Mechanisms underlying electrical and mechanical responses of the bovine retractor penis to inhibitory nerve stimulation and to an inhibitory extract.

PubMed Central

Byrne, N. G.; Muir, T. C.

1985-01-01

The response of the bovine retractor penis (BRP) to stimulation of non-adrenergic, non-cholinergic (NANC) inhibitory nerves and to an inhibitory extract prepared from this muscle have been studied using intracellular microelectrode, sucrose gap and conventional mechanical recording techniques. Both inhibitory nerve stimulation and inhibitory extract hyperpolarized the membrane potential and relaxed spontaneous or guanethidine (3 X 10(-5) M)-induced tone. These effects were accompanied by an increase in membrane resistance. Following membrane potential displacement from an average value of -53 +/- 7 mV (n = 184; Byrne & Muir, 1984) inhibitory potentials to nerve stimulation were abolished at approximately -30 mV; there was no evidence of reversal. Displacement by inward hyperpolarizing current over the range -45 to -60 mV increased the inhibitory response to nerve stimulation and to inhibitory extract; at more negative potential values (above approximately -60 mV) the inhibitory potential decreased and was abolished (approximately -103 mV). There was no evidence of reversal. Removal of [K+]o reversibly reduced hyperpolarization to nerve stimulation and inhibitory extract. No enhancement was observed. Increasing the [K+]o to 20 mM reduced the inhibitory potential to nerve stimulation but this was restored by passive membrane hyperpolarization. Inhibitory potentials were obtained at membrane potential values exceeding that of the estimated EK (-49 mV). [Cl-]o-free or [Cl-]o-deficient solutions reduced and abolished (after some 20-25 min) the hyperpolarization produced by inhibitory nerve stimulation or inhibitory extract. The inhibitory potential amplitude following nerve stimulation was not restored by passive displacement of the membrane potential from -26 to -104 mV approximately. Ouabain (1-5 X 10(-5) M) reduced then (45-60 min later) abolished the inhibitory potential to nerve stimulation. The effects of this drug on the extract were not investigated. It is concluded that the inhibitory response to nerve stimulation and extract in the BRP may involve several ionic species. However, unlike that in gastrointestinal muscles the NANC response in the BRP is accompanied by an increased membrane resistance and does not primarily involve K+. The underlying mechanisms for the inhibitory response to both NANC nerve stimulation and inhibitory extract appear to be similar, compatible with the view that the latter may contain the inhibitory transmitter released from these nerves in this tissue. PMID:4027462

Dietary Tocotrienol/γ-Cyclodextrin Complex Increases Mitochondrial Membrane Potential and ATP Concentrations in the Brains of Aged Mice

PubMed Central

Schloesser, Anke; Esatbeyoglu, Tuba; Piegholdt, Stefanie; Dose, Janina; Ikuta, Naoko; Okamoto, Hinako; Ishida, Yoshiyuki; Terao, Keiji; Matsugo, Seiichi; Rimbach, Gerald

2015-01-01

Brain aging is accompanied by a decrease in mitochondrial function. In vitro studies suggest that tocotrienols, including γ- and δ-tocotrienol (T3), may exhibit neuroprotective properties. However, little is known about the effect of dietary T3 on mitochondrial function in vivo. In this study, we monitored the effect of a dietary T3/γ-cyclodextrin complex (T3CD) on mitochondrial membrane potential and ATP levels in the brain of 21-month-old mice. Mice were fed either a control diet or a diet enriched with T3CD providing 100 mg T3 per kg diet for 6 months. Dietary T3CD significantly increased mitochondrial membrane potential and ATP levels compared to those of controls. The increase in MMP and ATP due to dietary T3CD was accompanied by an increase in the protein levels of the mitochondrial transcription factor A (TFAM). Furthermore, dietary T3CD slightly increased the mRNA levels of superoxide dismutase, γ-glutamyl cysteinyl synthetase, and heme oxygenase 1 in the brain. Overall, the present data suggest that T3CD increases TFAM, mitochondrial membrane potential, and ATP synthesis in the brains of aged mice. PMID:26301044

The Relationship between Membrane Potential and Calcium Dynamics in Glucose-Stimulated Beta Cell Syncytium in Acute Mouse Pancreas Tissue Slices

PubMed Central

Miller, Evan W.; Slak Rupnik, Marjan

2013-01-01

Oscillatory electrical activity is regarded as a hallmark of the pancreatic beta cell glucose-dependent excitability pattern. Electrophysiologically recorded membrane potential oscillations in beta cells are associated with in-phase oscillatory cytosolic calcium activity ([Ca2+]i) measured with fluorescent probes. Recent high spatial and temporal resolution confocal imaging revealed that glucose stimulation of beta cells in intact islets within acute tissue slices produces a [Ca2+]i change with initial transient phase followed by a plateau phase with highly synchronized [Ca2+]i oscillations. Here, we aimed to correlate the plateau [Ca2+]i oscillations with the oscillations of membrane potential using patch-clamp and for the first time high resolution voltage-sensitive dye based confocal imaging. Our results demonstrated that the glucose-evoked membrane potential oscillations spread over the islet in a wave-like manner, their durations and wave velocities being comparable to the ones for [Ca2+]i oscillations and waves. High temporal resolution simultaneous records of membrane potential and [Ca2+]i confirmed tight but nevertheless limited coupling of the two processes, with membrane depolarization preceding the [Ca2+]i increase. The potassium channel blocker tetraethylammonium increased the velocity at which oscillations advanced over the islet by several-fold while, at the same time, emphasized differences in kinetics of the membrane potential and the [Ca2+]i. The combination of both imaging techniques provides a powerful tool that will help us attain deeper knowledge of the beta cell network. PMID:24324777

Research on the Changes to the Lipid/Polymer Membrane Used in the Acidic Bitterness Sensor Caused by Preconditioning

PubMed Central

Harada, Yuhei; Noda, Junpei; Yatabe, Rui; Ikezaki, Hidekazu; Toko, Kiyoshi

2016-01-01

A taste sensor that uses lipid/polymer membranes can evaluate aftertastes felt by humans using Change in membrane Potential caused by Adsorption (CPA) measurements. The sensor membrane for evaluating bitterness, which is caused by acidic bitter substances such as iso-alpha acid contained in beer, needs an immersion process in monosodium glutamate (MSG) solution, called “MSG preconditioning”. However, what happens to the lipid/polymer membrane during MSG preconditioning is not clear. Therefore, we carried out three experiments to investigate the changes in the lipid/polymer membrane caused by the MSG preconditioning, i.e., measurements of the taste sensor, measurements of the amount of the bitterness substance adsorbed onto the membrane and measurements of the contact angle of the membrane surface. The CPA values increased as the preconditioning process progressed, and became stable after 3 d of preconditioning. The response potentials to the reference solution showed the same tendency of the CPA value change during the preconditioning period. The contact angle of the lipid/polymer membrane surface decreased after 7 d of MSG preconditioning; in short, the surface of the lipid/polymer membrane became hydrophilic during MSG preconditioning. The amount of adsorbed iso-alpha acid was increased until 5 d preconditioning, and then it decreased. In this study, we revealed that the CPA values increased with the progress of MSG preconditioning in spite of the decrease of the amount of iso-alpha acid adsorbed onto the lipid/polymer membrane, and it was indicated that the CPA values increase because the sensor sensitivity was improved by the MSG preconditioning. PMID:26891299

Dinuclear polypyridylruthenium(II) complexes: flow cytometry studies of their accumulation in bacteria and the effect on the bacterial membrane.

PubMed

Li, Fangfei; Feterl, Marshall; Warner, Jeffrey M; Keene, F Richard; Collins, J Grant

2013-12-01

To determine the energy dependency of and the contribution of the membrane potential to the cellular accumulation of the dinuclear complexes [{Ru(phen)2}2{μ-bbn}](4+) (Rubbn) and the mononuclear complexes [Ru(Me4phen)3](2+) and [Ru(phen)2(bb7)](2+) in Staphylococcus aureus and Escherichia coli, and to examine their effect on the bacterial membrane. The accumulation of the ruthenium complexes in bacteria was determined using flow cytometry at a range of temperatures. The cellular accumulation of the ruthenium complexes was also determined in cells that had been incubated with the metal complexes in the presence or absence of metabolic stimulators or inhibitors and/or commercial dyes to determine the membrane potential or membrane permeability. The accumulation of ruthenium complexes in the two bacterial strains was shown to increase with increasing incubation temperature, with the relative increase in accumulation greater with E. coli, particularly for Rubb12 and Rubb16. No decrease in accumulation was observed for Rubb12 in ATP-inhibited cells. While carbonyl cyanide m-chlorophenyl hydrazone (CCCP) did depolarize the cell membrane, no reduction in the accumulation of Rubb12 was observed; however, all ruthenium complexes, when incubated with S. aureus at concentrations twice their MIC, depolarized the membrane to a similar extent to CCCP. Except for the mononuclear complex [Ru(Me4phen)3](2+), incubation of any of the other ruthenium complexes allowed a greater quantity of the membrane-impermeable dye TO-PRO-3 to be taken up by S. aureus. The results indicate that the potential new antimicrobial Rubbn complexes enter the cell in an energy-independent manner, depolarize the cell membrane and significantly permeabilize the cellular membrane.

CATAPHORETIC CHARGES OF COLLODION PARTICLES AND ANOMALOUS OSMOSIS THROUGH COLLODION MEMBRANES FREE FROM PROTEIN

PubMed Central

Loeb, Jacques

1922-01-01

1. It had been shown in previous papers that when a salt solution is separated from pure water by a collodion membrane, water diffuses through the membrane as if it were positively charged and as if it were attracted by the anion of the salt in solution and repelled by the cation with a force increasing with the valency. In this paper, measurements of the P.D. across the membrane (E) are given, showing that when an electrical effect is added to the purely osmotic effect of the salt solution in the transport of water from the side of pure water to the solution, the latter possesses a considerable negative charge which increases with increasing valency of the anion of the salt and diminishes with increasing valency of the cation. It is also shown that a similar valency effect exists in the diffusion potentials between salt solutions and pure water without the interposition of a membrane. 2. This makes it probable that the driving force for the electrical transport of water from the side of pure water into solution is primarily a diffusion potential. 3. It is shown that the hydrogen ion concentration of the solution affects the transport curves and the diffusion potentials in a similar way. 4. It is shown, however, that the diffusion potential without interposition of the membrane differs in a definite sense from the P.D. across the membrane and that therefore the P.D. across the membrane (E) is a modified diffusion potential. 5. Measurements of the P.D. between collodion particles and aqueous solutions (ε) were made by the method of cataphoresis, which prove that water in contact with collodion particles free from protein practically always assumes a positive charge (except in the presence of salts with trivalent and probably tetravalent cations of a sufficiently high concentration). 6. It is shown that an electrical transport of water from the side of water into the solution is always superposed upon the osmotic transport when the sign of charge of the solution in the potential across the membrane (E) is opposite to that of the water in the P.D. between collodion particle and water (ε); supporting the theoretical deductions made by Bartell. 7. It is shown that the product of the P.D. across the membrane (E) into the cataphoretic P.D. between collodion particles and aqueous solution (ε) accounts in general semiquantitatively for that part of the transport of water into the solution which is due to the electrical forces responsible for anomalous osmosis. PMID:19871981

Transmembrane potential measurements on plant cells using the voltage-sensitive dye ANNINE-6.

PubMed

Flickinger, Bianca; Berghöfer, Thomas; Hohenberger, Petra; Eing, Christian; Frey, Wolfgang

2010-11-01

The charging of the plasma membrane is a necessary condition for the generation of an electric-field-induced permeability increase of the plasmalemma, which is usually explained by the creation and the growth of aqueous pores. For cells suspended in physiological buffers, the time domain of membrane charging is in the submicrosecond range. Systematic measurements using Nicotiana tabacum L. cv. Bright Yellow 2 (BY-2) protoplasts stained with the fast voltage-sensitive fluorescence dye ANNINE-6 have been performed using a pulsed laser fluorescence microscopy setup with a time resolution of 5 ns. A clear saturation of the membrane voltage could be measured, caused by a strong membrane permeability increase, commonly explained by enhanced pore formation, which prevents further membrane charging by external electric field exposure. The field strength dependence of the protoplast's transmembrane potential V (M) shows strong asymmetric saturation characteristics due to the high resting potential of the plants plasmalemma. At the pole of the hyperpolarized hemisphere of the cell, saturation starts at an external field strength of 0.3 kV/cm, resulting in a measured transmembrane voltage shift of ∆V(M) = -150 mV, while on the cathodic (depolarized) cell pole, the threshold for enhanced pore formation is reached at a field strength of approximately 1.0 kV/cm and ∆V(M) = 450 mV, respectively. From this asymmetry of the measured maximum membrane voltage shifts, the resting potential of BY-2 protoplasts at the given experimental conditions can be determined to V(R) = -150 mV. Consequently, a strong membrane permeability increase occurs when the membrane voltage diverges |V(M)| = 300 mV from the resting potential of the protoplast. The largest membrane voltage change at a given external electric field occurs at the cell poles. The azimuthal dependence of the transmembrane potential, measured in angular intervals of 10° along the circumference of the cell, shows a flattening and a slight decrease at higher fields at the pole region due to enhanced pore formation. Additionally, at the hyperpolarized cell pole, a polarization reversal could be observed at an external field range around 1.0 kV/cm. This behavior might be attributed to a fast charge transfer through the membrane at the hyperpolarized pole, e.g., by voltage-gated channels.

Microbial Attachment Inhibition through Low-Voltage Electrochemical Reactions on Electrically Conducting Membranes.

PubMed

Ronen, Avner; Duan, Wenyan; Wheeldon, Ian; Walker, Sharon; Jassby, David

2015-11-03

Bacterial biofilm formation on membrane surfaces remains a serious challenge in water treatment systems. The impact of low voltages on microbial attachment to electrically conducting ultrafiltration membranes was investigated using a direct observation cross-flow membrane system mounted on a fluorescence microscope. Escherichia coli and microparticle deposition and detachment rates were measured as a function of the applied electrical potential to the membrane surface. Selecting bacteria and particles with low surface charge minimized electrostatic interactions between the bacteria and charged membrane surface. Application of an electrical potential had a significant impact on the detachment of live bacteria in comparison to dead bacteria and particles. Image analysis indicated that when a potential of 1.5 V was applied to the membrane/counter electrode pair, the percent of dead bacteria was 32±2.1 and 67±3.6% when the membrane was used as a cathode or anode, respectively, while at a potential of 1 V, 92±2.4% were alive. The application of low electrical potentials resulted in the production of low (μM) concentrations of hydrogen peroxide (HP) through the electroreduction of oxygen. The electrochemically produced HP reduced microbial cell viability and increased cellular permeability. Exposure to low concentrations of electrochemically produced HP on the membrane surface prevents bacterial attachment, thus ensuring biofilm-free conditions during membrane filtration operations.

Low K+-induced hyperpolarizations trigger transient depolarizations and action potentials in rabbit ventricular myocytes

PubMed Central

Akuzawa-Tateyama, M; Tateyama, M; Ochi, R

1998-01-01

The effects of large reductions of [K+]o on membrane potential were studied in isolated rabbit ventricular myocytes using the whole-cell patch clamp technique.Decreasing [K+]o from the normal level of 5.4 mm to 0.1 mm increased resting membrane potential (Vrest) from −75.6 ± 0.3 to −140.3 ± 1.9 mV (means ± s.e.m; n = 127), induced irregular, transient depolarizations with mean maximal amplitudes of 19.5 ± 1.5 mV and elicited action potentials in 56.7 % of trials. The action potentials exhibited overshoots of 37.9 ± 1.5 mV (n = 72) and sustained plateaux.Addition of 0.1 mm La3+ in the presence of 0.1 mm[K+]o significantly increased Vrest but decreased the amplitude of transient depolarizations and suppressed the firing of action potentials.Replacement of external Na+ or Cl− with N-methyl-D-glucamine or aspartate, respectively, or internal dialysis with 10 mm EGTA or BAPTA had little effect on low [K+]o-induced membrane potential changes.Hyperpolarizing voltage clamp pulses to potentials between −110 and −200 mV activated irregular inward currents that increased in amplitude and frequency with increasing hyperpolarization and were depressed by 0.1 mm La3+.The generation of transient depolarizations by low [K+]o can be explained as being a consequence of decreasing the inward rectifier K+ current (IK1) and the appearance of inward currents reflecting electroporation resulting from strong electric fields across the membrane. PMID:9824717

Diatomite reinforced chitosan composite membrane as potential scaffold for guided bone regeneration.

PubMed

Tamburaci, Sedef; Tihminlioglu, Funda

2017-11-01

In this study, natural silica source, diatomite, incorporated novel chitosan based composite membranes were fabricated and characterized for bone tissue engineering applications as possible bone regeneration membrane. The effect of diatomite loading on the mechanical, morphological, chemical, thermal and surface properties, wettability and in vitro cytotoxicity and cell proliferation on of composite membranes were investigated and observed by tensile test, atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), protein adsorption assay, air/water contact angle analysis and WST-1 respectively. Swelling studies were also performed by water absorption capacity determination. Results showed that incorporation of diatomite to the chitosan matrix increased the surface roughness, swelling capacity and tensile modulus of membranes. An increase of about 52% in Young's modulus was achieved for 10wt% diatomite composite membranes compared with chitosan membranes. High cell viability results were obtained with indirect extraction method. Besides, in vitro cell proliferation and ALP activity results showed that diatom incorporation significantly increased the ALP activity of Saos-2 cells cultured on chitosan membranes. The novel composite membranes prepared in the present study with tunable properties can be considered as a potential candidate as a scaffold in view of its enhanced physical & chemical properties as well as biological activities for bone tissue engineering applications. Copyright © 2017 Elsevier B.V. All rights reserved.

A putative role for the plasma membrane potential in the control of the expression of the gene encoding the tomato high-affinity potassium transporter HAK5.

PubMed

Nieves-Cordones, Manuel; Miller, Anthony J; Alemán, Fernando; Martínez, Vicente; Rubio, Francisco

2008-12-01

A chimeric CaHAK1-LeHAK5 transporter with only 15 amino acids of CaHAK1 in the N-terminus mediates high-affinity K(+) uptake in yeast cells. Kinetic and expression analyses strongly suggest that LeHAK5 mediates a significant proportion of the high-affinity K(+) uptake shown by K(+)-starved tomato (Solanum lycopersicum) plants. The development of high-affinity K(+) uptake, putatively mediated by LeHAK5, was correlated with increased LeHAK5 mRNA levels and a more negative electrical potential difference across the plasma membrane of root epidermal and cortical cells. However, this increase in high-affinity K(+) uptake was not correlated with the root K(+) content. Thus, (i) growth conditions that result in a hyperpolarized root plasma membrane potential, such as K(+) starvation or growth in the presence of NH(4) (+), but which do not decrease the K(+) content, lead to increased LeHAK5 expression; (ii) the presence of NaCl in the growth solution, which prevents the hyperpolarization induced by K(+) starvation, also prevents LeHAK5 expression. Moreover, once the gene is induced, depolarization of the plasma membrane potential then produces a decrease in the LeHAK5 mRNA. On the basis of these results, we propose that the plant membrane electrical potential plays a role in the regulation of the expression of this gene encoding a high-affinity K(+) transporter.

The Effects of Various Ions on Resting and Spike Potentials of Barnacle Muscle Fibers

PubMed Central

Hagiwara, Susumu; Chichibu, Shiko; Naka, Ken-ichi

1964-01-01

Effects of monovalent cations and some anions on the electrical properties of the barnacle muscle fiber membrane were studied when the intra- or extracellular concentrations of those ions were altered by longitudinal intra-cellular injection. The resting potential of the normal fiber decreases linearly with increase of logarithm of [K+]out and the decrement for a tenfold increase in [K+]out is 58 mv when the product, [K+]out ·[Cl-]out, is kept constant. It also decreases with decreasing [K+]in but is always less than expected theoretically. The deviation becomes larger as [K+]in increases and the resting potential finally starts to decrease with increasing [K+]in for [K+]in > 250 mM. When the internal K+ concentration is decreased the overshoot of the spike potential increases and the time course of the spike potential becomes more prolonged. In substituting for the internal K+, Na+ and sucrose affect the resting and spike potentials similarly. Some organic cations (guanidine, choline, tris, and TMA) behave like sucrose while some other organic cations (TEA, TPA, and TBA) have a specific effect and prolong the spike potential if they are applied intracellularly or extracellularly. In all cases the active membrane potential increases linearly with the logarithm of [Ca++]out/[K+]in and the increment is about 29 mv for tenfold increase in this ratio. The fiber membrane is permeable to Cl- and other smaller anions (Br- and I-) but not to acetate- and larger anions (citrate-, sulfate-, and methanesulfonate-). PMID:14212147

Carbachol-Induced Reduction in the Activity of Adult Male Zebra Finch RA Projection Neurons.

PubMed

Meng, Wei; Wang, Song-Hua; Li, Dong-Feng

2016-01-01

Cholinergic mechanism is involved in motor behavior. In songbirds, the robust nucleus of the arcopallium (RA) is a song premotor nucleus in the pallium and receives cholinergic inputs from the basal forebrain. The activity of projection neurons in RA determines song motor behavior. Although many evidences suggest that cholinergic system is implicated in song production, the cholinergic modulation of RA is not clear until now. In the present study, the electrophysiological effects of carbachol, a nonselective cholinergic receptor agonist, were investigated on the RA projection neurons of adult male zebra finches through whole-cell patch-clamp techniques in vitro. Our results show that carbachol produced a significant decrease in the spontaneous and evoked action potential (AP) firing frequency of RA projection neurons, accompanying a hyperpolarization of the membrane potential, an increase in the evoked AP latency, afterhyperpolarization (AHP) peak amplitude, and AHP time to peak, and a decrease in the membrane input resistance, membrane time constant, and membrane capacitance. These results indicate that carbachol reduces the activity of RA projection neurons by hyperpolarizing the resting membrane potential and increasing the AHP and the membrane conductance, suggesting that the cholinergic modulation of RA may play an important role in song production.

The effects of membrane cholesterol and simvastatin on red blood cell deformability and ATP release.

PubMed

Forsyth, Alison M; Braunmüller, Susanne; Wan, Jiandi; Franke, Thomas; Stone, Howard A

2012-05-01

It is known that deformation of red blood cells (RBCs) is linked to ATP release from the cells. Further, membrane cholesterol has been shown to alter properties of the cell membrane such as fluidity and bending stiffness. Membrane cholesterol content is increased in some cardiovascular diseases, for example, in individuals with acute coronary syndromes and chronic stable angina, and therefore, because of the potential clinical relevance, we investigated the influence of altered RBC membrane cholesterol levels on ATP release. Because of the correlation between statins and reduced membrane cholesterol in vivo, we also investigated the effects of simvastatin on RBC deformation and ATP release. We found that reducing membrane cholesterol increases cell deformability and ATP release. We also found that simvastatin increases deformability by acting directly on the membrane in the absence of the liver, and that ATP release was increased for cells with enriched cholesterol after treatment with simvastatin. Copyright © 2012 Elsevier Inc. All rights reserved.

Use of reverse osmosis membranes to remove perfluorooctane sulfonate (PFOS) from semiconductor wastewater.

PubMed

Tang, Chuyang Y; Fu, Q Shiang; Robertson, A P; Criddle, Craig S; Leckie, James O

2006-12-01

Perfluorooctane sulfonate (PFOS) and related substances are persistent, bioaccumulative, and toxic, and thus of substantial environmental concern. PFOS is an essential photolithographic chemical in the semiconductor industry with no substitutes yet identified. The industry seeks effective treatment technologies. The feasibility of using reverse osmosis (RO) membranes for treating semiconductor wastewater containing PFOS has been investigated. Commercial RO membranes were characterized in terms of permeability, salt rejection, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and membrane surface zeta potential (streaming potential measurements). Filtration tests were performed to determine the membrane flux and PFOS rejection. Over a wide range of feed concentrations (0.5 - 1500 ppm), the RO membranes generally rejected 99% or more of the PFOS. Rejection was better for tighter membranes, but was not affected by membrane zeta potential. Flux decreased with increasing PFOS concentration. While the flux reduction was severe for a loose RO membrane probably due to its higher initial flux, very stable flux was maintained for tighter membranes. At a very high feed concentration (about 500 ppm), all the membranes exhibited an identical stable flux. Isopropyl alcohol, present in some semiconductor wastewaters, had a detrimental effect on membrane flux. Where present it needs to be removed from the wastewater prior to using RO membranes.

Membrane processes in biotechnology: an overview.

PubMed

Charcosset, Catherine

2006-01-01

Membrane processes are increasingly reported for various applications in both upstream and downstream technology, such as the established ultrafiltration and microfiltration, and emerging processes as membrane bioreactors, membrane chromatography, and membrane contactors for the preparation of emulsions and particles. Membrane systems exploit the inherent properties of high selectivity, high surface-area-per-unit-volume, and their potential for controlling the level of contact and/or mixing between two phases. This review presents these various membrane processes by focusing more precisely on membrane materials, module design, operating parameters and the large range of possible applications.

Surface modification of polyamide reverse osmosis membrane with sulfonated polyvinyl alcohol for antifouling

NASA Astrophysics Data System (ADS)

Zhang, Yang; Wan, Ying; Pan, Guoyuan; Shi, Hongwei; Yan, Hao; Xu, Jian; Guo, Min; Wang, Zhe; Liu, Yiqun

2017-10-01

Sulfonated polyvinyl alcohol (SPVA) was synthesized by esterification reaction of PVA and sulfuric acid, and the structure was characterized by FTIR spectrum. Then a series of TFC membranes modified with cross-linked SPVA layer were fabricated by coating method, with glutaraldehyde as the cross-linker. The resulting TFC membranes were characterized by SEM, AFM, ATR-FTIR, XPS, streaming potential as well as static contact angle. The TFC membranes modified with SPVA exhibit decreased water flux and increased NaCl rejection with SPVA content increasing in the coating aqueous solution. The optimal PA-SPVA-0.5 sample exhibits a NaCl rejection of 99.18%, which is higher than the 98.32% of the virgin PA membrane. More importantly, the PA-SPVA-0.5 membrane shows much more improved fouling resistance to BSA and CTAB than virgin PA membrane and the TFC sample modified with PVA (PA-PVA-0.5). PA-SPVA-0.5 membrane loses about 8% of the initial flux after BSA fouling for 12 h, which is much lower than those of virgin PA and PA-PVA-0.5 membranes (28% and 15%, respectively). Furthermore, the flux recovery of the PA-SPVA-0.5 membrane reaches above 95% after cleaning. Thus, the PA-SPVA-0.5 membrane shows potential applications as antifouling RO membrane for desalination and purification.

Surface modification of polyamide reverse osmosis membrane with organic-inorganic hybrid material for antifouling

NASA Astrophysics Data System (ADS)

Zhang, Yang; Wan, Ying; Pan, Guoyuan; Yan, Hao; Yao, Xuerong; Shi, Hongwei; Tang, Yujing; Wei, Xiangrong; Liu, Yiqun

2018-03-01

A series of thin-film composite reverse osmosis membranes based on polyamide have been modified by coating the polyvinyl alcohol and 3-mercaptopropyltriethoxysilane aqueous solution prepared by a sol-gel process on the membrane surface, followed by thermal crosslinking treatment. In order to improve the hydrophilicity of the modified TFC membranes, the membranes were then immersed into H2O2 aqueous solution to convert -SH into -SO3H. The resulting TFC membranes were characterized by SEM, AFM, ATR-FTIR, streaming potential, XPS as well as static contact angle. After surface modification with the organic-inorganic hybrid material, the TFC membranes show increased NaCl rejection and decreased water flux with increasing 3-mercaptopropyltrimethoxysilane content in coating solution. The optimal modification membrane (PA-SMPTES-0.8) exhibits a NaCl rejection of 99.29%, higher than that (97.20%) of the virgin PA membrane, and a comparable water flux to virgin PA membrane (41.7 L/m2 h vs 47.9 L/m2 h). More importantly, PA-SMPTES-0.8 membrane shows much more improved fouling resistance to BSA than virgin PA and PVA modified PA (PA-PVA-1.0) membranes. PA-SMPTES-0.8 membrane loses about 13% of the initial flux after BSA fouling for 12 h, which is lower than that of virgin PA and PA-PVA-1.0 membranes (42% and 18%). Furthermore, the flux recovery of PA-SMPTES-0.8 membrane reaches 94% after cleaning. Thus the TFC membranes modified by this organic-inorganic hybrid technology show potential applications as antifouling RO membrane for desalination and purification.

Effect of oxotremorine on resting membrane potential and cell volume in skeletal muscle fibers in rats after in vivo blockade of NO-synthase.

PubMed

Khairova, R A; Malomuzh, A I; Naumenko, N V; Urazaev, A Kh

2003-02-01

Denervation of rat phrenic muscle or block of NO-synthase in vivo increased the cross-section area of muscle fibers and decreased membrane resting potential. Oxotremorine prevented the development of denervation-induced or denervation-like (i.e. induced by NO-synthase blockade) membrane depolarization and increase of the cross-sectional area of muscle fibers. Pirenzepine abolished the effects of oxotremorine. It was concluded that non-quantal acetylcholine can be involved in the regulation of skeletal muscle fiber volume via activation of M1 muscarinic receptors followed by NO synthesis.

A carbon nanotube filled polydimethylsiloxane hybrid membrane for enhanced butanol recovery

PubMed Central

Xue, Chuang; Du, Guang-Qing; Chen, Li-Jie; Ren, Jian-Gang; Sun, Jian-Xin; Bai, Feng-Wu; Yang, Shang-Tian

2014-01-01

The carbon nanotubes (CNTs) filled polydimethylsiloxane (PDMS) hybrid membrane was fabricated to evaluate its potential for butanol recovery from acetone-butanol-ethanol (ABE) fermentation broth. Compared with the homogeneous PDMS membrane, the CNTs filled into the PDMS membrane were beneficial for the improvement of butanol recovery in butanol flux and separation factor. The CNTs acting as sorption-active sites with super hydrophobicity could give an alternative route for mass transport through the inner tubes or along the smooth surface. The maximum total flux and butanol separation factor reached up to 244.3 g/m2·h and 32.9, respectively, when the PDMS membrane filled with 10 wt% CNTs was used to separate butanol from the butanol/water solution at 80°C. In addition, the butanol flux and separation factor increased dramatically as temperature increased from 30°C to 80°C in feed solution since the higher temperature produced more free volumes in polymer chains to facilitate butanol permeation. A similar increase was also observed when butanol titer in solution increased from 10 g/L to 25 g/L. Overall, the CNTs/PDMS hybrid membrane with higher butanol flux and selectivity should have good potential for pervaporation separation of butanol from ABE fermentation broth. PMID:25081019

The influence of the chloride gradient across red cell membranes on sodium and potassium movements

PubMed Central

Cotterrell, D.; Whittam, R.

1971-01-01

1. A study has been made to see whether active and passive movements of sodium and potassium in human red blood cells are influenced by changing the chloride gradient and hence the potential difference across the cell membrane. 2. Chloride distribution was measured between red cells and isotonic solutions with a range of concentrations of chloride and non-penetrating anions (EDTA, citrate, gluconate). The cell chloride concentration was greater than that outside with low external chloride, suggesting that the sign of the membrane potential was reversed. The chloride ratio (internal/external) was approximately equal to the inverse of the hydrogen ion ratio at normal and low external chloride, and inversely proportional to external pH. These results show that chloride is passively distributed, making it valid to calculate the membrane potential from the chloride ratio. 3. Ouabain-sensitive (pump) potassium influx and sodium efflux were decreased by not more than 20 and 40% respectively on reversing the chloride gradient, corresponding to a change in membrane potential from -9 to +30 mV. In contrast, passive (ouabain-insensitive) movements were reversibly altered — potassium influx was decreased about 60% and potassium efflux was increased some tenfold. Sodium influx was unaffected by the nature of the anion and depended only on the external sodium concentration, whereas ouabain-insensitive sodium efflux was increased about threefold. When external sodium was replaced by potassium there was a decrease in ouabain-insensitive sodium efflux with normal chloride, but an increase in low-chloride medium. 4. Net movements of sodium and potassium were roughly in accord with the unidirectional fluxes. 5. The results suggest that reversing the chloride gradient and, therefore, the sign of the membrane potential, had little effect on the sodium pump, but caused a marked increase in passive outward movements of both sodium and potassium ions. PMID:4996368

Tandem neopentyl glycol maltosides (TNMs) for membrane protein stabilisation†

PubMed Central

Bae, Hyoung Eun; Mortensen, Jonas S.; Ribeiro, Orquidea; Du, Yang; Ehsan, Muhammad; Kobilka, Brian K.; Loland, Claus J.; Byrne, Bernadette

2017-01-01

A novel class of detergents, designated tandem neopentyl glycol maltosides (TNMs), were evaluated with four target membrane proteins. The best detergent varied depending on the target, but TNM-C12L and TNM-C11S were notable for their ability to confer increased membrane protein stability compared to DDM. These agents have potential for use in membrane protein research. PMID:27711401

Tandem neopentyl glycol maltosides (TNMs) for membrane protein stabilisation.

PubMed

Bae, Hyoung Eun; Mortensen, Jonas S; Ribeiro, Orquidea; Du, Yang; Ehsan, Muhammad; Kobilka, Brian K; Loland, Claus J; Byrne, Bernadette; Chae, Pil Seok

2016-10-04

A novel class of detergents, designated tandem neopentyl glycol maltosides (TNMs), were evaluated with four target membrane proteins. The best detergent varied depending on the target, but TNM-C12L and TNM-C11S were notable for their ability to confer increased membrane protein stability compared to DDM. These agents have potential for use in membrane protein research.

Relationship between the Amount of Bitter Substances Adsorbed onto Lipid/Polymer Membrane and the Electric Response of Taste Sensors

PubMed Central

Toko, Kiyoshi; Hara, Daichi; Tahara, Yusuke; Yasuura, Masato; Ikezaki, Hidekazu

2014-01-01

The bitterness of bitter substances can be measured by the change in the membrane electric potential caused by adsorption (CPA) using a taste sensor (electronic tongue). In this study, we examined the relationship between the CPA value due to an acidic bitter substance and the amount of the bitter substance adsorbed onto lipid/polymer membranes, which contain different lipid contents, used in the taste sensor. We used iso-α-acid which is an acidic bitter substance found in several foods and beverages. The amount of adsorbed iso-α-acid, which was determined by spectroscopy, showed a maximum at the lipid concentration 0.1 wt % of the membrane, and the same phenomenon was observed for the CPA value. At the higher lipid concentration, however, the amount adsorbed decreased and then remained constant, while the CPA value decreased monotonically to zero. This constant adsorption amount was observed when the membrane potential in the reference solution did not change with increasing lipid concentration. The decrease in CPA value in spite of the constant adsorption amount is caused by a decrease in the sensitivity of the membrane as the surface charge density increases. The reason why the peaks appeared in both the CPA value and adsorption amount is based on the contradictory adsorption properties of iso-α-acid. The increasing charged lipid concentration of the membrane causes an increasing electrostatic attractive interaction between iso-α-acid and the membrane, but simultaneously causes a decreasing hydrophobic interaction that results in decreasing adsorption of iso-α-acid, which also has hydrophobic properties, onto the membrane. Estimates of the amount of adsorption suggest that iso-α-acid molecules are adsorbed onto both the surface and interior of the membrane. PMID:25184491

Neutrophil Membrane Cholesterol Content is a Key Factor in Cystic Fibrosis Lung Disease.

PubMed

White, Michelle M; Geraghty, Patrick; Hayes, Elaine; Cox, Stephen; Leitch, William; Alfawaz, Bader; Lavelle, Gillian M; McElvaney, Oliver J; Flannery, Ryan; Keenan, Joanne; Meleady, Paula; Henry, Michael; Clynes, Martin; Gunaratnam, Cedric; McElvaney, Noel G; Reeves, Emer P

2017-09-01

Identification of mechanisms promoting neutrophil trafficking to the lungs of patients with cystic fibrosis (CF) is a challenge for next generation therapeutics. Cholesterol, a structural component of neutrophil plasma membranes influences cell adhesion, a key step in transmigration. The effect of chronic inflammation on neutrophil membrane cholesterol content in patients with CF (PWCF) remains unclear. To address this we examined neutrophils of PWCF to evaluate the cause and consequence of altered membrane cholesterol and identified the effects of lung transplantation and ion channel potentiator therapy on the cellular mechanisms responsible for perturbed membrane cholesterol and increased cell adhesion. PWCF homozygous for the ΔF508 mutation or heterozygous for the G551D mutation were recruited (n=48). Membrane protein expression was investigated by mass spectrometry. The effect of lung transplantation or ivacaftor therapy was assessed by ELISAs, and calcium fluorometric and μ-calpain assays. Membranes of CF neutrophils contain less cholesterol, yet increased integrin CD11b expression, and respond to inflammatory induced endoplasmic reticulum (ER) stress by activating μ-calpain. In vivo and in vitro, increased μ-calpain activity resulted in proteolysis of the membrane cholesterol trafficking protein caveolin-1. The critical role of caveolin-1 for adequate membrane cholesterol content was confirmed in caveolin-1 knock-out mice. Lung transplant therapy or treatment of PWCF with ivacaftor, reduced levels of circulating inflammatory mediators and actuated increased caveolin-1 and membrane cholesterol, with concurrent normalized neutrophil adhesion. Results demonstrate an auxiliary benefit of lung transplant and potentiator therapy, evident by a reduction in circulating inflammation and controlled neutrophil adhesion. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

Dipole potentials indicate restructuring of the membrane interface induced by gadolinium and beryllium ions

NASA Technical Reports Server (NTRS)

Ermakov, Y. A.; Averbakh, A. Z.; Yusipovich, A. I.; Sukharev, S.

2001-01-01

The dipole component of the membrane boundary potential, phi(d), is an integral parameter that may report on the conformational state of the lipid headgroups and their hydration. In this work, we describe an experimental approach to measurements of the dipole potential changes, Deltaphi(d), and apply it in studies of Be(2+) and Gd(3+) interactions with membranes composed of phosphatidylserine (PS), phosphatidylcholine (PC), and their mixtures. Deltaphi(d) is determined as the difference between the changes of the total boundary potential, phi(b), measured by the IFC method in planar lipid membranes and the surface potential, phi(s), determined from the electrophoretic mobility of liposomes. The Gouy-Chapman-Stern formalism, combined with the condition of mass balance, well describes the ion equilibria for these high-affinity cations. For the adsorption of Be(2+) and Gd(3+) to PC membranes, and of Mg(2+) to PS membranes, the values of Deltaphi(b) and Deltaphi(s) are the same, indicative of no change of phi(d). Binding of Gd(3+) to PS-containing membranes induces changes of phi(d) of opposite signs depending on the density of ionized PS headgroups in the bilayer. At low density, the induced Deltaphi(d) is negative (-30 mV), consistent with the effect of dehydration of the surface. At maximal density (pure PS, neutral pH), adsorption of Be(2+) or Gd(3+) induces an increase of phi(d) of 35 or 140 mV, respectively. The onset of the strong positive dipole effect on PS membranes with Gd(3+) is observed near the zero charge point and correlates with a six-fold increase of membrane tension. The observed phenomena may reflect concerted reorientation of dipole moments of PS headgroups as a result of ion adsorption and lipid condensation. Their possible implications to in-vivo effects of these high-affinity ions are discussed.

Effect of bauhinia bauhinioides kallikrein inhibitor on endothelial proliferation and intracellular calcium concentration.

PubMed

Bilgin, M; Burgazli, K M; Rafiq, A; Mericliler, M; Neuhof, C; Oliva, M L; Parahuleva, M; Soydan, N; Doerr, O; Abdallah, Y; Erdogan, A

2014-01-01

Proteinase inhibitors act as a defensive system against predators e.g. insects, in plants. Bauhinia bauhinioides kallikrein inhibitor (BbKI) is a serine proteinase inhibitor, isolated from seeds of Bauhinia bauhinioides and is structurally similar to plant Kunitz-type inhibitors but lacks disulfide bridges. In this study we evaluated the antiproliferative effect of BbKI on endothelial cells and its impact on changes in membrane potential and intracellular calcium. HUVEC proliferation was significantly reduced by incubation with BbKI 50 and 100 µM 12% and 13%. Furthermore, BbKI (100 µM) exposure caused a significant increase in intracellular Ca2+ concentration by 35% as compared to untreated control. The intracellular rise in calcium was not affected by the absence of extracellular calcium. BBKI also caused a significant change in the cell membrane potential but the antiproliferative effect was independent of changes in membrane potential. BBKI has an antiproliferative effect on HUVEC, which is independent of the changes in membrane potential, and it causes an increase in intracellular Ca2+.

Promotion of Water Channels for Enhanced Ion Transport in 14 nm Diameter Carbon Nanotubes.

PubMed

Sheng, Jiadong; Zhu, Qi; Zeng, Xian; Yang, Zhaohui; Zhang, Xiaohua

2017-03-29

Ion transport plays an important role in solar-to-electricity conversion, drug delivery, and a variety of biological processes. Carbon nanotube (CNT) is a promising material as an ion transporter in the applications of the mimicking of natural ion channels, desalination, and energy harvesting. Here, we demonstrate a unique, enhanced ion transport through a vertically aligned multiwall CNT membrane after the application of an electric potential across CNT membranes. Interestingly, electrowetting arising from the application of an electric potential is critical for the enhancement of overall ion transport rate through CNT membranes. The wettability of a liquid with high surface tension on the interior channel walls of CNTs increases during an electric potential treatment and promotes the formation of water channels in CNTs. The formation of water channels in CNTs induces an increase in overall ion diffusion through CNT membranes. This phenomenon is also related to a decrease in the charge transfer resistance of CNTs (R ct ) after an electric potential is applied. Correspondingly, the enhanced ion flow rate gives rise to an enhancement in the capacitive performance of CNT based membranes. Our observations might have profound impact on the development of CNT based energy storage devices as well as artificial ion channels.

Carbachol-Induced Reduction in the Activity of Adult Male Zebra Finch RA Projection Neurons

PubMed Central

Meng, Wei; Wang, Song-Hua; Li, Dong-Feng

2016-01-01

Cholinergic mechanism is involved in motor behavior. In songbirds, the robust nucleus of the arcopallium (RA) is a song premotor nucleus in the pallium and receives cholinergic inputs from the basal forebrain. The activity of projection neurons in RA determines song motor behavior. Although many evidences suggest that cholinergic system is implicated in song production, the cholinergic modulation of RA is not clear until now. In the present study, the electrophysiological effects of carbachol, a nonselective cholinergic receptor agonist, were investigated on the RA projection neurons of adult male zebra finches through whole-cell patch-clamp techniques in vitro. Our results show that carbachol produced a significant decrease in the spontaneous and evoked action potential (AP) firing frequency of RA projection neurons, accompanying a hyperpolarization of the membrane potential, an increase in the evoked AP latency, afterhyperpolarization (AHP) peak amplitude, and AHP time to peak, and a decrease in the membrane input resistance, membrane time constant, and membrane capacitance. These results indicate that carbachol reduces the activity of RA projection neurons by hyperpolarizing the resting membrane potential and increasing the AHP and the membrane conductance, suggesting that the cholinergic modulation of RA may play an important role in song production. PMID:26904300

Catecholamines release mediators in the opossum oesophageal circular smooth muscle.

PubMed Central

Daniel, E E; Jager, L P; Jury, J

1987-01-01

1. Effects of catecholamines applied exogenously to the circular smooth muscle layer of the body of the oesophagus of the opossum (Didelphis marsupialis) were studied, simultaneously measuring changes in the membrane potential, the membrane conductance and the contractility of the muscle, using the double sucrose-gap technique. 2. Superfusion of the smooth muscle with Krebs solution at 27 degrees C containing dopamine (10(-6)-10(-4) M) dose-dependently caused a hyperpolarization of the smooth muscle cells and an increased membrane resistance followed after gradual repolarization by oscillations of the membrane potential, often accompanied by muscle action potentials. During the hyperpolarization, the tendency for the membrane potential to sag during prolonged application of hyperpolarizing currents was reduced and the 'off' depolarization following such currents was increased. This muscle did not develop active tension prior to treatment; it therefore did not relax during the hyperpolarizations, but contracted following the depolarized phase of oscillations. 3. The non-adrenergic, non-cholinergic nerve-mediated inhibitory junction potential (i.j.p.) showed a small reduction in amplitude during superfusion with dopamine, explicable as a result of the drug-induced hyperpolarization. The 'off' response following the i.j.p., decreased transiently when the membrane potential was hyperpolarized to its maximum value. Then it increased to values larger than control as the membrane repolarized. Vasoactive intestinal polypeptide (VIP, 10(-6) M) produced a similar response but hyperpolarizations were smaller. 4. Of the tested catecholamines, isoprenaline, phenylephrine, butylated hydroxytoluene-920 (BHT-920) and clonidine were ineffective whereas the potency order for other catecholamines was dopamine greater than noradrenaline greater than or equal to adrenaline greater than DOPA. The catecholamine-induced responses were not affected by alpha- or beta-adrenoreceptor antagonists given alone or in combination. Of the dopamine receptor antagonists tested domperidone was without effect, whereas haloperidol reduced and bulbocapnine blocked the response. The findings suggested that a receptor resembling DA1-type peripheral receptor mediated the effects of dopamine on opossum oesophagus. 5. The catecholamine-induced responses and those to VIP disappeared completely in Cl-(-)free medium (isethionate replacement). 6. Conditioning depolarization of the smooth muscle cells decreased but hyperpolarization increased the amplitude of the hyperpolarization (up to 20 mV). With larger hyperpolarizations the responses decreased and disappeared at around 50 mV hyperpolarization.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:3625558

Women's expectations and experiences of rupture of membranes and views of the potential use of reagent pads for detecting amniotic fluid.

PubMed

Spiby, Helen; Borrelli, Sara; Hughes, Anita J

2017-12-01

To explore first-time mothers' expectations and experiences regarding rupture of membranes at term and their views on the potential use of reagent pads that detect amniotic fluid. There is little information available on women's experiences of spontaneous rupture of membranes, or interest in using methods to confirm rupture of membranes (e.g. reagent pads). Descriptive qualitative study, using focus groups and telephone interviews with women during pregnancy and after the birth of their first baby. Thematic analysis was undertaken to analyse women's responses. Ethics committee approval was obtained. Twenty-five women participated in the study of whom 13 contributed both during pregnancy and postpartum between October 2015-March 2016. Three overarching themes were identified from the data from women's expectations and experiences: uncertainty in how, when and where membranes may rupture; information which was felt to be limited and confirmation of rupture of membranes. The potential use of reagent pads met with varied responses. Women were interested in having facts and figures regarding rupture of membranes, such as characteristics of liquor; volume and probability of membranes rupturing spontaneously at term. Use of a pad as a means of confirmation was viewed as helpful, although the potential for increasing anxiety was raised. © 2017 John Wiley & Sons Ltd.

Ionic Current Measurements in the Squid Giant Axon Membrane

PubMed Central

Cole, Kenneth S.; Moore, John W.

1960-01-01

The concepts, experiments, and interpretations of ionic current measurements after a step change of the squid axon membrane potential require the potential to be constant for the duration and the membrane area measured. An experimental approach to this ideal has been developed. Electrometer, operational, and control amplifiers produce the step potential between internal micropipette and external potential electrodes within 40 microseconds and a few millivolts. With an internal current electrode effective resistance of 2 ohm cm.2, the membrane potential and current may be constant within a few millivolts and 10 per cent out to near the electrode ends. The maximum membrane current patterns of the best axons are several times larger but of the type described by Cole and analyzed by Hodgkin and Huxley when the change of potential is adequately controlled. The occasional obvious distortions are attributed to the marginal adequacy of potential control to be expected from the characteristics of the current electrodes and the axon. Improvements are expected only to increase stability and accuracy. No reason has been found either to question the qualitative characteristics of the early measurements or to so discredit the analyses made of them. PMID:13694548

[Changes in polarization of myometrial cells plasma and internal mitochondrial membranes under calixarenes action as inhibitors of plasma membrane Na+, K+-ATPase].

PubMed

Danylovych, H V; Danylovych, Iu V; Kolomiiets', O V; Kosterin, S O; Rodik, R V; Cherenok, S O; Kal'chenko, V I; Chunikhin, O Iu; Horchev, V F; Karakhim, S O

2012-01-01

The influence of supramolecular macrocyclic compounds--calix[4]arenes C-97, C-99, C-107, which are ouabainomymetic high affinity inhibitors of Na+, K(+)-ATPase, on the polarization level of plasmic and mitochondrial membranes of rat uterine smooth muscle cells was investigated. The influence of these compounds on the myocytes characteristic size was studied. By using a confocal microscopy and specific for mitochondrial MitoTracker Orange CM-H2TMRos dye it was proved that the potential-sensitive fluorescent probe DiOC6(3) interacts with mitochondria. Artificial potential collapse of plasmic membrane in this case was modeled by myocytes preincubation with ouabain (1 mM). Further experiments performed using the method of flow cytometry with DiOC6(3) have shown that the compounds C-97, C-99 and C-107 at concentration 50-100 nM caused depolarization of the plasma membrane (at the level of 30% relative to control values) in conditions of artificial collapse of mitochondrial potential by myocytes preincubation in the presence of 5 mM of sodium azide. Under artificial sarcolemma depolarization by ouabain, calixarenes C-97, C-99 and C-107 at 100 nM concentrations caused a transient increase of mitochondrial membrane potential, that is 40% of the control level and lasted about 5 minutes. Calixarenes C-99 and C-107 caused a significant increase in fluorescence of myocytes in these conditions, which was confirmed by confocal microscopy too. It was proved by photon correlation spectroscopy method that the C-99 and C-107 caused an increase of characteristic size of myocytes.

Recent Advances on Bioethanol Dehydration using Zeolite Membrane

NASA Astrophysics Data System (ADS)

Makertihartha, I. G. B. N.; Dharmawijaya, P. T.; Wenten, I. G.

2017-07-01

Renewable energy has gained increasing attention throughout the world. Bioethanol has the potential to replace existing fossil fuel usage without much modification in existing facilities. Bioethanol which generally produced from fermentation route produces low ethanol concentration. However, fuel grade ethanol requires low water content to avoid engine stall. Dehydration process has been increasingly important in fuel grade ethanol production. Among all dehydration processes, pervaporation is considered as the most promising technology. Zeolite possesses high potential in pervaporation of bioethanol into fuel grade ethanol. Zeolite membrane can either remove organic (ethanol) from aqueous mixture or water from the mixture, depending on the framework used. Hydrophilic zeolite membrane, e.g. LTA, can easily remove water from the mixture leaving high ethanol concentration. On the other hand, hydrophobic zeolite membrane, e.g. silicate-1, can remove ethanol from aqueous solution. This review presents the concept of bioethanol dehydration using zeolite membrane. Special attention is given to the performance of selected pathway related to framework selection.

Enhanced ethylene separation and plasticization resistance in polymer membranes incorporating metal-organic framework nanocrystals.

PubMed

Bachman, Jonathan E; Smith, Zachary P; Li, Tao; Xu, Ting; Long, Jeffrey R

2016-08-01

The implementation of membrane-based separations in the petrochemical industry has the potential to reduce energy consumption significantly relative to conventional separation processes. Achieving this goal, however, requires the development of new membrane materials with greater selectivity, permeability and stability than available at present. Here, we report composite materials consisting of nanocrystals of metal-organic frameworks dispersed within a high-performance polyimide, which can exhibit enhanced selectivity for ethylene over ethane, greater ethylene permeability and improved membrane stability. Our results suggest that framework-polymer interactions reduce chain mobility of the polymer while simultaneously boosting membrane separation performance. The increased stability, or plasticization resistance, is expected to improve membrane utility under real process conditions for petrochemical separations and natural gas purification. Furthermore, this approach can be broadly applied to numerous polymers that encounter aggressive environments, potentially making gas separations possible that were previously inaccessible to membranes.

Membrane Capacitive Memory Alters Spiking in Neurons Described by the Fractional-Order Hodgkin-Huxley Model

PubMed Central

Weinberg, Seth H.

2015-01-01

Excitable cells and cell membranes are often modeled by the simple yet elegant parallel resistor-capacitor circuit. However, studies have shown that the passive properties of membranes may be more appropriately modeled with a non-ideal capacitor, in which the current-voltage relationship is given by a fractional-order derivative. Fractional-order membrane potential dynamics introduce capacitive memory effects, i.e., dynamics are influenced by a weighted sum of the membrane potential prior history. However, it is not clear to what extent fractional-order dynamics may alter the properties of active excitable cells. In this study, we investigate the spiking properties of the neuronal membrane patch, nerve axon, and neural networks described by the fractional-order Hodgkin-Huxley neuron model. We find that in the membrane patch model, as fractional-order decreases, i.e., a greater influence of membrane potential memory, peak sodium and potassium currents are altered, and spike frequency and amplitude are generally reduced. In the nerve axon, the velocity of spike propagation increases as fractional-order decreases, while in a neural network, electrical activity is more likely to cease for smaller fractional-order. Importantly, we demonstrate that the modulation of the peak ionic currents that occurs for reduced fractional-order alone fails to reproduce many of the key alterations in spiking properties, suggesting that membrane capacitive memory and fractional-order membrane potential dynamics are important and necessary to reproduce neuronal electrical activity. PMID:25970534

Functional membranes. Present and future

NASA Technical Reports Server (NTRS)

Kunitake, T.

1982-01-01

The present situation and the future development of the functional membrane are discussed. It is expected that functional membranes will play increasingly greater roles in the chemical industry of the coming decade. These membranes are formed from polymer films, liquid membranes or bilayer membranes. The two most important technologies based on the polymeric membrane are reverse osmosis and ion exchange. The liquid membrane is used for separation of ionic species; an extension of the solvent extraction process. By using appropriate ligands and ionophores, highly selective separations are realized. The active transport is made possible if the physical and chemical potentials are applied to the transport process. More advanced functional membranes may be designed on the basis of the synthetic bilayer membrane.

Effects of changing the ionic environment on passive and active membrane properties of pregnant rat uterus

PubMed Central

Abe, Y.

1971-01-01

1. In pregnant rat myometrium electrotonic potentials, produced by externally applied current, were recorded intracellularly. 2. The space constant, λ, was 1·8 mm, the time constant, τm, 120 msec. The values obtained on the 7th day and on the 20th day of pregnancy were the same. 3. The magnitude of the electrotonic potential and the time constant of the membrane were increased in the absence of potassium from the external solution and decreased by excess potassium. 4. The magnitude of the electrotonic potential and the time constant of the membrane were increased by the replacement of chloride with C6H5SO3- or SO42-, and decreased with NO3- or I- replacement. 5. When the sodium chloride was replaced with sucrose (16·7 mM sodium remaining in the buffers) the spontaneous spikes deteriorated and activity stopped within 30 min. However, for periods up to 4 hr, a spike of larger amplitude and faster rate of rise than in normal solution could be evoked when a depolarizing current was applied. 6. When the external calcium concentration was raised (5 and 10 mM) the amplitude and the rate of rise of the evoked spike were increased. They were decreased by reducing calcium. In zero calcium spontaneous activity stopped within 15 min. 7. The effects of calcium deficiency were much less marked and slower in onset when, simultaneously, the sodium concentration was reduced to 16·7 mM. 8. When calcium was replaced with strontium (2·5 mM), the membrane was depolarized and the duration of the spontaneous and evoked action potential was prolonged, mainly due to a slowed rate of repolarization. When the concentration of strontium was raised to 7·5 or 12·5 mM the membrane was hyperpolarized, the duration of the action potential became short and the amplitude of the spike was increased. 9. Addition of barium or the replacement of calcium with barium caused depolarization and oscillatory membrane activity. However, a spike could be evoked by applying conditioning hyperpolarization. 10. Manganese abolished the spontaneous and evoked spike. Tetrodotoxin had no effect. 11. The results show that rat uterus has cable-like properties. The action potential may be due to calcium entry, while sodium, by influencing the membrane potential in competition with calcium, may be involved in the spontaneous spike generation and the spread of excitation. PMID:5103422

Electrophysiological properties of the membrane and acetylcholine receptor in developing rat and chick myotubes

PubMed Central

1975-01-01

Membrane properties of rat and chick myotubes in various stages of development were studied. Resting membrane potentials (Em) increased from -8 to -55 mV in both rat and chick as the myotubes developed from myoblasts to large multinucleated fibers. In the rat myotubes, this increase was not accompanied by significant changes in specific membrane resistivity or changes in Na+ and K+ ion distribution. Nor have we observed a significant electrogenic component to the resting Em of mature rat myotubes under normal circumstances. A progressive increase in the passive permeability of the membrane to K+ relative to Na+ ions has been observed which can account for the changes in Em with development. In contrast to the changes in the ionic selectivity of the membrane, we have found that the ionic selectivity of the ACh receptor of rat and chick myotubes remains constant during the same period of myotube development. PMID:1176950

Cellulose acetate membranes functionalized with resveratrol by covalent immobilization for improved osseointegration

NASA Astrophysics Data System (ADS)

Pandele, A. M.; Neacsu, P.; Cimpean, A.; Staras, A. I.; Miculescu, F.; Iordache, A.; Voicu, S. I.; Thakur, V. K.; Toader, O. D.

2018-04-01

Covalent immobilization of resveratrol onto cellulose acetate polymeric membranes used as coating on a Mg-1Ca-0.2Mn-0.6Zr alloy is presented for potential application in the improvement of osseointegration processes. For this purpose, cellulose acetate membrane is hydrolysed in the presence of potassium hydroxide, followed by covalent immobilization of aminopropyl triethoxy silane. Resveratrol was immobilized onto membranes using glutaraldehyde as linker. The newly synthesised functional membranes were thoroughly characterized for their structural characteristics determination employing X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (FT-IR), Raman spectroscopy, thermogravimetric analysis (TGA/DTG) and scanning electron microscopy (SEM) techniques. Subsequently, in vitro cellular tests were performed for evaluating the cytotoxicity biocompatibility of synthesized materials and also the osseointegration potential of obtained derivatised membrane material. It was demonstrated that both polymeric membranes support viability and proliferation of the pre-osteoblastic MC3T3-E1 cells, thus providing a good protection against the potential harmful effects of the compounds released from coated alloys. Furthermore, cellulose acetate membrane functionalized with resveratrol exhibits a significant increase in alkaline phosphatase activity and extracellular matrix mineralization, suggesting its suitability to function as an implant surface coating for guided bone regeneration.

Mechanisms of CO2/H+ chemoreception by respiratory rhythm generator neurons in the medulla from newborn rats in vitro.

PubMed

Kawai, Akira; Onimaru, Hiroshi; Homma, Ikuo

2006-04-15

We investigated mechanisms of CO(2)/H(+) chemoreception in the respiratory centre of the medulla by measuring membrane potentials of pre-inspiratory neurons, which are putative respiratory rhythm generators, in the brainstem-spinal cord preparation of the neonatal rat. Neuronal response was tested by changing superfusate CO(2) concentration from 2% to 8% at constant HCO(3)(-) concentration (26 mm) or by changing pH from 7.8 to 7.2 by reducing HCO(3)(-) concentration at constant CO(2) (5%). Both respiratory and metabolic acidosis lead to depolarization of neurons with increased excitatory synaptic input and increased burst rate. Respiratory acidosis potentiated the amplitude of the neuronal drive potential. In the presence of tetrodotoxin (TTX), membrane depolarization persisted during respiratory and metabolic acidosis. However, the depolarization was smaller than that before application of TTX, which suggests that some neurons are intrinsically, and others synaptically, chemosensitive to CO(2)/H(+). Application of Ba(2+) blocked membrane depolarization by respiratory acidosis, whereas significant depolarization in response to metabolic acidosis still remained after application of Cd(2+) and Ba(2+). We concluded that the intrinsic responses to CO(2)/H(+)changes were mediated by potassium channels during respiratory acidosis, and that some other mechanisms operate during metabolic acidosis. In low-Ca(2+), high-Mg(2+) solution, an increased CO(2) concentration induced a membrane depolarization with a simultaneous increase of the burst rate. Pre-inspiratory neurons could adapt their baseline membrane potential to external CO(2)/H(+) changes by integration of these mechanisms to modulate their burst rates. Thus, pre-inspiratory neurons might play an important role in modulation of respiratory rhythm by central chemoreception in the brainstem-spinal cord preparation.

Mechanisms of CO2/H+ chemoreception by respiratory rhythm generator neurons in the medulla from newborn rats in vitro

PubMed Central

Kawai, Akira; Onimaru, Hiroshi; Homma, Ikuo

2006-01-01

We investigated mechanisms of CO2/H+ chemoreception in the respiratory centre of the medulla by measuring membrane potentials of pre-inspiratory neurons, which are putative respiratory rhythm generators, in the brainstem–spinal cord preparation of the neonatal rat. Neuronal response was tested by changing superfusate CO2 concentration from 2% to 8% at constant HCO3− concentration (26 mm) or by changing pH from 7.8 to 7.2 by reducing HCO3− concentration at constant CO2 (5%). Both respiratory and metabolic acidosis lead to depolarization of neurons with increased excitatory synaptic input and increased burst rate. Respiratory acidosis potentiated the amplitude of the neuronal drive potential. In the presence of tetrodotoxin (TTX), membrane depolarization persisted during respiratory and metabolic acidosis. However, the depolarization was smaller than that before application of TTX, which suggests that some neurons are intrinsically, and others synaptically, chemosensitive to CO2/H+. Application of Ba2+ blocked membrane depolarization by respiratory acidosis, whereas significant depolarization in response to metabolic acidosis still remained after application of Cd2+ and Ba2+. We concluded that the intrinsic responses to CO2/H+changes were mediated by potassium channels during respiratory acidosis, and that some other mechanisms operate during metabolic acidosis. In low-Ca2+, high-Mg2+ solution, an increased CO2 concentration induced a membrane depolarization with a simultaneous increase of the burst rate. Pre-inspiratory neurons could adapt their baseline membrane potential to external CO2/H+ changes by integration of these mechanisms to modulate their burst rates. Thus, pre-inspiratory neurons might play an important role in modulation of respiratory rhythm by central chemoreception in the brainstem–spinal cord preparation. PMID:16469786

Nonlinear dynamic characteristics of dielectric elastomer membranes

NASA Astrophysics Data System (ADS)

Fox, Jason W.; Goulbourne, Nakhiah C.

2008-03-01

The dynamic response of dielectric elastomer membranes subject to time-varying voltage inputs for various initial inflation states is investigated. These results provide new insight into the differences observed between quasi-static and dynamic actuation and presents a new challenge to modeling efforts. Dielectric elastomer membranes are a potentially enabling technology for soft robotics and biomedical devices such as implants and surgical tools. In this work, two key system parameters are varied: the chamber volume and the voltage signal offset. The chamber volume experiments reveal that increasing the size of the chamber onto which the membrane is clamped will increase the deformations as well as cause the membrane's resonance peaks to shift and change in number. For prestretched dielectric elastomer membranes at the smallest chamber volume, the maximum actuation displacement is 81 microns; while at the largest chamber volume, the maximum actuation displacement is 1431 microns. This corresponds to a 1767% increase in maximum pole displacement. In addition, actuating the membrane at the resonance frequencies provides hundreds of percent increase in strain compared to the quasi-static strain. Adding a voltage offset to the time-varying input signal causes the membrane to oscillate at two distinct frequencies rather than one and also presents a unique opportunity to increase the output displacement without electrically overloading the membrane. Experiments to capture the entire motion of the membrane reveal that classical membrane mode shapes are electrically generated although all points of the membrane do not pass through equilibrium at the same moments in time.

MSL1 is a mechanosensitive ion channel that dissipates mitochondrial membrane potential and maintains redox homeostasis in mitochondria during abiotic stress

PubMed Central

Lee, Chun Pong; Maksaev, Grigory; Jensen, Gregory S.; Murcha, Monika W.; Wilson, Margaret E.; Fricker, Mark; Hell, Ruediger; Haswell, Elizabeth S.; Millar, A. Harvey; Sweetlove, Lee

2016-01-01

Mitochondria must maintain tight control over the electrochemical gradient across their inner membrane to allow ATP synthesis while maintaining a redox-balanced electron transport chain and avoiding excessive reactive oxygen species production. However, there is a scarcity of knowledge about the ion transporters in the inner mitochondrial membrane that contribute to control of membrane potential. We show that loss of MSL1, a member of a family of mechanosensitive ion channels related to the bacterial channel MscS, leads to increased membrane potential of Arabidopsis mitochondria under specific bioenergetic states. We demonstrate that MSL1 localises to the inner mitochondrial membrane. When expressed in E. coli, MSL1 forms a stretch-activated ion channel with a slight preference for anions and provides protection against hypo-osmotic shock. In contrast, loss of MSL1 in Arabidopsis did not prevent swelling of isolated mitochondria in hypo-osmotic conditions. Instead, our data suggest that ion transport by MSL1 leads to dissipation of mitochondrial membrane potential when it becomes too high. The importance of MSL1 function was demonstrated by the observation of a higher oxidation state of the mitochondrial glutathione pool in msl1-1 mutants under moderate heat- and heavy-metal-stress. Furthermore, we show that MSL1 function is not directly implicated in mitochondrial membrane potential pulsing but is complementary and appears to be important under similar conditions. PMID:27505616

MEMBRANE POTENTIAL OF THE SQUID GIANT AXON DURING CURRENT FLOW

PubMed Central

Cole, Kenneth S.; Curtis, Howard J.

1941-01-01

The squid giant axon was placed in a shallow narrow trough and current was sent in at two electrodes in opposite sides of the trough and out at a third electrode several centimeters away. The potential difference across the membrane was measured between an inside fine capillary electrode with its tip in the axoplasm between the pair of polarizing electrodes, and an outside capillary electrode with its tip flush with the surface of one polarizing electrode. The initial transient was roughly exponential at the anode make and damped oscillatory at the sub-threshold cathode make with the action potential arising from the first maximum when threshold was reached. The constant change of membrane potential, after the initial transient, was measured as a function of the total polarizing current and from these data the membrane potential is obtained as a function of the membrane current density. The absolute value of the resting membrane resistance approached at low polarizing currents is about 23 ohm cm.2. This low value is considered to be a result of the puncture of the axon. The membrane was found to be an excellent rectifier with a ratio of about one hundred between the high resistance at the anode and the low resistance at the cathode for the current range investigated. On the assumption that the membrane conductance is a measure of its ion permeability, these experiments show an increase of ion permeability under a cathode and a decrease under an anode. PMID:19873234

MSL1 is a mechanosensitive ion channel that dissipates mitochondrial membrane potential and maintains redox homeostasis in mitochondria during abiotic stress.

