Changes In Ionic Permeability Research Articles

Membrane-Disruptive Effects of Fatty Acid and Monoglyceride Mitigants on E. coli Bacteria-Derived Tethered Lipid Bilayers.

We report electrochemical impedance spectroscopy measurements to characterize the membrane-disruptive properties of medium-chain fatty acid and monoglyceride mitigants interacting with tethered bilayer lipid membrane (tBLM) platforms composed of E. coli bacterial lipid extracts. The tested mitigants included capric acid (CA) and monocaprin (MC) with 10-carbon long hydrocarbon chains, and lauric acid (LA) and glycerol monolaurate (GML) with 12-carbon long hydrocarbon chains. All four mitigants disrupted E. coli tBLM platforms above their respective critical micelle concentration (CMC) values; however, there were marked differences in the extent of membrane disruption. In general, CA and MC caused larger changes in ionic permeability and structural damage, whereas the membrane-disruptive effects of LA and GML were appreciably smaller. Importantly, the distinct magnitudes of permeability changes agreed well with the known antibacterial activity levels of the different mitigants against E. coli, whereby CA and MC are inhibitory and LA and GML are non-inhibitory. Mechanistic insights obtained from the EIS data help to rationalize why CA and MC are more effective than LA and GML at disrupting E. coli membranes, and these measurement capabilities support the potential of utilizing bacterial lipid-derived tethered lipid bilayers for predictive assessment of antibacterial drug candidates and mitigants.

Chitosan-Glycolic Acid Gel Modification of Chloride Ion Transport in Mammalian Skin: An In Vitro Study.

Chitosan, a polyaminosaccharide with high medical and cosmetic potential, can be combined with the beneficial properties of glycolic acid to form a gel that not only moisturizes the skin, but also has a regenerative effect. Its involvement in the activation of biochemical processes may be associated with the activity of skin ion channels. Therefore, the aim of the research was to evaluate the immediate (15 s) and long-term (24 h) effect of chitosan-glycolic acid gel (CGG) on the transepithelial electric potential and the transepithelial electric resistance (R) of skin specimens tested in vitro. Stimulation during immediate and prolonged application of CGG to skin specimens resulted in a significant decrease in the measured minimal transepithelial electric potential (PDmin). The absence of any change in the R after the CGG application indicates that it does not affect the skin transmission, or cause distortion, microdamage or changes in ion permeability. However, the reduction in potential may be due to the increased transport of chloride ions, and thus water, from outside the cell into the cell interior. Increased secretion of chloride ions is achieved by stimulating the action of the CFTR (cystic fibrosis transmembrane conductance). It can be assumed that chitosan gently stimulates the secretion of chlorides, while maintaining a tendency to reduce the transport of sodium ions, without causing deformation or tissue damage.

Ion dehydration using magnetic fields and impacts on permeability across RO membranes

Magnetic fields have been used as a mitigation process for controlling mineral scaling in diverse applications, including membrane systems. Changes in scale formation have been attributed, in part, to changes in ion hydration. The objective of this study was to evaluate how passage through a multi-directional magnetic field affected the permeability of relevant cations and anions through a seawater reverse osmosis membrane (SW30HR). Changes in ion permeability were evaluated as a function of flow velocity through the magnetic system and described in terms of changes in the ion hydration and in turn changes in the energy penalty that a given ion must incur to permeate across the RO membrane. Ion permeability across the SW30HR membrane increased after having passed through the magnetic system. Increases in ion permeability became most pronounced once a flow velocity through the magnetic system was ≥35 cm/s and were a function of the ion charge density for ions of the same valence. Increases in ion permeability were attributed to dehydration of the ions by the magnetic system resulting in a reduction in the energy penalty required for the relevant ions to transport across the membrane barrier.

