Movement Of Counterions Research Articles

Gold Nanoparticle in Chemoelectronics: Fundamentals, Challenges, and Future Prospects

AbstractThe basic components of modern electronics are primarily fabricated by using semiconductor material in which the movement of charges can be electrically modulated. For metallic material, however, such modulation is almost impossible because of its field‐shielding characteristics, leading to insensitive response toward applied potentials. In this perspective, how to overcome this limitation of bulk metals (here, gold is taken as a particular example) is demonstrated by reducing the size to the nanoscale and functionalizing these nanogolds with charged molecules. The movement of mobile counterions within gold nanoparticle (AuNP) layers can generate charge gradients that feed back and control the motion of electrons which enables to design and fabricate several important components such as the diode, transistor, logic circuits, memristor, and various chemiresistive sensors. The assembly of AuNP electronic components and sensors gives rise to a new class of nanoparticle‐based “chemoelectronic” logic circuits that can sense, process, and ultimately report various chemical signals. The gas sensors are believed to be the most appropriate candidates for such integration as no solvent/solution is required and therefore, in the end, the combination of AuNP gas sensors and memristors is outlooked to achieve all‐gold‐nanoparticle in‐sensor computing for the development of future artificial olfactory.

Field-Created Coordinate Cation Bridges Enable Conductance Modulation and Artificial Synapse within Metal Nanoparticles

When metal nanoparticles are functionalized with charged ligands, the movement of counterions and conduction electrons is coupled, which enables us to develop electronic devices, including diodes, transistors, and logic gates, but dynamically modulating the conductivity of a synaptic device within these materials has proved challenging. Here we show that an artificial synapse can be created from thin films of functionalized metal nanoparticles using an active silver electrode. The electric-field-injected Ag+ coordinates with carboxyl ligands that sets up a conduction bridge to increase the nanoparticle conductivity by reducing the electron tunneling/hopping energy barriers. The dynamic modulation of conductivity allows us to implement several important synaptic functions such as potentiation/depression, paired-pulse facilitation, learning behaviors including short-term to long-term memory transition, self-learning, and massed leaning vs spaced learning. Finally, based on the nonvolatile characteristics, the metal nanoparticle synapse is used to build a single-layer hardware spiking neural network (SNN) for pattern recognition.

High-Performance Ternary Perovskite-Organic Solar Cells.

Perovskite solar cells in which 2D perovskites are incorporated within a 3D perovskite network exhibit improved stability with respect to purely 3D systems, but lower record power conversion efficiencies (PCEs). Here, a breakthrough is reported in achieving enhanced PCEs, increased stability, and suppressed photocurrent hysteresis by incorporating n-type, low-optical-gap conjugated organic molecules into 2D:3D mixed perovskite composites. The resulting ternary perovskite-organic composites display extended absorption in the near-infrared region, improved film morphology, enlarged crystallinity, balanced charge transport, efficient photoinduced charge transfer, and suppressed counter-ion movement. As a result, the ternary perovskite-organic solar cells exhibit PCEs over 23%, which are among the best PCEs for perovskite solar cells with p-i-n device structure. Moreover, the ternary perovskite-organic solar cells possess dramatically enhanced stability and diminished photocurrent hysteresis. All these results demonstrate that the strategy of exploiting ternary perovskite-organic composite thin films provides a facile way to realize high-performance perovskite solar cells.