PubMed

Lee, Chun Pong; Maksaev, Grigory; Jensen, Gregory S; Murcha, Monika W; Wilson, Margaret E; Fricker, Mark; Hell, Ruediger; Haswell, Elizabeth S; Millar, A Harvey; Sweetlove, Lee J

2016-12-01

Mitochondria must maintain tight control over the electrochemical gradient across their inner membrane to allow ATP synthesis while maintaining a redox-balanced electron transport chain and avoiding excessive reactive oxygen species production. However, there is a scarcity of knowledge about the ion transporters in the inner mitochondrial membrane that contribute to control of membrane potential. We show that loss of MSL1, a member of a family of mechanosensitive ion channels related to the bacterial channel MscS, leads to increased membrane potential of Arabidopsis mitochondria under specific bioenergetic states. We demonstrate that MSL1 localises to the inner mitochondrial membrane. When expressed in Escherichia coli, MSL1 forms a stretch-activated ion channel with a slight preference for anions and provides protection against hypo-osmotic shock. In contrast, loss of MSL1 in Arabidopsis did not prevent swelling of isolated mitochondria in hypo-osmotic conditions. Instead, our data suggest that ion transport by MSL1 leads to dissipation of mitochondrial membrane potential when it becomes too high. The importance of MSL1 function was demonstrated by the observation of a higher oxidation state of the mitochondrial glutathione pool in msl1-1 mutants under moderate heat- and heavy-metal-stress. Furthermore, we show that MSL1 function is not directly implicated in mitochondrial membrane potential pulsing, but is complementary and appears to be important under similar conditions. © 2016 The Authors The Plant Journal © 2016 John Wiley & Sons Ltd.

Vanadium Redox Flow Batteries Using meta-Polybenzimidazole-Based Membranes of Different Thicknesses.

PubMed

Noh, Chanho; Jung, Mina; Henkensmeier, Dirk; Nam, Suk Woo; Kwon, Yongchai

2017-10-25

15, 25, and 35 μm thick meta-polybenzimidazole (PBI) membranes are doped with H 2 SO 4 and tested in a vanadium redox flow battery (VRFB). Their performances are compared with those of Nafion membranes. Immersed in 2 M H 2 SO 4 , PBI absorbs about 2 mol of H 2 SO 4 per mole of repeat unit. This results in low conductivity and low voltage efficiency (VE). In ex-situ tests, meta-PBI shows a negligible crossover of V 3+ and V 4+ ions, much lower than that of Nafion. This is due to electrostatic repulsive forces between vanadium cations and positively charged protonated PBI backbones, and the molecular sieving effect of PBI's nanosized pores. It turns out that charge efficiency (CE) of VRFBs using meta-PBI-based membranes is unaffected by or slightly increases with decreasing membrane thickness. Thick meta-PBI membranes require about 100 mV larger potentials to achieve the same charging current as thin meta-PBI membranes. This additional potential may increase side reactions or enable more vanadium ions to overcome the electrostatic energy barrier and to enter the membrane. On this basis, H 2 SO 4 -doped meta-PBI membranes should be thin to achieve high VE and CE. The energy efficiency of 15 μm thick PBI reaches 92%, exceeding that of Nafion 212 and 117 (N212 and N117) at 40 mA cm -2 .

Amino-Functionalized Ceramic Capillary Membranes for Controlled Virus Retention.

PubMed

Bartels, Julia; Souza, Marina N; Schaper, Amelie; Árki, Pál; Kroll, Stephen; Rezwan, Kurosch

2016-02-16

A straightforward chemical functionalization strategy using aminosilanes for high-flux yttria-stabilized zirconia capillary membranes is presented (macroporous, d50 = 144 nm, open porosity =49%, membrane flux ∼150 L/(m(2)hbar)). Three different aminosilanes with one, two or three amino groups per silane molecule, namely 3-aminopropyltriethoxysilane (APTES), N-(2-aminoethyl)-3-aminopropyltriethoxysilane (AE-APTES) and N-(3-trimethoxysilylpropyl)diethylenetriamine (TPDA), are used to generate the amino-functionalized membranes. With a higher number of amino groups per silane molecule increased loading capacities between 0.44 and 1.01 accessible amino groups/nm(2) membrane are achieved. Streaming potential measurements confirm that the zeta-potential of the membrane surface is converted from negative (non-functionalized) to positive (amino-functionalized). By operation in dead-end filtration mode using the model virus MS2 (diameter = 25 nm, IEP = 3.9) the virus retention capacity of the amino-functionalized membranes is significantly increased and log reduction values (LRVs) of up to 9.6 ± 0.3 (TPDA) are obtained whereas a LRV < 0.3 is provided by the non-functionalized membranes. Long-term dead-end filtration experiments for 1 week reveal a high stability of immobilized aminosilanes (TPDA), being robust against leaching. By iterative backflushing with desorption buffer MS2-loaded membranes are successfully regenerated being reusable for a new filtration cycle. The presented functionalization platform is highly promising for controlled virus retention.

Spontaneous fluctuation of the resting membrane potential in Paramecium: amplification caused by intracellular Ca2+.

PubMed

Nakaoka, Yasuo; Imaji, Takafumi; Hara, Masahiro; Hashimoto, Noboru

2009-01-01

The ciliated protozoan Paramecium spontaneously changes its swimming direction in the absence of external stimuli. Such behavior is based on resting potential fluctuations, the amplitudes of which reach a few mV. When the resting potential fluctuation is positive and large, a spike-like depolarization is frequently elicited that reverses the beating of the cilia associated with directional changes during swimming. We aimed to study how the resting potential fluctuation is amplified. Simultaneous measurements of the resting potential and intracellular Ca(2+) ([Ca(2+)](i)) from a deciliated cell showed that positive potential fluctuations were frequently accompanied by a small increase in [Ca(2+)](i). This result suggests that Ca(2+) influx through the somatic membrane occurs during the resting state. The mean amplitude of the resting potential fluctuation was largely decreased by either an intracellular injection of a calcium chelater (BAPTA) or by an extracellular addition of Ba(2+). Hence, a small increase in [Ca(2+)](i) amplifies the resting potential fluctuation. Simulation analysis of the potential fluctuation was made by assuming that Ca(2+) and K(+) channels of surface membrane are fluctuating between open and closed states. The simulated fluctuation increased to exhibit almost the same amplitude as the measured fluctuation using the assumption that a small Ca(2+) influx activates Ca(2+) channels in a positive feedback manner.

Effect of phloretin on the permeability of thin lipid membranes

PubMed Central

1976-01-01

Phloretin dramatically increases cation conductances and decreases anion conductances of membranes treated with ion carriers (nonactin, valinomycin, carbonyl-cyanide-m-chlorophenylhydrazone [CCCP], and Hg(C6F5)2) or lipophilic ions (tetraphenylarsonium [tphAs+] and tetraphenylborate [TPhB-]). For example, on phosphatidylethanolamine membranes, 10(-4) M phloretin increases K+ -nonactin and TPhAs+ conductances and decreases CCCP- and TPhB- conductances 10(3)-fold; on lecithin: cholesterol membranes, it increases K+-nonactin conductance 10(5)-fold and decreases CCCP- conductance 10(3)-fold. Similar effects are obtained with p- and m-nitrophenol at 10(-2) M. These effects are produced by the un-ionized form of phloretin and the nitrophenols. We believe that phloretin, which possesses a large dipole moment, adsorbs and orients at the membrane surface to introduce a dipole potential of opposite polarity to the preexisting positive one, thus increasing the partition coefficient of cations into the membrane interior and decreasing the partition coefficient of anions. (Phloretin may also increase the fluidity of cholesterol-containing membranes; this is manifested by its two- to three-fold increase in nonelectrolyte permeability and its asymmetrical effect on cation and anion conductances in cholesterol-containing membranes.) It is possible that pholoretin's inhibition of chloride, urea, and glucose transport in biological membranes results from the effects of these intense intrafacial dipole fields on the translocator(s) of these molecules. PMID:946975

ω-3 polyunsaturated fatty acids direct differentiation of the membrane phenotype in mesenchymal stem cells to potentiate osteogenesis

PubMed Central

Levental, Kandice R.; Surma, Michal A.; Skinkle, Allison D.; Lorent, Joseph H.; Zhou, Yong; Klose, Christian; Chang, Jeffrey T.; Hancock, John F.; Levental, Ilya

2017-01-01

Mammalian cells produce hundreds of dynamically regulated lipid species that are actively turned over and trafficked to produce functional membranes. These lipid repertoires are susceptible to perturbations from dietary sources, with potentially profound physiological consequences. However, neither the lipid repertoires of various cellular membranes, their modulation by dietary fats, nor their effects on cellular phenotypes have been widely explored. We report that differentiation of human mesenchymal stem cells (MSCs) into osteoblasts or adipocytes results in extensive remodeling of the plasma membrane (PM), producing cell-specific membrane compositions and biophysical properties. The distinct features of osteoblast PMs enabled rational engineering of membrane phenotypes to modulate differentiation in MSCs. Specifically, supplementation with docosahexaenoic acid (DHA), a lipid component characteristic of osteoblast membranes, induced broad lipidomic remodeling in MSCs that reproduced compositional and structural aspects of the osteoblastic PM phenotype. The PM changes induced by DHA supplementation potentiated osteogenic differentiation of MSCs concurrent with enhanced Akt activation at the PM. These observations prompt a model wherein the DHA-induced lipidome leads to more stable membrane microdomains, which serve to increase Akt activity and thereby enhance osteogenic differentiation. More broadly, our investigations suggest a general mechanism by which dietary fats affect cellular physiology through remodeling of membrane lipidomes, biophysical properties, and signaling. PMID:29134198

Presynaptic membrane potential affects transmitter release in an identified neuron in Aplysia by modulating the Ca2+ and K+ currents.

PubMed

Shapiro, E; Castellucci, V F; Kandel, E R

1980-01-01

We have examined the relationships between the modulation of transmitter release and of specific ionic currents by membrane potential in the cholinergic interneuron L10 of the abdominal ganglion of Aplysia californica. The presynaptic cell body was voltage-clamped under various pharmacological conditions and transmitter release from the terminals was assayed simultaneously by recording the synaptic potentials in the postsynaptic cell. When cell L10 was voltage-clamped from a holding potential of -60 mV in the presence of tetrodotoxin, graded transmitter release was evoked by depolarizing command pulses in the membrane voltage range (-35 mV to + 10 mV) in which the Ca(2+) current was also increasing. Depolarizing the holding potential of L10 results in increased transmitter output. Two ionic mechanisms contribute to this form of plasticity. First, depolarization inactivates some K(+) channels so that depolarizing command pulses recruit a smaller K(+) current. In unclamped cells the decreased K(+) conductance causes spike-broadening and increased influx of Ca(2+) during each spike. Second, small depolarizations around resting potential (-55 mV to -35 mV) activate a steady-state Ca(2+) current that also contributes to the modulation of transmitter release, because, even with most presynaptic K(+) currents blocked pharmacologically, depolarizing the holding potential still increases transmitter release. In contrast to the steady-state Ca(2+) current, the transient inward Ca(2+) current evoked by depolarizing clamp steps is relatively unchanged from various holding potentials.

Influence of Glucose Deprivation on Membrane Potentials of Plasma Membranes, Mitochondria and Synaptic Vesicles in Rat Brain Synaptosomes.

PubMed

Hrynevich, Sviatlana V; Pekun, Tatyana G; Waseem, Tatyana V; Fedorovich, Sergei V

2015-06-01

Hypoglycemia can cause neuronal cell death similar to that of glutamate-induced cell death. In the present paper, we investigated the effect of glucose removal from incubation medium on changes of mitochondrial and plasma membrane potentials in rat brain synaptosomes using the fluorescent dyes DiSC3(5) and JC-1. We also monitored pH gradients in synaptic vesicles and their recycling by the fluorescent dye acridine orange. Glucose deprivation was found to cause an inhibition of K(+)-induced Ca(2+)-dependent exocytosis and a shift of mitochondrial and plasma membrane potentials to more positive values. The sensitivity of these parameters to the energy deficit caused by the removal of glucose showed the following order: mitochondrial membrane potential > plasma membrane potential > pH gradient in synaptic vesicles. The latter was almost unaffected by deprivation compared with the control. The pH-dependent dye acridine orange was used to investigate synaptic vesicle recycling. However, the compound's fluorescence was shown to be enhanced also by the mixture of mitochondrial toxins rotenone (10 µM) and oligomycin (5 µg/mL). This means that acridine orange can presumably be partially distributed in the intermembrane space of mitochondria. Glucose removal from the incubation medium resulted in a 3.7-fold raise of acridine orange response to rotenone + oligomycin suggesting a dramatic increase in the mitochondrial pH gradient. Our results suggest that the biophysical characteristics of neuronal presynaptic endings do not favor excessive non-controlled neurotransmitter release in case of hypoglycemia. The inhibition of exocytosis and the increase of the mitochondrial pH gradient, while preserving the vesicular pH gradient, are proposed as compensatory mechanisms.

Comparison of fouling characteristics in different pore-sized submerged ceramic membrane bioreactors.

PubMed

Jin, Le; Ong, Say Leong; Ng, How Yong

2010-12-01

Membrane fouling, the key disadvantage that inevitably occurs continuously in the membrane bioreactor (MBR), baffles the wide-scale application of MBR. Ceramic membrane, which possesses high chemical and thermal resistance, has seldom been used in MBR to treat municipal wastewater. Four ceramic membranes with the same materials but different pore sizes, ranging from 80 to 300 nm, were studied in parallel using four lab-scale submerged MBRs (i.e., one type of ceramic membrane in one MBR). Total COD and ammonia nitrogen removal efficiencies were observed to be consistently above 94.5 and 98%, respectively, in all submerged ceramic membrane bioreactors. The experimental results showed that fouling was mainly affected by membrane's microstructure, surface roughness and pore sizes. Ceramic membrane with the roughest surface and biggest pore size (300 nm) had the highest fouling potential with respect to the TMP profile. The 80 nm membrane with a smoother surface and relatively uniform smaller pore openings experienced least membrane fouling with respect to TMP increase. The effects of the molecular weight distribution, particle size distribution and other biomass characteristics such as extracellular polymeric substances, zeta potential and capillary suction time, were also investigated in this study. Results showed that no significant differences of these attributes were observed. These observations indicate that the membrane surface properties are the dominant factors leading to different fouling potential in this study. Copyright © 2010 Elsevier Ltd. All rights reserved.

Preparation of novel poly(vinylidene fluoride)/TiO2 photocatalysis membranes for use in direct contact membrane distillation

NASA Astrophysics Data System (ADS)

Li, Yukun; Dong, Shuying; Zhu, Liang

2018-03-01

Immobilization of TiO2 is a potential approach to obtain photocatalytic membranes that could eliminate concentration polarization in sewage disposal for direct contact membrane distillation (DCMD) process. A simple non-solvent-induced phase separation (NIPS) method was proposed to prepare poly(vinylidene fluoride) (PVDF) membrane, and the double-coating technology was further used to prepare the self-cleaning membranes with different TiO2 content. The effects of TiO2 nano-particles on membrane crystal form, morphology, porosity, pore size, pore size distribution, hydrophobicity, permeation, and photocatalytic efficiency were investigated, respectively. The flux of the prepared membranes is higher than the membrane (MS) provided by Membrane Solutions, LLC, in DCMD process. The contact angle between water and membrane could be increased 22° by introducing photocatalytic layer containing TiO2. During the photocatalytic test, 65.78-96.31% degrading rate of 15 mg/L Rhodamine B (RhB) was achieved. The relative flux of the membrane T-3 can be recovered to 0.96 in photocatalysis-membrane reactor for 8 h UV radiation. The fabricated membrane has great potential in high-salty dyeing wastewater treatment due to its high hydrophobicity and photocatalytic capability. [Figure not available: see fulltext.

Membrane processing technology in the food industry: food processing, wastewater treatment, and effects on physical, microbiological, organoleptic, and nutritional properties of foods.

PubMed

Kotsanopoulos, Konstantinos V; Arvanitoyannis, Ioannis S

2015-01-01

Membrane processing technology (MPT) is increasingly used nowadays in a wide range of applications (demineralization, desalination, stabilization, separation, deacidification, reduction of microbial load, purification, etc.) in food industries. The most frequently applied techniques are electrodialysis (ED), reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF). Several membrane characteristics, such as pore size, flow properties, and the applied hydraulic pressure mainly determine membranes' potential uses. In this review paper the basic membrane techniques, their potential applications in a large number of fields and products towards the food industry, the main advantages and disadvantages of these methods, fouling phenomena as well as their effects on the organoleptic, qualitative, and nutritional value of foods are synoptically described. Some representative examples of traditional and modern membrane applications both in tabular and figural form are also provided.

Functional consequences of sphingomyelinase-induced changes in erythrocyte membrane structure.

PubMed

Dinkla, S; Wessels, K; Verdurmen, W P R; Tomelleri, C; Cluitmans, J C A; Fransen, J; Fuchs, B; Schiller, J; Joosten, I; Brock, R; Bosman, G J C G M

2012-10-18

Inflammation enhances the secretion of sphingomyelinases (SMases). SMases catalyze the hydrolysis of sphingomyelin into phosphocholine and ceramide. In erythrocytes, ceramide formation leads to exposure of the removal signal phosphatidylserine (PS), creating a potential link between SMase activity and anemia of inflammation. Therefore, we studied the effects of SMase on various pathophysiologically relevant parameters of erythrocyte homeostasis. Time-lapse confocal microscopy revealed a SMase-induced transition from the discoid to a spherical shape, followed by PS exposure, and finally loss of cytoplasmic content. Also, SMase treatment resulted in ceramide-associated alterations in membrane-cytoskeleton interactions and membrane organization, including microdomain formation. Furthermore, we observed increases in membrane fragility, vesiculation and invagination, and large protein clusters. These changes were associated with enhanced erythrocyte retention in a spleen-mimicking model. Erythrocyte storage under blood bank conditions and during physiological aging increased the sensitivity to SMase. A low SMase activity already induced morphological and structural changes, demonstrating the potential of SMase to disturb erythrocyte homeostasis. Our analyses provide a comprehensive picture in which ceramide-induced changes in membrane microdomain organization disrupt the membrane-cytoskeleton interaction and membrane integrity, leading to vesiculation, reduced deformability, and finally loss of erythrocyte content. Understanding these processes is highly relevant for understanding anemia during chronic inflammation, especially in critically ill patients receiving blood transfusions.

Advanced Wastewater Treatment Engineering—Investigating Membrane Fouling in both Rotational and Static Membrane Bioreactor Systems Using Empirical Modelling

PubMed Central

Paul, Parneet; Jones, Franck Anderson

2016-01-01

Advanced wastewater treatment using membranes are popular environmental system processes since they allow reuse and recycling. However, fouling is a key limiting factor and so proprietary systems such as Avanti’s RPU-185 Flexidisks membrane bioreactor (MBR) use novel rotating membranes to assist in ameliorating it. In earlier research, this rotating process was studied by creating a simulation model based on first principles and traditional fouling mechanisms. In order to directly compare the potential benefits of this rotational system, this follow-up study was carried out using Avanti’s newly developed static (non-rotating) Flexidisks MBR system. The results from operating the static pilot unit were simulated and modelled using the rotational fouling model developed earlier however with rotational switching functions turned off and rotational parameters set to a static mode. The study concluded that a rotating MBR system could increase flux throughput when compared against a similar static system. It is thought that although the slowly rotating spindle induces a weak crossflow shear, it is still able to even out cake build up across the membrane surface, thus reducing the likelihood of localised critical flux being exceeded at the micro level and lessening the potential of rapid trans-membrane pressure increases at the macro level. PMID:26742053

Effects of thallium(I) and thallium(III) on liposome membrane physical properties.

PubMed

Villaverde, Marcela S; Verstraeten, Sandra V

2003-09-15

The hypothesis that thallium (Tl) interaction with membrane phospholipids could result in the alteration of membrane physical properties was investigated. Working with liposomes composed of brain phosphatidylcholine and phosphatidylserine, we found that Tl(+), Tl(3+), and Tl(OH)(3) (0.5-25 microM): (a) increased membrane surface potential, (b) decreased the fluidity of the anionic regions of the membrane, in association with an increased fluidity in the cationic regions, and (c) promoted the rearrangement of lipids through lateral phase separation. The magnitude of these effects followed the order Tl(3+), Tl(OH)(3)>Tl(+). In addition, Tl(3+) also decreased the hydration of phospholipid polar headgroups and induced membrane permeabilization. The present results show that Tl interacts with membranes inducing major alterations in the rheology of the bilayer, which could be partially responsible for the neurotoxic effects of this metal.

Removal of oxides from alkali metal melts by reductive titration to electrical resistance-change end points

DOEpatents

Tsang, Floris Y.

1980-01-01

Alkali metal oxides dissolved in alkali metal melts are reduced with soluble metals which are converted to insoluble oxides. The end points of the reduction is detected as an increase in electrical resistance across an alkali metal ion-conductive membrane interposed between the oxide-containing melt and a material capable of accepting the alkali metal ions from the membrane when a difference in electrical potential, of the appropriate polarity, is established across it. The resistance increase results from blocking of the membrane face by ions of the excess reductant metal, to which the membrane is essentially non-conductive.

Effect of membrane properties on the performance of a hybrid GAC and ultrafiltration process for water treatment.

PubMed

Qiao, Tiejun; Wu, Guangxue; Zhang, Xihui; Au, Doris W T; Zhang, Jinsong

2012-06-01

The performance of a hybrid granular activated carbon (GAC) and ultrafiltration (UF) process for water treatment was investigated using five types of UF membranes. The removal percentages for chemical oxygen demand (COD(Mn)), particles (> or = 2 microm) and total bacteria by the hybrid process were 30-40%, 98-99% and 76-92%, respectively. No invertebrates were detected in the hybrid process effluent. Transmembrane pressure and specific permeate flux (SPF) of the five types of membranes varied. With decreasing membrane pore sizes, removal of COD(Mn) and particles increased, whereas SPF firstly decreased and then increased. Hydrophilic membranes had a relatively high COD(Mn) removal potential, but did not obviously affect particle removal or SPF.

The effect of native silk fibroin powder on the physical properties and biocompatibility of biomedical polyurethane membrane.

PubMed

Zhuang, Yan; Zhang, Qian; Feng, Jinqi; Wang, Na; Xu, Weilin; Yang, Hongjun

2017-04-01

Naturally derived fibers such as silk fibroin can potentially enhance the biocompatibility of currently used biomaterials. This study investigated the physical properties of native silk fibroin powder and its effect on the biocompatibility of biomedical polyurethane. Native silk fibroin powder with an average diameter of 3 µm was prepared on a purpose-built machine. A simple method of phase inversion was used to produce biomedical polyurethane/native silk fibroin powder hybrid membranes at different blend ratios by immersing a biomedical polyurethane/native silk fibroin powder solution in deionized water at room temperature. The physical properties of the membranes including morphology, hydrophilicity, roughness, porosity, and compressive modulus were characterized, and in vitro biocompatibility was evaluated by seeding the human umbilical vein endothelial cells on the top surface. Native silk fibroin powder had a concentration-dependent effect on the number and morphology of human umbilical vein endothelial cells growing on the membranes; cell number increased as native silk fibroin powder content in the biomedical polyurethane/native silk fibroin powder hybrid membrane was increased from 0% to 50%, and cell morphology changed from spindle-shaped to cobblestone-like as the native silk fibroin powder content was increased from 0% to 70%. The latter change was related to the physical characteristics of the membrane, including hydrophilicity, roughness, and mechanical properties. The in vivo biocompatibility of the native silk fibroin powder-modified biomedical polyurethane membrane was evaluated in a rat model; the histological analysis revealed no systemic toxicity. These results indicate that the biomedical polyurethane/native silk fibroin powder hybrid membrane has superior in vitro and in vivo biocompatibility relative to 100% biomedical polyurethane membranes and thus has potential applications in the fabrication of small-diameter vascular grafts and in tissue engineering.

Ionic dependence of adrenal steroidogenesis and ACTH-induced changes in the membrane potential of adrenocortical cells

PubMed Central

Matthews, E. K.; Saffran, M.

1973-01-01

1. The effects of changes of ionic environment upon corticosteroid production by rabbit adrenal glands have been investigated in vitro using a superfusion technique and on-line steroid analysis by an automated fluorescence method. In some experiments micro-electrode recordings of adrenocortical transmembrane potentials were made concomitantly with measurement of steroid output. 2. Adrenocorticotrophic hormone (ACTH), 10 m-u./ml., induced a sevenfold increase in corticosteroid production rate in normal Krebs solution. 3. The steroidogenic response to ACTH was not impaired after omission of [K]o for 1 hr but was inhibited following exposure to K+-free medium for 3 hr. Increase of [K]o tenfold to 47 mM increased the basal but not the ACTH-stimulated output of corticosteroid whereas raising [K]o twentyfold to 94 mM enhanced both the basal and ACTH-stimulated steroid production rate. In K+-free solution the adrenocortical cells hyperpolarized from - 67 to - 86 mV; subsequently on addition of ACTH they depolarized. Reintroduction of K+ restored the membrane potential. 4. Omission of Ca2+ partially depolarized the cells but only affected the steroidogenic response to ACTH in the presence of EDTA. A threefold increase of [Ca]o, to 7·68 mM, had no effect on either membrane potentials or steroid formation, but increasing [Ca]o tenfold to 25·6 mM partially blocked ACTH action. Increasing [Mg]o twentyfold to 22·6 mM had little effect on ACTH-stimulated corticosteroid output and Sr 2·56 mM, in substitution for Ca2+, supported ACTH action, but La, 0·25 mM, completely blocked the steroidogenic effect of ACTH. 5. Replacement of NaCl, 118 mM by choline chloride, 118 mM, was without effect on ACTH-induced steroidogenesis, whereas LiCl, 118 mM, reduced it by 50%. NaF, 1 and 10 mM, inhibited ACTH-induced steroidogenesis by approximately 60%. 6. Nupercaine, 10-4 M, inhibited the steroid response to ACTH with no effect upon membrane potentials: increasing the nupercaine concentration to 10-3 M inhibited the steroid response and depolarized the cells. Ouabain, 10-5 M, induced complete depolarization and suppression of the steroidogenic response to ACTH. 7. Action-potential-like changes in membrane potential appeared in cells exposed to ACTH in a K+-free medium. The amplitude of the action potentials ranged from 10 to 60 mV according to cell, with a frequency up to 36/min; the frequency tended to increase with time. Tetrodotoxin, 10-6 g/ml., did not inhibit ACTH-induced action potentials in K+-free medium. 8. These observations are discussed in relation to the ionic requirements for the steroidogenic action of ACTH. The results further emphasize the dissociation of membrane polarization and the secretion of steroid. The mechanism of output of steroid hormone from the adrenocortical cell may thus differ fundamentally from the secretory mechanisms in other, particle-storing cells. PMID:4358269

Liposomes as model for taste cells: receptor sites for bitter substances including N-C=S substances and mechanism of membrane potential changes.

PubMed

Kumazawa, T; Nomura, T; Kurihara, K

1988-02-23

Various bitter substances were found to depolarize liposomes. The results obtained are as follows: (1) Changes in the membrane potential of azolectin liposomes in response to various bitter substances were monitored by measuring changes in the fluorescence intensity of 3,3'-dipropylthiocarbocyanine iodide [diS-C3(5)]. All the bitter substances examined increased the fluorescence intensity of the liposome-dye suspension, which indicates that the substances depolarize the liposomes. There existed a good correlation between the minimum concentrations of the bitter substances to depolarize the liposomes and the taste thresholds in humans. (2) The effects of changed lipid composition of liposomes on the responses to various bitter substances vary greatly among bitter substances, suggesting that the receptor sites for bitter substances are multiple. The responses to N-C=S substances and sucrose octaacetate especially greatly depended on the lipid composition; these compounds depolarized only liposomes having certain lipid composition, while no or hyperpolarizing responses to these compounds were observed in other liposomes examined. This suggested that the difference in "taster" and "nontaster" for these substances can be explained in terms of difference in the lipid composition of taste receptor membranes. (3) It was confirmed that the membrane potential of the planar lipid bilayer is changed in response to bitter substances. The membrane potential changes in the planar lipid bilayer as well as in liposomes in response to the bitter substances occurred under the condition that there is no ion gradient across the membranes. These results suggested that the membrane potential changes in response to bitter substances stem from the phase boundary potential changes induced by adsorption of the substances on the hydrophobic region of the membranes.

[Cyclosporin A causes oxidative stress and mitochondrial dysfunction in renal tubular cells].

PubMed

Pérez de Hornedo, J; de Arriba, G; Calvino, M; Benito, S; Parra, T

2007-01-01

Reactive oxygen species (ROS) have been implicated in cyclosporin A (CsA) nephrotoxicity. As mitochondria are one of the main sources of ROS in cells, we evaluated the role of CsA in mitochondrial structure and function in LLC-PK1 cells. We incubated cells with CsA 1 microM for 24 hours and studies were performed with flow citometry and confocal microscopy. We studied mitochondrial NAD(P)H content, superoxide anion (O2.-) production (MitoSOX Red), oxidation of cardiolipin of inner mitochondrial membrane (NAO) and mitochondrial membrane potential (DIOC2(3)). Also we analyzed the intracellular ROS synthesis (H2DCF-DA) and reduced glutation (GSH) of cells. Our results showed that CsA decreased NAD(P)H and membrane potential, and increased O2.- in mitochondria. CsA also provoked oxidation of cardiolipin. Furthermore, CsA increased intracellular ROS production and decreased GSH content. These results suggest that CsA has crucial effects in mitochondria. CsA modified mitochondrial physiology through the decrease of antioxidant mitochondrial compounds as NAD(P)H and the dissipation of mitochondrial membrane potential and increase of oxidants as O2.-. Also, CsA alters lipidic structure of inner mitochondrial membrane through the oxidation of cardiolipin. These effects trigger a chain of events that favour intracellular synthesis of ROS and depletion of GSH that can compromise cellular viability. Nephrotoxic cellular effects of CsA can be explained, at least in part, through its influence on mitochondrial functionalism.

Generation of action potentials in a mathematical model of corticotrophs.

PubMed Central

LeBeau, A P; Robson, A B; McKinnon, A E; Donald, R A; Sneyd, J

1997-01-01

Corticotropin-releasing hormone (CRH) is an important regulator of adrenocorticotropin (ACTH) secretion from pituitary corticotroph cells. The intracellular signaling system that underlies this process involves modulation of voltage-sensitive Ca2+ channel activity, which leads to the generation of Ca2+ action potentials and influx of Ca2+. However, the mechanisms by which Ca2+ channel activity is modulated in corticotrophs are not currently known. We investigated this process in a Hodgkin-Huxley-type mathematical model of corticotroph plasma membrane electrical responses. We found that an increase in the L-type Ca2+ current was sufficient to generate action potentials from a previously resting state of the model. The increase in the L-type current could be elicited by either a shift in the voltage dependence of the current toward more negative potentials, or by an increase in the conductance of the current. Although either of these mechanisms is potentially responsible for the generation of action potentials, previous experimental evidence favors the former mechanism, with the magnitude of the shift required being consistent with the experimental findings. The model also shows that the T-type Ca2+ current plays a role in setting the excitability of the plasma membrane, but does not appear to contribute in a dynamic manner to action potential generation. Inhibition of a K+ conductance that is active at rest also affects the excitability of the plasma membrane. PMID:9284294

Reversible and irreversible low-pressure membrane foulants in drinking water treatment: Identification by principal component analysis of fluorescence EEM and mitigation by biofiltration pretreatment.

PubMed

Peldszus, Sigrid; Hallé, Cynthia; Peiris, Ramila H; Hamouda, Mohamed; Jin, Xiaohui; Legge, Raymond L; Budman, Hector; Moresoli, Christine; Huck, Peter M

2011-10-15

With the increased use of membranes in drinking water treatment, fouling--particularly the hydraulically irreversible type--remains the main operating issue that hinders performance and increases operational costs. The main challenge in assessing fouling potential of feed water is to accurately detect and quantify feed water constituents responsible for membrane fouling. Utilizing fluorescence excitation-emission matrices (EEM), protein-like substances, humic and fulvic acids, and particulate/colloidal matter can be detected with high sensitivity in surface waters. The application of principal component analysis to fluorescence EEMs allowed estimation of the impact of surface water constituents on reversible and irreversible membrane fouling. This technique was applied to experimental data from a two year bench-scale study that included thirteen experiments investigating the fouling potential of Grand River water (Ontario, Canada) and the effect of biofiltration pre-treatment on the level of foulants during ultrafiltration (UF). Results showed that, although the content of protein-like substances in this membrane feed water (=biofiltered natural water) was much lower than commonly found in wastewater applications, the content of protein-like substances was still highly correlated with irreversible fouling of the UF membrane. In addition, there is evidence that protein-like substances and particulate/colloidal matter formed a combined fouling layer, which contributed to both reversible and irreversible fouling. It is suggested that fouling transitions from a reversible to an irreversible regime depending on feed composition and operating time. Direct biofiltration without prior coagulant addition reduced the protein-like content of the membrane feed water which in turn reduced the irreversible fouling potential for UF membranes. Biofilters also decreased reversible fouling, and for both types of fouling higher biofilter contact times were beneficial. Copyright © 2011 Elsevier Ltd. All rights reserved.

Studies on the role of goat heart galectin-1 as an erythrocyte membrane perturbing agent.

PubMed

Ashraf, Ghulam Md; Perveen, Asma; Zaidi, Syed Kashif; Tabrez, Shams; Kamal, Mohammad A; Banu, Naheed

2015-01-01

Galectins are β-galactoside binding lectins with a potential hemolytic role on erythrocyte membrane integrity and permeability. In the present study, goat heart galectin-1 (GHG-1) was purified and investigated for its hemolytic actions on erythrocyte membrane. When exposed to various saccharides, lactose and sucrose provided maximum protection against hemolysis, while glucose and galactose provided lesser protection against hemolysis. GHG-1 agglutinated erythrocytes were found to be significantly hemolyzed in comparison with unagglutinated erythrocytes. A concentration dependent rise in the hemolysis of trypsinized rabbit erythrocytes was observed in the presence of GHG-1. Similarly, a temperature dependent gradual increase in percent hemolysis was observed in GHG-1 agglutinated erythrocytes as compared to negligible hemolysis in unagglutinated cells. The hemolysis of GHG-1 treated erythrocytes showed a sharp rise with the increasing pH up to 7.5 which became constant till pH 9.5. The extent of erythrocyte hemolysis increased with the increase in the incubation period, with maximum hemolysis after 5 h of incubation. The results of this study establish the ability of galectins as a potential hemolytic agent of erythrocyte membrane, which in turn opens an interesting avenue in the field of proteomics and glycobiology.

Accelerating bioelectric functional development of neural stem cells by graphene coupling: Implications for neural interfacing with conductive materials.

PubMed

Guo, Rongrong; Zhang, Shasha; Xiao, Miao; Qian, Fuping; He, Zuhong; Li, Dan; Zhang, Xiaoli; Li, Huawei; Yang, Xiaowei; Wang, Ming; Chai, Renjie; Tang, Mingliang

2016-11-01

In order to govern cell-specific behaviors in tissue engineering for neural repair and regeneration, a better understanding of material-cell interactions, especially the bioelectric functions, is extremely important. Graphene has been reported to be a potential candidate for use as a scaffold and neural interfacing material. However, the bioelectric evolvement of cell membranes on these conductive graphene substrates remains largely uninvestigated. In this study, we used a neural stem cell (NSC) model to explore the possible changes in membrane bioelectric properties - including resting membrane potentials and action potentials - and cell behaviors on graphene films under both proliferation and differentiation conditions. We used a combination of single-cell electrophysiological recordings and traditional cell biology techniques. Graphene did not affect the basic membrane electrical parameters (capacitance and input resistance), but resting membrane potentials of cells on graphene substrates were more strongly negative under both proliferation and differentiation conditions. Also, NSCs and their progeny on graphene substrates exhibited increased firing of action potentials during development compared to controls. However, graphene only slightly affected the electric characterizations of mature NSC progeny. The modulation of passive and active bioelectric properties on the graphene substrate was accompanied by enhanced NSC differentiation. Furthermore, spine density, synapse proteins expressions and synaptic activity were all increased in graphene group. Modeling of the electric field on conductive graphene substrates suggests that the electric field produced by the electronegative cell membrane is much higher on graphene substrates than that on control, and this might explain the observed changes of bioelectric development by graphene coupling. Our results indicate that graphene is able to accelerate NSC maturation during development, especially with regard to bioelectric evolvement. Our findings provide a fundamental understanding of the role of conductive materials in tuning the membrane bioelectric properties in a graphene model and pave the way for future studies on the development of methods and materials for manipulating membrane properties in a controllable way for NSC-based therapies. Copyright © 2016 Elsevier Ltd. All rights reserved.

Kinetic analysis of the interaction between poly(amidoamine) dendrimers and model lipid membranes.

PubMed

Tiriveedhi, Venkataswarup; Kitchens, Kelly M; Nevels, Kerrick J; Ghandehari, Hamidreza; Butko, Peter

2011-01-01

We used fluorescence spectroscopy and surface tensiometry to study the interaction between low-generation (G1 and G4) poly(amidoamine) (PAMAM) dendrimers, potential vehicles for intracellular drug delivery, and model lipid bilayers. Membrane association of fluorescently labeled dendrimers, measured by fluorescence anisotropy, increased with increasing size of the dendrimer and with increasing negative charge density in the membrane, indicating the electrostatic nature of the interaction. When the membrane was doped with pyrene-labeled phosphatidyl glycerol (pyrene-PG), pyrene excimer fluorescence demonstrated a dendrimer-induced selective aggregation of negatively charged lipids when the membrane was in the liquid crystalline state. A nonlinear Stern-Volmer quenching of dendrimer fluorescence with cobalt bromide suggested a dendrimer-induced aggregation of lipid vesicles, which increased with the dendrimer's generation number. Surface tensiometry measurements showed that dendrimers penetrated into the lipid monolayer only at subphysiologic surface pressures (<30mN/m). We conclude that the low-generation PAMAM dendrimers associate with lipid membranes predominantly electrostatically, without significantly compromising the bilayer integrity. They bind stronger to membranes with higher fluidity and lower surface pressure, which are characteristic of rapidly dividing cells. Copyright © 2010 Elsevier B.V. All rights reserved.

Effect of hydraulically reversible and hydraulically irreversible fouling on the removal of MS2 and φX174 bacteriophage by an ultrafiltration membrane.

PubMed

ElHadidy, Ahmed M; Peldszus, Sigrid; Van Dyke, Michele I

2014-09-15

The effect of membrane fouling on the removal of enteric virus surrogates MS2 and φX174 bacteriophage by an ultrafiltration membrane was assessed under simulated full-scale drinking water treatment operating conditions. Filtration experiments of up to 8 days using either river or lake water ascertained how the membrane fouling layer affected virus removal. Organic carbon fractionation techniques identified potential foulants, including biopolymers, in the feed water and in the permeate. Hydraulically irreversible fouling could greatly improve the removal of both viruses at moderate and severe fouling conditions by up to 2.5 logs. Hydraulically reversible fouling increased virus removal only slightly, and increased removal of >0.5 log for both phage were only obtained under severe fouling conditions. The increase in virus removal due to irreversible and reversible fouling differed between the two water sources. As the degree of fouling increased, differences between the removal of the two phage decreased. Maintenance cleaning partially removed membrane foulants, however virus removal following maintenance cleaning was lower than that of the fouled membrane, it remained higher than that of the clean membrane. Copyright © 2014 Elsevier Ltd. All rights reserved.

Myo-conductive and osteo-inductive free-standing polysaccharide membranes

PubMed Central

Caridade, Sofia G.; Monge, Claire; Almodóvar, Jorge; Guillot, Raphael; Lavaud, Jonathan; Josserand, Véronique; Coll, Jean-Luc; Mano, João F.; Picart, Catherine

2015-01-01

Free-standing (FS) membranes have increasing applications in the biomedical field as drug delivery systems for wound healing and tissue engineering. Here, we studied the potential of free-standing membranes made by the layer-by-layer assembly of chitosan and alginate to be used as a simple biomimetic system of the periosteum. The design of a periosteum-like membrane implies the elaboration of a thick membrane suitable for both muscle and bone formation. Our aim was to produce well defined ~50 μm thick polysaccharide membranes that could be easily manipulated, be mechanically resistant, and enable both myogenesis and osteogenesis in vitro and in vivo. The membranes were chemically crosslinked to improve their mechanical properties. Crosslinking chemistry was followed via FTIR and the mechanical properties of the membranes were assessed using dynamic mechanical analysis. The loading and release of the potent osteoinductive growth factor bone morphogenetic protein 2 (BMP-2) inside and outside of the FS membrane was followed by fluorescence spectroscopy in a physiological buffer over one month. The myogenic and osteogenic potential of the membranes in vitro was assessed using BMP-2 responsive skeletal myoblasts. Finally, their osteoinductive properties in vivo were studied in a preliminary experiment using a mouse ectopic model. Our results showed that the more crosslinked FS membranes enabled a more efficient myoblast differentiation in myotubes. In addition, we showed that a tunable amount of BMP-2 can be loaded in and subsequently released from the membranes depending on the crosslinking degree and BMP-2 initial concentration in solution. Only the more crosslinked membranes were found to be osteoinductive in vivo. These polysaccharide-based membranes have strong potential as a periosteum-mimetic scaffold for bone tissue regeneration. PMID:25575853

Membrane potentials in pinched-off presynaptic nerve ternimals monitored with a fluorescent probe: evidence that synaptosomes have potassium diffusion potentials.

PubMed Central

Blaustein, M P; Goldring, J M

1975-01-01

1. Some physiological properties of tissue fractions from rat brain homogenates have been examined. Of the three fractions studied (presynaptic nerve terminals, mitochondria and fragmented membranes), only the nerve terminals (synaptosomes) have the ability to accumulate 42K from physiological salt solutions. 2. The ability to accumulate and retain K is lost if synaptosomes are exposed to very hypotonic solutions. The K uptake and total K content is reduced by ouabain and by inhibitors of glycolysis and oxidative phosphorylation. 3. These results suggest that synaptosomes in physiological saline accumulate K against a concentration gradient, and may have K diffusion potentials across their surface membranes. The voltage-sensitive fluorescent probe, 3,3'-dipentyl 2,2'-oxacarbocyanine (CC5), was used to test this possibility. 4. In the squid axon, the fluorescent emission of CC5 is directly proportional to membrane potential; depolarization causes an increase in fluorescence. 5. The fluorescence of synaptosomes ('synaptosome fluorescence') treated with CC5 is increased when [K]o is increased or [K]o is reduced; replacement of external Na by Li or choline has little effect on the synaptosome fluorescence. In quantitative terms, synaptosome fluorescence is proportional to log ([K]o plus 0-05[Na]o). Rb is about as effective as K in enhancing synaptosome fluorescence; Cs is about 1/4 as effective. The effect of increased [K]o is reversible. 6. The fluorescence data provide corroborative evidence that there is normally a large K gradient ([K]o smaller than [I]i) across the synaptosome surface membrane. The data suggest the [K]i may be in excess of 100 mM. 7. Replacement of Cl- by methylsulphate did not significantly affect the relationship between synaptosome fluorescence and [K]o, nor did removal of external Ca. 8. The fluorescence of CC5-treated mitochondria, membrane fragmnets, or lysed synaptosomes is unaffected by changes in the K concentration of the medium. 9. Veratridine and gramicidin D, both of which enhance Na permeability (PNa) in some intact tissues, increase synaptosome fluorescence when added to the standard medium. The increment is greatly reduced or abolished when external Na is replaced by choline. 10. If synaptosomes are first Na-loaded (by pre-treatment with cyanide + iodoacetate), and then placed in a choline medium, addition of gramicidin D significantly decreases fluorescence. This effect could be explained if, with [Na]o smaller than [Na]i, the increase in PNa causes the synaptosomes to hyperpolarize. 11. The veratridine-induced increase in synaptosome fluorescence was prevented by 3 times 10- minus 7M tetrodotoxin, which also blocks the depolarizing effect of veratridine in intact neurones. 12. The main conclusion is that synaptosomes may retain resting membrane potentials and the ability to increase Na permeability. PMID:49421

Role of Alcohols in Growth, Lipid Composition, and Membrane Fluidity of Yeasts, Bacteria, and Archaea ▿

PubMed Central

Huffer, Sarah; Clark, Melinda E.; Ning, Jonathan C.; Blanch, Harvey W.; Clark, Douglas S.

2011-01-01

Increased membrane fluidity, which causes cofactor leakage and loss of membrane potential, has long been documented as a cause for decreased cell growth during exposure to ethanol, butanol, and other alcohols. Reinforcement of the membrane with more complex lipid components is thus thought to be beneficial for the generation of more tolerant organisms. In this study, organisms with more complex membranes, namely, archaea, did not maintain high growth rates upon exposure to alcohols, indicating that more complex lipids do not necessarily fortify the membrane against the fluidizing effects of alcohols. In the presence of alcohols, shifts in lipid composition to more saturated and unbranched lipids were observed in most of the organisms tested, including archaea, yeasts, and bacteria. However, these shifts did not always result in a decrease in membrane fluidity or in greater tolerance of the organism to alcohol exposure. In general, organisms tolerating the highest concentrations of alcohols maintained membrane fluidity after alcohol exposure, whereas organisms that increased membrane rigidity were less tolerant. Altered lipid composition was a common response to alcohol exposure, with the most tolerant organisms maintaining a modestly fluid membrane. Our results demonstrate that increased membrane fluidity is not the sole cause of growth inhibition and that alcohols may also denature proteins within the membrane and cytosol, adversely affecting metabolism and decreasing cell growth. PMID:21784917

Mitochondrial Targeted Coenzyme Q, Superoxide, and Fuel Selectivity in Endothelial Cells

PubMed Central

Fink, Brian D.; O'Malley, Yunxia; Dake, Brian L.; Ross, Nicolette C.; Prisinzano, Thomas E.; Sivitz, William I.

2009-01-01

Background Previously, we reported that the “antioxidant” compound “mitoQ” (mitochondrial-targeted ubiquinol/ubiquinone) actually increased superoxide production by bovine aortic endothelial (BAE) cell mitochondria incubated with complex I but not complex II substrates. Methods and Results To further define the site of action of the targeted coenzyme Q compound, we extended these studies to include different substrate and inhibitor conditions. In addition, we assessed the effects of mitoquinone on mitochondrial respiration, measured respiration and mitochondrial membrane potential in intact cells, and tested the intriguing hypothesis that mitoquinone might impart fuel selectivity in intact BAE cells. In mitochondria respiring on differing concentrations of complex I substrates, mitoquinone and rotenone had interactive effects on ROS consistent with redox cycling at multiple sites within complex I. Mitoquinone increased respiration in isolated mitochondria respiring on complex I but not complex II substrates. Mitoquinone also increased oxygen consumption by intact BAE cells. Moreover, when added to intact cells at 50 to 1000 nM, mitoquinone increased glucose oxidation and reduced fat oxidation, at doses that did not alter membrane potential or induce cell toxicity. Although high dose mitoquinone reduced mitochondrial membrane potential, the positively charged mitochondrial-targeted cation, decyltriphenylphosphonium (mitoquinone without the coenzyme Q moiety), decreased membrane potential more than mitoquinone, but did not alter fuel selectivity. Therefore, non-specific effects of the positive charge were not responsible and the quinone moiety is required for altered nutrient selectivity. Conclusions In summary, the interactive effects of mitoquinone and rotenone are consistent with redox cycling at more than one site within complex I. In addition, mitoquinone has substrate dependent effects on mitochondrial respiration, increases repiration by intact cells, and alters fuel selectivity favoring glucose over fatty acid oxidation at the intact cell level. PMID:19158951

Mitochondrial targeted coenzyme Q, superoxide, and fuel selectivity in endothelial cells.

PubMed

Fink, Brian D; O'Malley, Yunxia; Dake, Brian L; Ross, Nicolette C; Prisinzano, Thomas E; Sivitz, William I

2009-01-01

Previously, we reported that the "antioxidant" compound "mitoQ" (mitochondrial-targeted ubiquinol/ubiquinone) actually increased superoxide production by bovine aortic endothelial (BAE) cell mitochondria incubated with complex I but not complex II substrates. To further define the site of action of the targeted coenzyme Q compound, we extended these studies to include different substrate and inhibitor conditions. In addition, we assessed the effects of mitoquinone on mitochondrial respiration, measured respiration and mitochondrial membrane potential in intact cells, and tested the intriguing hypothesis that mitoquinone might impart fuel selectivity in intact BAE cells. In mitochondria respiring on differing concentrations of complex I substrates, mitoquinone and rotenone had interactive effects on ROS consistent with redox cycling at multiple sites within complex I. Mitoquinone increased respiration in isolated mitochondria respiring on complex I but not complex II substrates. Mitoquinone also increased oxygen consumption by intact BAE cells. Moreover, when added to intact cells at 50 to 1000 nM, mitoquinone increased glucose oxidation and reduced fat oxidation, at doses that did not alter membrane potential or induce cell toxicity. Although high dose mitoquinone reduced mitochondrial membrane potential, the positively charged mitochondrial-targeted cation, decyltriphenylphosphonium (mitoquinone without the coenzyme Q moiety), decreased membrane potential more than mitoquinone, but did not alter fuel selectivity. Therefore, non-specific effects of the positive charge were not responsible and the quinone moiety is required for altered nutrient selectivity. In summary, the interactive effects of mitoquinone and rotenone are consistent with redox cycling at more than one site within complex I. In addition, mitoquinone has substrate dependent effects on mitochondrial respiration, increases repiration by intact cells, and alters fuel selectivity favoring glucose over fatty acid oxidation at the intact cell level.

Cell damage of hepatoma-22 cells exposed to continuous wave ultrasound.

PubMed

Wang, Pan; Wang, Xiaobing; Liu, Quanhong

2012-01-01

The cellular response of hepatoma-22 cells to ultrasonic irradiation and the potential cause for the action were evaluated. Hepatoma-22 cells were subjected to ultrasound irradiation at a frequency of 2.17 MHz and a spatial average intensity of 1.6 W/cm2 for variable periods of time, and several biological parameters were analyzed. The terephthalic acid (TA) dosimetry method was used to evaluate the efficacies of irradiation parameters on the acoustic cavitation activity by monitoring hydroxyl radical (OH) production. Lactate dehydrogenase (LDH) leakage was assayed to investigate cell membrane integrity. The polarization value of fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH) was measured to monitor plasma membrane fluidity. The malonaldehyde content in cells was determined to reflect lipid peroxidation. Trypan blue exclusion was used to detect cell viability. Additionally, electron microscopy was used to observe morphological changes. The generation of intracellular reactive oxygen species, mitochondria swelling and the loss of mitochondria membrane potential were also investigated. The results showed that 1) the concentration of ·OH production by ultrasonic irradiation in air-saturated cell suspensions increased as ultrasound exposure time increased; 2) compared with control, lactate dehydrogenase leakage, the polarization value of 1,6-diphenyl-1,3,5-hexatriene, malonaldehyde content and cell lysis were significantly elevated when cells were treated by ultrasound for 60 s; 3) cytotoxicity by ultrasound irradiation was also accompanied by an increase in production of intracellular reactive oxygen species and dissipation of mitochondria membrane potential as well as by mitochondria swelling. Presently available information indicates that the plasma membrane and mitochondria are the main targets for ultrasound treatment, and free radicals formation such as ·OH due to ultrasound cavitation may play an important role in mediating these cellular response processes. Moreover the mechanical effect might also be involved in inducing cell damage because there was significant mitochondria membrane potential loss and no visible ROS detection when cells were exposed to ultrasound for 30 s.

Electrical filtering in gerbil isolated type I semicircular canal hair cells

NASA Technical Reports Server (NTRS)

Rennie, K. J.; Ricci, A. J.; Correia, M. J.

1996-01-01

1. Membrane potential responses of dissociated gerbil type I semicircular canal hair cells to current injections in whole cell current-clamp have been measured. The input resistance of type I cells was 21.4 +/- 14.3 (SD) M omega, (n = 25). Around the zero-current potential (Vz = -66.6 +/- 9.3 mV, n = 25), pulsed current injections (from approximately -200 to 750 pA) produced only small-amplitude, pulse-like changes in membrane potential. 2. Injecting constant current to hyperpolarize the membrane to around -100 mV resulted in a approximately 10-fold increase in membrane resistance. Current pulses superimposed on this constant hyperpolarization produced larger and more complex membrane potential changes. Depolarizing currents > or = 200 pA caused a rapid transient peak voltage before a plateau. 3. Membrane voltage was able to faithfully follow sine-wave current injections around Vz over the range 1-1,000 Hz with < 25% attenuation at 1 kHz. A previously described K conductance, IKI, which is active at Vz, produces the low input resistance and frequency response. This was confirmed by pharmacologically blocking IKI. This conductance, present in type I cells but not type II hair cells, would appear to confer on type I cells a lower gain, but a much broader bandwidth at Vz, than seen in type II cells.

Reduction of low potential electron acceptors requires the CbcL inner membrane cytochrome of Geobacter sulfurreducens

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zacharoff, Lori; Chan, Chi Ho; Bond, Daniel R.

2015-09-05

The respiration of metals by the bacterium Geobacter sulfurreducens requires electrons generated by metabolism to pass from the interior of the cell to electron acceptors beyond the cell membranes. The G. sulfurreducens inner membrane multiheme c-type cytochrome ImcH is required for respiration to extracellular electron acceptors with redox potentials greater than - 0.1 V vs. SHE, but ImcH is not essential for electron transfer to lower potential acceptors. In contrast, deletion of cbcL, encoding an inner membrane protein consisting of b-type and multiheme c-type cytochrome domains, severely affected reduction of low potential electron acceptors such as Fe(III)-oxides and electrodes poisedmore » at - 0.1 V vs. SHE. Catalytic cyclic voltammetry of a ΔcbcL strain growing on poised electrodes revealed a 50 mV positive shift in driving force required for electron transfer out of the cell. In non-catalytic conditions, low-potential peaks present in wild type biofilms were absent in ΔcbcL mutants. Expression of cbcL in trans increased growth at low redox potential and restored features to cyclic voltammetry. This evidence supports a model where CbcL is a component of a second electron transfer pathway out of the G. sulfurreducens inner membrane that dominates when redox potential is at or below - 0.1 V vs. SHE.« less

Reduction of low potential electron acceptors requires the CbcL inner membrane cytochrome of Geobacter sulfurreducens.

PubMed

Zacharoff, Lori; Chan, Chi Ho; Bond, Daniel R

2016-02-01

The respiration of metals by the bacterium Geobacter sulfurreducens requires electrons generated by metabolism to pass from the interior of the cell to electron acceptors beyond the cell membranes. The G. sulfurreducens inner membrane multiheme c-type cytochrome ImcH is required for respiration to extracellular electron acceptors with redox potentials greater than -0.1 V vs. SHE, but ImcH is not essential for electron transfer to lower potential acceptors. In contrast, deletion of cbcL, encoding an inner membrane protein consisting of b-type and multiheme c-type cytochrome domains, severely affected reduction of low potential electron acceptors such as Fe(III)-oxides and electrodes poised at -0.1 V vs. SHE. Catalytic cyclic voltammetry of a ΔcbcL strain growing on poised electrodes revealed a 50 mV positive shift in driving force required for electron transfer out of the cell. In non-catalytic conditions, low-potential peaks present in wild type biofilms were absent in ∆cbcL mutants. Expression of cbcL in trans increased growth at low redox potential and restored features to cyclic voltammetry. This evidence supports a model where CbcL is a component of a second electron transfer pathway out of the G. sulfurreducens inner membrane that dominates when redox potential is at or below -0.1 V vs. SHE. Copyright © 2015. Published by Elsevier B.V.

Synaptic input correlations leading to membrane potential decorrelation of spontaneous activity in cortex.

PubMed

Graupner, Michael; Reyes, Alex D

2013-09-18

Correlations in the spiking activity of neurons have been found in many regions of the cortex under multiple experimental conditions and are postulated to have important consequences for neural population coding. While there is a large body of extracellular data reporting correlations of various strengths, the subthreshold events underlying the origin and magnitude of signal-independent correlations (called noise or spike count correlations) are unknown. Here we investigate, using intracellular recordings, how synaptic input correlations from shared presynaptic neurons translate into membrane potential and spike-output correlations. Using a pharmacologically activated thalamocortical slice preparation, we perform simultaneous recordings from pairs of layer IV neurons in the auditory cortex of mice and measure synaptic potentials/currents, membrane potentials, and spiking outputs. We calculate cross-correlations between excitatory and inhibitory inputs to investigate correlations emerging from the network. We furthermore evaluate membrane potential correlations near resting potential to study how excitation and inhibition combine and affect spike-output correlations. We demonstrate directly that excitation is correlated with inhibition thereby partially canceling each other and resulting in weak membrane potential and spiking correlations between neurons. Our data suggest that cortical networks are set up to partially cancel correlations emerging from the connections between neurons. This active decorrelation is achieved because excitation and inhibition closely track each other. Our results suggest that the numerous shared presynaptic inputs do not automatically lead to increased spiking correlations.

Effects of K(+) channel openers on spontaneous action potentials in detrusor smooth muscle of the guinea-pig urinary bladder.

PubMed

Takagi, Hiroaki; Hashitani, Hikaru

2016-10-15

The modulation of spontaneous excitability in detrusor smooth muscle (DSM) upon the pharmacological activation of different populations of K(+) channels was investigated. Effects of distinct K(+) channel openers on spontaneous action potentials in DSM of the guinea-pig bladder were examined using intracellular microelectrode techniques. NS1619 (10μM), a large conductance Ca(2+)-activated K(+) (BK) channel opener, transiently increased action potential frequency and then prevented their generation without hyperpolarizing the membrane in a manner sensitive to iberiotoxin (IbTX, 100nM). A higher concentration of NS1619 (30μM) hyperpolarized the membrane and abolished action potential firing. NS309 (10μM) and SKA31 (100μM), small conductance Ca(2+)-activated K(+) (SK) channel openers, dramatically increased the duration of the after-hyperpolarization and then abolished action potential firing in an apamin (100nM)-sensitive manner. Flupirtine (10μM), a Kv7 channel opener, inhibited action potential firing without hyperpolarizing the membrane in a manner sensitive to XE991 (10μM), a Kv7 channel blocker. BRL37344 (10μM), a β3-adrenceptor agonist, or rolipram (10nM), a phosphodiesterase 4 inhibitor, also inhibited action potential firing. A higher concentration of rolipram (100nM) hyperpolarized the DSM and abolished the action potentials. IbTX (100nM) prevented the rolipram-induced blockade of action potentials but not the hyperpolarization. BK and Kv7 channels appear to predominantly contribute to the stabilization of DSM excitability. Spare SK channels could be pharmacologically activated to suppress DSM excitability. BK channels appear to be involved in the cyclic AMP-induced inhibition of action potentials but not the membrane hyperpolarization. Copyright © 2016 Elsevier B.V. All rights reserved.

Apoptosis of leukemia K562 and Molt-4 cells induced by emamectin benzoate involving mitochondrial membrane potential loss and intracellular Ca2+ modulation.

PubMed

Yun, Xinming; Rao, Wenbing; Xiao, Ciying; Huang, Qingchun

2017-06-01

Leukemia threatens millions of people's health and lives, and the pesticide-induced leukemia has been increasingly concerned because of the etiologic exposure. In this paper, cytotoxic effect of emamectin benzoate (EMB), an excellent natural-product insecticide, was evaluated through monitoring cell viability, cell apoptosis, mitochondrial membrane potential and intracellular Ca 2+ concentration ([Ca 2+ ] i ) in leukemia K562 and Molt-4 cells. Following the exposure to EMB, cell viability was decreased and positive apoptosis of K562 and Molt-4 cells was increased in a concentration- and time- dependent fashion. In the treatment of 10μM EMB, apoptotic cells accounted for 93.0% to K562 cells and 98.9% to Molt-4 cells based on the control, meanwhile, 63.47% of K562 cells and 81.15% of Molt-4 cells exhibited late apoptotic and necrotic features with damaged cytoplasmic membrane. 48h exposure to 10μM EMB increased significantly the great number of cells with mitochondrial membrane potential (MMP) loss, and the elevation of [Ca 2+ ] i level was peaked and persisted within 70s in K562 cells whilst 50s in Molt-4 cells. Moreover, a stronger cytotoxicity of EMB was further observed than that of imatinib. The results authenticate the efficacious effect of EMB as a potential anti-leukemia agent and an inconsistency with regard to insecticide-induced leukemia. Copyright © 2017 Elsevier B.V. All rights reserved.

Membrane Technology for the Recovery of Lignin: A Review

PubMed Central

Humpert, Daniel; Ebrahimi, Mehrdad; Czermak, Peter

2016-01-01

Utilization of renewable resources is becoming increasingly important, and only sustainable processes that convert such resources into useful products can achieve environmentally beneficial economic growth. Wastewater from the pulp and paper industry is an unutilized resource offering the potential to recover valuable products such as lignin, pigments, and water [1]. The recovery of lignin is particularly important because it has many applications, and membrane technology has been investigated as the basis of innovative recovery solutions. The concentration of lignin can be increased from 62 to 285 g∙L−1 using membranes and the recovered lignin is extremely pure. Membrane technology is also scalable and adaptable to different waste liquors from the pulp and paper industry. PMID:27608047

Analytical approach to an integrate-and-fire model with spike-triggered adaptation

NASA Astrophysics Data System (ADS)

Schwalger, Tilo; Lindner, Benjamin

2015-12-01

The calculation of the steady-state probability density for multidimensional stochastic systems that do not obey detailed balance is a difficult problem. Here we present the analytical derivation of the stationary joint and various marginal probability densities for a stochastic neuron model with adaptation current. Our approach assumes weak noise but is valid for arbitrary adaptation strength and time scale. The theory predicts several effects of adaptation on the statistics of the membrane potential of a tonically firing neuron: (i) a membrane potential distribution with a convex shape, (ii) a strongly increased probability of hyperpolarized membrane potentials induced by strong and fast adaptation, and (iii) a maximized variability associated with the adaptation current at a finite adaptation time scale.

Evaluation of sericin/collagen membranes as prospective wound dressing biomaterial.

PubMed

Akturk, Omer; Tezcaner, Aysen; Bilgili, Hasan; Deveci, M Salih; Gecit, M Rusen; Keskin, Dilek

2011-09-01

Sericin, a silk protein, has high potential for use in biomedical applications. In this study, wound dressing membranes of Sericin (S) and Collagen (C) were prepared by glutaraldehyde cross-linking at S/C; 2:1, 1:1, 1:2, and 0:1 weight ratios. They were stable in water for 4 weeks. However, increasing the proportion of sericin had decreasing effect on the membrane stability. Water swelling property of membranes was enhanced with sericin. The highest water swelling was obtained in 1:1 group (9.06 g/g), but increasing collagen or sericin content in the membranes had a diminishing effect. Highest water vapor transmission rate was obtained with 1:2 group (1013.80 g/m(2)/day). Oxygen permeability results showed that 1:2 (7.67 mg/L) and 2:1 (7.85 mg/L) S/C groups were better than the other groups. While sericin decreased the tensile strength and elongation of membranes, it increased modulus. Sericin also increased brittleness of membranes, but their UTS range (24.93-44.92 MPa) was still suitable for a wound dressing. Membranes were not penetrable to microorganisms. Cytotoxicity studies showed that fibroblasts and keratinocytes attached and gained their characteristic morphologies. They also proliferated on membranes significantly. After 1 week of subcutaneous implantation, a fibrous capsule formed around all membranes with an acute inflammation. Sericin containing membranes showed signs of degradation (at 2nd week), while collagen only membranes remained largely intact. Eventually, sericin containing membranes degraded in 3 weeks with moderate inflammatory response. Overall results suggest that sericin/collagen membranes would be favorable as wound dressing material when sericin ratio is less than or equal to the collagen component. Copyright © 2011 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

GABAergic excitation of spider mechanoreceptors increases information capacity by increasing entropy rather than decreasing jitter.

PubMed

Pfeiffer, Keram; French, Andrew S

2009-09-02

Neurotransmitter chemicals excite or inhibit a range of sensory afferents and sensory pathways. These changes in firing rate or static sensitivity can also be associated with changes in dynamic sensitivity or membrane noise and thus action potential timing. We measured action potential firing produced by random mechanical stimulation of spider mechanoreceptor neurons during long-duration excitation by the GABAA agonist muscimol. Information capacity was estimated from signal-to-noise ratio by averaging responses to repeated identical stimulation sequences. Information capacity was also estimated from the coherence function between input and output signals. Entropy rate was estimated by a data compression algorithm and maximum entropy rate from the firing rate. Action potential timing variability, or jitter, was measured as normalized interspike interval distance. Muscimol increased firing rate, information capacity, and entropy rate, but jitter was unchanged. We compared these data with the effects of increasing firing rate by current injection. Our results indicate that the major increase in information capacity by neurotransmitter action arose from the increased entropy rate produced by increased firing rate, not from reduction in membrane noise and action potential jitter.

Pore channel surface modification for enhancing anti-fouling membrane distillation

NASA Astrophysics Data System (ADS)

Qiu, Haoran; Peng, Yuelian; Ge, Lei; Villacorta Hernandez, Byron; Zhu, Zhonghua

2018-06-01

Membrane surface modification by forming a functional layer is an effective way to improve the anti-fouling properties of membranes; however, the additional layer and the potential blockage of bulk pores may increase the mass transfer resistance and reduce the permeability. In this study, we applied a novel method of preparing anti-fouling membranes for membrane distillation by dispersing graphene oxide (GO) on the channel surface of polyvinylidene fluoride membranes. The surface morphology and properties were characterized by scanning electron microscopy, atomic force microscope, and Fourier transform infrared spectrometry. Compared to the membrane surface modification by nanoparticles (e.g. SiO2), GO was mainly located on the pore surface of the membrane bulk, rather than being formed as an individual layer onto the membrane surface. The performance was evaluated via a direct-contact membrane distillation process with anionic and cationic surfactants as the foulants, separately. Compared to the pristine PVDF membrane, the anti-fouling behavior and distillate flux of the GO-modified membranes were improved, especially when using the anionic surfactant as the foulant. The enhanced anti-fouling performance can be attributed to the oxygen containing functional groups in GO and the healing of the membrane pore defects. This method may provide an effective route to manipulate membrane pore surface properties for anti-fouling separation without increasing mass transfer resistance.

Cholinergically-induced changes in outward currents in hair cells isolated from the semicircular canal of the frog.