Effect of composition on the conformational dynamics of disordered cytosolic C-terminal of GluN2B protein involved in the multicomponent condensate formation

N-methyl-D-aspartate receptors (NMDARs) are glutamate-gated ionotropic channels with high calcium permeability that play important roles in synaptic plasticity. The extracellular and transmembrane domains maintain the communication between pre- and post-synapse through ligand-induced changes in ion permeability, which have been extensively explored down to the atomic level. In contrast, structural and functional understanding of the intracellular C-terminal domain (CTD) remains still elusive. The long CTDs of GluN2 subunits recruit other proteins as part of the signaling pathways downstream of NMDARs, which have been linked to condensate formation through PSD-95 and SynGAP.

HCN2 activation modulation: An electrophysiological and molecular study of the well-preserved LCI sequence in the pore channel

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels belong to the superfamily of voltage-gated potassium (Kv) and cyclic nucleotide-gated (CNG) channels. HCN channels contain the glycine-tyrosine-glycine (GYG) sequence that forms part of the selectivity filter, a similar structure than some potassium channels; however, they permeate both sodium and potassium, giving rise to an inward current. Yet a second amino acid sequence, leucine-cysteine-isoleucine (LCI), next to GYG, is well-preserved in all HCNs but not in the selective potassium channels. In this study we used site-directed mutagenesis and electrophysiology in frog oocytes to determine whether the LCI sequence affects the kinetics of HCN2 currents. Permeability and voltage dependence were evaluated, and we found a role of LCI in the gating mechanism combined with changes in ion permeability. The I residue resulted critical to this function.

Altered expression of TIAM1 in endotoxin-challenged airway epithelial cells and rodent septic models.

In sepsis, reorganization of the actin cytoskeleton in the epithelium during inflammation will lead to a breakdown of epithelial barrier integrity, and contribute to the pathogenesis of sepsis, but the exact changes of various components regulating the actin cytoskeleton pathway remain unclear. We used lipopolysaccharide (LPS) challenged primary epithelial cells cultured at the air-liquid interface (ALI) to mimic epithelial barrier dysfunction during sepsis. Then we detected differential expression of T-lymphoma invasion and metastasis 1 (TIAM1) gene in lung epithelial cells and septic models. LPS induced barrier dysfunction in human tracheobronchial epithelial cells (HTBEs) as measured by statistically significant changes in ionic and macromolecular permeability. We observed differential expression of TIAM1 gene. The protein expression of TIAM1 was decreased after LPS challenge, in human bronchial epithelial cells. Furthermore, the expression levels of both TIAM1 mRNA and protein were decreased in lungs of septic rodent models. Given that expression levels of TIAM1 have been associated with mortality among sepsis patients, our findings have the potential for the development of diagnostic and treatment strategies relevant for patient management.

THE EFFECT OF HYPOXIA ON ELECTRICAL AND CONTRACTILE PROPERTIES OF SMOOTH MUSCLES OF THE GUINEA PIG URETER

Aim. The effect of hypoxia on the electrical and contractile activities of smooth muscles cells (SMCs) of the guinea pig ureter was studied by the method of the double sucrose bridge. Materials and methods. This method allows registering simultaneously parameters of the action potential (AP) and the contraction of SMCs, caused by an electrical stimulus. Results. It was found that lowering the oxygen content in the perfusion solution for 10 min resulted to an increase of electrical and contractile activity of ureteral SMCs. Addition of tetraethylammonium chloride (TEA, 5 mM) – nonselective blocker of potassium membrane conductance – in hypoxic conditions causing an additional increase in the amplitude of the AP, duration of the AP plateau and the contractile responses of smooth muscles. Thus, the hypoxia decreased the potassium membrane conductance of ureteral SMCs. Inhibition of the effect of the α1 -adrenergic receptors agonist phenylephrine (PE, 10 mM) on the electrical and contractile properties of SMCs in hypoxic condition indicate the involvement of the protein kinase C-dependent signaling system in effects of hypoxia. Pretreatment of ureteral smooth muscles with bumetanide (100 mM) – selective inhibitor of Na+,K+,2Cl- - cotransporter (NKCC) – caused a decrease of the activating effect of hypoxia on the SMCs of guinea pig ureter. Conclusion.Thus, the impact of hypoxia on the regulation of electrical activity and contractions of smooth muscles of guinea pig ureter may be due to changes in ion permeability of membranes SMCs and operation of ion-transporting systems.

