-fold, and this change is reversible upon washout of Ca(2+). In contrast, "soft" divalent cations such as Cd(2+) interact covalently with cystic fibrosis transmembrane conductance regulator (CFTR). These metals decrease both opening and closing rates of the channel, and the effects are not reversed by washout. Oxidation of CFTR channels with a variety of oxidants resulted in a similar slowing of channel gating. In contrast, reducing agents had the opposite effect, increasing both opening and closing rates of the channel. In cell-attached patches, CFTR channels exhibit both oxidized and reduced types of gating, raising the possibility that regulation of the redox state of the channel may be a physiological mode of control of CFTR channel activity.
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Affiliation(s)
- M A Harrington
- Department of Biological Sciences, Stanford University, Stanford, California 94305-5020, USA.
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12
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Affiliation(s)
- R K Rude
- University of Southern California, Los Angeles 90033, USA
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13
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Hilgemann DW. Cytoplasmic ATP-dependent regulation of ion transporters and channels: mechanisms and messengers. Annu Rev Physiol 1997; 59:193-220. [PMID: 9074761 DOI: 10.1146/annurev.physiol.59.1.193] [Citation(s) in RCA: 129] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Many ion transporters and channels appear to be regulated by ATP-dependent mechanisms when studied in planar bilayers, excised membrane patches, or with whole-cell patch clamp. Protein kinases are obvious candidates to mediate ATP effects, but other mechanisms are also implicated. They include lipid kinases with the generation of phosphatidylinositol phosphates as second messengers, allosteric effects of ATP binding, changes of actin cytoskeleton, and ATP-dependent phospholipases. Phosphatidylinositol-4,5-bisphosphate (PIP2) is a possible membrane-delimited messenger that activates cardiac sodium-calcium exchange, KATP potassium channels, and other inward rectifier potassium channels. Regulation of PIP2 by phospholipase C, lipid phosphatases, and lipid kinases would thus tie surface membrane transport to phosphatidylinositol signaling. Sodium-hydrogen exchange is activated by ATP through a phosphorylation-independent mechanism, whereas ion cotransporters are activated by several protein kinase mechanisms. Ion transport in epithelium may be particularly sensitive to changes of cytoskeleton that are regulated by ATP-dependent cell signaling mechanisms.
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Affiliation(s)
- D W Hilgemann
- University of Texas Southwestern, Medical Center at Dallas 75235-9040, USA
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14
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Wiles ME, Wagner TL, Weglicki WB. Effect of acute magnesium deficiency (MgD) on aortic endothelial cell (EC) oxidant production. Life Sci 1996; 60:221-36. [PMID: 9000647 DOI: 10.1016/s0024-3205(96)00619-4] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Magnesium deficiency (MgD) has been associated with production of reactive oxygen species, cytokines, and eicosanoids, as well as vascular compromise in vivo. Although MgD-induced inflammatory change occurs during "chronic" MgD in vivo, acute MgD may also affect the vasculature and consequently, predispose endothelial cells (EC) to perturbations associated with chronic MgD. As oxyradical production is a significant component of chronic MgD, we examined the effect of acute MgD on EC oxidant production in vitro. In addition we determined EC; pH, mitochondrial function, lysosomal integrity and general cellular antioxidant capacity. Decreasing Mg2+ (< or = 250microM) significantlyincreased EC oxidant production relative to control Mg2+ (1000microM). MgD-induced oxidant production, occurring within 30min, was attenuated by EC treatment with oxyradical scavengers and inhibitors of eicosanoid biosynthesis. Coincident with increased oxidant production were reductions in intracellular glutathione (GSH) and corresponding EC alkalinization. These data suggest that acute MgD is sufficient for induction of EC oxidant production, the extent of which may determine, at least in part, the extent of EC dysfunction/injury associated with chronic MgD.
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Affiliation(s)
- M E Wiles
- The George Washington University Medical Center, Division of Experimental Medicine, Washington, D.C., USA.