PubMed

Housley, G D; Norris, C H; Guth, P S

1990-01-01

Two cholinergically-induced modulations of membrane conductances have been identified in hair cells isolated from the crista ampullaris of the leopard frog (Rana pipiens), using the whole cell recording configuration of the patch clamp technique. Of 56 crista hair cells tested, 28 showed drug-induced changes in membrane current or membrane potential which were repeatable and could be reversed with washout of drug. The predominant effect (observed in 20 hair cells) of acetylcholine (Ach, 100 microM) to 1mM) or carbachol (1 microM to 50 microM) applied to these hair cells was the reduction of an outward current corresponding to a change in conductance of approximately -0.22 nS. This action by Ach on hair cells has been inferred from previous studies of afferent fiber discharge which reported an increase in firing rate with stimulation of efferent fibers or exogenous application of cholinomimetics (Bernard et al., 1985; Valli et al., 1986; Guth et al., 1986; Norris et al., 1988a). The Ach-induced reduction in outward current was associated with a depolarization of the zero-current membrane potential by approximately +2.5 mV. In a total of 8 hair cells, an Ach-induced reversible increase in outward current was recorded. Changes in conductance were approximately +0.13 nS and were associated with a hyperpolarization of the zero-current membrane potential by approximately -2.2 mV. This current increase is likely to be responsible for the inhibitory post-synaptic potentials (IPSPs) which have previously been recorded intracellularly from acoustico-lateralis hair cells during stimulation of the efferent innervation (Flock and Russell, 1976; Ashmore and Russell, 1982; Art et al., 1984, 1985). Of the remaining 28 hair cells, six cells failed to exhibit any change in membrane conductance or membrane potential in the presence of cholinomimetics while an additional 15 cells exhibited decreases, and 7 cells exhibited increases in outward conductance, during application of Ach or carbachol, which were neither reversible with washout nor repeatable. The Ach-induced decrease in outward current could be reversible blocked by removal of Ca2+ from the external solution. The antagonism of the Ach-induced decrease in outward current by atropine (10(-5) M) suggests that this current may correspond to a facilitatory, 'atropine-preferring' Ach receptor mediated response previously identified in the isolated semicircular canal (Norris et al., 1988a).(ABSTRACT TRUNCATED AT 400 WORDS)

Frequency-Dependent Capacitance of Hydrophobic Membranes Containing Fixed Negative Charges

PubMed Central

Ilani, Asher

1968-01-01

Filters containing fixed negative charges were saturated with hydrophobic solvent and interposed between aqueous solutions. The capacitance of such membranes was measured in the frequency range of 0.05-30 kc. The capacitance increased with decrease in frequency. The frequency dependence of the capacitance was sensitive to nature of the cation present and to salt concentration in the aqueous solution. It is suggested that variation of membrane resistivity in the space charge region of the membrane is responsible for this phenomenon. Possible effects of the potential and counterion concentration profiles at the membrane-water interface are discussed. PMID:5699796

Methanol-tolerant cathode catalyst composite for direct methanol fuel cells

DOEpatents

Zhu, Yimin; Zelenay, Piotr

2006-09-05

A direct methanol fuel cell (DMFC) having a methanol fuel supply, oxidant supply, and its membrane electrode assembly (MEA) formed of an anode electrode and a cathode electrode with a membrane therebetween, a methanol oxidation catalyst adjacent the anode electrode and the membrane, an oxidant reduction catalyst adjacent the cathode electrode and the membrane, comprises an oxidant reduction catalyst layer of Pt.sub.3Cr/C so that oxidation at the cathode of methanol that crosses from the anode through the membrane to the cathode is reduced with a concomitant increase of net electrical potential at the cathode electrode.

Methanol-Tolerant Cathode Catalyst Composite For Direct Methanol Fuel Cells

DOEpatents

Zhu, Yimin; Zelenay, Piotr

2006-03-21

A direct methanol fuel cell (DMFC) having a methanol fuel supply, oxidant supply, and its membrane electrode assembly (MEA) formed of an anode electrode and a cathode electrode with a membrane therebetween, a methanol oxidation catalyst adjacent the anode electrode and the membrane, an oxidant reduction catalyst adjacent the cathode electrode and the membrane, comprises an oxidant reduction catalyst layer of a platinum-chromium alloy so that oxidation at the cathode of methanol that crosses from the anode through the membrane to the cathode is reduced with a concomitant increase of net electrical potential at the cathode electrode.

Effect of copper chloride exposure on the membrane potential and cytosolic free calcium in primary cultured chicken hepatocytes.

PubMed

Jia, Xuexia; Chen, Long; Li, Jingtao; Su, Rongsheng; Shi, Dayou; Tang, Zhaoxin

2012-09-01

This study was conducted to examine the effects of copper on membrane potential and cytosolic free calcium in isolated primary chicken hepatocytes which were exposed to different concentration of Cu(2+) (0, 10, 50, 100 μM) or a mixture of Cu(2+) and vitamin C (50 and 50 μM, respectively). Viability, membrane potential, and cytosolic free Ca(2+) of monolayer cultured hepatocytes were investigated at the indicated time point. Results showed that, among the different concentrations of Cu(2+) exposure, the viability of hepatocytes treated with 100 μM Cu(2+) was the worst at the 12th and 24th hours. The effects of Cu(2+) on viability and proliferation were time and dose dependent. Further investigation indicated that Cu(2+) exposure significantly enhanced cytosolic free Ca(2+) in hepatocytes, compared to that in control group, at the 24th hour. Meanwhile, membrane potential was noticeably reduced in hepatocytes increasing concentration of Cu(2+). Taking these results together, we have shown that Cu(2+) can cause toxicity to primary chicken hepatocytes in excessive dose and the effect of Cu(2+) exposure on membrane potential is not site specific, which is probably mediated by the changes of cytosolic free Ca(2+).

Quantitative study of electrophoretic and electroosmotic enhancement during alternating current iontophoresis across synthetic membranes.

PubMed

Yan, Guang; Li, S Kevin; Peck, Kendall D; Zhu, Honggang; Higuchi, William I

2004-12-01

One of the primary safety and tolerability limitations of direct current iontophoresis is the potential for electrochemical burns associated with the necessary current densities and/or application times required for effective treatment. Alternating current (AC) transdermal iontophoresis has the potential to eliminate electrochemical burns that are frequently observed during direct current transdermal iontophoresis. Although it has been demonstrated that the intrinsic permeability of skin can be increased by applying low-to-moderate AC voltages, transdermal transport phenomena and enhancement under AC conditions have not been systematically studied and are not well understood. The aim of the present work was to study the fundamental transport mechanisms of square-wave AC iontophoresis using a synthetic membrane system. The model synthetic membrane used was a composite Nuclepore membrane. AC frequencies ranging from 20 to 1000 Hz and AC fields ranging from 0.25 to 0.5 V/membrane were investigated. A charged permeant, tetraethyl ammonium, and a neutral permeant, arabinose, were used. The transport studies showed that flux was enhanced by increasing the AC voltage and decreasing AC frequency. Two theoretical transport models were developed: one is a homogeneous membrane model; the other is a heterogeneous membrane model. Experimental transport data were compared with computer simulations based on these models. Excellent agreement between model predictions and experimental data was observed when the data were compared with the simulations from the heterogeneous membrane model. (c) 2004 Wiley-Liss, Inc. and the American Pharmacists Association

Direct measurement of concentration distribution within the boundary layer of an ion-exchange membrane.

PubMed

Choi, Jae-Hwan; Park, Jin-Soo; Moon, Seung-Hyeon

2002-07-15

In this study the concentration distributions within the diffusion boundary layer were obtained by directly measuring the potential drops while the currents (under- and overlimiting) passed through the Neosepta CMX cation-exchange membrane (Tokuyama Corp., Japan). Potential drops according to the distance from the membrane surface on the depleted side were measured using a microelectrode to obtain the concentration profile. From the concentration profiles obtained, it was observed that the diffusion boundary layers existed in the range of 300-350 microm, which reasonably coincide with the theoretical diffusion boundary layer thickness calculated from the limiting current density. Although there were some deviations between the concentrations determined from the Nernst model and those from experiments, it was confirmed that the Nernst model effectively depicts the transport phenomena in the ion-exchange membrane system. In addition it was found that the salt concentration at the membrane surface increased when the currents applied exceeded the limiting current. It is thought that the concentration polarization formed in the diffusion boundary layer at currents near or lower than the limiting current was disturbed by a turbulent convection when the current was greater than the limiting current. As a consequence, the concentration at the membrane surface increased to a sufficient level for generation of the overlimiting current.

Tuning of Hemes b Equilibrium Redox Potential Is Not Required for Cross-Membrane Electron Transfer.

PubMed

Pintscher, Sebastian; Kuleta, Patryk; Cieluch, Ewelina; Borek, Arkadiusz; Sarewicz, Marcin; Osyczka, Artur

2016-03-25

In biological energy conversion, cross-membrane electron transfer often involves an assembly of two hemesb The hemes display a large difference in redox midpoint potentials (ΔEm_b), which in several proteins is assumed to facilitate cross-membrane electron transfer and overcome a barrier of membrane potential. Here we challenge this assumption reporting on hemebligand mutants of cytochromebc1in which, for the first time in transmembrane cytochrome, one natural histidine has been replaced by lysine without loss of the native low spin type of heme iron. With these mutants we show that ΔEm_b can be markedly increased, and the redox potential of one of the hemes can stay above the level of quinone pool, or ΔEm_b can be markedly decreased to the point that two hemes are almost isopotential, yet the enzyme retains catalytically competent electron transfer between quinone binding sites and remains functionalin vivo This reveals that cytochromebc1can accommodate large changes in ΔEm_b without hampering catalysis, as long as these changes do not impose overly endergonic steps on downhill electron transfer from substrate to product. We propose that hemesbin this cytochrome and in other membranous cytochromesbact as electronic connectors for the catalytic sites with no fine tuning in ΔEm_b required for efficient cross-membrane electron transfer. We link this concept with a natural flexibility in occurrence of several thermodynamic configurations of the direction of electron flow and the direction of the gradient of potential in relation to the vector of the electric membrane potential. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

[Effect of sludge bulking on membrane fouling of MBR under low temperature].

PubMed

Ren, Nan-qi; Liu, Jiao; Wang, Xiu-heng

2009-01-01

The performance and membrane fouling of submerged membrane bioreactor were studied in the case of active sludge bulking under low temperature. The factors contributing to membrane fouling were discussed from the microorganism aspect. The results showed that COD removal efficiencies of supernatant and permeate were 85% and 92% respectively and filamentous sludge bulking had little impact on them. The sludge settleability became bad and the filament index (FI) increased from 2 to 5 during the formation of filamentous sludge bulking under low temperature. The filamentous bacteria extending from the sludge flocs formed net structure. Membrane fouling changed with time in linear under low temperature and the operation period of MBR was 15 d. However, membrane fouling was more serious in the condition of filamentous sludge bulking at low temperature, shortening the operation period of MBR to 7 d. The extracellular polymeric substances (EPS) content of bulking sludge was three times as that of normal sludge and the relative hydrophobicity (RH) of sludge flocs was decreased as FI increased. The increase of EPS and RH may cause more materials to deposit on the membrane surface, thus the membrane fouling rate improved and the operation period of MBR became short. Further analysis indicated that the mixed liquid viscosity, Zeta potential and sludge floc structure were all important factors of membrane fouling.

Hyperpolarization of the plasma membrane potential provokes reorganization of the actin cytoskeleton and increases the stability of adherens junctions in bovine corneal endothelial cells in culture.

PubMed

Nin, Verónica; Hernández, Julio A; Chifflet, Silvia

2009-12-01

In previous works we showed that the depolarization of the plasma membrane potential (PMP) determines a reorganization of the cytoskeleton of diverse epithelia in culture, consisting mainly of a reallocation of peripheral actin toward the cell center, ultimately provoking intercellular disruption. In view of this evidence, we explored in this study the possible effects of membrane potential hyperpolarization on the cytoskeletal organization and adherens junction (AJ) morphology and the stability of confluent bovine corneal endothelial cells in culture. For this purpose, hyperpolarization was achieved by substitution of extracellular sodium by nondiffusible cations or via the incorporation of valinomycin to the control solution. Actin compactness at the cell periphery was assessed by quantitative analysis of fluorescence microscopy images. The stability of the AJ was challenged by calcium deprivation or temperature decrease. Our results showed that plasma membrane hyperpolarization provokes a compaction of AJ-associated actin filaments toward the plasma membrane and an increase in the stability of the AJs. We also observed that the hyperpolarizing procedures determined similar modifications in the actin cytoskeleton of endothelial cells in whole bovine corneas. Together with our previous work, the results of this study contribute to the idea that modifications in the PMP of nonexcitable cells participate in cellular adaptive responses involving reorganization of cytoskeletal components. (c) 2009 Wiley-Liss, Inc.

The Role of Water Distribution Controlled by Transmembrane Potentials in the Cytochrome c-Cardiolipin Interaction: Revealing from Surface-Enhanced Infrared Absorption Spectroscopy.

PubMed

Zeng, Li; Wu, Lie; Liu, Li; Jiang, Xiue

2017-11-02

The interaction of cytochrome c (cyt c) with cardiolipin (CL) plays a crucial role in apoptotic functions, however, the changes of the transmembrane potential in governing the protein behavior at the membrane-water interface have not been studied due to the difficulties in simultaneously monitoring the interaction and regulating the electric field. Herein, surface-enhanced infrared absorption (SEIRA) spectroelectrochemistry is employed to study the mechanism of how the transmembrane potentials control the interaction of cyt c with CL membranes by regulating the electrode potentials of an Au film. When the transmembrane potential decreases, the water content at the interface of the membranes can be increased to slow down protein adsorption through decreasing the hydrogen-bond and hydrophobic interactions, but regulates the redox behavior of CL-bound cyt c through a possible water-facilitated proton-coupled electron transfer process. Our results suggest that the potential drop-induced restructure of the CL conformation and the hydration state could modify the structure and function of CL-bound cyt c on the lipid membrane. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Miltefosine has post-antifungal effect and induces apoptosis in Cryptococcus yeasts.

PubMed

Spadari, Cristina de Castro; Vila, Taissa; Rozental, Sonia; Ishida, Kelly

2018-05-29

Cryptococcus spp. are common opportunistic fungal pathogens, particularly in HIV patients. The approved drug miltefosine (MFS) has potential as an alternative antifungal against cryptococcosis; however, the mechanism of action of MFS in Cryptococcus is poorly understood. Here, we examined the effects of MFS on C. neoformans and C. gattii yeasts (planktonic and biofilm lifestyles), to clarify its mechanism of action. MFS presented inhibitory and fungicidal effects against planktonic Cryptococcus cells, with similar activity against dispersion biofilm cells, while sessile biofilm cells were less sensitive to MFS. Interestingly, MFS had post-antifungal effect on Cryptococcus , with a proliferation delay of up to 8.15 h after short exposure to fungicidal doses. MFS at fungicidal concentrations increased plasma membrane permeability, likely due to direct interaction with ergosterol, as suggested by competition assays with exogenous ergosterol. Moreover, MFS reduced the mitochondrial membrane potential, increased ROS production, and induced DNA fragmentation and condensation, all of which are hallmarks of apoptosis. Transmission electron microscopy analysis showed that MFS-treated yeasts had a reduced mucopolysaccharide capsule (confirmed by morphometry in light microscopy), plasma membrane irregularities, mitochondrial swelling and a less conspicuous cell wall. Our results suggest that MFS increases plasma membrane permeability in Cryptococcus via interaction with ergosterol, and also affects the mitochondrial membrane, eventually leading to apoptosis, in line with its fungicidal activity. These findings confirm the potential of MFS as an antifungal against C. neoformans and C. gattii, and warrants further studies to establish clinical protocols for MFS use against cryptococcosis. Copyright © 2018 American Society for Microbiology.

Mouse Sperm Membrane Potential Hyperpolarization Is Necessary and Sufficient to Prepare Sperm for the Acrosome Reaction*

PubMed Central

De La Vega-Beltran, Jose Luis; Sánchez-Cárdenas, Claudia; Krapf, Darío; Hernandez-González, Enrique O.; Wertheimer, Eva; Treviño, Claudia L.; Visconti, Pablo E.; Darszon, Alberto

2012-01-01

Mammalian sperm are unable to fertilize the egg immediately after ejaculation; they acquire this capacity during migration in the female reproductive tract. This maturational process is called capacitation and in mouse sperm it involves a plasma membrane reorganization, extensive changes in the state of protein phosphorylation, increases in intracellular pH (pHi) and Ca2+ ([Ca2+]i), and the appearance of hyperactivated motility. In addition, mouse sperm capacitation is associated with the hyperpolarization of the cell membrane potential. However, the functional role of this process is not known. In this work, to dissect the role of this membrane potential change, hyperpolarization was induced in noncapacitated sperm using either the ENaC inhibitor amiloride, the CFTR agonist genistein or the K+ ionophore valinomycin. In this experimental setting, other capacitation-associated processes such as activation of a cAMP-dependent pathway and the consequent increase in protein tyrosine phosphorylation were not observed. However, hyperpolarization was sufficient to prepare sperm for the acrosome reaction induced either by depolarization with high K+ or by addition of solubilized zona pellucida (sZP). Moreover, K+ and sZP were also able to increase [Ca2+]i in non-capacitated sperm treated with these hyperpolarizing agents but not in untreated cells. On the other hand, in conditions that support capacitation-associated processes blocking hyperpolarization by adding valinomycin and increasing K+ concentrations inhibited the agonist-induced acrosome reaction as well as the increase in [Ca2+]i. Altogether, these results suggest that sperm hyperpolarization by itself is key to enabling mice sperm to undergo the acrosome reaction. PMID:23095755

Effect of extremely low frequency electromagnetic fields on bacterial membrane.

PubMed

Oncul, Sule; Cuce, Esra M; Aksu, Burak; Inhan Garip, Ayse

2016-01-01

The effect of extremely low frequency electromagnetic fields (ELF-EMF) on bacteria has attracted attention due to its potential for beneficial uses. This research aimed to determine the effect of ELF-EMF on bacterial membrane namely the membrane potential, surface potential, hydrophobicity, respiratory activity and growth. Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli were subjected to ELF-EMF, 50 Hz, 1 mT for 2 h. Membrane potential was determined by fluorescence spectroscopy with or without EDTA (Ethylenediaminetetraacetic acid) with DisC3(5) (3,3-dipropylthiacarbocyanine iodide), zeta potential measurements were performed by electrophoretic mobility, hydrophobicity of the membrane was measured with MATH (Microbial Adhesion to Hydrocarbons) test, respiratory activity was determined with CTC (5-Cyano-2,3-ditolyl tetrazolium chloride), colony forming unit (CFU) and DAPI (4',6-diamidino-2-phenylindole, dihydrochloride) was used for growth determinations. ELF-EMF caused changes in physicochemical properties of both Gram-positive and Gram-negative bacteria. Hyperpolarization was seen in S. aureus and EDTA-treated E. coli. Surface potential showed a positive shift in S. aureus contrariwise to the negative shift seen in EDTA-untreated E. coli. Respiratory activity increased in both bacteria. A slight decrease in growth was observed. These results show that ELF-EMF affects the crucial physicochemical processes in both Gram-positive and Gram-negative bacteria which need further research.

Acetylcholine-induced current in perfused rat myoballs

PubMed Central

1980-01-01

Spherical "myoballs" were grown under tissue culture conditions from striated muscle of neonatal rat thighs. The myoballs were examined electrophysiologically with a suction pipette which was used to pass current and perfuse internally. A microelectrode was used to record membrane potential. Experiments were performed with approximately symmetrical (intracellular and extracellular) sodium aspartate solutions. The resting potential, acetylcholine (ACh) reversal potential, and sodium channel reversal potential were all approximately 0 mV. ACh-induced currents were examined by use of both voltage jumps and voltage ramps in the presence of iontophoretically applied agonist. The voltage-jump relaxations had a single exponential time-course. The time constant, tau, was exponentially related to membrane potential, increasing e-fold for 81 mV hyperpolarization. The equilibrium current- voltage relationship was also approximately exponential, from -120 to +81 mV, increasing e-fold for 104 mV hyperpolarization. The data are consistent with a first-order gating process in which the channel opening rate constant is slightly voltage dependent. The instantaneous current-voltage relationship was sublinear in the hyperpolarizing direction. Several models are discussed which can account for the nonlinearity. Evidence is presented that the "selectivity filter" for the ACh channel is located near the intracellular membrane surface. PMID:7381423

Membrane Potentials of the Lobster Giant Axon Obtained by Use of the Sucrose-Gap Technique

PubMed Central

Julian, Fred J.; Moore, John W.; Goldman, David E.

1962-01-01

A method similar to the sucrose-gap technique introduced be Stäpfli is described for measuring membrane potential and current in singly lobster giant axons (diameter about 100 micra). The isotonic sucrose solution used to perfuse the gaps raises the external leakage resistance so that the recorded potential is only about 5 per cent less than the actual membrane potential. However, the resting potential of an axon in the sucrose-gap arrangement is increased 20 to 60 mv over that recorded by a conventional micropipette electrode when the entire axon is bathed in sea water. A complete explanation for this effect has not been discovered. The relation between resting potential and external potassium and sodium ion concentrations shows that potassium carries most of the current in a depolarized axon in the sucrose-gap arrangement, but that near the resting potential other ions make significant contributions. Lowering the external chloride concentration decreases the resting potential. Varying the concentration of the sucrose solution has little effect. A study of the impedance changes associated with the action potential shows that the membrane resistance decreases to a minimum at the peak of the spike and returns to near its initial value before repolarization is complete (a normal lobster giant axon action potential does not have an undershoot). Action potentials recorded simultaneously by the sucrose-gap technique and by micropipette electrodes are practically superposable. PMID:14452759

Theoretical Application of Irreversible (Nonequilibrium) Thermodynamic Principles to Enhance Solute Fluxes across Nanofabricated Hemodialysis Membranes

PubMed Central

Hedayat, Assem; Elmoselhi, Hamdi; Shoker, Ahmed

2012-01-01

Objective. Nanotechnology has the potential to improve hemodialysis membrane technology. Thus, a major objective is to understand how to enhance toxic solute fluxes across these membranes. The aim of this concept building study is to review the application of irreversible thermodynamic (IT) to solute fluxes. Methods. We expanded the application of the Nernst-Planck equation to include the Kedem-Katchalsky equation, pH, membrane thickness, pore size, and electric potential as variables. Results. (1) Reducing the membrane's thickness from 25 μm to 25 nm increased the flux of creatinine, β2-microglobulin, and tumor necrosis factor-α (TNF-α) by a thousand times but prevented completely albumin flux, (2) applying an electric potential of 50–400 mV across the membrane enhanced the flux of the respective molecules by 71.167 × 10−3, 38.7905 × 10−8, and 0.595 × 10−13 mol/s, and (3) changing the pH from 7.35 to 7.42 altered the fluxes minimally. Conclusions. The results supported an argument to investigate the application of IT to study forces of fluxes across membranes. Reducing the membrane's thickness—together with the application of an electrical potential—qualities achievable by nanotechnology, can enhance the removal of uremic toxins by many folds. However, changing the pH at a specific membrane thickness does not affect the flux significantly. PMID:23209903

El Tor hemolysin of Vibrio cholerae O1 forms channels in planar lipid bilayer membranes.

PubMed

Ikigai, H; Ono, T; Iwata, M; Nakae, T; Shimamura, T

1997-05-15

We investigated the channel formation by El Tor hemolysin (molecular mass, 65 kDa) of Vibrio cholerae O1 biotype El Tor in planar lipid bilayers. The El Tor hemolysin channel exhibited asymmetric and hyperbolic membrane current with increasing membrane potential, meaning that the channel is voltage dependent. The zero-current membrane potential measured in KCI solution showed that permeability ratio PK+/PCl- was 0.16, indicating that the channel is 6-fold more anion selective over cation. The hemolysin channel frequently flickered in the presence of divalent cations, suggesting that the channel spontaneously opens and closes. These data imply that the El Tor hemolysin damages target cells by the formation of transmembrane channels and, consequently, is the cause of osmotic cytolysis.

NAD+/NADH and/or CoQ/CoQH2 ratios from plasma membrane electron transport may determine ceramide and sphingosine-1-phosphate levels accompanying G1 arrest and apoptosis.

PubMed

De Luca, Thomas; Morré, Dorothy M; Zhao, Haiyun; Morré, D James

2005-01-01

To elucidate possible biochemical links between growth arrest from antiproliferative chemotherapeutic agents and apoptosis, our work has focused on agents (EGCg, capsaicin, cis platinum, adriamycin, anti-tumor sulfonylureas, phenoxodiol) that target tNOX. tNOX is a cancer-specific cell surface NADH oxidase (ECTO-NOX protein), that functions in cancer cells as the terminal oxidase for plasma membrane electron transport. When tNOX is active, coenzyme Q(10) (ubiquinone) of the plasma membrane is oxidized and NADH is oxidized at the cytosolic surface of the plasma membrane. However, when tNOX is inhibited and plasma membrane electron transport is diminished, both reduced coenzyme Q(10) (ubiquinol) and NADH would be expected to accumulate. To relate inhibition of plasma membrane redox to increased ceramide levels and arrest of cell proliferation in G(1) and apoptosis, we show that neutral sphingomyelinase, a major contributor to plasma membrane ceramide, is inhibited by reduced glutathione and ubiquinone. Ubiquinol is without effect or stimulates. In contrast, sphingosine kinase, which generates anti-apoptotic sphingosine-1-phosphate, is stimulated by ubiquinone but inhibited by ubiquinol and NADH. Thus, the quinone and pyridine nucleotide products of plasma membrane redox, ubiquinone and ubiquinol, as well as NAD(+) and NADH, may directly modulate in a reciprocal manner two key plasma membrane enzymes, sphingomyelinase and sphingosine kinase, potentially leading to G(1) arrest (increase in ceramide) and apoptosis (loss of sphingosine-1-phosphate). As such, the findings provide potential links between coenzyme Q(10)-mediated plasma membrane electron transport and the anticancer action of several clinically-relevant anticancer agents.

Effect of phloretin on the binding of 1-anilino-8-naphtalene sulfonate (ANS) to 1,2-Dimyristoyl-sn-glycero-3-phosphocoline (DMPC) vesicles in the gel and liquid-crystalline state.

PubMed

Cutró, Andrea C; Montich, Guillermo; Roveri, Oscar A

2015-02-01

Phloretin is a known modifier of the internal dipole potential of lipid membranes. We studied the interaction of phloretin with model lipid membranes and how it influences the membrane dipole organization using ANS as fluorescent probe. The fluorescence increase observed when ANS binds to DMPC liposomes in gel phase (13 °C) was 2.5 times larger in the presence of phloretin. This effect was due to an increase in ANS affinity, which can be related to the known capability of phloretin in decreasing the dipole potential. Conversely, when the experiments were carried out at 33 °C (liquid crystalline phase), phloretin completely inhibited the increase in ANS fluorescence. In addition, phloretin only affected the electrical properties of the membrane in the gel phase, whereas it modifies structural ones in the liquid-crystalline state. We postulate that phloretin was bound only to the DMPC interface in the gel phase decreasing the surface negative charge density without modifying the structural properties of the ANS binding sites. In the liquid-crystalline phase instead, it increased the accessibility of water to the ANS binding sites decreasing the intrinsic affinity and the fluorescence quantum yield of ANS.

Studies on the role of goat heart galectin-1 as an erythrocyte membrane perturbing agent

PubMed Central

Ashraf, Ghulam Md; Perveen, Asma; Zaidi, Syed Kashif; Tabrez, Shams; Kamal, Mohammad A.; Banu, Naheed

2014-01-01

Galectins are β-galactoside binding lectins with a potential hemolytic role on erythrocyte membrane integrity and permeability. In the present study, goat heart galectin-1 (GHG-1) was purified and investigated for its hemolytic actions on erythrocyte membrane. When exposed to various saccharides, lactose and sucrose provided maximum protection against hemolysis, while glucose and galactose provided lesser protection against hemolysis. GHG-1 agglutinated erythrocytes were found to be significantly hemolyzed in comparison with unagglutinated erythrocytes. A concentration dependent rise in the hemolysis of trypsinized rabbit erythrocytes was observed in the presence of GHG-1. Similarly, a temperature dependent gradual increase in percent hemolysis was observed in GHG-1 agglutinated erythrocytes as compared to negligible hemolysis in unagglutinated cells. The hemolysis of GHG-1 treated erythrocytes showed a sharp rise with the increasing pH up to 7.5 which became constant till pH 9.5. The extent of erythrocyte hemolysis increased with the increase in the incubation period, with maximum hemolysis after 5 h of incubation. The results of this study establish the ability of galectins as a potential hemolytic agent of erythrocyte membrane, which in turn opens an interesting avenue in the field of proteomics and glycobiology. PMID:25561893

Carbon dioxide and water transport through plant aquaporins.

PubMed

Groszmann, Michael; Osborn, Hannah L; Evans, John R

2017-06-01

Aquaporins are channel proteins that function to increase the permeability of biological membranes. In plants, aquaporins are encoded by multigene families that have undergone substantial diversification in land plants. The plasma membrane intrinsic proteins (PIPs) subfamily of aquaporins is of particular interest given their potential to improve plant water relations and photosynthesis. Flowering plants have between 7 and 28 PIP genes. Their expression varies with tissue and cell type, through development and in response to a variety of factors, contributing to the dynamic and tissue specific control of permeability. There are a growing number of PIPs shown to act as water channels, but those altering membrane permeability to CO 2 are more limited. The structural basis for selective substrate specificities has not yet been resolved, although a few key amino acid positions have been identified. Several regions important for dimerization, gating and trafficking are also known. PIP aquaporins assemble as tetramers and their properties depend on the monomeric composition. PIPs control water flux into and out of veins and stomatal guard cells and also increase membrane permeability to CO 2 in mesophyll and stomatal guard cells. The latter increases the effectiveness of Rubisco and can potentially influence transpiration efficiency. © 2016 John Wiley & Sons Ltd.

Modification and properties characterization of heterogeneous anion-exchange membranes by electrodeposition of graphene oxide (GO)

NASA Astrophysics Data System (ADS)

Li, Yujiao; Shi, Shaoyuan; Cao, Hongbin; Zhao, Zhijuan; Wen, Hao

2018-06-01

The heterogeneous anion exchange membranes (AEMs) were modified by electrodeposition of graphene oxide (GO) under different conditions. The physicochemical properties of GO-modified membranes were characterized systemically to obtain the optimized conditions for the electrodeposition of GO on the surface of AEMs. The results indicated that the contact angle and zeta potential of the modified AEMs decreased when increasing the concentration of GO from 0.05 g/L to 0.1 g/L. The higher concentration of NaCl, as the supporting electrolyte, could hinder the electrodeposition of GO on the AEMs for the competitive migration between the GO and Cl- ions. The increase of current density had a positive effect on properties of GO-modified membranes in the range of 1-5 mA/cm2. Compared with the pristine AEM, all the GO-modified AEMs exhibited smoother surface, higher hydrophilicity and negative zeta potential. It was also found that the GO modifying layer did not increase electrical resistance and had only a negligible effect on the desalination performance of AEMs. In the fouling experiments with sodium dodecyl benzene sulfonate (SDBS) as the model foulant, the GO-modified AEMs exhibited improved fouling resistance to SDBS.

Molecular Dynamics Simulations of Hydration Effects on Solvation, Diffusivity, and Permeability in Chitosan/Chitin Films.

PubMed

McDonnell, Marshall T; Greeley, Duncan A; Kit, Kevin M; Keffer, David J

2016-09-01

The effects of hydration on the solvation, diffusivity, solubility, and permeability of oxygen molecules in sustainable, biodegradable chitosan/chitin food packaging films were studied via molecular dynamics and confined random walk simulations. With increasing hydration, the membrane has a more homogeneous water distribution with the polymer chains being fully solvated. The diffusivity increased by a factor of 4 for oxygen molecules and by an order of magnitude for water with increasing the humidity. To calculate the Henry's constant and solubility of oxygen in the membranes with changing hydration, the excess chemical potential was calculated via free energy perturbation, thermodynamic integration and direct particle deletion methods. The simulations predicted a higher solubility and permeability for the lower humidity, in contradiction to experimental results. All three methods for calculating the solubility were in good agreement. It was found that the Coulombic interactions in the potential caused the oxygen to bind too strongly to the protonated amine group. Insight from this work will help guide molecular modeling of chitosan/chitin membranes, specifically permeability measurements for small solute molecules. Efforts to chemically tailor chitosan/chitin membranes to favor discrete as opposed to continuous aqueous domains could reduce oxygen permeability.

Roles of cyclic AMP and Ca in epithelial ion transport across corneal epithelium: a review.

PubMed

Reinach, P S

1985-04-01

The messenger roles of cyclic AMP and the calcium ion in stimulus-secretion coupling are considered in the frog and bovine corneal epithelium, respectively. In the frog cornea, epinephrine stimulates net C1 transport by increasing cyclic AMP content. This stimulation is associated with a larger apical membrane C1 conductance and basolateral membrane ionic conductance. The response of the apical membrane conductance is thought to result from an increase in cyclic AMP content whereas the basolateral membrane ionic conductance increase is unrelated based on measurements of the effects of the calcium channel antagonist, diltiazem, and the beta agonist, isoproterenol, on the electrical parameters and cyclic AMP content. The basolateral membrane is essentially K permselective since the K channel blocker, Ba, depolarized the intracellular potential difference and increased the basolateral membrane resistance. Diltiazem had even larger effects on these parameters suggesting that this compound is a more effective inhibitor of K channel activity than barium. In broken cell preparations of bovine corneal epithelium, a high affinity form of Ca + Mg activated ATPase is present (Km = .06 microM for Ca) and is essentially of plasma membrane origin. This ATPase activation is at a Ca activity similar to the expected intracellular value and suggests that this activity is the enzymatic basis for net Ca transport.

Cyclization improves membrane permeation by antimicrobial peptoids

DOE PAGES

Andreev, Konstantin; Martynowycz, Michael W.; Ivankin, Andrey; ...

2016-10-28

The peptidomimetic approach has emerged as a powerful tool for overcoming the inherent limitations of natural antimicrobial peptides, where the therapeutic potential can be improved by increasing the selectivity and bioavailability. Restraining the conformational flexibility of a molecule may reduce the entropy loss upon its binding to the membrane. Experimental findings demonstrate that the cyclization of linear antimicrobial peptoids increases their bactericidal activity against Staphylococcus aureus while maintaining high hemolytic concentrations. Surface X-ray scattering shows that macrocyclic peptoids intercalate into Langmuir monolayers of anionic lipids with greater efficacy than for their linear analogues. Lastly, it is suggested that cyclization maymore » increase peptoid activity by allowing the macrocycle to better penetrate the bacterial cell membrane.« less

Cyclization improves membrane permeation by antimicrobial peptoids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andreev, Konstantin; Martynowycz, Michael W.; Ivankin, Andrey

The peptidomimetic approach has emerged as a powerful tool for overcoming the inherent limitations of natural antimicrobial peptides, where the therapeutic potential can be improved by increasing the selectivity and bioavailability. Restraining the conformational flexibility of a molecule may reduce the entropy loss upon its binding to the membrane. Experimental findings demonstrate that the cyclization of linear antimicrobial peptoids increases their bactericidal activity against Staphylococcus aureus while maintaining high hemolytic concentrations. Surface X-ray scattering shows that macrocyclic peptoids intercalate into Langmuir monolayers of anionic lipids with greater efficacy than for their linear analogues. Lastly, it is suggested that cyclization maymore » increase peptoid activity by allowing the macrocycle to better penetrate the bacterial cell membrane.« less

Negatively charged polysulfone membranes with hydrophilicity and antifouling properties based on in situ cross-linked polymerization.

PubMed

Zhu, Lijing; Song, Haiming; Zhang, Dawei; Wang, Gang; Zeng, Zhixiang; Xue, Qunji

2017-07-15

Polysulfone (PSf) membrane has been widely used in water separation and purification, although, membrane fouling is still a serious problem limiting its potential. We aim to improve the antifouling of PSf membranes via a very simple and efficient method. In this work, antifouling PSf membranes were fabricated via in situ cross-linked polymerization coupled with non-solvent induced phase separation. In brief, acrylic acid (AA) and vinyltriethoxysilane (VTEOS) were copolymerized in PSf solution, then directly casted into membranes without purification. With the increase of monomers concentration, the morphology of the as-cast membranes changed from a finger-like morphology to a fully sponge-like structure due to the increased viscosity and decreased precipitation rate of the polymer solutions. Meanwhile, the hydrophilicity and electronegativity of modified membranes were highly improved leading to inhibited protein adsorption and improved antifouling property. Furthermore, in order to further find out the different roles player by AA and VTESO, the modified membrane without VTEOS was prepared and characterized. The results indicated that AA is more effective in the membrane hydrophilicity improvement, VTEOS is more crucial to improve membrane stability. This work provides valuable guidance for fabricating PSf membranes with hydrophilicity and antifouling property via in situ cross-linked polymerization. Copyright © 2017 Elsevier Inc. All rights reserved.

Motoneuron membrane potentials follow a time inhomogeneous jump diffusion process.

PubMed

Jahn, Patrick; Berg, Rune W; Hounsgaard, Jørn; Ditlevsen, Susanne

2011-11-01

Stochastic leaky integrate-and-fire models are popular due to their simplicity and statistical tractability. They have been widely applied to gain understanding of the underlying mechanisms for spike timing in neurons, and have served as building blocks for more elaborate models. Especially the Ornstein-Uhlenbeck process is popular to describe the stochastic fluctuations in the membrane potential of a neuron, but also other models like the square-root model or models with a non-linear drift are sometimes applied. Data that can be described by such models have to be stationary and thus, the simple models can only be applied over short time windows. However, experimental data show varying time constants, state dependent noise, a graded firing threshold and time-inhomogeneous input. In the present study we build a jump diffusion model that incorporates these features, and introduce a firing mechanism with a state dependent intensity. In addition, we suggest statistical methods to estimate all unknown quantities and apply these to analyze turtle motoneuron membrane potentials. Finally, simulated and real data are compared and discussed. We find that a square-root diffusion describes the data much better than an Ornstein-Uhlenbeck process with constant diffusion coefficient. Further, the membrane time constant decreases with increasing depolarization, as expected from the increase in synaptic conductance. The network activity, which the neuron is exposed to, can be reasonably estimated to be a threshold version of the nerve output from the network. Moreover, the spiking characteristics are well described by a Poisson spike train with an intensity depending exponentially on the membrane potential.

Voltage-dependent K+ channels improve the energy efficiency of signalling in blowfly photoreceptors

PubMed Central

2017-01-01

Voltage-dependent conductances in many spiking neurons are tuned to reduce action potential energy consumption, so improving the energy efficiency of spike coding. However, the contribution of voltage-dependent conductances to the energy efficiency of analogue coding, by graded potentials in dendrites and non-spiking neurons, remains unclear. We investigate the contribution of voltage-dependent conductances to the energy efficiency of analogue coding by modelling blowfly R1-6 photoreceptor membrane. Two voltage-dependent delayed rectifier K+ conductances (DRs) shape the membrane's voltage response and contribute to light adaptation. They make two types of energy saving. By reducing membrane resistance upon depolarization they convert the cheap, low bandwidth membrane needed in dim light to the expensive high bandwidth membrane needed in bright light. This investment of energy in bandwidth according to functional requirements can halve daily energy consumption. Second, DRs produce negative feedback that reduces membrane impedance and increases bandwidth. This negative feedback allows an active membrane with DRs to consume at least 30% less energy than a passive membrane with the same capacitance and bandwidth. Voltage-dependent conductances in other non-spiking neurons, and in dendrites, might be organized to make similar savings. PMID:28381642

Voltage-dependent K+ channels improve the energy efficiency of signalling in blowfly photoreceptors.

PubMed

Heras, Francisco J H; Anderson, John; Laughlin, Simon B; Niven, Jeremy E

2017-04-01

Voltage-dependent conductances in many spiking neurons are tuned to reduce action potential energy consumption, so improving the energy efficiency of spike coding. However, the contribution of voltage-dependent conductances to the energy efficiency of analogue coding, by graded potentials in dendrites and non-spiking neurons, remains unclear. We investigate the contribution of voltage-dependent conductances to the energy efficiency of analogue coding by modelling blowfly R1-6 photoreceptor membrane. Two voltage-dependent delayed rectifier K + conductances (DRs) shape the membrane's voltage response and contribute to light adaptation. They make two types of energy saving. By reducing membrane resistance upon depolarization they convert the cheap, low bandwidth membrane needed in dim light to the expensive high bandwidth membrane needed in bright light. This investment of energy in bandwidth according to functional requirements can halve daily energy consumption. Second, DRs produce negative feedback that reduces membrane impedance and increases bandwidth. This negative feedback allows an active membrane with DRs to consume at least 30% less energy than a passive membrane with the same capacitance and bandwidth. Voltage-dependent conductances in other non-spiking neurons, and in dendrites, might be organized to make similar savings. © 2017 The Author(s).

Eicosapentaenoic acid and docosahexaenoic acid have distinct membrane locations and lipid interactions as determined by X-ray diffraction.

PubMed

Sherratt, Samuel C R; Mason, R Preston

2018-01-31

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) differentially influence lipid oxidation, signal transduction, fluidity, and cholesterol domain formation, potentially due in part to distinct membrane interactions. We used small angle X-ray diffraction to evaluate the EPA and DHA effects on membrane structure. Membrane vesicles composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and cholesterol (C) (0.3C:POPC mole ratio) were prepared and treated with vehicle, EPA, or DHA (1:10 mol ratio to POPC). Electron density profiles generated from the diffraction data showed that EPA increased membrane hydrocarbon core electron density over a broad area, up to ± 20 Å from the membrane center, indicating an energetically favorable extended orientation for EPA likely stabilized by van der Waals interactions. By contrast, DHA increased electron density in the phospholipid head group region starting at ± 12 Å from the membrane center, presumably due to DHA-surface interactions, with coincident reduction in electron density in the membrane hydrocarbon core centered ± 7-9 Å from the membrane center. The membrane width (d-space) decreased by 5 Å in the presence of vehicle as the temperature increased from 10 °C to 30 °C due to increased acyl chain trans-gauche isomerizations, which was unaffected by addition of EPA or DHA. The influence of DHA on membrane structure was modulated by temperature changes while the interactions of EPA were unaffected. The contrasting EPA and DHA effects on membrane structure indicate distinct molecular locations and orientations that may contribute to observed differences in biological activity. Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.

Aldosterone Upregulates Transient Receptor Potential Melastatin 7 (TRPM7)*

PubMed Central

Valinsky, William C.; Jolly, Anna; Miquel, Perrine

2016-01-01

Transient receptor potential melastatin 7 (TRPM7) is a ubiquitously expressed Mg2+-permeable ion channel fused to a C-terminal α-kinase domain. Recently, aldosterone was shown to increase intracellular Mg2+ levels and alter inflammatory signaling in TRPM7-expressing HEK293 cells. This study was undertaken to assess whether these effects were related to an aldosterone-mediated increase of TRPM7 current and/or plasma membrane localization. Using HEK293 cells stably expressing WT-TRPM7, we found that 18-h application of aldosterone significantly increased TRPM7 current and TRPM7 plasma membrane protein expression by 48% and 34%, respectively. The aldosterone-mediated increase of TRPM7 current was inhibited by eplerenone, a mineralocorticoid receptor (MR) blocker, and GSK-650394, an inhibitor of the serum- and glucocorticoid-regulated kinase 1 (SGK1). SGK1 blockade also prevented the aldosterone-induced increase of TRPM7 plasma membrane protein. It was further determined that K1648R-TRPM7, the phosphotransferase-inactive TRPM7 mutant, was unresponsive to aldosterone. Therefore, chronic aldosterone treatment increases the plasma membrane expression of TRPM7, which is associated with an increase of TRPM7 current. This process occurs via an MR-dependent, genomic signaling cascade involving SGK1 and a functioning TRPM7 α-kinase domain. We suggest that this mechanism may be of general relevance when interpreting the effects of aldosterone because the MR receptor is found in multiple tissues, and TRPM7 and SGK1 are ubiquitously expressed. PMID:27466368

Enhanced proton transport in nanostructured polymer electrolyte/ionic liquid membranes under water-free conditions.

PubMed

Kim, Sung Yeon; Kim, Suhan; Park, Moon Jeong

2010-10-05

Proton exchange fuel cells (PEFCs) have the potential to provide power for a variety of applications ranging from electronic devices to transportation vehicles. A major challenge towards economically viable PEFCs is finding an electrolyte that is both durable and easily passes protons. In this article, we study novel anhydrous proton-conducting membranes, formed by incorporating ionic liquids into synthetic block co-polymer electrolytes, poly(styrenesulphonate-b-methylbutylene) (S(n)MB(m)), as high-temperature PEFCs. The resulting membranes are transparent, flexible and thermally stable up to 180 °C. The increases in the sulphonation level of S(n)MB(m) co-polymers (proton supplier) and the concentration of the ionic liquid (proton mediator) produce an overall increase in conductivity. Morphology effects were studied by X-ray scattering and electron microscopy. Compared with membranes having discrete ionic domains (including Nafion 117), the nanostructured membranes revealed over an order of magnitude increase in conductivity with the highest conductivity of 0.045 S cm(-1) obtained at 165 °C.

Pre-Combustion Carbon Capture by a Nanoporous, Superhydrophobic Membrane Contactor Process

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meyer, Howard; Zhou, S James; Ding, Yong

2012-03-31

This report summarizes progress made during Phase I and Phase II of the project: "Pre-Combustion Carbon Capture by a Nanoporous, Superhydrophobic Membrane Contactor Process," under contract DE-FE-0000646. The objective of this project is to develop a practical and cost effective technology for CO{sub 2} separation and capture for pre-combustion coal-based gasification plants using a membrane contactor/solvent absorption process. The goals of this technology development project are to separate and capture at least 90% of the CO{sub 2} from Integrated Gasification Combined Cycle (IGCC) power plants with less than 10% increase in the cost of energy services. Unlike conventional gas separationmore » membranes, the membrane contactor is a novel gas separation process based on the gas/liquid membrane concept. The membrane contactor is an advanced mass transfer device that operates with liquid on one side of the membrane and gas on the other. The membrane contactor can operate with pressures that are almost the same on both sides of the membrane, whereas the gas separation membranes use the differential pressure across the membrane as driving force for separation. The driving force for separation for the membrane contactor process is the chemical potential difference of CO{sub 2} in the gas phase and in the absorption liquid. This process is thus easily tailored to suit the needs for pre-combustion separation and capture of CO{sub 2}. Gas Technology Institute (GTI) and PoroGen Corporation (PGC) have developed a novel hollow fiber membrane technology that is based on chemically and thermally resistant commercial engineered polymer poly(ether ether ketone) or PEEK. The PEEK membrane material used in the membrane contactor during this technology development program is a high temperature engineered plastic that is virtually non-destructible under the operating conditions encountered in typical gas absorption applications. It can withstand contact with most of the common treating solvents. GTI and PGC have developed a nanoporous and superhydrophobic PEEK-based hollow fiber membrane contactor tailored for the membrane contactor/solvent absorption application for syngas cleanup. The membrane contactor modules were scaled up to 8-inch diameter commercial size modules. We have performing extensive laboratory and bench testing using pure gases, simulated water-gas-shifted (WGS) syngas stream, and a slipstream from a gasification derived syngas from GTI's Flex-Fuel Test Facility (FFTF) gasification plant under commercially relevant conditions. The team have also carried out an engineering and economic analysis of the membrane contactor process to evaluate the economics of this technology and its commercial potential. Our test results have shown that 90% CO{sub 2} capture can be achieved with several physical solvents such as water and chilled methanol. The rate of CO{sub 2} removal by the membrane contactor is in the range of 1.5 to 2.0 kg/m{sup 2}/hr depending on the operating pressures and temperatures and depending on the solvents used. The final economic analysis has shown that the membrane contactor process will cause the cost of electricity to increase by 21% from the base plant without CO{sub 2} capture. The goal of 10% increase in levelized cost of electricity (LCOE) from base DOE Case 1(base plant without capture) is not achieved by using the membrane contactor. However, the 21% increase in LCOE is a substantial improvement as compared with the 31.6% increase in LCOE as in DOE Case 2(state of art capture technology using 2-stages of Selexol{TM}).« less

Crossing boundaries: the importance of cellular membranes in industrial biotechnology.

PubMed

Jezierska, Sylwia; Van Bogaert, Inge N A

2017-05-01

How small molecules cross cellular membranes is an often overlooked issue in an industrial microbiology and biotechnology context. This is to a large extent governed by the technical difficulties to study these transport systems or by the lack of knowledge on suitable efflux pumps. This review emphasizes the importance of microbial cellular membranes in industrial biotechnology by highlighting successful strategies of membrane engineering towards more resistant and hence better performing microorganisms, as well as transporter and other engineering strategies for increased efflux of primary and secondary metabolites. Furthermore, the benefits and limitations of eukaryotic subcellular compartmentalization are discussed, as well as the biotechnological potential of membrane vesicles.

Light energy conservation processes in Halobacterium halobium cells

NASA Technical Reports Server (NTRS)

Bogomolni, R. A.

1977-01-01

Proton pumping driven by light or by respiration generates an electrochemical potential difference across the membrane in Halobacterium halobium. The pH changes induced by light or by respiration in cell suspensions are complicated by proton flows associated with the functioning of the cellular energy transducers. A proton-per-ATP ratio of about 3 is calculated from simultaneous measurements of phosphorylation and the proton inflow. This value is compatible with the chemiosmotic coupling hypothesis. The time course of the light-induced changes in membrane potential indicates that light-driven pumping increases a dark pre-existing potential of about 130 mV only by a small amount (20 to 30 mV). The complex kinetic features of the membrane potential changes do not closely follow those of the pH changes, which suggests that flows of ions other than protons are involved. A qualitative model consistent with the available data is presented.

Membrane potential dynamics of grid cells

PubMed Central

Domnisoru, Cristina; Kinkhabwala, Amina A.; Tank, David W.

2014-01-01

During navigation, grid cells increase their spike rates in firing fields arranged on a strikingly regular triangular lattice, while their spike timing is often modulated by theta oscillations. Oscillatory interference models of grid cells predict theta amplitude modulations of membrane potential during firing field traversals, while competing attractor network models predict slow depolarizing ramps. Here, using in-vivo whole-cell recordings, we tested these models by directly measuring grid cell intracellular potentials in mice running along linear tracks in virtual reality. Grid cells had large and reproducible ramps of membrane potential depolarization that were the characteristic signature tightly correlated with firing fields. Grid cells also exhibited intracellular theta oscillations that influenced their spike timing. However, the properties of theta amplitude modulations were not consistent with the view that they determine firing field locations. Our results support cellular and network mechanisms in which grid fields are produced by slow ramps, as in attractor models, while theta oscillations control spike timing. PMID:23395984

Engineering Surface Energy and Nanostructure of Microporous Films for Expanded Membrane Distillation Applications.

PubMed

Boo, Chanhee; Lee, Jongho; Elimelech, Menachem

2016-08-02

We investigated the factors that determine surface omniphobicity of microporous membranes and evaluated the potential application of these membranes in desalination of low surface tension wastewaters by membrane distillation (MD). Specifically, the effects of surface morphology and surface energy on membrane surface omniphobicity were systematically investigated by evaluating wetting resistance to low surface tension liquids. Single and multilevel re-entrant structures were achieved by using cylindrical glass fibers as a membrane substrate and grafting silica nanoparticles (SiNPs) on the fibers. Surface energy of the membrane was tuned by functionalizing the fiber substrate with fluoroalkylsilane (FAS) having two different lengths of fluoroalkyl chains. Results show that surface omniphobicity of the modified fibrous membrane increased with higher level of re-entrant structure and with lower surface energy. The secondary re-entrant structure achieved by SiNP coating on the cylindrical fibers was found to play a critical role in enhancing the surface omniphobicity. Membranes coated with SiNPs and chemically modified by the FAS with a longer fluoroalkyl chain (or lower surface energy) exhibited excellent surface omniphobicity and showed wetting resistance to low surface tension liquids such as ethanol (22.1 mN m(-1)). We further evaluated performance of the membranes in desalination of saline feed solutions with varying surface tensions by membrane distillation (MD). The engineered membranes exhibited stable MD performance with low surface tension feed waters, demonstrating the potential application omniphobic membranes in desalinating complex, high salinity industrial wastewaters.

UCP2 muscle gene transfer modifies mitochondrial membrane potential.

PubMed

Marti, A; Larrarte, E; Novo, F J; Garcia, M; Martinez, J A

2001-01-01

The aim of this work was to evaluate the effect of uncoupling protein 2 (UCP2) muscle gene transfer on mitochondrial activity. Five week-old male Wistar rats received an intramuscular injection of plasmid pXU1 containing UCP2 cDNA in the right tibialis anterior muscles. Left tibialis anterior muscles were injected with vehicle as control. Ten days after DNA injection, tibialis anterior muscles were dissected and muscle mitochondria isolated and analyzed. There were two mitochondrial populations in the muscle after UCP2 gene transfer, one of low fluorescence and complexity and the other, showing high fluorescence and complexity. UCP2 gene transfer resulted in a 3.6 fold increase in muscle UCP2 protein levels compared to control muscles assessed by Western blotting. Furthermore, a significant reduction in mitochondria membrane potential assessed by spectrofluorometry and flow cytometry was observed. The mitochondria membrane potential reduction might account for a decrease in fluorescence of the low fluorescence mitochondrial subpopulation. It has been demonstrated that UCP2 muscle gene transfer in vivo is associated with a lower mitochondria membrane potential. Our results suggest the potential involvement of UCP2 in uncoupling respiration. International Journal of Obesity (2001) 25, 68-74

Effects of redox and sulfhydryl reagents on the bioelectric properties of the giant axon of the squid.

PubMed

Huneeus-Cox, F; Fernandez, H L; Smith, B H

1966-09-01

The effects of internally and externally applied sulfhydryl reagents on the bioelectric properties of the giant axon of the squid Loligo pealeii and Dosidicus gigas were studied. Cysteine-HCl (400 mM, pH 7.3) was used to remove axoplasm from the perfusion channel. Oxidizing agents (1 to 60 mM) tended to increase the duration of the action potential and had a slow, irreversible blocking effect when perfused internally; the membrane potential was little affected. Reducing agents applied internally caused a decrease in the spike duration without affecting its height or the membrane potential, although at high concentrations there was reversible deterioration of the action potential. Both external and internal perfusion of mercaptide-forming reagents caused deterioration in the action and membrane potentials with conduction block occurring in 5 to 45 min. 2-mercaptoethanol reversed the effects. Thiol alkylating reagents, iodoacetate and iodoacetamide, were without effect. N-ethylmaleimide did, however, block. Tests with chelating agents for nonheme iron in the membrane brought about no change in the electrical parameters. The implications of the present findings with regard to the macromolecular mechanism of excitation are discussed.

Effects of Redox and Sulfhydryl Reagents on the Bioelectric Properties of the Giant Axon of the Squid

PubMed Central

Huneeus-Cox, F.; Fernandez, H. L.; Smith, B. H.

1966-01-01

The effects of internally and externally applied sulfhydryl reagents on the bioelectric properties of the giant axon of the squid Loligo pealeii and Dosidicus gigas were studied. Cysteine-HCl (400 mM, pH 7.3) was used to remove axoplasm from the perfusion channel. Oxidizing agents (1 to 60 mM) tended to increase the duration of the action potential and had a slow, irreversible blocking effect when perfused internally; the membrane potential was little affected. Reducing agents applied internally caused a decrease in the spike duration without affecting its height or the membrane potential, although at high concentrations there was reversible deterioration of the action potential. Both external and internal perfusion of mercaptide-forming reagents caused deterioration in the action and membrane potentials with conduction block occurring in 5 to 45 min. 2-mercaptoethanol reversed the effects. Thiol alkylating reagents, iodoacetate and iodoacetamide, were without effect. N-ethylmaleimide did, however, block. Tests with chelating agents for nonheme iron in the membrane brought about no change in the electrical parameters. The implications of the present findings with regard to the macromolecular mechanism of excitation are discussed. ImagesFigure 1 PMID:5970570

Effect of acetic acid on Saccharomyces carlsbergensis ATCC 6269 batch ethanol production monitored by flow cytometry.

PubMed

Freitas, Cláudia; Neves, Elisabete; Reis, Alberto; Passarinho, Paula C; da Silva, Teresa Lopes

2012-11-01

Bioethanol produced from lignocellulosic materials has been considered a sustainable alternative fuel. Such type of raw materials have a huge potential, but their hydrolysis into mono-sugars releases toxic compounds such as weak acids, which affect the microorganisms' physiology, inhibiting the growth and ethanol production. Acetic acid (HAc) is the most abundant weak acid in the lignocellulosic materials hydrolysates. In order to understand the physiological changes of Saccharomyces carlsbergensis when fermenting in the presence of different acetic acid (HAc) concentrations, the yeast growth was monitored by multi-parameter flow cytometry at same time that the ethanol production was assessed. The membrane potential stain DiOC(6)(3) fluorescence intensity decreased as the HAc concentration increased, which was attributed to the plasmic membrane potential reduction as a result of the toxic effect of the HAc undissociated form. Nevertheless, the proportion of cells with permeabilized membrane did not increase with the HAc concentration increase. Fermentations ending at lower external pH and higher ethanol concentrations depicted the highest proportions of permeabilized cells and cells with increased reactive oxygen species levels. Flow cytometry allowed monitoring, near real time (at-line), the physiological states of the yeast during the fermentations. The information obtained can be used to optimize culture conditions to improve bioethanol production.

Dog red blood cells: Na and K diffusion potentials with extracellular ATP

PubMed Central

1977-01-01

External ATP causes a prompt increase in the Na and K permeability of dog red blood cells. By manipulating intra- and extracellular ion composition it is possible to observe ATP-induced net fluxes which can be explained in terms of the contribution of Na or K diffusion potentials to the membrane potential. Measurements of membrane voltage by a fluorescent dye technique confirm the existence of such potentials. A rough calculation of chloride permeability gives a value of the order of 10(-8) cm/s, which agrees with results in other species. The cells appear to be somewhat more permeable to bromide than to chloride. PMID:853285

Anion Channel Inhibitor NPPB-Inhibited Fluoride Accumulation in Tea Plant (Camellia sinensis) Is Related to the Regulation of Ca2+, CaM and Depolarization of Plasma Membrane Potential

PubMed Central

Zhang, Xian-Chen; Gao, Hong-Jian; Yang, Tian-Yuan; Wu, Hong-Hong; Wang, Yu-Mei; Zhang, Zheng-Zhu; Wan, Xiao-Chun

2016-01-01

Tea plant is known to be a hyper-accumulator of fluoride (F). Over-intake of F has been shown to have adverse effects on human health, e.g., dental fluorosis. Thus, understanding the mechanisms fluoride accumulation and developing potential approaches to decrease F uptake in tea plants might be beneficial for human health. In the present study, we found that pretreatment with the anion channel inhibitor NPPB reduced F accumulation in tea plants. Simultaneously, we observed that NPPB triggered Ca2+ efflux from mature zone of tea root and significantly increased relative CaM in tea roots. Besides, pretreatment with the Ca2+ chelator (EGTA) and CaM antagonists (CPZ and TFP) suppressed NPPB-elevated cytosolic Ca2+ fluorescence intensity and CaM concentration in tea roots, respectively. Interestingly, NPPB-inhibited F accumulation was found to be significantly alleviated in tea plants pretreated with either Ca2+ chelator (EGTA) or CaM antagonists (CPZ and TFP). In addition, NPPB significantly depolarized membrane potential transiently and we argue that the net Ca2+ and H+ efflux across the plasma membrane contributed to the restoration of membrane potential. Overall, our results suggest that regulation of Ca2+-CaM and plasma membrane potential depolarization are involved in NPPB-inhibited F accumulation in tea plants. PMID:26742036

Continued clearance of apoptotic cells critically depends on the phagocyte Ucp2 protein

PubMed Central

Park, Daeho; Han, Claudia; Elliott, Michael R.; Kinchen, Jason M.; Trampont, Paul C.; Das, Soumita; Collins, Sheila; Lysiak, Jeffrey J.; Hoehn, Kyle L.; Ravichandran, Kodi S.

2012-01-01

Rapid and efficient removal of apoptotic cells by phagocytes plays a key role during development, tissue homeostasis, and in controlling immune responses1–5. An important feature of efficient clearance is the capacity of a single phagocyte to ingest multiple apoptotic cells successively, and to process the increased load of corpse-derived cellular material6–9. However, factors that influence sustained phagocytic capacity or how they in turn influence continued clearance by phagocytes are not known. Here we identify that the ability of a phagocyte to control its mitochondrial membrane potential is a critical factor in the capacity of a phagocyte to engulf apoptotic cells. Changing the phagocyte mitochondrial membrane potential (genetically or pharmacologically) significantly affected phagocytosis, with lower potential enhancing engulfment and higher membrane potential inhibiting uptake. We then identified that Ucp2, a mitochondrial membrane protein that acts to lower the mitochondrial membrane potential10–12, is upregulated in phagocytes engulfing apoptotic cells (but not synthetic targets, bacteria, or yeast). Loss of Ucp2 limited the capacity of phagocytes to continually ingest apoptotic cells, while overexpression of Ucp2 increased the capacity for engulfment and the ability to engulf multiple apoptotic cells. Mutational and pharmacological inhibition of Ucp2 uncoupling activity reversed the positive effect of Ucp2 on engulfment capacity, suggesting a direct role for Ucp2-mediated mitochondrial function in phagocytosis. Macrophages from Ucp2-deficient mice13, 14 were impaired in their capacity to engulf apoptotic cells in vitro, and Ucp2-deficient mice displayed profound in vivo defects in clearing dying cells in the thymus and the testes. Collectively, these data suggest that phagocytes alter the mitochondrial membrane potential during engulfment to regulate uptake of sequential apoptotic cells, and that Ucp2 is a key molecular determinant of this step in vivo. Since Ucp2 function has also been linked to metabolic diseases and atherosclerosis14–16, these data identifying a new role for Ucp2 in regulating apoptotic cell clearance may provide additional insights toward understanding the complex etiology and pathogenesis of these diseases. PMID:21857682

Multilayer affinity adsorption of albumin on polymer brushes modified membranes in a continuous-flow system.

PubMed

Hu, Meng-Xin; Li, Xiang; Li, Ji-Nian; Huang, Jing-Jing; Ren, Ge-Rui

2018-02-23

Polymer brushes modified surfaces have been widely used for protein immobilization and isolation. Modification of membranes with polymer brushes increases the surface concentration of affinity ligands used for protein binding. Albumin is one of the transporting proteins and shows a high affinity to bile acids. In this work, the modified membranes with cholic acid-containing polymer brushes can be facilely prepared by the immobilization of cholic acid on the poly(2-hydroxyethyl methacrylate) grafted microporous polypropylene membranes (MPPMs) for affinity adsorption of albumin. ATR/FT-IR and X-ray photoelectron spectroscopy were used to characterize the chemical composition of the modified membranes. Water contact angle measurements were used to analyze the hydrophilic/hydrophobic properties of the membrane surface. The modified MPPMs show a high affinity to albumin and have little non-specific adsorption of hemoglobin. The dynamic binding capacity of albumin in the continous-flow system increases with the cycle number and feed rate as the binding degree of cholic acid is moderate. The highest binding capacity of affinity membranes is about 52.49 g/m 2 membrane, which is about 24 times more than the monolayer binding capacity. These results reveal proteins could be captured in multilayers by the polymer brushes containing affinity ligands similar to the polymer brushes containing ion-exchange groups, which open up the potential of the polymer brushes containing affinity ligands in protein or another components separation. And the cholic acid containing polymer brushes modified membranes has the promising potential for albumin separation and purification rapidly from serum or fermented solution in medical diagnosis and bioseparation. Copyright © 2018 Elsevier B.V. All rights reserved.

Effects of lubiprostone on human uterine smooth muscle cells.

PubMed

Cuppoletti, John; Malinowska, Danuta H; Chakrabarti, Jayati; Ueno, Ryuji

2008-06-01

Lubiprostone, a bicyclic fatty acid derivative and member of a new class of compounds called prostones, locally activates ClC-2 Cl(-) channels without activation of prostaglandin receptors. The present study was specifically designed to test and compare lubiprostone and prostaglandin effects at the cellular level using human uterine smooth muscle cells. Effects on [Ca(2+)](i), membrane potential and [cAMP](i) in human uterine smooth muscle cells were measured. 10 nM lubiprostone significantly decreased [Ca(2+)](i) from 188 to 27 nM, which was unaffected by 100 nM SC-51322, a prostaglandin EP receptor antagonist. In contrast 10nM PGE(2) and PGE(1) both increased [Ca(2+)](i) 3-5-fold which was blocked by SC-51322. Similarly, lubiprostone and prostaglandins had opposite/different effects on membrane potential and [cAMP](i). Lubiprostone caused SC-51322-insensitive membrane hyperpolarization and no effect on [cAMP](i). PGE(2) and PGE(1) both caused SC-51322-sensitive membrane depolarization and increased [cAMP](i). Lubiprostone has fundamentally different cellular effects from prostaglandins that are not mediated by EP receptors.

Generation of nanobubbles by ceramic membrane filters: The dependence of bubble size and zeta potential on surface coating, pore size and injected gas pressure.

PubMed

Ahmed, Ahmed Khaled Abdella; Sun, Cuizhen; Hua, Likun; Zhang, Zhibin; Zhang, Yanhao; Zhang, Wen; Marhaba, Taha

2018-07-01

Generation of gaseous nanobubbles (NBs) by simple, efficient, and scalable methods is critical for industrialization and applications of nanobubbles. Traditional generation methods mainly rely on hydrodynamic, acoustic, particle, and optical cavitation. These generation processes render issues such as high energy consumption, non-flexibility, and complexity. This research investigated the use of tubular ceramic nanofiltration membranes to generate NBs in water with air, nitrogen and oxygen gases. This system injects pressurized gases through a tubular ceramic membrane with nanopores to create NBs. The effects of membrane pores size, surface energy, and the injected gas pressures on the bubble size and zeta potential were examined. The results show that the gas injection pressure had considerable effects on the bubble size, zeta potential, pH, and dissolved oxygen of the produced NBs. For example, increasing the injection air pressure from 69 kPa to 414 kPa, the air bubble size was reduced from 600 to 340 nm respectively. Membrane pores size and surface energy also had significant effects on sizes and zeta potentials of NBs. The results presented here aim to fill out the gaps of fundamental knowledge about NBs and development of efficient generation methods. Copyright © 2018 Elsevier Ltd. All rights reserved.

Interleukin-4 activates large-conductance, calciumactivated potassium (BKCa) channels in human airway smooth muscle cells

PubMed Central

Martin, Gilles; O’Connell, Robert J.; Pietrzykowski, Andrzej Z.; Treistman, Steven N.; Ethier, Michael F.; Madison, J. Mark

2014-01-01

Large-conductance, calcium-activated potassium (BKCa) channels are regulated by voltage and near-membrane calcium concentrations and are determinants of membrane potential and excitability in airway smooth muscle cells. Since the T helper–2 (Th2) cytokine, interleukin (IL)-4, is an important mediator of airway inflammation, we investigated whether IL-4 rapidly regulated BKCa activity in normal airway smooth muscle cells. On-cell voltage clamp recordings were made on subconfluent, cultured human bronchial smooth muscle cells (HBSMC). Interleukin-4 (50 ng ml−1), IL-13 (50 ng ml−1) or histamine (10 μm) was added to the bath during the recordings. Immunofluorescence studies with selective antibodies against the α and β1 subunits of BKCa were also performed. Both approaches demonstrated that HBSMC membranes contained large-conductance channels (>200 pS) with both calcium and voltage sensitivity, all of which is characteristic of the BKCa channel. Histamine caused a rapid increase in channel activity, as expected. A new finding was that perfusion with IL-4 stimulated rapid, large increases in BKCa channel activity (77.2 ± 63.3-fold increase, P < 0.05, n = 18). This large potentiation depended on the presence of external calcium. In contrast, IL-13 (50 ng ml−1) had little effect on BKCa channel activity, but inhibited the effect of IL-4. Thus, HBSMC contain functional BKCa channels whose activity is rapidly potentiated by the cytokine, IL-4, but not by IL-13.These findings are consistent with a model in which IL-4 rapidly increases near-membrane calcium concentrations to regulate BKCa activity. PMID:18403443

Effect of tension and curvature on the chemical potential of lipids in lipid aggregates.