Mathematical Modeling in Neuroscience: Neuronal Activity and Its Modulation by Astrocytes.

Mathematical Modeling in Neuroscience: Neuronal Activity and Its Modulation by Astrocytes.

Role of Ion Channels in the Sperm Acrosome Reaction.

The acrosome reaction (AR) is a unique exocytotic process where the acrosome, a single membrane-delimited specialized organelle, overlying the nucleus in the sperm head of many species, fuses with the overlying plasma membrane. This reaction, triggered by physiological inducers from the female gamete, its vicinity, or other stimuli, discharges the acrosomal content modifying the plasma membrane, incorporating the inner acrosomal membrane, and exposing it to the extracellular medium. The AR is essential for sperm-egg coat penetration, fusion with the eggs' plasma membrane, and fertilization. As in most exocytotic processes Ca(2+) is crucial for the AR, as well as intracellular pH and membrane potential changes. Thus, among the required processes needed for this reaction, ion permeability changes involving channels are pivotal. In spite of the key role ion channels play in the AR, their identity and regulation is not fully understood. Though molecular and pharmacological evidence indicates that various ionic channels participate during the AR, such as store-operated Ca(2+) channels and voltage-dependent Ca(2+) channels, whole cell patch clamp recordings have failed to detect some of them until now. Since sperm display a very high resistance and a minute cytoplasmic volume, very few channels are needed to achieve large membrane potential and concentration changes. Functional detection of few channels in the morphologically complex and tiny sperm poses technical problems, especially when their conductance is very small, as in the case of SOCs. Single channel recordings and novel fluorescence microscopy strategies will help to define the participation of ionic channels in the intertwined signaling network that orchestrates the AR.

ЗАСТОСУВАННЯ ІНФОРМАЦІЙНИХ ТЕХНОЛОГІЙ ДЛЯ ОЦІНКИ ОСОБЛИВОСТЕЙ РЕАКТИВНОСТІ ОРГАНІЗМУ МОЛОДИХ ЩУРІВ ПРИ ЕКСПЕРИМЕНТАЛЬНІЙ ГІПОКСІЇ

<p>Research of adaptation mechanisms in young body to factors such as hypoxic effect is an actual scientific problem. The aim of the experiment was to determine the functional consequences of changes in ion permeability of cell membranes in the associative cortex in young rats ufter incubation at hypoxic environment under conditions of low atmospheric pressure.<br />Incubation of rats in the hypoxic environment under conditions of moderately low atmospheric pressure leads to increased permeability of cell membranes for Na + and Cl- ions at the associative cortex. This is a functional feature of hypoxic damage to membrane structures of nerve tissue that causes compensatory limit the activity of the central contour regulation of heart rate and decrease activity of the sympathetic regulation. Peculiarities in reactivity of young rats exist due to the immaturity of fronto-thalamic brain system.</p>

Amiloride-sensitive sodium currents in fungiform taste cells of rats chronically exposed to nicotine

Many studies have demonstrated that chronic exposure to nicotine, one of the main components of tobacco smoke, has profound effects on the functionality of the mammalian taste system. However, the mechanisms underlying nicotine action are poorly understood. In particular no information is available on the chronic effect of nicotine on the functioning of taste cells, the peripheral detectors which transduce food chemicals into electrical signals to the brain. To address this issue, I studied the membrane properties of rat fungiform taste cells and evaluated the effect of long-term exposure to nicotine on the amiloride-sensitive sodium currents (ASSCs). These currents are mediated by the epithelial sodium channels (ENaC) thought to be important, at least in part, in the transduction of salty stimuli. Patch-clamp recording data indicated that ASSCs in taste cells from rats chronically treated with nicotine had a reduced amplitude compared to controls. The pharmacological and biophysical analysis of ASSCs revealed that amplitude reduction was not dependent on changes in amiloride sensitivity or channel ionic permeability, but likely derived from a decrease in the activity of ENaCs. Since these channels are considered to be sodium receptors in taste cells, my results suggest that chronic exposure to nicotine hampers the capability of these cells to respond to sodium ions. This might represent a possible cellular mechanism underlying the reduced taste sensitivity to salt typically found in smokers.

