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Abstract
The demarcation membrane system (DMS) develops to provide additional surface membrane for the process of platelet production. The DMS is an invagination of the plasma membrane that can extend throughout the extranuclear volume of mature megakaryocytes and its lumen is continuous with the extracellular solution. DMS ultrastructure in fixed samples has been extensively studied using transmission electron microscopy (TEM) and more recently with focused ion beam scanning EM. In addition, whole cell patch clamp membrane capacitance provides a direct measurement of DMS content in living megakaryocytes. However, fluorescence methods to image and quantify the DMS in living megakaryocytes provide several advantages. For example, confocal fluorescence microscopy is easier to use compared to EM or electrophysiological methods and the required equipment is more readily available. In addition, use of living cells avoids artifacts known to occur during the fixation, dehydration, or embedding steps used to prepare EM samples. Here we describe the use of styryl dyes such as FM 1-43 or di-8-ANEPPS and impermeant fluorescent indicators of the extracellular space as simple approaches for imaging and quantification of the DMS.
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Affiliation(s)
- Sangar Osman
- Department of Molecular and Cell Biology, Lancaster Road, University of Leicester, Leicester, UK
| | - Daniel Dalmay
- Department of Molecular and Cell Biology, Lancaster Road, University of Leicester, Leicester, UK
| | - Martyn Mahaut-Smith
- Department of Molecular and Cell Biology, Lancaster Road, University of Leicester, Leicester, UK.
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Rolf M, Brearley C, Mahaut-Smith M. Platelet Shape Change Evoked by Selective Activation of P2X1 Purinoceptors with α,β-Methylene ATP. Thromb Haemost 2017. [DOI: 10.1055/s-0037-1615684] [Citation(s) in RCA: 59] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
SummarySimultaneous measurements of [Ca2+]i and light transmission were used to examine the relationship between P2X1 receptor activation and functional platelet responses. The P2X1 agonist α,β-MeATP evoked a transient [Ca2+]i increase and a reversible decrease in light transmission; both responses required external Ca2+ and the nucleotidase apyrase. The transmission response was due to shape change only, verified by scanning electron microscopy and insensitivity to Reopro, a GPIIbIIIa antagonist. α,β-MeATP stimulated smaller shape changes than ADP, however P2X1 responses had a lifespan of <2 h following resuspension in saline and may be considerably larger in vivo. A peak [Ca2+]i increase of >50 nM was required for detectable shape change. Overlap of concentration-response relationships for α,β-MeATP-evoked [Ca2+]i and shape change suggests that other second messengers are not involved. Therefore, the physiological P2X1 agonist ATP can contribute to platelet activation, in contrast to its previously described inhibitory action at metabotropic platelet purinoceptors.
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Abstract
SummaryG-protein-coupled P2Y1 and P2Y12 receptors play key roles in platelet activation, however the importance of ionotropic P2X1 receptors remains unclear. Platelet P2X1 responses are highly labile in vitro, but were greatly enhanced by increasing [Ca2+]o in the range 1–10 mM. The P2X1 agonist α,β-MeATP stimulated a shape change which saturated at peak [Ca2+]i of ≥ 400 nM, without evidence for aggregation. The maximal P2X1-evoked transmission decrease was 82% of that obtained via P2Y1 receptors. α., β-MeATP caused a disc to sphere transformation in virtually all platelets, but lacked the long processes produced by ADP. Following block of P2Y1 receptors with A3P5PS, co-stimulation with α., β-MeATP and ADP failed to induce aggregation despite the generation of peak [Ca2+]i responses similar to those stimulated via P2Y1 receptors. Therefore early, transient Ca2+ influx via P2X1 receptors can contribute to platelet activation by stimulating a significant morphological change, but does not readily synergise with P2Y12 receptors to support aggregation.