PubMed

Grafmüller, Andrea; Lipowsky, Reinhard; Knecht, Volker

2013-01-21

Understanding the factors that influence the free energy of lipids in bilayer membranes is an essential step toward understanding exchange processes of lipids between membranes. In general, both lipid composition and membrane geometry can affect lipid exchange rates between bilayer membranes. Here, the free energy change ΔG(des) for the desorption of dipalmitoyl-phosphatidylcholine (DPPC) lipids from different lipid aggregates has been computed using molecular dynamics simulations and umbrella sampling. The value of ΔG(des) is found to depend strongly on the local properties of the aggregate, in that both tension and curvature lead to an increase in ΔG(des). A detailed analysis shows that the increased desorption free energy for tense bilayers arises from the increased conformational entropy of the lipid tails, which reduces the favorable component -TΔS(L) of the desorption free energy.

Fluconazole affects the alkali-metal-cation homeostasis and susceptibility to cationic toxic compounds of Candida glabrata.

PubMed

Elicharova, Hana; Sychrova, Hana

2014-08-01

Candida glabrata is a salt-tolerant and fluconazole (FLC)-resistant yeast species. Here, we analyse the contribution of plasma-membrane alkali-metal-cation exporters, a cation/proton antiporter and a cation ATPase to cation homeostasis and the maintenance of membrane potential (ΔΨ). Using a series of single and double mutants lacking CNH1 and/or ENA1 genes we show that the inability to export potassium and toxic alkali-metal cations leads to a slight hyperpolarization of the plasma membrane of C. glabrata cells; this hyperpolarization drives more cations into the cells and affects cation homeostasis. Surprisingly, a much higher hyperpolarization of C. glabrata plasma membrane was produced by incubating cells with subinhibitory concentrations of FLC. FLC treatment resulted in a substantially increased sensitivity of cells to various cationic drugs and toxic cations that are driven into the cell by negative-inside plasma-membrane potential. The effect of the combination of FLC plus cationic drug treatment was enhanced by the malfunction of alkali-metal-cation transporters that contribute to the regulation of membrane potential and cation homeostasis. In summary, we show that the combination of subinhibitory concentrations of FLC and cationic drugs strongly affects the growth of C. glabrata cells. © 2014 The Authors.

An Investigation on bilayer structures of electrospun polyacrylonitrile nanofibrous membrane and cellulose membrane used as filtration media for apple juice clarification

NASA Astrophysics Data System (ADS)

Sawitri, Asti; Miftahul Munir, Muhammad; Edikresnha, Dhewa; Sandi, Ahzab; Fauzi, Ahmad; Rajak, Abdul; Natalia, Dessy; Khairurrijal, Khairurrijal

2018-05-01

Nanofibrous membrane has a potential to use in filtration technology with electrospinning as one of the techniques used in synthesizing nanofibers. Polyacrylonitrile (PAN) nanofibrous membranes with various fibers diameters were electrospun by varying its precursor solution concentration. The average fibers diameters of the PAN nanofibrous membranes obtained from the precursor solution concentrations of 6, 9, 12, and 14 wt% were 341, 534, 1274, and 2107 nm, respectively. Filtration media for apple juice clarification were bilayer-structured membranes made of PAN nanofibrous membranes on commercial cellulose microfibrous membranes. It has been shown that the reduction of apple juice color or turbidity performed by the cellulose microfibrous membrane was well enhanced by the presence of the PAN nanofibrous membrane in the bilayer-structured membrane. In addition, the apple-juice color and turbidity reductions increased with decreasing the average fibers diameter of the PAN nanofibrous membrane. Furthermore, the PAN nanofibrous membrane also helped the cellulose microfibrous membrane in the bilayer-structured membrane enhance the reductions of total phenols, protein, and glucose of the apple juice.

Addition of insulin-like growth factor I to the maturation medium of bovine oocytes subjected to heat shock: effects on the production of reactive oxygen species, mitochondrial activity and oocyte competence.

PubMed

Ascari, I J; Alves, N G; Jasmin, J; Lima, R R; Quintão, C C R; Oberlender, G; Moraes, E A; Camargo, L S A

2017-07-01

This study was performed to investigate the effects of insulin-like growth factor-I (IGF-I) addition to in vitro maturation (IVM) medium on apoptosis, mitochondrial membrane potential, ROS production, and developmental competence of bovine oocytes subjected to heat shock. Two temperatures (conventional: 24 h at 38.5°C, or heat shock: 12 h at 41°C followed by 12 h at 38.5°C) and 3 IGF-I concentrations (0, 25, and 100 ng/mL) were tested during IVM. The oocytes were then fertilized in vitro, and the presumptive zygotes were cultured until reaching the blastocyst stage. There was no interaction between temperature and IGF-I concentration for any variable evaluated (P > 0.05). The addition of IGF-I did not alter the proportion of nuclear maturation, TUNEL-positive oocytes and caspase-3 activity, or blastocyst proportion on Days 7 and 8 post-fertilization. Furthermore, the total number of cells and the number of cells in the inner cell mass (ICM) in the blastocyst were not altered (P > 0.05). However, IGF-I increased (P < 0.05) the mitochondrial membrane potential and the production of ROS in oocytes and decreased (P < 0.05) the proportion of apoptotic cells in the ICM in blastocysts. Heat shock increased (P < 0.05) the proportion of TUNEL-positive oocytes and ROS production and reduced (P < 0.05) the mitochondrial membrane potential. Moreover, heat shock increased (P < 0.05) the apoptosis proportion in the ICM cells. In conclusion, supplementing IVM medium with IGF-I may increase the mitochondrial membrane potential and ROS production in oocytes and decrease apoptosis in the ICM in blastocysts. Heat shock for 12 h compromised oocyte developmental competence and increased apoptosis within the ICM cells of the blastocysts. Copyright © 2017 Elsevier Inc. All rights reserved.

Transcriptome and membrane fatty acid analyses reveal different strategies for responding to permeating and non-permeating solutes in the bacterium Sphingomonas wittichii

PubMed Central

2011-01-01

Background Sphingomonas wittichii strain RW1 can completely oxidize dibenzo-p-dioxins and dibenzofurans, which are persistent contaminants of soils and sediments. For successful application in soil bioremediation systems, strain RW1 must cope with fluctuations in water availability, or water potential. Thus far, however, little is known about the adaptive strategies used by Sphingomonas bacteria to respond to changes in water potential. To improve our understanding, strain RW1 was perturbed with either the cell-permeating solute sodium chloride or the non-permeating solute polyethylene glycol with a molecular weight of 8000 (PEG8000). These solutes are assumed to simulate the solute and matric components of the total water potential, respectively. The responses to these perturbations were then assessed and compared using a combination of growth assays, transcriptome profiling, and membrane fatty acid analyses. Results Under conditions producing a similar decrease in water potential but without effect on growth rate, there was only a limited shared response to perturbation with sodium chloride or PEG8000. This shared response included the increased expression of genes involved with trehalose and exopolysaccharide biosynthesis and the reduced expression of genes involved with flagella biosynthesis. Mostly, the responses to perturbation with sodium chloride or PEG8000 were very different. Only sodium chloride triggered the increased expression of two ECF-type RNA polymerase sigma factors and the differential expression of many genes involved with outer membrane and amino acid metabolism. In contrast, only PEG8000 triggered the increased expression of a heat shock-type RNA polymerase sigma factor along with many genes involved with protein turnover and repair. Membrane fatty acid analyses further corroborated these differences. The degree of saturation of membrane fatty acids increased after perturbation with sodium chloride but had the opposite effect and decreased after perturbation with PEG8000. Conclusions A combination of growth assays, transcriptome profiling, and membrane fatty acid analyses revealed that permeating and non-permeating solutes trigger different adaptive responses in strain RW1, suggesting these solutes affect cells in fundamentally different ways. Future work is now needed that connects these responses with the responses observed in more realistic scenarios of soil desiccation. PMID:22082453

Sustainable green technology on wastewater treatment: The evaluation of enhanced single chambered up-flow membrane-less microbial fuel cell.

PubMed

Thung, Wei-Eng; Ong, Soon-An; Ho, Li-Ngee; Wong, Yee-Shian; Ridwan, Fahmi; Oon, Yoong-Ling; Oon, Yoong-Sin; Lehl, Harvinder Kaur

2018-04-01

This study demonstrated the potential of single chamber up-flow membrane-less microbial fuel cell (UFML-MFC) in wastewater treatment and power generation. The purpose of this study was to evaluate and enhance the performance under different operational conditions which affect the chemical oxygen demand (COD) reduction and power generation, including the increase of KCl concentration (MFC1) and COD concentration (MFC2). The results showed that the increase of KCl concentration is an important factor in up-flow membrane-less MFC to enhance the ease of electron transfer from anode to cathode. The increase of COD concentration in MFC2 could led to the drop of voltage output due to the prompt of biofilm growth in MFC2 cathode which could increase the internal resistance. It also showed that the COD concentration is a vital issue in up-flow membrane-less MFC. Despite the COD reduction was up to 96%, the power output remained constrained. Copyright © 2017. Published by Elsevier B.V.

In situ synthesis of nanocomposite membranes: comprehensive improvement strategy for direct methanol fuel cells.

PubMed

Rao, Siyuan; Xiu, Ruijie; Si, Jiangju; Lu, Shanfu; Yang, Meng; Xiang, Yan

2014-03-01

In situ synthesis is a powerful approach to control nanoparticle formation and consequently confers extraordinary properties upon composite membranes relative to conventional doping methods. Herein, uniform nanoparticles of cesium hydrogen salts of phosphotungstic acid (CsPW) are controllably synthesized in situ in Nafion to form CsPW–Nafion nanocomposite membranes with both improved proton conductivity and methanol-crossover suppression. A 101.3% increase of maximum power density has been achieved relative to pristine Nafion in a direct methanol fuel cell (DMFC), indicating a potential pathway for large-scale fabrication of DMFC alternative membranes.

Evidence for a Na/H Antiporter in Membrane Vesicles Isolated from Roots of the Halophyte Atriplex nummularia.

PubMed

Braun, Y; Hassidim, M; Lerner, H R; Reinhold, L

1988-05-01

The ATP-dependent establishment of a positive membrane potential (measured as S(14)CN(-)-accumulation) in membrane vesicles isolated from the roots of Atriplex nummularia Lindl. was not inhibited by NaMes and KMes at concentrations up to 140 millimolar. On the other hand, the formation of DeltapH (measured as (14)C-methylamine accumulation or quenching of quinacrine fluorescence), was depressed by NaMes concentrations as low as 30 millimolar. Supply of NaMes after the DeltapH had been established brought about partial dissipation within 30 seconds. Extent of dissipation of DeltapH increased with NaMes concentration over the range tested (up to 180 millimolar). The H(+)/Na(+) exchange indicated by these results was not due to the creation of a Na(+) diffusion potential. Formation of DeltapH in these vesicles was stable to NO(3) (-) up to 100 millimolar; further, the dissipating effect of Na(+) supply was apparent on a DeltapH formed in the presence of 30 millimolar NO(3) (-). Additional evidence that the origin of the membrane vesicles observed in this investigation was not the tonoplast and was probably the plasmalemma included the vanadate sensitivity of the establishment of the membrane potential.

Effects of CNT size on the desalination performance of an outer-wall CNT slit membrane.

PubMed

Ang, Elisa Y M; Ng, Teng Yong; Yeo, Jingjie; Lin, Rongming; Liu, Zishun; Geethalakshmi, K R

2018-05-23

We investigate the effect of varying carbon nanotube (CNT) size on the desalination performance through slit confinements formed by horizontally aligned CNTs stacked on top of one another. By increasing the CNT size, the results obtained from this study indicate a corresponding increase in the water flow rate, accompanied by a slight reduction in salt rejection performance. However, due to the increase in the membrane area with CNT size, the permeability performance is observed to reduce as the CNT size increases. Nevertheless, a comparison with nanoporous 2D membranes shows that the permeability of an outer-wall CNT slit membrane remains significantly higher for all CNT sizes considered. This indicates that precise dimensions of the CNTs are not highly crucial for achieving ultra-high permeability performance in such membranes, as long as the critical slit size is maintained. In-depth analytical studies were further conducted to correlate the influence of curvature effects due to increasing CNT size on the flow characteristcis of the outer-wall CNT membrane. These include the analysis of the measured velocity profiles, oxygen density mapping, potential of mean force profile and friction profile. The present numerical results demonstrate the superb desalination performance of the outer-wall CNT slit membrane, regardless of the size of CNTs used. In addition, an extensive analysis conducted provides detailed characterization of how the curvature affects flow across outer-wall CNTs, and can be used to guide future design and fabrication for experimental testing.

Electron paramagnetic resonance investigation on modulatory effect of benidipine on membrane fluidity of erythrocytes in essential hypertension.

PubMed

Tsuda, Kazushi

2008-03-01

It has been shown that benidipine, a long-lasting calcium (Ca) channel blocker, may exert its protective effect against vascular disorders by increasing nitric oxide (NO) production. The purpose of the present study was to investigate whether orally administered benidipine might influence the membrane function in patients with essential hypertension. We measured the membrane fluidity of erythrocytes by using an electron paramagnetic resonance (EPR) and spin-labeling method. In the preliminary study using erythrocytes obtained from healthy volunteers, benidipine decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (ho/h-1) for 16-NS in the EPR spectra in vitro. The finding indicated that benidipine increased the membrane fluidity and improved the microviscosity of erythrocytes. In addition, it was demonstrated that the effect of benidipine on membrane fluidity of erythrocytes was significantly potentiated by the NO-substrate, L-arginine. In the separate series of the study, we observed that orally administered benidipine for 4 weeks significantly increased the membrane fluidity of erythrocytes with a concomitant increase in plasma NO metabolite levels in hypertensive subjects. The results of the present study demonstrated that benidipine might increase the membrane fluidity and improve the microviscosity of erythrocytes both in vitro and in vivo, to some extent, by the NO-dependent mechanism. Furthermore, it is strongly suggested that orally administered benidipine might have a beneficial effect on the rheologic behavior of erythrocytes and the improvement of the microcirculation in hypertensive subjects.

Functional consequences of sphingomyelinase-induced changes in erythrocyte membrane structure

PubMed Central

Dinkla, S; Wessels, K; Verdurmen, W P R; Tomelleri, C; Cluitmans, J C A; Fransen, J; Fuchs, B; Schiller, J; Joosten, I; Brock, R; Bosman, G J C G M

2012-01-01

Inflammation enhances the secretion of sphingomyelinases (SMases). SMases catalyze the hydrolysis of sphingomyelin into phosphocholine and ceramide. In erythrocytes, ceramide formation leads to exposure of the removal signal phosphatidylserine (PS), creating a potential link between SMase activity and anemia of inflammation. Therefore, we studied the effects of SMase on various pathophysiologically relevant parameters of erythrocyte homeostasis. Time-lapse confocal microscopy revealed a SMase-induced transition from the discoid to a spherical shape, followed by PS exposure, and finally loss of cytoplasmic content. Also, SMase treatment resulted in ceramide-associated alterations in membrane–cytoskeleton interactions and membrane organization, including microdomain formation. Furthermore, we observed increases in membrane fragility, vesiculation and invagination, and large protein clusters. These changes were associated with enhanced erythrocyte retention in a spleen-mimicking model. Erythrocyte storage under blood bank conditions and during physiological aging increased the sensitivity to SMase. A low SMase activity already induced morphological and structural changes, demonstrating the potential of SMase to disturb erythrocyte homeostasis. Our analyses provide a comprehensive picture in which ceramide-induced changes in membrane microdomain organization disrupt the membrane–cytoskeleton interaction and membrane integrity, leading to vesiculation, reduced deformability, and finally loss of erythrocyte content. Understanding these processes is highly relevant for understanding anemia during chronic inflammation, especially in critically ill patients receiving blood transfusions. PMID:23076218

Genotoxic effect of 6-gingerol on human hepatoma G2 cells.

PubMed

Yang, Guang; Zhong, Laifu; Jiang, Liping; Geng, Chengyan; Cao, Jun; Sun, Xiance; Ma, Yufang

2010-04-15

6-gingerol, a major component of ginger, has antioxidant, anti-apoptotic, and anti-inflammatory activities. However, some dietary phytochemicals possess pro-oxidant effects as well, and the risk of adverse effects is increased by raising the use of doses. The aim of this study was to assess the genotoxic effects of 6-gingerol and to clarify the mechanisms, using human hepatoma G2 (HepG2) cells. Exposure of the cells to 6-gingerol caused significant increase of DNA migration in comet assay, increase of micronuclei frequencies at high concentrations at 20-80 and 20-40 microM, respectively. These results indicate that 6-gingerol caused DNA strand breaks and chromosome damage. To further elucidate the underlying mechanisms, we tested lysosomal membrane stability, mitochondrial membrane potential, the intracellular generation of reactive oxygen species (ROS) and reduced glutathione (GSH). In addition, the level of oxidative DNA damage was evaluated by immunocytochemical analysis on 8-hydroxydeoxyguanosine (8-OHdG). Results showed that lysosomal membrane stability was reduced after treatment by 6-gingerol (20-80 microM) for 40 min, mitochondrial membrane potential decreased after treatment for 50 min, GSH and ROS levels were significantly increased after treatment for 60 min. These suggest 6-gingerol induces genotoxicity probably by oxidative stress; lysosomal and mitochondrial damage were observed in 6-gingerol-induced toxicity. Copyright 2010 Elsevier Ireland Ltd. All rights reserved.

Mitochondrial ryanodine-sensitive Ca2+ channels of rat liver.

PubMed

Kupynyak, N I; Ikkert, O V; Shlykov, S G; Babich, L G; Manko, V V

2017-01-01

To examine ryanodine-sensitive Ca 2+ channels in mitochondria of rat hepatocytes and their role in energy state of the cells via investigation of the ryanodine effect on mitochondrial membrane potential. Oxygen consumption was measured by polarography using the Clark electrode. The substrates of oxidation such as pyruvate (5mM), α-ketoglutarate (5mM), or succinate (5mM) were used. Oxidative phosphorylation was stimulated by the addition of adenosine diphosphate (200nM). Mitochondrial membrane potential was measured using a voltage-sensitive fluorescent probe tetramethylrhodamine-methyl-ester (0.1μM) and was analyzed by a flow cytometer. To evaluate the intact mitochondria, we used carbonil cyanide m-chlorophenyl hydrazone (CCCP, 10μM). Changes in the ionized calcium concentration in rat liver mitochondria were measured using a fluorescent probe Fluo-4 AM. Effect of ryanodine on oxygen consumption of rat liver mitochondria depends on the oxidation substrate and the incubation time. Oxidation of pyruvate in the presence of ryanodine (0.05μM) decreased the membrane potential of rat liver mitochondria by 38.4%. At higher concentrations, ryanodine (0.1μM or 1μM) led to decrease of membrane potential by 51.7% and 42.8%, respectively. In contrast, oxidation of α-ketoglutarate in the presence of ryanodine (0.05μM) increased mitochondrial membrane potential by 16.8%. However, at higher concentrations, ryanodine (0.1μM or 1μM) triggered a decreasing of membrane potential by 42.5% and 31.0%, respectively. Therefore, ryanodine at various concentrations (0.05μM, 0.1μM, or 1μM) causes differential effects on Ca 2+ concentration in the mitochondria matrix under oxidation of pyruvate or α-ketoglutarate. The data suggest the presence of ryanodine receptors in mitochondrial membrane of rat hepatocytes. Their inhibition with higher concentrations of ryanodine leads to decreasing of intra-mitochondrial Ca 2+ concentration and affecting the energy state of mictochondria in hepatocytes. Copyright © 2017 John Wiley & Sons, Ltd.

Fabrication of porous matrix membrane (PMM) using metal-organic framework as green template for water treatment.

PubMed

Lee, Jian-Yuan; Tang, Chuyang Y; Huo, Fengwei

2014-01-17

Pressure-driven membranes with high porosity can potentially be fabricated by removing template, such as low water stability metal-organic frameworks (MOFs) or other nanoparticles, in polymeric matrix. We report on the use of benign MOFs as green template to enhance porosity and interconnectivity of the water treatment membranes. Significantly enhanced separation performance was observed which might be attributed to the mass transfer coefficient of the substrate layer increased in ultrafiltration (UF) application.

Aldosterone Upregulates Transient Receptor Potential Melastatin 7 (TRPM7).

PubMed

Valinsky, William C; Jolly, Anna; Miquel, Perrine; Touyz, Rhian M; Shrier, Alvin

2016-09-16

Transient receptor potential melastatin 7 (TRPM7) is a ubiquitously expressed Mg(2+)-permeable ion channel fused to a C-terminal α-kinase domain. Recently, aldosterone was shown to increase intracellular Mg(2+) levels and alter inflammatory signaling in TRPM7-expressing HEK293 cells. This study was undertaken to assess whether these effects were related to an aldosterone-mediated increase of TRPM7 current and/or plasma membrane localization. Using HEK293 cells stably expressing WT-TRPM7, we found that 18-h application of aldosterone significantly increased TRPM7 current and TRPM7 plasma membrane protein expression by 48% and 34%, respectively. The aldosterone-mediated increase of TRPM7 current was inhibited by eplerenone, a mineralocorticoid receptor (MR) blocker, and GSK-650394, an inhibitor of the serum- and glucocorticoid-regulated kinase 1 (SGK1). SGK1 blockade also prevented the aldosterone-induced increase of TRPM7 plasma membrane protein. It was further determined that K1648R-TRPM7, the phosphotransferase-inactive TRPM7 mutant, was unresponsive to aldosterone. Therefore, chronic aldosterone treatment increases the plasma membrane expression of TRPM7, which is associated with an increase of TRPM7 current. This process occurs via an MR-dependent, genomic signaling cascade involving SGK1 and a functioning TRPM7 α-kinase domain. We suggest that this mechanism may be of general relevance when interpreting the effects of aldosterone because the MR receptor is found in multiple tissues, and TRPM7 and SGK1 are ubiquitously expressed. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

Lipophilic organic pollutants induce changes in phospholipid and membrane protein composition leading to Vero cell morphological change.

PubMed

Liao, Ting T; Wang, Lei; Jia, Ru W; Fu, Xiao H; Chua, Hong

2014-01-01

Membrane damage related to morphological change in Vero cells is a sensitive index of the composite biotoxicity of trace lipophilic chemicals. However, judging whether the morphological change in Vero cells happens and its ratio are difficult because it is not a quantitative characteristic. To find biomarkers of cell morphological change for quantitatively representing the ratio of morphological changed cell, the mechanism of cell membrane damage driven by typical lipophilic chemicals, such as trichlorophenol (TCP) and perfluorooctanesulphonate (PFOS), was explored. The ratio of morphologically changed cells generally increased with increased TCP or PFOS concentrations, and the level of four major components of phospholipids varied with concentrations of TCP or PFOS, but only the ratio of phosphatidylcholine (PC)/phosphatidylethanolamine (PE) decreased regularly as TCP or PFOS concentrations increased. Analysis of membrane proteins showed that the level of vimentin in normal cell membranes is high, while it decreases or vanishes after TCP exposure. These variations in phospholipid and membrane protein components may result in membrane leakage and variation in rigid structure, which leads to changes in cell morphology. Therefore, the ratio of PC/PE and amount of vimentin may be potential biomarkers for representing the ratio of morphological changed Vero cell introduced by trace lipophilic compounds, thus their composite bio-toxicity.

[Protective effect of hydrogen against hyperoxia-induced type II alveolar epithelial cell injury].

PubMed

Yao, Lan; Xu, Feng; Luo, Chong; Yu, Pan; Dong, Xinxin; Sun, Xuejun; Liu, Chengjun

2013-02-01

To investigate the protective effect of hydrogen against hyperoxia-induced oxidative stress injury in premature rat type II alveolar epithelial cells (AECs). The type II AECs isolated from premature rats were randomly divided into air (21% oxygen) control group, hyperoxia (95% oxygen) control group, air + hydrogen group, and hyperoxia+ hydrogen group. The cells with hydrogen treatment were cultured in the presence of rich hydrogen. After the corresponding exposure for 24 h, the cell morphology was observed microscopically. MTT assay was used to evaluated the cell proliferation ability, and JC-1 fluorescence probe was used to detect the mitochondrial membrane potential (δφ) changes of the type II AECs. The concentration of maleic dialdehyde (MDA) and superoxide dismutase (SOD) activity in the cell supernatant were detected using colorimetric method. No significant differences were found in cell growth or measurements between air control and air + hydrogen groups. Compared with air control group, the cells exposed to hyperoxia showed significantly suppressed proliferation, reduced mitochondrial membrane potential, increased MDA content, and decreased SOD activity. Intervention with hydrogen resulted in significantly increased cell proliferation and SOD activity and lowered MDA content, and restored the mitochondrial membrane potential in the cells with hyperoxia exposure (P<0.05). Hydrogen can significantly reduce hyperoxia-induced oxidative stress injury in premature rat type II AECs, improve the cellular antioxidant capacity, stabilize the mitochondrial membrane potential, and reduce the inhibitory effect of hyperoxia on cell proliferation.

Electrical and mechanical responses to inhibition of cell respiration in vascular smooth muscle of the rat portal vein.

PubMed

Ekmehag, B L

1989-09-01

Metabolic regulation of contractility in vascular smooth muscle was studied in the spontaneously active rat portal vein using respiratory depression by cyanide (0.2-2.0 mM) as a model for tissue hypoxia. Intracellular recordings of electrical activity were done with concomitant registration of force development. Average membrane potential in the absence of cyanide was -61 +/- 1 mV (n = 27). Addition of cyanide to normal Krebs solution resulted in a reduction of force amplitude and the number of action potentials per burst, with a relatively more pronounced effect on the mechanical activity. At moderate levels of inhibition of force amplitude the frequency of spontaneous bursts of action potentials transiently increased concomitant with a slight depolarization, but after prolonged (15-20 min) exposure to cyanide the membrane repolarized to the level prior to cyanide addition and the burst frequency decreased to be equal to or lower than that in the absence of cyanide. Higher concentrations of cyanide totally inhibited spontaneous mechanical and electrical activity. In contrast to the results with glucose, it was found that when beta-hydroxybutyrate was used as substrate the addition of 2 mM cyanide led to a marked hyperpolarization (13 +/- 1 mV) after total inhibition of spontaneous activity. The hyperpolarization was not prevented by administration of 4-aminopyridine (2.5 mM) or tetraethylammonium (4-6 mM) prior to the addition of cyanide. To investigate the effects of increased metabolic demand on the relation between force and membrane potential in cyanide-treated muscle, high-K+ (40 mM) contractures were studied. Contractures were associated with depolarization of 34 +/- 3 mV (n = 5). 1 mM cyanide reduced the amplitude of the contractures to about 9% of control with a moderate reduction in the amount of depolarization (28 +/- 1 mV, n = 5). It is concluded that the decrease of mechanical activity during respiratory inhibition may partly reflect a reduction in the number of spikes per burst but that other mechanisms, independent of membrane activity, also contribute to the inhibition. The increase of glycolysis during respiratory inhibition seems to prevent more pronounced changes in membrane potential.

Modification of poly(vinylidene fluoride) ultrafiltration membranes with poly(vinyl alcohol) for fouling control in drinking water treatment.

PubMed

Du, Jennifer R; Peldszus, Sigrid; Huck, Peter M; Feng, Xianshe

2009-10-01

A commercial poly(vinylidene fluoride) flat sheet membrane was modified by surface coating with a dilute poly(vinyl alcohol) (PVA) aqueous solution followed by solid-vapor interfacial crosslinking. The resulting PVA layer increased membrane smoothness and hydrophilicity and resulted in comparable pure water permeation between the modified and unmodified membranes. Fouling tests using a 5 mg/L protein solution showed that a short period of coating and crosslinking improved the anti-fouling performance. After 18 h ultrafiltration of a surface water with a TOC of approximately 7 mg C/L, the flux of the modified membrane was twice as high as that of the unmodified membrane. The improved fouling resistance of the modified membrane was related to the membrane physiochemical properties, which were confirmed by pure water permeation, X-ray photoelectron spectroscopy, and contact angle, zeta potential and roughness measurements.

Effects of cell volume changes on membrane ionic permeabilities and sodium transport in frog skin (Rana ridibunda).

PubMed

Costa, P M; Fernandes, P L; Ferreira, H G; Ferreira, K T; Giraldez, F

1987-12-01

1. Membrane potential and conductances and short-circuit current were continuously measured with microelectrodes and conventional electrophysiological techniques in a stripped preparation of frog skin epithelium. The effects of the removal of chloride or sodium ions and the concentration or dilution of the serosal (inner) bathing solution were studied. 2. Chloride- or sodium-free solutions produced a cell depolarization of about 30 mV in parallel with a fall in the short-circuit current. Mucosal and serosal membrane conductances both decreased and the sodium permeability of the mucosal barrier was calculated to fall to about one-half its value in standard Ringer solution. The observed decrease in the short-circuit current is probably related to the combined effect of the decrease in sodium permeability and the decrease in the driving force across the mucosal membrane. 3. The removal of chloride or sodium ions reduced the depolarization caused by serosal perfusion with high-potassium solutions (50 mM-KCl). The ratio of the change in cell membrane potential under short-circuit conditions to the change in the potassium equilibrium potential (delta Ec(s.c.)/delta EK), was 0.59 in standard Ringer solution and 0.26 and 0.24 after the removal of chloride or sodium respectively. The depolarizing effect of barium-containing solutions (2 mM-BaCl2) was also markedly reduced in chloride- or sodium-free solutions, suggesting a decrease of the potassium selectivity of the serosal membrane in these conditions. 4. Increasing the osmolality of the serosal bathing solution produced similar effects, i.e. cell depolarization, fall in the short-circuit current and membrane conductances and reduction of the depolarizing effect of high-potassium and barium solutions. On the contrary, dilution of the serosal bath produced the opposite effects, consistent with an increase in the serosal permeability to potassium. 5. The effects of chloride- or sodium-free solutions were reversed by the dilution of the serosal bath. Cells repolarized when exposed to low-osmolality solutions after being in the absence of serosal chloride or sodium. The repolarization ran in parallel with the restoration of the short-circuit current and the potassium selectivity of the serosal membrane. 6. The results show that the effects produced by the removal of sodium or chloride ions from the serosal bathing solution are most probably mediated by a reduction in cell volume. Cell volume changes would lead to changes in the serosal membrane selectivity to potassium and thus to changes in cell membrane potential and sodium transport.(ABSTRACT TRUNCATED AT 400 WORDS)

Membrane-targeted strategies for modulating APP and Aβ-mediated toxicity

PubMed Central

Price, Katherine A; Crouch, Peter J; Donnelly, Paul S; Masters, Colin L; White, Anthony R; Curtain, Cyril C

2009-01-01

Abstract Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by numerous pathological features including the accumulation of neurotoxic amyloid-β (Aβ) peptide. There is currently no effective therapy for AD, but the development of therapeutic strategies that target the cell membrane is gaining increased interest. The amyloid precursor protein (APP) from which Aβ is formed is a membrane-bound protein, and Aβ production and toxicity are both membrane mediated events. This review describes the critical role of cell membranes in AD with particular emphasis on how the composition and structure of the membrane and its specialized regions may influence toxic or benign Aβ/APP pathways in AD. The putative role of copper (Cu) in AD is also discussed, and we highlight how targeting the cell membrane with Cu complexes has therapeutic potential in AD. PMID:19278455

Improving Hemocompatibility of Membranes for Extracorporeal Membrane Oxygenators by Grafting Nonthrombogenic Polymer Brushes.

PubMed

Obstals, Fabian; Vorobii, Mariia; Riedel, Tomáš; de Los Santos Pereira, Andres; Bruns, Michael; Singh, Smriti; Rodriguez-Emmenegger, Cesar

2018-03-01

Nonthrombogenic modifications of membranes for extracorporeal membrane oxygenators (ECMOs) are of key interest. The absence of hemocompatibility of these membranes and the need of anticoagulation of patients result in severe and potentially life-threatening complications during ECMO treatment. To address the lack of hemocompatibility of the membrane, surface modifications are developed, which act as barriers to protein adsorption on the membrane and, in this way, prevent activation of the coagulation cascade. The modifications are based on nonionic and zwitterionic polymer brushes grafted directly from poly(4-methyl-1-pentene) (TPX) membranes via single electron transfer-living radical polymerization. Notably, this work introduces the first example of well-controlled surface-initiated radical polymerization of zwitterionic brushes. The antifouling layers markedly increase the recalcification time (a proxy of initiation of coagulation) compared to bare TPX membranes. Furthermore, platelet and leukocyte adhesion is drastically decreased, rendering the ECMO membranes hemocompatible. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Permeation and gating properties of the L-type calcium channel in mouse pancreatic beta cells

PubMed Central

1993-01-01

Ba2+ currents through L-type Ca2+ channels were recorded from cell- attached patches on mouse pancreatic beta cells. In 10 mM Ba2+, single- channel currents were recorded at -70 mV, the beta cell resting membrane potential. This suggests that Ca2+ influx at negative membrane potentials may contribute to the resting intracellular Ca2+ concentration and thus to basal insulin release. Increasing external Ba2+ increased the single-channel current amplitude and shifted the current-voltage relation to more positive potentials. This voltage shift could be modeled by assuming that divalent cations both screen and bind to surface charges located at the channel mouth. The single- channel conductance was related to the bulk Ba2+ concentration by a Langmuir isotherm with a dissociation constant (Kd(gamma)) of 5.5 mM and a maximum single-channel conductance (gamma max) of 22 pS. A closer fit to the data was obtained when the barium concentration at the membrane surface was used (Kd(gamma) = 200 mM and gamma max = 47 pS), which suggests that saturation of the concentration-conductance curve may be due to saturation of the surface Ba2+ concentration. Increasing external Ba2+ also shifted the voltage dependence of ensemble currents to positive potentials, consistent with Ba2+ screening and binding to membrane surface charge associated with gating. Ensemble currents recorded with 10 mM Ca2+ activated at more positive potentials than in 10 mM Ba2+, suggesting that external Ca2+ binds more tightly to membrane surface charge associated with gating. The perforated-patch technique was used to record whole-cell currents flowing through L-type Ca2+ channels. Inward currents in 10 mM Ba2+ had a similar voltage dependence to those recorded at a physiological Ca2+ concentration (2.6 mM). BAY-K 8644 (1 microM) increased the amplitude of the ensemble and whole-cell currents but did not alter their voltage dependence. Our results suggest that the high divalent cation solutions usually used to record single L-type Ca2+ channel activity produce a positive shift in the voltage dependence of activation (approximately 32 mV in 100 mM Ba2+). PMID:7687645

The antifungal activity and membrane-disruptive action of dioscin extracted from Dioscorea nipponica.

PubMed

Cho, Jaeyong; Choi, Hyemin; Lee, Juneyoung; Kim, Mi-Sun; Sohn, Ho-Yong; Lee, Dong Gun

2013-03-01

Dioscin is a kind of steroidal saponin isolated from the root bark of wild yam Dioscorea nipponica. We investigated the antifungal effect of dioscin against different fungal strains and its antifungal mechanism(s) in Candida albicans cells. Using the propidium iodide assay and calcein-leakage measurement, we confirmed that dioscin caused fungal membrane damage. Furthermore, we evaluated the ability of dioscin to disrupt the plasma membrane potential, using 3,3'-dipropylthiadicarbocyanine iodide [DiSC(3)(5)] and bis-(1,3-dibarbituric acid)-trimethine oxanol [DiBAC(4)(3)]. Cells stained with the dyes had a significant increase in fluorescent intensity after exposure to dioscin, indicating that dioscin has an effect on the membrane potential. To visualize the effect of dioscin on the cell membrane, we synthesized rhodamine-labeled giant unilamellar vesicles (GUVs) mimicking the outer leaflet of the plasma membrane of C. albicans. As seen in the result, the membrane disruptive action of dioscin caused morphological change and rhodamine leakage of the GUVs. In three-dimensional contour-plot analysis using flow cytometry, we observed a decrease in cell size, which is in agreement with our result from the GUV assay. These results suggest that dioscin exerts a considerable antifungal activity by disrupting the structure in membrane after invading into the fungal membrane, resulting in fungal cell death. Copyright © 2012 Elsevier B.V. All rights reserved.

Polyamines cause plasma membrane depolarization, activate Ca2+-, and modulate H+-ATPase pump activity in pea roots.

PubMed

Pottosin, Igor; Velarde-Buendía, Ana María; Bose, Jayakumar; Fuglsang, Anja T; Shabala, Sergey

2014-06-01

Polyamines regulate a variety of cation and K(+) channels, but their potential effects on cation-transporting ATPases are underexplored. In this work, noninvasive microelectrode ion flux estimation and conventional microelectrode techniques were applied to study the effects of polyamines on Ca(2+) and H(+) transport and membrane potential in pea roots. Externally applied spermine or putrescine (1mM) equally activated eosin yellow (EY)-sensitive Ca(2+) pumping across the root epidermis and caused net H(+) influx or efflux. Proton influx induced by spermine was suppressed by EY, supporting the mechanism in which Ca(2+) pump imports 2 H(+) per each exported Ca(2+). Suppression of the Ca(2+) pump by EY diminished putrescine-induced net H(+) efflux instead of increasing it. Thus, activities of Ca(2+) and H(+) pumps were coupled, likely due to the H(+)-pump inhibition by intracellular Ca(2+). Additionally, spermine but not putrescine caused a direct inhibition of H(+) pumping in isolated plasma membrane vesicles. Spermine, spermidine, and putrescine (1mM) induced membrane depolarization by 70, 50, and 35 mV, respectively. Spermine-induced depolarization was abolished by cation transport blocker Gd(3+), was insensitive to anion channels' blocker niflumate, and was dependent on external Ca(2+). Further analysis showed that uptake of polyamines but not polyamine-induced cationic (K(+)+Ca(2+)+H(+)) fluxes were a main cause of membrane depolarization. Polyamine increase is a common component of plant stress responses. Activation of Ca(2+) efflux by polyamines and contrasting effects of polyamines on net H(+) fluxes and membrane potential can contribute to Ca(2+) signalling and modulate a variety of transport processes across the plasma membrane under stress. © The Author 2014. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.

Physical properties and biocompatibility of oligochitosan membrane film as wound dressing.

PubMed

Ujang, Zanariah; Abdul Rashid, Ahmad Hazri; Suboh, Siti Kasmarizawaty; Halim, Ahmad Sukari; Lim, Chin Keong

2014-12-30

The physical and biological characteristics of oligochitosan (O-C) film, including its barrier and mechanical properties, in vitro cytotoxicity and in vivo biocompatibility, were studied to assess its potential use as a wound dressing. Membrane films were prepared from water-soluble O-C solution blended with various concentrations of glycerol to modify the physical properties of the films. In vitro and in vivo biocompatibility evaluations were performed using primary human skin fibroblast cultures and subcutaneous implantation in a rat model, respectively. Addition of glycerol significantly influenced the barrier and mechanical properties of the films. Water absorption capacity was in the range of 80%-160%, whereas water vapor transmission rate varied from 1,180 to 1,618 g/m2 per day. Both properties increased with increasing glycerol concentration. Tensile strength decreased while elongation at break increased with the addition of glycerol. O-C films were found to be noncytotoxic to human fibroblast cultures and histological examination proved that films are biocompatible. These results indicate that the membrane film from O-C has potential application as a wound-dressing material.

A Novel Fabrication Approach for Multifunctional Graphene-based Thin Film Nano-composite Membranes with Enhanced Desalination and Antibacterial Characteristics.

PubMed

Hegab, Hanaa M; ElMekawy, Ahmed; Barclay, Thomas G; Michelmore, Andrew; Zou, Linda; Losic, Dusan; Saint, Christopher P; Ginic-Markovic, Milena

2017-08-08

A practical fabrication technique is presented to tackle the trade-off between the water flux and salt rejection of thin film composite (TFC) reverse osmosis (RO) membranes through controlled creation of a thinner active selective polyamide (PA) layer. The new thin film nano-composite (TFNC) RO membranes were synthesized with multifunctional poly tannic acid-functionalized graphene oxide nanosheets (pTA-f-GO) embedded in its PA thin active layer, which is produced through interfacial polymerization. The incorporation of pTA-f-GOL into the fabricated TFNC membranes resulted in a thinner PA layer with lower roughness and higher hydrophilicity compared to pristine membrane. These properties enhanced both the membrane water flux (improved by 40%) and salt rejection (increased by 8%) of the TFNC membrane. Furthermore, the incorporation of biocidal pTA-f-GO nanosheets into the PA active layer contributed to improving the antibacterial properties by 80%, compared to pristine membrane. The fabrication of the pTA-f-GO nanosheets embedded in the PA layer presented in this study is a very practical, scalable and generic process that can potentially be applied in different types of separation membranes resulting in less energy consumption, increased cost-efficiency and improved performance.

Placental membrane aging and HMGB1 signaling associated with human parturition.

PubMed

Menon, Ramkumar; Behnia, Faranak; Polettini, Jossimara; Saade, George R; Campisi, Judith; Velarde, Michael

2016-02-01

Aging is associated with the onset of several diseases in various organ systems; however, different tissues may age differently, rendering some of them dysfunctional sooner than others. Placental membranes (fetal amniochorionic membranes) protect the fetus throughout pregnancy, but their longevity is limited to the duration of pregnancy. The age-associated dysfunction of these membranes is postulated to trigger parturition. Here, we investigated whether cellular senescence-the loss of cell division potential as a consequence of stress-is involved in placental membrane function at term. We show telomere reduction, p38 MAPK activation, increase in p21 expression, loss of lamin B1 loss, increase in SA-β-galactosidase , and senescence-associated secretory phenotype (SASP) gene expression in placental membranes after labor and delivery (term labor [TL]) compared to membranes prior to labor at term (term, not-in-labor [TNIL]). Exposing TNIL placental membranes to cigarette smoke extract, an oxidative stress inducer, also induced markers of cellular senescence similar to those in TL placental membranes. Bioinformatics analysis of differentially expressed SASP genes revealed HMGB1 signaling among the top pathways involved in labor. Further, we show that recombinant HMGB1 upregulates the expression of genes associated with parturition in myometrial cells. These data suggest that the natural physiologic aging of placental tissues is associated with cellular senescence and human parturition.

Simulation of action potential propagation in plants.

PubMed

Sukhov, Vladimir; Nerush, Vladimir; Orlova, Lyubov; Vodeneev, Vladimir

2011-12-21

Action potential is considered to be one of the primary responses of a plant to action of various environmental factors. Understanding plant action potential propagation mechanisms requires experimental investigation and simulation; however, a detailed mathematical model of plant electrical signal transmission is absent. Here, the mathematical model of action potential propagation in plants has been worked out. The model is a two-dimensional system of excitable cells; each of them is electrically coupled with four neighboring ones. Ion diffusion between excitable cell apoplast areas is also taken into account. The action potential generation in a single cell has been described on the basis of our previous model. The model simulates active and passive signal transmission well enough. It has been used to analyze theoretically the influence of cell to cell electrical conductivity and H(+)-ATPase activity on the signal transmission in plants. An increase in cell to cell electrical conductivity has been shown to stimulate an increase in the length constant, the action potential propagation velocity and the temperature threshold, while the membrane potential threshold being weakly changed. The growth of H(+)-ATPase activity has been found to induce the increase of temperature and membrane potential thresholds and the reduction of the length constant and the action potential propagation velocity. Copyright © 2011 Elsevier Ltd. All rights reserved.

Ling's Adsorption Theory as a Mechanism of Membrane Potential Generation Observed in Both Living and Nonliving Systems.

PubMed

Tamagawa, Hirohisa; Funatani, Makoto; Ikeda, Kota

2016-01-26

The potential between two electrolytic solutions separated by a membrane impermeable to ions was measured and the generation mechanism of potential measured was investigated. From the physiological point of view, a nonzero membrane potential or action potential cannot be observed across the impermeable membrane. However, a nonzero membrane potential including action potential-like potential was clearly observed. Those observations gave rise to a doubt concerning the validity of currently accepted generation mechanism of membrane potential and action potential of cell. As an alternative theory, we found that the long-forgotten Ling's adsorption theory was the most plausible theory. Ling's adsorption theory suggests that the membrane potential and action potential of a living cell is due to the adsorption of mobile ions onto the adsorption site of cell, and this theory is applicable even to nonliving (or non-biological) system as well as living system. Through this paper, the authors emphasize that it is necessary to reconsider the validity of current membrane theory and also would like to urge the readers to pay keen attention to the Ling's adsorption theory which has for long years been forgotten in the history of physiology.

Lipids and topological rules of membrane protein assembly: balance between long and short range lipid-protein interactions.

PubMed

Vitrac, Heidi; Bogdanov, Mikhail; Heacock, Phil; Dowhan, William

2011-04-29

The N-terminal six-transmembrane domain (TM) bundle of lactose permease of Escherichia coli is uniformly inverted when assembled in membranes lacking phosphatidylethanolamine (PE). Inversion is dependent on the net charge of cytoplasmically exposed protein domains containing positive and negative residues, net charge of the membrane surface, and low hydrophobicity of TM VII acting as a molecular hinge between the two halves of lactose permease (Bogdanov, M., Xie, J., Heacock, P., and Dowhan, W. (2008) J. Cell Biol. 182, 925-935). Net neutral lipids suppress the membrane translocation potential of negatively charged amino acids, thus increasing the cytoplasmic retention potential of positively charged amino acids. Herein, TM organization of sucrose permease (CscB) and phenylalanine permease (PheP) as a function of membrane lipid composition was investigated to extend these principles to other proteins. For CscB, topological dependence on PE only becomes evident after a significant increase in the net negative charge of the cytoplasmic surface of the N-terminal TM bundle. High negative charge is required to overcome the thermodynamic block to inversion due to the high hydrophobicity of TM VII. Increasing the positive charge of the cytoplasmic surface of the N-terminal TM hairpin of PheP, which is misoriented in PE-lacking cells, favors native orientation in the absence of PE. PheP and CscB also display co-existing dual topologies dependent on changes in the charge balance between protein domains and the membrane lipids. Therefore, the topology of both permeases is dependent on PE. However, CscB topology is governed by thermodynamic balance between opposing lipid-dependent electrostatic and hydrophobic interactions.

Ultrathin self-assembled anionic polymer membranes for superfast size-selective separation

NASA Astrophysics Data System (ADS)

Deng, Chao; Zhang, Qiu Gen; Han, Guang Lu; Gong, Yi; Zhu, Ai Mei; Liu, Qing Lin

2013-10-01

Nanoporous membranes with superior separation performance have become more crucial with increasing concerns in functional nanomaterials. Here novel ultrahigh permeable nanoporous membranes have been fabricated on macroporous supports by self-assembly of anionic polymer on copper hydroxide nanostrand templates in organic solution. This facile approach has a great potential for the fabrication of ultrathin anionic polymer membranes as a general method. The as-fabricated self-assembled membranes have a mean pore size of 5-12 nm and an adjustable thickness as low as 85 nm. They allow superfast permeation of water, and exhibit excellent size-selective separation properties and good fouling resistance for negatively-charged solutes during filtration. The 85 nm thick membrane has an ultrahigh water flux (3306 l m-2 h-1 bar-1) that is an order of magnitude larger than commercial membranes, and can highly efficiently separate 5 and 15 nm gold nanoparticles from their mixtures. The newly developed nanoporous membranes have a wide application in separation and purification of biomacromolecules and nanoparticles.Nanoporous membranes with superior separation performance have become more crucial with increasing concerns in functional nanomaterials. Here novel ultrahigh permeable nanoporous membranes have been fabricated on macroporous supports by self-assembly of anionic polymer on copper hydroxide nanostrand templates in organic solution. This facile approach has a great potential for the fabrication of ultrathin anionic polymer membranes as a general method. The as-fabricated self-assembled membranes have a mean pore size of 5-12 nm and an adjustable thickness as low as 85 nm. They allow superfast permeation of water, and exhibit excellent size-selective separation properties and good fouling resistance for negatively-charged solutes during filtration. The 85 nm thick membrane has an ultrahigh water flux (3306 l m-2 h-1 bar-1) that is an order of magnitude larger than commercial membranes, and can highly efficiently separate 5 and 15 nm gold nanoparticles from their mixtures. The newly developed nanoporous membranes have a wide application in separation and purification of biomacromolecules and nanoparticles. Electronic supplementary information (ESI) available: Synthesis and characterization of SPEK-C; effect of the sulfonation degree on membrane formation; structure and properties of the self-assembled membranes; separation of cyt.c by the self-assembled membranes; size-selective separation of gold nanoparticles by the self-assembled membranes; comparison with commercial flat sheet ultrafiltration membranes. See DOI: 10.1039/c3nr03362g

Effect of oxygen at high pressure on spontaneous transmitter release.

PubMed

Colton, J S; Colton, C A

1978-11-01

The effect of oxygen at high pressure (OHP) on resting membrane properties (effective membrane resistance (Reff) and membrane potential (Vm)) and the spontaneous release of excitatory transmitter were examined at the lobster neuromuscular junction. Pressurization with 100% oxygen to 150 pounds per square inch gauge pressure (psig) or with nitrogen to 150 psig (7,000 mmHg nitrogen and 135 mmHg oxygen) produced a decrease in Reff associated with a hyperpolarization of Vm. These changes, however, returned to control values within 20--30 min after completion of pressurization. Spontaneous release of excitatory transmitter was shown to increase dramatically in the presence of 100% oxygen at 150 psig. The increase in miniature end-plate potential (MEPP) frequency persisted beyond the transient changes seen with Reff and Vm. This effect was selective to oxygen, as pressurization with nitrogen did not produce an increase in MEPP frequency. No change in average MEPP amplitude was seen with either OHP or pressure alone. An OHP-induced increase in MEPP frequency was also seen at the frog neuromuscular junction. The results indicate that both glutamate-mediated and acetylcholine-mediated synaptic transmission are altered by OHP.

Investigating the effect of a single glycine to alanine substitution on interactions of antimicrobial peptide latarcin 2a with a lipid membrane.

PubMed

Idiong, Grace; Won, Amy; Ruscito, Annamaria; Leung, Bonnie O; Hitchcock, Adam P; Ianoul, Anatoli

2011-09-01

Latarcins are linear, α-helical antimicrobial peptides purified from the venom of the Central Asian spider Lachesana tarabaevi, with lytic activity against Gram-positive and Gram-negative bacteria, erythrocytes, and yeast at micromolar concentrations. In this work, we investigated the role of the hinge in latarcin 2a (ltc2a, GLFGKLIKKFGRKAISYAVKKARGKH-COOH), which adopts a helix-hinge-helix conformation in membrane-mimicking environments, on peptide-membrane interactions and its potential effect on the selective toxicity of the peptide. A modified latarcin 2a, ltc2aG11A, obtained by replacing the glycine at position 11 with alanine (ltc2aG11A, GLFGKLIKKFARKAISYAVKKARGKH-COOH), adopts a more rigid structure due to the reduced conformational flexibility. Langmuir monolayer measurements combined with atomic force microscopy and X-ray photoemission electron microscopy (X-PEEM) indicate that both peptides bind and insert preferentially into anionic compared with zwitterionic phospholipid monolayers. Modified ltc2aG11A was found to be more disruptive of supported phospholipid bilayer modeling mammalian cell membrane. However, no considerable difference in lytic activity of the two peptides toward bacterial membrane was found. Overall the data indicate that decrease in the flexibility of ltc2a induced by the modification in the hinge region is likely to increase the peptide's nonspecific interactions with zwitterionic cell membranes and potentially increase its toxicity against eukaryotic cells.

Basolateral K channels in an insect epithelium. Channel density, conductance, and block by barium

PubMed Central

Hanrahan, JW; Wills, NK; Phillips, JE; Lewis, SA

1986-01-01

K channels in the basolateral membrane of insect hindgut were studied using current fluctuation analysis and microelectrodes. Locust recta were mounted in Ussing-type chambers containing Cl-free saline and cyclic AMP (cAMP). A transepithelial K current was induced by raising serosal [K] under short-circuit conditions. Adding Ba to the mucosal (luminal) side under these conditions had no effect; however, serosal Ba reversibly inhibited the short-circuit current (Isc), increased transepithelial resistance (Rt), and added a Lorentzian component to power density spectra of the Isc. A nonlinear relationship between corner frequency and serosal [Ba] was observed, which suggests that the rate constant for Ba association with basolateral channels increased as [Ba] was elevated. Microelectrode experiments revealed that the basolateral membrane hyperpolarized when Ba was added: this change in membrane potential could explain the nonlinearity of the 2 pi fc vs. [Ba] relationship if external Ba sensed about three-quarters of the basolateral membrane field. Conventional microelectrodes were used to determine the correspondence between transepithelially measured current noise and basolateral membrane conductance fluctuations, and ion-sensitive microelectrodes were used to measure intracellular K activity (acK). From the relationship between the net electrochemical potential for K across the basolateral membrane and the single channel current calculated from noise analysis, we estimate that the conductance of basolateral K channels is approximately 60 pS, and that there are approximately 180 million channels per square centimeter of tissue area. PMID:2420918

Cytosolic Nucleotides Block and Regulate the Arabidopsis Vacuolar Anion Channel AtALMT9*

PubMed Central

Zhang, Jingbo; Martinoia, Enrico; De Angeli, Alexis

2014-01-01

The aluminum-activated malate transporters (ALMTs) form a membrane protein family exhibiting different physiological roles in plants, varying from conferring tolerance to environmental Al3+ to the regulation of stomatal movement. The regulation of the anion channels of the ALMT family is largely unknown. Identifying intracellular modulators of the activity of anion channels is fundamental to understanding their physiological functions. In this study we investigated the role of cytosolic nucleotides in regulating the activity of the vacuolar anion channel AtALMT9. We found that cytosolic nucleotides modulate the transport activity of AtALMT9. This modulation was based on a direct block of the pore of the channel at negative membrane potentials (open channel block) by the nucleotide and not by a phosphorylation mechanism. The block by nucleotides of AtALMT9-mediated currents was voltage dependent. The blocking efficiency of intracellular nucleotides increased with the number of phosphate groups and ATP was the most effective cellular blocker. Interestingly, the ATP block induced a marked modification of the current-voltage characteristic of AtALMT9. In addition, increased concentrations of vacuolar anions were able to shift the ATP block threshold to a more negative membrane potential. The block of AtALMT9-mediated anion currents by ATP at negative membrane potentials acts as a gate of the channel and vacuolar anion tune this gating mechanism. Our results suggest that anion transport across the vacuolar membrane in plant cells is controlled by cytosolic nucleotides and the energetic status of the cell. PMID:25028514

Cytosolic nucleotides block and regulate the Arabidopsis vacuolar anion channel AtALMT9.

PubMed

Zhang, Jingbo; Martinoia, Enrico; De Angeli, Alexis

2014-09-12

The aluminum-activated malate transporters (ALMTs) form a membrane protein family exhibiting different physiological roles in plants, varying from conferring tolerance to environmental Al(3+) to the regulation of stomatal movement. The regulation of the anion channels of the ALMT family is largely unknown. Identifying intracellular modulators of the activity of anion channels is fundamental to understanding their physiological functions. In this study we investigated the role of cytosolic nucleotides in regulating the activity of the vacuolar anion channel AtALMT9. We found that cytosolic nucleotides modulate the transport activity of AtALMT9. This modulation was based on a direct block of the pore of the channel at negative membrane potentials (open channel block) by the nucleotide and not by a phosphorylation mechanism. The block by nucleotides of AtALMT9-mediated currents was voltage dependent. The blocking efficiency of intracellular nucleotides increased with the number of phosphate groups and ATP was the most effective cellular blocker. Interestingly, the ATP block induced a marked modification of the current-voltage characteristic of AtALMT9. In addition, increased concentrations of vacuolar anions were able to shift the ATP block threshold to a more negative membrane potential. The block of AtALMT9-mediated anion currents by ATP at negative membrane potentials acts as a gate of the channel and vacuolar anion tune this gating mechanism. Our results suggest that anion transport across the vacuolar membrane in plant cells is controlled by cytosolic nucleotides and the energetic status of the cell. © 2014 by The American Society for Biochemistry and Molecular Biology, Inc.

Effects of the new imidazopyridine CL 86-02-01 on isolated papillary muscle of guinea-pig hearts.

PubMed

Studenik, C; Lemmens-Gruber, R; Heistracher, P

1998-06-01

Inotropic activity and the effect of CL 86-02-01 (2-(3-methoxy-5-methylsulfinyl-2-thienyl)-1H-imidazo[4,5-c]pyridine hydrochloride, CAS 109 792-24-7) on membrane resting and action potentials were studied in isolated guinea-pig papillary muscles. Membrane resting potential and action potential parameters were not significantly changed, while CL 86-02-01 exerted a concentration-dependent inotropic effect by increasing the maximum rate of force development and maximum rate of force relaxation. Time to peak force, relaxation time and total contraction time were reduced. These effects are similar to those of beta-adrenergic drugs and phosphodiesterase inhibitors, but markedly differ from those described for other positive inotropic agents like cardiac glycosides, calcium agonists, alpha-adrenergic drugs or increased extracellular calcium concentration.

Drinking water treatment using a submerged internal-circulation membrane coagulation reactor coupled with permanganate oxidation.

PubMed

Zhang, Zhongguo; Liu, Dan; Qian, Yu; Wu, Yue; He, Peiran; Liang, Shuang; Fu, Xiaozheng; Li, Jiding; Ye, Changqing

2017-06-01

A submerged internal circulating membrane coagulation reactor (MCR) was used to treat surface water to produce drinking water. Polyaluminum chloride (PACl) was used as coagulant, and a hydrophilic polyvinylidene fluoride (PVDF) submerged hollow fiber microfiltration membrane was employed. The influences of trans-membrane pressure (TMP), zeta potential (ZP) of the suspended particles in raw water, and KMnO 4 dosing on water flux and the removal of turbidity and organic matter were systematically investigated. Continuous bench-scale experiments showed that the permeate quality of the MCR satisfied the requirement for a centralized water supply, according to the Standards for Drinking Water Quality of China (GB 5749-2006), as evaluated by turbidity (<1 NTU) and total organic carbon (TOC) (<5mg/L) measurements. Besides water flux, the removal of turbidity, TOC and dissolved organic carbon (DOC) in the raw water also increased with increasing TMP in the range of 0.01-0.05MPa. High ZP induced by PACl, such as 5-9mV, led to an increase in the number of fine and total particles in the MCR, and consequently caused serious membrane fouling and high permeate turbidity. However, the removal of TOC and DOC increased with increasing ZP. A slightly positive ZP, such as 1-2mV, corresponding to charge neutralization coagulation, was favorable for membrane fouling control. Moreover, dosing with KMnO 4 could further improve the removal of turbidity and DOC, thereby mitigating membrane fouling. The results are helpful for the application of the MCR in producing drinking water and also beneficial to the research and application of other coagulation and membrane separation hybrid processes. Copyright © 2016. Published by Elsevier B.V.

Generation of membrane potential beyond the conceptual range of Donnan theory and Goldman-Hodgkin-Katz equation.

PubMed

Tamagawa, Hirohisa; Ikeda, Kota

2017-09-01

Donnan theory and Goldman-Hodgkin-Katz equation (GHK eq.) state that the nonzero membrane potential is generated by the asymmetric ion distribution between two solutions separated by a semipermeable membrane and/or by the continuous ion transport across the semipermeable membrane. However, there have been a number of reports of the membrane potential generation behaviors in conflict with those theories. The authors of this paper performed the experimental and theoretical investigation of membrane potential and found that (1) Donnan theory is valid only when the macroscopic electroneutrality is sufficed and (2) Potential behavior across a certain type of membrane appears to be inexplicable on the concept of GHK eq. Consequently, the authors derived a conclusion that the existing theories have some limitations for predicting the membrane potential behavior and we need to find a theory to overcome those limitations. The authors suggest that the ion adsorption theory named Ling's adsorption theory, which attributes the membrane potential generation to the mobile ion adsorption onto the adsorption sites, could overcome those problems.

Tight ceramic UF membrane as RO pre-treatment: the role of electrostatic interactions on phosphate rejection.

PubMed

Shang, Ran; Verliefde, Arne R D; Hu, Jingyi; Zeng, Zheyi; Lu, Jie; Kemperman, Antoine J B; Deng, Huiping; Nijmeijer, Kitty; Heijman, Sebastiaan G J; Rietveld, Luuk C

2014-01-01

Phosphate limitation has been reported as an effective approach to inhibit biofouling in reverse osmosis (RO) systems for water purification. The rejection of dissolved phosphate by negatively charged TiO2 tight ultrafiltration (UF) membranes (1 kDa and 3 kDa) was observed. These membranes can potentially be adopted as an effective process for RO pre-treatment in order to constrain biofouling by phosphate limitation. This paper focuses on electrostatic interactions during tight UF filtration. Despite the larger pore size, the 3 kDa ceramic membrane exhibited greater phosphate rejection than the 1 kDa membrane, because the 3 kDa membrane has a greater negative surface charge and thus greater electrostatic repulsion against phosphate. The increase of pH from 6 to 8.5 led to a substantial increase in phosphate rejection by both membranes due to increased electrostatic repulsion. At pH 8.5, the maximum phosphate rejections achieved by the 1 kDa and 3 kDa membrane were 75% and 86%, respectively. A Debye ratio (ratio of the Debye length to the pore radius) is introduced in order to evaluate double layer overlapping in tight UF membranes. Threshold Debye ratios were determined as 2 and 1 for the 1 kDa and 3 kDa membranes, respectively. A Debye ratio below the threshold Debye ratio leads to dramatically decreased phosphate rejection by tight UF membranes. The phosphate rejection by the tight UF, in combination with chemical phosphate removal by coagulation, might accomplish phosphate-limited conditions for biological growth and thus prevent biofouling in the RO systems. Copyright © 2013 Elsevier Ltd. All rights reserved.

FXYD2, a γ subunit of Na+,K+-ATPase, maintains persistent mechanical allodynia induced by inflammation

PubMed Central

Wang, Feng; Cai, Bing; Li, Kai-Cheng; Hu, Xu-Ye; Lu, Ying-Jin; Wang, Qiong; Bao, Lan; Zhang, Xu

2015-01-01

Na+,K+-ATPase (NKA) is required to generate the resting membrane potential in neurons. Nociceptive afferent neurons express not only the α and β subunits of NKA but also the γ subunit FXYD2. However, the neural function of FXYD2 is unknown. The present study shows that FXYD2 in nociceptive neurons is necessary for maintaining the mechanical allodynia induced by peripheral inflammation. FXYD2 interacted with α1NKA and negatively regulated the NKA activity, depolarizing the membrane potential of nociceptive neurons. Mechanical allodynia initiated in FXYD2-deficient mice was abolished 4 days after inflammation, whereas it persisted for at least 3 weeks in wild-type mice. Importantly, the FXYD2/α1NKA interaction gradually increased after inflammation and peaked on day 4 post inflammation, resulting in reduction of NKA activity, depolarization of neuron membrane and facilitation of excitatory afferent neurotransmission. Thus, the increased FXYD2 activity may be a fundamental mechanism underlying the persistent hypersensitivity to pain induced by inflammation. PMID:25633594

Effect of mass and charge transport speed and direction in porous anodes on microbial electrolysis cell performance.

PubMed

Sleutels, Tom H J A; Hamelers, Hubertus V M; Buisman, Cees J N

2011-01-01

The use of porous electrodes like graphite felt as anode material has the potential of achieving high volumetric current densities. High volumetric current densities, however, may also lead to mass transport limitations within these porous materials. Therefore, in this study we investigated the mass and charge transport limitations by increasing the speed of the forced flow and changing the flow direction through the porous anode. Increase of the flow speed led to a decrease in current density when the flow was directed towards the membrane caused by an increase in anode resistance. Current density increased at higher flow speed when the flow was directed away from the membrane. This was caused by a decrease in transport resistance of ions through the membrane which increased the buffering effect of the system. Furthermore, the increase in flow speed led to an increase of the coulombic efficiency by 306%. Copyright © 2010 Elsevier Ltd. All rights reserved.