Electrochemical Actuation in Porous Silicon

We show large and reversible electrochemical actuation in a material based on self-organised nanoporosity in silicon (pSi) in combination with the electrically conductive polymer polypyrrole (PPy), which is introduced inside the pore space. On a single-pore scale the electrochemical actuation can be traced to the high porosity of 50 % and to potential-dependent pressures of up to 15 MPa acting at the single-pore scale. These pressures originate in charging or discharging and the related counter-ion movements. The exceptionally small operation voltages (0.4-0.9V) and the simple synthesis enable a silicon based actor. INTRODUCTION Self-organized nano-porosity in silicon has been attracting interest from a fundamental point of view and for applications due to its special thermal, electrical and optical properties and its bio compatibility [1]. However, the absence of the piezo-electric effect in silicon makes applications in the field of electro-mechanics for this widely used semiconductor difficult. The aim of this work is to study the sensor and actuator characteristics of bare pSi and pSi filled with PPy. An electrochemical change in the oxidation state of PPy can increase or decrease the number of delocalised charges in the polymer. Immersed in an electrolyte this is also accompanied by a reversible counter-ion uptake or expulsion and thus with a marcroscopic contraction or swelling under electrical potential control, making PPy one of the most employed artificial muscle materials [2]. The material is immersed in an electrolyte solution and studied by different techniques as in-situ dilatometry and in-situ X-ray diffraction. EXPERIMENTAL RESULTS AND DISCUSSIONS Porous silicon is prepared by an electrochemical anodization process in a solution of hydrofluoric acid and ethanol by applying a constant current between a platinum cathode and a highly doped silicon wafer. The resulting pores are characteristically straight and orthogonally aligned to the silicon surface. The pore diameter amounts to 7.6 nm and is determined via nitrogen sorption isotherm as is the porosity of 50 %. In a second step PPy is incorporated inside the pores via an electro-polymerisation in galvanostatic mode.Dilatometry measurements in an in-situ electrochemical setup are performed in order to characterize the actuating properties of the resulting pSi-PPy hybrid material. The sample is therefore immersed in perchloric acid (HClO4) and positioned in the setup, so that the pores are pointing in a horizontal direction, i.e. the sample is standing upright.Measuring the sample length change while recording Cyclovoltammograms (CVs) allows a detailed characterisation of the electrochemical actuation. The potential E is reversibly changed from 0.4 V to 0.9 V versus the normal hydrogen electrode potential. An increasing potential leads to an increased insertion of chlorate-anions in the PP. Vice versa, decreasing the potential expells anions from the PPy. It is found, that the repetitive change in sample length coincides linearly with E. So, the incorporation of anions leads to an expansion of the sample and the release of the anions lets the sample contract.For obtaining a further understanding of the electrochemical actuation mechanism of the PPy filled pSi membranes, the micromechanical properties are modelled based on the microstructure as recorded by electron transmission micrographs.REFERENCES[1] M. J. Sailor, Porous Silicon in Practice - Preparation, Characterization and Applications, Wiley-VCH, 2011.[2] E. Smela, Adv. Mater., 2003, 15, 481–494.

Single-Particle Evaluation of Nano and Micro-Sized Redox-Active Polymers for Energy Storage

Redox active polymers (RAPs) and redox active colloids (RACs) are new energy storage materials for size-exclusion redox flow batteries (RFBs).1-3 RAPs show beneficial characteristics for RFBs including high capacity, high solubility, electrochemical reversibility and tailorable properties via synthetic methods.1,2,4 Their crosslinked counterparts, RACs, are well defined spheres that can be nano- or micro-sized and have many similar characteristics to RAPs while showing even higher capacities and greater crossover rejection.3 As with other macromolecular systems, much remains unknown about the applicability and practicality of energy storage systems involving organic macromolecules capable of storing 106-109 electrons per molecule. In this presentation, I want to discuss methodologies we have been using to analyze stability and evolution of the RAC charge/discharge process during cycling with a focus on measuring a single or a limited number of particles. As with other non-conjugated RAPs, the mechanism of charge transfer across a RAC involves electron hopping between redox active pendants and simultaneous counterion movement.3,5 We recently investigated the electron transfer process within viologen-based RACs through various analytical methods based on scanning electrochemical microscopy (SECM) and modeling through COMSOL.6 SECM is a scanning probe technique that can assess local redox reactivity at the micro or nanoscale in a liquid electrolyte amenable to real battery environments.7 With SECM, single RACs could be imaged, sized and directly reduced/oxidized through making contact with an SECM probe. We were also able to evaluate monolayer films of nanometer sized RACs with a spectroelectrochemical setup using a coupled Raman-SECM instrument. This study provided some useful fundamental information and analytical tools/methods to guide future development and refinement for long time-scale experiments on RACs. I will present on recent cycling experiments involving SECM and modified electrodes. Both chronoamperometric steps and cyclic voltammetry (CV) have been used to measure the cycling process and to manipulate capacity access during cycling. Our data indicate that RACs undergo some conditioning before higher charge recovery and the proportion of reduced to oxidized viologen, or state-of-charge (SoC), will affect the amount of charge that can be recollected from the RAC. I will also discuss measurements involving Raman coupled to electrochemistry for single and few RACs. Refining and developing effective analytical methods is the key to understanding electron transfer, storage and failure within RACs and all battery materials. Our methods are pushing the limits of electrochemistry on single macromolecules but hopefully will be extended to other energy storage and electron transfer systems. J. Am. Chem. Soc. 2014, 136 (46), 16309-16316. Nature 2015, 527 (7576), 78-81. J. Am. Chem. Soc. 2016, 138 (40), 13230-13237. Chem. Mater. 2016, 28 (20), 7362-7374. J. Phys. Chem. 1991, 95 (16), 6383-6389. Langmuir 2017, 33 (37), 9455-9463. Scanning electrochemical microscopy. CRC Press: 2012.

