The effects of sound stimulation on the permeability of K channel of Chrysanthemum Callus plasma

The patch-clamp technology is used to analyze the sound stimulation effects on the K⁺ channel of plasma membrane. The results indicate that there are K⁺ channels on the plasma membrane that are sensitive to the sound stimulation. The single channel current is 42 ps, and the current is obviously voltage-dependent. The opening frequency of the K⁺ channels increases under the sound stimulation.     

Prolonged stochastic single ion channel recordings in S-layer protein stabilized lipid bilayer membranes

S-layer proteins are commonly found in bacteria and archaea as two-dimensional monomolecular crystalline arrays as the outermost cell membrane component. These proteins have the unique property that following disruption by chemical agents, monomers of the protein can re-assemble to their original lattice structure. This unique property makes S-layers interesting for utilization in bio-nanotechnological applications. Here, we show that the addition of S-layer proteins to bilayer lipid membranes increases the lifetime and the stability of the bilayer. M2delta ion channels were functionally incorporated into these S-layer stabilized membranes and we were able to record their activity for up to 20 h. Transmission electron microscopy (TEM) was used to visualize the 2D crystalline pattern of the S-layer and the M2delta ion channel characteristics in bilayer lipid membrane's were compared in the presence and absence of S-layers.     

Conductance of KCI-Glycerol Solutions: Test of the Fuoss Paired Ion Model

Abstract

The electrical conductance of KC1 in glycerol solutions has been measured at concentrations between 1.5 mol m^?3 and 353 mol m^?3 at 22°C. The results are compared with the Fuoss paired ion model and fits to the data are obtained assuming a Gurney co-sphere having a radius in the approximate range 6 ± 10^?10 m to 9 ± 10^?10 m. The model leads to an estimate of ionic association which is less than that given by the theory of Bjerrum.     

Spatial distribution of ion channel activity in biological membranes: the role of noise

A new approach is proposed to model a collective ion channel dynamics. We have assumed that ion channels create a two-component spatio-temporal interaction field. Every channel at its current spatial location in membrane contributes permanently to this field with its state (open or closed) and coupling strength to other channels. This field is described by a reaction-diffusion equation, the transition of ion channel from closed to open state (and vice versa) is described by a master equation, and migration of channels in membrane is described by a set of Langevin equations coupled by the interaction field. Within this model, we have investigated critical conditions for spatial distribution of ion channel activity.     

Facilitated Ion Transfer Across the Micro-liquid/Liquid Interface Supported at the Tip of a Silanized Micropipette

IntroductionIon transfer across a liquid/liquid( L/L) inter-face or an interface between two immiscible elec-trolyte solutions( ITIES) plays a significant role inmany biochemical fields and technological systemsfrom biological membrane and drug delivery to ex-traction process and chemical sensors[1] . Theminiaturization of ITIESwas firstachieved by Tay-lor and Girault via supporting the interface at thetip of a micropipette in1 986[2 ] .Later on a nano-ITIES supported at a nanopipette …     

Effects of La3+ on inward K+ channels at plasma membrane in guard cells

The effects of La3+ on inward K+ channels at plasma membrane in vicia guard cells are investigated using the whole-cell patch-clamp recording mode. It is shown that La3+ on both sides of plasma membrane blocks inward K+ currents in a concentration- dependent manner, indicating that La3+ binding sites may exist on both sides of plasma membrane in guard cells in vicia. The dose response is fitted by the Michaelis-Menten relation characterized by an inhibitor constant Ki of 2.56±0.25μmol·L-1 (outside membrane) and (1.18±0.11)×10-15 mol·L-1 (inside membrane). Intracellular La3+ has much stronger inhibitory effect on inward K+ currents than extracellular La3+ does, suggesting there may exist stronger binding sites inside membrane than outside membrane. Since ion channel activities of guard cells directly affect plant stomatal movement and water status, our results imply that rare earth elements might have potential practical values in regulating plant water status and strengthening plant drought endurance.     