Rapid regulation of the plasma membrane H+-ATPase activity is essential to salinity tolerance in two halophyte species, Atriplex lentiformis and Chenopodium quinoa

PubMed Central

Bose, Jayakumar; Rodrigo-Moreno, Ana; Lai, Diwen; Xie, Yanjie; Shen, Wenbiao; Shabala, Sergey

2015-01-01

Background and Aims The activity of H+-ATPase is essential for energizing the plasma membrane. It provides the driving force for potassium retention and uptake through voltage-gated channels and for Na+ exclusion via Na+/H+ exchangers. Both of these traits are central to plant salinity tolerance; however, whether the increased activity of H+-ATPase is a constitutive trait in halophyte species and whether this activity is upregulated at either the transcriptional or post-translation level remain disputed. Methods The kinetics of salt-induced net H+, Na+ and K+ fluxes, membrane potential and AHA1/2/3 expression changes in the roots of two halophyte species, Atriplex lentiformis (saltbush) and Chenopodium quinoa (quinoa), were compared with data obtained from Arabidopsis thaliana roots. Key Results Intrinsic (steady-state) membrane potential values were more negative in A. lentiformis and C. quinoa compared with arabidopsis (−144 ± 3·3, −138 ± 5·4 and −128 ± 3·3 mV, respectively). Treatment with 100 mm NaCl depolarized the root plasma membrane, an effect that was much stronger in arabidopsis. The extent of plasma membrane depolarization positively correlated with NaCl-induced stimulation of vanadate-sensitive H+ efflux, Na+ efflux and K+ retention in roots (quinoa > saltbush > arabidopsis). NaCl-induced stimulation of H+ efflux was most pronounced in the root elongation zone. In contrast, H+-ATPase AHA transcript levels were much higher in arabidopsis compared with quinoa plants, and 100 mm NaCl treatment led to a further 3-fold increase in AHA1 and AHA2 transcripts in arabidopsis but not in quinoa. Conclusions Enhanced salinity tolerance in the halophyte species studied here is not related to the constitutively higher AHA transcript levels in the root epidermis, but to the plant’s ability to rapidly upregulate plasma membrane H+-ATPase upon salinity treatment. This is necessary for assisting plants to maintain highly negative membrane potential values and to exclude Na+, or enable better K+ retention in the cytosol under saline conditions. PMID:25471095

Oriented MOF-polymer Composite Nanofiber Membranes for High Proton Conductivity at High Temperature and Anhydrous Condition

PubMed Central

Wu, Bin; Pan, Jiefeng; Ge, Liang; Wu, Liang; Wang, Huanting; Xu, Tongwen

2014-01-01

The novel oriented electrospun nanofiber membrane composed of MOFs and SPPESK has been synthesized for proton exchange membrane fuel cell operating at high temperature and anhydrous conditions. It is clear that the oriented nanofiber membrane displays the higher proton conductivity than that of the disordered nanofiber membrane or the membrane prepared by conventional solvent-casting method (without nanofibers). Nanofibers within the membranes are significantly oriented. The proton conductivity of the oriented nanofiber membrane can reach up to (8.2 ± 0.16) × 10−2 S cm−1 at 160°C under anhydrous condition for the highly orientation of nanofibers. Moreover, the oxidative stability and resistance of methanol permeability of the nanofibers membrane are obviously improved with an increase in orientation of nanofibers. The observed methanol permeability of 0.707 × 10−7 cm2 s−1 is about 6% of Nafion-115. Consequently, orientated nanofibers membrane is proved to be a promising material as the proton exchange membrane for potential application in direct methanol fuel cells. PMID:25082522

Polarizing intestinal epithelial cells electrically through Ror2

PubMed Central

Cao, Lin; McCaig, Colin D.; Scott, Roderick H.; Zhao, Siwei; Milne, Gillian; Clevers, Hans; Zhao, Min; Pu, Jin

2014-01-01

ABSTRACT The apicobasal polarity of enterocytes determines where the brush border membrane (apical membrane) will form, but how this apical membrane faces the lumen is not well understood. The electrical signal across the epithelium could serve as a coordinating cue, orienting and polarizing enterocytes. Here, we show that applying a physiological electric field to intestinal epithelial cells, to mimic the natural electric field created by the transepithelial potential difference, polarized phosphorylation of the actin-binding protein ezrin, increased expression of intestinal alkaline phosphatase (ALPI, a differentiation marker) and remodeled the actin cytoskeleton selectively on the cathode side. In addition, an applied electric field also activated ERK1/2 and LKB1 (also known as STK11), key molecules in apical membrane formation. Disruption of the tyrosine protein kinase transmembrane receptor Ror2 suppressed activation of ERK1/2 and LKB1 significantly, and subsequently inhibited apical membrane formation in enterocytes. Our findings indicate that the endogenous electric field created by the transepithelial potential difference might act as an essential coordinating signal for apical membrane formation at a tissue level, through activation of LKB1 mediated by Ror2–ERK signaling. PMID:24928904

Fabrication of hydrophobic fluorinated silica-polyamide thin film nanocomposite reverse osmosis membranes with dramatically improved salt rejection.

PubMed

Pang, Ruizhi; Zhang, Kaisong

2018-01-15

Thin film nanocomposite reverse osmosis (TFN RO) membranes incorporated with hydrophilic nanoparticles show a potential problem that the salt rejection can not be improved significantly. In this study, novel TFN RO membranes incorporated with hydrophobic fluorinated silica nanoparticles were fabricated to improve the salt rejection. Fluorinated silica nanoparticles were well dispersed in organic phase during the interfacial polymerization (IP) process. The TFN RO membranes were characterized with attenuated total reflectance infra-red, field emission scanning electron microscopy, atomic force microscopy and water contact angle measurements. The preparation conditions of TFN RO membranes, including IP reaction time, organic solvent removal time, and fluorinated silica loading, were optimized by characterizing desalination performance using 2000ppm NaCl aqueous solution at 1.55MPa and 25°C. The salt rejection increased significantly from 96.0% without fluorinated silica nanoparticles to 98.6% with the optimal 0.12% (w/v) fluorinated silica nanoparticles, while the water flux decreased slightly from 0.99m 3 /m 2 /day to 0.93m 3 /m 2 /day. This study demonstrated the potential use of hydrophobic nanoparticles in high-performance TFN RO membranes. Copyright © 2017 Elsevier Inc. All rights reserved.

Biguanides inhibit complex I, II and IV of rat liver mitochondria and modify their functional properties.

PubMed

Drahota, Z; Palenickova, E; Endlicher, R; Milerova, M; Brejchova, J; Vosahlikova, M; Svoboda, P; Kazdova, L; Kalous, M; Cervinkova, Z; Cahova, M

2014-01-01

In this study, we focused on an analysis of biguanides effects on mitochondrial enzyme activities, mitochondrial membrane potential and membrane permeability transition pore function. We used phenformin, which is more efficient than metformin, and evaluated its effect on rat liver mitochondria and isolated hepatocytes. In contrast to previously published data, we found that phenformin, after a 5 min pre-incubation, dose-dependently inhibits not only mitochondrial complex I but also complex II and IV activity in isolated mitochondria. The enzymes complexes inhibition is paralleled by the decreased respiratory control index and mitochondrial membrane potential. Direct measurements of mitochondrial swelling revealed that phenformin increases the resistance of the permeability transition pore to Ca(2+) ions. Our data might be in agreement with the hypothesis of Schäfer (1976) that binding of biguanides to membrane phospholipids alters membrane properties in a non-specific manner and, subsequently, different enzyme activities are modified via lipid phase. However, our measurements of anisotropy of fluorescence of hydrophobic membrane probe diphenylhexatriene have not shown a measurable effect of membrane fluidity with the 1 mM concentration of phenformin that strongly inhibited complex I activity. Our data therefore suggest that biguanides could be considered as agents with high efficacy but low specifity.

Cochlear potential difference between endolymph fluid and the hair cell's interior: a retold interpretation based on the Goldman equation.

PubMed

Kurbel, Sven; Borzan, Vladimir; Golem, Hilda; Dinjar, Kristijan

2017-02-01

Reported cochlear potential values of near 150 mV are often attributed to endolymph itself, although membrane potentials result from ion fluxes across the adjacent semipermeable membranes due to concentration gradients. Since any two fluids separated by a semipermeable membrane develop potential due to differences in solute concentrations, a proposed interpretation here is that positive potential emanates from the Reissner membrane due to small influx of sodium from perilymph to endolymph. Basolateral hair cell membranes leak potassium into the interstitial fluid and this negative potential inside hair cells further augments the electric gradient of cochlear potential. Taken together as a sum, these two potentials are near the reported values of cochlear potential. This is based on reported data for cochlear fluids used for the calculation of Nernst and Goldman potentials. The reported positive potential of Reissner membrane can be explained almost entirely by the traffic of Na+ that enters endolymph through this membrane. At the apical membrane of hair cells, acoustic stimulation modulates stereocillia permeability to potassium. Potassium concentration gradients on the apical membrane are low (the calculated Nernst value is <+3 mV), suggesting that the potassium current is not caused by the local potassium concentration gradient, but an electric field between the positive sodium generated potential on the Reissner membrane and negative inside hair cells. Potassium is forced by this overall electric field to enter hair cells when stereocilia are permeable due to mechanical bending. Copyright© by the Medical Assotiation of Zenica-Doboj Canton.

Synthesis of antimicrobial Nisin-phosphorylated soybean protein isolate/poly(L-lactic acid)/ZrO2 membranes.

PubMed

Jiang, Suwei; Wang, Hualin; Chu, Chenjiang; Ma, Xingkong; Sun, Min; Jiang, Shaotong

2015-01-01

Electrospinning technique was used to fabricate the model drug Nisin loaded phosphorylated soybean protein isolate/poly(l-lactic acid)/zirconium dioxide (Nisin-PSPI/PLLA/ZrO2) nanofibrous membranes. The average diameter of drug carrier PSPI/PLLA/ZrO2 nanofibers increased with the increase of content PSPI and some spindle-shape beads appeared when PSPI content reached 25 wt%. The loading dosage of Nisin caused no significant changes in the size and morphology of nanofibers when Nisin content was below 9 wt%. There existed hydrogen and Zr-O-C bonds among PSPI, PLLA and ZrO2 units, and the crystalline of PLLA matrix decreased owning to the introducing of PSPI and ZrO2 units. Moreover, the water absorption capability and degradation rate of PSPI/PLLA/ZrO2 nanofibrous membranes increased with increasing PSPI content. The antimicrobial activity and release experimental results showed that Nisin-PSPI/PLLA/ZrO2 nanofibrous membranes displayed well controlled release and better antimicrobial activity against Staphylococcus aureus (S. aureus), and the Nisin release from the medicated nanofibers could be described by Fickian diffusion model. The Nisin-PSPI/PLLA/ZrO2 nanofibrous membranes may have potential as a new nanofibrous membrane in drug delivery, food active packaging and wound dressing. Copyright © 2014 Elsevier B.V. All rights reserved.

Chemicals and energy co-generation from direct hydrocarbons/oxygen proton exchange membrane fuel cell

NASA Astrophysics Data System (ADS)

Li, W. S.; Lu, D. S.; Luo, J. L.; Chuang, K. T.

A proton exchange membrane fuel cell for chemicals and energy co-generation was set up with hydrocarbons ethane, propane and butane as fuels, and the electrochemical performance of the cell was studied by using linear potential sweep, alternating current impedance and gas chromatography. The cell performance can be improved to a great extent by increasing the platinum load in the catalyst, by treating the membrane with phosphoric acid and by elevating temperature. The improvement of cell performance by the increase of platinum load is ascribed to the increase of reaction sites for hydrocarbon oxidation, that by phosphoric acid treatment to the increase of proton conductivity in Nafion membrane, and that by elevating temperature to the improvement in thermodynamic as well as kinetic aspects. Only a small fraction of the hydrocarbon is converted to carbon dioxide in this cell during its power generation. The current efficiency is 5% for the conversion of ethane to carbon dioxide in the ethane/oxygen fuel cell with 20% carbon-supported platinum as catalyst and phosphoric acid-treated membrane as proton exchange membrane at 0.2 V, 80 °C and ambient pressure. The reaction activity of hydrocarbons at the anode is in the order of propane, butane and ethane. The possible chemicals produced from the cell were hydrocarbons with more than six carbons, which are inactive at the anode under cell conditions.

Quasi-equilibrium analysis of the ion-pair mediated membrane transport of low-permeability drugs.

PubMed

Miller, Jonathan M; Dahan, Arik; Gupta, Deepak; Varghese, Sheeba; Amidon, Gordon L

2009-07-01

The aim of this research was to gain a mechanistic understanding of ion-pair mediated membrane transport of low-permeability drugs. Quasi-equilibrium mass transport analyses were developed to describe the ion-pair mediated octanol-buffer partitioning and hydrophobic membrane permeation of the model basic drug phenformin. Three lipophilic counterions were employed: p-toluenesulfonic acid, 2-naphthalenesulfonic acid, and 1-hydroxy-2-naphthoic acid (HNAP). Association constants and intrinsic octanol-buffer partition coefficients (Log P(AB)) of the ion-pairs were obtained by fitting a transport model to double reciprocal plots of apparent octanol-buffer distribution coefficients versus counterion concentration. All three counterions enhanced the lipophilicity of phenformin, with HNAP providing the greatest increase in Log P(AB), 3.7 units over phenformin alone. HNAP also enhanced the apparent membrane permeability of phenformin, 27-fold in the PAMPA model, and 4.9-fold across Caco-2 cell monolayers. As predicted from a quasi-equilibrium analysis of ion-pair mediated membrane transport, an order of magnitude increase in phenformin flux was observed per log increase in counterion concentration, such that log-log plots of phenformin flux versus HNAP concentration gave linear relationships. These results provide increased understanding of the underlying mechanisms of ion-pair mediated membrane transport, emphasizing the potential of this approach to enable oral delivery of low-permeability drugs.

Evidence for a Na+/H+ Antiporter in Membrane Vesicles Isolated from Roots of the Halophyte Atriplex nummularia1

PubMed Central

Braun, Yael; Hassidim, Miriam; Lerner, Henri R.; Reinhold, Leonora

1988-01-01

The ATP-dependent establishment of a positive membrane potential (measured as S14CN−-accumulation) in membrane vesicles isolated from the roots of Atriplex nummularia Lindl. was not inhibited by NaMes and KMes at concentrations up to 140 millimolar. On the other hand, the formation of ΔpH (measured as 14C-methylamine accumulation or quenching of quinacrine fluorescence), was depressed by NaMes concentrations as low as 30 millimolar. Supply of NaMes after the ΔpH had been established brought about partial dissipation within 30 seconds. Extent of dissipation of ΔpH increased with NaMes concentration over the range tested (up to 180 millimolar). The H+/Na+ exchange indicated by these results was not due to the creation of a Na+ diffusion potential. Formation of ΔpH in these vesicles was stable to NO3− up to 100 millimolar; further, the dissipating effect of Na+ supply was apparent on a ΔpH formed in the presence of 30 millimolar NO3−. Additional evidence that the origin of the membrane vesicles observed in this investigation was not the tonoplast and was probably the plasmalemma included the vanadate sensitivity of the establishment of the membrane potential. PMID:16666082

Polyamine uptake by the intraerythrocytic malaria parasite, Plasmodium falciparum.

PubMed

Niemand, J; Louw, A I; Birkholtz, L; Kirk, K

2012-09-01

Polyamines and the enzymes involved in their biosynthesis are present at high levels in rapidly proliferating cells, including cancer cells and protozoan parasites. Inhibition of polyamine biosynthesis in asexual blood-stage malaria parasites causes cytostatic arrest of parasite development under in vitro conditions, but does not cure infections in vivo. This may be due to replenishment of the parasite's intracellular polyamine pool via salvage of exogenous polyamines from the host. However, the mechanism(s) of polyamine uptake by the intraerythrocytic parasite are not well understood. In this study, the uptake of the polyamines, putrescine and spermidine, into Plasmodium falciparum parasites functionally isolated from their host erythrocyte was investigated using radioisotope flux techniques. Both putrescine and spermidine were taken up into isolated parasites via a temperature-dependent process that showed cross-competition between different polyamines. There was also some inhibition of polyamine uptake by basic amino acids. Inhibition of polyamine biosynthesis led to an increase in the total amount of putrescine and spermidine taken up from the extracellular medium. The uptake of putrescine and spermidine by isolated parasites was independent of extracellular Na(+) but increased with increasing external pH. Uptake also showed a marked dependence on the parasite's membrane potential, decreasing with membrane depolarization and increasing with membrane hyperpolarization. The data are consistent with polyamines being taken up into the parasite via an electrogenic uptake process, energised by the parasite's inwardly negative membrane potential. Copyright © 2012 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.

The Hv1 proton channel responds to mechanical stimuli.

PubMed

Pathak, Medha M; Tran, Truc; Hong, Liang; Joós, Béla; Morris, Catherine E; Tombola, Francesco

2016-11-01

The voltage-gated proton channel, Hv1, is expressed in tissues throughout the body and plays important roles in pH homeostasis and regulation of NADPH oxidase. Hv1 operates in membrane compartments that experience strong mechanical forces under physiological or pathological conditions. In microglia, for example, Hv1 activity is potentiated by cell swelling and causes an increase in brain damage after stroke. The channel complex consists of two proton-permeable voltage-sensing domains (VSDs) linked by a cytoplasmic coiled-coil domain. Here, we report that these VSDs directly respond to mechanical stimuli. We find that membrane stretch facilitates Hv1 channel opening by increasing the rate of activation and shifting the steady-state activation curve to less depolarized potentials. In the presence of a transmembrane pH gradient, membrane stretch alone opens the channel without the need for strong depolarizations. The effect of membrane stretch persists for several minutes after the mechanical stimulus is turned off, suggesting that the channel switches to a "facilitated" mode in which opening occurs more readily and then slowly reverts to the normal mode observed in the absence of membrane stretch. Conductance simulations with a six-state model recapitulate all the features of the channel's response to mechanical stimulation. Hv1 mechanosensitivity thus provides a mechanistic link between channel activation in microglia and brain damage after stroke. © 2016 Pathak et al.

Utilization of photoinduced charge-separated state of donor-acceptor-linked molecules for regulation of cell membrane potential and ion transport.

PubMed

Numata, Tomohiro; Murakami, Tatsuya; Kawashima, Fumiaki; Morone, Nobuhiro; Heuser, John E; Takano, Yuta; Ohkubo, Kei; Fukuzumi, Shunichi; Mori, Yasuo; Imahori, Hiroshi

2012-04-11

The control of ion transport across cell membranes by light is an attractive strategy that allows targeted, fast control of precisely defined events in the biological membrane. Here we report a novel general strategy for the control of membrane potential and ion transport by using charge-separation molecules and light. Delivery of charge-separation molecules to the plasma membrane of PC12 cells by a membranous nanocarrier and subsequent light irradiation led to depolarization of the membrane potential as well as inhibition of the potassium ion flow across the membrane. Photoregulation of the cell membrane potential and ion transport by using charge-separation molecules is highly promising for control of cell functions. © 2012 American Chemical Society

Transient features in nanosecond pulsed electric fields differentially modulate mitochondria and viability.

PubMed

Beebe, Stephen J; Chen, Yeong-Jer; Sain, Nova M; Schoenbach, Karl H; Xiao, Shu

2012-01-01

It is hypothesized that high frequency components of nanosecond pulsed electric fields (nsPEFs), determined by transient pulse features, are important for maximizing electric field interactions with intracellular structures. For monopolar square wave pulses, these transient features are determined by the rapid rise and fall of the pulsed electric fields. To determine effects on mitochondria membranes and plasma membranes, N1-S1 hepatocellular carcinoma cells were exposed to single 600 ns pulses with varying electric fields (0-80 kV/cm) and short (15 ns) or long (150 ns) rise and fall times. Plasma membrane effects were evaluated using Fluo-4 to determine calcium influx, the only measurable source of increases in intracellular calcium. Mitochondria membrane effects were evaluated using tetramethylrhodamine ethyl ester (TMRE) to determine mitochondria membrane potentials (ΔΨm). Single pulses with short rise and fall times caused electric field-dependent increases in calcium influx, dissipation of ΔΨm and cell death. Pulses with long rise and fall times exhibited electric field-dependent increases in calcium influx, but diminished effects on dissipation of ΔΨm and viability. Results indicate that high frequency components have significant differential impact on mitochondria membranes, which determines cell death, but lesser variances on plasma membranes, which allows calcium influxes, a primary determinant for dissipation of ΔΨm and cell death.

Proteomic mapping of cytosol-facing outer mitochondrial and ER membranes in living human cells by proximity biotinylation

PubMed Central

Hung, Victoria; Lam, Stephanie S; Udeshi, Namrata D; Svinkina, Tanya; Guzman, Gaelen; Mootha, Vamsi K; Carr, Steven A; Ting, Alice Y

2017-01-01

The cytosol-facing membranes of cellular organelles contain proteins that enable signal transduction, regulation of morphology and trafficking, protein import and export, and other specialized processes. Discovery of these proteins by traditional biochemical fractionation can be plagued with contaminants and loss of key components. Using peroxidase-mediated proximity biotinylation, we captured and identified endogenous proteins on the outer mitochondrial membrane (OMM) and endoplasmic reticulum membrane (ERM) of living human fibroblasts. The proteomes of 137 and 634 proteins, respectively, are highly specific and highlight 94 potentially novel mitochondrial or ER proteins. Dataset intersection identified protein candidates potentially localized to mitochondria-ER contact sites. We found that one candidate, the tail-anchored, PDZ-domain-containing OMM protein SYNJ2BP, dramatically increases mitochondrial contacts with rough ER when overexpressed. Immunoprecipitation-mass spectrometry identified ribosome-binding protein 1 (RRBP1) as SYNJ2BP’s ERM binding partner. Our results highlight the power of proximity biotinylation to yield insights into the molecular composition and function of intracellular membranes. DOI: http://dx.doi.org/10.7554/eLife.24463.001 PMID:28441135

Soy lecithin interferes with mitochondrial function in frozen-thawed ram spermatozoa.

PubMed

Del Valle, I; Gómez-Durán, A; Holt, W V; Muiño-Blanco, T; Cebrián-Pérez, J A

2012-01-01

Egg yolk and milk are the 2 major membrane cryoprotectants commonly used in freezing media for the long-term preservation of semen (alone or in combination with others). However, in recent years, there have been increasing arguments against the use of egg yolk or milk because of the risk of introducing diseases through the use of cryopreserved semen. In this study, we analyzed the protective effect of lecithin as an alternative to egg yolk for the cryopreservation of ram semen, using a range of functional markers for sperm viability, motility, apoptosis, and mitochondrial functionality analyses (mitochondrial inner membrane surface [MIMS], mitochondrial inner membrane potential [MIMP], and cell membrane potential) as methods of assessment in samples diluted in 3 different media: Tris-citrate-glucose as control and 2 media supplemented with soy lecithin or egg yolk. The results showed that lecithin was able to effectively protect certain sperm quality characteristics against freezing-induced damage. However, lecithin induced loss of mitochondrial membrane potential or mitochondrial loss that was not reflected by modifications in sperm motility in fresh semen. MIMS and MIMP values decreased in thawed lecithin-treated samples, concomitant with a lower (P < .05) percentage of total and progressively motile cells, compared with those in egg yolk-containing samples. Further incubation of thawed samples revealed changes in motility and mitochondrial functionality that otherwise would not have been detected. These results indicated that lecithin may have affected the inner mitochondrial membrane in frozenthawed spermatozoa and confirmed that sublethal damages that seriously affect sperm functionality, not detected by classic sperm quality analyses, can be evidenced by changes in the inner mitochondrial membrane surface. These findings strengthen the relationship between mitochondrial membrane potential and motility and show that the mitochondrial alterations induced by the cryopreservation process could be specific targets for the improvement of semen cryopreservation protocols.

Cast and 3D printed ion exchange membranes for monolithic microbial fuel cell fabrication

NASA Astrophysics Data System (ADS)

Philamore, Hemma; Rossiter, Jonathan; Walters, Peter; Winfield, Jonathan; Ieropoulos, Ioannis

2015-09-01

We present novel solutions to a key challenge in microbial fuel cell (MFC) technology; greater power density through increased relative surface area of the ion exchange membrane that separates the anode and cathode electrodes. The first use of a 3D printed polymer and a cast latex membrane are compared to a conventionally used cation exchange membrane. These new techniques significantly expand the geometric versatility available to ion exchange membranes in MFCs, which may be instrumental in answering challenges in the design of MFCs including miniaturisation, cost and ease of fabrication. Under electrical load conditions selected for optimal power transfer, peak power production (mean 10 batch feeds) was 11.39 μW (CEM), 10.51 μW (latex) and 0.92 μW (Tangoplus). Change in conductivity and pH of anolyte were correlated with MFC power production. Digital and environmental scanning electron microscopy show structural changes to and biological precipitation on membrane materials following long term use in an MFC. The cost of the novel membranes was lower than the conventional CEM. The efficacy of two novel membranes for ion exchange indicates that further characterisation of these materials and their fabrication techniques, shows great potential to significantly increase the range and type of MFCs that can be produced.

[Effect of 3-bromopyruvate on mitochondrial membrane potential and apoptosis of human breast carcinoma SK-BR-3 cells].

PubMed

Zhang, Yuanyuan; Liu, Zhe; Zhang, Qianwen; Chao, Zhenhua; Zhang, Pei; Xia, Fei; Jiang, Chenchen; Liu, Hao; Jiang, Zhiwen

2013-09-01

To study the effect of glycolysis inhibitor 3-bromopyruvate (3-BrPA) in inducing apoptosis of human breast carcinoma cells SK-BR-3 and the possible mechanism. MTT assay was used to detect the growth inhibition induced by 3-BrPA in breast cancer cells SK-BR-3. The apoptotic cells were detected by flow cytometry with propidium iodide (PI). ATP levels in the cells were detected by ATP assay kit, and DHE fluorescent probe technique was used to determine superoxide anion levels; the mitochondrial membrane potential was assessed using JC-1 staining assay. MTT assay showed that the proliferation of SK-BR-3 cells was inhibited by 3-BrPA in a time- and concentration-dependent manner. Exposure to 80, 160, and 320 µmol·L(-1) 3-BrPA for 24 h resulted in cell apoptosis rates of 6.7%, 22.3%, and 79.6%, respectively, and the intracellular ATP levels of SK-BR-3 cells treated with 80, 160, 320 µmol·L(-1) 3-BrPA for 5 h were 87.7%, 60.6%, and 23.7% of the control levels. 3-BrPA at 160 µmol·L(-1) increased reactive oxygen levels and lowered mitochondrial membrane potential of SK-BR-3 cells. 3-BrPA can inhibit cell proliferation, reduce the mitochondrial membrane potential and induce apoptosis in SK-BR-3 cells, the mechanism of which may involve a reduced ATP level by inhibiting glycolysis and increasing the reactive oxygen level in the cells.

Tunable hydrogen separation in porous graphene membrane: first-principle and molecular dynamic simulation.

PubMed

Tao, Yehan; Xue, Qingzhong; Liu, Zilong; Shan, Meixia; Ling, Cuicui; Wu, Tiantian; Li, Xiaofang

2014-06-11

First-principle density functional theory (DFT) calculation and molecular dynamic (MD) simulation are employed to investigate the hydrogen purification performance of two-dimensional porous graphene material (PG-ESX). First, the pore size of PG-ES1 (3.2775 Å) is expected to show high selectivity of H2 by DFT calculation. Then MD simulations demonstrate the hydrogen purification process of the PG-ESX membrane. The results indicate that the selectivity of H2 over several other gas molecules that often accompany H2 in industrial steam methane reforming or dehydrogenation of alkanes (such as N2, CO, and CH4) is sensitive to the pore size of the membrane. PG-ES and PG-ES1 membranes both exhibit high selectivity for H2 over other gases, but the permeability of the PG-ES membrane is much lower than the PG-ES1 membrane because of the smaller pore size. The PG-ES2 membrane with bigger pores demonstrates low selectivity for H2 over other gases. Energy barrier and electron density have been used to explain the difference of selectivity and permeability of PG-ESX membranes by DFT calculations. The energy barrier for gas molecules passing through the membrane generally increase with the decreasing of pore sizes or increasing of molecule kinetic diameter, due to the different electron overlap between gas and a membrane. The PG-ES1 membrane is far superior to other carbon membranes and has great potential applications in hydrogen purification, energy clean combustion, and making new concept membrane for gas separation.

Piezoelectric Response of Aligned Electrospun Polyvinylidene Fluoride/Carbon Nanotube Nanofibrous Membranes.

PubMed

Wu, Chang-Mou; Chou, Min-Hui; Zeng, Wun-Yuan

2018-06-10

Polyvinylidene fluoride (PVDF) shows piezoelectricity related to its β-phase content and mechanical and electrical properties influenced by its morphology and crystallinity. Electrospinning (ES) can produce ultrafine and well-aligned PVDF nanofibers. In this study, the effects of the presence of carbon nanotubes (CNT) and optimized ES parameters on the crystal structures and piezoelectric properties of aligned PVDF/CNT nanofibrous membranes were examined. The optimal β content and piezoelectric coefficient (d 33 ) of the aligned electrospun PVDF reached 88% and 27.4 pC/N; CNT addition increased the β-phase content to 89% and d 33 to 31.3 pC/N. The output voltages of piezoelectric units with aligned electrospun PVDF/CNT membranes increased linearly with applied loading and showed good stability during cyclic dynamic compression and tension. The sensitivities of the piezoelectric units with the membranes under dynamic compression and tension were 2.26 mV/N and 4.29 mV/%, respectively. In bending tests, the output voltage increased nonlinearly with bending angle because complicated forces were involved. The output of the aligned membrane-based piezoelectric unit with CNT was 1.89 V at the bending angle of 100°. The high electric outputs indicate that the aligned electrospun PVDF/CNT membranes are potentially effective for flexible wearable sensor application with high sensitivity.

Regulation of Hippocampal Glutamate Receptors: Evidence for the Involvement of a Calcium-Activated Protease

NASA Astrophysics Data System (ADS)

Baudry, Michel; Lynch, Gary

1980-04-01

Specific [3H]glutamate binding to rat hippocampal membranes and the calcium-induced increase in this binding are markedly temperature-sensitive and are inhibited by alkylating or reducing agents as well as by various protease inhibitors. N-Ethylmaleimide, chloromethyl ketone derivatives of lysine and phenylalanine, and tosylarginine methyl ester decrease the maximum number of [3H]glutamate binding sites without changing their affinity for glutamate. Preincubation of the membranes with glutamate does not protect the glutamate ``receptors'' from the suppressive effects of these agents. The proteases trypsin and α -chymotrypsin increase the maximum number of [3H]glutamate binding sites. The effects of calcium on glutamate binding are different across brain regions. Cerebellar membranes are almost insensitive whereas hippocampal and striatal membranes exhibit a strong increase in the number of binding sites after exposure to even low concentrations of calcium. These results suggest that an endogenous membrane-associated thiol protease regulates the number of [3H]glutamate binding sites in hippocampal membranes and that this is the mechanism by which calcium stimulates glutamate binding. The possibility is discussed that the postulated mechanisms participate in synaptic physiology and in particular may be related to the long-term potentiation of transmission found in hippocampus under certain conditions.

A Salt-Induced 60-Kilodalton Plasma Membrane Protein Plays a Potential Role in the Extreme Halotolerance of the Alga Dunaliella.

PubMed Central

Fisher, M.; Pick, U.; Zamir, A.

1994-01-01

The halotolerant alga Dunaliella salina grows in saline conditions as varied as 0.5 and 5 M NaCl, maintaining throughout this range a low intracellular ion concentration. To discover factors potentially involved in ionic homeostasis, we grew cells in media with different salinities or osmolarities and compared their protein profiles. The comparisons indicated that the amount of a 60-kD protein, p60, greatly increased with an increase in salinity and was moderately enhanced when NaCl was substituted with iso-osmotic glycerol. Cells transferred from low to high NaCl or from high glycerol to iso-osmotic NaCl media transiently ceased to grow, and resumption of growth coincided approximately with an increase in p60. The protein, extracted from a plasma membrane fraction, was purified to homogeneity. Anti-p60 antibodies cross-reacted with a 60-kD protein in Dunaliella bardawil. Immunoelectron microscopy of D. salina cell sections indicated that p60 was exclusively located in the plasma membrane. Its induction by salt, the correlation between its accumulation and growth resumption in high concentrations of salt, and its plasma membrane localization suggest the possibility that p60 could play a role in ionic homeostasis in conditions of high salinity, although different types of function could also be considered. PMID:12232413

External K+ dependence of strong inward rectifier K+ channel conductance is caused not by K+ but by competitive pore blockade by external Na.

PubMed

Ishihara, Keiko

2018-06-15

Strong inward rectifier K + (sKir) channels determine the membrane potentials of many types of excitable and nonexcitable cells, most notably the resting potentials of cardiac myocytes. They show little outward current during membrane depolarization (i.e., strong inward rectification) because of the channel blockade by cytoplasmic polyamines, which depends on the deviation of the membrane potential from the K + equilibrium potential ( V - E K ) when the extracellular K + concentration ([K + ] out ) is changed. Because their open - channel conductance is apparently proportional to the "square root" of [K + ] out , increases/decreases in [K + ] out enhance/diminish outward currents through sKir channels at membrane potentials near their reversal potential, which also affects, for example, the repolarization and action-potential duration of cardiac myocytes. Despite its importance, however, the mechanism underlying the [K + ] out dependence of the open sKir channel conductance has remained elusive. By studying Kir2.1, the canonical member of the sKir channel family, we first show that the outward currents of Kir2.1 are observed under the external K + -free condition when its inward rectification is reduced and that the complete inhibition of the currents at 0 [K + ] out results solely from pore blockade caused by the polyamines. Moreover, the noted square-root proportionality of the open sKir channel conductance to [K + ] out is mediated by the pore blockade by the external Na + , which is competitive with the external K + Our results show that external K + itself does not activate or facilitate K + permeation through the open sKir channel to mediate the apparent external K + dependence of its open channel conductance. The paradoxical increase/decrease in outward sKir channel currents during alternations in [K + ] out , which is physiologically relevant, is caused by competition from impermeant extracellular Na . © 2018 Ishihara.

Interaction of Mastoparan with Model Membranes

NASA Astrophysics Data System (ADS)

Haloot, Justin

2010-10-01

The use of antimicrobial agents began during the 20th century to reduce the effects of infectious diseases. Since the 1990s, antimicrobial resistance has become an ever-increasing global problem. Our laboratory recently found that small antimicrobial peptides (AMPs) have potent antimicrobial activity against a wide range of Gram-negative and Gram-positive organisms including antibiotic resistant organisms. These AMPs are potential therapeutic agents against the growing problem of antimicrobial resistance. AMPs are small peptides produced by plants, insects and animals. Several hypotheses concede that these peptides cause some type of structural perturbations and increased membrane permeability in bacteria however, how AMPs kill bacteria remains unclear. The goal of this study was to design an assay that would allow us to evaluate and monitor the pore forming ability of an AMP, Mastoparan, on model membrane structures called liposomes. Development of this model will facilitate the study of how mastoparan and related AMPs interact with the bacterial membrane.

[Does a lateral gradient of membrane potential on the plasma membrane of growing pollen tube of germinating pollen grain exist?].

PubMed

Andreev, I M

2011-01-01

The data presented in the article by Breigina et al. (2009) "Changes in the membrane potential during pollen grain germination and pollen tube growth" (Tsitologiya. 51 (10): 815-823) and concerning the measurement of electric membrane potential (Delta Psi) on the plasma membrane of growing pollen tube of germinating pollen grain with the use of fluorescent potential-sensitive dye, di-4-ANEPPS, were critically analyzed in order to clarify whether a lateral gradient of Delta Psi on this membrane indeed exists. This analysis showed that the main conclusion of the authors of the above article on the existence of polar distribution of Delta Psi along the pollen tube plasma membrane is not in accordance with a number of known peculiarities of di-4-ANEPPS behavior in biological membranes and requires a significant revision. The findings in question reported by the authors, in my opinion, might be interpreted as evidence for the presence on the plasma membrane of growing pollen tube not only the membrane potential Delta Psi but also lateral gradient of so called intra-membrane dipole potential. Based on the comments made, another interpretation of the experimental results described by Breigina et al. has been offered. In addition, some drawbacks in the methodology used by the authors for measurement of Delta Psi with other fluorescent potential-sensitive dye, DiBAC3(3), are also shortly considered.

Cytoplasmic membrane response to copper and nickel in Acidithiobacillus ferrooxidans.

PubMed

Mykytczuk, N C S; Trevors, J T; Ferroni, G D; Leduc, L G

2011-03-20

Metal tolerance has been found to vary among Acidithiobacillus ferrooxidans strains and this can impact the efficiency of biomining practices. To explain observed strain variability for differences in metal tolerance we examined the effects of Cu(2+) and Ni(2+) concentrations (1-200 mM) on cytoplasmic membrane properties of two A. ferrooxidans type strains (ATCC 23270 and 19859) and four strains isolated from AMD water around Sudbury, Ontario, Canada. Growth rate, membrane fluidity and phase, determined from the fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH), and fatty acid profiles indicated that three different modes of adaptation were present and could separate between strains showing moderate, or high metal tolerance from more sensitive strains. To compensate for the membrane ordering effects of the metals, significant remodelling of the membrane was used to either maintain homeoviscous adaptation in the moderately tolerant strains or to increase membrane fluidity in the sensitive strains. Shifts in the gel-to-liquid crystalline transition temperature in the moderately tolerant strains led to multiple phase transitions, increasing the potential for phase separation and compromised membrane integrity. The metal-tolerant strain however, was able to tolerate increases in membrane order without significant compensation via fatty acid composition. Our multivariate analyses show a common adaptive response which involves changes in the abundant 16:0 and 18:1 fatty acids. However, fatty acid composition and membrane properties showed no difference in response to either copper or nickel suggesting that adaptive response was non-specific and tolerance dependent. We demonstrate that strain variation can be evaluated using differences in membrane properties as intrinsic determinants of metal susceptibility. Copyright © 2010 Elsevier GmbH. All rights reserved.

Carbon nanotube embedded PVDF membranes: Effect of solvent composition on the structural morphology for membrane distillation

NASA Astrophysics Data System (ADS)

Mapunda, Edgar C.; Mamba, Bhekie B.; Msagati, Titus A. M.

2017-08-01

Rapid population increase, growth in industrial and agricultural sectors and global climate change have added significant pressure on conventional freshwater resources. Tapping freshwater from non-conventional water sources such as desalination and wastewater recycling is considered as sustainable alternative to the fundamental challenges of water scarcity. However, affordable and sustainable technologies need to be applied for the communities to benefit from the treatment of non-conventional water source. Membrane distillation is a potential desalination technology which can be used sustainably for this purpose. In this work multi-walled carbon nanotube embedded polyvinylidene fluoride membranes for application in membrane distillation desalination were prepared via non-solvent induced phase separation method. The casting solution was prepared using mixed solvents (N, N-dimethylacetamide and triethyl phosphate) at varying ratios to study the effect of solvent composition on membrane morphological structures. Membrane morphological features were studied using a number of techniques including scanning electron microscope, atomic force microscope, SAXSpace tensile strength analysis, membrane thickness, porosity and contact angle measurements. It was revealed that membrane hydrophobicity, thickness, tensile strength and surface roughness were increasing as the composition of N, N-dimethylacetamide in the solvent was increasing with maximum values obtained between 40 and 60% N, N-dimethylacetamide. Internal morphological structures were changing from cellular structures to short finger-like and sponge-like pores and finally to large macro void type of pores when the amount of N, N-dimethylacetamide in the solvent was changed from low to high respectively. Multi-walled carbon nanotube embedded polyvinylidene fluoride membranes of desired morphological structures and physical properties can be synthesized by regulating the composition of solvents used to prepare the casting solution.

Aluminum Trichloride Induces Hypertension and Disturbs the Function of Erythrocyte Membrane in Male Rats.

PubMed

Zhang, Qiuyue; Cao, Zheng; Sun, Xudong; Zuang, Cuicui; Huang, Wanyue; Li, Yanfei

2016-05-01

Aluminum (Al) is the most abundant metal in the earth's crust. Al accumulates in erythrocyte and causes toxicity on erythrocyte membrane. The dysfunction of erythrocyte membrane is a potential risk to hypertension. The high Al content in plasma was associated with hypertension. To investigate the effect of AlCl3 on blood pressure and the function of erythrocyte membrane, the rats were intragastrically exposed to 0, 64(1/20 LD50), 128(1/10 LD50), and 256(1/5 LD50) mg/kg body weight AlCl3 in double distilled water for 120 days, respectively. Then, we determined the systolic and mean arterial blood pressures of rats, the osmotic fragility, the percentage of membrane proteins, the activities of Na(+)/K(+)-ATPase, Mg(2+)-ATPase, Ca(2+)-ATPase, catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GSH-pX), and malondialdehyde (MDA) content of the erythrocyte membrane in this experiment. The results showed that AlCl3 elevated the systolic and mean arterial blood pressure of rats, increased the osmotic fragility, decreased the percentage of membrane protein, inhibited the activities of Na(+)/K(+)-ATPase, Mg(2+)-ATPase, Ca(2+)-ATPase, CAT, SOD and GSH-pX, and increased the MDA content of erythrocyte membrane. These results indicate that AlCl3 may induce hypertension by disturbing the function of erythrocyte membrane.

Placental membrane aging and HMGB1 signaling associated with human parturition

PubMed Central

Menon, Ramkumar; Behnia, Faranak; Polettini, Jossimara; Saade, George R; Campisi, Judith; Velarde, Michael

2016-01-01

Aging is associated with the onset of several diseases in various organ systems; however, different tissues may age differently, rendering some of them dysfunctional sooner than others. Placental membranes (fetal amniochorionic membranes) protect the fetus throughout pregnancy, but their longevity is limited to the duration of pregnancy. The age-associated dysfunction of these membranes is postulated to trigger parturition. Here, we investigated whether cellular senescence—the loss of cell division potential as a consequence of stress—is involved in placental membrane function at term. We show telomere reduction, p38 MAPK activation, increase in p21 expression, loss of lamin B1 loss, increase in SA-β-galactosidase, and senescence-associated secretory phenotype (SASP) gene expression in placental membranes after labor and delivery (term labor [TL]) compared to membranes prior to labor at term (term, not-in-labor [TNIL]). Exposing TNIL placental membranes to cigarette smoke extract, an oxidative stress inducer, also induced markers of cellular senescence similar to those in TL placental membranes. Bioinformatics analysis of differentially expressed SASP genes revealed HMGB1 signaling among the top pathways involved in labor. Further, we show that recombinant HMGB1 upregulates the expression of genes associated with parturition in myometrial cells. These data suggest that the natural physiologic aging of placental tissues is associated with cellular senescence and human parturition. PMID:26851389

Preparation of robust braid-reinforced poly(vinyl chloride) ultrafiltration hollow fiber membrane with antifouling surface and application to filtration of activated sludge solution.

PubMed

Zhou, Zhuang; Rajabzadeh, Saeid; Fang, Lifeng; Miyoshi, Taro; Kakihana, Yuriko; Matsuyama, Hideto

2017-08-01

Braid-reinforced hollow fiber membranes with high mechanical properties and considerable antifouling surface were prepared by blending poly(vinyl chloride) (PVC) with poly(vinyl chloride-co-poly(ethylene glycol) methyl ether methacrylate) (poly(VC-co-PEGMA)) copolymer via non-solvent induced phase separation (NIPS). The tensile strength of the braid-reinforced PVC hollow fiber membranes were significantly larger than those of previously reported various types of PVC hollow fiber membranes. The high interfacial bonding strength indicated the good compatibility between the coating materials and the surface of polyethylene terephthalate (PET)-braid. Owing to the surface segregation phenomena, the membrane surface PEGMA coverage increased upon increasing the poly(VC-co-PEGMA)/PVC blending ratio, resulting in higher hydrophilicities and bovine serum albumin (BSA) repulsion. To compare the fouling properties, membranes with similar PWPs were prepared by adjusting the dope solution composition to eliminate the effect of hydrodynamic conditions on the membrane fouling performance. The blend membranes surface exhibited considerable fouling resistance to the molecular adsorption from both BSA solution and activated sludge solution. In both cases, the flux recovered to almost 80% of the initial flux using only water backflush. Considering their great mechanical properties and antifouling resistance to activated sludge solution, these novel membranes show good potential for application in wastewater treatment. Copyright © 2017 Elsevier B.V. All rights reserved.

Mammalian plasma membrane proteins as potential biomarkers and drug targets.

PubMed

Rucevic, Marijana; Hixson, Douglas; Josic, Djuro

2011-06-01

Defining the plasma membrane proteome is crucial to understand the role of plasma membrane in fundamental biological processes. Change in membrane proteins is one of the first events that take place under pathological conditions, making plasma membrane proteins a likely source of potential disease biomarkers with prognostic or diagnostic potential. Membrane proteins are also potential targets for monoclonal antibodies and other drugs that block receptors or inhibit enzymes essential to the disease progress. Despite several advanced methods recently developed for the analysis of hydrophobic proteins and proteins with posttranslational modifications, integral membrane proteins are still under-represented in plasma membrane proteome. Recent advances in proteomic investigation of plasma membrane proteins, defining their roles as diagnostic and prognostic disease biomarkers and as target molecules in disease treatment, are presented. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

P2 purinoceptors regulate calcium-activated chloride and fluid transport in 31EG4 mammary epithelia.

PubMed

Blaug, Sasha; Rymer, Jodi; Jalickee, Stephen; Miller, Sheldon S

2003-04-01

It has been reported that secretory mammary epithelial cells (MEC) release ATP, UTP, and UDP upon mechanical stimulation. Here we examined the physiological changes caused by ATP/UTP in nontransformed, clonal mouse mammary epithelia (31EG4 cells). In control conditions, transepithelial potential (apical side negative) and resistance were -4.4 +/- 1.3 mV (mean +/- SD, n = 12) and 517.7 +/- 39.4 Omega. cm(2), respectively. The apical membrane potential was -43.9 +/- 1.7 mV, and the ratio of apical to basolateral membrane resistance (R(A)/R(B)) was 3.5 +/- 0.2. Addition of ATP or UTP to the apical or basolateral membranes caused large voltage and resistance changes with an EC(50) of approximately 24 microM (apical) and approximately 30 microM (basal). Apical ATP/UTP (100 microM) depolarized apical membrane potential by 17.6 +/- 0.8 mV (n = 7) and decreased R(A)/R(B) by a factor of approximately 3. The addition of adenosine to either side (100 microM) had no effect on any of these parameters. The ATP/UTP responses were partially inhibited by DIDS and suramin and mediated by a transient increase in free intracellular Ca(2+) concentration (427 +/- 206 nM; 15-25 microM ATP, apical; n = 6). This Ca(2+) increase was blocked by cyclopiazonic acid, by BAPTA, or by xestospongin C. 31EG4 MEC monolayers also secreted or absorbed fluid in the resting state, and ATP or UTP increased fluid secretion by 5.6 +/- 3 microl x cm(-2) x h(-1) (n = 10). Pharmacology experiments indicate that 31EG4 epithelia contain P2Y(2) purinoceptors on the apical and basolateral membranes, which upon activation stimulate apical Ca(2+)-dependent Cl channels and cause fluid secretion across the monolayer. This suggests that extracellular nucleotides could play a fundamental role in mammary gland paracrine signaling and the regulation of milk composition in vivo.

Caloric restriction improves efficiency and capacity of the mitochondrial electron transport chain in Saccharomyces cerevisiae

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, Joon-Seok; Choi, Kyung-Mi; Lee, Cheol-Koo, E-mail: cklee2005@korea.ac.kr

2011-06-03

Highlights: {yields} Calorie restriction (CR) increases electron transport chain (ETC) at both RNA and protein level. {yields} CR enhances mitochondrial membrane potential, and, regardless of ages, reduces reactive oxygen species. {yields} CR increases both efficiency and capacity of the ETC. {yields} CR induces intensive modulation at mitochondrial ETC where might be a major site leading to extension of lifespan. -- Abstract: Caloric restriction (CR) is known to extend lifespan in a variety of species; however, the mechanism remains unclear. In this study, we found that CR potentiated the mitochondrial electron transport chain (ETC) at both the transcriptional and translational levels.more » Indeed, mitochondrial membrane potential (MMP) was increased by CR, and, regardless of ages, overall reactive oxygen species (ROS) generation was decreased by CR. With these changes, overall growth rate of cells was maintained under various CR conditions, just like cells under a non-restricted condition. All of these data support increased efficiency and capacity of the ETC by CR, and this change might lead to extension of lifespan.« less

The influence of hydrolysis induced biopolymers from recycled aerobic sludge on specific methanogenic activity and sludge filterability in an anaerobic membrane bioreactor.

PubMed

Buntner, D; Spanjers, H; van Lier, J B

2014-03-15

The objective of the present study was to evaluate the impact of excess aerobic sludge on the specific methanogenic activity (SMA), in order to establish the maximum allowable aerobic sludge loading. In batch tests, different ratios of aerobic sludge to anaerobic inoculum were used, i.e. 0.03, 0.05, 0.10 and 0.15, showing that low ratios led to an increased SMA. However, the ratio 0.15 caused more than 20% SMA decrease. In addition to the SMA tests, the potential influence of biopolymers and extracellular substances, that are generated as a result of excess aerobic sludge hydrolysis, on membrane performance was determined by assessing the fouling potential of the liquid broth, taking into account parameters such as specific resistance to filtration (SRF) and supernatant filterability (SF). Addition of aerobic sludge to the anaerobic biomass resulted in a high membrane fouling potential. The increase in biopolymers could be ascribed to aerobic sludge hydrolysis. A clear positive correlation between the concentration of the colloidal fraction of biopolymer clusters (cBPC) and the SRF was observed and a negative correlation between the cBPC and the SF measured at the end of the above described SMA tests. The latter implies that sludge filtration resistance increases when more aerobic sludge is hydrolyzed, and thus more cBPC is released. During AnMBR operation, proteins significantly contributed to sludge filterability decrease expressed as SRF and SF, whereas the carbohydrate fraction of SMP was of less importance due to low concentrations. On the contrary, carbohydrates seemed to improve filterability and diminish SRF of the sludge. Albeit, cBPC increase caused an increase in mean TMP during the AnMBR operation, confirming that cBPC is positively correlated to membrane fouling. Copyright © 2013 Elsevier Ltd. All rights reserved.

The role of extracorporeal membrane oxygenation in patients after irreversible cardiac arrest as potential organ donors

PubMed Central

Puślecki, Mateusz; Zieliński, Marcin; Mandecki, Michał; Ligowski, Marcin; Stefaniak, Sebastian; Dąbrowski, Marek; Karczewski, Marek; Gąsiorowski, Łukasz; Sip, Maciej; Dąbrowska, Agata; Telec, Wojciech; Perek, Bartłomiej; Jemielity, Marek

2017-01-01

The number of people waiting for a kidney or liver transplant is growing systematically. Due to the latest advances in transplantation, persons after irreversible cardiac arrest and confirmation of death have become potential organ donors. It is estimated that they may increase the number of donations by more than 40%. However, without good organization and communication between pre-hospital care providers, emergency departments, intensive care units and transplantation units, it is almost impossible to save the organs of potential donors in good condition. Various systems, including extracorporeal membrane oxygenation (ECMO), supporting perfusion of organs for transplantation play a key role. In 2016 the “ECMO for Greater Poland” program was established. Although its main goal is to improve the survival rate of patients suffering from life-threatening cardiopulmonary conditions, one of its branches aims to increase the donation rate in patients with irreversible cardiac arrest. In this review, the role of ECMO in the latter group as the potential organ donors is presented. PMID:29354178

Properties of an inward rectifying K channel in the membrane of guinea-pig atrial cardioballs.

PubMed

Bechem, M; Glitsch, H G; Pott, L

1983-11-01

Single channel outward current fluctuations are recorded in excised (outside-out) membrane patches of isolated atrial cells in culture (cardioballs) from hearts of adult guinea-pigs. The ionic channel displays a high selectivity to K ions. Accordingly the reversal potential of the single channel current is close to the K equilibrium potential. The open channel conductance is unaffected by the membrane potential but depends on the K concentration of the outside solution (19.7pS at 2 mM Ko to 30.7pS at 20 mM Ko). The open state probability (Po) of the channel shows a marked voltage dependence. Po amounts to c.0.9 at -40 mV and decreases to c.0.1 at +40 mV. Under the assumption of no channel interaction a macroscopic steady state current voltage relationship is reconstructed from the single channel data. The relationship displays inward-going rectification. The rectification is due to the voltage dependence of Po. The I-V curve displays a negative slope at membrane potentials positive to -15 mV. In bathing solutions containing Ba ions (0.2 mM) Po is reduced by rapid closures which interrupt the open state events. The unit channel conductance is unaffected by Ba ions. The channel block exerted by Ba ions is augmented with increasing membrane hyperpolarization. The results suggest that the channel studied may represent a background K conductance.

Electroporation of DC-3F cells is a dual process.

PubMed

Wegner, Lars H; Frey, Wolfgang; Silve, Aude

2015-04-07

Treatment of biological material by pulsed electric fields is a versatile technique in biotechnology and biomedicine used, for example, in delivering DNA into cells (transfection), ablation of tumors, and food processing. Field exposure is associated with a membrane permeability increase usually ascribed to electroporation, i.e., formation of aqueous membrane pores. Knowledge of the underlying processes at the membrane level is predominantly built on theoretical considerations and molecular dynamics (MD) simulations. However, experimental data needed to monitor these processes with sufficient temporal resolution are scarce. The whole-cell patch-clamp technique was employed to investigate the effect of millisecond pulsed electric fields on DC-3F cells. Cellular membrane permeabilization was monitored by a conductance increase. For the first time, to our knowledge, it could be established experimentally that electroporation consists of two clearly separate processes: a rapid membrane poration (transient electroporation) that occurs while the membrane is depolarized or hyperpolarized to voltages beyond so-called threshold potentials (here, +201 mV and -231 mV, respectively) and is reversible within ∼100 ms after the pulse, and a long-term, or persistent, permeabilization covering the whole voltage range. The latter prevailed after the pulse for at least 40 min, the postpulse time span tested experimentally. With mildly depolarizing or hyperpolarizing pulses just above threshold potentials, the two processes could be separated, since persistent (but not transient) permeabilization required repetitive pulse exposure. Conductance increased stepwise and gradually with depolarizing and hyperpolarizing pulses, respectively. Persistent permeabilization could also be elicited by single depolarizing/hyperpolarizing pulses of very high field strength. Experimental measurements of propidium iodide uptake provided evidence of a real membrane phenomenon, rather than a mere patch-clamp artifact. In short, the response of DC-3F cells to strong pulsed electric fields was separated into a transient electroporation and a persistent permeabilization. The latter dominates postpulse membrane properties but to date has not been addressed by electroporation theory or MD simulations. Copyright © 2015 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Electrophysiological analysis of bicarbonate permeation across the peritubular cell membrane of rat kidney proximal tubule. II. Exclusion of HCO3(-)-effects on other ion permeabilities and of coupled electroneutral HCO3(-)-transport.

PubMed

Burckhardt, B C; Cassola, A C; Frömter, E

1984-05-01

Cell membrane potentials of rat kidney proximal tubules were measured in response to peritubular ion substitutions in vivo with conventional and Cl- sensitive microelectrodes in order to test possible alternative explanations of the bicarbonate dependent cell potential transients reported in the preceding paper. Significant direct effects of bicarbonate on peritubular K+, Na+, and Cl- conductances could be largely excluded by blocking K+ permeability with Ba2+ and replacing all Na+ and Cl- by choline or respectively SO4(2-) isethionate, or gluconate. Under those conditions the cell membrane response to HCO3- was essentially preserved. In addition it was observed that peritubular Cl- conductance is negligibly small, that Cl-/HCO3- exchange - if present at all - is insignificant, and that rheogenic HCO3- flow with coupling to Na+ flow is also absent or insignificant. A transient disturbance of the Na+ pump or a transient unspecific increase of the membrane permeability was also excluded by experiments with ouabain and by the observation that SITS (4-acetamido-4'-isothiocyano-2,2' disulphonic stilbene) blocked the HCO3- response instantaneously. The data strongly support the notion that the potential changes in response to peritubular HCO3- concentration changes arise from passive rheogenic bicarbonate transfer across the peritubular cell membrane, and hence that this membrane has a high conductance for bicarbonate buffer.

Regulation of Yeast H+-ATPase by Protein Kinases Belonging to a Family Dedicated to Activation of Plasma Membrane Transporters

PubMed Central

Goossens, Alain; de la Fuente, Natalia; Forment, Javier; Serrano, Ramon; Portillo, Francisco

2000-01-01

The regulation of electrical membrane potential is a fundamental property of living cells. This biophysical parameter determines nutrient uptake, intracellular potassium and turgor, uptake of toxic cations, and stress responses. In fungi and plants, an important determinant of membrane potential is the electrogenic proton-pumping ATPase, but the systems that modulate its activity remain largely unknown. We have characterized two genes from Saccharomyces cerevisiae, PTK2 and HRK1 (YOR267c), that encode protein kinases implicated in activation of the yeast plasma membrane H+-ATPase (Pma1) in response to glucose metabolism. These kinases mediate, directly or indirectly, an increase in affinity of Pma1 for ATP, which probably involves Ser-899 phosphorylation. Ptk2 has the strongest effect on Pma1, and ptk2 mutants exhibit a pleiotropic phenotype of tolerance to toxic cations, including sodium, lithium, manganese, tetramethylammonium, hygromycin B, and norspermidine. A plausible interpretation is that ptk2 mutants have a decreased membrane potential and that diverse cation transporters are voltage dependent. Accordingly, ptk2 mutants exhibited reduced uptake of lithium and methylammonium. Ptk2 and Hrk1 belong to a subgroup of yeast protein kinases dedicated to the regulation of plasma membrane transporters, which include Npr1 (regulator of Gap1 and Tat2 amino acid transporters) and Hal4 and Hal5 (regulators of Trk1 and Trk2 potassium transporters). PMID:11003661

Ultrafiltration and nanofiltration membrane fouling by natural organic matter: Mechanisms and mitigation by pre-ozonation and pH.

PubMed

Yu, Wenzheng; Liu, Teng; Crawshaw, John; Liu, Ting; Graham, Nigel

2018-08-01

The fouling of ultrafiltration (UF) and nanofiltration (NF) membranes during the treatment of surface waters continues to be of concern and the particular role of natural organic matter (NOM) requires further investigation. In this study the effect of pH and surface charge on membrane fouling during the treatment of samples of a representative surface water (Hyde Park recreational lake) were evaluated, together with the impact of pre-ozonation. While biopolymers in the surface water could be removed by the UF membrane, smaller molecular weight (MW) fractions of NOM were poorly removed, confirming the importance of membrane pore size. For NF membranes the removal of smaller MW fractions (800 Da-10 kDa) was less than expected from their pore size; however, nearly all of the hydrophobic, humic-type substances could be removed by the hydrophilic NF membranes for all MW distributions (greater than 90%). The results indicated the importance of the charge and hydrophilic nature of the NOM. Thus, the hydrophilic NF membrane could remove the hydrophobic organic matter, but not the hydrophilic substances. Increasing charge effects (more negative zeta potentials) with increasing solution pH were found to enhance organics removal and reduce fouling (flux decline), most likely through greater membrane surface repulsion. Pre-ozonation of the surface water increased the hydrophilic fraction and anionic charge of NOM and altered their size distributions. This resulted in a decreased fouling (less flux decline) for the UF and smaller pore NF, but a slight increase in fouling for the larger pore NF. The differences in the NF behavior are believed to relate to the relative sizes of ozonated organic fractions and the NF pores; a similar size of ozonated organic fractions and the NF pores causes significant membrane fouling. Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.

Application of pulsed UV-irradiation and pre-coagulation to control ultrafiltration membrane fouling in the treatment of micro-polluted surface water.

PubMed

Yu, Wenzheng; Campos, Luiza C; Graham, Nigel

2016-12-15

A major cause of ultrafiltration (UF) membrane fouling is the accumulation of microorganisms and their associated soluble products. To mitigate fouling the application of pulsed short-wavelength ultraviolet (UVC) light (around 254 nm) within the membrane tank together with pre-coagulation was investigated. In mini-pilot-scale tests carried out in parallel with conventional pre-treatment (CUF), the impact of pulsed UV (CUF-UV) at different UV irradiances and fluxes on the increase of trans-membrane pressure (TMP) was evaluated and explained in terms of the quantity and nature of membrane deposits in the membrane cake layer and pores. The results indicated that at a flux of 20 L m -2  h -1 , the pulsed UV (1 min within 31 min cycle) at 3.17 × 10 -2  W/cm 2 prevented any measureable increase in TMP over a period of 32 days, while there was a fourfold increase in TMP for the conventional pre-treatment. For the CUF-UV system the concentration of bacteria and soluble microbial products was much less than the conventional CUF system, and the cake layer was thinner and contained less biopolymers (proteins and polysaccharides). In addition, the pores of the CUF-UV membrane appeared to have less organic deposits, and particularly fractions with a high molecular weight (>10 kDa). At a lower UV irradiance (1.08 × 10 -2  W/cm 2 ), or higher flux (40 L m -2  h -1 ) with the same UV irradiance, there was a measurable increase in TMP, indicating some fouling of the CUF-UV membrane, but the rate of TMP development was significantly lower (∼50%) than the conventional CUF membrane system. Overall, the results show the potential advantages of applying intermittent (pulsed) UVC irradiation with coagulation to control UF membrane fouling. Copyright © 2016 Elsevier Ltd. All rights reserved.

Feasibility study of custom manufacturing methods of ionic polymer-metal composite sensors

NASA Astrophysics Data System (ADS)

Nelson, Shelby E.

The ability to create an ion exchange membrane with any shape or thickness through custom manufacturing techniques is highly desirable in ionic polymer-metal composite (IPMC) research. This is caused by the poor selection and limited availability of certain thicknesses of commercial ion exchange membranes. The objective of this study is to determine the feasibility of manufacturing custom ion exchange membranes for IPMC sensors. The manufacturing methods used in this study are extrusion, injection molding, and hot pressing. A commercial membrane from Golden Energy Fuel Cells (GEFC) is used as a comparison. After the membranes are fabricated, certain properties of the membranes are tested throughout each processing stage to determine if they are suitable to be developed into IPMCs. The three processing stages are pre-activation, activation (hydrated and dehydrated), and IPMC. It was observed that the stiffness of the membranes increased from pre-activation to activation and decreased from activation to IPMC. A more flexible membrane in an IPMC allows for larger cation displacement within the membrane. The extruded and injection molded membranes showed the most potential with having the lowest stiffness of all the samples; however, they were not able to be made into IPMCs due to repeated membrane failures in the primary plating process. Gas accumulated between the layers that formed in the membranes due to the extrusion and injection molding cooling process during manufacturing. The hot pressed membrane was the only custom manufactured membrane to be fully processed into an IPMC. The hot pressed and GEFC IPMC sensors were operated at 1 Hz, 5 Hz, and 10 Hz frequencies with the GEFC IPMC producing the strongest output voltage signal. While the extruded and injection molded membranes showed potential to become IPMCs with their high water uptake percentage, high ion exchange capacity, and low stiffness, more development is needed within the manufacturing process to make a uniform sample that does not fail during chemical processing.

Effect of mitochondrial apoptotic activation through the mitochondrial membrane permeability transition pore on yak meat tenderness during postmortem aging.

PubMed

Wang, Lin-Lin; Han, Ling; Ma, Xiu-Li; Yu, Qun-Li; Zhao, Suo-Nan

2017-11-01

The effect of membrane permeability transition pore dependent mitochondrial apoptotic activation on yak meat tenderness was investigated. Results indicate that MPTP opening increased significantly and the mitochondrial membrane potential decreased markedly in the early aging process (P<0.05). Cytochrome c was released from the mitochondria to the cytoplasm via the MPTP in the early period. Meanwhile, the activation of procaspase-9 occurred earlier than that of procaspase-3. Cyclosporin A suppressed the MPTP opening, depolarization of the mitochondrial membrane potential, activities of caspase-9 and caspase-3, apoptosis rate, myofibril fragmentation index, reactive oxygen species generation, and Ca 2+ levels. These results demonstrated that MPTP mediated the release of cytochrome c in the mitochondrial apoptotic pathway. Furthermore, yak meat tenderness was improved by mitochondrial apoptotic pathway during aging. MPTP opening may be influenced by the ROS generation and Ca 2+ overloading in yak meat during postmortem aging. Copyright © 2017 Elsevier Ltd. All rights reserved.

Membrane Distillation Bioreactor (MDBR) - A lower Green-House-Gas (GHG) option for industrial wastewater reclamation.

PubMed

Goh, Shuwen; Zhang, Jinsong; Liu, Yu; Fane, Anthony G

2015-12-01

A high-retention membrane bioreactor system, the Membrane Distillation Bioreactor (MDBR) is a wastewater reclamation process which has the potential to tap on waste heat generated in industries to produce high quality product water. There are a few key factors which could make MDBR an attractive advanced treatment option, namely tightening legal requirements due to increasing concerns on the micropollutants in industrial wastewater effluents as well as concerns over the electrical requirement of pressurized advanced treatment processes and greenhouse gas emissions associated with wastewater reclamation. This paper aims to provide a consolidated review on the current state of research for the MDBR system and to evaluate the system as a possible lower Green House Gas (GHG) emission option for wastewater reclamation using the membrane bioreactor-reverse osmosis (MBR-RO) system as a baseline for comparison. The areas for potential applications and possible configurations for MDBR applications are discussed. Copyright © 2014 Elsevier Ltd. All rights reserved.

Simulation of axonal excitability using a Spreadsheet template created in Microsoft Excel.

PubMed

Brown, A M

2000-08-01

The objective of this present study was to implement an established simulation protocol (A.M. Brown, A methodology for simulating biological systems using Microsoft Excel, Comp. Methods Prog. Biomed. 58 (1999) 181-90) to model axonal excitability. The simulation protocol involves the use of in-cell formulas directly typed into a spreadsheet and does not require any programming skills or use of the macro language. Once the initial spreadsheet template has been set up the simulations described in this paper can be executed with a few simple keystrokes. The model axon contained voltage-gated ion channels that were modeled using Hodgkin Huxley style kinetics. The basic properties of axonal excitability modeled were: (1) threshold of action potential firing, demonstrating that not only are the stimulus amplitude and duration critical in the generation of an action potential, but also the resting membrane potential; (2) refractoriness, the phenomenon of reduced excitability immediately following an action potential. The difference between the absolute refractory period, when no amount of stimulus will elicit an action potential, and relative refractory period, when an action potential may be generated by applying increased stimulus, was demonstrated with regard to the underlying state of the Na(+) and K(+) channels; (3) temporal summation, a process by which two sub-threshold stimuli can unite to elicit an action potential was shown to be due to conductance changes outlasting the first stimulus and summing with the second stimulus-induced conductance changes to drive the membrane potential past threshold; (4) anode break excitation, where membrane hyperpolarization was shown to produce an action potential by removing Na(+) channel inactivation that is present at resting membrane potential. The simulations described in this paper provide insights into mechanisms of axonal excitation that can be carried out by following an easily understood protocol.

Interaction of phloretin with lipid monolayers: relationship between structural changes and dipole potential change.

PubMed Central

Cseh, R; Benz, R

1999-01-01

Phloretin is known to adsorb to lipid surfaces and alters the dipole potential of lipid monolayers and bilayers. Its adsorption to biological and artificial membranes results in a change of the membrane permeability for a variety of charged and neutral compounds. In this respect phloretin represents a model substance to study the effect of dipole potentials on membrane permeability. In this investigation we studied the interaction of phloretin with monolayers formed of different lipids in the liquid-expanded and the condensed state. Phloretin integrated into the monolayers as a function of the aqueous concentration of its neutral form, indicated by an increase of the surface pressure in the presence of phloretin. Simultaneous recording of the surface potential of the monolayers allowed us to correlate the degree of phloretin integration and the phloretin-induced dipole potential change. Increasing the surface pressure decreased the phloretin-induced shift of the isotherms, but did not influence the phloretin-induced surface potential change. This means that phloretin adsorption to the lipid surface can occur without affecting the lipid packing. The surface potential effect of phloretin is accompanied by a change of the lipid dipole moment vector dependent on the lipid packing. This means that the relation between the surface potential change and the lipid packing cannot be described by a static model alone. Taking into account the deviations of the surface potential change versus molecular area isotherms of the experimental data to the theoretically predicted course, we propose a model that relates the area change to the dipole moment in a dynamic manner. By using this model the experimental data can be described much better than with a static model. PMID:10465758

Bioinspired Synthesis of Photocatalytic Nanocomposite Membranes Based on Synergy of Au-TiO2 and Polydopamine for Degradation of Tetracycline under Visible Light.