The effect of wetting property on electrochromic properties offunctionalized poly(3,4-ethylenedioxythiophene) films

We have prepared three poly(3,4-ethylenedioxythiophene) (PEDOT) derivatives including PEDOT, hydroxymethyl PEDOT (PEDOT-OH) and perfluoro-substituted PEDOT (PEDOT-F), along with its electrochemical and electrochromic (EC) characterization. The three PEDOT derivatives have variable degree of wettability; which have been compared systematically to investigate the effect of moisture on EC property. The bulky substituents lead to large inter-chain separation and facilitate the movement of counter ions leading to better ionic transport. Furthermore, with perfluoro-functionalized side groups, the PEDOT-F exhibits a water contact angle of 134.7°, significantly higher than that of PEDOT (57.8°), clearly indicating its hydrophobic property. This hydrophobic property of PEDOT-F can prevent it from damage by water within the electrolyte during redox reaction. Combining the advantages of better ionic transport and moisture resistance, the PEDOT-F reveals a better EC lifetime.

Modeling the light-induced electric potential difference (ΔΨ), the pH difference (ΔpH) and the proton motive force across the thylakoid membrane in C3 leaves

A model was constructed which includes electron transport (linear and cyclic and Mehler type reaction) coupled to proton translocation, counter ion movement, ATP synthesis, and Calvin-Benson cycle. The focus is on modeling of the light-induced total electric potential difference (ΔΨ) which in this model originates from the bulk phase electric potential difference (ΔΨb), the localized electric potential difference (ΔΨc), as well as the surface electric potential difference (ΔΨs). The measured dual wavelength transmittance signal (ΔA515–560nm, electrochromic shift) was used as a proxy for experimental ΔΨ. The predictions for theoretical ΔΨ vary with assumed contribution of ΔΨs, which might imply that the measured ΔA515–560nm trace on a long time scale reflects the interplay of the ΔΨ components. Simulations also show that partitioning of proton motive force (pmf) to ΔΨb and ΔpH components is sensitive to the stoichiometric ratio of H+/ATP, energy barrier for ATP synthesis, ionic strength, buffer capacity and light intensity. Our model shows that high buffer capacity promotes the establishment of ΔΨb, while the formation of pHi minimum is not ‘dissipated’ but ‘postponed’ until it reaches the same level as that for low buffer capacity. Under physiologically optimal conditions, the output of the model shows that at steady state in light, the ΔpH component is the main contributor to pmf to drive ATP synthesis while a low ΔΨb persists energizing the membrane. Our model predicts 11mV as the resting electric potential difference across the thylakoid membrane in dark. We suggest that the model presented in this work can be integrated as a module into a more comprehensive model of oxygenic photosynthesis.

