Understanding Ion Channel Gating Mechanisms by Molecular Dynamics Simulations.

Ion channels importantly contribute to the function of endothelial cells. They serve as the major source of intracellular Ca2+, which, in turn, controls the production of endothelium-derived vasodilators, the permeability of the endothelium, gene expression, and other properties of endothelial cells. In addition, the activity of ion channels determines the membrane potential of endothelial cells that serves as an important signal for cell-cell communication between endothelial cells and between endothelial cells and overlying smooth muscle cells, and may feed-back to regulate the activity of the ion channels themselves. This review provides an overview of the expression and function of endothelial ion channels that contribute to Ca2+ and membrane potential signaling that is involved in the regulation and modulation of vasomotor tone of resistance arteries and arterioles. Channels discussed include inositol 1,4,5 trisphosphate receptors that mediate agonist-induced Ca2+ release from endoplasmic reticulum stores; members of the transient receptor potential family and other channels that mediate agonist-induced Ca2+ influx through the plasma membrane; Ca2+-activated K+ channels that mediate agonist-induced membrane hyperpolarization; and inward rectifier K+ channels that serve as sensors for changes in extracellular K+ and amplifiers of hyperpolarization induced by the activity of other ion channels. It is emphasized that all of these channels exist as members of macromolecular signaling complexes providing a rich environment for regulation of their activity and the function of endothelial cells in resistance arteries and arterioles.

Magnetogenetics was developed to remotely control genetically targeted neurons. A variant of magnetogenetics uses magnetic fields to activate transient receptor potential vanilloid (TRPV) channels when coupled with ferritin. Stimulation with static or RF magnetic fields of neurons expressing these channels induces Ca2+ transients and modulates behavior. However, the validity of ferritin-based magnetogenetics has been questioned due to controversies surrounding the underlying mechanisms and deficits in reproducibility. Here, we validated the magnetogenetic approach Ferritin-iron Redistribution to Ion Channels (FeRIC) using electrophysiological (Ephys) and imaging techniques. Previously, interference from RF stimulation rendered patch-clamp recordings inaccessible for magnetogenetics. We solved this limitation for FeRIC, and we studied the bioelectrical properties of neurons expressing TRPV4 (nonselective cation channel) and transmembrane member 16A (TMEM16A; chloride-permeable channel) coupled to ferritin (FeRIC channels) under RF stimulation. We used cultured neurons obtained from the rat hippocampus of either sex. We show that RF decreases the membrane resistance (Rm) and depolarizes the membrane potential in neurons expressing TRPV4FeRIC RF does not directly trigger action potential firing but increases the neuronal basal spiking frequency. In neurons expressing TMEM16AFeRIC, RF decreases the Rm, hyperpolarizes the membrane potential, and decreases the spiking frequency. Additionally, we corroborated the previously described biochemical mechanism responsible for RF-induced activation of ferritin-coupled ion channels. We solved an enduring problem for ferritin-based magnetogenetics, obtaining direct Ephys evidence of RF-induced activation of ferritin-coupled ion channels. We found that RF does not yield instantaneous changes in neuronal membrane potentials. Instead, RF produces responses that are long-lasting and moderate, but effective in controlling the bioelectrical properties of neurons.

Deletion of Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) envelope (E) gene attenuates the virus. E gene encodes a small multifunctional protein that possesses ion channel (IC) activity, an important function in virus-host interaction. To test the contribution of E protein IC activity in virus pathogenesis, two recombinant mouse-adapted SARS-CoVs, each containing one single amino acid mutation that suppressed ion conductivity, were engineered. After serial infections, mutant viruses, in general, incorporated compensatory mutations within E gene that rendered active ion channels. Furthermore, IC activity conferred better fitness in competition assays, suggesting that ion conductivity represents an advantage for the virus. Interestingly, mice infected with viruses displaying E protein IC activity, either with the wild-type E protein sequence or with the revertants that restored ion transport, rapidly lost weight and died. In contrast, mice infected with mutants lacking IC activity, which did not incorporate mutations within E gene during the experiment, recovered from disease and most survived. Knocking down E protein IC activity did not significantly affect virus growth in infected mice but decreased edema accumulation, the major determinant of acute respiratory distress syndrome (ARDS) leading to death. Reduced edema correlated with lung epithelia integrity and proper localization of Na+/K+ ATPase, which participates in edema resolution. Levels of inflammasome-activated IL-1β were reduced in the lung airways of the animals infected with viruses lacking E protein IC activity, indicating that E protein IC function is required for inflammasome activation. Reduction of IL-1β was accompanied by diminished amounts of TNF and IL-6 in the absence of E protein ion conductivity. All these key cytokines promote the progression of lung damage and ARDS pathology. In conclusion, E protein IC activity represents a new determinant for SARS-CoV virulence.

Activation of the M2 ion channel of influenza virus: a role for the transmembrane domain histidine residue

Ion transport across biomembranes plays a major role in living cells. This fundamental function is normally carried out by molecules with both a hydrophobic and a hydrophilic side (amphiphilic molecules), which aggregate within the membrane forming a hydrophilic pore (the ion channel) permitting the selective translocation of permeant ions. Countless papers report the conformation of these ion channels in lipid vesicles using several techniques, such as circular dichroism and solid‐state NMR spectroscopies. However, the functional activity of ion channels can only be investigated by varying the transmembrane potential. This is also the situation in which ion channels operate in commercialized drugs with intracellular targeting activities, of great interest in pharmaceutical research. A suitable biomimetic membrane must consist of a conducting or semiconducting support, whose “heart” is a lipid bilayer in contact with the aqueous solution of interest on one side. The other side must comprise a hydrophilic region thick enough to completely decouple the lipid bilayer from the support, giving rise to a “tethered bilayer lipid membrane” (tBLM). This review aims to describe the numerous efforts made over time to approach this goal, the most recent achievements, and the perspectives of future development. Special emphasis will be placed on the electrochemical aspects of tBLMs, and a qualitative overview of the main optical and scanning probe techniques employed will be provided.