PubMed

Wang, Chen; Wu, Yilin; Lu, Jian; Zhao, Juan; Cui, Jiuyun; Wu, Xiuling; Yan, Yongsheng; Huo, Pengwei

2017-07-19

A bioinspired photocatalytic nanocomposite membrane was successfully prepared via polydopamine (pDA)-coated poly(vinylidene fluoride) (PVDF) membrane, as a secondary platform for vacuum-filtrated Au-TiO 2 nanocomposites, with enhanced photocatalytic activity. The degradation efficiency of Au-TiO 2 /pDA/PVDF membranes reached 92% when exposed to visible light for 120 min, and the degradation efficiency of Au-TiO 2 /pDA/PVDF membranes increased by 26% compared to that of Au-TiO 2 powder and increased by 51% compared to that of TiO 2 /pDA/PVDF nanocomposite membranes. The degradation efficiency remained about 90% after five cycle experiments, and the Au-TiO 2 /pDA/PVDF nanocomposite membranes showed good stability, regeneration performance, and easy recycling. The pDA coating not only served as a bioadhesion interface to improve the bonding force between the catalyst and the membrane substrate but also acted as a photosensitizer to broaden the wavelength response range of TiO 2 , and the structure of Au-TiO 2 /pDA/PVDF also improves the transfer rate of photogenerated electrons; the surface plasmon resonance effect of Au also played a positive role in improving the activity of the catalyst. Therefore, we believe that this study opens up a new strategy in preparing the bioinspired photocatalytic nanocomposite membrane for potential wastewater purification, catalysis, and as a membrane separation field.

Novel polymer membrane process for pre-combustion CO{sub 2} capture from coal-fired syngas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Merkel, Tim

2011-09-14

This final report describes work conducted for the Department of Energy (DOE NETL) on development of a novel polymer membrane process for pre-combustion CO{sub 2} capture from coalfired syngas (award number DE-FE0001124). The work was conducted by Membrane Technology and Research, Inc. (MTR) from September 15, 2009, through December 14, 2011. Tetramer Technologies, LLC (Tetramer) was our subcontract partner on this project. The National Carbon Capture Center (NCCC) at Wilsonville, AL, provided access to syngas gasifier test facilities. The main objective of this project was to develop a cost-effective membrane process that could be used in the relatively near-term tomore » capture CO{sub 2} from shifted syngas generated by a coal-fired Integrated Gasification Combined Cycle (IGCC) power plant. In this project, novel polymeric membranes (designated as Proteus™ membranes) with separation properties superior to conventional polymeric membranes were developed. Hydrogen permeance of up to 800 gpu and H{sub 2}/CO{sub 2} selectivity of >12 was achieved using a simulated syngas mixture at 150°C and 50 psig, which exceeds the original project targets of 200 gpu for hydrogen permeance and 10 for H{sub 2}/CO{sub 2} selectivity. Lab-scale Proteus membrane modules (with a membrane area of 0.13 m{sup 2}) were also developed using scaled-up Proteus membranes and high temperature stable module components identified during this project. A mixed-gas hydrogen permeance of about 160 gpu and H{sub 2}/CO{sub 2} selectivity of >12 was achieved using a simulated syngas mixture at 150°C and 100 psig. We believe that a significant improvement in the membrane and module performance is likely with additional development work. Both Proteus membranes and lab-scale Proteus membrane modules were further evaluated using coal-derived syngas streams at the National Carbon Capture Center (NCCC). The results indicate that all module components, including the Proteus membrane, were stable under the field conditions (feed pressures: 150-175 psig and feed temperatures: 120-135°C) for over 600 hours. The field performance of both Proteus membrane stamps and Proteus membrane modules is consistent with the results obtained in the lab, suggesting that the presence of sulfur-containing compounds (up to 780 ppm hydrogen sulfide), saturated water vapor, carbon monoxide and heavy hydrocarbons in the syngas feed stream has no adverse effect on the Proteus membrane or module performance. We also performed an economic analysis for a number of membrane process designs developed in this project (using hydrogen-selective membranes, alone or in the combination with CO{sub 2}- selective membranes). The current field performance for Proteus membranes was used in the design analysis. The study showed the current best design has the potential to reduce the increase in Levelized Cost of Electricity (LCOE) caused by 90% CO{sub 2} capture to about 15% if co-sequestration of H{sub 2}S is viable. This value is still higher than the DOE target for increase in LCOE (10%); however, compared to the base-case Selexol process that gives a 30% increase in LCOE at 90% CO2 capture, the membrane-based process appears promising. We believe future improvements in membrane performance have the potential to reach the DOE target.« less

Activation mechanism of erythrocyte cathepsin E. evidence for the occurrence of the membrane-associated active enzyme.

PubMed

Ueno, E; Sakai, H; Kato, Y; Yamamoto, K

1989-06-01

Activation of the erythrocyte cathepsin E located on the cytoplasmic surface of the membrane in a latent form was studied in stripped inside-out membrane vesicles prepared from human erythrocyte membranes. Incubation of the vesicles at 40 degrees C at pH 4 resulted in increased degradation of the membrane proteins, especially band 3. This proteolysis was selectively inhibited by the inclusion of pepstatin (isovaleryl-Val-Val-statyl-Ala-statine) or H 297 [Pro-Thr-Glu-Phe(CH2-NH)Nle-Arg-Leu] in the incubation mixtures, indicating that cathepsin E, as the only aspartic proteinase in erythrocytes, is responsible for the proteolysis. Two potential active-site-directed inhibitors of aspartic proteinases, pepstatin and H 297, were used to prove the occurrence of the membrane-associated active enzyme. To minimize potential errors arising from non-specific binding, the concentrations of the inhibitors used in the binding assay (pepstatin, 5 x 10(-8) M; H 297, 1 x 10(-5) M) were determined by calibration for purified and membrane-associated cathepsin E. The inhibition of the membrane-associated cathepsin E by each inhibitor, which showed the binding of the inhibitor to the activated enzyme, was temperature- and time-dependent. The binding of each inhibitor to the enzyme on the exposed surface of the membrane at pH 4 was highly specific, saturable, and reversible. The present study thus provides the first evidence that cathepsin E tightly bound to the membrane is converted to the active enzyme in the membrane-associated form, and suggests that this enzyme may be responsible for the degradation of band 3.

Cellulose Acetate Modified Titanium Dioxide (TiO2) Nanoparticles Electrospun Composite Membranes: Fabrication and Characterization

NASA Astrophysics Data System (ADS)

Das, Chandan; Gebru, Kibrom Alebel

2017-12-01

Hybrid membranes from Cellulose Acetate (CA) and titanium oxide (TiO2) nanoparticles were fabricated using electrospinning technique. The electrospun hybrid membranes were characterized using field emission scanning electron microscopy, high energy electrons of the energy dispersive X-ray spectroscopy, X-ray diffraction patterns, atomic force microscopy, zeta potential (ζ), and thermo gravimetric analysis. The impact of TiO2 contents on the electrospun membranes matrix was studied in detail. All these characterization results indicated that TiO2 were uniformly distributed within the CA electrospun membrane's matrix. The addition of TiO2 caused formation of largely interconnected fiber networks which in turn have a positive effect on the enhancement of the membrane pore structures. As the amount of TiO2 addition was raised from 0 to 6.5 wt%, the entanglements of the fibers and the spider-net like network among fibers were increased.

Performance evaluation of startup for a yeast membrane bioreactor (MBRy) treating landfill leachate.

PubMed

Amaral, Míriam C S; Gomes, Rosimeire F; Brasil, Yara L; Oliveira, Sílvia M A; Moravia, Wagner G

2017-12-06

The startup process of a membrane bioreactor inoculated with yeast biomass (Saccharomyces cerevisiae) and used in the treatment of landfill leachate was evaluated. The yeast membrane bioreactor (MBRy) was inoculated with an exogenous inoculum, a granulated active dry commercial bakers' yeast. The MBRy was successfully started up with a progressive increase in the landfill leachate percentage in the MBRy feed and the use of Sabouraud Dextrose Broth. The membrane plays an important role in the startup phase because of its full biomass retention and removal of organic matter. MBRy is a suitable and promising process to treat recalcitrant landfill leachate. After the acclimation period, the COD and NH 3 removal efficiency reached values of 72 ± 3% and 39 ± 2% respectively. MBRy shows a low membrane-fouling potential. The membrane fouling was influenced by soluble microbial products, extracellular polymeric substances, sludge particle size, and colloidal dissolved organic carbon.

Depolarization- and transmitter-induced changes in intracellular Ca2+ of rat cerebellar granule cells in explant cultures.

PubMed

Connor, J A; Tseng, H Y; Hockberger, P E

1987-05-01

Digital imaging of the Ca indicator fura-2 has been used to study the responses of developing granule cells in culture to depolarization and transmitter action. Unstimulated cells bathed in Krebs saline exhibited cytoplasmic Ca ion concentrations, [Ca2+], that were generally in the 30-60 nM range. Exposure of cells to high-potassium (25 mM) saline depolarized the membrane potential and produced an immediate rise in [Ca2+] that recovered within 2-3 min in normal saline. The response grew progressively larger over the first 20 d in culture. Transient increases in [Ca2+] to levels greater than 1 microM were observed after 12-14 d in vitro, at which time the cells displayed intense electrical activity when exposed to high K. At this stage, the increases were attenuated by blocking action potential activity with TTX. In TTX-treated or immature cells, in which the transient phase of the Ca change was relatively small, a second exposure to high K typically produced a much larger Ca response that the initial exposure. The duration of this facilitation of the response persisted for periods longer than 5 min. Application of the neurotransmitter GABA induced a transient increase in membrane conductance, with a reversal potential near resting potential (approx. -60 mV), and caused an intracellular Ca2+ increase that outlasted the exposure to GABA by several minutes. Glutamate, or kainate, induced an increase in membrane conductance but with a reversal potential more positive than spike threshold. These agents also elevated intracellular Ca2+, but unlike the case with GABA, this Ca response reversed rapidly upon removal of the transmitter. The facilitatory effect of repeated exposures to high-K saline, as well as the persistent Ca elevation following a brief GABA application, suggests that granule cells possess the capability of displaying activity-dependent changes in Ca levels in culture.

Laser Ablation Increases PEM/Catalyst Interfacial Area

NASA Technical Reports Server (NTRS)

Whitacre, Jay; Yalisove, Steve

2009-01-01

An investigational method of improving the performance of a fuel cell that contains a polymer-electrolyte membrane (PEM) is based on the concept of roughening the surface of the PEM, prior to deposition of a thin layer of catalyst, in order to increase the PEM/catalyst interfacial area and thereby increase the degree of utilization of the catalyst. The roughening is done by means of laser ablation under carefully controlled conditions. Next, the roughened membrane surface is coated with the thin layer of catalyst (which is typically platinum), then sandwiched between two electrode/catalyst structures to form a membrane/ele c t - rode assembly. The feasibility of the roughening technique was demonstrated in experiments in which proton-conducting membranes made of a perfluorosulfonic acid-based hydrophilic, protonconducting polymer were ablated by use of femtosecond laser pulses. It was found that when proper combinations of the pulse intensity, pulse-repetition rate, and number of repetitions was chosen, the initially flat, smooth membrane surfaces became roughened to such an extent as to be converted to networks of nodules interconnected by filaments (see Figure 1). In further experiments, electrochemical impedance spectroscopy (EIS) was performed on a pristine (smooth) membrane and on two laser-roughened membranes after the membranes were coated with platinum on both sides. Some preliminary EIS data were interpreted as showing that notwithstanding the potential for laser-induced damage, the bulk conductivities of the membranes were not diminished in the roughening process. Other preliminary EIS data (see Figure 2) were interpreted as signifying that the surface areas of the laser-roughened membranes were significantly greater than those of the smooth membrane. Moreover, elemental analyses showed that the sulfur-containing molecular groups necessary for proton conduction remained intact, even near the laser-roughened surfaces. These preliminary results can be taken as indications that laser-roughened PEMs should function well in fuel cells and, in particular, should exhibit current and power densities greater than those attainable by use of smooth membranes.

Model for the dynamic responses of taste receptor cells to salty stimuli. I. Function of lipid bilayer membranes.

PubMed Central

Naito, M; Fuchikami, N; Sasaki, N; Kambara, T

1991-01-01

The dynamic response of the lipid bilayer membrane is studied theoretically using a microscopic model of the membrane. The time courses of membrane potential variations due to monovalent salt stimulation are calculated explicitly under various conditions. A set of equations describing the time evolution of membrane surface potential and diffusion potential is derived and solved numerically. It is shown that a rather simple membrane such as lipid bilayer has functions capable of reproducing the following properties of dynamic response observed in gustatory receptor potential. Initial transient depolarization does not occur under Ringer adaptation but does under water. It appears only for comparatively rapid flows of stimuli, the peak height of transient response is expressed by a power function of the flow rate, and the membrane potential gradually decreases after reaching its peak under long and strong stimulation. The dynamic responses in the present model arise from the differences between the time dependences in the surface potential phi s and the diffusion potential phi d across a membrane. Under salt stimulation phi d cannot immediately follow the variation in phi s because of the delay due to the charging up of membrane capacitance. It is suggested that lipid bilayer in the apical membrane is the most probable agency producing the initial phasic response to the stimulation. PMID:1873461

Boric acid permeation in forward osmosis membrane processes: modeling, experiments, and implications.

PubMed

Jin, Xue; Tang, Chuyang Y; Gu, Yangshuo; She, Qianhong; Qi, Saren

2011-03-15

Forward osmosis (FO) is attracting increasing interest for its potential applications in desalination. In FO, permeation of contaminants from feed solution into draw solution through the semipermeable membrane can take place simultaneously with water diffusion. Understanding the contaminants transport through and rejection by FO membrane has significant technical implications in the way to separate clean water from the diluted draw solution. In this study, a model was developed to predict boron flux in FO operation. A strong agreement between modeling results and experimental data indicates that the model developed in this study can accurately predict the boron transport through FO membranes. Furthermore, the model can guide the fabrication of improved FO membranes with decreased boron permeability and structural parameter to minimize boron flux. Both theoretical model and experimental results demonstrated that when membrane active layer was facing draw solution, boron flux was substantially greater compared to the other membrane orientation due to more severe internal concentration polarization. In this investigation, for the first time, rejection of contaminants was defined in FO processes. This is critical to compare the membrane performance between different membranes and experimental conditions.

Effect of ubiquinone Q(10) and antioxidant vitamins on free radical oxidation of phospholipids in biological membranes of rat liver.

PubMed

Tikhaze, A K; Konovalova, G G; Lankin, V Z; Kaminnyi, A I; Kaminnaja, V I; Ruuge, E K; Kukharchuk, V V

2005-08-01

We studied the effects of 30-day peroral treatment with beta-carotene, a complex of antioxidant vitamins (vitamins C and E and provitamin A) and selenium, and solubilized ubiquinone Q(10) on the antioxidant potential in rat liver (ascorbate-dependent free radical oxidation of unsaturated membrane phospholipids). beta-Carotene irrespective of the administration route increased antioxidant potential of the liver by 2-3.5 times. The complex of antioxidant vitamins and selenium increased this parameter by more than 15 times. Antiradical activity in rat liver was extremely high after administration of solubilized ubiquinone Q(10) (increase by more than by 36 times). It can be expected that reduced ubiquinone Q(10) in vivo should produce a more pronounced protective effect due to activity of the system for bioregeneration of this natural antioxidant.

Spirulina platensis prevents high glucose-induced oxidative stress mitochondrial damage mediated apoptosis in cardiomyoblasts.

PubMed

Jadaun, Pratiksha; Yadav, Dhananjay; Bisen, Prakash Singh

2018-04-01

The current study was undertaken to study the effect of Spirulina platensis (Spirulina) extract on enhanced oxidative stress during high glucose induced cell death in H9c2 cells. H9c2 cultured under high glucose (33 mM) conditions resulted in a noteworthy increase in oxidative stress (free radical species) accompanied by loss of mitochondrial membrane potential, release of cytochrome c, increase in caspase activity and pro-apoptotic protein (Bax). Spirulina extract (1 μg/mL), considerably inhibited increased ROS and RNS levels, reduction in cytochrome c release, raise in mitochondrial membrane potential, decreased the over expression of proapoptotic protein Bax and suppressed the Bax/Bcl2 ratio with induced apoptosis without affecting cell viability. Overall results suggest that Spirulina extract plays preventing role against enhanced oxidative stress during high glucose induced apoptosis in cardiomyoblasts as well as related dysfunction in H9c2 cells.

Omega-3 PUFA concentration by a novel PVDF nano-composite membrane filled with nano-porous silica particles.

PubMed

Ghasemian, Samaneh; Sahari, Mohammad Ali; Barzegar, Mohsen; Ahmadi Gavlighi, Hasan

2017-09-01

In this study, polyvinylidene fluoride (PVDF) and nano-porous silica particle were used to fabricate an asymmetric nano-composite membrane. Silica particles enhanced the thermal stability of PVDF/SiO 2 membranes; increasing the decomposition temperature from 371°C to 408°C. Cross sectional morphology showed that silica particles were dispersed in polymer matrix uniformly. However, particle agglomeration was found at higher loading of silica (i.e., 20 by weight%). The separation performance of nano-composite membranes was also evaluated using the omega-3 polyunsaturated fatty acids (PUFA) concentration at a temperature and pressure of 30°C and 4bar, respectively. Silica particle increased the omega-3PUFA concentration from 34.8 by weight% in neat PVDF to 53.9 by weight% in PVDF with 15 by weight% of silica. Moreover, PVDF/SiO 2 nano-composite membranes exhibited enhanced anti-fouling property compared to neat PVDF membrane. Fouling mechanism analysis revealed that complete pore blocking was the predominant mechanism occurring in oil filtration. The concentration of omega-3 polyunsaturated fatty acids (PUFA) is important in the oil industries. While the current methods demand high energy consumptions in concentrating the omega-3, membrane separation technology offers noticeable advantages in producing pure omega-3 PUFA. Moreover, concentrating omega-3 via membrane separation produces products in the triacylglycerol form which possess better oxidative stability. In this work, the detailed mechanisms of fouling which limits the performance of membrane separation were investigated. Incorporating silica particles to polymeric membrane resulted in the formation of mixed matrix membrane with improved anti-fouling behaviour compared to the neat polymeric membrane. Hence, the industrial potential of membrane processing to concentrate omega-3 fatty acids is enhanced. Copyright © 2017. Published by Elsevier Ltd.

Iron-tannin-framework complex modified PES ultrafiltration membranes with enhanced filtration performance and fouling resistance.

PubMed

Fang, Xiaofeng; Li, Jiansheng; Li, Xin; Pan, Shunlong; Sun, Xiuyun; Shen, Jinyou; Han, Weiqing; Wang, Lianjun; Van der Bruggen, Bart

2017-11-01

In this work, an iron-tannin-framework (ITF) complex was introduced to a poly (ether sulfone) (PES) casting solution as a hydrophilic additive to fabricate ITF/PES ultrafiltration (UF) membranes via non-solvent-induced phase separation (NIPS). The structure and performance of the PES membranes with ITF concentrations ranging from 0 to 0.9wt.% were systematically investigated by scanning electron microscopy, water contact angle, permeability, protein rejection and fouling resistance measurements. The results indicate that the pore structure and surface properties of PES UF membranes can be regulated by incorporating the ITF complex. Compared with classical PES membranes, ITF/PES membranes were found to have an increased hydrophilicity and porosity and reduced surface pore size. Importantly, a simultaneous enhancement of permeability and separation performance was observed for the blend membranes, which indicates that the introduction of the ITF complex can break through the trade-off between permeability and selectivity of UF membranes.When the ITF content was 0.3wt.%, the permeability reached a maximum of 319.4(L/m 2 h) at 0.1MPa, which is 1.6 times higher than that of the classical PES membrane. Furthermore, the BSA rejection increased from 25.9% for the PES membrane to 95.9% for the enhanced membrane. In addition, the same membrane showed an improved fouling resistance (higher flux recovery and lower adhesion force) and stable hydrophilicity (unchanged after incubation in deionized water for 30days). The simple, green and cost-effective preparation process and the outstanding filtration performance highlight the potential of ITF/PES membranes for practical applications. Copyright © 2017 Elsevier Inc. All rights reserved.

Phenol separation from phenol-laden saline wastewater by membrane aromatic recovery system-like membrane contactor using superhydrophobic/organophilic electrospun PDMS/PMMA membrane.

PubMed

Ren, Long-Fei; Adeel, Mister; Li, Jun; Xu, Cong; Xu, Zheng; Zhang, Xiaofan; Shao, Jiahui; He, Yiliang

2018-05-15

Phenol recovery from phenol-laden saline wastewater plays an important role in the waste reclamation and pollution control. A membrane aromatic recovery system-like membrane contactor (MARS-like membrane contactor) was set up in this study using electrospun polydimethylsiloxane/polymethyl methacrylate (PDMS/PMMA) membrane with 0.0048 m 2 effective area to separate phenol from saline wastewater. Phenol and water contact angles of 0° and 162° were achieved on this membrane surface simultaneously, indicating its potential in the separation of phenol and water-soluble salt. Feed solution (500 mL) of 0.90 L/h and receiving solution (500 mL) of 1.26 L/h were investigated to be the optimum conditions for phenol separation, which corresponds to the employed Reynolds number of 14.6 and 20.5. During 108-h continuous separation for feed solution (2.0 g/L phenol, 10.0 g/L NaCl) under room temperature (20 °C), 42.6% of phenol was recycled in receiving solution with a salt rejection of 99.95%. Meanwhile, the mean phenol mass transfer coefficient (K ov ) was 6.7 × 10 -7  m s -1 . As a membrane-based process, though the permeated phenol increased with the increase of phenol concentration in feed solution, the phenol recovery ratio was determined by the membrane properties rather than the pollutant concentrations. Phenol was found to permeate this membrane via adsorption, diffusion and desorption, and therefore, the membrane fouling generated from pore blockage in other membrane separation processes was totally avoided. Copyright © 2018 Elsevier Ltd. All rights reserved.

Robust performance of a membrane bioreactor for removing antibiotic resistance genes exposed to antibiotics: Role of membrane foulants.

PubMed

Zhu, Yijing; Wang, Yayi; Zhou, Shuai; Jiang, Xuxin; Ma, Xiao; Liu, Chao

2018-03-01

Antibiotic resistance genes (ARGs) are an emerging concern in wastewater treatment plants (WWTPs), as dissemination of ARGs can pose a serious risk to human health. Few studies, however, have quantified ARGs in membrane bioreactors (MBRs), although MBRs have been widely used for both municipal and industrial wastewater treatment. To reveal the capacity of MBRs for removal of ARGs and the response of membrane fouling after antibiotic exposure, five typical ARG subtypes (sulI, sulII, tetC, tetX and ereA) and int1 were quantified affiliated by systematic membrane foulants analysis in a laboratory-scale anoxic/aerobic membrane bioreactor (A/O-MBR). Sulfamethoxazole and tetracycline hydrochloride additions increased ARG abundances by 0.5-1.4 orders of magnitude in the activated sludge, while the ARG removal performance of the membrane module remained stable (or even increased with ARG absolute abundance in several cases), with the abundance of removed ARGs ranging from 0.6 to 5.6 orders of magnitude. Specifically, the distribution of ARGs in membrane foulants accounted for 13%-25% of the total absolute abundance of all tested MBR samples. Indeed, substantial fouling occurred after the antibiotic additions, with the mean concentrations of soluble microbial product (SMP) and extracellular polymeric substance (EPS) increasing by 340% and 220%, respectively, in a membrane fouling cycle; moreover, the contents of EPS and SMP in the membrane foulants were significantly correlated with the ARG absolute abundance of membrane foulants (p < 0.05), among which more significant correlations occurred between both the protein and polysaccharide of foulants than that with humic acid. The dense membrane fouling layer and the membrane itself constituted dual barriers that effectively avoided the leakage of ARGs from the membrane module. Our findings provide fundamental insights into the proliferation and removal of ARGs in MBR systems, and highlight the contribution of membrane fouling to ARG removals in terms of the potential of MBR as an effective strategy to reduce ARG levels in WWTP effluent. Copyright © 2017 Elsevier Ltd. All rights reserved.

[Effect of trimebutine on cholinergic transmission in neurons of the inferior mesenteric ganglion of the rabbit].

PubMed

Julé, Y

1987-01-01

We analyzed the effects of trimebutine on the synaptic activity of neurons of the rabbit inferior mesenteric ganglion, using intracellular recording techniques. The synaptic activity was produced by subthreshold stimuli (0.5 Hz) applied individually, on lumbar splanchnic and lumbar colonic nerves. These stimuli triggered cholinergic responses corresponding to fast excitatory postsynaptic potentials. In 8 of 20 neurones tested trimebutine (10(-6) g/ml) produced an inhibition of excitatory postsynaptic potentials, without any change in the resting membrane potential. In 6 of 20 neurons tested, trimebutine produced, successively, an early facilitation followed by a late inhibition of excitatory postsynaptic potentials. Both effects occurred without change in the resting membrane potential. The inhibitory and facilitatory effects of trimebutine were accompanied, by an increase and a decrease in the number of failures of nerve stimulation respectively. These results indicate that inhibitory and facilitatory effects of trimebutine correspond respectively to a decrease and an increase in the amount of acetylcholine released from presynaptic nerve terminals originating from the spinal cord and the distal colon.

Osteoconductive Potential of Barrier NanoSiO2 PLGA Membranes Functionalized by Plasma Enhanced Chemical Vapour Deposition

PubMed Central

Terriza, Antonia; Vilches-Pérez, Jose I.; de la Orden, Emilio; Yubero, Francisco; Gonzalez-Caballero, Juan L.; González-Elipe, Agustin R.; Vilches, José; Salido, Mercedes

2014-01-01

The possibility of tailoring membrane surfaces with osteoconductive potential, in particular in biodegradable devices, to create modified biomaterials that stimulate osteoblast response should make them more suitable for clinical use, hopefully enhancing bone regeneration. Bioactive inorganic materials, such as silica, have been suggested to improve the bioactivity of synthetic biopolymers. An in vitro study on HOB human osteoblasts was performed to assess biocompatibility and bioactivity of SiO2 functionalized poly(lactide-co-glycolide) (PLGA) membranes, prior to clinical use. A 15 nm SiO2 layer was deposited by plasma enhanced chemical vapour deposition (PECVD), onto a resorbable PLGA membrane. Samples were characterized by X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, and infrared spectroscopy (FT-IR). HOB cells were seeded on sterilized test surfaces where cell morphology, spreading, actin cytoskeletal organization, and focal adhesion expression were assessed. As proved by the FT-IR analysis of samples, the deposition by PECVD of the SiO2 onto the PLGA membrane did not alter the composition and other characteristics of the organic membrane. A temporal and spatial reorganization of cytoskeleton and focal adhesions and morphological changes in response to SiO2 nanolayer were identified in our model. The novedous SiO2 deposition method is compatible with the standard sterilization protocols and reveals as a valuable tool to increase bioactivity of resorbable PLGA membranes. PMID:24883304

Hemocompatibility evaluation of poly(1,8-octanediol citrate) blend polyethersulfone membranes.

PubMed

Zailani, Muhamad Zulhilmi; Ismail, Ahmad Fauzi; Sheikh Abdul Kadir, Siti Hamimah; Othman, Mohd Hafiz Dzarfan; Goh, Pei Sean; Hasbullah, Hasrinah; Abdullah, Mohd Sohaimi; Ng, Be Cheer; Kamal, Fatmawati

2017-05-01

In this study, poly (1,8-octanediol citrate) (POC) was used to modify polyethersulfone (PES)-based membrane to enhance its hemocompatibility. Different compositions of POC (0-3%) were added into the polyethersulfone (PES) dope solutions and polyvinylpyrrolidone (PVP) was used as pore forming agent. The hemocompatible POC modified PES membranes were fabricated through phase-inversion technique. The prepared membranes were characterized using attenuated total reflectance-Fourier transform infrared (ATR-FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Atomic-force microscopy (AFM), contact angle, Zeta-potential, membrane porosity and pore size and pure water flux (PWF) and BSA rejection. The hemocompatibility of the modified PES membranes was evaluated by human serum fibrinogen (FBG) protein adsorption, platelet adhesion, activated partial thromboplastin time (APTT) and prothrombin time (PT), and thrombin-antithrombin III (TAT), complement (C3a and C5a) activation and Ca 2+ absorption on membrane. Results showed that by increasing POC concentration, FBG adsorption was reduced, less platelets adhesion, prolonged APTT and PT, lower TAT, C5a and C3a activation and absorb more Ca 2+ ion. These results indicated that modification of PES with POC has rendered improved hemocompatibility properties for potential application in the field of blood purification, especially in hemodialysis. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1510-1520, 2017. © 2017 Wiley Periodicals, Inc.

Analysis of the pressure-induced potential arising through composite membranes with selective surface layers.

PubMed

Szymczyk, Anthony; Sbaï, Mohammed; Fievet, Patrick

2005-03-01

When a pressure gradient is applied through a charged selective membrane, the transmembrane electrical potential difference, called the filtration potential, results from both the applied pressure and induced concentration difference across the membrane. In this work we investigate the electrokinetic properties relative to both active and support layers of a composite ceramic membrane close to the nanofiltration range. First, the volume charge density of the active layer is obtained by fitting a transport model to experimental rejection rates (which are controlled by the active layer only). Next, the value of the volume charge density is used to compute the theoretical filtration potential through the active layer. For sufficiently high permeate volume fluxes, the concentration difference across the active layer becomes constant, which allows assessing the membrane potential of the active layer. Experimental measurements of the overall filtration potential arising through the whole membrane are performed. The contribution of the support layer to this overall filtration potential is put in evidence. That implies that the membrane potential of the active layer cannot be deduced directly from the overall filtration potential measurements. Finally, the contribution of the support layer is singled out by subtracting the theoretical filtration potential of the active layer from the experimental filtration potential measured across the whole membrane (i.e., support + active layers). The amphoteric behavior of both layers is put in evidence, which is confirmed by electrophoretic measurements carried out with the powdered support layer and by recently reported tangential streaming potential measurements.

[Effect of glutamate on membrane potential and volume of the skeletal muscle fibers in rats following NO-synthase inhibition in vivo].

PubMed

Khairova, P A; Malomuzh, A I; Naumenko, N V; Urazaev, A Kh

2002-11-01

Cross-sectional area (CSA) of muscle fibers incubated in culture medium 199 for 3 hours dramatically increases, whereas resting membrane potential (RMP) decreases compared to "freshly-isolated" muscles. Both glutamate and sodium nitroprusside prevent these changes. MK-801, a specific inhibitor of NMDA-receptors, eliminates protective effects of glutamate on both CSA and RMP. NO-synthase inhibition in vivo promotes an increase of initial CSA and decrease of mean RMP. Under these conditions, effects of glutamate and sodium nitroprusside on CSA and RMP of denervated muscles are less obvious. It has been concluded that synaptic glutamate is able to participate in regulation of RMP and cell volume in muscle fibers through the activation of postsynaptic NMDA-receptors and muscle NO-synthase.

Selective Antimicrobial Activities and Action Mechanism of Micelles Self-Assembled by Cationic Oligomeric Surfactants.

PubMed

Zhou, Chengcheng; Wang, Fengyan; Chen, Hui; Li, Meng; Qiao, Fulin; Liu, Zhang; Hou, Yanbo; Wu, Chunxian; Fan, Yaxun; Liu, Libing; Wang, Shu; Wang, Yilin

2016-02-17

This work reports that cationic micelles formed by cationic trimeric, tetrameric, and hexameric surfactants bearing amide moieties in spacers can efficiently kill Gram-negative E. coli with a very low minimum inhibitory concentration (1.70-0.93 μM), and do not cause obvious toxicity to mammalian cells at the concentrations used. With the increase of the oligomerization degree, the antibacterial activity of the oligomeric surfactants increases, i.e., hexameric surfactant > tetrameric surfactant > trimeric surfactant. Isothermal titration microcalorimetry, scanning electron microscopy, and zeta potential results reveal that the cationic micelles interact with the cell membrane of E. coli through two processes. First, the integrity of outer membrane of E. coli is disrupted by the electrostatic interaction of the cationic ammonium groups of the surfactants with anionic groups of E. coli, resulting in loss of the barrier function of the outer membrane. The inner membrane then is disintegrated by the hydrophobic interaction of the surfactant hydrocarbon chains with the hydrophobic domains of the inner membrane, leading to the cytoplast leakage. The formation of micelles of these cationic oligomeric surfactants at very low concentration enables more efficient interaction with bacterial cell membrane, which endows the oligomeric surfactants with high antibacterial activity.

Estriol improves membrane fluidity of erythrocytes by the nitric oxide-dependent mechanism: an electron paramagnetic resonance study.

PubMed

Tsuda, K; Shimamoto, Y; Kimura, K; Nishio, I; Masuyama, Y

2001-05-01

The present in vitro study was performed to investigate the effects of estriol (E3) on membrane fluidity of erythrocytes by means of an electron paramagnetic resonance (EPR) and spin-labeling method. E3 was shown to significantly decrease the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (ho/h-1) for 16-NS obtained from EPR spectra of erythrocyte membranes. This finding indicated that E3 might increase the membrane fluidity of erythrocytes. The effect of E3 was significantly potentiated by the nitric oxide (NO) donor, S-nitroso-N-acetylpenicillamine (SNAP), and a cyclic guanosine 3',5'-monophosphate (cGMP) analog, 8-bromo-cGMP. In contrast, the change in the membrane fluidity induced by E3 was antagonized by the NO synthase inhibitor, L-NG-nitroarginine-methyl-ester (L-NAME), and asymmetric dimethyl-L-arginine (ADMA). The results of the present study showed that E3 significantly increased the membrane fluidity and improved the microviscosity of erythrocyte membranes, partially mediated by an NO- and cGMP-dependent pathway. Furthermore, the data might be consistent with the hypothesis that E3 could have a beneficial effect on the rheological behavior of erythrocytes and may play a crucial role in the regulation of microcirculation.

Continuous enzymatic hydrolysis of lignocellulosic biomass in a membrane-reactor system: Continuous enzymatic hydrolysis of lignocellulosic biomass in a membrane-reactor system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stickel, Jonathan J.; Adhikari, Birendra; Sievers, David A.

Converting abundant lignocellulosic biomass to sugars as fungible precursors to fuels and chemicals has the potential to diversify the supply chain for those products, but further process improvements are needed to achieve economic viability. In the current work, process intensification of the key enzymatic hydrolysis unit operation is demonstrated by means of a membrane reactor system that was operated continuously. Lignocellulosic biomass (pretreated corn stover) and buffered enzyme solution were fed to a continuously stirred-tank reactor, and clarified sugar solution was withdrawn via a commercial tubular ultrafiltration membrane. The membrane permeance decline and membrane cleaning efficacy were studied and didmore » not vary significantly when increasing fraction insoluble solids (FIS) from 2.5% to 5%. Continuous enzymatic hydrolysis was successfully operated for more than 80 h. A model for the reactor system was able to predict dynamic behavior that was in reasonable agreement with experimental results. The modeled technical performance of anticipated commercial batch and continuous enzymatic hydrolysis processes were compared and showed that continuous operation would provide at least twice the volumetric productivity for the conditions studied. Further improvements are anticipated by better membrane selection and by increasing FIS.« less

Continuous enzymatic hydrolysis of lignocellulosic biomass in a membrane-reactor system: Continuous enzymatic hydrolysis of lignocellulosic biomass in a membrane-reactor system

DOE PAGES

Stickel, Jonathan J.; Adhikari, Birendra; Sievers, David A.; ...

2018-02-21

Converting abundant lignocellulosic biomass to sugars as fungible precursors to fuels and chemicals has the potential to diversify the supply chain for those products, but further process improvements are needed to achieve economic viability. In the current work, process intensification of the key enzymatic hydrolysis unit operation is demonstrated by means of a membrane reactor system that was operated continuously. Lignocellulosic biomass (pretreated corn stover) and buffered enzyme solution were fed to a continuously stirred-tank reactor, and clarified sugar solution was withdrawn via a commercial tubular ultrafiltration membrane. The membrane permeance decline and membrane cleaning efficacy were studied and didmore » not vary significantly when increasing fraction insoluble solids (FIS) from 2.5% to 5%. Continuous enzymatic hydrolysis was successfully operated for more than 80 h. A model for the reactor system was able to predict dynamic behavior that was in reasonable agreement with experimental results. The modeled technical performance of anticipated commercial batch and continuous enzymatic hydrolysis processes were compared and showed that continuous operation would provide at least twice the volumetric productivity for the conditions studied. Further improvements are anticipated by better membrane selection and by increasing FIS.« less

The Rcs-Regulated Colanic Acid Capsule Maintains Membrane Potential in Salmonella enterica serovar Typhimurium

PubMed Central

Pando, Jasmine M.; Karlinsey, Joyce E.; Lara, Jimmie C.; Libby, Stephen J.

2017-01-01

ABSTRACT The Rcs phosphorelay and Psp (phage shock protein) systems are envelope stress responses that are highly conserved in gammaproteobacteria. The Rcs regulon was found to be strongly induced during metal deprivation of Salmonella enterica serovar Typhimurium lacking the Psp response. Nineteen genes activated by the RcsA-RcsB response regulator make up an operon responsible for the production of colanic acid capsular polysaccharide, which promotes biofilm development. Despite more than half a century of research, the physiological function of colanic acid has remained elusive. Here we show that Rcs-dependent colanic acid production maintains the transmembrane electrical potential and proton motive force in cooperation with the Psp response. Production of negatively charged exopolysaccharide covalently bound to the outer membrane may enhance the surface potential by increasing the local proton concentration. This provides a unifying mechanism to account for diverse Rcs/colanic acid-related phenotypes, including susceptibility to membrane-damaging agents and biofilm formation. PMID:28588134

Distinct pH regulation of slow and rapid anion channels at the plasma membrane of Arabidopsis thaliana hypocotyl cells.

PubMed

Colcombet, Jean; Lelièvre, Françoise; Thomine, Sébastien; Barbier-Brygoo, Hélène; Frachisse, Jean-Marie

2005-07-01

Variations in both intracellular and extracellular pH are known to be involved in a wealth of physiological responses. Using the patch-clamp technique on Arabidopsis hypocotyl cells, it is shown that rapid-type and slow-type anion channels at the plasma membrane are both regulated by pH via distinct mechanisms. Modifications of pH modulate the voltage-dependent gating of the rapid channel. While intracellular alkalinization facilitates channel activation by shifting the voltage gate towards negative potentials, extracellular alkalinization shifts the activation threshold to more positive potentials, away from physiological resting membrane potentials. By contrast, pH modulates slow anion channel activity in a voltage-independent manner. Intracellular acidification and extracellular alkalinization increase slow anion channel currents. The possible role of these distinct modulations in physiological processes involving anion efflux and modulation of extracellular and/or intracellular pH, such as elicitor and ABA signalling, are discussed.

Voltage-gated sodium channel expression and action potential generation in differentiated NG108-15 cells.

PubMed

Liu, Jinxu; Tu, Huiyin; Zhang, Dongze; Zheng, Hong; Li, Yu-Long

2012-10-25

The generation of action potential is required for stimulus-evoked neurotransmitter release in most neurons. Although various voltage-gated ion channels are involved in action potential production, the initiation of the action potential is mainly mediated by voltage-gated Na+ channels. In the present study, differentiation-induced changes of mRNA and protein expression of Na+ channels, Na+ currents, and cell membrane excitability were investigated in NG108-15 cells. Whole-cell patch-clamp results showed that differentiation (9 days) didn't change cell membrane excitability, compared to undifferentiated state. But differentiation (21 days) induced the action potential generation in 45.5% of NG108-15 cells (25/55 cells). In 9-day-differentiated cells, Na+ currents were mildly increased, which was also found in 21-day differentiated cells without action potential. In 21-day differentiated cells with action potential, Na+ currents were significantly enhanced. Western blot data showed that the expression of Na+ channels was increased with differentiated-time dependent manner. Single-cell real-time PCR data demonstrated that the expression of Na+ channel mRNA was increased by 21 days of differentiation in NG108-15 cells. More importantly, the mRNA level of Na+ channels in cells with action potential was higher than that in cells without action potential. Differentiation induces expression of voltage-gated Na+ channels and action potential generation in NG108-15 cells. A high level of the Na+ channel density is required for differentiation-triggered action potential generation.

STRETCH-DEPENDENT SENSITIZATION OF POST-JUNCTIONAL NEURAL EFFECTORS IN COLONIC MUSCLES

PubMed Central

Won, Kyung-Jong; Sanders, Kenton M.; Ward, Sean M.

2012-01-01

Background The colon undergoes distension-induced changes in motor activity as luminal contents or feces increases wall pressure. Input from enteric motor neurons regulates motility. Here we examined stretch-dependent responses in circular muscle strips of murine colon. Methods Length-ramps (6–31μm s−1) were applied in the axis of the circular muscle layer in a controlled manner until 5 mN isometric force was reached. Key Results Length-ramps produced transient membrane potential hyperpolarizations and attenuation of action potential (AP) complexes. Responses were reproducible when ramps were applied every 30s. Stretch-dependent hyperpolarization was blocked by TTX, suggesting AP-dependent release of inhibitory neurotransmitter(s). Atropine did not potentiate stretch-induced hyperpolarizations, but increased compliance of the circular layer. L-NNA inhibited stretch-dependent hyperpolarization and decreased muscle compliance, suggesting release of NO mediates stretch-dependent inhibition. Control membrane potential was restored by the NO donor SNP. Stretch-dependent hyperpolarizations were blocked by L-methionine, an inhibitor of stretch-dependent K+ (SDK) channels in colonic muscles. Loss of ICC, elicited by Kit neutralizing antibody, also inhibited responses to stretch. In presence of L-NNA and apamin, stretch responses became excitatory and were characterized by membrane depolarization and increased AP firing. A neurokinin-1 receptor antagonist inhibited this stretch-dependent increase in excitability. Conclusions & Inferences Our data show that stretch-dependent responses in colonic muscles require tonic firing of enteric inhibitory neurons, but reflex activation of neurons does not appear to be necessary. NO causes activation of SDK channels, and stretch of muscles further activates these channels, explaining the inhibitory response to stretch in colonic muscle strips. PMID:23279087

The comprehensive electrophysiological study of curcuminoids on delayed-rectifier K+ currents in insulin-secreting cells.

PubMed

Kuo, Ping-Chung; Yang, Chia-Jung; Lee, Yu-Chi; Chen, Pei-Chun; Liu, Yen-Chin; Wu, Sheng-Nan

2018-01-15

Curcumin (CUR) has been demonstrated to induce insulin release from pancreatic β-cells; however, how curcuminoids (including demethoxycurcumin (DMC) and bisdemethoxycurcumin (BDMC)) exert any possible effects on membrane ion currents inherently in insulin-secreting cells remains largely unclear. The effects of CUR and other structurally similar curcuminoids on ion currents in rat insulin-secreting (INS-1) insulinoma cells were therefore investigated in this study. The effects of these compounds on ionic currents and membrane potential were studied by patch-clamp technique. CUR suppressed the amplitude of delayed-rectifier K + current (I K(DR) ) in a time-, state- and concentration-dependent manner in these cells and the inhibition was not reversed by diazoxide, nicorandil or chlorotoxin. The value of dissociation constant for CUR-induced suppression of I K(DR) in INS-1 cells was 1.26μM. Despite the inability of CUR to alter the activation rate of I K(DR) , it accelerated current inactivation elicited by membrane depolarization. Increasing CUR concentrations shifted the inactivation curve of I K(DR) to hyperpolarized potential and slowed the recovery of I K(DR) inactivation. CUR, DMC, and BDMC all exerted depressant actions on I K(DR) amplitude to a similar magnitude, although DMC and BDMC did not increase current inactivation clearly. CUR slightly suppressed the peak amplitude of voltage-gated Na + current. CUR, DMC and BDMC depolarized the resting potential and increased firing frequency of action potentials. The CUR-mediated decrease of I K(DR) and the increase of current inactivation also occurred in βTC-6 INS-1 cells. Taken these results together, these effects may be one of the possible mechanisms contributing their insulin-releasing effect. Copyright © 2017 Elsevier B.V. All rights reserved.

Membrane potential and human erythrocyte shape.

PubMed Central

Gedde, M M; Huestis, W H

1997-01-01

Altered external pH transforms human erythrocytes from discocytes to stomatocytes (low pH) or echinocytes (high pH). The process is fast and reversible at room temperature, so it seems to involve shifts in weak inter- or intramolecular bonds. This shape change has been reported to depend on changes in membrane potential, but control experiments excluding roles for other simultaneously varying cell properties (cell pH, cell water, and cell chloride concentration) were not reported. The present study examined the effect of independent variation of membrane potential on red cell shape. Red cells were equilibrated in a set of solutions with graduated chloride concentrations, producing in them a wide range of membrane potentials at normal cell pH and cell water. By using assays that were rapid and accurate, cell pH, cell water, cell chloride, and membrane potential were measured in each sample. Cells remained discoid over the entire range of membrane potentials examined (-45 to +45 mV). It was concluded that membrane potential has no independent effect on red cell shape and does not mediate the membrane curvature changes known to occur in red cells equilibrated at altered pH. Images FIGURE 2 FIGURE 9 PMID:9138568

Fabrication and application of coaxial polyvinyl alcohol/chitosan nanofiber membranes

NASA Astrophysics Data System (ADS)

Kuo, Ting-Yun; Jhang, Cuei-Fang; Lin, Che-Min; Hsien, Tzu-Yang; Hsieh, Hsyue-Jen

2017-12-01

It is difficult to fabricate chitosan-wrapped coaxial nanofibers, because highly viscous chitosan solutions might hinder the manufacturing process. To overcome this difficulty, our newly developed method, which included the addition of a small amount of gum arabic, was utilized to prepare much less viscous chitosan solutions. In this way, coaxial polyvinyl alcohol (PVA)/chitosan (as core/shell) nanofiber membranes were fabricated successfully by coaxial electrospinning. The core/shell structures were confirmed by TEM, and the existence of PVA and chitosan was also verified using FT-IR and TGA. The tensile strength of the nanofiber membranes was increased from 0.6-0.7 MPa to 0.8-0.9 MPa after being crosslinked with glutaraldehyde. The application potential of the PVA/chitosan nanofiber membranes was tested in drug release experiments by loading the core (PVA) with theophylline as a model drug. The use of the coaxial PVA/chitosan nanofiber membranes in drug release extended the release time of theophylline from 5 minutes to 24 hours. Further, the release mechanisms could be described by the Korsmeyer-Peppas model. In summary, by combining the advantages of PVA and chitosan (good mechanical strength and good biocompatibility respectively), the coaxial PVA/chitosan nanofiber membranes are potential biomaterials for various biomedical applications.

Simulation of flux during electro-membrane extraction based on the Nernst-Planck equation.

PubMed

Gjelstad, Astrid; Rasmussen, Knut Einar; Pedersen-Bjergaard, Stig

2007-12-07

The present work has for the first time described and verified a theoretical model of the analytical extraction process electro-membrane extraction (EME), where target analytes are extracted from an aqueous sample, through a thin layer of 2-nitrophenyl octylether immobilized as a supported liquid membrane (SLM) in the pores in the wall of a porous hollow fibre, and into an acceptor solution present inside the lumen of the hollow fibre by the application of an electrical potential difference. The mathematical model was based on the Nernst-Planck equation, and described the flux over the SLM. The model demonstrated that the magnitude of the electrical potential difference, the ion balance of the system, and the absolute temperature influenced the flux of analyte across the SLM. These conclusions were verified by experimental data with five basic drugs. The flux was strongly dependent of the potential difference over the SLM, and increased potential difference resulted in an increase in the flux. The ion balance, defined as the sum of ions in the donor solution divided by the sum of ions in the acceptor solution, was shown to influence the flux, and high ionic concentration in the acceptor solution relative to the sample solution was advantageous for high flux. Different temperatures also led to changes in the flux in the EME system.

Phospholipid Nonwoven Electrospun Membranes

NASA Astrophysics Data System (ADS)

McKee, Matthew G.; Layman, John M.; Cashion, Matthew P.; Long, Timothy E.

2006-01-01

Nonwoven fibrous membranes were formed from electrospinning lecithin solutions in a single processing step. As the concentration of lecithin increased, the micellar morphology evolved from spherical to cylindrical, and at higher concentrations the cylindrical micelles overlapped and entangled in a fashion similar to polymers in semi-dilute or concentrated solutions. At concentrations above the onset of entanglements of the wormlike micelles, electrospun fibers were fabricated with diameters on the order of 1 to 5 micrometers. The electrospun phospholipid fibers offer the potential for direct fabrication of biologically based, high-surface-area membranes without the use of multiple synthetic steps, complicated electrospinning designs, or postprocessing surface treatments.

Contribution of assimilable organic carbon to biological fouling in seawater reverse osmosis membrane treatment.

PubMed

Weinrich, Lauren; LeChevallier, Mark; Haas, Charles N

2016-09-15

Biological fouling occurs on RO membranes when bacteria and nutrients are present in conditions that are conducive to growth and proliferation of the bacteria. Controlling microbial growth on the membranes is typically limited to biocide application (i.e., disinfectants) in seawater RO plants. However, biological growth and subsequent fouling has not been well-managed. Pretreatment has not been focused on nutrient limitation. This project used a biological assay, the assimilable organic carbon (AOC) test to evaluate pretreatment effects on the nutrient supply. The AOC test provided a useful surrogate measurement for the biodegradability or biofouling potential of RO feed water. Biofouling observed in controlled conditions at the bench- and pilot-scale resulted in statistically significant correlations between AOC and the operational effects caused by biofouling. Membrane fouling rates are observed through operational changes over time such as increased differential pressure between the membrane feed and concentrate locations and decreased permeate flux through the membrane. In full scale plants there were strong correlations when AOC was used as a predictor variable for increased differential pressure (0.28-0.55 bar from September-December 2012) and decreased specific flux (1.40 L per hour/(m(2) · bar)). Increased differential pressure was associated with RO membrane biological fouling when the median AOC was 50 μg/L during pilot testing. Conditions were also evaluated at the bench-scale using a flat sheet RO membrane. In a comparison test using 30 and 1000 μg/L AOC, fouling was detected on more portions of the membrane when AOC was higher. Biofilm and bacterial deposits were apparent from scanning electron microscope imaging and biomass measurements using ATP. Copyright © 2016 Elsevier Ltd. All rights reserved.

Synergistic effect of fisetin combined with sorafenib in human cervical cancer HeLa cells through activation of death receptor-5 mediated caspase-8/caspase-3 and the mitochondria-dependent apoptotic pathway.

PubMed

Lin, Ming-Te; Lin, Chia-Liang; Lin, Tzu-Yu; Cheng, Chun-Wen; Yang, Shun-Fa; Lin, Chu-Liang; Wu, Chih-Chien; Hsieh, Yi-Hsien; Tsai, Jen-Pi

2016-05-01

Combining antitumor agents with bioactive compounds is a potential strategy for improving the effect of chemotherapy on cancer cells. The goal of this study was to elucidate the antitumor effect of the flavonoid, fisetin, combined with the multikinase inhibitor, sorafenib, against human cervical cancer cells in vitro and in vivo. The combination of fisetin and sorafenib synergistically induced apoptosis in HeLa cells, which is accompanied by a marked increase in loss of mitochondrial membrane potential. Apoptosis induction was achieved by caspase-3 and caspase-8 activation which increased the ratio of Bax/Bcl-2 and caused the subsequent cleavage of PARP level while disrupting the mitochondrial membrane potential in HeLa cells. Decreased Bax/Bcl-2 ratio level and mitochondrial membrane potential were also observed in siDR5-treated HeLa cells. In addition, in vivo studies revealed that the combined fisetin and sorafenib treatment was clearly superior to sorafenib treatment alone using a HeLa xenograft model. Our study showed that the combination of fisetin and sorafenib exerted better synergistic effects in vitro and in vivo than either agent used alone against human cervical cancer, and this synergism was based on apoptotic potential through a mitochondrial- and DR5-dependent caspase-8/caspase-3 signaling pathway. This combined fisetin and sorafenib treatment represents a novel therapeutic strategy for further clinical developments in advanced cervical cancer.

The timing of cortical granule fusion, content dispersal, and endocytosis during fertilization of the hamster egg: an electrophysiological and histochemical study.

PubMed

Kline, D; Stewart-Savage, J

1994-03-01

To determine the temporal relationship between cortical granule exocytosis and the repetitive calcium transients, which are characteristic of mammalian fertilization, we monitored membrane addition from exocytosis during fertilization of hamster eggs. Continuous measurement of membrane capacitance by applying a 3.1-nA alternating current at 375 Hz showed addition of cortical granule membrane. Simultaneous measurement of membrane potential revealed each calcium transient by the appearance of transient hyperpolarizing responses due to calcium-activated potassium channels in the egg. The initial membrane capacitance of the eggs averaged 736 +/- 44 pF (mean +/- SD; n = 7) and an increase in capacitance of 61 +/- 19 pF occurred within 4 sec of the start of the first hyperpolarizing response (HR) after fertilization. Immediately after the first increase in capacitance there was a gradual decline in membrane capacitance in all eggs and in five/seven eggs the capacitance returned to the unfertilized level in 7.8 +/- 4.4 min. The gradual decline in capacitance after the first increase indicated endocytosis, which was confirmed by the internalization of fluorescently labeled dextran. Superimposed on the gradual decline in membrane capacitance were smaller increases in capacitance that occurred with the second and later HRs. The total increase in capacitance from the first three events averaged 72 +/- 19 pF, representing an average increase in capacitance of about 10% of the capacitance of the unfertilized egg. By labeling eggs before and after permeabilization with two different fluorochromes attached to Lens culinaris agglutinin, we demonstrate that the dispersal of the cortical granules contents does not occur immediately after exocytosis. Our results demonstrate that cortical granule exocytosis in hamster eggs is closely coupled to the periodic increases in calcium, that the contents of the cortical granules are slow to disperse, and that after exocytosis, the surface area of the egg returns to the unfertilized level because of a period of endocytosis.

Impact of higher alginate expression on deposition of Pseudomonas aeruginosa in radial stagnation point flow and reverse osmosis systems.

PubMed

Herzberg, Moshe; Rezene, Tesfalem Zere; Ziemba, Christopher; Gillor, Osnat; Mathee, Kalai

2009-10-01

Extracellular polymeric substances (EPS) have major impact on biofouling of reverse osmosis (RO) membranes. On one hand, EPS can reduce membrane permeability and on the other, EPS production by the primary colonizers may influence their deposition and attachment rate and subsequently affect the biofouling propensity of the membrane. The role of bacterial exopolysaccharides in bacterial deposition followed by the biofouling potential of an RO membrane was evaluated using an alginate overproducing (mucoid) Pseudomonas aeruginosa. The mucoid P. aeruginosa PAOmucA22 was compared with its isogenic nonmucoid prototypic parent PAO1 microscopically in a radial stagnation point flow (RSPF) system for their bacterial deposition characteristics. Then, biofouling potential of PAO1 and PAOmucA22 was determined in a crossflow rectangular plate-and-frame membrane cell, in which the strains were cultivated on a thin-film composite, polyamide, flat RO membrane coupon (LFC-1) under laminar flow conditions. In the RSPF system, the observed deposition rate of the mucoid strain was between 5- and 10-fold lower than of the wild type using either synthetic wastewater medium (with ionic strength of 14.7 mM and pH 7.4) or 15 mM KCl solution (pH of 6.2). The slower deposition rate of the mucoid strain is explained by 5- to 25-fold increased hydrophilicity of the mucoid strain as compared to the isogenic wild type, PAO1. Corroborating with these results, a significant delay in the onset of biofouling of the RO membrane was observed when the mucoid strain was used as the membrane colonizer, in which the observed time for the induced permeate flux decline was delayed (ca. 2-fold). In conclusion, the lower initial cell attachment of the mucoid strain decelerated biofouling of the RO membrane. Bacterial deposition and attachment is a critical step in biofilm formation and governed by intimate interactions between outer membrane proteins of the bacteria and the surface. Shielding these interactions by a hydrated and hydrophilic alginate capsule is shown to dramatically lessen the biofouling potential of the membrane colonizers.

Do Membranes Dream of Electric Tubes? Advanced Membranes Using Carbon Nanotube - Polymer Nanocomposites

NASA Astrophysics Data System (ADS)

de Lannoy, Charles-Francois Pedro Claude Karolek Ghislain

Membrane technologies represent an energy efficient, effective solution for treating municipal and commercial waters/wastewaters. Membranes are predominantly polymer-based and despite steady advances in polymeric materials, they continue to suffer from operational problems including biofouling and breakages. This work addresses these two disparate problems by developing novel CNT-polymer nanocomposite materials that contain variously functionalized carbon nanotubes (fCNTs) in low quantities (<0.5wt%). Several strategies have been employed to achieve highly functional CNT-polymer nanocomposite membranes including blend mixing, ionic charge association, and covalent cross-linking with monomer and oligomer constituents. These CNT-polymer nanocomposite membranes were compared to traditional polymer membranes across various properties including increased Young's Modulus, changes in surface hydrophilicity, fine control over molecular weight cut-off and flux, and surface electrical conductivity. Membranes with high surface electrical conductivity were further tested for their anti-biofouling properties. Finally, CNT stability and polymer compatibility were evaluated throughout membrane manufacture, use, and cleaning. The incorporation of CNTs mixed in bulk phase and linked through ionic associations in polymer matrices showed significant (50%) increases in Young's modulus for certain CNT functionalizations and derivatization percent. Membranes formed with high surface electrical conductivity demonstrated almost complete resistance to biofouling (> 95%) in long-term bacterially challenged experiments. CNTs and polymer mixtures that lacked covalent or ionic bonds were susceptible to significant (up to 10%) loss of CNTs during membrane non-solvent gelation and aggressive chemical cleaning treatment. Functionalized carbon nanotubes endow polymer membranes with their unique strength and electrically conductive properties. These added properties were demonstrated to greatly improve membrane operational efficiency and membrane longevity. CNT-polymer nanocomposite membranes offer low-energy, high-efficiency, and long-lifetime alternatives to traditional polymer membranes. With further advances in polymeric nanomaterials, membrane technology has the potential for wide applicability across many fields outside of water filtration and desalination.

Curvature Forces in Membrane Lipid-Protein Interactions

PubMed Central

Brown, Michael F.

2012-01-01

Membrane biochemists are becoming increasingly aware of the role of lipid-protein interactions in diverse cellular functions. This review describes how conformational changes of membrane proteins—involving folding, stability, and membrane shape transitions—potentially involve elastic remodeling of the lipid bilayer. Evidence suggests that membrane lipids affect proteins through interactions of a relatively long-range nature, extending beyond a single annulus of next-neighbor boundary lipids. It is assumed the distance scale of the forces is large compared to the molecular range of action. Application of the theory of elasticity to flexible soft surfaces derives from classical physics, and explains the polymorphism of both detergents and membrane phospholipids. A flexible surface model (FSM) describes the balance of curvature and hydrophobic forces in lipid-protein interactions. Chemically nonspecific properties of the lipid bilayer modulate the conformational energetics of membrane proteins. The new biomembrane model challenges the standard model (the fluid mosaic model) found in biochemistry texts. The idea of a curvature force field based on data first introduced for rhodopsin gives a bridge between theory and experiment. Influences of bilayer thickness, nonlamellar-forming lipids, detergents, and osmotic stress are all explained by the FSM. An increased awareness of curvature forces suggests that research will accelerate as structural biology becomes more closely entwined with the physical chemistry of lipids in explaining membrane structure and function. PMID:23163284

Altered Escherichia coli membrane protein assembly machinery allows proper membrane assembly of eukaryotic protein vitamin K epoxide reductase.

PubMed

Hatahet, Feras; Blazyk, Jessica L; Martineau, Eugenie; Mandela, Eric; Zhao, Yongxin; Campbell, Robert E; Beckwith, Jonathan; Boyd, Dana

2015-12-08

Functional overexpression of polytopic membrane proteins, particularly when in a foreign host, is often a challenging task. Factors that negatively affect such processes are poorly understood. Using the mammalian membrane protein vitamin K epoxide reductase (VKORc1) as a reporter, we describe a genetic selection approach allowing the isolation of Escherichia coli mutants capable of functionally expressing this blood-coagulation enzyme. The isolated mutants map to components of membrane protein assembly and quality control proteins YidC and HslV. We show that changes in the VKORc1 sequence and in the YidC hydrophilic groove along with the inactivation of HslV promote VKORc1 activity and dramatically increase its expression level. We hypothesize that such changes correct for mismatches in the membrane topogenic signals between E. coli and eukaryotic cells guiding proper membrane integration. Furthermore, the obtained mutants allow the study of VKORc1 reaction mechanisms, inhibition by warfarin, and the high-throughput screening for potential anticoagulants.

Altered Escherichia coli membrane protein assembly machinery allows proper membrane assembly of eukaryotic protein vitamin K epoxide reductase

PubMed Central

Hatahet, Feras; Blazyk, Jessica L.; Martineau, Eugenie; Mandela, Eric; Zhao, Yongxin; Campbell, Robert E.; Beckwith, Jonathan; Boyd, Dana

2015-01-01

Functional overexpression of polytopic membrane proteins, particularly when in a foreign host, is often a challenging task. Factors that negatively affect such processes are poorly understood. Using the mammalian membrane protein vitamin K epoxide reductase (VKORc1) as a reporter, we describe a genetic selection approach allowing the isolation of Escherichia coli mutants capable of functionally expressing this blood-coagulation enzyme. The isolated mutants map to components of membrane protein assembly and quality control proteins YidC and HslV. We show that changes in the VKORc1 sequence and in the YidC hydrophilic groove along with the inactivation of HslV promote VKORc1 activity and dramatically increase its expression level. We hypothesize that such changes correct for mismatches in the membrane topogenic signals between E. coli and eukaryotic cells guiding proper membrane integration. Furthermore, the obtained mutants allow the study of VKORc1 reaction mechanisms, inhibition by warfarin, and the high-throughput screening for potential anticoagulants. PMID:26598701

The effects of surface-charged submicron polystyrene particles on the structure and performance of PSF forward osmosis membrane

NASA Astrophysics Data System (ADS)

Zuo, Hao-Ran; Fu, Jia-Bei; Cao, Gui-Ping; Hu, Nian; Lu, Hui; Liu, Hui-Qing; Chen, Peng-Peng; Yu, Jie

2018-04-01

Monodisperse surface-charged submicron polystyrene particles were designed, synthesized, and blended into polysulfone (PSF) support layer to prepare forward osmosis (FO) membrane with high performance. The membrane incorporated with particles were characterized with respect to morphology, porosity, and internal osmotic pressure (IOP). Results showed that the polymer particles not only increased the hydrophilicity and porosity of support layer, but also generated considerable IOP, which helped markedly decreasing the structure parameter from 1550 to 670 μm. The measured mass transfer parameters further confirmed the beneficial effects of the surface-charged submicron polymer particles on the performance of FO membrane. For instance, the water permeability coefficient (5.37 L m-2 h-1 bar-1) and water flux (49.7 L m-2 h-1) of the FO membrane incorporated with 5 wt% particles were almost twice as much as that of FO membrane without incorporation. This study suggests that monodisperse surface-charged submicron polymer particles are potential modifiers for improving the performance of FO membranes.

Comparative study of the energy potential of cyanide waters using two osmotic membrane modules under dead-end flow

NASA Astrophysics Data System (ADS)

García-Díaz, Y.; Quiñones-Bolaños, E.; Bustos-Blanco, C.; Vives-Pérez, L.; Bustillo-Lecompte, C.; Saba, M.

2017-12-01

The energy potential of the osmotic pressure gradient of cyanide waters is evaluated using two membrane modules, horizontal and vertical, operated under dead-end flow. The membrane was characterized using Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectroscopy (EDS). The membrane is mainly composed of carbon, oxygen, and sulphur. The properties of the membrane were unchanged and had no pore clogging after exposure to the cyanide waters. Potentials of 1.78×10-4 and 6.36×10-5Wm-2 were found for the horizontal and vertical modules, respectively, using the Van’t Hoff equation. Likewise, the permeability coefficient of the membrane was higher in the vertical module. Although the energy potential is low under the studied conditions the vertical configuration has a greater potential due to the action of gravity and the homogenous contact of the fluid with the membrane.

Effect of garlic-derived organosulfur compounds on mitochondrial function and integrity in isolated mouse liver mitochondria.

PubMed

Caro, Andres A; Adlong, Luke W; Crocker, Samuel J; Gardner, Michael W; Luikart, Emily F; Gron, Liz U

2012-10-17

The objectives of this work were to evaluate the direct effects of diallysulfide (DAS) and diallyldisulfide (DADS), two major organosulfur compounds of garlic oil, on mitochondrial function and integrity, by using isolated mouse liver mitochondria in a cell-free system. DADS produced concentration-dependent mitochondrial swelling over the range 125-1000μM, while DAS was ineffective. Swelling experiments performed with de-energized or energized mitochondria showed similar maximal swelling amplitudes. Cyclosporin A (1μM), or ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA, 1mM) were ineffective in inhibiting DADS-induced mitochondrial swelling. DADS produced a minor (12%) decrease in mitochondrial membrane protein thiols, but did not induce clustering of mitochondrial membrane proteins. Incubation of mitochondria with DADS (but not DAS) produced an increase in the oxidation rate of 2',7' dichlorofluorescein diacetate (DCFH-DA), together with depletion of reduced glutathione (GSH) and increased lipid peroxidation. DADS (but not DAS) produced a concentration-dependent dissipation of the mitochondrial membrane potential, but did not induce cytochrome c release. DADS-dependent effects, including mitochondrial swelling, DCFH-DA oxidation, lipid peroxidation and loss of mitochondrial membrane potential, were inhibited by antioxidants and iron chelators. These results suggest that DADS causes direct impairment of mitochondrial function as the result of oxidation of the membrane lipid phase initiated by the GSH- and iron-dependent generation of oxidants. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

Use of a Ceramic Membrane to Improve the Performance of Two-Separate-Phase Biocatalytic Membrane Reactor.

PubMed

Ranieri, Giuseppe; Mazzei, Rosalinda; Wu, Zhentao; Li, Kang; Giorno, Lidietta

2016-03-14

Biocatalytic membrane reactors (BMR) combining reaction and separation within the same unit have many advantages over conventional reactor designs. Ceramic membranes are an attractive alternative to polymeric membranes in membrane biotechnology due to their high chemical, thermal and mechanical resistance. Another important use is their potential application in a biphasic membrane system, where support solvent resistance is highly needed. In this work, the preparation of asymmetric ceramic hollow fibre membranes and their use in a two-separate-phase biocatalytic membrane reactor will be described. The asymmetric ceramic hollow fibre membranes were prepared using a combined phase inversion and sintering technique. The prepared fibres were then used as support for lipase covalent immobilization in order to develop a two-separate-phase biocatalytic membrane reactor. A functionalization method was proposed in order to increase the density of the reactive hydroxyl groups on the surface of ceramic membranes, which were then amino-activated and treated with a crosslinker. The performance and the stability of the immobilized lipase were investigated as a function of the amount of the immobilized biocatalytst. Results showed that it is possible to immobilize lipase on a ceramic membrane without altering its catalytic performance (initial residual specific activity 93%), which remains constant after 6 reaction cycles.

Cholesterol Promotes Protein Binding by Affecting Membrane Electrostatics and Solvation Properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Doktorova, Milka; Heberle, Frederick A.; Kingston, Richard L.

