scholarly journals Possible Magneto-Mechanical and Magneto-Thermal Mechanisms of Ion Channel Activation by Iron-Loaded Ferritin in Magnetogenetics

2019 ◽  
Author(s):  
Mladen Barbic
Keyword(s):  
Ion Channels ◽  
Magnetic Fields ◽  
Ion Channel ◽  
New Technology ◽  
Genetically Engineered ◽  
Channel Activation ◽  
Iron Storage ◽  
Magnetic Spin ◽  
Genetic Constructs

AbstractThe palette of tools for stimulation and regulation of neural activity is continually expanding. One of the new methods being introduced is magnetogenetics, where mechano-sensitive and thermo-sensitive ion channels are genetically engineered to be closely coupled to the iron-storage protein ferritin. Such genetic constructs could provide a powerful new way of non-invasively activating ion channels in-vivo using external magnetic fields that easily penetrate biological tissue. Initial reports that introduced this new technology have sparked a vigorous debate on the plausibility of physical mechanisms of ion channel activation by means of external magnetic fields. I argue that the initial criticisms leveled against magnetogenetics as being physically implausible were possibly based on the overly simplistic and unnecessarily pessimistic assumptions about the magnetic spin configurations of iron in ferritin protein. Additionally, all the possible magnetic-field-based mechanisms of ion channel activation in magnetogenetics might not have been fully considered. I present and propose several new magneto-mechanical and magneto-thermal mechanisms of ion channel activation by iron-loaded ferritin protein that may elucidate and clarify some of the mysteries that presently challenge our understanding of the reported biological experiments. Finally, I present some additional puzzles that will require further theoretical and experimental investigation.

scholarly journals Possible magneto-mechanical and magneto-thermal mechanisms of ion channel activation in magnetogenetics

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Mladen Barbic
Keyword(s):  
Experimental Investigation ◽  
Ion Channel ◽  
Neural Activity ◽  
Storage Protein ◽  
Genetically Engineered ◽  
Channel Activation ◽  
Iron Storage ◽  
Physical Mechanisms ◽  
Magnetic Spin ◽  
Iron Storage Protein

The palette of tools for perturbation of neural activity is continually expanding. On the forefront of this expansion is magnetogenetics, where ion channels are genetically engineered to be closely coupled to the iron-storage protein ferritin. Initial reports on magnetogenetics have sparked a vigorous debate on the plausibility of physical mechanisms of ion channel activation by means of external magnetic fields. The criticism leveled against magnetogenetics as being physically implausible is based on the specific assumptions about the magnetic spin configurations of iron in ferritin. I consider here a wider range of possible spin configurations of iron in ferritin and the consequences these might have in magnetogenetics. I propose several new magneto-mechanical and magneto-thermal mechanisms of ion channel activation that may clarify some of the mysteries that presently challenge our understanding of the reported biological experiments. Finally, I present some additional puzzles that will require further theoretical and experimental investigation.

scholarly journals OSCA/TMEM63 are an evolutionarily conserved family of mechanically activated ion channels

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Swetha E Murthy ◽  
Adrienne E Dubin ◽  
Tess Whitwam ◽  
Sebastian Jojoa-Cruz ◽  
Stuart M Cahalan ◽  
...  
Keyword(s):  
Arabidopsis Thaliana ◽  
Ion Channels ◽  
Ion Channel ◽  
Molecular Mechanisms ◽  
Deep Insight ◽  
Evolutionarily Conserved ◽  
Bona Fide ◽  
Physical Forces ◽  
Insight Into

Mechanically activated (MA) ion channels convert physical forces into electrical signals, and are essential for eukaryotic physiology. Despite their importance, few bona-fide MA channels have been described in plants and animals. Here, we show that various members of the OSCA and TMEM63 family of proteins from plants, flies, and mammals confer mechanosensitivity to naïve cells. We conclusively demonstrate that OSCA1.2, one of the Arabidopsis thaliana OSCA proteins, is an inherently mechanosensitive, pore-forming ion channel. Our results suggest that OSCA/TMEM63 proteins are the largest family of MA ion channels identified, and are conserved across eukaryotes. Our findings will enable studies to gain deep insight into molecular mechanisms of MA channel gating, and will facilitate a better understanding of mechanosensory processes in vivo across plants and animals.