Dielectric analysis of different spherical polyelectrolyte brushes: Influence of pH and mass fraction on movement of counterions and electrical properties for different SPBs

Abstract;l Dielectric behaviors of spherical polyelectrolyte brushes (SPBs) suspensions with different properties, length brushes under various mass fractions of SPBs and pH of solution were investigated in a frequency range of 40 Hz to 110 MHz. In this paper, the SPBs consist of polystyrene (PS) core and the negative poly(acrylic acid) (PAA) named PS-PAA of different length and cationic poly(2-aminoethylmethacrylate hydrochloride) (PAEMH) chains named PS-PAEMH grafted on the polystyrene (PS) core. Two unique relaxations are found at either about 10 kHz or 1−10 MHz, respectively, the former due to the movement of counterions and the latter resulting from the interfacial polarization. Using dielectric parameters of the high-frequency relaxation and the Cell model, the information about the brush length, the volume fraction, the electrical and phase parameters of the SPBs and the bulk solutions can be obtained. The surface conductivity of SPBs, the Zeta potential, and the fixed charge density in the SPBs also can be derived. While the low-frequency relaxation shows two separate mechanisms when the brushes are collapsed and stretched: tangential movement of counterions along the SPB particles for PS-PAA with different mass fraction; diffusion movement of counterions along the brush between the brush and the bulk solution for PS-PAA with different pH, PS-PAEMH with different mass fraction, respectively. Significantly larger conductivity and relaxation strength are obtained for PS-PAA with longer brushes. PAA brushes exhibit a transition with increasing pH in which the chains are stretched from collapsed to nearly full length under the domination of the equilibrium between the penetration and diffusion of counterions in the brushes. We found that cationic SPB PS-PAEMH, whose brush dissociation degree is bigger than PS-PAA with negative brush in the acidic solution. These findings lay the foundation for different SPBs’ different applications.

Role of Counterions in Acidification in Mouse Liver Lysosomes

The lysosome is a membrane-bound compartment that digests macromolecules and cellular debris. To function properly, lysosomes must maintain an acidic environment (pH 4.5-5.0), generated by the proton-pumping action of a v-type H+ ATPase. However, since the ATPase is highly electrogenic, the voltage generated by its action must be dissipated by another ion movement, known as the ‘counterion pathway.’ The mechanism of counterion movement is controversial, with proposals that it involves Cl- ions entering the lysosome or cations exiting. The ClC-7 Cl-/H+ antiporter, aCLC gene family member which is the primary pathway for Cl- movement across the membranes of rat liver lysosomes, has been proposed as an important contributor to the counterion pathway. However, several studies suggested that lysosomal pH is unaffected in cultured cells from ClC-7 knockout mice, hinting that other ion conductances contribute to the counterion pathway. Here, we sought to comprehensively analyze the role of ClC-7 and the Cl- movement it mediates in a single well-characterized system: liver lysosomes isolated from mice with tissue specific knockouts of the transporter. We loaded lysosomes with the pH-sensitive fluorescent probe FITC-dextran by intraperitoneal injection of mice, then isolated lysosomes or liver cells for further characterization. Acidification in mouse liver lysosomes is strongly dependent on the presence of Cl- in the bathing buffer, and is minimally affected by varying buffer concentrations of K+, suggesting that Cl- indeed serves as the counterion. As expected, knocking out the ClC-7 gene in these cells abolishes the previously described H+-coupled Cl- transport. Lysosomes from the knockout mouse liver are strongly reduced in ATP-driven acidification, consistent with ClC-7 acting as the primary counterion pathway in this system.

Electrochemical loading of TEM grids used for the study of potential dependent morphology of polyaniline nanofibres.

An electrochemical method for loading electroactive materials over the TEM grid is reported. The protocol has been demonstrated using polyaniline as an example. The electroactive polymer was directly deposited over the Au TEM grid, used as working electrode in a 3 electrode electrochemical cell. The undisturbed as-deposited morphologies under the influence of various counter ions and ex situ electrochemical states have been studied and compared. Contrary to behaviour in bulk the individual polyaniline fibre was found thinner at anodic potentials. The movement of counter ions as a function of the electrochemical state of the polymer was studied using STEM-EDX elemental mapping.