苯并吡喃-4-脲、硫脲和氰胍类化合物的合成及其血管舒张活性

钾通道开放剂;苯并吡喃-4-脲、硫脲和氰胍类化合物的合成及其血管舒张活性     

Ion channels of N-terminally linked alamethicin dimers: enhancement of cation-selectivity by substitution of Glu for Gln at position 7

Alamethicin forms voltage-gated ion channels that have moderate cation-selectivity. The enhancement of the cation-selectivity by introducing negatively charged residues at positions 7 and 18 has been studied using the tethered homodimers of alamethicin with Q7 and E18 (di-alm-Q7E18) and its analog with E7 and Q18 (di-alm-E7Q18). In the dimeric peptides, monomer peptides are linked at the N-termini by a disulfide bond. Both the peptides formed long lasting ion channels at cis-positive voltages when added to the cis-side membrane. Their long open duration enabled us to obtain current-voltage (I-V(m)) relations and reversal potentials at the single-channel level by applying a voltage ramp during the channel opening. The reversal potentials measured in asymmetric KCl solutions indicated that ionized E7 provided strong cation-selectivity, whereas ionized E18 little influenced the charge selectivity. This was also the case for the macroscopic charge selectivity determined from the reversal potentials obtained by the macroscopic I-V(m) measurements. The results are accounted for by stronger electrostatic interactions between permeant ions and negatively charged residues at the narrowest part of the pore than at the pore mouth.     

Influence of solvent structure on ion pair association: The conductance of potassium perchlorate in ethylene carbonate-acetonitrile mixtures at 25°C

The conductance of potassium perchlorate in mixtures of ethylene carbonate and acetonitrile covering the range 82.6 D 36.0 in dielectric constant has been measured. The Walden products in these aprotic solvents are approximately one-half as large as the products for the same salt in isodielectric mixtures of water and tetramethylene sulfone. This alters the distribution between electrostatic and hydrodynamic terms in the theoretical conductance function in such a way that the calculated association constants for potassium perchlorate are much smaller in the aprotic mixtures.     

Discrete Helmholtz model: a single layer of correlated counter-ions. Metal oxides and silica interfaces,ion-exchange and biological membranes

The mechanism by which interfaces in solution can be polarised depends on the nature of the charge carriers. In the case of a conductor, the charge carriers are electrons and the polarisation is homogeneous in the plane of the electrode. In the case of an insulator covered by ionic moieties, the polarisation is inhomogeneous and discrete in the plane of the interface. Despite these fundamental differences, these systems are usually treated in the same theoretical framework that relies on the Poisson–Boltzmann equation for the solution side. In this perspective, we show that interfaces polarised by discrete charge distributions are rather ubiquitous and that their associated potential drop significantly differs from those of conductor–electrolyte interfaces. We show that these configurations, spanning liquid–liquid interfaces, charged silica–water interfaces, metal oxide interfaces, supercapacitors, ion-exchange membranes and even biological membranes can be uniformly treated under a common “Discrete Helmholtz” model where the discrete charges are compensated by a single layer of correlated counter-ions, thereby generating a sharp potential drop at the interface.

Electrolytes in solution are strongly correlated with discrete charges at insulating interfaces inducing a behavior significantly different from that of conducting interfaces.     

Flow of water through channels filled with deformable polymer gels

A mathematical model is developed for the flow of water through a channel impregnated with a polymer gel that is treated as an elastic and deformable porous medium. The model uses a Brinkman equation along with an experimentally observed velocity-dependent permeability. Numerical and approximate analytical solutions are given. These results show that the gel intrinsic properties, i.e., gel reference permeability and elastic index, control the water flow. First, the permeability of water flow through the gel increases with an increase of gel reference permeability. Second, the velocity of water decreases when the gel velocity exponent increases. Our theoretical results show that the velocity-dependent permeability of water flow through polymer gels is in fact an intrinsic property of the gel rather than a property of the channel or some interaction between the gel and the pore walls.     