Investigation of membrane potential changes in Nitellopsis obtusa cells induced by blue and red light stimulation

Light controls multiple physiological processes in plants. Membrane potential is widely used to report the early events as­sociated with changes in ion permeability, thus the effect of monochromatic light on bioelectrical parameters of Nitellopsis ob­tusa cells was examined. In this study blue, red and far-red light-induced membrane potential changes, light-induced photoelectrical reaction and membrane excitability were investigated using K’-anaesthesia method. All investigated lights cause the same bioelectrical events in Nitellopsis obtusa cells. It can be concluded that all photoreception systems exert their effects by first altering the permeability of the plasma membrane to ions and later ion channels perform signal-transducing functions in the complex array of mechanisms that determine plant physiology.

Participation of the Cl−/HCO3− Exchangers SLC26A3 and SLC26A6, the Cl− Channel CFTR, and the Regulatory Factor SLC9A3R1 in Mouse Sperm Capacitation1

Sperm capacitation is required for fertilization and involves several ion permeability changes. Although Cl(-) and HCO(3)(-) are essential for capacitation, the molecular entities responsible for their transport are not fully known. During mouse sperm capacitation, the intracellular concentration of Cl(-) ([Cl(-)](i)) increases and membrane potential (Em) hyperpolarizes. As in noncapacitated sperm, the Cl(-) equilibrium potential appears to be close to the cell resting Em, opening of Cl(-) channels could not support the [Cl(-)](i) increase observed during capacitation. Alternatively, the [Cl(-)](i) increase might be mediated by anion exchangers. Among them, SLC26A3 and SLC26A6 are good candidates, since, in several cell types, they increase [Cl(-)](i) and interact with cystic fibrosis transmembrane conductance regulator (CFTR), a Cl(-) channel present in mouse and human sperm. This interaction is known to be mediated and probably regulated by the Na(+)/H(+) regulatory factor-1 (official symbol, SLC9A3R1). Our RT-PCR, immunocytochemistry, Western blot, and immunoprecipitation data indicate that SLC26A3, SLC26A6, and SLC9A3R1 are expressed in mouse sperm, localize to the midpiece, and interact between each other and with CFTR. Moreover, we present evidence indicating that CFTR and SLC26A3 are involved in the [Cl(-)](i) increase induced by db-cAMP in noncapacitated sperm. Furthermore, we found that inhibitors of SLC26A3 (Tenidap and 5099) interfere with the Em changes that accompany capacitation. Together, these findings indicate that a CFTR/SLC26A3 functional interaction is important for mouse sperm capacitation.

Effect of Cholesterol on the Pore Dilation of TRPV1

The transient receptor potential vanilloid 1 (TRPV1) ion channel is expressed in nociceptors, where pharmacological modulation of its function may offer a way of easing pain and neurogenic inflammation processes in the human body. The aim of this study was to investigate how depletion of cholesterol from the cell membrane may modulate ion-permeability of the TRPV1 ion channel expressed in CHO-cells. The ion-permeability properties of TRPV1 measured with whole-cell patch clamp on a Chinese hamster ovary (CHO) cell line expressing TRPV1. Sustained capsaicin-induced activation of TRPV1 with N-methyl-D-glucamine (NMDG) as the sole external cation, generated a biphasic current, with a first outward current and a second inward current. Similarly, sustained proton-activation (pH 5.5) of TRPV1 in the absence of external calcium also generated a biphasic current, with a first fast current peak followed by a second larger one. Also, patch clamp recordings of reversal potentials revealed a change of the ion-permeability during prolonged activation of the TRPV1 channel in extremely low extracellular calcium. Our findings show that depletion of cholesterol from the cell membrane inhibited both the second current resulting from sustained agonist-activation, and the change in ion-permeability of the TRPV1 channel. Our results propose a novel mechanism by which cholesterol-depletion may modulate the ion channel function of TRPV1, which may constitute a novel pharmacological based approach for the treatment of pain and neurogenic pain.