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.

Müller cells are mainly involved in controlling extracellular homeostasis in the retina, where intense neural activity alters ion concentrations and osmotic gradients, thus favoring cell swelling. This increase in cell volume is followed by a regulatory volume decrease response (RVD), which is known to be partially mediated by the activation of K+ and anion channels. However, the precise mechanisms underlying osmotic swelling and subsequent cell volume regulation in Müller cells have been evaluated by only a few studies. Although the activation of ion channels during the RVD response may alter transmembrane potential (Vm), no studies have actually addressed this issue in Müller cells. The aim of the present work is to evaluate RVD using a retinal Müller cell line (MIO-M1) under different extracellular ionic conditions, and to study a possible association between RVD and changes in Vm. Cell volume and Vm changes were evaluated using fluorescent probe techniques and a mathematical model. Results show that cell swelling and subsequent RVD were accompanied by Vm depolarization followed by repolarization. This response depended on the composition of extracellular media. Cells exposed to a hypoosmotic solution with reduced ionic strength underwent maximum RVD and had a larger repolarization. Both of these responses were reduced by K+ or Cl− channel blockers. In contrast, cells facing a hypoosmotic solution with the same ionic strength as the isoosmotic solution showed a lower RVD and a smaller repolarization and were not affected by blockers. Together, experimental and simulated data led us to propose that the efficiency of the RVD process in Müller glia depends not only on the activation of ion channels, but is also strongly modulated by concurrent changes in the membrane potential. The relationship between ionic fluxes, changes in ion permeabilities and ion concentrations –all leading to changes in Vm– define the success of RVD.

A radiohistochemical measure of [ 3H]TCP binding to the activated NMDA-receptor-gated ion channel in rat brain

Chapter 17 The plasma membrane as a transducer and amplifier

Ion channels are widely expressed in living cells and play critical roles in various cellular biological functions. Dysfunctional ion channels can cause a variety of diseases, making ion channels attractive targets for drug discovery. Computational approaches, such as molecular docking and molecular dynamic simulations, provide economic and efficient tools for finding modulators of ion channels and for elucidating the action mechanisms of small molecules. In this review, we focus primarily on four types of ion channels (voltage-gated, ligand-gated, acid-sensing, and virus matrix 2 ion channels). The current advancements in computer-aided drug discovery and design targeting ion channels are summarized. First, ligand-based studies for drug design are briefly outlined. Then, we focus on the structurebased studies targeting pore domains, endogenous binding sites and allosteric sites of ion channels. Moreover, we also review the contribution of computational methods to the field of ligand binding and unbinding pathways of ion channels. Finally, we propose future developments for the field.

Glass and fused-quartz nanopore membranes containing a single conically shaped pore are promising solid supports for lipid bilayer ion-channel recordings due to the high inherent stability of lipid bilayers suspended across the nanopore orifice, as well as the favorable electrical properties of glass and fused quartz. Fluorescence microscopy is used here to investigate the structure of the suspended lipid bilayer as a function of the pressure applied across a fused-quartz nanopore membrane. When a positive pressure is applied across the bilayer, from the nanopore interior relative to the exterior bulk solution, insertion or reconstitution of operative ion channels (e.g., α-hemolysin (α-HL) and gramicidin) in the bilayer is observed; conversely, reversing the direction of the applied pressure results in loss of all channel activity, although the bilayer remains intact. The dependence of the bilayer structure on pressure was explored by imaging the fluorescence intensity from Nile red dye doped into suspended 1,2-diphytanoyl-sn-glycero-3-phosphocholine bilayers, while simultaneously recording the activity of an α-HL channel. The fluorescence images suggest that a positive pressure results in compression of the bilayer leaflets and an increase in the bilayer curvature, making it suitable for ion-channel formation and activity. At negative pressure, the fluorescence images are consistent with separation of the lipid leaflets, resulting in the observed loss of the ion-channel activity. The fluorescence data indicate that the changes in the pressure-induced bilayer structure are reversible, consistent with the ability to repeatedly switch the ion-channel activity on and off by applying positive and negative pressures, respectively.

Is the proliferation of human chondrocytes regulated by ionic channels?

Beyond hydrodynamics: The role of ion channels in dentine hypersensitivity.

Ion channel reconstitution in lipid bilayers.

SummaryElectrophysiology and the study of ion channels has generally been the province of neurobiologists. However, since the application of patch clamp techniques to microbial membranes, it is evident that microbes possess a variety of ion channel activities. Microbial genome sequencing projects have revealed that, in fact, nearly all microbes that have been surveyed possess ion channel homologues. For some of these microbial ion channel genes, the corresponding ion channel activity has been identified, notably the mechanosensitive ion channel from Escherichia coli (MscL), the K+ ion channel homologue from Streptomyces lividans (KscA) and the dual-pore K+ channel from Saccharomyces cerevisiae (Tok1). This has allowed a more detailed examination of the structure/function of these ion channels. More remarkably, due to the greater ease of purification and crystallization of microbial ion channels than mammalian ion channels, the crystal structures of both MscL and KscA have been determined. For KscA, this has given great insights into the structure of the potassium ion filter in all K+ channels. An often-neglected question concerns the function of ion channels in microbes. For MscL, this question has begun to be answered with the discovery of MscS, which functions in parallel with MscL to protect cells from osmotic stress. However, the function of KscA and Tokl and many other ion channel homologues has as yet to be discovered. It is fascinating that the evolution of human sentience is based upon a molecule that is present in even simple forms of life.