Carfilzomib-Induced Hypertension Is Mediated By Ion Channel Dysregulation in the Kidneys; The Potent Role of AMP-Activated Kinase α

Blood ◽  
2020 ◽  
Vol 136 (Supplement 1) ◽  
pp. 34-35
Author(s):  
Panagiotis Efentakis ◽  
Sofia Lamprou ◽  
Polyzois Dimas ◽  
Constantinos Dimitriou ◽  
Manousos Makridakis ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Ion Channels ◽  
Ion Channel ◽  
Board Of Directors ◽  
Research Funding ◽  
Collecting Duct ◽  
Histological Evaluation ◽  
Advisory Committees ◽  
Induced Hypertension

Introduction: Carfilzomib (Cfz), an irreversible proteasome inhibitor (PI), is an approved agent against relapsed/refractory multiple myeloma (R/R MM). Cfz is associated with high incidence of cardiovascular adverse effects. Hypertension stands as the most frequent cardiovascular complication of Cfz. Even though thrombotic microangiopathy (TMA) is inculpated of Cfz's hypertensive phenotype, its exact pathophysiology is still elusive. In our previous work, we showed that Cfz establishes cardiotoxicity in vivo in a Protein Phosphatase 2A (PP2A)-AMP-activated kinase α (AMPKα)-dependent manner (Efentakis P et al. Blood. 2019;133(7):710-723) but does not lead to a permanent vascular deficit, indicating that hypertension is not vascular derived [Efentakis P et al. IJMS 2020;21(15):E5185]. Taking under consideration that renal homeostasis plays an important role in blood pressure regulation we sought to (i) characterize the dose-dependent manifestation of Cfz-induced hypertension; (ii) investigate the molecular signaling of Cfz in the kidneys by proteomic and immunoblotting analyses and (iii) study the renal ion channels regulation. Methods: Forty C57Bl/6 mice (12-14 weeks of age) were randomly assigned to: (i) Acute Protocol: a. Control [Normal Saline (N/S) 0.9%] and b. Cfz (8mg/kg) for two days and (ii) Sub-acute Protocol: a) Control (N/S 0.9%,) and b) Cfz (8mg/kg) for seven days. Intraperitoneal administration of N/S 0.9% and Cfz was performed at two consecutive and on alternate days for the acute and sub-acute protocols respectively. At baseline and endpoint of the experiments, systolic (SBP) and diastolic blood pressure (DBP) were measured, and subsequently mice were sacrificed for the collection of blood and renal samples. Blood samples were collected in citrate buffer for hematological/coagulation profiling [prothrombin time (PT) and INR estimation] and for cleaved Von Willebrand Factor (cl. VWF) immunoblotting assessment as well as for blood testing of white blood cells (WBCs) and platelets. Renal samples underwent histological proteomic and molecular analyses. Results: SBP and DBP were found to be elevated in Cfz group only in the sub-acute protocol compared to control (SBP: 78.5±2.0 vs 68.2±0.7, p<0.01 and DBP: 104.1±2.3 vs 97.4±2.4, p<0.05, respectively). Neutrophil count in the whole blood was elevated both in the acute and sub-acute protocols, while platelet count was decreased in the acute protocol and restored after sub-acute Cfz administration. Mice presented a thrombotic phenotype characterized by increased PT and INR and decreased cl. VWF after acute Cfz treatment, and a hemorrhagic phenotype with restored cl. VWF after sub-acute Cfz administration. However, the presence of TMA was not confirmed by histological evaluation of the kidneys in any of the protocols. Nonetheless histological evaluation of the kidneys revealed inflammation of the perirenal adipose tissue only in the sub-acute protocol. Proteomic analysis presented that proteasome regulation, metabolism and transport of organic anion processes are affected by Cfz administration. Molecular analysis of the renal tissue showed that Cfz induced an increase in the inducible nitric oxide synthase (iNOS) and microtubule-associated proteins 1A/1B light chain 3B (LC3-B) expression and a decreased AMPKα phosphorylation. Moreover, RT-PCR analysis of the renal samples revealed that collecting duct ion channels epithelial Na+ channel (ENaC), Na+/K+/ATPase and urea transporter 1 (UTA-1) mRNA levels were increased in Cfz group. Conclusion: Sub-acute Cfz treatment establishes a renal-derived hypertensive phenotype and a circulating inflammatory phenotype as indicated by the increased neutrophil and WBCs count in the blood. TMA does not seem to be implicated with the observed phenotype in vivo as investigated molecularly and histologically. Cfz-induced dephosphorylation of AMPKα and the subsequent dysregulation of the collecting duct renal ion channel homeostasis is found to be responsible for the observed effect. Therefore, Cfz seems to induce hypertension by a dysregulation of water-ion re-absorbance leading to increased cardiac preload. The latter comes in agreement with clinical data showing that some Cfz-treated patients present with fluid retention, which can be attributed to the aforementioned renal effects of the drug. Disclosures Efentakis: Amgen: Research Funding. Kastritis:Amgen: Consultancy, Honoraria, Research Funding; Genesis Pharma: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Honoraria. Dimopoulos:BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Personal fees; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Personal fees, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Personal fees, Speakers Bureau; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Personal fees, Research Funding, Speakers Bureau; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Personal fees, Research Funding, Speakers Bureau. Andreadou:Amgen: Research Funding. Terpos:Amgen: Honoraria, Research Funding; Genesis pharma SA: Honoraria, Other: travel expenses , Research Funding; Janssen: Honoraria, Research Funding; Takeda: Honoraria, Other: travel expenses , Research Funding; Celgene: Honoraria; Sanofi: Honoraria; BMS: Honoraria.