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Lörinczi E, Helliwell M, Finch A, Stansfeld PJ, Davies NW, Mahaut-Smith M, Muskett FW, Mitcheson JS. Calmodulin Regulates Human Ether à Go-Go 1 (hEAG1) Potassium Channels through Interactions of the Eag Domain with the Cyclic Nucleotide Binding Homology Domain. J Biol Chem 2016; 291:17907-18. [PMID: 27325704 PMCID: PMC5016179 DOI: 10.1074/jbc.m116.733576] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Indexed: 11/24/2022] Open
Abstract
The ether à go-go family of voltage-gated potassium channels is structurally distinct. The N terminus contains an eag domain (eagD) that contains a Per-Arnt-Sim (PAS) domain that is preceded by a conserved sequence of 25–27 amino acids known as the PAS-cap. The C terminus contains a region with homology to cyclic nucleotide binding domains (cNBHD), which is directly linked to the channel pore. The human EAG1 (hEAG1) channel is remarkably sensitive to inhibition by intracellular calcium (Ca2+i) through binding of Ca2+-calmodulin to three sites adjacent to the eagD and cNBHD. Here, we show that the eagD and cNBHD interact to modulate Ca2+-calmodulin as well as voltage-dependent gating. Sustained elevation of Ca2+i resulted in an initial profound inhibition of hEAG1 currents, which was followed by a phase when current amplitudes partially recovered, but activation gating was slowed and shifted to depolarized potentials. Deletion of either the eagD or cNBHD abolished the inhibition by Ca2+i. However, deletion of just the PAS-cap resulted in a >15-fold potentiation in response to elevated Ca2+i. Mutations of residues at the interface between the eagD and cNBHD have been linked to human cancer. Glu-600 on the cNBHD, when substituted with residues with a larger volume, resulted in hEAG1 currents that were profoundly potentiated by Ca2+i in a manner similar to the ΔPAS-cap mutant. These findings provide the first evidence that eagD and cNBHD interactions are regulating Ca2+-dependent gating and indicate that the binding of the PAS-cap with the cNBHD is required for the closure of the channels upon CaM binding.
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Affiliation(s)
- Eva Lörinczi
- From the Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN
| | - Matthew Helliwell
- From the Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN, the School of Physiology and Pharmacology, University of Bristol, Bristol BS5 1TD, and
| | - Alina Finch
- From the Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN
| | - Phillip J Stansfeld
- the Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Noel W Davies
- From the Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN
| | - Martyn Mahaut-Smith
- From the Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN
| | - Frederick W Muskett
- From the Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN
| | - John S Mitcheson
- From the Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN,
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Wright A, Mahaut-Smith M, Symon F, Sylvius N, Ran S, Bafadhel M, Muessel M, Bradding P, Wardlaw A, Vial C. Impaired P2X1 Receptor-Mediated Adhesion in Eosinophils from Asthmatic Patients. J Immunol 2016; 196:4877-84. [PMID: 27183585 DOI: 10.4049/jimmunol.1501585] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Subscribe] [Scholar Register] [Received: 07/16/2015] [Accepted: 04/08/2016] [Indexed: 12/13/2022]
Abstract
Eosinophils play an important role in the pathogenesis of asthma and can be activated by extracellular nucleotides released following cell damage or inflammation. For example, increased ATP concentrations were reported in bronchoalveolar lavage fluids of asthmatic patients. Although eosinophils are known to express several subtypes of P2 receptors for extracellular nucleotides, their function and contribution to asthma remain unclear. In this article, we show that transcripts for P2X1, P2X4, and P2X5 receptors were expressed in healthy and asthmatic eosinophils. The P2X receptor agonist α,β-methylene ATP (α,β-meATP; 10 μM) evoked rapidly activating and desensitizing inward currents (peak 18 ± 3 pA/pF at -60 mV) in healthy eosinophils, typical of P2X1 homomeric receptors, which were abolished by the selective P2X1 antagonist NF449 (1 μM) (3 ± 2 pA/pF). α,β-meATP-evoked currents were smaller in eosinophils from asthmatic patients (8 ± 2 versus 27 ± 5 pA/pF for healthy) but were enhanced following treatment with a high concentration of the nucleotidase apyrase (17 ± 5 pA/pF for 10 IU/ml and 11 ± 3 pA/pF for 0.32 IU/ml), indicating that the channels are partially desensitized by extracellular nucleotides. α,β-meATP (10 μM) increased the expression of CD11b activated form in eosinophils from healthy, but not asthmatic, donors (143 ± 21% and 108 ± 11% of control response, respectively). Furthermore, α,β-meATP increased healthy (18 ± 2% compared with control 10 ± 1%) but not asthmatic (13 ± 1% versus 10 ± 0% for control) eosinophil adhesion. Healthy human eosinophils express functional P2X1 receptors whose activation leads to eosinophil αMβ2 integrin-dependent adhesion. P2X1 responses are constitutively reduced in asthmatic compared with healthy eosinophils, probably as the result of an increase in extracellular nucleotide concentration.