Dielectric Relaxation of Spherical Polyelectrolyte Brushes: Movement of Counterions and Electrical Properties of the Brush Layer.

Dielectric behaviors of spherical polyelectrolyte brush (SPB) suspensions under various mass fractions of SPB and the pH of solution were investigated in a frequency range of 40 Hz to 110 MHz. The SPB consists of a polystyrene (PS) core grafted with poly(acrylic acid) (PAA) chains. Two unique relaxations were found at either about 10 kHz or 1-10 MHz, respectively, with the former due to the diffusion of counterions and the latter resulting from the interfacial polarization. Using dielectric parameters of two relaxations, we obtained information about the migration of counterion and the conformation of polyelectrolyte chains. The PAA chains are fully stretched when pH is about 8 under the domination of the equilibrium between the penetration and diffusion of counterions in the brushes. A dielectric model is proposed to describe the high-frequency relaxation, and the permittivity and conductivity of SPB and its volume fraction were also calculated on the basis of the model. The surface conductivity of SPB, the Donnan potential, and the fixed charge density in the brush layer were derived from these paramaters. The distribution of the Donnan potential was also simulated by using Poisson-Boltzmann equations, and the result is in accordance with these obtained on the basis of the dielectric model.

Possible Magnetic Resonance Signal Due to the Movement of Counterions around a Polyelectrolyte with Rotational Symmetry

Experimental, theoretical and computational studies revealed that the characteristic time scales involved in counterion dynamics in polyelectrolytes systems might span several orders of magnitude ranging from subnanosecond times to time scales corresponding to acoustic-like phonon mode frequencies, with an structural organization of counterions in charge density waves (CDWs). These facts raise the possibility of observing Magnetic Resonance (MR) signals due to the movement of counterions in polyelectrolytes. In case that this signal is detected in macroions or other biological systems, like micelles, vesicles, organeles, etc. with rotational symmetry, this method opens a new tool to measure with precission the counterions velocity.

Invited: Electron Flow in GC8 DNA Strand

DNA molecules are quasi one-dimensional structures consisting of two strands in a double helix form. Each strand consists of four building blocks, Adenine (A), Thymine (T), Cytosine (C) and Guanine (G). The diameter of the DNA molecule is approximately 2 nm. These nanoscale building blocks can be reproducibly engineered in arbitrary sequences of A, T, C and G, and chemists have for long studied sequence dependent charge transfer in DNA [1]. The distinct energy levels and ionization potentials of the building blocks provides a framework to construct DNA sequences with interesting device properties. One can think of quantum wells and barriers constructed from DNA having resonances akin to double barrier resonant tunneling diodes and superlattices [2]. Of great interest are also recent experiments which show the potential to detect diseases [3] and sequence DNA [4], by measuring the electrical conductance of a single DNA molecule. These studies demonstrate potential for an all-electrical method for disease detection. In this talk, we present our understanding of how electrons flow in DNA at room temperature. We will first discuss results from phase coherent calculations, which reveal that the conductance without decoherence is orders of magnitude smaller than the experimental values of conductance [5]. The floppy nature of DNA molecules, electromagnetic fluctuations, and, the movement of water molecules and counter-ions in the case of wet DNA, creates an effective mechanism for decoherence, which facilitates electron flow [5]. While modeling the nature of these fluctuations from ab initio methods is insightful, they have so far not been applied to explain experiments where electrons flow between two metal contacts - a very challenging problem. Rather than apply brute force ab initio molecular dynamics, we explore the applicability of a simple model for decoherence based on Buttiker probes, which when applied to the case of DNA helps understand the magnitude of conductance seen in experiments and capture the sequence dependence in some cases.[1] E. Meggers, M. E. Michel-Beyerle, and B. Giese, Sequence dependent long range hole transport in DNA. J. Am. Chem. Soc., vol. 120, p. 12950 (1998)[2] Ch. Adessi, S. Walch and M. P. Anantram, Environment and structure influence on DNA conduction, Phys. Rev. B, vol. 67, p. 81405(RC) (2003); J. Qi, M. G. Rabbani, S. Edirisinghe, and M. P. Anantram, Transport of charge in DNA heterostructures, 11th IEEE Conference on Nanotechnology (IEEE-NANO), pp. 487-491, 2011; H. Mehrez and M. P. Anantram, Inter-base electronic coupling for transport through DNA, Phys. Rev. B, vol. 71, p. 115405 (2005)[3] J. Hihath, S. Guo, P. Zhang, and N. Tao, Effect of cytosine methylation on DNA charge transport, J. Phys.: Condens. Matter, vol. 24, 164204 (2012)[4] M. Tsutsui, K. Matsubara, T. Ohshiro, M. Furuhashi, M. Taniguchi, and T. Kawai, Electrical Detection of Single Methylcytosines in a DNA Oligomer, J. Am. Chem. Soc., vol. 133, p. 9124 (2011)[5] J. Qi, N. Edirisinghe, M. G. Rabbani, and M. P. Anantram, Unified model for conductance through DNA with the Landauer-Buttiker formalism, Physical Review B, vol. 87, p. 085404 (2013)[6] A.K.Mahapatro, K. J. Jeong, G. U. Lee, and D. B. Janes, Sequence specific electronic conduction through polyion-stabilized double-stranded DNA in nanoscale break junctions, Nanotechnology, vol. 18, 195202 (2007)