Binding of the retroviral structural protein Gag to the cellular plasma membrane is mediated by the protein’s matrix (MA) domain. Prominent among MA-PM interactions is electrostatic attraction between the positively charged MA domain and the negatively charged plasma membrane inner leaflet. Previously, we reported that membrane association of HIV-1 Gag, as well as purified Rous sarcoma virus (RSV) MA and Gag, depends strongly on the presence of acidic lipids and is enhanced by cholesterol (Chol). The mechanism underlying this enhancement was unclear. Here in this paper, using a broad set of in vitro and in silico techniques we addressed molecularmore » mechanisms of association between RSV MA and model membranes, and investigated how Chol enhances this association. In neutron scattering experiments with liposomes in the presence or absence of Chol, MA preferentially interacted with preexisting POPS-rich clusters formed by nonideal lipid mixing, binding peripherally to the lipid headgroups with minimal perturbation to the bilayer structure. Molecular dynamics simulations showed a stronger MA-bilayer interaction in the presence of Chol, and a large Chol-driven increase in lipid packing and membrane surface charge density. Although in vitro MA-liposome association is influenced by disparate variables, including ionic strength and concentrations of Chol and charged lipids, continuum electrostatic theory revealed an underlying dependence on membrane surface potential. Together, these results conclusively show that Chol affects RSV MA-membrane association by making the electrostatic potential at the membrane surface more negative, while decreasing the penalty for lipid headgroup desolvation. The presented approach can be applied to other viral and nonviral proteins.« less

Cholesterol Promotes Protein Binding by Affecting Membrane Electrostatics and Solvation Properties

DOE PAGES

Doktorova, Milka; Heberle, Frederick A.; Kingston, Richard L.; ...

2017-11-07

Binding of the retroviral structural protein Gag to the cellular plasma membrane is mediated by the protein’s matrix (MA) domain. Prominent among MA-PM interactions is electrostatic attraction between the positively charged MA domain and the negatively charged plasma membrane inner leaflet. Previously, we reported that membrane association of HIV-1 Gag, as well as purified Rous sarcoma virus (RSV) MA and Gag, depends strongly on the presence of acidic lipids and is enhanced by cholesterol (Chol). The mechanism underlying this enhancement was unclear. Here in this paper, using a broad set of in vitro and in silico techniques we addressed molecularmore » mechanisms of association between RSV MA and model membranes, and investigated how Chol enhances this association. In neutron scattering experiments with liposomes in the presence or absence of Chol, MA preferentially interacted with preexisting POPS-rich clusters formed by nonideal lipid mixing, binding peripherally to the lipid headgroups with minimal perturbation to the bilayer structure. Molecular dynamics simulations showed a stronger MA-bilayer interaction in the presence of Chol, and a large Chol-driven increase in lipid packing and membrane surface charge density. Although in vitro MA-liposome association is influenced by disparate variables, including ionic strength and concentrations of Chol and charged lipids, continuum electrostatic theory revealed an underlying dependence on membrane surface potential. Together, these results conclusively show that Chol affects RSV MA-membrane association by making the electrostatic potential at the membrane surface more negative, while decreasing the penalty for lipid headgroup desolvation. The presented approach can be applied to other viral and nonviral proteins.« less

Low-intensity repetitive magnetic stimulation lowers action potential threshold and increases spike firing in layer 5 pyramidal neurons in vitro.

PubMed

Tang, Alexander D; Hong, Ivan; Boddington, Laura J; Garrett, Andrew R; Etherington, Sarah; Reynolds, John N J; Rodger, Jennifer

2016-10-29

Repetitive transcranial magnetic stimulation (rTMS) has become a popular method of modulating neural plasticity in humans. Clinically, rTMS is delivered at high intensities to modulate neuronal excitability. While the high-intensity magnetic field can be targeted to stimulate specific cortical regions, areas adjacent to the targeted area receive stimulation at a lower intensity and may contribute to the overall plasticity induced by rTMS. We have previously shown that low-intensity rTMS induces molecular and structural plasticity in vivo, but the effects on membrane properties and neural excitability have not been investigated. Here we investigated the acute effect of low-intensity repetitive magnetic stimulation (LI-rMS) on neuronal excitability and potential changes on the passive and active electrophysiological properties of layer 5 pyramidal neurons in vitro. Whole-cell current clamp recordings were made at baseline prior to subthreshold LI-rMS (600 pulses of iTBS, n=9 cells from 7 animals) or sham (n=10 cells from 9 animals), immediately after stimulation, as well as 10 and 20min post-stimulation. Our results show that LI-rMS does not alter passive membrane properties (resting membrane potential and input resistance) but hyperpolarises action potential threshold and increases evoked spike-firing frequency. Increases in spike firing frequency were present throughout the 20min post-stimulation whereas action potential (AP) threshold hyperpolarization was present immediately after stimulation and at 20min post-stimulation. These results provide evidence that LI-rMS alters neuronal excitability of excitatory neurons. We suggest that regions outside the targeted region of high-intensity rTMS are susceptible to neuromodulation and may contribute to rTMS-induced plasticity. Copyright © 2016 IBRO. All rights reserved.

Glucose recruits K(ATP) channels via non-insulin-containing dense-core granules.

PubMed

Yang, Shao-Nian; Wenna, Nancy Dekki; Yu, Jia; Yang, Guang; Qiu, Hua; Yu, Lina; Juntti-Berggren, Lisa; Köhler, Martin; Berggren, Per-Olof

2007-09-01

beta cells rely on adenosine triphosphate-sensitive potassium (K(ATP)) channels to initiate and end glucose-stimulated insulin secretion through changes in membrane potential. These channels may also act as a constituent of the exocytotic machinery to mediate insulin release independent of their electrical function. However, the molecular mechanisms whereby the beta cell plasma membrane maintains an appropriate number of K(ATP) channels are not known. We now show that glucose increases K(ATP) current amplitude by increasing the number of K(ATP) channels in the beta cell plasma membrane. The effect was blocked by inhibition of protein kinase A (PKA) as well as by depletion of extracellular or intracellular Ca(2+). Furthermore, glucose promoted recruitment of the potassium inward rectifier 6.2 to the plasma membrane, and intracellular K(ATP) channels localized in chromogranin-positive/insulin-negative dense-core granules. Our data suggest that glucose can recruit K(ATP) channels to the beta cell plasma membrane via non-insulin-containing dense-core granules in a Ca(2+)- and PKA-dependent manner.

Non-linear osmosis

PubMed Central

Diamond, Jared M.

1966-01-01

1. The relation between osmotic gradient and rate of osmotic water flow has been measured in rabbit gall-bladder by a gravimetric procedure and by a rapid method based on streaming potentials. Streaming potentials were directly proportional to gravimetrically measured water fluxes. 2. As in many other tissues, water flow was found to vary with gradient in a markedly non-linear fashion. There was no consistent relation between the water permeability and either the direction or the rate of water flow. 3. Water flow in response to a given gradient decreased at higher osmolarities. The resistance to water flow increased linearly with osmolarity over the range 186-825 m-osM. 4. The resistance to water flow was the same when the gall-bladder separated any two bathing solutions with the same average osmolarity, regardless of the magnitude of the gradient. In other words, the rate of water flow is given by the expression (Om — Os)/[Ro′ + ½k′ (Om + Os)], where Ro′ and k′ are constants and Om and Os are the bathing solution osmolarities. 5. Of the theories advanced to explain non-linear osmosis in other tissues, flow-induced membrane deformations, unstirred layers, asymmetrical series-membrane effects, and non-osmotic effects of solutes could not explain the results. However, experimental measurements of water permeability as a function of osmolarity permitted quantitative reconstruction of the observed water flow—osmotic gradient curves. Hence non-linear osmosis in rabbit gall-bladder is due to a decrease in water permeability with increasing osmolarity. 6. The results suggest that aqueous channels in the cell membrane behave as osmometers, shrinking in concentrated solutions of impermeant molecules and thereby increasing membrane resistance to water flow. A mathematical formulation of such a membrane structure is offered. PMID:5945254

Testosterone decreases urinary bladder smooth muscle excitability via novel signaling mechanism involving direct activation of the BK channels

PubMed Central

Hristov, Kiril L.; Parajuli, Shankar P.; Provence, Aaron

2016-01-01

In addition to improving sexual function, testosterone has been reported to have beneficial effects in ameliorating lower urinary tract symptoms by increasing bladder capacity and compliance, while decreasing bladder pressure. However, the cellular mechanisms by which testosterone regulates detrusor smooth muscle (DSM) excitability have not been elucidated. Here, we used amphotericin-B perforated whole cell patch-clamp and single channel recordings on inside-out excised membrane patches to investigate the regulatory role of testosterone in guinea pig DSM excitability. Testosterone (100 nM) significantly increased the depolarization-induced whole cell outward currents in DSM cells. The selective pharmacological inhibition of the large-conductance voltage- and Ca2+-activated K+ (BK) channels with paxilline (1 μM) completely abolished this stimulatory effect of testosterone, suggesting a mechanism involving BK channels. At a holding potential of −20 mV, DSM cells exhibited transient BK currents (TBKCs). Testosterone (100 nM) significantly increased TBKC activity in DSM cells. In current-clamp mode, testosterone (100 nM) significantly hyperpolarized the DSM cell resting membrane potential and increased spontaneous transient hyperpolarizations. Testosterone (100 nM) rapidly increased the single BK channel open probability in inside-out excised membrane patches from DSM cells, clearly suggesting a direct BK channel activation via a nongenomic mechanism. Live-cell Ca2+ imaging showed that testosterone (100 nM) caused a decrease in global intracellular Ca2+ concentration, consistent with testosterone-induced membrane hyperpolarization. In conclusion, the data provide compelling mechanistic evidence that under physiological conditions, testosterone at nanomolar concentrations directly activates BK channels in DSM cells, independent from genomic testosterone receptors, and thus regulates DSM excitability. PMID:27605581

Impaired Bioenergetics in Mutant Mitochondrial DNA Determines Cell Fate During Seizure-Like Activity.

PubMed

Kovac, Stjepana; Preza, Elisavet; Houlden, Henry; Walker, Matthew C; Abramov, Andrey Y

2018-04-27

Mutations in genes affecting mitochondrial proteins are increasingly recognised in patients with epilepsy, but the factors determining cell fate during seizure activity in these mutations remain unknown. Fluorescent dye imaging techniques were applied to fibroblast cell lines from patients suffering from common mitochondrial mutations and to age-matched controls. Using live cell imaging techniques in fibroblasts, we show that fibroblasts with mutations in the mitochondrial genome had reduced mitochondrial membrane potential and NADH pools and higher redox indices, indicative of respiratory chain dysfunction. Increasing concentrations of ferutinin, a Ca 2+ ionophore, led to oscillatory Ca 2+ signals in fibroblasts resembling dynamic Ca 2+ changes that occur during seizure-like activity. Co-monitoring of mitochondrial membrane potential (ΔΨ m ) changes induced by ferutinin showed accelerated membrane depolarisation and cell collapse in fibroblasts with mutations in the mitochondrial genome when compared to controls. Ca 2+ flash photolysis using caged Ca 2+ confirmed impaired Ca 2+ handling in fibroblasts with mitochondrial mutations. Findings indicate that intracellular Ca 2+ levels cannot be compensated during periods of hyperexcitability, leading to Ca 2+ overload and subsequent cell death in mitochondrial diseases.

MitoQ regulates autophagy by inducing a pseudo-mitochondrial membrane potential

PubMed Central

Sun, Chao; Liu, Xiongxiong; Di, Cuixia; Wang, Zhenhua; Mi, Xiangquan; Liu, Yang; Zhao, Qiuyue; Mao, Aihong; Chen, Weiqiang; Gan, Lu; Zhang, Hong

2017-01-01

ABSTRACT During the process of oxidative phosphorylation, protons are pumped into the mitochondrial intermembrane space to establish a mitochondrial membrane potential (MMP). The electrochemical gradient generated allows protons to return to the matrix through the ATP synthase complex and generates ATP in the process. MitoQ is a lipophilic cationic drug that is adsorbed to the inner mitochondrial membrane; however, the cationic moiety of MitoQ remains in the intermembrane space. We found that the positive charges in MitoQ inhibited the activity of respiratory chain complexes I, III, and IV, reduced proton production, and decreased oxygen consumption. Therefore, a pseudo-MMP (PMMP) was formed via maintenance of exogenous positive charges. Proton backflow was severely impaired, leading to a decrease in ATP production and an increase in AMP production. Excess AMP activates AMP kinase, which inhibits the MTOR (mechanistic target of rapamycin) pathway and induces macroautophagy/autophagy. Therefore, we conclude that MitoQ increases PMMP via proton displacement with exogenous positive charges. In addition, PMMP triggered autophagy in hepatocellular carcinoma HepG2 cells via modification of mitochondrial bioenergetics pathways. PMID:28121478

MitoQ regulates autophagy by inducing a pseudo-mitochondrial membrane potential.

PubMed

Sun, Chao; Liu, Xiongxiong; Di, Cuixia; Wang, Zhenhua; Mi, Xiangquan; Liu, Yang; Zhao, Qiuyue; Mao, Aihong; Chen, Weiqiang; Gan, Lu; Zhang, Hong

2017-04-03

During the process of oxidative phosphorylation, protons are pumped into the mitochondrial intermembrane space to establish a mitochondrial membrane potential (MMP). The electrochemical gradient generated allows protons to return to the matrix through the ATP synthase complex and generates ATP in the process. MitoQ is a lipophilic cationic drug that is adsorbed to the inner mitochondrial membrane; however, the cationic moiety of MitoQ remains in the intermembrane space. We found that the positive charges in MitoQ inhibited the activity of respiratory chain complexes I, III, and IV, reduced proton production, and decreased oxygen consumption. Therefore, a pseudo-MMP (PMMP) was formed via maintenance of exogenous positive charges. Proton backflow was severely impaired, leading to a decrease in ATP production and an increase in AMP production. Excess AMP activates AMP kinase, which inhibits the MTOR (mechanistic target of rapamycin) pathway and induces macroautophagy/autophagy. Therefore, we conclude that MitoQ increases PMMP via proton displacement with exogenous positive charges. In addition, PMMP triggered autophagy in hepatocellular carcinoma HepG2 cells via modification of mitochondrial bioenergetics pathways.

Sodium and potassium conductance changes during a membrane action potential.

PubMed

Bezanilla, F; Rojas, E; Taylor, R E

1970-12-01

1. A method for turning a membrane potential control system on and off in less than 10 musec is described. This method was used to record membrane currents in perfused giant axons from Dosidicus gigas and Loligo forbesi after turning on the voltage clamp system at various times during the course of a membrane action potential.2. The membrane current measured just after the capacity charging transient was found to have an almost linear relation to the controlled membrane potential.3. The total membrane conductance taken from these current-voltage curves was found to have a time course during the action potential similar to that found by Cole & Curtis (1939).4. The instantaneous current voltage curves were linear enough to make it possible to obtain a good estimate of the individual sodium and potassium channel conductances, either algebraically or by clamping to the sodium, or potassium, reversal potentials. Good general agreement was obtained with the predictions of the Hodgkin-Huxley equations.5. We consider these results to constitute the first direct experimental demonstration of the conductance changes to sodium and potassium during the course of an action potential.

Mitochondrial decay in hepatocytes from old rats: Membrane potential declines, heterogeneity and oxidants increase

PubMed Central

Hagen, Tory M.; Yowe, David L.; Bartholomew, James C.; Wehr, Carol M.; Do, Katherine L.; Park, Jin-Y.; Ames, Bruce N.

1997-01-01

Mitochondrial function during aging was assessed in isolated rat hepatocytes to avoid the problem of differential lysis when old, fragile mitochondria are isolated. Rhodamine 123, a fluorescent dye that accumulates in mitochondria on the basis of their membrane potential, was used as a probe to determine whether this key function is affected by aging. A marked fluorescent heterogeneity was observed in hepatocytes from old (20–28 months) but not young (3–5 months) rats, suggesting age-associated alterations in mitochondrial membrane potential, the driving force for ATP synthesis. Three distinct cell subpopulations were separated by centrifugal elutriation; each exhibited a unique rhodamine 123 fluorescence pattern, with the largest population from old rats having significantly lower fluorescence than that seen in young rats. This apparent age-associated alteration in mitochondrial membrane potential was confirmed by measurements with radioactive tetraphenylphosphonium bromide. Cells from young rats had a calculated membrane potential of −154 mV, in contrast to that of the three subpopulations from old rats of −70 mV (the largest population), −93 mV, and −154 mV. Production of oxidants was examined using 2′,7′dichlorofluorescin, a dye that forms a fluorescent product upon oxidation. The largest cell subpopulation and a minor one from old animals produced significantly more oxidants than cells from young rats. To investigate the molecular cause(s) for the heterogeneity, we determined the levels of an age-associated mtDNA deletion. No significant differences were seen in the three subpopulations, indicating that the mitochondrial decay is due to other mutations, epigenetic changes, or both. PMID:9096346

A kainate receptor subunit promotes the recycling of the neuron-specific K+-Cl- co-transporter KCC2 in hippocampal neurons.

PubMed

Pressey, Jessica C; Mahadevan, Vivek; Khademullah, C Sahara; Dargaei, Zahra; Chevrier, Jonah; Ye, Wenqing; Huang, Michelle; Chauhan, Alamjeet K; Meas, Steven J; Uvarov, Pavel; Airaksinen, Matti S; Woodin, Melanie A

2017-04-14

Synaptic inhibition depends on a transmembrane gradient of chloride, which is set by the neuron-specific K + -Cl - co-transporter KCC2. Reduced KCC2 levels in the neuronal membrane contribute to the generation of epilepsy, neuropathic pain, and autism spectrum disorders; thus, it is important to characterize the mechanisms regulating KCC2 expression. In the present study, we determined the role of KCC2-protein interactions in regulating total and surface membrane KCC2 expression. Using quantitative immunofluorescence in cultured mouse hippocampal neurons, we discovered that the kainate receptor subunit GluK2 and the auxiliary subunit Neto2 significantly increase the total KCC2 abundance in neurons but that GluK2 exclusively increases the abundance of KCC2 in the surface membrane. Using a live cell imaging assay, we further determined that KCC2 recycling primarily occurs within 1-2 h and that GluK2 produces an ∼40% increase in the amount of KCC2 recycled to the membrane during this time period. This GluK2-mediated increase in surface recycling translated to a significant increase in KCC2 expression in the surface membrane. Moreover, we found that KCC2 recycling is enhanced by protein kinase C-mediated phosphorylation of the GluK2 C-terminal residues Ser-846 and Ser-868. Lastly, using gramicidin-perforated patch clamp recordings, we found that the GluK2-mediated increase in KCC2 recycling to the surface membrane translates to a hyperpolarization of the reversal potential for GABA (E GABA ). In conclusion, our results have revealed a mechanism by which kainate receptors regulate KCC2 expression in the hippocampus. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

Excess chemical potential of small solutes across water--membrane and water--hexane interfaces

NASA Technical Reports Server (NTRS)

Pohorille, A.; Wilson, M. A.

1996-01-01

The excess chemical potentials of five small, structurally related solutes, CH4, CH3F, CH2F2, CHF3, and CF4, across the water-glycerol 1-monooleate bilayer and water-hexane interfaces were calculated at 300, 310, and 340 K using the particle insertion method. The excess chemical potentials of nonpolar molecules (CH4 and CF4) decrease monotonically or nearly monotonically from water to a nonpolar phase. In contrast, for molecules that possess permanent dipole moments (CH3F, CH2F, and CHF3), the excess chemical potentials exhibit an interfacial minimum that arises from superposition of two monotonically and oppositely changing contributions: electrostatic and nonelectrostatic. The nonelectrostatic term, dominated by the reversible work of creating a cavity that accommodates the solute, decreases, whereas the electrostatic term increases across the interface from water to the membrane interior. In water, the dependence of this term on the dipole moment is accurately described by second order perturbation theory. To achieve the same accuracy at the interface, third order terms must also be included. In the interfacial region, the molecular structure of the solvent influences both the excess chemical potential and solute orientations. The excess chemical potential across the interface increases with temperature, but this effect is rather small. Our analysis indicates that a broad range of small, moderately polar molecules should be surface active at the water-membrane and water-oil interfaces. The biological and medical significance of this result, especially in relation to the mechanism of anesthetic action, is discussed.

Highly Permeable Oligo(ethylene oxide)- co-poly(dimethylsiloxane) Membranes for Carbon Dioxide Separation

DOE PAGES

Hong, Tao; Lai, Sophia C.; Mahurin, Shannon Mark; ...

2017-12-27

Here, a series of cross–linked, freestanding oligo(ethylene oxide)– co–(polydimethylsiloxane–norbornene) membranes with varied composition is synthesized via in situ ring–opening metathesis polymerization. These membranes show remarkably high CO 2 permeabilities (3400 Barrer) and their separation performance approaches the Robeson upper bound. The excellent permeability of these copolymer membranes provides great potential for real–world applications where enormous volumes of gases must be separated. The gas transport properties of these films are found to be directly proportional to oligo(ethylene oxide) content incorporation, which stems from the increased solubility selectivity change within the copolymer matrix. This work provides a systematic study of how gasmore » separation performance in rubbery membranes can be enhanced by tuning the CO 2–philicity of their constituent monomeric subunits.« less

Potentialities of a membrane reactor with laccase grafted membranes for the enzymatic degradation of phenolic compounds in water.

PubMed

Chea, Vorleak; Paolucci-Jeanjean, Delphine; Sanchez, José; Belleville, Marie-Pierre

2014-10-06

This paper describes the degradation of phenolic compounds by laccases from Trametes versicolor in an enzymatic membrane reactor (EMR). The enzymatic membranes were prepared by grafting laccase on a gelatine layer previously deposited onto α-alumina tubular membranes. The 2,6-dimethoxyphenol (DMP) was selected  from among the three different phenolic compounds tested (guaiacol, 4-chlorophenol and DMP) to study the performance of the EMR in dead end configuration. At the lowest feed substrate concentration tested (100 mg·L-1), consumption increased with flux (up to 7.9 × 103 mg·h-1·m-2 at 128 L·h-1·m-2), whereas at the highest substrate concentration (500 mg·L-1), it was shown that the reaction was limited by the oxygen content.

Potentialities of a Membrane Reactor with Laccase Grafted Membranes for the Enzymatic Degradation of Phenolic Compounds in Water

PubMed Central

Chea, Vorleak; Paolucci-Jeanjean, Delphine; Sanchez, José; Belleville, Marie-Pierre

2014-01-01

This paper describes the degradation of phenolic compounds by laccases from Trametes versicolor in an enzymatic membrane reactor (EMR). The enzymatic membranes were prepared by grafting laccase on a gelatine layer previously deposited onto α-alumina tubular membranes. The 2,6-dimethoxyphenol (DMP) was selected  from among the three different phenolic compounds tested (guaiacol, 4-chlorophenol and DMP) to study the performance of the EMR in dead end configuration. At the lowest feed substrate concentration tested (100 mg·L−1), consumption increased with flux (up to 7.9 × 103 mg·h−1·m−2 at 128 L·h−1·m−2), whereas at the highest substrate concentration (500 mg·L−1), it was shown that the reaction was limited by the oxygen content. PMID:25295628

Assessment of amphotericin B susceptibility in Leishmania infantum promastigotes by flow cytometric membrane potential assay.

PubMed

Azas, N; Di Giorgio, C; Delmas, F; Gasquet, M; Timon-David, P

1997-06-01

Flow cytometry was used for measuring the effects of amphotericin B on the membrane of Leishmania infantum strains. The technique was adapted from the rapid flow cytometric membrane potential assay developed by Ordonez and Wehman (Cytometry 22:154-157, 1995) for evaluating antibiotic-susceptibility of Candida species. The study consisted of measuring membrane potential changes induced by amphotericin B in 3 initial strains and 12 laboratory-generated variants adapted to grow with amphotericin B. Results showed that, after 3 h of incubation, amphotericin B induced a dose-related decrease of membrane potential that reached its maximal level at the same concentrations that inhibited parasite growth. These results suggest that the flow cytometric membrane potential assay could be used to assess the susceptibility of Leishmania promastigotes to amphotericin B.

A novel approach to regulate cell membrane permeability for ATP and NADH formation in Saccharomyces cerevisiae induced by air cold plasma

NASA Astrophysics Data System (ADS)

Dong, Xiaoyu; Liu, Tingting; Xiong, Yuqin

2017-02-01

Air cold plasma has been used as a novel method for enhancing microbial fermentation. The aim of this work was to explore the effect of plasma on membrane permeability and the formation of ATP and NADH in Saccharomyces cerevisiae, so as to provide valuable information for large-scale application of plasma in the fermentation industry. Suspensions of S. cerevisiae cells were exposed to air cold plasma for 0, 1, 2, 3, 4 and 5 min, and then subjected to various analyses prior to fermentation (0 h) and at the 9 and 21 h stages of fermentation. Compared with non-exposed cells, cells exposed to plasma for 1 min exhibited a marked increase in cytoplasmic free Ca2+ concentration as a result of the significant increase in membrane potential prior to fermentation. At the same time, the ATP level in the cell suspension decreased by about 40%, resulting in a reduction of about 60% in NADH prior to culturing. However, the levels of ATP and NADH in the culture at the 9 and 21 h fermentation stages were different from the level at 0 h. Taken together, the results indicated that exposure of S. cerevisiae to air cold plasma could increase its cytoplasmic free Ca2+ concentration by improving the cell membrane potential, consequently leading to changes in ATP and NADH levels. Supported by National Natural Science Foundation of China (Nos. 21246012, 21306015 and 21476032).

Effect of urinary trypsin inhibitor on potassium currents: fetus modulates membrane excitability by production of UTI.

PubMed

Takeuchi, Kinya; Fukuda, Atsuo; Kanayama, Naohiro

2004-01-01

Amniotic fluid contains a significant level of urinary trypsin inhibitor (UTI). Previously, we reported that UTI inhibits calcium influx of myometrium and it is effective in preventing uterine contraction. This study examined the effects of UTI upon potassium channels, which is important for membrane excitability. Whole-cell patch-clamp recordings were performed in fibroblasts derived from human fetal skin. Potassium currents were recorded and the effects of exogenous UTI and/or cadmium determined. Tetraethylammonium sensitive potassium currents were elicited by step or ramp stimulations at depolarized membrane potentials (over +30 mV). Administration of 1 micro M UTI significantly increased these potassium currents by 16.9%. When calcium channels were blocked by the administration of cadmium, UTI increased the rest of the potassium currents by 4.8%. This indicates that UTI increased calcium-dependent potassium currents by 94.8% but only increased voltage-dependent potassium currents by 4.8%. Urinary trypsin inhibitor is a physiological substance of fetal origin that modulates calcium-dependent and voltage-dependent potassium channels. These data suggest that UTI is capable of regulating the membrane properties of the fetal and myometrial cells in contact with amniotic fluid.

Coagulation and oxidation for controlling ultrafiltration membrane fouling in drinking water treatment: Application of ozone at low dose in submerged membrane tank.

PubMed

Yu, Wenzheng; Graham, Nigel J D; Fowler, Geoffrey D

2016-05-15

Coagulation prior to ultrafiltration (UF) is widely applied for treating contaminated surface water sources for potable supply. While beneficial, coagulation alone is unable to control membrane fouling effectively in many cases, and there is continuing interest in the use of additional, complementary methods such as oxidation in the pre-treatment of raw water prior to UF. In this study, the application of ozone at low dose in the membrane tank immediately following coagulation has been evaluated at laboratory-scale employing model raw water. In parallel tests with and without the application of ozone, the impact of applied ozone doses of 0.5 mg L(-1) and 1.5 mg L(-1) (approximately 0.18 mg L(-1) and 0.54 mg L(-1) consumed ozone, respectively) on the increase of trans-membrane pressure (TMP) was evaluated and correlated with the quantity and nature of membrane deposits, both as a cake layer and within membrane pores. The results showed that a dose of 0.5 mgO3 L(-1) gave a membrane fouling rate that was substantially lower than without ozone addition, while a dose of 1.5 mgO3 L(-1) was able to prevent fouling effects significantly (no increase in TMP). Ozone was found to decrease the concentration of bacteria (especially the concentration of bacteria per suspended solid) in the membrane tank, and to alter the nature of dissolved organic matter by increasing the proportion of hydrophilic substances. Ozone decreased the concentration of extracellular polymeric substances (EPS), such as polysaccharides and proteins, in the membrane cake layer; the reduced EPS and bacterial concentrations resulted in a much thinner cake layer, although the suspended solids concentration was much higher in the ozone added membrane tank. Ozone also decreased the accumulation and hydrophobicity of organic matter within the membrane pores, leading to minimal irreversible fouling. Therefore, the application of low-dose ozone within the UF membrane tank is a potentially important approach for fully mitigating membrane fouling. Crown Copyright © 2016. Published by Elsevier Ltd. All rights reserved.

Cell Membrane Coating Nanotechnology.

PubMed

Fang, Ronnie H; Kroll, Ashley V; Gao, Weiwei; Zhang, Liangfang

2018-06-01

Nanoparticle-based therapeutic, prevention, and detection modalities have the potential to greatly impact how diseases are diagnosed and managed in the clinic. With the wide range of nanomaterials available, the rational design of nanocarriers on an application-specific basis has become increasingly commonplace. Here, a comprehensive overview is provided on an emerging platform: cell-membrane-coating nanotechnology. As a fundamental unit of biology, cells carry out a wide range of functions, including the remarkable ability to interface and interact with their surrounding environment. Instead of attempting to replicate such functions via synthetic techniques, researchers are now directly leveraging naturally derived cell membranes as a means of bestowing nanoparticles with enhanced biointerfacing capabilities. This top-down technique is facile, highly generalizable, and has the potential to greatly augment existing nanocarriers. Further, the introduction of a natural membrane substrate onto nanoparticles surfaces has enabled additional applications beyond those traditionally associated with nanomedicine. Despite its relative youth, there exists an impressive body of literature on cell membrane coating, which is covered here in detail. Overall, there is still significant room for development, as researchers continue to refine existing workflows while finding new and exciting applications that can take advantage of this developing technology. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Poloxamer 188 (p188) as a membrane resealing reagent in biomedical applications.

PubMed

Moloughney, Joseph G; Weisleder, Noah

2012-12-01

Maintenance of the integrity of the plasma membrane is essential for maintenance of cellular function and prevention of cell death. Since the plasma membrane is frequently exposed to a variety of mechanical and chemical insults the cell has evolved active processes to defend against these injuries by resealing disruptions in the plasma membrane. Cell membrane repair is a conserved process observed in nearly every cell type where intracellular vesicles are recruited to sites of membrane disruption where they can fuse with themselves or the plasma membrane to create a repair patch. When disruptions are extensive or there is an underlying pathology that reduces the membrane repair capacity of a cell this defense mechanism may prove insufficient and the cell could die due to breakdown of the plasma membrane. Extensive loss of cells can compromise the integrity and function of tissues and leading to disease. Thus, methods to increase membrane resealing capacity could have broad utility in a number of disease states. Efforts to find reagents that can modulate plasma membrane reseal found that specific tri-block copolymers, such as poloxamer 188 (P188, or Pluronic F68), can increase the structural stability and resealing of the plasma membrane. Here we review several current patents and patent applications that present inventions making use of P188 and other copolymers to treat specific disease states such as muscular dystrophy, heart failure, neurodegenerative disorders and electrical injuries, or to facilitate biomedical applications such as transplantation. There appears to be promise for the application of poloxamers in the treatment of various diseases, however there are potential concerns with toxicity with long term application and bioavailability in some cases.

Reverse osmosis desalination of chitosan cross-linked graphene oxide/titania hybrid lamellar membranes.

PubMed

Deng, Hui; Sun, Penzhan; Zhang, Yingjiu; Zhu, Hongwei

2016-07-08

With excellent mass transport properties, graphene oxide (GO)-based lamellar membranes are believed to have great potential in water desalination. In order to quantify whether GO-based membranes are indeed suitable for reverse osmosis (RO) desalination, three sub-micrometer thick GO-based lamellar membranes: GO-only, reduced GO (RGO)/titania (TO) nanosheets and RGO/TO/chitosan (CTS) are prepared, and their RO desalination performances are evaluated in a home-made RO test apparatus. The photoreduction of GO by TO improves the salt rejection, which increases slowly with the membrane thickness. The RGO/TO/CTS hybrid membranes exhibit higher rejection rates of only about 30% (greater than threefold improvement compared with a GO-only membrane) which is still inferior compared to other commercial RO membranes. The low rejection rates mainly arise from the pressure-induced weakening of the ion-GO interlayer interactions. Despite the advantages of simple, low-cost preparation, high permeability and selectivity of GO-based lamellar membranes, as the current desalination performances are not high enough to afford practical application, there still remains a great challenge to realize high performance separation membranes for water desalination applications.

Copper effects on key metabolic enzymes and mitochondrial membrane potential in gills of the estuarine crab Neohelice granulata at different salinities.

PubMed

Lauer, Mariana Machado; de Oliveira, Camila Bento; Yano, Natalia Lie Inocencio; Bianchini, Adalto

2012-11-01

The estuarine crab Neohelice granulata was exposed (96 h) to a sublethal copper concentration under two different physiological conditions (hyperosmoregulating crabs: 2 ppt salinity, 1 mg Cu/L; isosmotic crabs: 30 ppt salinity, 5 mg Cu/L). After exposure, gills (anterior and posterior) were dissected and activities of enzymes involved in glycolysis (hexokinase, phosphofructokinase, pyruvate kinase, lactate dehydrogenase), Krebs cycle (citrate synthase), and mitochondrial electron transport chain (cytochrome c oxidase) were analyzed. Membrane potential of mitochondria isolated from anterior and posterior gill cells was also evaluated. In anterior gills of crabs acclimated to 2 ppt salinity, copper exposure inhibited hexokinase, phosphofructokinase, pyruvate kinase, and citrate synthase activity, increased lactate dehydrogenase activity, and reduced the mitochondrial membrane potential. In posterior gills, copper inhibited hexokinase and pyruvate kinase activity, and increased citrate synthase activity. In anterior gills of crabs acclimated to 30 ppt salinity, copper exposure inhibited phosphofructokinase and citrate synthase activity, and increased hexokinase activity. In posterior gills, copper inhibited phosphofructokinase and pyruvate kinase activity, and increased hexokinase and lactate dehydrogenase activity. Copper did not affect cytochrome c oxidase activity in either anterior or posterior gills of crabs acclimated to 2 and 30 ppt salinity. These findings indicate that exposure to a sublethal copper concentration affects the activity of enzymes involved in glycolysis and Krebs cycle, especially in anterior (respiratory) gills of hyperosmoregulating crabs. Changes observed indicate a switch from aerobic to anaerobic metabolism, characterizing a situation of functional hypoxia. In this case, reduced mitochondrial membrane potential would suggest a decrease in ATP production. Although gills of isosmotic crabs were also affected by copper exposure, changes observed suggest no impact in the overall tissue ATP production. Also, findings suggest that copper exposure would stimulate the pentose phosphate pathway to support the antioxidant system requirements. Although N. granulata is very tolerant to copper, acute exposure to this metal can disrupt the energy balance by affecting biochemical systems involved in carbohydrate metabolism. Copyright © 2012 Elsevier Inc. All rights reserved.

Phytol shows anti-angiogenic activity and induces apoptosis in A549 cells by depolarizing the mitochondrial membrane potential.

PubMed

Sakthivel, Ravi; Malar, Dicson Sheeja; Devi, Kasi Pandima

2018-06-13

In the present study, the antiproliferative activity of phytol and its mechanism of action against human lung adenocarcinoma cell line A549 were studied in detail. Results showed that phytol exhibited potent antiproliferative activity against A549 cells in a dose and time-dependent manner with an IC 50 value of 70.81 ± 0.32 μM and 60.7 ± 0.47 μM at 24 and 48 h, respectively. Phytol showed no adverse toxic effect in normal human lung cells (L-132), but mild toxic effect was observed when treated with maximum dose (67 and 84 μM). No membrane-damaging effect was evidenced by PI staining and SEM analysis. The results of mitochondrial membrane potential analysis, cell cycle analysis, FT-IR and Western blotting analysis clearly demonstrated the molecular mechanism of phytol as induction of apoptosis in A549 cells, as evidenced by formation of shrinked cell morphology with membrane blebbing, depolarization of mitochondrial membrane potential, increased cell population in the sub-G0 phase, band variation in the DNA and lipid region, downregulation of Bcl-2, upregulation of Bax and the activation of caspase-9 and -3. In addition, phytol inhibited the CAM vascular growth as evidenced by CAM assay, which positively suggests that phytol has anti-angiogenic potential. Taken together, these findings clearly demonstrate the mode of action by which phytol induces cell death in A549 lung adenocarcinoma cells. Copyright © 2018 Elsevier Masson SAS. All rights reserved.

Cell membrane disruption stimulates cAMP and Ca2+ signaling to potentiate cell membrane resealing in neighboring cells.

PubMed

Togo, Tatsuru

2017-12-15

Disruption of cellular plasma membranes is a common event in many animal tissues, and the membranes are usually rapidly resealed. Moreover, repeated membrane disruptions within a single cell reseal faster than the initial wound in a protein kinase A (PKA)- and protein kinase C (PKC)-dependent manner. In addition to wounded cells, recent studies have demonstrated that wounding of Madin-Darby canine kidney (MDCK) cells potentiates membrane resealing in neighboring cells in the short-term by purinergic signaling, and in the long-term by nitric oxide/protein kinase G signaling. In the present study, real-time imaging showed that cell membrane disruption stimulated cAMP synthesis and Ca 2+ mobilization from intracellular stores by purinergic signaling in neighboring MDCK cells. Furthermore, inhibition of PKA and PKC suppressed the ATP-mediated short-term potentiation of membrane resealing in neighboring cells. These results suggest that cell membrane disruption stimulates PKA and PKC via purinergic signaling to potentiate cell membrane resealing in neighboring MDCK cells. © 2017. Published by The Company of Biologists Ltd.

Differential natural organic matter fouling of ceramic versus polymeric ultrafiltration membranes.

PubMed

Lee, Seung-Jin; Kim, Jae-Hong

2014-01-01

Ceramic ultrafiltration membranes has drawn increasing attention in drinking water treatment sectors as an alternative to traditional polymeric counterparts, yet only limited information has been made available about the characteristics of ceramic membrane fouling by natural organic matter. The effects of solution chemistry including ionic strength, divalent ion concentration and pH on the flux behavior were comparatively evaluated for ceramic and polymeric ultrafiltration of synthetic water containing model natural organic matter. Filtration characteristics were further probed via resistance-in-series model analysis, fouling visualization using quantum dots, batch adsorption test, contact angle measurement, solute-membrane surface adhesion force measurement, and quantitative comparison of fouling characteristics between ceramic and polymeric membranes. The results collectively suggested that the effects of solution chemistry on fouling behavior of ceramic membranes were generally similar to polymeric counterparts in terms of trends, while the extent varied significantly depending on water quality parameters. Lower fouling tendency and enhanced cleaning efficiency were observed with the ceramic membrane, further promoting the potential for ceramic membrane application to surface water treatment. Copyright © 2013 Elsevier Ltd. All rights reserved.

Compositional changes in lipid microdomains of air-blood barrier plasma membranes in pulmonary interstitial edema.

PubMed

Palestini, Paola; Calvi, Chiara; Conforti, Elena; Daffara, Rossella; Botto, Laura; Miserocchi, Giuseppe

2003-10-01

We evaluated in anesthetized rabbits the compositional changes of plasmalemmal lipid microdomains from lung tissue samples after inducing pulmonary interstitial edema (0.5 ml/kg for 3 h, leading to approximately 5% increase in extravascular water). Lipid microdomains (lipid rafts and caveolae) were present in the detergent-resistant fraction (DRF) obtained after discontinuous sucrose density gradient. DRF was enriched in caveolin-1, flotillin, aquaporin-1, GM1, cholesterol, sphingomyelin, and phosphatidylserine, and their contents significantly increased in interstitial edema. The higher DRF content in caveolin, flotillin, and aquaporin-1 and of the ganglioside GM1 suggests an increase both in caveolar domains and in lipid rafts, respectively. Compositional changes could be ascribed to endothelial and epithelial cells that provide most of plasma membrane surface area in the air-blood barrier. Alterations in lipid components in the plasma membrane may reflect rearrangement of floating lipid platforms within the membrane and/or lipid translocation from intracellular stores. Lipid traffic could be stimulated by the marked increase in hydraulic interstitial pressure after initial water accumulation, from approximately -10 to 5 cmH2O, due to the low compliance of the pulmonary tissue, in particular in the basement membranes and in the interfibrillar substance. Compositional changes in lipid microdomains represent a sign of cellular activation and suggest the potential role of mechanotransduction in response to developing interstitial edema.

Spray- and spin-assisted layer-by-layer assembly of copper nanoparticles on thin-film composite reverse osmosis membrane for biofouling mitigation.

PubMed

Ma, Wen; Soroush, Adel; Van Anh Luong, Tran; Brennan, Gregory; Rahaman, Md Saifur; Asadishad, Bahareh; Tufenkji, Nathalie

2016-08-01

Copper nanoparticles (CuNPs) have long been considered as highly effective biocides; however, the lack of suitable methods for loading CuNPs onto polymeric membranes is recognized as being one of the primary reasons for the limited research concerning their application in membrane industries. A highly efficient spray- and spin-assisted layer-by-layer (SSLbL) method was developed to functionalize the TFC polyamide RO membranes with controllable loading of CuNPs for biofouling control. The SSLbL method was able to produce a uniform bilayer of polyethyleneimine-coated CuNPs and poly(acrylic) acid in less than 1 min, which is far more efficient than the traditional dipping approach (25-60 min). The successful loading of CuNPs onto the membrane surface was confirmed by XPS analysis. Increasing the number of bilayers from 2 to 10 led to an increased quantity of CuNPs on the membrane surface, from 1.75 to 23.7 μg cm(-2). Multi-layer coating exhibited minor impact on the membrane water permeation flux (13.3% reduction) while retaining the original salt rejection ability. Both static bacterial inactivation and cross-flow filtration tests demonstrated that CuNPs could significantly improve anti-biofouling property of a polyamide membrane and effectively inhibit the permeate flux reduction caused by bacterial deposition on the membrane surface. Once depleted, CuNPs can also be potentially regenerated on the membrane surface via the same SSLbL method. Copyright © 2016 Elsevier Ltd. All rights reserved.

Preparation and characterization of polymer blend based on sulfonated poly (ether ether ketone) and polyetherimide (SPEEK/PEI) as proton exchange membranes for fuel cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hashim, Nordiana; Ali, Ab Malik Marwan; Lepit, Ajis

2015-08-28

Blends of sulfonated poly (ether ether ketone) (SPEEK) and polyetherimide (PEI) were prepared in five different weight ratios using N-methyl-2-pyrrolidone (NMP) as solvent by the solution cast technique. The degree of sulfonation (DS) of the sulfonated PEEK was determined from deuterated dimethyl sulfoxide (DMSO-d{sub 6}) solution of the purified polymer using {sup 1}H NMR method. The properties studied in the present investigation includes conductivity, water uptake, thermal stability and structure analysis of pure SPEEK as well as SPEEK-PEI polymer blend membranes. The experimental results show that the conductivity of the membranes increased with increase in temperature from 30 to 80°C,more » except for that of pure SPEEK membrane which increased with temperature from 30 to 60°C while its conductivity decreased with increasing temperature from 60 to 80°C. The conductivity of 70wt.%SPEEK-30wt.%PEI blend membrane at 80% relative humidity (RH) is found to be 1.361 × 10{sup −3} Scm{sup −1} at 30°C and 3.383 × 10{sup −3} Scm{sup −1} at 80°C respectively. It was also found that water uptake and thermal stability of the membranes slightly improved upon blending with PEI. Structure analysis was carried out using Fourier Transform Infrared (FTIR) spectroscopy which revealed considerable interactions between sulfonic acid group of SPEEK and imide groups of PEI. Modification of SPEEK by blending with PEI shows good potential for improving the electrical and physical properties of proton exchange membranes.« less

Fluidization of Membrane Lipids Enhances the Tolerance of Saccharomyces cerevisiae to Freezing and Salt Stress▿

PubMed Central

Rodríguez-Vargas, Sonia; Sánchez-García, Alicia; Martínez-Rivas, Jose Manuel; Prieto, Jose Antonio; Randez-Gil, Francisca

2007-01-01

Unsaturated fatty acids play an essential role in the biophysical characteristics of cell membranes and determine the proper function of membrane-attached proteins. Thus, the ability of cells to alter the degree of unsaturation in their membranes is an important factor in cellular acclimatization to environmental conditions. Many eukaryotic organisms can synthesize dienoic fatty acids, but Saccharomyces cerevisiae can introduce only a single double bond at the Δ9 position. We expressed two sunflower (Helianthus annuus) oleate Δ12 desaturases encoded by FAD2-1 and FAD2-3 in yeast cells of the wild-type W303-1A strain (trp1) and analyzed their effects on growth and stress tolerance. Production of the heterologous desaturases increased the content of dienoic fatty acids, especially 18:2Δ9,12, the unsaturation index, and the fluidity of the yeast membrane. The total fatty acid content remained constant, and the level of monounsaturated fatty acids decreased. Growth at 15°C was reduced in the FAD2 strains, probably due to tryptophan auxotrophy, since the trp1 (TRP1) transformants that produced the sunflower desaturases grew as well as the control strain did. Our results suggest that changes in the fluidity of the lipid bilayer affect tryptophan uptake and/or the correct targeting of tryptophan transporters. The expression of the sunflower desaturases, in either Trp+ or Trp− strains, increased NaCl tolerance. Production of dienoic fatty acids increased the tolerance to freezing of wild-type cells preincubated at 30°C or 15°C. Thus, membrane fluidity is an essential determinant of stress resistance in S. cerevisiae, and engineering of membrane lipids has the potential to be a useful tool of increasing the tolerance to freezing in industrial strains. PMID:17071783

Membrane Electromechanics at Hair-Cell Synapses

NASA Astrophysics Data System (ADS)

Brownell, W. E.; Farrell, B.; Raphael, R. M.

2003-02-01

Both outer hair cell electromotility and neurotransmission at the inner hair cell synapse are rapid mechanical events that are synchronized to the hair-cell receptor potential. We analyze whether the forces and potentials resulting from membrane flexoelectricity could affect synaptic vesicle fusion. The results suggest that the coupling of membrane curvature with membrane potential is of sufficient magnitude to influence neurotransmitter release.

Aniline Induces Oxidative Stress and Apoptosis of Primary Cultured Hepatocytes.

PubMed

Wang, Yue; Gao, Hong; Na, Xiao-Lin; Dong, Shu-Ying; Dong, Hong-Wei; Yu, Jia; Jia, Li; Wu, Yong-Hui

2016-11-30

The toxicity and carcinogenicity of aniline in humans and animals have been well documented. However, the molecular mechanism involved in aniline-induced liver toxicity and carcinogenesis remains unclear. In our research, primary cultured hepatocytes were exposed to aniline (0, 1.25, 2.50, 5.0 and 10.0 μg/mL) for 24 h in the presence or absence of N -acetyl-l-cysteine (NAC). Levels of reactive oxygen species (ROS), malondialdehyde (MDA), and glutathione (GSH), activities of superoxide dismutase (SOD) and catalase (CAT), mitochondrial membrane potential, DNA damage, cell viability, and apoptosis were detected. Levels of ROS and MDA were significantly increased and levels of GSH and CAT, activity of SOD, and mitochondrial membrane potential in hepatocytes were significantly decreased by aniline compared with the negative control group. The tail moment and DNA content of the tail in exposed groups were significantly higher than those in the negative control group. Cell viability was reduced and apoptotic death was induced by aniline in a concentration-dependent manner. The phenomena of ROS generation, oxidative damage, loss of mitochondrial membrane potential, DNA damage and apoptosis could be prevented if ROS inhibitor NAC was added. ROS generation is involved in the loss of mitochondrial membrane potential and DNA injury, which may play a role in aniline-induced apoptosis in hepatocytes. Our study provides insight into the mechanism of aniline-induced toxicity and apoptosis of hepatocytes.

Aniline Induces Oxidative Stress and Apoptosis of Primary Cultured Hepatocytes

PubMed Central

Wang, Yue; Gao, Hong; Na, Xiao-Lin; Dong, Shu-Ying; Dong, Hong-Wei; Yu, Jia; Jia, Li; Wu, Yong-Hui

2016-01-01

The toxicity and carcinogenicity of aniline in humans and animals have been well documented. However, the molecular mechanism involved in aniline-induced liver toxicity and carcinogenesis remains unclear. In our research, primary cultured hepatocytes were exposed to aniline (0, 1.25, 2.50, 5.0 and 10.0 μg/mL) for 24 h in the presence or absence of N-acetyl-l-cysteine (NAC). Levels of reactive oxygen species (ROS), malondialdehyde (MDA), and glutathione (GSH), activities of superoxide dismutase (SOD) and catalase (CAT), mitochondrial membrane potential, DNA damage, cell viability, and apoptosis were detected. Levels of ROS and MDA were significantly increased and levels of GSH and CAT, activity of SOD, and mitochondrial membrane potential in hepatocytes were significantly decreased by aniline compared with the negative control group. The tail moment and DNA content of the tail in exposed groups were significantly higher than those in the negative control group. Cell viability was reduced and apoptotic death was induced by aniline in a concentration-dependent manner. The phenomena of ROS generation, oxidative damage, loss of mitochondrial membrane potential, DNA damage and apoptosis could be prevented if ROS inhibitor NAC was added. ROS generation is involved in the loss of mitochondrial membrane potential and DNA injury, which may play a role in aniline-induced apoptosis in hepatocytes. Our study provides insight into the mechanism of aniline-induced toxicity and apoptosis of hepatocytes. PMID:27916916

Technological advances in extracorporeal membrane oxygenation for respiratory failure.

PubMed

Rehder, Kyle J; Turner, David A; Bonadonna, Desiree; Walczak, Richard J; Rudder, Robert J; Cheifetz, Ira M

2012-08-01

Extracorporeal membrane oxygenation (ECMO) for neonatal and pediatric cardiac and/or respiratory failure is well established, and its use for adult respiratory failure is rapidly increasing. Management strategies developed over the past 30 years coupled with significant recent technological advances have led to improved ECMO survival. These new technologies are expanding the potential applications for ECMO in exciting ways, including new patient populations and the ability to make ECMO mobile for both intra- and inter-hospital transport. In this article, we highlight some of the recent technological advances and their impact on the utilization of ECMO in increasingly diverse patient populations.

Electrogenic active proton pump in Rana esculenta skin and its role in sodium ion transport.

PubMed

Ehrenfeld, J; Garcia-Romeu, F; Harvey, B J

1985-02-01

Kinetic and electrophysiological studies were carried out in the in vitro Rana esculenta skin, bathed in dilute sodium solution, to characterize the proton pump and coupling between sodium absorption (JNa+n) and proton excretion (JH+n). JNa+n and JH+n were both dependent on transepithelial potential (psi ms); hyperpolarizing the skin decreased JNa+n and increased JH+n; depolarization produced the opposite effects. Amiloride (5 X 10(-5) M) at a clamped psi ms of +50 mV inhibited JNa+n without affecting JH+n. Variations of psi ms or pH had identical effects on JH+n. Ethoxzolamide inhibited JH+n and simultaneously increased psi ms by 15-30 mV. These changes were accompanied by depolarization of the apical membrane potential psi mc from -47 to -25 mV and an increase in apical membrane resistance of 30%; no significant effects on basolateral membrane potential (psi cs) and resistance (Rb) nor on shunt resistance (Rj) were observed. The proton pump appears to be localized at the apical membrane. The proton pump was also inhibited by deoxygenation, oligomycin, dicyclohexylcarbodiimide and vanadate (100, 78, 83 and 100% inhibition respectively). The variations of JH+n and of the measured electrical currents were significantly correlated. These findings are supportive evidence of a primary active proton pump, electrogenic and strictly linked to aerobic metabolism. The current-voltage (I-V) relation of the proton pump was obtained as the difference in the I-V curves of the apical membrane extracted before and after proton-pump inhibition by ethoxzolamide during amiloride block of sodium transport. The proton-pump current (IP) was best described by a saturable exponential function of psi mc. Maximal pump current (ImaxP) was calculated to be 200 nequiv h-1 cm-2 at a psi mc of +50 mV and the pump reversal potential ERP was -130 mV. The effect of ethoxzolamide to depolarize psi mc was dependent on the relation between psi mc and ERP. Maximal induced depolarization occurred at a psi mc of +50 mV whereas ethoxzolamide exerted minimal effect on psi mc when the ERP was approached either by voltage clamping the apical membrane or by the addition of amiloride. We show that electroneutral sodium-proton countertransport is not the mechanism of active proton excretion in frog skin but that it is the proton excretion which provides a favourable electrical driving force for passive apical sodium entry.(ABSTRACT TRUNCATED AT 400 WORDS)

Electrogenic active proton pump in Rana esculenta skin and its role in sodium ion transport.

PubMed Central

Ehrenfeld, J; Garcia-Romeu, F; Harvey, B J

1985-01-01

Kinetic and electrophysiological studies were carried out in the in vitro Rana esculenta skin, bathed in dilute sodium solution, to characterize the proton pump and coupling between sodium absorption (JNa+n) and proton excretion (JH+n). JNa+n and JH+n were both dependent on transepithelial potential (psi ms); hyperpolarizing the skin decreased JNa+n and increased JH+n; depolarization produced the opposite effects. Amiloride (5 X 10(-5) M) at a clamped psi ms of +50 mV inhibited JNa+n without affecting JH+n. Variations of psi ms or pH had identical effects on JH+n. Ethoxzolamide inhibited JH+n and simultaneously increased psi ms by 15-30 mV. These changes were accompanied by depolarization of the apical membrane potential psi mc from -47 to -25 mV and an increase in apical membrane resistance of 30%; no significant effects on basolateral membrane potential (psi cs) and resistance (Rb) nor on shunt resistance (Rj) were observed. The proton pump appears to be localized at the apical membrane. The proton pump was also inhibited by deoxygenation, oligomycin, dicyclohexylcarbodiimide and vanadate (100, 78, 83 and 100% inhibition respectively). The variations of JH+n and of the measured electrical currents were significantly correlated. These findings are supportive evidence of a primary active proton pump, electrogenic and strictly linked to aerobic metabolism. The current-voltage (I-V) relation of the proton pump was obtained as the difference in the I-V curves of the apical membrane extracted before and after proton-pump inhibition by ethoxzolamide during amiloride block of sodium transport. The proton-pump current (IP) was best described by a saturable exponential function of psi mc. Maximal pump current (ImaxP) was calculated to be 200 nequiv h-1 cm-2 at a psi mc of +50 mV and the pump reversal potential ERP was -130 mV. The effect of ethoxzolamide to depolarize psi mc was dependent on the relation between psi mc and ERP. Maximal induced depolarization occurred at a psi mc of +50 mV whereas ethoxzolamide exerted minimal effect on psi mc when the ERP was approached either by voltage clamping the apical membrane or by the addition of amiloride. We show that electroneutral sodium-proton countertransport is not the mechanism of active proton excretion in frog skin but that it is the proton excretion which provides a favourable electrical driving force for passive apical sodium entry.(ABSTRACT TRUNCATED AT 400 WORDS) Images Fig. 6 Fig. 7 PMID:2582114

Potentiating the Activity of Nisin against Escherichia coli

PubMed Central

Zhou, Liang; van Heel, Auke J.; Montalban-Lopez, Manuel; Kuipers, Oscar P.

2016-01-01

Lantibiotics are antimicrobial (methyl)lanthionine-containing peptides produced by various Gram-positive bacteria. The model lantibiotic, nisin, binds lipid II in the cell membrane. Additionally, after binding it can insert into the membrane creating a pore. Nisin can efficiently inhibit the growth of Gram-positive bacteria and resistance is rarely observed. However, the activity of lantibiotics is at least 100-fold lower against certain Gram-negative bacteria. This is caused by the fact that Gram-negative bacteria have an outer membrane that hinders the peptides to reach lipid II, which is located in the inner membrane. Improving the activity of lantibiotics against Gram-negative bacteria could be achieved if the outer membrane traversing efficiency is increased. Here, several anti-Gram-negative peptides (e.g., apidaecin 1b, oncocin), or parts thereof, were fused to the C-terminus of either a truncated version of nisin containing the first three/five rings or full length nisin. The activities of these fusion peptides were tested against Gram-negative pathogens. Our results showed that when an eight amino acids (PRPPHPRL) tail from apidaecin 1b was attached to nisin, the activity of nisin against Escherichia coli CECT101 was increased more than two times. This research presents a new and promising method to increase the anti-Gram-negative activity of lantibiotics. PMID:26904542

Review of Membrane Oxygen Enrichment for Efficient Combustion

NASA Astrophysics Data System (ADS)

Ariono, Danu; Kusuma Wardani, Anita

2017-07-01

Oxygen enrichment from air is a simple way of increasing the efficiency of combustion process, as in oxy-combustion. Oxy-combustion has become one of the most attracting combustion technologies because of its potential to address both pollutant reduction and CO2 capture. In oxy-combustion, the fuel and recycled flue gas are combusted with oxygen enriched air (OEA). By using OEA, many benefits can be obtained, such as increasing available heat, improving ignition characteristics, flue gas reduction, increasing productivity, energy efficiency, turndown ratio, and flame stability. Membrane-based gas separation for OEA production becomes an attractive technology over the conventional technology due to the some advantages, including low capital cost, low energy consumption, compact size, and modularity. A single pass through membrane usually can enrich O2 concentration in the air up to 35% and a 50% concentration can be achieved with a double pass of membrane. The use of OEA in the combustion process eliminates the presence of nitrogen in the flue gas. Hence, the flue gas is mainly composed of CO2 and condensable water that can be easily separated. This paper gives an overview of oxy-combustion with membrane technology for oxygen enrichment process. Special attention is given to OEA production and the effect of OEA to the efficiency of combustion.

The role of membrane fluidization in the gel-assisted formation of giant polymersomes

DOE PAGES

Greene, Adrienne C.; Henderson, Ian M.; Gomez, Andrew; ...

2016-07-13

Polymersomes are being widely explored as synthetic analogs of lipid vesicles based on their enhanced stability and potential uses in a wide variety of applications in (e.g., drug delivery, cell analogs, etc.). Controlled formation of giant polymersomes for use in membrane studies and cell mimetic systems, however, is currently limited by low-yield production methodologies. Here, we describe for the first time, how the size distribution of giant poly(ethylene glycol)-poly(butadiene) (PEO-PBD) polymersomes formed by gel-assisted rehydration may be controlled based on membrane fluidization. We first show that the average diameter and size distribution of PEO-PBD polymersomes may be readily increased bymore » increasing the temperature of the rehydration solution. Further, we describe a correlative relationship between polymersome size and membrane fluidization through the addition of sucrose during rehydration, enabling the formation of PEO-PBD polymersomes with a range of diameters, including giant-sized vesicles (>100 μm). This correlative relationship suggests that sucrose may function as a small molecule fluidizer during rehydration, enhancing polymer diffusivity during formation and increasing polymersome size. Altogether the ability to easily regulate the size of PEO-PBD polymersomes based on membrane fluidity, either through temperature or fluidizers, has broadly applicability in areas including targeted therapeutic delivery and synthetic biology.« less

Membrane-Targeting DCAP Analogues with Broad-Spectrum Antibiotic Activity against Pathogenic Bacteria

PubMed Central

2015-01-01

We performed a structure–activity relationship study of 2-((3-(3,6-dichloro-9H-carbazol-9-yl)-2-hydroxypropyl)amino)-2-(hydroxymethyl)propane-1,3-diol (DCAP), which is an antibacterial agent that disrupts the membrane potential and permeability of bacteria. The stereochemistry of DCAP had no effect on the biological activity of DCAP. The aromaticity and electronegativity of the chlorine-substituted carbazole was required for activity, suggesting that its planar and dipolar characteristics orient DCAP in membranes. Increasing the hydrophobicity of the tail region of DCAP enhanced its antibiotic activity. Two DCAP analogues displayed promising antibacterial activity against the BSL-3 pathogens Bacillus anthracis and Francisella tularensis. Codosing DCAP analogues with ampicillin or kanamycin increased their potency. These studies demonstrate that DCAP and its analogues may be a promising scaffold for developing chemotherapeutic agents that bind to bacterial membranes and kill strains of slow-growing or dormant bacteria that cause persistent infections. PMID:25941556

Ion channels to inactivate neurons in Drosophila.

PubMed

Hodge, James J L

2009-01-01

Ion channels are the determinants of excitability; therefore, manipulation of their levels and properties provides an opportunity for the investigator to modulate neuronal and circuit function. There are a number of ways to suppress electrical activity in Drosophila neurons, for instance, over-expression of potassium channels (i.e. Shaker Kv1, Shaw Kv3, Kir2.1 and DORK) that are open at resting membrane potential. This will result in increased potassium efflux and membrane hyperpolarisation setting resting membrane potential below the threshold required to fire action potentials. Alternatively over-expression of other channels, pumps or co-transporters that result in a hyperpolarised membrane potential will also prevent firing. Lastly, neurons can be inactivated by, disrupting or reducing the level of functional voltage-gated sodium (Nav1 paralytic) or calcium (Cav2 cacophony) channels that mediate the depolarisation phase of action potentials. Similarly, strategies involving the opposite channel manipulation should allow net depolarisation and hyperexcitation in a given neuron. These changes in ion channel expression can be brought about by the versatile transgenic (i.e. Gal4/UAS based) systems available in Drosophila allowing fine temporal and spatial control of (channel) transgene expression. These systems are making it possible to electrically inactivate (or hyperexcite) any neuron or neural circuit in the fly brain, and much like an exquisite lesion experiment, potentially elucidate whatever interesting behaviour or phenotype each network mediates. These techniques are now being used in Drosophila to reprogram electrical activity of well-defined circuits and bring about robust and easily quantifiable changes in behaviour, allowing different models and hypotheses to be rapidly tested.

Free-radicals and advanced chemistries involved in cell membrane organization influence oxygen diffusion and pathology treatment.

PubMed

Petersen, Richard C

2017-01-01

A breakthrough has been discovered in pathology chemistry related to increasing molecular structure that can interfere with oxygen diffusion through cell membranes. Free radicals can crosslink unsaturated low-viscosity fatty acid oils by chain-growth polymerization into more viscous liquids and even solids. Free radicals are released by mitochondria in response to intermittent hypoxia that can increase membrane molecular organization to reduce fluidity and oxygen diffusion in a possible continuing vicious cycle toward pathological disease. Alternate computational chemistry demonstrates molecular bond dynamics in free energy for cell membrane physiologic movements. Paired electrons in oxygen and nitrogen atoms require that oxygen bonds rotate and nitrogen bonds invert to seek polar nano-environments and hide from nonpolar nano-environments thus creating fluctuating instability at a nonpolar membrane and polar biologic fluid interface. Subsequent mechanomolecular movements provide free energy to increase diffusion by membrane transport of molecules and oxygen into the cell, cell-membrane signaling/recognition/defense in addition to protein movements for enzyme mixing. In other chemistry calcium bonds to membrane phosphates primarily on the outer plasma cell membrane surface to influence the membrane firing threshold for excitability and better seal out water permeation. Because calcium is an excellent metal conductor and membrane phosphate headgroups form a semiconductor at the biologic fluid interface, excess electrons released by mitochondria may have more broad dissipation potential by safe conduction through calcium atomic-sized circuits on the outer membrane surface. Regarding medical conditions, free radicals are known to produce pathology especially in age-related disease in addition to aging. Because cancer cell membranes develop extreme polymorphism that has been extensively followed in research, accentuated easily-visualized free-radical models are developed. In terms of treatment, use of vitamin nutrient supplements purported to be antioxidants that remove free radicals has not proved worthwhile in clinical trials presumably due to errors with early antioxidant measurements based on inaccurate colorimetry tests. However, newer covalent-bond shrinkage tests now provide accurate measurements for free-radical inhibitor hydroquinone and other molecules toward drug therapy.

Free-radicals and advanced chemistries involved in cell membrane organization influence oxygen diffusion and pathology treatment

PubMed Central

Petersen, Richard C

2017-01-01

A breakthrough has been discovered in pathology chemistry related to increasing molecular structure that can interfere with oxygen diffusion through cell membranes. Free radicals can crosslink unsaturated low-viscosity fatty acid oils by chain-growth polymerization into more viscous liquids and even solids. Free radicals are released by mitochondria in response to intermittent hypoxia that can increase membrane molecular organization to reduce fluidity and oxygen diffusion in a possible continuing vicious cycle toward pathological disease. Alternate computational chemistry demonstrates molecular bond dynamics in free energy for cell membrane physiologic movements. Paired electrons in oxygen and nitrogen atoms require that oxygen bonds rotate and nitrogen bonds invert to seek polar nano-environments and hide from nonpolar nano-environments thus creating fluctuating instability at a nonpolar membrane and polar biologic fluid interface. Subsequent mechanomolecular movements provide free energy to increase diffusion by membrane transport of molecules and oxygen into the cell, cell-membrane signaling/recognition/defense in addition to protein movements for enzyme mixing. In other chemistry calcium bonds to membrane phosphates primarily on the outer plasma cell membrane surface to influence the membrane firing threshold for excitability and better seal out water permeation. Because calcium is an excellent metal conductor and membrane phosphate headgroups form a semiconductor at the biologic fluid interface, excess electrons released by mitochondria may have more broad dissipation potential by safe conduction through calcium atomic-sized circuits on the outer membrane surface. Regarding medical conditions, free radicals are known to produce pathology especially in age-related disease in addition to aging. Because cancer cell membranes develop extreme polymorphism that has been extensively followed in research, accentuated easily-visualized free-radical models are developed. In terms of treatment, use of vitamin nutrient supplements purported to be antioxidants that remove free radicals has not proved worthwhile in clinical trials presumably due to errors with early antioxidant measurements based on inaccurate colorimetry tests. However, newer covalent-bond shrinkage tests now provide accurate measurements for free-radical inhibitor hydroquinone and other molecules toward drug therapy. PMID:29202036

VDAC electronics: 1. VDAC-hexo(gluco)kinase generator of the mitochondrial outer membrane potential.

PubMed

Lemeshko, Victor V

2014-05-01

The simplest mechanism of the generation of the mitochondrial outer membrane potential (OMP) by the VDAC (voltage-dependent anion channel)-hexokinase complex (VHC), suggested earlier, and by the VDAC-glucokinase complex (VGC), was computationally analyzed. Even at less than 4% of VDACs bound to hexokinase, the calculated OMP is high enough to trigger the electrical closure of VDACs beyond the complexes at threshold concentrations of glucose. These results confirmed our previous hypothesis that the Warburg effect is caused by the electrical closure of VDACs, leading to global restriction of the outer membrane permeability coupled to aerobic glycolysis. The model showed that the inhibition of the conductance and/or an increase in the voltage sensitivity of a relatively small fraction of VDACs by factors like tubulin potentiate the electrical closure of the remaining free VDACs. The extrusion of calcium ions from the mitochondrial intermembrane space by the generated OMP, positive inside, might increase cancer cell resistance to death. Within the VGC model, the known effect of induction of ATP release from mitochondria by accumulated glucose-6-phosphate in pancreatic beta cells might result not only of the known effect of GK dissociation from the VDAC-GK complex, but also of a decrease in the free energy of glucokinase reaction, leading to the OMP decrease and VDAC opening. We suggest that the VDAC-mediated electrical control of the mitochondrial outer membrane permeability, dependent on metabolic conditions, is a fundamental physiological mechanism of global regulation of mitochondrial functions and of cell death. Copyright © 2014 Elsevier B.V. All rights reserved.