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Affiliation(s)
- Adam Wright
- Institute for Lung Health, National Institute for Health Research Respiratory Biomedical Research Unit, University Hospitals of Leicester National Health Service Trust, Leicester LE3 9QP, United Kingdom
| | - Martyn Mahaut-Smith
- Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN, United Kingdom
| | - Fiona Symon
- Institute for Lung Health, National Institute for Health Research Respiratory Biomedical Research Unit, University Hospitals of Leicester National Health Service Trust, Leicester LE3 9QP, United Kingdom; Department of Infection, Immunity and Inflammation, University of Leicester, Leicester LE1 9HN, United Kingdom
| | - Nicolas Sylvius
- Core Biotechnology Services, University of Leicester, Leicester LE1 9HN, United Kingdom; and
| | - Shaun Ran
- Institute for Lung Health, National Institute for Health Research Respiratory Biomedical Research Unit, University Hospitals of Leicester National Health Service Trust, Leicester LE3 9QP, United Kingdom; Department of Infection, Immunity and Inflammation, University of Leicester, Leicester LE1 9HN, United Kingdom
| | - Mona Bafadhel
- Respiratory Medicine Unit, Nuffield Department of Clinical Medicine, University of Oxford, Oxford OX3 7FZ, United Kingdom
| | - Michelle Muessel
- Institute for Lung Health, National Institute for Health Research Respiratory Biomedical Research Unit, University Hospitals of Leicester National Health Service Trust, Leicester LE3 9QP, United Kingdom; Department of Infection, Immunity and Inflammation, University of Leicester, Leicester LE1 9HN, United Kingdom
| | - Peter Bradding
- Institute for Lung Health, National Institute for Health Research Respiratory Biomedical Research Unit, University Hospitals of Leicester National Health Service Trust, Leicester LE3 9QP, United Kingdom; Department of Infection, Immunity and Inflammation, University of Leicester, Leicester LE1 9HN, United Kingdom
| | - Andrew Wardlaw
- Institute for Lung Health, National Institute for Health Research Respiratory Biomedical Research Unit, University Hospitals of Leicester National Health Service Trust, Leicester LE3 9QP, United Kingdom; Department of Infection, Immunity and Inflammation, University of Leicester, Leicester LE1 9HN, United Kingdom
| | - Catherine Vial
- Institute for Lung Health, National Institute for Health Research Respiratory Biomedical Research Unit, University Hospitals of Leicester National Health Service Trust, Leicester LE3 9QP, United Kingdom; Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN, United Kingdom;
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Rinne A, Mobarec JC, Mahaut-Smith M, Kolb P, Bünemann M. The mode of agonist binding to a G protein-coupled receptor switches the effect that voltage changes have on signaling. Sci Signal 2015; 8:ra110. [PMID: 26535008 DOI: 10.1126/scisignal.aac7419] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Signaling by many heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs) is either enhanced or attenuated by changes in plasma membrane potential. To identify structural correlates of the voltage sensitivity of GPCR signaling, we chose muscarinic acetylcholine receptors (the M1, M3, and M5 isoforms) as a model system. We combined molecular docking analysis with Förster resonance energy transfer (FRET)-based assays that monitored receptor activity under voltage clamp conditions. When human embryonic kidney (HEK) 293 cells expressing the individual receptors were stimulated with the agonist carbachol, membrane depolarization enhanced signaling by the M1 receptor but attenuated signaling by the M3 and M5 receptors. Furthermore, whether membrane depolarization enhanced or inhibited receptor signaling depended on the type of agonist. Membrane depolarization attenuated M3 receptor signaling when the receptor was bound to carbachol or acetylcholine, whereas depolarization enhanced signaling when the receptor was bound to either choline or pilocarpine. Docking calculations predicted that there were two distinct binding modes for these ligands, which were associated with the effect of depolarization on receptor function. From these calculations, we identified a residue in the M3 receptor that, when mutated, would alter the binding mode of carbachol to resemble that of pilocarpine in silico. Introduction of this mutated M3 receptor into cells confirmed that the membrane depolarization enhanced, rather than attenuated, signaling by the carbachol-bound receptor. Together, these data suggest that the directionality of the voltage sensitivity of GPCR signaling is defined by the specific binding mode of each ligand to the receptor.
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Affiliation(s)
- Andreas Rinne
- Department of Cardiovascular Physiology, Ruhr University Bochum, Universitätsstr. 150, D-44780 Bochum, Germany
| | - Juan Carlos Mobarec
- Department of Pharmaceutical Chemistry, Philipps University Marburg, Marbacher Weg 6, D-35032 Marburg, Germany
| | - Martyn Mahaut-Smith
- Department of Cell Physiology and Pharmacology, University of Leicester, University Road, P. O. Box 138, Leicester LE1 9HN, UK
| | - Peter Kolb
- Department of Pharmaceutical Chemistry, Philipps University Marburg, Marbacher Weg 6, D-35032 Marburg, Germany
| | - Moritz Bünemann
- Department of Pharmacology and Clinical Pharmacy, Philipps University Marburg, Karl-von-Frisch-Str. 1, D-35043 Marburg, Germany.