The calcium-activated chloride channel Anoctamin 1 contributes to the regulation of renal function

The role of calcium-activated chloride channels for renal function is unknown. By immunohistochemistry we demonstrate dominant expression of the recently identified calcium-activated chloride channels, Anoctamin 1 (Ano1, TMEM16A) in human and mouse proximal tubular epithelial (PTE) cells, with some expression in podocytes and other tubular segments. Ano1-null mice had proteinuria and numerous large reabsorption vesicles in PTE cells. Selective knockout of Ano1 in podocytes (Ano1-/-/Nphs2-Cre) did not impair renal function, whereas tubular knockout in Ano1-/-/Ksp-Cre mice increased urine protein excretion and decreased urine electrolyte concentrations. Purinergic stimulation activated calcium-dependent chloride currents in isolated proximal tubule epithelial cells from wild-type but not from Ano1-/-/Ksp-Cre mice. Ano1 currents were activated by acidic pH, suggesting parallel stimulation of Ano1 chloride secretion with activation of the proton-ATPase. Lack of calcium-dependent chloride secretion in cells from Ano1-/-/Ksp-Cre mice was paralleled by attenuated proton secretion and reduced endosomal acidification, which compromised proximal tubular albumin uptake. Tubular knockout of Ano1 enhanced serum renin and aldosterone concentrations, probably leading to enhanced compensatory distal tubular reabsorption, thus maintaining normal blood pressure levels. Thus, Ano1 has a role in proximal tubular proton secretion and protein reabsorption. The results correspond to regulation of the proton-ATPase by the Ano1-homolog Ist2 in yeast.

Role of Candidate Counterions in Clathrin Coated Vesicle Acidification

Organelles such as endosomes and lysosomes maintain a characteristic internal pH essential for their function. This acidic luminal pH is generated and maintained by the V-type ATPase, a protein that hydrolyzes ATP to pump protons (H+) into the organelle against their electrochemical gradient. H+-pumping generates a voltage across the membrane and an additional ion, known as a counterion, must move to dissipate the charge buildup and allow additional proton pumping. The counterion could be an anion moving into the organelle, a cation exiting, or a combination of both. Though progress has been made in probing the counterion pathways involved in lysosomal acidification, counterion movement in endosomes is poorly understood, partly because of the difficulty of isolating a homogeneous endosome population. However, clathrin-coated vesicles (CCVs), a subpopulation of early endosomes, can be more readily obtained. We have isolated highly-enriched bovine brain CCVs to probe their acidification mechanism and the role of counterion movement. We find that CCVs acidify robustly upon the addition of ATP when monitored with the pH-responsive fluorophore acridine orange. This acidification is completely dependent on external Cl-, although some other monovalent anions can partially substitute. Further, acidification is essentially independent of the external monovalent cation, suggesting a prominent role for Cl- transport in the counterion pathway in these organelles. We continue to investigate the identity and mechanistic transport properties of the Cl- dependence in CCVs, ultimately hoping to understand the role of Cl- transport in endosomal acidification using CCVs as a model system.