Effect of the novel high-affinity glycine-site N-methyl-d-aspartate antagonist ACEA-1021 on 125I-MK-801 binding after subdural hematoma in the rat: an in vivo autoradiographic study

1996 ◽  
Vol 85 (4) ◽  
pp. 655-661 ◽  
Author(s):  
Xiao Di ◽  
Ross Bullock
Keyword(s):  
Nmda Receptor ◽  
Ion Channel ◽  
Subdural Hematoma ◽  
Nmda Antagonist ◽  
Channel Activation ◽  
Content Type ◽  
Mk 801 ◽  
High Affinity ◽  
Fine Print

✓ Acute subdural hematoma (SDH) complicates 20% of severe human head injuries and causes death or severe disability in 60% of these cases, due to brain swelling and high intracranial pressure. Although the mechanisms for these phenomena are unknown, previous studies have implicated excitatory amino acid—mediated mechanisms in both humans and animal models. The authors therefore performed in vivo autoradiography using 125I-MK-801, a high-affinity noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonist, as a tracer to evaluate NMDA ion channel activation spatially and temporally as a factor causing cytotoxic swelling. Acute SDH was induced in 16 anesthetized rats using 0.4 ml autologous venous blood. Fifty microcuries of 125I-MK-801 was injected via an aortic arch cannula 30 minutes after onset of SDH. The effect of a new putatively neuroprotective drug, ACEA-1021, a glycine-specific binding site NMDA antagonist, on 125I-MK-801 binding was tested on five animals. “Nonspecific” 125I-MK-801 binding in the rat brain was assessed by pretreatment with “cold” (nonradiolabeled) MK-801 in five more animals. Four hours later the animals were sacrificed and brain sections were apposed to radiation-detecting high-sensitivity photographic film with precalibrated plastic standards for 4 weeks. A striking and highly significant 1.7- to 4.8-fold increase in 125I-MK-801 binding was seen in the penumbra of viable tissue surrounding the ischemic zone beneath the acute SDH, when compared to contralateral hemisphere binding (p < 0.001). The MK-801 pretreatment markedly reduced 125I-MK-801 uptake in this penumbral zone (4.73 ± 0.36 nCi/mg control vs. 2.85 ± 0.08 nCi/mg cold MK-801; p < 0.0001), indicating that the increased binding in the penumbra of the lesion was due to NMDA ion channel activation. Pretreatment with ACEA-1021 reduced 125I-MK-801 uptake by 28% (3.41 ± 0.26 nCi/mg vs. 4.73 ± 0.36 nCi/mg; p < 0.05), indicating that this agent prevents opening of the NMDA ion channel and, thus, exposure of its receptor for MK-801 binding. These studies show intense foci of penumbral NMDA receptor-mediated ion channel activation after onset of SDH, which is markedly reduced by an NMDA antagonist. Such agents are thus likely to reduce cell swelling after SDH occurs.

Genetic screening for novel Drosophila mutants with discrepancies in iron metabolism

2008 ◽  
Vol 36 (6) ◽  
pp. 1313-1316 ◽  
Author(s):  
Anuja Mehta ◽  
Abhyuday Deshpande ◽  
Fanis Missirlis
Keyword(s):  
Iron Metabolism ◽  
Fluorescent Protein ◽  
Random Mutagenesis ◽  
Model Organism ◽  
Genetic Screen ◽  
Genetically Engineered ◽  
Chromosomal Locus ◽  
Iron Storage ◽  
Green Fluorescent