Effects of BaCl<Subscript>2</Subscript> on slow vacuolar ion channels on radish by patch-clamp

The effects of BaCl₂ on slow vacuolar (SV) currents of radish are studied by using the whole-vacuolar patch-clamp recording mode. The Ca²⁺-dependent SV channel can be activated by cytosolic Ca²⁺. When 1 mmol/L BaCl₂ is added into pipette solution, SV currents are suppressed remarkably. Then adding BaCl₂ of different concentrations into the bath solution, SV currents reflect different effects. The results show that BaCl₂ with a lower concentration (<3 mmol/L) promotes the channel currents and the currents are saturated when BaCl₂ concentrations are between 1 μmol/L and 1 mmol/L, but BaCl₂ with higher concentration (≥ 3 mmol/L) inhibits SV currents.     

Absolute configuration assignment of caffeic acid ester derivatives from Tithonia diversifolia by vibrational circular dichroism: the pitfalls of deuteration

Recently, it was observed that infrared (IR) and vibrational circular dichroism (VCD) calculations including deuterated hydroxyl groups in phenolic and saccharide moieties improved significantly the agreement with experimental data obtained in methanol-d₄. In the present study, the relative and absolute configurations of three methanol-soluble caffeic acid ester derivatives 1–3, isolated from Tithonia diversifolia, were established by a combined use of experimental and calculated ¹³C NMR chemical shifts, as well as electronic circular dichroism (ECD) and VCD spectroscopies. Interestingly, the attempt to reproduce the deuteration pattern arising from possible isotopic exchange in methanol-d₄ solution led to nearly mirror image calculated VCD spectra for 1 when compared to the non-deuterated molecule with the same absolute configuration. This latter fact can potentially lead to absolute configuration misassignments. A closer inspection of the vibrational chiroptical properties of 1 revealed that the deuteration status of the tertiary hydroxyl group at C-2 is critical for the correct reproduction of experimental VCD data in protic solvents. Therefore, in the case of stereochemical analysis of polar chiral natural product molecules, a combination of VCD and ECD is recommended.     

Detailed balance in ion channels: Application of Feinberg’s theorem

Detailed balance helps reduce the number of necessary measurements on ion channel models. Even imprecise formulations may lead to correct conditions because of the special structure of these models.     

A Simple Fluorometric Method Using Chlorophyll a for Determination of Hg2+ Ion

A simple and green analytical procedure based on chlorophyll a is presented for the determination of Hg²⁺ ion. Chlorophyll a was extracted and purified from the leaves of pea and is employed as a reagent for analysis of Hg²⁺ ion. It displays remarkable fluorescence emission at 674 nm when excited at 412 nm. The emission intensity decreased significantly on exposure to various concentrations of Hg²⁺ ion. This forms the basis for the determination of Hg²⁺ ion. The proposed method was evaluated for sensitivity and selectivity. The linear concentration range was found to be 2.0–10 μM with r² = 0.997 and the limit of detection for Hg²⁺ ion was 1.3 μM. Ions including Pb²⁺, Cd²⁺, Ag⁺, Zn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Mg²⁺, Mn²⁺, Ru³⁺, Er³⁺, K⁺, Na⁺, NH₄⁺, Cl⁻, NO₃⁻, CH₃COO⁻ and SO₄²⁻ did not interfere with the measurement of Hg²⁺ ion even at 500-fold excess. Since chlorophyll a is widely available in the leaves of most plants, and the extraction and purification process is simple, this technique can provide an alternative, sensitive and economical way to determine Hg²⁺ ion.     

New catalytic methods for the synthesis of vitamins K: K3, K4 and Vikasol

A series of catalysts is developed for synthesis of vitamins K from easily available l-naphthol. The corresponding catalytic reactions compose the background of VIKASIB technology, which is friendly to the enviroment.     

Comments on the separation efficiency of asymmetrical flow field-flow fractionation in channels of constant channel and crossflow velocities leading to constant separation efficiency

It is shown theoretically that a claim in the literature about the overall separation efficiency of asymmetrical flow FFF channels being improved by geometries that permit a uniform channel flow velocity throughout the channel length is untrue.