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Vaiyapuri S, Jones CI, Sasikumar P, Moraes LA, Ali MS, Sage T, Simon AM, Mahaut-Smith M, Gibbins JM. GAP JUNCTIONS AND CONNEXIN HEMICHANNELS UNDERPIN HAEMOSTASIS AND THROMBOSIS. Heart 2014. [DOI: 10.1136/heartjnl-2014-306916.53] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
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Qiu MR, Jiang L, Matthaei KI, Schoenwaelder SM, Kuffner T, Mangin P, Joseph JE, Low J, Connor D, Valenzuela SM, Curmi PMG, Brown LJ, Mahaut-Smith M, Jackson SP, Breit SN. Generation and characterization of mice with null mutation of the chloride intracellular channel 1 gene. Genesis 2010; 48:127-36. [PMID: 20049953 DOI: 10.1002/dvg.20590] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
CLIC1 belongs to a family of highly conserved and widely expressed intracellular chloride ion channel proteins existing in both soluble and membrane integrated forms. To study the physiological and biological role of CLIC1 in vivo, we undertook conditional gene targeting to engineer Clic1 gene knock-out mice. This represents creation of the first gene knock-out of a vertebrate CLIC protein family member. We first generated a Clic1 Knock-in (Clic1(FN)) allele, followed by Clic1 knock-out (Clic1(-/-)) mice by crossing Clic1(FN) allele with TNAP-cre mice, resulting in germline gene deletion through Cre-mediated recombination. Mice heterozygous or homozygous for these alleles are viable and fertile and appear normal. However, Clic1(-) (/-) mice show a mild platelet dysfunction characterized by prolonged bleeding times and decreased platelet activation in response to adenosine diphosphate stimulation linked to P2Y(12) receptor signaling.
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Affiliation(s)
- Min Ru Qiu
- St. Vincent's Centre for Applied Medical Research, St. Vincent's Hospital and University of New South Wales, Sydney, New South Wales, Australia
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Qiu MR, Jiang L, Matthaei KI, Schoenwaelder SM, Kuffner T, Mangin P, Joseph JE, Low J, Connor D, Valenzuela SM, Curmi PM, Brown LJ, Mahaut-Smith M, Jackson SP, Breit SN. Generation and characterization of mice with null mutation of the chloride intracellular channel 1 gene. Genesis 2010. [DOI: 10.1002/dvg.20616] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Floto RA, Mahaut-Smith M, Allen JM. IFN-gamma and dibutyryl cAMP pre-treatment of U937 cells results in different Ca2+ signals triggered by antibody cross-linking of the human high affinity receptor for IgG (Fc gamma RI). Biochem Soc Trans 1995; 23:122S. [PMID: 7758684 DOI: 10.1042/bst023122s] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
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Bacskai BJ, Hochner B, Mahaut-Smith M, Adams SR, Kaang BK, Kandel ER, Tsien RY. Spatially resolved dynamics of cAMP and protein kinase A subunits in Aplysia sensory neurons. Science 1993; 260:222-6. [PMID: 7682336 DOI: 10.1126/science.7682336] [Citation(s) in RCA: 419] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Cyclic adenosine monophosphate (cAMP)-dependent protein kinase, labeled with fluorescein and rhodamine on the catalytic and regulatory subunits, respectively, was injected into Aplysia sensory neurons either in culture or in intact cell clusters. Energy transfer between the subunits, a measure of cytosolic cAMP concentration ([cAMP]), and compartmentation of the dissociated subunits were monitored by confocal fluorescence microscopy. Bath application of serotonin produced a much greater elevation of [cAMP] in the processes than in the central bodies of the neurons. The resulting gradients must drive a sizable centripetal flux of cAMP because direct microinjection of cAMP showed that it diffused readily. Perinuclear increases in [cAMP] slowly caused the translocation of the freed catalytic subunit into the nucleus to an extent proportional to the percentage of its dissociation from the regulatory subunit.
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Affiliation(s)
- B J Bacskai
- Howard Hughes Medical Institute, University of California, San Diego, La Jolla 92093-0647
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