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15
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Song Y, Liu QY, Vassalle M. On the antiarrhythmic actions of magnesium in single guinea-pig ventricular myocytes. Clin Exp Pharmacol Physiol 1996; 23:830-8. [PMID: 8911722 DOI: 10.1111/j.1440-1681.1996.tb01188.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
1. The hypotheses that magnesium quickly abolishes arrhythmias by acting as a calcium antagonist or by increasing outward potassium currents were tested in guinea-pig isolated ventricular myocytes by recording membrane potentials and currents by means of a single microelectrode discontinuous voltage clamp method. 2. High [Mg2+]o (4-16 mmol/L) slightly increased the amplitude and duration of the action potential (AP) in some myocytes, but overall the changes were not significant. 3. High [Mg2+]o did not decrease the slow inward current (ICa) and had little effect on voltage- and time-dependent outward potassium currents whether or not ICa was allowed to flow. 4. Zero [Mg2+]o decreased the duration, but not amplitude, of the AP. Zero [Mg2+]o had little effect on ICa and on outward currents except for a small increase in outward current in the region of the negative slope of the inward rectifier current-voltage relationship. 5. In our myocytes, in contrast to [Mg2+]o, high [Ca2+]o significantly increased the amplitude and decreased the duration of the AP; at the same time, high [Ca2+]o increases ICa and the outward potassium current. 6. High [Mg2+]o decreased the amplitude of the oscillatory potentials (Vos)induced by various Ca(2+)-overloading procedures (high [Ca2+]o, noradrenaline, strophanthidin and barium). 7. It is concluded that the mechanisms by which high [Mg2+]o quickly suppresses cardiac arrhythmias are related to an extracellular action of Mg2+ and do not include a block of ICa or an increase in outward current. Mg2+ can be antiarrhythmic by decreasing Vos amplitude and possibly by screening the fixed negative charges at the external surface of the sarcolemma.
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Affiliation(s)
- Y Song
- Department of Physiology, State University of New York, Brooklyn 11203, USA
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16
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Keenan D, Romani A, Scarpa A. Differential regulation of circulating Mg2+ in the rat by beta 1- and beta 2-adrenergic receptor stimulation. Circ Res 1995; 77:973-83. [PMID: 7554152 DOI: 10.1161/01.res.77.5.973] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Extracellular Mg2+ homeostasis was studied in vivo in the anesthetized rat. Animals were infused with isoproterenol (ISO) for 10 minutes, and serum Mg2+ was measured after the infusion and then 10 and 20 minutes later. A dose-dependent increase in circulating Mg2+ was observed in animals infused with ISO at a rate of 0.1 microgram.kg-1.min-1 or higher. The time course of the effect demonstrated that circulating Mg2+ continued to increase 20 minutes after the end of the ISO infusion. A predicted maximal increase in serum Mg2+ concentration of 19.3% was derived with a predicted EC50 of 0.08 microgram.kg-1.min-1. The maximal percent increase corresponded to a net increase of 6.7 mumol/300 g body wt. Because infusion of ISO resulted in changes in hemodynamic parameters, most notably a drop in blood pressure, a group of animals was infused with nitroprusside to mimic the hypotensive response via a nonadrenergic mechanism. Under these conditions, there was a transient increase in circulating Mg2+ that was largely inhibited by propranolol, indicating that hypotension per se was not responsible for the mobilization of Mg2+. Infusion of salbutamol, but not prenalterol, also induced an increase in circulating Mg2+. Pretreatment with butoxamine, ICI-118551, or propranolol prevented the ISO-induced increase in serum Mg2+. Pretreatment with atenolol minimally affected the ISO-induced changes in circulating Mg2+. Pretreatment with CGP-20271A actually enhanced the ISO-induced increase in circulating Mg2+. This evidence demonstrates the existence of a pool of Mg2+ that is mobilized into the circulation in response to selective beta 2-adrenergic stimulation.
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Affiliation(s)
- D Keenan
- Department of Physiology and Biophysics, Case Western Reserve University, School of Medicine, Cleveland, OH 44106, USA
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