Barrier function of the tight junction protein tricellulin

Tricellulin is a tight junction protein localized in tricellular junctions (tTJ), the meeting points of three cells, but also in bicellular junctions (bTJ). The barrier function of tricellulin in bTJ and tTJ has been characterized by overexpression experiments in kidney tubule MDCK II cells. When expressed in the tTJ alone, tricellulin impeded the permability for macromolecules, while after expression in both, tTJ and bTJ, tricellulin impeded the permeability for macromolecules and also for ions. The surprising finding that in tTJ no changes in ion permeability occured is explained by the fact that tTJ central tubes are wide enough for macromolecular passage but too rare to contribute significantly to ion permeability. In conclusion, tricellulin forms a barrier against macromolecular passage in the tTJ and, if present there, also in the bTJ.

Clotrimazole as an amplifier of hemin-induced damage to human erythrocytes. Antioxidant-independent protective effects of flavonoids

This study is focused on the effect of the antifungal drug clotrimazole (CLT), also possessing anti-malarial and anticancer activities, on hemin-induced hemolysis and changes in ion permeability and filter-ability of human erythrocytes. In the presence of 10 μM clotrimazole, the hemolytic response of erythrocytes to exogenous hemin at concentrations as low as 2–8 μM was considerably potentiated and their filterability, as measured by passing them through a 5-μm nuclepore filter, dropped sharply. Flavonoids quercetin (Q) and taxifolin (DHQ), unlike the standard antioxidant Trolox, abolished the effects of clotrimazole, suggesting that protection of hemin-treated erythrocytes by flavonoids is not related to their antioxidant properties.

Energy exchange and ultrastructure of plant cells under generation of nitric oxide

The effects of nitric oxide (NO) on oxygen consumption, heat generation, and cell ultrastructure were investigated in the seedlings of wheat (Triticum aestivum L.). The experiments were conducted with the excised roots of 5-day-old seedlings grown in the solution of CaCl2 (2.5 × 10−4 M). The source of NO was NaNO2 (5 × 10−3 M) where the roots were incubated. Production of NO was determined by means of EPR, respiration — gasometrically, heat generation — using a microcalorimeter. The results showed that NO was formed in the presence of NaNO2. This was accompanied by a decrease in the respiration rate by about 30%, which lasted for 5–6 h. Apparently, NO inhibited mitochondrial oxidation because stimulation of oxygen consumption induced by 2,4-DNP was completely removed in the presence of NaNO2. When the cells were affected by succinic acid in the presence of NaNO2, respiration was strongly inhibited. The effects of succinic acid and NaNO2 were negated by ascorbic acid. A decrease in the rate of respiration was accompanied by a reduction in heat generation. Moreover, the efflux of potassium ions to the root incubation medium was stimulated, which may point to changes in ionic membrane permeability. The observed changes in energy exchange were accompanied by disturbances in the cell ultrastructure. Nitric oxide induced a clarification of the mitochondrial matrix and a reduction in the number of cristae. It was concluded that NO excess in plant tissues brings about a deceleration of energy exchange, disturbance of the ultrastructural organization, and cell death.