Impaired Bone Formation in TRIC-B-Knockout Mice

Osteogenesis imperfect (OI) is a heritable bone dysplasia characterized by bone fragility, but has divergent phenotypic manifestations, suggesting heterogeneous OI-responsible genes in the human genome. Most of OI cases result from defected type I collagen; structural mutations and altered post-translational modifications lead to its insufficient content, folding and trafficking errors, and also compromised matrix incorporation. Recently, a homozygous deletion mutation in the TRIC-B (also referred to as TMEM38B) locus has been identified in Saudi Arabic and Bedouin Israeli OI pedigrees. The OI mutant gene encodes a truncated TRIC-B protein lacking its C-terminal half, and is likely associated with severe impairment of TRIC-B channel activity in various cell types. However, pathological mechanism is still unknown in the OI pedigrees.The TRIC (trimeric intracellular cation) channel subtypes, namely TRIC-A and TRIC-B, form homotrimeric complexes to function as intracellular monovalent cation-specific channels. TRIC-A channels are predominantly expressed in muscle and brain, while TRIC-B channels are ubiquitously detected throughout excitable and non-excitable cell types. Based on our observations in knockout mice, TRIC channels seem to mediate, in part, counterion movements to support efficient Ca2+ release from the sarco/endoplasmic reticulum. Tric-b-knockout mice develop respiratory failure at birth, and the mutant alveolar epithelial cells exhibit compromised IP3R-mediated Ca2+ release and insufficient handling of surfactant lipids. In skeleton preparations from Tric-b-knockout neonates, semi-translucent parts were frequently detected in major bones, indicating impaired bone formation. Indeed, insufficient bone mineralization was confirmed by computed tomography imaging and histochemical analysis. RT-PCR experiments detected decreased expression of osteocalcin and RanklmRNAs as osteoblast makers in Tric-b-knockout femoral bones, suggesting the possibility that Tric-b deficiency may affect osteoblast functions. Therefore, Tric-b-knockout neonates provide a useful model for OI bearing the mutant TRIC-B gene.

Facilitated Hyperpolarization Signaling in Vascular Smooth Muscle-overexpressing TRIC-A Channels

The TRIC channel subtypes, namely TRIC-A and TRIC-B, are intracellular monovalent cation-specific channels and likely mediate counterion movements to support efficient Ca(2+) release from the sarco/endoplasmic reticulum. Vascular smooth muscle cells (VSMCs) contain both TRIC subtypes and two Ca(2+) release mechanisms; incidental opening of ryanodine receptors (RyRs) generates local Ca(2+) sparks to induce hyperpolarization and relaxation, whereas agonist-induced activation of inositol trisphosphate receptors produces global Ca(2+) transients causing contraction. Tric-a knock-out mice develop hypertension due to insufficient RyR-mediated Ca(2+) sparks in VSMCs. Here we describe transgenic mice overexpressing TRIC-A channels under the control of a smooth muscle cell-specific promoter. The transgenic mice developed congenital hypotension. In Tric-a-overexpressing VSMCs from the transgenic mice, the resting membrane potential decreased because RyR-mediated Ca(2+) sparks were facilitated and cell surface Ca(2+)-dependent K(+) channels were hyperactivated. Under such hyperpolarized conditions, L-type Ca(2+) channels were inactivated, and thus, the resting intracellular Ca(2+) levels were reduced in Tric-a-overexpressing VSMCs. Moreover, Tric-a overexpression impaired inositol trisphosphate-sensitive stores to diminish agonist-induced Ca(2+) signaling in VSMCs. These altered features likely reduced vascular tonus leading to the hypotensive phenotype. Our Tric-a-transgenic mice together with Tric-a knock-out mice indicate that TRIC-A channel density in VSMCs is responsible for controlling basal blood pressure at the whole-animal level.