Ferritin, a symmetrical 24-subunit heteropolymer composed of heavy and light chains, is the primary iron-storage molecule in bacteria, plants and animals. We used a genetically engineered strain of the model organism Drosophila melanogaster which expresses a GFP (green fluorescent protein)-tagged ferritin 1 heavy chain homologue from its native chromosomal locus and incorporated it into endogenous functional ferritin, enabling in vivo visualization of the protein and permitting easy assessment of ferritin status following environmental or genetic perturbations. Random mutagenesis was induced, and individual mutagenized chromosomes were recovered by classic crossing schemes involving phenotypical markers and balancer chromosomes. In wild-type larvae, ferritin is predominantly localized in the brain, in regions of the intestine, in wreath cells and in pericardial cells. A pilot genetic screen revealed a mutant fruitfly strain expressing GFP–ferritin in the anal pads, a pair of organs located ventrally in the posterior end of the fruitfly larva, possibly involved in ion absorption and osmoregulation, which are normally devoid of ferritin. Our continuing genetic screen could reveal transcription factors involved in ferritin regulation and novel proteins important in iron metabolism, hopefully with conserved functions in evolution.

Theoretical evaluation of cell membrane ion channel activation by applied magnetic fields

2000 ◽  
Vol 29 (6) ◽  
pp. 455-456 ◽  
Author(s):  
Tim G. St. Pierre ◽  
Jon Dobson
Keyword(s):  
Magnetic Fields ◽  
Cell Membrane ◽  
Ion Channel ◽  
Theoretical Evaluation ◽  
Channel Activation

scholarly journals Ion channel depolarization increases repulsions between positive S4 charges to drive activation

2019 ◽  
Author(s):  
H. R. Leuchtag
Keyword(s):  
Amino Acids ◽  
Ion Channels ◽  
Ion Channel ◽  
Nerve Impulse ◽  
Electrostatic Repulsion ◽  
Channel Activation ◽  
Voltage Sensors ◽  
Repulsion Energy ◽  
Repulsive Forces ◽  
The Way

AbstractThe positively charged residues, arginine and lysine, of the S4 segments of voltage-sensitive ion channels repel each other with Coulomb forces inversely proportional to the mean channel dielectric permittivity ε. Dipole moments induced at rest potential in the branched sidechains of leucine, isoleucine and valine lend high values of ε to the channel. High ε keeps electrostatic forces small at rest, leaving the channel in a compact conformation closed to ion conduction. On membrane depolarization beyond threshold, the repulsive forces between positive S4 charges increase greatly on a sharp decrease in ε due to the collapse of induced dipoles, causing an expansion of the S4 segments, which drives the channel into activation. Model calculations based on α helical S4 geometry, neglecting the small number of negative charges, provide estimates of electrostatic energy for different values of open-channel ε and numbers of positive S4 charges. When theShakerK+channel is depolarized, the repulsion energy in each S4 segment increases from about 0.2 kcal/mol to about 120 kJ/mol (30 kcal/mol). The S4 expansions lengthen and widen the pore domain, expanding the hydrogen bonds of its α helices, thus providing sites for permeant ions. Ion percolation via these sites produces the stochastic ion currents observed in activated channels. The model proposed, Channel Activation by Electrostatic Repulsion (CAbER), explains observed features of voltage-sensitive channel behavior and offers predictions that can be tested by experiment.SIGNIFICANCE STATEMENTScience walks on two legs, experiment and theory. Experiment provides the facts that theory seeks to explain; the predictions of a theoretical model are then tested in the laboratory.Rigid adherence to an inadequate model can lead to stagnation of a field.The way in which a protein molecule straddling a lipid membrane in a nerve or muscle fiber responds to a voltage change by allowing certain ions to cross it is currently modeled by simple devices such as gated pores, screws and paddles. Since molecules and everyday objects are worlds apart, these devices don’t provide productive models of the way a voltage-sensitive ion channel is activated when the voltage across the resting membrane is eliminated in a nerve impulse. A change of paradigm is needed.Like all matter, ion channels obey the laws of physics. One such law says that positive charges repel other positive charges. Since each of these ion channels has four “voltage sensors” studded with positive charges, they store repulsion energy in a membrane poised to conduct an impulse. To see how that stored energy is released in activation, we must turn to condensed-state physics. Recent advances in materials called ferroelectric liquid crystals, with structures resembling those of voltage-sensitive ion channels, provide a bridge between physics and biology. This bridge leads to a new model, Channel Activation by Electrostatic Repulsion,Three amino acids scattered throughout the molecules have side chains split at their ends, which makes them highly sensitive to changing electric fields. The calculations that form the core of this report examine the effect of these branched-chain amino acids on the repulsions between the positive charges in the voltage sensors. The numbers tell us that the voltage sensors expand on activation, popping the ion channel into a porous structure through which specific ions are able to cross the membrane and so carry the nerve impulse along.This model may someday enable us to learn more about diseases caused by mutations in voltage-sensitive ion channels. But for now, the ball is in the court of the experimentalists to test whether the predictions of this model are confirmed in the laboratory.