Factors governing the reversible change in ionic permeability of a low-density monolayer

Abstract The dynamic response of low-density self-assembled monolayers (SAMs) on gold has been investigated with electrochemical impedance spectroscopy (EIS) under non-faradaic conditions and contact angle measurements. The impedance of low-density 16-mercaptohexadecanoic acid (LD-MHA) SAMs is compared with that of densely-packed MHA and tetraethylammonium–MHA (TEA–MHA) ion-pair monolayers in 0.1 M KCl (pH 8.4). The films composed of ion-pairs and loosely-packed MHA have higher capacitance and are more permeable to ions than fully-packed MHA SAMs. The impedance phase angle of the LD-MHA SAM at 0.1 Hz decreases reversibly by 10° upon scanning the applied potential from −0.1 V to +0.3 V (vs. SCE). Fitting the impedance data to an equivalent circuit correlates the decrease in phase angle with an order-of-magnitude drop in monolayer resistance (i.e. increase in the ionic permeability of the monolayer). The ion-pair and dense MHA SAMs do not exhibit an increase in permeability upon scanning the applied potential from −0.1 V to +0.3 V (vs. SCE). The capacitances of the LD-MHA and TEA–MHA films exhibit a small, but significant (15%), change with applied potential between −0.1 V and +0.3 V (vs. SCE). The impedance of the LD-MHA SAM is found to be independent of the electrolyte concentration (0.01–1 M KCl), and displays hysteresis with the direction of the potential scan. Receding contact angle measurements performed at −0.1 V and +0.3 V using the same electrolyte show that the higher ionic permeability of the LD-MHA SAM at +0.3 V is caused by a voltage-induced structural change (molecular re-organization) within the film. The agreement between EIS measurements performed at pH 3.3 and pH 8.4 shows that electrostatic attraction between a negatively-charged thiol tailgroup and oppositely-charged gold electrode is not required for this structural change to occur.

Characteristics of chitosan membranes modified by argon plasmas

Dense chitosan membranes were prepared and studied for surface modification using argon plasma produced at low pressures from 6.67–133.3 Pa with RF frequencies at a power ranging from 6–90 W. Glutaraldehyde and sulfuric acid in methanol were used as linking reagents before the plasma treatment. When the plasma density was fixed at conditions of 6 W and 49 W at 66.7 Pa, the membrane wettability was measured as a decrease in contact angle between the water drop and the membrane surface. Water swelling properties were increased in glutaraldehyde cross-linked membrane. It was found that the ionic permeability of the membranes did not depend linearly on the plasma density used. The density at 6 W was smaller than that produced at 49 W, but it increased the Cl − to K + permeability ratio of the membranes by 1.4–1.8 times, with the maximum increase found in glutaraldehyde cross-linked membranes. Results from AFM showed that plasma treatment caused roughness at the membrane surface, and consequently, the hydraulic permeability of the membranes was reduced. Moreover, results from ATR-FTIR showed a major increase in the absorption spectra of C O, C–H, and C–O functional groups. The results were similar for the sulfuric acid cross-linked and the control membrane. In contrast, a glutaraldehyde cross-linked membrane was not affected greatly by plasma treatment. This study indicates that surface modification by argon plasma leads to changes in filtration characteristics and ionic permeability of chitosan membranes.

Tunable Calcium Current through TRPV1 Receptor Channels

TRPV1 receptors are polymodal cation channels that open in response to diverse stimuli including noxious heat, capsaicin, and protons. Because Ca2+ is vital for TRPV1 signaling, we sought to precisely measure its contribution to TRPV1 responses and discovered that the Ca2+ current was tuned by the mode of activation. Using patch clamp photometry, we found that the fraction of the total current carried by Ca2+ (called the Pf%) was significantly smaller for TRPV1 currents evoked by protons than for those evoked by capsaicin. Using site-directed mutagenesis, we discovered that the smaller Pf% was due to protonation of three acidic amino acids (Asp646, Glu648, and Glu651) that are located in the mouth of the pore. Thus, in keeping with recent reports of time-dependent changes in the ionic permeability of some ligand-gated ion channels, we now show for the first time that the physiologically important Ca2+ current of the TRPV1 receptor is also dynamic and depends on the mode of activation. This current is significantly smaller when the receptor is activated by a change in pH, owing to atomic scale interactions of H+ and Ca2+ with the fixed negative charge of side chains in the pore.