Modulation of physical properties of reverse hexagonal mesophases: A dielectric spectroscopy study

The structural, dynamic, and kinetic aspects of the HII systems based on glycerol monooleate (GMO), phosphatidylcholine (PC), triacylglycerol (TAG), and water were investigated by dielectric spectroscopy in a frequency range of 10-2–106 Hz, and a temperature range of 290–320 K. Three distinct processes as well as a temperature-activated dc conductivity were detected and examined. These were assigned to the reorientation of the GMO polar heads, the tangential movement of counterions at the interface, the transport of TAGs through the lipids tails, and the ion mobility within the water cylinders.Upon addition of PC, the critical temperature (T0) of the dehydration of the GMO headgroups increased. The optimal concentration found for structural stabilization of the HII mesophase was 10 wt% PC, since it imparted the strongest bonding at the interfacial layer and increased the association between the lipid tails. Within the HII cluster, TAG percolated and shifted between the hexagonal rods themselves.The present study demonstrated the benefit of controlling the critical temperature of the HII mesophase partial dehydration and softening, as well as the percolation of TAGs. These factors influence the diffusion mode of embedded drugs in the physiological temperature range.

Hypotension in SM-Specific TRIC-A-Transgenic Mice

TRIC (trimeric intracellular cation) channel subtypes, namely TRIC-A and TRIC-B, likely mediate counter-ion movements coupled with rapid Ca2+ release from intracellular stores in various cell types. The Tric-a-knockout mice suffered from hypertension due to enhanced myogenic tone in resistance arteries. Conversely, smooth muscle (SM)-specific Tric-a-transgenic mice developed hypotension. To maintain vascular tonus, two Ca2+ release mechanisms are functioning in vascular smooth muscle cells (VSMCs); incidental opening of ryanodine receptors (RyRs) generates local Ca2+ sparks to induce hyperpolarization, while agonist-induced activation of inositol trisphosphate receptors (IP3Rs) evokes global Ca2+ transients causing contraction.To investigate the mechanism of hypotension in the Tric-a-transgenic mice, we performed Ca2+ imaging and Ca2+ spark measurements. Mutant VSMCs from the transgenic mice showed elevated Ca2+ spark generation, enhanced spontaneous transient outward currents (STOCs) and lowered resting Ca2+ levels.The observation may suggest that overexpression of TRIC-A channels activates RyRs and enhances hyperpolarization signaling generated by functional coupling between RyRs and BK channels in VSMCs. In this situation, deactivated voltage-dependent Ca2+ channels may reduce resting Ca2+ levels and spontaneous tonus in the mutant VSMCs.

TRIC(Trimeric Intracellular Cation)-A Channels Contribute to Blood Pressure Maintenance in Vascular Smooth Muscle

TRIC (trimeric intracellular cation) channel subtypes, namely TRIC-A and TRIC-B, are intracellular monovalent cation channels postulated to mediate counter-ion movements facilitating physiological Ca²⁺ release from intracellular stores. Tric-a-knockout mice developed hypertension during the daytime due to enhanced myogenic tone in resistance arteries. There are two Ca²⁺ release mechanisms in vascular smooth muscle cells (VSMCs); incidental opening of ryanodine receptors (RyRs) generates local Ca²⁺ sparks to induce hyperpolarization, while agonist-induced activation of inositol trisphosphate receptors (IP₃Rs) evokes global Ca²⁺ transients causing contraction. Tric-a gene ablation inhibited RyR-mediated hyperpolarization signaling to stimulate voltage-dependent Ca²⁺ influx, and adversely enhanced IP₃R-mediated Ca²⁺ transients by overloading Ca²⁺ stores in VSMCs. Therefore, TRIC-A channels contribute to maintaining blood pressure in vascular smooth muscles.