scholarly journals Fuel Cell Using Squid Axon Electrolyte and Its Proton Conductivity

2020 ◽  
Vol 11 (4) ◽  
pp. 86
Author(s):  
Tomoki Furuseki ◽  
Yasumitsu Matsuo
Keyword(s):  
Fuel Cell ◽  
Ion Channels ◽  
Ion Channel ◽  
Power Density ◽  
Proton Conductivity ◽  
Clean Energy ◽  
Squid Axon ◽  
High Proton Conductivity ◽  
High Proton

Fuel cells using biomaterials have the potential for environmentally friendly clean energy and have attracted a lot of interest. Moreover, biomaterials are expected to develop into in vivo electrical devices such as pacemakers with no side effects. Ion channels, which are membrane proteins, are known to have a fast ion transport capacity. Therefore, by using ion channels, the realization of fuel cell electrolytes with high-proton conductivity can be expected. In this study, we have fabricated a fuel cell using an ion channel electrolyte for the first time and investigated the electrical properties of the ion channel electrolyte. It was found that the fuel cell using the ion channel membrane shows a power density of 0.78 W/cm2 in the humidified condition. On the other hand, the power density of the fuel cell blocking the ion channel with the channel blocker drastically decreased. These results indicate that the fuel cell using the ion channel electrolyte operates through the existence of the ion channel and that the ion channel membrane can be used as the electrolyte of the fuel cell in humidified conditions. Furthermore, the proton conductivity of the ion channel electrolyte drastically increases above 85% relative humidity (RH) and becomes 2 × 10−2 S/m at 96% RH. This result indicates that the ion channel becomes active above 96%RH. In addition, it was deduced from the impedance analysis that the high proton conductivity of the ion channel electrolyte above 96% RH is caused by the activation of ion channels, which are closely related to the fractionalization of water molecule clusters. From these results, it was found that a fuel cell using the squid axon becomes a new fuel cell using the function of the ion channel above 96% RH.

scholarly journals Swapping of transmembrane domains in the epithelial calcium channel TRPV6

2017 ◽  
Author(s):  
Appu K. Singh ◽  
Kei Saotome ◽  
Alexander I. Sobolevsky
Keyword(s):  
Ion Channels ◽  
Ion Channel ◽  
Calcium Channel ◽  
Transmembrane Domain ◽  
Transmembrane Domains ◽  
Domain Swapping ◽  
Structural Determinants ◽  
Disease States ◽  
Pore Domains

AbstractTetrameric ion channels have either swapped or non-swapped arrangements of the S1-S4 and pore domains. Here we show that mutations in the transmembrane domain of TRPV6 can result in conversion from a domain-swapped to non-swapped fold. These results reveal structural determinants of domain swapping and raise the possibility that a single ion channel subtype can fold into either arrangement in vivo, affecting its function in normal or disease states.

scholarly journals Mining recent brain proteomic databases for ion channel phosphosite nuggets

2010 ◽  
Vol 137 (1) ◽  
pp. 3-16 ◽  
Author(s):  
Oscar Cerda ◽  
Je-Hyun Baek ◽  
James S. Trimmer
Keyword(s):  
Ion Channels ◽  
Ion Channel ◽  
Mammalian Brain ◽  
Phosphorylation Sites ◽  
Dynamic Regulation ◽  
Voltage Gated ◽  
Voltage Gated Ion Channels ◽  
Α Subunits

Voltage-gated ion channels underlie electrical activity of neurons and are dynamically regulated by diverse cell signaling pathways that alter their phosphorylation state. Recent global mass spectrometric–based analyses of the mouse brain phosphoproteome have yielded a treasure trove of new data as to the extent and nature of phosphorylation of numerous ion channel principal or α subunits in mammalian brain. Here we compile and review data on 347 phosphorylation sites (261 unique) on 42 different voltage-gated ion channel α subunits that were identified in these recent studies. Researchers in the ion channel field can now begin to explore the role of these novel in vivo phosphorylation sites in the dynamic regulation of the localization, activity, and expression of brain ion channels through multisite phosphorylation of their principal subunits.

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