The physostigmine depolarization potentiating effect of salicylate in frog skeletal muscle.

PubMed

Varga, E; Kovács, L; Szücs, G; Illés, B

1975-01-01

1) The frog's sartorius muscle was depolarized depending on the degree of concentration 2--4 times more intensely by physostigmine salicylate than by physostigmine sulphate. 2) In normal Ringer's solution, 1 mM physostigmine salicylate decreased the sensitivity of the membrane to potassium depolarization by about 90%. Under similar experimental conditions, physostigmine sulphate and Na salicylate, respectively, decrease the sensitivity of the membrane to potassium depolarization by about 30%. 3) The difference manifested in the depolarizing effect of salicylate and other physostigmine salts (chloride, sulphate, phosphate, formiate, acetate, monochloracetate, benzoate and para-oxy-benzoate) is expressed already at 1 mM concentration (about 10-fold), if the muscle had been equilibrated in chloride-free glucuronate or sulphate milieu. 4) The depolarization develops slowly. It takes 30--60 minutes for the new steady state to develop even in the superficial sartorius fibres. If depolarization has reached its maximum on an average 100 mV, the membrane potential remains unchanged for hours. 5) Depolarization ensues at an unchanged degree in the presence of Na-free (choline) Ringer as well as in the presence of 2X10(-8) g/ml tetrodotoxin; therefore, it is not a Na-dependent process. 6) Under the influence of 1 mM physostigmine salicylate the membrane's resistance to the inward potassium current increased about twofold, while the increase was only 15% to the outward potassium current. It is assumed that the salicylate anion is characteristically capable of potentiating the decreasing effect of physostigmine on potassium permeability, though the role of the metabolic effect of salicylate cannot be excluded.

In vitro additive antitumor effects of dimethoxycurcumin and 5-fluorouracil in colon cancer cells.

PubMed

Zhao, Huiying; Liu, Qingchun; Wang, Saisai; Dai, Fang; Cheng, Xiaofei; Cheng, Xiaobin; Chen, Wenbin; Zhang, Min; Chen, Dong

2017-07-01

Dimethoxycurcumin (DMC) is a lipophilic analog of curcumin, an effective treatment for colon cancer, which has greater chemical and metabolic stability. Chemotherapy treatments, such as 5-fluorouracil (5-Fu), play a key role in the current management of colon cancer. In this study, we investigated the antitumor efficacy of DMC in combination with 5-Fu in SW480 and SW620 colon cancer cells. CCK-8 assay was used to evaluate the inhibitory effect of DMC and 5-Fu on cancer cells proliferation, and the combination index was calculated. The influence of DMC and 5-Fu on cell cycle, apoptosis, reactive oxygen species (ROS) production, and mitochondrial membrane potential in SW480 and SW620 cells was determined using flow cytometry, and the related signaling pathways were detected by western blot. Transmission electron microscopy was used to observe endoplasmic reticulum expansion. DMC- and/or 5-Fu-induced apoptosis, stimulated G0/G1 phase arrest, increased ROS levels, decreased mitochondrial membrane potential, and enhanced endoplasmic reticulum expansion. The induction of apoptosis is involved in the increasing of Bax and cytochrome c and decreasing of Bcl2 expressions. Increased production of ROS was accompanied by upregulation of CHOP and Noxa. Combination therapy of DMC and 5-Fu had increased efficacy on the above pathways compared with either drug alone. Based on the calculated IC 50 , combination treatment with DMC and 5-Fu had an additive antitumor effect in both cell lines. Combined treatment with DMC and 5-Fu led to an additive antitumor effect in colon cancer cells that was related to apoptosis induction, G0/G1 phase arrest, increased ROS production, decreased mitochondrial membrane potential, and enhanced endoplasmic reticulum expansion. © 2017 The Authors. Cancer Medicine published by John Wiley & Sons Ltd.

Effects of Ag+ on ion transport by the corneal epithelium of the rabbit.

PubMed

Klyce, S D; Marshall, W S

1982-01-01

Exposure of the in vitro rabbit corneal epithelium to Ag+ by the addition of AgNO3 (10(-7)-10(-5) M) to the apical surface or by the use of imperfectly chlorided Ag/AgCl half-cells in Ussing-style membrane chambers, greatly increases short-circuit current and transepithelial potential. The early phase (the first 30 min) of the short-circuit current stimulation by Ag+ is linearly dependent on tear-side sodium concentration, is largely a result of a tenfold increase in net Na+ uptake and is incompletely inhibited by ouabain, suggesting that Ag+ increases cation (primarily Na+) conductance of the apical membrane. This mechanism for the Ag+ effect is supported by microelectrode experiments, wherein Ag+ depolarizes specifically the apical barrier potential and increases apical barrier conductance. A later phase in the effect (0.5-3 hr) is characterized by a gradual increase in 36Cl- and 14C-mannitol unidirectional fluxes, by a decline in epithelial resting potential and short-circuit current, by complete ouabain inhibition and by fit to saturation kinetics with respect to Na+ concentration in the bathing media. This phase of the effect apparently reflects a nonselective opening of the paracellular pathway in the epithelium and is rate-limited by Na+ pump activity at the basolateral membrane. Both phases are associated with swelling of the corneal stroma and may be rapidly reversed using thiol agents (reduced glutathione and dithiothreitol). The results suggest that Ag+ may be useful in the study of cation transport by epithelia and the work provides basic physiological information that is pertinent to the prophylactic use of AgNO3 in clinical ophthalmology.

On the causes and consequences of the uncoupler-like effects of quercetin and dehydrosilybin in H9c2 cells

PubMed Central

Mouithys-Mickalad, Ange; Dostal, Zdenek; Serteyn, Didier; Modriansky, Martin

2017-01-01

Quercetin and dehydrosilybin are polyphenols which are known to behave like uncouplers of respiration in isolated mitochondria. Here we investigated whether the effect is conserved in whole cells. Following short term incubation, neither compound uncouples mitochondrial respiration in whole H9c2 cells below 50μM. However, following hypoxia, or long term incubation, leak (state IV with oligomycin) oxygen consumption is increased by quercetin. Both compounds partially protected complex I respiration, but not complex II in H9c2 cells following hypoxia. In a permeabilised H9c2 cell model, the increase in leak respiration caused by quercetin is lowered by increased [ADP] and is increased by adenine nucleotide transporter inhibitor, atractyloside, but not bongkrekic acid. Both quercetin and dehydrosilybin dissipate mitochondrial membrane potential in whole cells. In the case of quercetin, the effect is potentiated post hypoxia. Genetically encoded Ca++ sensors, targeted to the mitochondria, enabled the use of fluorescence microscopy to show that quercetin decreased mitochondrial [Ca++] while dehydrosilybin did not. Likewise, quercetin decreases accumulation of [Ca++] in mitochondria following hypoxia. Fluorescent probes were used to show that both compounds decrease plasma membrane potential and increase cytosolic [Ca++]. We conclude that the uncoupler-like effects of these polyphenols are attenuated in whole cells compared to isolated mitochondria, but downstream effects are nevertheless apparent. Results suggest that the effect of quercetin observed in whole and permeabilised cells may originate in the mitochondria, while the mechanism of action of cardioprotection by dehydrosilybin may be less dependent on mitochondrial uncoupling than originally thought. Rather, protective effects may originate due to interactions at the plasma membrane. PMID:28977033

Preparation, characterization, physical testing and performance of fluorocarbon membranes and separators

NASA Technical Reports Server (NTRS)

Lagow, R. J.; Dumitru, E. T.

1982-01-01

The direct fluorination method of converting carefully selected hydrocarbon substrates to fluorinated membranes was successfully applied to produce promising, novel membranes for electrochemical devices. A family of polymer blends was identified which permits wide latitude in the concentration of both crosslinks and carboxyl groups in hydrocarbon membranes. These membranes were successfully fluorinated and are potentially competitive with commercial membranes in performance, and potentially much cheaper in price.

Carbonate and Bicarbonate Ion Transport in Alkaline Anion Exchange Membranes

DTIC Science & Technology

2013-06-25

membranes (AEMs) are being developed for potential use in fuel cell systems which include portable power applications. In a fuel cell , these membranes...Alkaline Anion Exchange Membranes Report Title ABSTRACT Anion exchange membranes (AEMs) are being developed for potential use in fuel cell systems which...include portable power applications. In a fuel cell , these membranes transport hydroxide ions from the cathode to the anode. If carbon dioxide is

Functional TASK-3-Like Channels in Mitochondria of Aldosterone-Producing Zona Glomerulosa Cells.

PubMed

Yao, Junlan; McHedlishvili, David; McIntire, William E; Guagliardo, Nick A; Erisir, Alev; Coburn, Craig A; Santarelli, Vincent P; Bayliss, Douglas A; Barrett, Paula Q

2017-08-01

Ca 2+ drives aldosterone synthesis in the cytosolic and mitochondrial compartments of the adrenal zona glomerulosa cell. Membrane potential across each of these compartments regulates the amplitude of the Ca 2+ signal; yet, only plasma membrane ion channels and their role in regulating cell membrane potential have garnered investigative attention as pathological causes of human hyperaldosteronism. Previously, we reported that genetic deletion of TASK-3 channels (tandem pore domain acid-sensitive K + channels) from mice produces aldosterone excess in the absence of a change in the cell membrane potential of zona glomerulosa cells. Here, we report using yeast 2-hybrid, immunoprecipitation, and electron microscopic analyses that TASK-3 channels are resident in mitochondria, where they regulate mitochondrial morphology, mitochondrial membrane potential, and aldosterone production. This study provides proof of principle that mitochondrial K + channels, by modulating inner mitochondrial membrane morphology and mitochondrial membrane potential, have the ability to play a pathological role in aldosterone dysregulation in steroidogenic cells. © 2017 American Heart Association, Inc.

Sodium and potassium conductance changes during a membrane action potential

PubMed Central

Bezanilla, Francisco; Rojas, Eduardo; Taylor, Robert E.

1970-01-01

1. A method for turning a membrane potential control system on and off in less than 10 μsec is described. This method was used to record membrane currents in perfused giant axons from Dosidicus gigas and Loligo forbesi after turning on the voltage clamp system at various times during the course of a membrane action potential. 2. The membrane current measured just after the capacity charging transient was found to have an almost linear relation to the controlled membrane potential. 3. The total membrane conductance taken from these current—voltage curves was found to have a time course during the action potential similar to that found by Cole & Curtis (1939). 4. The instantaneous current voltage curves were linear enough to make it possible to obtain a good estimate of the individual sodium and potassium channel conductances, either algebraically or by clamping to the sodium, or potassium, reversal potentials. Good general agreement was obtained with the predictions of the Hodgkin—Huxley equations. 5. We consider these results to constitute the first direct experimental demonstration of the conductance changes to sodium and potassium during the course of an action potential. PMID:5505231

Fouling and long-term durability of an integrated forward osmosis and membrane distillation system.

PubMed

Husnain, T; Mi, B; Riffat, R

2015-01-01

An integrated forward osmosis (FO) and membrane distillation (MD) system has great potential for sustainable wastewater reuse. However, the fouling and long-term durability of the system remains largely unknown. This study investigates the fouling behaviour and efficiency of cleaning procedures of FO and MD membranes used for treating domestic wastewater. Results showed that a significant decline in flux of both FO and MD membranes were observed during treatment of wastewater with organic foulants. However, shear force generated by the increased cross-flow physically removed the loosely attached foulants from the FO membrane surface and resulted in 86-88% recovery of flux by cleaning with tap water. For the MD membrane, almost no flux recovery was achieved due to adsorption of organic foulants on the hydrophobic membrane surface, thus indicating significant irreversible fouling/wetting, which may not be effectively cleaned even with chemical reagents. Long-term (10 d) tests showed consistent performance of the FO membrane by rejecting the contaminants. However, organic foulants reduced the hydrophobicity of the MD membrane, caused wetting problems and allowed contaminants to pass through. The results demonstrate that combination of the FO and MD processes can effectively reduce irreversible membrane fouling and solve the wetting problem of the MD membrane.

Cardiolipin effects on membrane structure and dynamics.

PubMed

Unsay, Joseph D; Cosentino, Katia; Subburaj, Yamunadevi; García-Sáez, Ana J

2013-12-23

Cardiolipin (CL) is a lipid with unique properties solely found in membranes generating electrochemical potential. It contains four acyl chains and tends to form nonlamellar structures, which are believed to play a key role in membrane structure and function. Indeed, CL alterations have been linked to disorders such as Barth syndrome and Parkinson's disease. However, the molecular effects of CL on membrane organization remain poorly understood. Here, we investigated the structure and physical properties of CL-containing membranes using confocal microscopy, fluorescence correlation spectroscopy, and atomic force microscopy. We found that the fluidity of the lipid bilayer increased and its mechanical stability decreased with CL concentration, indicating that CL decreases the packing of the membrane. Although the presence of up to 20% CL gave rise to flat, stable bilayers, the inclusion of 5% CL promoted the formation of flowerlike domains that grew with time. Surprisingly, we often observed two membrane-piercing events in atomic force spectroscopy experiments with CL-containing membranes. Similar behavior was observed with a lipid mixture mimicking the mitochondrial outer membrane composition. This suggests that CL promotes the formation of membrane areas with apposed double bilayers or nonlamellar structures, similar to those proposed for mitochondrial contact sites. All together, we show that CL induces membrane alterations that support the role of CL in facilitating bilayer structure remodeling, deformation, and permeabilization.

Atomic force microscope-related study membrane-associated cytotoxicity in human pterygium fibroblasts induced by mitomycin C.

PubMed

Cai, Xiaofang; Yang, Xiaoxi; Cai, Jiye; Wu, Shixian; Chen, Qian

2010-03-25

Mitomycin C (MMC) has been shown to have a therapeutic effect against human pterygium fibroblasts (HPFs) by inducing apoptosis. However, there is little data about the effect of it on plasma membrane. In the present study, the cytotoxicity of MMC to HPFs including inhibiting cell growth, inducing apoptosis and bringing about membrane toxicity was investigated. It was found that MMC could significantly suppress the proliferation of HPFs in a dose-dependent manner by CCK-8 assay. Flow cytometric analysis also revealed that treatment with MMC resulted in increased percentages of apoptotic cells in a dose-dependent manner. Membrane lipid peroxidation level, lactate dehydrogenase (LDH) leakage, membrane surface topography, and membrane rigidity alterations were investigated to assess the membrane toxicity induced by MMC. Treatment with MMC at different concentrations accelerated membrane lipid peroxidation and potentiated LDH leakage, which was consistent with disturbance of membrane surface and decrease of membrane elasticity detected by atomic force microscopy. All the above changes led to the disturbed intracellular Ca(2+) homeostasis, which was an important signal triggering apoptosis. Hence, the membrane toxicity induced by MMC might play an important role in the process of apoptotic induction and the calcium channel may be one of the apoptosis mechanisms.

Effect of ion concentration, solution and membrane permittivity on electric energy storage and capacitance.

PubMed

Tajparast, Mohammad; Glavinović, Mladen I

2018-06-06

Bio-membranes as capacitors store electric energy, but their permittivity is low whereas the permittivity of surrounding solution is high. To evaluate the effective capacitance of the membrane/solution system and determine the electric energy stored within the membrane and in the solution, we estimated their electric variables using Poisson-Nernst-Planck simulations. We calculated membrane and solution capacitances from stored electric energy. The effective capacitance was calculated by fitting a six-capacitance model to charges (fixed and ion) and associated potentials, because it cannot be considered as a result of membrane and solution capacitance in series. The electric energy stored within the membrane (typically much smaller than that in the solution), depends on the membrane permittivity, but also on the external electric field, surface charge density, water permittivity and ion concentration. The effect on capacitances is more specific. Solution capacitance rises with greater solution permittivity or ion concentration, but the membrane capacitance (much smaller than solution capacitance) is only influenced by its permittivity. Interestingly, the effective capacitance is independent of membrane or solution permittivity, but rises as the ion concentration increases and surface charge becomes positive. Experimental estimates of membrane capacitance are thus not necessarily a reliable index of its surface area. Copyright © 2018. Published by Elsevier B.V.

Observing a model ion channel gating action in model cell membranes in real time in situ: membrane potential change induced alamethicin orientation change.

PubMed

Ye, Shuji; Li, Hongchun; Wei, Feng; Jasensky, Joshua; Boughton, Andrew P; Yang, Pei; Chen, Zhan

2012-04-11

Ion channels play crucial roles in transport and regulatory functions of living cells. Understanding the gating mechanisms of these channels is important to understanding and treating diseases that have been linked to ion channels. One potential model peptide for studying the mechanism of ion channel gating is alamethicin, which adopts a split α/3(10)-helix structure and responds to changes in electric potential. In this study, sum frequency generation vibrational spectroscopy (SFG-VS), supplemented by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), has been applied to characterize interactions between alamethicin (a model for larger channel proteins) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid bilayers in the presence of an electric potential across the membrane. The membrane potential difference was controlled by changing the pH of the solution in contact with the bilayer and was measured using fluorescence spectroscopy. The orientation angle of alamethicin in POPC lipid bilayers was then determined at different pH values using polarized SFG amide I spectra. Assuming that all molecules adopt the same orientation (a δ distribution), at pH = 6.7 the α-helix at the N-terminus and the 3(10)-helix at the C-terminus tilt at about 72° (θ(1)) and 50° (θ(2)) versus the surface normal, respectively. When pH increases to 11.9, θ(1) and θ(2) decrease to 56.5° and 45°, respectively. The δ distribution assumption was verified using a combination of SFG and ATR-FTIR measurements, which showed a quite narrow distribution in the angle of θ(1) for both pH conditions. This indicates that all alamethicin molecules at the surface adopt a nearly identical orientation in POPC lipid bilayers. The localized pH change in proximity to the bilayer modulates the membrane potential and thus induces a decrease in both the tilt and the bend angles of the two helices in alamethicin. This is the first reported application of SFG to the study of model ion channel gating mechanisms in model cell membranes. © 2012 American Chemical Society

Removal of micropollutants from Sakarya River water by ozone and membrane processes.

PubMed

Yaman, Fatma Büşra; Çakmakcı, Mehmet; Yüksel, Ebubekir; Özen, İsmail; Gengeç, Erhan

2017-09-01

The removal of some pollutants in the Sakarya River was investigated in this study. Sakarya River located in Turkey flows from the northeast of Afyonkarahisar City to the Black Sea. Nineteen different micropollutants including trihalomethanes (THMs), haloacetic acids (HAAs), endocrine disrupting compound (EDC) and pharmaceuticals personal care product (PPCP) groups, and water quality parameters such as dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm wavelength (UV 254 ), hardness, and conductivity values were examined. To remove the micropollutants and improve the water quality, the treatment was performed with ozone, microfiltration (MF), and ultra-filtration (UF) membranes. The highest treatment efficiency was obtained with 1 mg/L ozone dosage and UP005 UF membrane. The trihalomethan formation potential (THMFP) and haloacetic acid formation potential (HAAFP) decreased with ozone + membrane at a concentration of 79 and 75%, respectively. After the treatment with ozone + membrane, the concentration of the micropollutants in the EDC and PPCP group remained below the detection limit. It was found that by using only membrane and only ozone, the maximum DOC removal efficiency achieved was 46 and 18%, respectively; and with ozone + membrane, this efficiency increased up to 82%. The results from the High-Pressure Size Exclusion Chromatography (HPSEC) analyses pointed that the substances with high molecular weight were converted into substances with low molecular weight after the treatment. The Fourier Transform Infrared (FTIR) analysis results showed that the aromatic and aliphatic functional groups in water changed after the treatment with ozone and that the peak values decreased more after the ozone + membrane treatment.

THE CRITICAL ROLE OF VOLTAGE-DEPENDENT CALCIUM CHANNEL IN AXONAL REPAIR FOLLOWING MECHANICAL TRAUMA

PubMed Central

Nehrt, Ashley; Rodgers, Richard; Shapiro, Scott; Borgens, Richard; Shi, Riyi

2009-01-01

Membrane disruption following mechanical injury likely plays a critical role in the pathology of spinal cord trauma. It is known that intracellular calcium is a key factor that is essential to membrane resealing. However, the differential role of calcium influx through the injury site and through voltage dependent calcium channels (VDCC) has not been examined in detail. Using a well established ex vivo guinea pig spinal cord white matter preparation, we have found that axonal membrane resealing was significantly inhibited following transection or compression in the presence of cadmiun, a non-specific calcium channel blocker, or nimodipine, a specific L-type calcium channel blocker. Membrane resealing was assessed by the changes of membrane potential and compound action potential (CAP), and exclusion of horseradish peroxidase 60 minutes following trauma. Furthermore, 1 μM BayK 8644, a VDCC agonist, significantly enhanced membrane resealing. Interestingly, this effect was completely abolished when the concentration of BayK 8644 was increased to 30 μM. These data suggest that VDCC play a critical role in membrane resealing. Further, there is likely an appropriate range of calcium influx through VDCC which ensures effective axonal membrane resealing. Since elevated intracellular calcium has also been linked to axonal deterioration, blockage of VDCC is proposed to be a clinical treatment for various injuries. The knowledge gained in this study will likely help us better understand the role of calcium in various CNS trauma, which is critical for designing new approaches or perhaps optimizing the effectiveness of existing methods in the treatment of CNS trauma. PMID:17448606

Na+/H+ Exchange Activity in the Plasma Membrane of Arabidopsis1

PubMed Central

Qiu, Quan-Sheng; Barkla, Bronwyn J.; Vera-Estrella, Rosario; Zhu, Jian-Kang; Schumaker, Karen S.

2003-01-01

In plants, Na+/H+ exchangers in the plasma membrane are critical for growth in high levels of salt, removing toxic Na+ from the cytoplasm by transport out of the cell. The molecular identity of a plasma membrane Na+/H+ exchanger in Arabidopsis (SOS1) has recently been determined. In this study, immunological analysis provided evidence that SOS1 localizes to the plasma membrane of leaves and roots. To characterize the transport activity of this protein, purified plasma membrane vesicles were isolated from leaves of Arabidopsis. Na+/H+ exchange activity, monitored as the ability of Na to dissipate an established pH gradient, was absent in plants grown without salt. However, exchange activity was induced when plants were grown in 250 mm NaCl and increased with prolonged salt exposure up to 8 d. H+-coupled exchange was specific for Na, because chloride salts of other monovalent cations did not dissipate the pH gradient. Na+/H+ exchange activity was dependent on Na (substrate) concentration, and kinetic analysis indicated that the affinity (apparent Km) of the transporter for Na+ is 22.8 mm. Data from two experimental approaches supports electroneutral exchange (one Na+ exchanged for one proton): (a) no change in membrane potential was measured during the exchange reaction, and (b) Na+/H+ exchange was unaffected by the presence or absence of a membrane potential. Results from this research provide a framework for future studies into the regulation of the plant plasma membrane Na+/H+ exchanger and its relative contribution to the maintenance of cellular Na+ homeostasis during plant growth in salt. PMID:12805632

Na+/H+ exchange activity in the plasma membrane of Arabidopsis.

PubMed

Qiu, Quan-Sheng; Barkla, Bronwyn J; Vera-Estrella, Rosario; Zhu, Jian-Kang; Schumaker, Karen S

2003-06-01

In plants, Na+/H+ exchangers in the plasma membrane are critical for growth in high levels of salt, removing toxic Na+ from the cytoplasm by transport out of the cell. The molecular identity of a plasma membrane Na+/H+ exchanger in Arabidopsis (SOS1) has recently been determined. In this study, immunological analysis provided evidence that SOS1 localizes to the plasma membrane of leaves and roots. To characterize the transport activity of this protein, purified plasma membrane vesicles were isolated from leaves of Arabidopsis. Na+/H+ exchange activity, monitored as the ability of Na to dissipate an established pH gradient, was absent in plants grown without salt. However, exchange activity was induced when plants were grown in 250 mm NaCl and increased with prolonged salt exposure up to 8 d. H+-coupled exchange was specific for Na, because chloride salts of other monovalent cations did not dissipate the pH gradient. Na+/H+ exchange activity was dependent on Na (substrate) concentration, and kinetic analysis indicated that the affinity (apparent Km) of the transporter for Na+ is 22.8 mm. Data from two experimental approaches supports electroneutral exchange (one Na+ exchanged for one proton): (a) no change in membrane potential was measured during the exchange reaction, and (b) Na+/H+ exchange was unaffected by the presence or absence of a membrane potential. Results from this research provide a framework for future studies into the regulation of the plant plasma membrane Na+/H+ exchanger and its relative contribution to the maintenance of cellular Na+ homeostasis during plant growth in salt.

An Extended Proteome Map of the Lysosomal Membrane Reveals Novel Potential Transporters*

PubMed Central

Chapel, Agnès; Kieffer-Jaquinod, Sylvie; Sagné, Corinne; Verdon, Quentin; Ivaldi, Corinne; Mellal, Mourad; Thirion, Jaqueline; Jadot, Michel; Bruley, Christophe; Garin, Jérôme; Gasnier, Bruno; Journet, Agnès

2013-01-01

Lysosomes are membrane-bound endocytic organelles that play a major role in degrading cell macromolecules and recycling their building blocks. A comprehensive knowledge of the lysosome function requires an extensive description of its content, an issue partially addressed by previous proteomic analyses. However, the proteins underlying many lysosomal membrane functions, including numerous membrane transporters, remain unidentified. We performed a comparative, semi-quantitative proteomic analysis of rat liver lysosome-enriched and lysosome-nonenriched membranes and used spectral counts to evaluate the relative abundance of proteins. Among a total of 2,385 identified proteins, 734 proteins were significantly enriched in the lysosomal fraction, including 207 proteins already known or predicted as endo-lysosomal and 94 proteins without any known or predicted subcellular localization. The remaining 433 proteins had been previously assigned to other subcellular compartments but may in fact reside on lysosomes either predominantly or as a secondary location. Many membrane-associated complexes implicated in diverse processes such as degradation, membrane trafficking, lysosome biogenesis, lysosome acidification, signaling, and nutrient sensing were enriched in the lysosomal fraction. They were identified to an unprecedented extent as most, if not all, of their subunits were found and retained by our screen. Numerous transporters were also identified, including 46 novel potentially lysosomal proteins. We expressed 12 candidates in HeLa cells and observed that most of them colocalized with the lysosomal marker LAMP1, thus confirming their lysosomal residency. This list of candidate lysosomal proteins substantially increases our knowledge of the lysosomal membrane and provides a basis for further characterization of lysosomal functions. PMID:23436907

Incubation of human sperm with micelles made from glycerophospholipid mixtures increases sperm motility and resistance to oxidative stress

PubMed Central

Costa, Carlos; Bassaizteguy, Verónica; Cardozo, Romina; Montes, José; Settineri, Robert; Nicolson, Garth L.

2018-01-01

Membrane integrity is essential in maintaining sperm viability, signaling, and motility, which are essential for fertilization. Sperm are highly susceptible to oxidative stress, as they are rich in sensitive polyunsaturated fatty acids (PUFA), and are unable to synthesize and repair many essential membrane constituents. Because of this, sperm cellular membranes are important targets of this process. Membrane Lipid Replacement (MLR) with glycerophospholipid mixtures (GPL) has been shown to ameliorate oxidative stress in cells, restore their cellular membranes, and prevent loss of function. Therefore, we tested the effects of MLR on sperm by tracking and monitoring GPL incorporation into their membrane systems and studying their effects on sperm motility and viability under different experimental conditions. Incubation of sperm with mixtures of exogenous, unoxidized GPL results in their incorporation into sperm membranes, as shown by the use of fluorescent dyes attached to GPL. The percent overall (total) sperm motility was increased from 52±2.5% to 68±1.34% after adding GPL to the incubation media, and overall sperm motility was recovered from 7±2% after H2O2 treatment to 58±2.5%)(n = 8, p<0.01) by the incorporation of GPL into sperm membranes. When sperm were exposed to H2O2, the mitochondrial inner membrane potential (MIMP), monitored using the MIMP tracker dye JC-1 in flow cytometry, diminished, whereas the addition of GPL prevented the decrease in MIMP. Confocal microscopy with Rhodamine-123 and JC-1 confirmed the mitochondrial localization of the dyes. We conclude that incubation of human sperm with glycerolphospholipids into the membranes of sperm improves sperm viability, motility, and resistance to oxidizing agents like H2O2. This suggests that human sperm might be useful to test innovative new treatments like MLR, since such treatments could improve fertility when it is adversely affected by increased oxidative stress. PMID:29856778

Endoplasmic reticulum stress is increased after spontaneous labor in human fetal membranes and myometrium where it regulates the expression of prolabor mediators.

PubMed

Liong, Stella; Lappas, Martha

2014-09-01

Increasing evidence indicates that endoplasmic reticulum (ER) stress is involved in various diseases. In nongestational tissues, several markers of the unfolded protein response (UPR) have been shown to regulate the inflammatory response. Thus, the aim of this study was to determine the effect of human labor on markers of ER stress in fetal membranes and myometrium. In addition, the effect of ER stress inhibition on the expression and secretion of proinflammatory and prolabor mediators was also assessed. The markers of ER stress, GRP78, IRE1, and spliced XBP1 (XBP1s), were significantly increased in fetal membranes and myometrium after term and preterm labor compared to nonlaboring samples. Given that inflammation is considered to be one of the leading causes of spontaneous preterm birth, here we used bacterial endotoxin lipopolysaccharide (LPS) as a model for infection-induced preterm birth. In term nonlabored fetal membranes and myometrium, LPS induced UPR activation as evidenced by a significant increase in the expression of GRP78, IRE1, and XBP1s in fetal membranes and myometrium. The use of the chemical chaperones 4-phenylbutyric acid (4-PBA) and tauroursodeoxycholic acid (TUDCA) alleviated ER stress induced by LPS. 4-PBA and TUDCA also ameliorated the increase in LPS-induced prolabor mediators. Our data suggest that the UPR may regulate the inflammatory responses associated with labor or infection in fetal membranes and myometrium of pregnant term and preterm women. Thus, the use of ER stress inhibitors, in particular 4-PBA or TUDCA, may be a potential therapeutic strategy for the prevention of infection-mediated spontaneous preterm birth. © 2014 by the Society for the Study of Reproduction, Inc.

Hysteresis in voltage-gated channels.

PubMed

Villalba-Galea, Carlos A

2017-03-04

Ion channels constitute a superfamily of membrane proteins found in all living creatures. Their activity allows fast translocation of ions across the plasma membrane down the ion's transmembrane electrochemical gradient, resulting in a difference in electrical potential across the plasma membrane, known as the membrane potential. A group within this superfamily, namely voltage-gated channels, displays activity that is sensitive to the membrane potential. The activity of voltage-gated channels is controlled by the membrane potential, while the membrane potential is changed by these channels' activity. This interplay produces variations in the membrane potential that have evolved into electrical signals in many organisms. These signals are essential for numerous biological processes, including neuronal activity, insulin release, muscle contraction, fertilization and many others. In recent years, the activity of the voltage-gated channels has been observed not to follow a simple relationship with the membrane potential. Instead, it has been shown that the activity of voltage-gated channel displays hysteresis. In fact, a growing number of evidence have demonstrated that the voltage dependence of channel activity is dynamically modulated by activity itself. In spite of the great impact that this property can have on electrical signaling, hysteresis in voltage-gated channels is often overlooked. Addressing this issue, this review provides examples of voltage-gated ion channels displaying hysteretic behavior. Further, this review will discuss how Dynamic Voltage Dependence in voltage-gated channels can have a physiological role in electrical signaling. Furthermore, this review will elaborate on the current thoughts on the mechanism underlying hysteresis in voltage-gated channels.

Ammonia toxicity: from head to toe?

PubMed

Dasarathy, Srinivasan; Mookerjee, Rajeshwar P; Rackayova, Veronika; Rangroo Thrane, Vinita; Vairappan, Balasubramaniyan; Ott, Peter; Rose, Christopher F

2017-04-01

Ammonia is diffused and transported across all plasma membranes. This entails that hyperammonemia leads to an increase in ammonia in all organs and tissues. It is known that the toxic ramifications of ammonia primarily touch the brain and cause neurological impairment. However, the deleterious effects of ammonia are not specific to the brain, as the direct effect of increased ammonia (change in pH, membrane potential, metabolism) can occur in any type of cell. Therefore, in the setting of chronic liver disease where multi-organ dysfunction is common, the role of ammonia, only as neurotoxin, is challenged. This review provides insights and evidence that increased ammonia can disturb many organ and cell types and hence lead to dysfunction.

Molecular dynamics studies of simple membrane-water interfaces: Structure and functions in the beginnings of cellular life

NASA Technical Reports Server (NTRS)

Pohorille, Andrew; Wilson, Michael A.

1995-01-01

Molecular dynamics computer simulations of the structure and functions of a simple membrane are performed in order to examine whether membranes provide an environment capable of promoting protobiological evolution. Our model membrane is composed of glycerol 1-monooleate. It is found that the bilayer surface fluctuates in time and space, occasionally creating thinning defects in the membrane. These defects are essential for passive transport of simple ions across membranes because they reduce the Born barrier to this process by approximately 40%. Negative ions are transferred across the bilayer more readily than positive ions due to favorable interactions with the electric field at the membrane-water interface. Passive transport of neutral molecules is, in general, more complex than predicted by the solubility-diffusion model. In particular, molecules which exhibit sufficient hydrophilicity and lipophilicity concentrate near membrane surfaces and experience 'interfacial resistance' to transport. The membrane-water interface forms an environment suitable for heterogeneous catalysis. Several possible mechanisms leading to an increase of reaction rates at the interface are discussed. We conclude that vesicles have many properties that make them very good candidates for earliest protocells. Some potentially fruitful directions of experimental and theoretical research on this subject are proposed.

Temperature and Pressure Effects of Desalination Using a MFI-Type Zeolite Membrane

PubMed Central

Zhu, Bo; Kim, Jun Hyun; Na, Yong-Han; Moon, Il-Shik; Connor, Greg; Maeda, Shuichi; Morris, Gayle; Gray, Stephen; Duke, Mikel

2013-01-01

Zeolites are potentially a robust desalination alternative, as they are chemically stable and possess the essential properties needed to reject ions. Zeolite membranes could desalinate “challenging” waters, such as saline secondary effluent, without any substantial pre-treatment, due to the robust mechanical properties of ceramic membranes. A novel MFI-type zeolite membrane was developed on a tubular α-Al2O3 substrate by a combined rubbing and secondary hydrothermal growth method. The prepared membrane was characterised by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and single gas (He or N2) permeation and underwent desalination tests with NaCl solutions under different pressures (0.7 MPa and 7 MPa). The results showed that higher pressure resulted in higher Na+ rejection and permeate flux. The zeolite membrane achieved a good rejection of Na+ (~82%) for a NaCl feed solution with a TDS (total dissolved solids) of 3000 mg·L−1 at an applied pressure of 7 MPa and 21 °C. To explore the opportunity for high salinity and high temperature desalination, this membrane was also tested with high concentration NaCl solutions (up to TDS 90,000 mg·L−1) and at 90 °C. This is the first known work at such high salinities of NaCl. It was found that increasing the salinity of the feed solution decreased both Na+ rejection and flux. An increase in testing temperature resulted in an increase in permeate flux, but a decrease in ion rejection. PMID:24956943

The force exerted by the membrane potential during protein import into the mitochondrial matrix

NASA Technical Reports Server (NTRS)

Shariff, Karim; Ghosal, Sandip; Matouschek, Andreas

2004-01-01

The force exerted on a targeting sequence by the electrical potential across the inner mitochondrial membrane is calculated on the basis of continuum electrostatics. The force is found to vary from 3.0 pN to 2.2 pN (per unit elementary charge) as the radius of the inner membrane pore (assumed aqueous) is varied from 6.5 to 12 A, its measured range. In the present model, the decrease in force with increasing pore width arises from the shielding effect of water. Since the pore is not very much wider than the distance between water molecules, the full shielding effect of water may not be present; the extreme case of a purely membranous pore without water gives a force of 3.2 pN per unit charge, which should represent an upper limit. When applied to mitochondrial import experiments on the protein barnase, these results imply that forces between 11 +/- 2 pN and 13.5 +/- 2.5 pN catalyze the unfolding of barnase in those experiments. A comparison of these results with unfolding forces measured using atomic force microscopy is made.

Low-power laser effects at the single-cell level: a confocal microscopy study

NASA Astrophysics Data System (ADS)

Alexandratou, Eleni; Yova, Dido M.; Atlamazoglou, Vassilis; Handris, Panagiotis; Kletsas, Dimitris; Loukas, Spyros

2000-11-01

Confocal microscopy was used for irradiation and observation of the same area of interest, allowing the imaging of low power laser effects in subcellular components and functions, at the single cell level. Coverslips cultures of human fetal foreskin fibroblasts (HFFF2) were placed in a small incubation chamber for in vivo microscopic observation. Cells were stimulated by the 647 nm line of the Argon- Krypton laser of the confocal microscope (0.1 mW/cm2). Membrane permeability, mitochondrial membrane potential ((delta) Psim), intracellular pHi, calcium alterations and nuclear chromatin accessibility were monitored, at different times after irradiation, using specific fluorescent vital probes. Images were stored to the computer and quantitative evaluation was performed using image- processing software. After irradiation, influx and efflux of the appropriate dyes monitored changes in cell membrane permeability. Laser irradiation caused alkalizatoin of the cytosolic pHi and increase of the mitochondrial membrane potential ((delta) Psim). Temporary global Ca2+ responses were also observed. No such effects were noted in microscopic fields other than the irradiated ones. No toxic effects were observed, during time course of the experiment.

Effects of Replacement of External Sodium Chloride with Sucrose on Membrane Currents of the Squid Giant Axon

PubMed Central

Adelman, William J.; Taylor, Robert E.

1964-01-01

It was observed that a reduction of the sodium chloride concentration in the external solution bathing a squid giant axon by replacement with sucrose resulted in marked decreases in the peak inward and steady-state outward currents through the axon membrane following a step decrease in membrane potential. These effects are quantitatively acounted for by the increase in series resistance resulting from the decreased conductivity of the sea water and the assumption that the sodium current obeys a relation of the form I = k1C1 - k2C2 where C1, C2 are internal and external ion activities and k1, k2 are independent of concentration. It is concluded that the potassium ion current is independent of the sodium concentration. That the inward current is carried by sodium ions has been confirmed. The electrical potential (or barrier height) profile in the membrane which drives sodium ions appears to be independent of sodium ion concentration or current. A specific effect of the sucrose on hyperpolarizing currents was observed and noted but not investigated in detail. PMID:14232131

Optogenetic control of mitochondrial metabolism and Ca2+ signaling by mitochondria-targeted opsins.

PubMed

Tkatch, Tatiana; Greotti, Elisa; Baranauskas, Gytis; Pendin, Diana; Roy, Soumitra; Nita, Luliaoana I; Wettmarshausen, Jennifer; Prigge, Matthias; Yizhar, Ofer; Shirihai, Orian S; Fishman, Daniel; Hershfinkel, Michal; Fleidervish, Ilya A; Perocchi, Fabiana; Pozzan, Tullio; Sekler, Israel

2017-06-27

Key mitochondrial functions such as ATP production, Ca 2+ uptake and release, and substrate accumulation depend on the proton electrochemical gradient (ΔμH + ) across the inner membrane. Although several drugs can modulate ΔμH + , their effects are hardly reversible, and lack cellular specificity and spatial resolution. Although channelrhodopsins are widely used to modulate the plasma membrane potential of excitable cells, mitochondria have thus far eluded optogenetic control. Here we describe a toolkit of optometabolic constructs based on selective targeting of channelrhodopsins with distinct functional properties to the inner mitochondrial membrane of intact cells. We show that our strategy enables a light-dependent control of the mitochondrial membrane potential (Δψ m ) and coupled mitochondrial functions such as ATP synthesis by oxidative phosphorylation, Ca 2+ dynamics, and respiratory metabolism. By directly modulating Δψ m , the mitochondria-targeted opsins were used to control complex physiological processes such as spontaneous beats in cardiac myocytes and glucose-dependent ATP increase in pancreatic β-cells. Furthermore, our optometabolic tools allow modulation of mitochondrial functions in single cells and defined cell regions.

Atomic force microscopy study of erythrocyte shape and membrane structure after treatment with a dihydropyridinic drug

NASA Astrophysics Data System (ADS)

Girasole, M.; Cricenti, A.; Generosi, R.; Congiu-Castellano, A.; Boffi, F.; Arcovito, A.; Boumis, G.; Amiconi, G.

2000-06-01

The overall shape and membrane surface of human erythrocytes (RBCs) in the presence of nifedipine (a dihydropyridinic drug used in the clinical treatment of hypertension and angina pectoris) were imaged by contact-mode atomic force microscopy. Nifedipine induces in RBCs relevant morphological changes the extent of which increases as a function of drug concentration and incubation time. The modifications have been interpreted as mainly due to insertion of nifedipine into the outer layer of the RBC membrane. The potential effect of nifedipine as a hemoglobin denaturant has been ruled out by x-ray absorption near-edge structure and optical spectroscopies.

Cholesterol Promotes Protein Binding by Affecting Membrane Electrostatics and Solvation Properties.

PubMed

Doktorova, Milka; Heberle, Frederick A; Kingston, Richard L; Khelashvili, George; Cuendet, Michel A; Wen, Yi; Katsaras, John; Feigenson, Gerald W; Vogt, Volker M; Dick, Robert A

2017-11-07

Binding of the retroviral structural protein Gag to the cellular plasma membrane is mediated by the protein's matrix (MA) domain. Prominent among MA-PM interactions is electrostatic attraction between the positively charged MA domain and the negatively charged plasma membrane inner leaflet. Previously, we reported that membrane association of HIV-1 Gag, as well as purified Rous sarcoma virus (RSV) MA and Gag, depends strongly on the presence of acidic lipids and is enhanced by cholesterol (Chol). The mechanism underlying this enhancement was unclear. Here, using a broad set of in vitro and in silico techniques we addressed molecular mechanisms of association between RSV MA and model membranes, and investigated how Chol enhances this association. In neutron scattering experiments with liposomes in the presence or absence of Chol, MA preferentially interacted with preexisting POPS-rich clusters formed by nonideal lipid mixing, binding peripherally to the lipid headgroups with minimal perturbation to the bilayer structure. Molecular dynamics simulations showed a stronger MA-bilayer interaction in the presence of Chol, and a large Chol-driven increase in lipid packing and membrane surface charge density. Although in vitro MA-liposome association is influenced by disparate variables, including ionic strength and concentrations of Chol and charged lipids, continuum electrostatic theory revealed an underlying dependence on membrane surface potential. Together, these results conclusively show that Chol affects RSV MA-membrane association by making the electrostatic potential at the membrane surface more negative, while decreasing the penalty for lipid headgroup desolvation. The presented approach can be applied to other viral and nonviral proteins. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Raft-like membrane domains in pathogenic microorganisms.

PubMed

Farnoud, Amir M; Toledo, Alvaro M; Konopka, James B; Del Poeta, Maurizio; London, Erwin

2015-01-01

The lipid bilayer of the plasma membrane is thought to be compartmentalized by the presence of lipid-protein microdomains. In eukaryotic cells, microdomains composed of sterols and sphingolipids, commonly known as lipid rafts, are believed to exist, and reports on the presence of sterol- or protein-mediated microdomains in bacterial cell membranes are also appearing. Despite increasing attention, little is known about microdomains in the plasma membrane of pathogenic microorganisms. This review attempts to provide an overview of the current state of knowledge of lipid rafts in pathogenic fungi and bacteria. The current literature on characterization of microdomains in pathogens is reviewed, and their potential role in growth, pathogenesis, and drug resistance is discussed. Better insight into the structure and function of membrane microdomains in pathogenic microorganisms might lead to a better understanding of their pathogenesis and development of raft-mediated approaches for therapy. Copyright © 2015 Elsevier Inc. All rights reserved.

[Optimization of Energy Saving Measures with ABR-MBR Integrated Process].

PubMed

Wu, Peng; Lu, Shuang-jun; Xu, Yue-zhong; Liu, Jie; Shen, Yao-liang

2015-08-01

High energy consumption and membrane fouling are important factors that limit the wide use of membrane bioreactor (MBR). In order to reduce energy consumption and delay the process of membrane fouling, the process of anaerobic baffled reactor (ABR)-MBR was used to treat domestic sewage. The structure of the process and conditions of nitrogen and phosphorus removal were optimized in this study. The results showed that energy consumption was reduced by 43% through optimizing the structure of ABR-MBR process. Meanwhile, the process achieved a high level of COD, NH: -N, TN and TP removal, with the average removal efficiencies of 91%, 85%, 76% and 86%, respectively. In addition, the added particulate media could effectively delay membrane fouling, while the formation process of membrane fouling was changed. The extracted amount of carbohydrates increased while the amount of proteins decreased. Finally, the potential was enhanced for the practical application of MBR.

Prominin-1-containing membrane vesicles: origins, formation, and utility.

PubMed

Marzesco, Anne-Marie

2013-01-01

The stem cell antigen prominin-1 (CD133) is associated with two major types (small and large) of extracellular membrane vesicles in addition to its selective concentration in various kinds of plasma membrane protrusion. During development of the mammalian central nervous system, differentiating neuroepithelial stem cells release these vesicles into the embryonic cerebrospinal fluid. In glioblastoma patients, an increase of such vesicles, particularly the smaller ones, have been also observed in cerebrospinal fluid. Similarly, hematopoietic stem and progenitor cells release small ones concomitantly with their differentiation. Although the functional significance of these prominin-1-containing membrane vesicles is poorly understood, a link between differentiation of stem (and cancer stem) cells and their release is emerging. In this chapter, I will summarize our knowledge about prominin-1-containing membrane vesicles including a potential role in cell-cell communication and highlight their prospective value as a new biomarker for tumorigenesis diagnostics.

Synaptotagmin-1 may be a distance regulator acting upstream of SNARE nucleation

PubMed Central

van den Bogaart, Geert; Thutupalli, Shashi; Risselada, Jelger H.; Meyenberg, Karsten; Holt, Matthew; Riedel, Dietmar; Diederichsen, Ulf; Herminghaus, Stephan; Grubmüller, Helmut; Jahn, Reinhard

2011-01-01

Synaptotagmin-1 triggers Ca2+-sensitive, rapid neurotransmitter release by promoting the interaction of SNARE proteins between the synaptic vesicles and the plasma membrane. How synaptotagmin-1 promotes this interaction is controversial, and the massive increase in membrane fusion efficiency of Ca2+-synaptotagmin-1 has not been reproduced in vitro. However, previous experiments have been performed at relatively high salt concentrations, screening potentially important electrostatic interactions. Using functional reconstitution in liposomes, we show here that at low ionic strength SNARE-mediated membrane fusion becomes strictly dependent on both Ca2+ and synaptotagmin-1. Under these conditions, synaptotagmin-1 functions as a distance regulator: tethering the liposomes too far for SNARE nucleation in the absence of Ca2+, but brings the liposomes close enough for membrane fusion in the presence of Ca2+. These results may explain how the relatively weak electrostatic interactions of synaptotagmin-1 with membranes substantially accelerate fusion. PMID:21642968

Reinforcement of poly-l-lactic acid electrospun membranes with strontium borosilicate bioactive glasses for bone tissue engineering.

PubMed

Fernandes, João S; Gentile, Piergiorgio; Martins, Margarida; Neves, Nuno M; Miller, Cheryl; Crawford, Aileen; Pires, Ricardo A; Hatton, Paul; Reis, Rui L

2016-10-15

Herein, for the first time, we combined poly-l-lactic acid (PLLA) with a strontium borosilicate bioactive glass (BBG-Sr) using electrospinning to fabricate a composite bioactive PLLA membrane loaded with 10% (w/w) of BBG-Sr glass particles (PLLA-BBG-Sr). The composites were characterised by scanning electron microscopy (SEM) and microcomputer tomography (μ-CT), and the results showed that we successfully fabricated smooth and uniform fibres (1-3μm in width) with a homogeneous distribution of BBG-Sr microparticles (<45μm). Degradation studies (in phosphate buffered saline) demonstrated that the incorporation of BBG-Sr glass particles into the PLLA membranes increased their degradability and water uptake with a continuous release of cations. The addition of BBG-Sr glass particles enhanced the membrane's mechanical properties (69% higher Young modulus and 36% higher tensile strength). Furthermore, cellular in vitro evaluation using bone marrow-derived mesenchymal stem cells (BM-MSCs) demonstrated that PLLA-BBG-Sr membranes promoted the osteogenic differentiation of the cells as demonstrated by increased alkaline phosphatase activity and up-regulated osteogenic gene expression (Alpl, Sp7 and Bglap) in relation to PLLA alone. These results strongly suggest that the composite PLLA membranes reinforced with the BBG-Sr glass particles have potential as an effective biomaterial capable of promoting bone regeneration. PLLA membranes were reinforced with 10% (w/w) of strontium-bioactive borosilicate glass microparticles, and their capacity to induce the osteogenic differentiation of bone marrow mesenchymal stem cells (BM-MSCs) was evaluated. These membranes presented an increased: degradability, water uptake, Young modulus and tensile strength. We also demonstrated that these membranes are non-cytotoxic and promote the attachment of BM-MSCs. The addition of the glass microparticles into the PLLA membranes promoted the increase of ALP activity (under osteogenic conditions), as well as the BM-MSCs osteogenic differentiation as shown by the upregulation of Alpl, Sp7 and Bglap gene expression. Overall, we demonstrated that the reinforcement of PLLA with glass microparticles results in a biomaterial with the appropriate properties for the regeneration of bone tissue. Copyright © 2016 Acta Materialia Inc. All rights reserved.

Comparison of ionic and non-ionic drug release from multi-membrane spherical aerogels.

PubMed

Veronovski, Anja; Knez, Zeljko; Novak, Zoran

2013-09-15

The presented research was oriented towards the preparation of dry biodegradable alginate aerogels with multi-membranes using a multi-step sol-gel process with potential applications as carriers during oral drug delivery. First alginate spherical hydrogels were formed in CaCl2 or BaCl2 solutions by ionic cross-linking. These cores were further immersed into alginate sodium solution, filtered through a sieve, and dropped into the salt solution again. Multi-membrane hydrogels were obtained by repeating the above process. They were further converted into aerogels by supercritical drying. The effect of the number of membranes was investigated regarding the loading and release of the model drugs nicotinic acid and theophylline. Moreover, the efficiencies of Ba(2+) and Ca(2+) metal ions for forming tridimensional networks that retain and extend drug release were also investigated. Nicotinic acid release was prolonged by adding membranes around the core and using Ca(2+) for cross-linking. However, retarded theophylline release was only obtained by using Ba(2+) for cross-linking. Namely, by increasing the number of membranes and BaCl2 concentration drug release became linear versus time in all studied cases. In the case of nicotinic acid loading increased by adding membranes around the core, however, for theophylline the opposite results were obtained due to the different nature of the model drugs. Copyright © 2013 Elsevier B.V. All rights reserved.

Morphometric analysis of the translocation of lumenal membrane between cytoplasm and cell surface of transitional epithelial cells during the expansion-contraction cycles of mammalian urinary bladder

PubMed Central

1978-01-01

The flow of membrane between the cytoplasm and the lumenal surface during the expansion-contraction cycle of urinary bladder was estimated by stereological examination of electron micrographs of urothelial cells from guinea pigs, gerbils, hamsters, rabbits, and rats. The quantitative data obtained allowed an approximation of the surface area, volume, and numbers of lumenal membranelike vesicles and infoldings per unit volume of cytoplasm. Depending upon the species, approximately 85 to approximately 94% of the membrane surface area translocated into and out of the cytoplasm was in the form of discoidal vesicles. The remainder was accounted for by infoldings of the lumenal plasma membrane. The density of vesicles involved in transfer of membrane was quite similar in all the species examined, except guinea pigs which yielded lower values. In contrast, the densities of the total cytoplasmic pools of discoidal vesicles potentially available for translocation varied greatly among the different species. In general, species of animals with a highly concentrated urine had a greater density of discoidal vesicles than species with a less concentrated urine. This correlation may indicate an authentic relationship between lumenal membranes and the tonicity of urine, such as increased membrane recycling or turnover with increasingly hypertonic urine; or it may signify the existence of some other, more obscure relationship. PMID:681453

Relations among passive electrical properties of lumbar alpha-motoneurones of the cat.

PubMed Central

Gustafsson, B; Pinter, M J

1984-01-01

The relations among passive membrane properties have been examined in cat motoneurones utilizing exclusively electrophysiological techniques. A significant relation was found to exist between the input resistance and the membrane time constant. The estimated electrotonic length showed no evident tendency to vary with input resistance but did show a tendency to decrease with increasing time constant. Detailed analysis of this trend suggests, however, that a variation in dendritic geometry is likely to exist among cat motoneurones, such that the dendritic trees of motoneurones projecting to fast-twitch muscle units are relatively more expansive than those of motoneurones projecting to slow-twitch units. Utilizing an expression derived from the Rall neurone model, the total capacitance of the equivalent cylinder corresponding to a motoneurone has been estimated. With the assumption of a constant and uniform specific capacitance of 1 mu F/cm2, the resulting values have been used as estimates of cell surface area. These estimates agree well with morphologically obtained measurements from cat motoneurones reported by others. Both membrane time constant (and thus likely specific membrane resistivity) and electrotonic length showed little tendency to vary with surface area. However, after-hyperpolarization (a.h.p.) duration showed some tendency to vary such that cells with brief a.h.p. duration were, on average, larger than those with longer a.h.p. durations. Apart from motoneurones with the lowest values, axonal conduction velocity was only weakly related to variations in estimated surface area. Input resistance and membrane time constant were found to vary systematically with the a.h.p. duration. Analysis suggested that the major part of the increase in input resistance with a.h.p. duration was related to an increase in membrane resistivity and a variation in dendritic geometry rather than to differences in surface area among the motoneurones. The possible effects of imperfect electrode seals have been considered. According to an analysis of a passive membrane model, soma leaks caused by impalement injury will result in underestimates of input resistance and time constant and over-estimates of electrotonic length and total capacitance. Assuming a non-injured resting potential of -80 mV, a comparison of membrane potentials predicted by various relative leaks (leak conductance/input conductance) with those actually observed suggests that the magnitude of these errors in the present material will not unduly affect the presented results.+4 PMID:6520792

A patch clamp study on reconstituted calcium permeable channels of human sperm plasma membranes.

PubMed

Ma, X H; Shi, Y L

1999-10-01

Ionic flux is thought to be important in the initiating process of gamete interaction such as acrosome reaction. However, modern electrophysiological methods, intracellular recording and patch-clamping, are difficult to approach the ion channels in mammal sperm membrane of an intact sperm due to its small size. In this work, by reconstituting the channel protein into lipid bilayer, Ca2+ channels in human spermatozoa were investigated with voltage clamp technique. Membrane proteins isolated from human sperm of 12 healthy donors were incorporated into lipid bilayer via fusion. In a cis 50//trans 10 mmol/L CaCl2 solution system, two types of channel events with similar reversal potential near the value of a perfect Ca2+ electrode, and sensitive to nifedipine and verapamil, were observed. Their unit conductance was 40 and 25 pS respectively. Percentage of channel open time was not dependent to holding potential for the former. However, for the channels of 25 pS, the percentage increased when the holding potential was changed from -20 to 100 mV. Ca(2+)-permeable channels were also detected from the spermatozoon samples of two infertile donors. Abnormal open time of these channels indicates that there are some defects in the conformation of the channel protein of infertile sperm membrane.

Vanadium As a Potential Membrane Material for Carbon Capture: Effects of Minor Flue Gas Species.

PubMed

Yuan, Mengyao; Liguori, Simona; Lee, Kyoungjin; Van Campen, Douglas G; Toney, Michael F; Wilcox, Jennifer

2017-10-03

Vanadium and its surface oxides were studied as a potential nitrogen-selective membrane material for indirect carbon capture from coal or natural gas power plants. The effects of minor flue gas components (SO 2 , NO, NO 2 , H 2 O, and O 2 ) on vanadium at 500-600 °C were investigated by thermochemical exposure in combination with X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and in situ X-ray diffraction (XRD). The results showed that SO 2 , NO, and NO 2 are unlikely to have adsorbed on the surface vanadium oxides at 600 °C after exposure for up to 10 h, although NO and NO 2 may have exhibited oxidizing effects (e.g., exposure to 250 ppmv NO/N 2 resulted in an 2.4 times increase in surface V 2 O 5 compared to exposure to just N 2 ). We hypothesize that decomposition of surface vanadium oxides and diffusion of surface oxygen into the metal bulk are both important mechanisms affecting the composition and morphology of the vanadium membrane. The results and hypothesis suggest that the carbon capture performance of the vanadium membrane can potentially be strengthened by material and process improvements such as alloying, operating temperature reduction, and flue gas treatment.

UV-Enhanced Sacrificial Layer Stabilised Graphene Oxide Hollow Fibre Membranes for Nanofiltration

NASA Astrophysics Data System (ADS)

Chong, J. Y.; Aba, N. F. D.; Wang, B.; Mattevi, C.; Li, K.

2015-11-01

Graphene oxide (GO) membranes have demonstrated great potential in gas separation and liquid filtration. For upscale applications, GO membranes in a hollow fibre geometry are of particular interest due to the high-efficiency and easy-assembly features at module level. However, GO membranes were found unstable in dry state on ceramic hollow fibre substrates, mainly due to the drying-related shrinkage, which has limited the applications and post-treatments of GO membranes. We demonstrate here that GO hollow fibre membranes can be stabilised by using a porous poly(methyl methacrylate) (PMMA) sacrificial layer, which creates a space between the hollow fibre substrate and the GO membrane thus allowing stress-free shrinkage. Defect-free GO hollow fibre membrane was successfully determined and the membrane was stable in a long term (1200 hours) gas-tight stability test. Post-treatment of the GO membranes with UV light was also successfully accomplished in air, which induced the creation of controlled microstructural defects in the membrane and increased the roughness factor of the membrane surface. The permeability of the UV-treated GO membranes was greatly enhanced from 0.07 to 2.8 L m-2 h-1 bar-1 for water, and 0.14 to 7.5 L m-2 h-1 bar-1 for acetone, with an unchanged low molecular weight cut off (~250 Da).

Positive zeta potential of a negatively charged semi-permeable plasma membrane

NASA Astrophysics Data System (ADS)

Sinha, Shayandev; Jing, Haoyuan; Das, Siddhartha

2017-08-01

The negative charge of the plasma membrane (PM) severely affects the nature of moieties that may enter or leave the cells and controls a large number of ion-interaction-mediated intracellular and extracellular events. In this letter, we report our discovery of a most fascinating scenario, where one interface (e.g., membrane-cytosol interface) of the negatively charged PM shows a positive surface (or ζ) potential, while the other interface (e.g., membrane-electrolyte interface) still shows a negative ζ potential. Therefore, we encounter a completely unexpected situation where an interface (e.g., membrane-cytosol interface) that has a negative surface charge density demonstrates a positive ζ potential. We establish that the attainment of such a property by the membrane can be ascribed to an interplay of the nature of the membrane semi-permeability and the electrostatics of the electric double layer established on either side of the charged membrane. We anticipate that such a membrane property can lead to such capabilities of the cell (in terms of accepting or releasing certain kinds of moieties as well regulating cellular signaling) that was hitherto inconceivable.

Estimation of the membrane potential of cultured macrophages from the fast potential transient upon microelectrode entry

PubMed Central

Ince, C; Ypey, DL; Van Furth, R; Verveen, AA

1983-01-01

Analysis of membrane potential recordings upon microelectrode impalement of four types of macrophages (cell lines P388D1 and PU5-1.8, cultured mouse peritoneal macrophages, and cultured human monocytes) reveals that these cells have membrane potentials at least two times more negative than sustained potential values (E(s)) frequently reported. Upon microelectrode entry into the cell (P388D1), the recorded potential drops to a peak value (E(p)) (mean -37 mV for 50 cells, range -15 to -70 mV) within 2 ms, after which it decays to a depolarized potential (E(n)) (mean -12 mV) in about 20 ms. Thereafter, the membrane develops one or a series of slow hyperpolarizations before a final sustained membrane potential (E(s)) (mean -14 mV, range -5 to -40) is established. The mean value of the peak of the first hyperpolarization (E(h)) is -30 mV (range -10 to -55 mV). The initial fast peak transient, measured upon microelectrode entry, was first described and analyzed by Lassen et al. (Lassen, U.V., A.M. T. Nielson, L. Pape, and L. O. Simonsen, 1971, J. Membr. Biol. 6:269-288 for other change in the membrane potential from its real value before impalement to a sustained depolarized value. This was shown to be true for macrophages by two-electrode impalements of single cells. Values of E(p), E(n), E(h), E(s), and membrane resistance (R(m)) measured for the other macrophages were similar to those of P388D1. From these results we conclude that E(p) is a better estimate of the true membrane potential of macrophages than E(s), and that the slow hyperpolarizations upon impalement should be regarded as transient repolarizations back to the original membrane potentials. Thus, analysis of the initial fast impalement transient can be a valuable aid in the estimation of the membrane potential of various sorts of small isolated cells by microelectrodes. PMID:6833384

Electrostatic interactions among hydrophobic ions in lipid bilayer membranes.

PubMed Central

Andersen, O S; Feldberg, S; Nakadomari, H; Levy, S; McLaughlin, S

1978-01-01

We have shown that the absorption of tetraphenylborate into black lipid membranes formed from either bacterial phosphatidylethanolamine or glycerolmonooleate produces concentration-dependent changes in the electrostatic potential between the membrane interior and the bulk aqueous phases. These potential changes were studied by a variety of techniques: voltage clamp, charge pulse, and "probe" measurements on black lipid membranes; electrophroetic mobility measurements on phospholipid vesicles; and surface potential measurements on phospholipid monolayers. The magnitude of the potential changes indicates that tetraphenylborate absorbs into a region of the membrane with a low dielectric constant, where it produces substantial boundary potentials, as first suggested by Markin et al. (1971). Many features of our data can be explained by a simple three-capacitor model, which we develop in a self-consistent manner. Some discrepancies between our data and the simple model suggest that discrete charge phenomena may be important within these thin membranes. PMID:620077

Effect of aniracetam on phosphatidylinositol transfer protein alpha in cytosolic and plasma membrane fractions of astrocytes subjected to simulated ischemia in vitro.

PubMed

Gabryel, Bozena; Chalimoniuk, Małgorzata; Małecki, Andrzej; Strosznajder, Joanna B

2005-01-01

Brain ischemia affects phosphoinositide metabolism and the level of lipid-derived second messengers. Phosphatidylinositol transfer proteins (PI-PTs) are responsible for the transport of phosphatidylinositol (PI) and other phospholipids through membranes. Isoform of PI-TPs (PI-TPalpha) is an essential component in ensuring substrate supply for phospholipase C (PLC). The current study was conducted to examine potential effect of aniracetam on PI-TPalpha expression and to characterize the PI-TPalpha isoform distribution between membrane and cytosol fractions of astrocytes exposed to simulated ischemia in vitro. After 8 h period of ischemia, the level of PI-TPalpha was significantly higher in cytosol (by about 28%) as well as in membrane fraction (by about 80%) in comparison with control. We have found that aniracetam treatment of astrocytes in normoxia significantly increased the level of PI-TPalpha in membrane fraction with a maximal effect at 0.1 microM concentration of aniracetam (by about 195% of control). In membrane fractions of ischemic cells, aniracetam increased PI-TPalpha expression in a concentration-dependent manner. In ischemic cells, aniracetam (10 microM) has elevated PI-TPalpha expression up to 155% and 428% in cytosolic and membrane fractions in comparison with ischemic untreated cells, respectively. The study has shown that aniracetam significantly activates PI-TPalpha in cell membrane fraction and this effect might be connected with previously described activation of MAP kinase cascade.

Interactions between peroxiredoxin 2, hemichrome and the erythrocyte membrane.

PubMed

Bayer, Simone B; Low, Felicia M; Hampton, Mark B; Winterbourn, Christine C

2016-12-01

Peroxiredoxin 2 (Prx2) is an abundant antioxidant protein in erythrocytes that protects against hemolytic anemia resulting from hemoglobin oxidation and Heinz body formation. A small fraction of Prx2 is bound to the cell membrane, but the mechanism and relevance of binding are not clear. We have investigated Prx2 interactions with the erythrocyte membrane and oxidized hemoglobin and whether these interactions are dependent on Prx2 redox state. Membrane binding of Prx2 in erythrocytes decreased when the cells were treated with H 2 O 2 , but studies with purified Prx2 and isolated ghosts showed that the interaction was independent of Prx2 redox state. Hemoglobin oxidation leads to the formation of hemichrome, a denatured form of the protein that binds to Band3 protein in the cell membrane as part of the senescence process and is a precursor of Heinz bodies. Hemichrome competed with Prx2 and decreased Prx2 binding to the membrane, potentially explaining the decreased binding in oxidant-exposed cells. The increased membrane binding of Prx2 seen with increasing intracellular calcium was less sensitive to H 2 O 2 or hemichrome, suggesting an alternative mode of binding. Prx2 was also shown to exhibit chaperone-like activity by retarding the precipitation of pre-formed hemichrome. Our results suggest that Prx2, by restricting membrane binding of hemichrome, could impede Band3 clustering and exposure of senescence antigens. This mechanism, plus the observed chaperone activity for oxidized hemoglobin, may help protect against hemolytic anemia.

Superhydrophilic Functionalization of Microfiltration Ceramic Membranes Enables Separation of Hydrocarbons from Frac and Produced Water.

PubMed

Maguire-Boyle, Samuel J; Huseman, Joseph E; Ainscough, Thomas J; Oatley-Radcliffe, Darren L; Alabdulkarem, Abdullah A; Al-Mojil, Sattam Fahad; Barron, Andrew R

2017-09-25

The environmental impact of shale oil and gas production by hydraulic fracturing (fracking) is of increasing concern. The biggest potential source of environmental contamination is flowback and produced water, which is highly contaminated with hydrocarbons, bacteria and particulates, meaning that traditional membranes are readily fouled. We show the chemical functionalisation of alumina ceramic microfiltration membranes (0.22 μm pore size) with cysteic acid creates a superhydrophilic surface, allowing for separation of hydrocarbons from frac and produced waters without fouling. The single pass rejection coefficients was >90% for all samples. The separation of hydrocarbons from water when the former have hydrodynamic diameters smaller than the pore size of the membrane is due to the zwitter ionically charged superhydrophilic pore surface. Membrane fouling is essentially eliminated, while a specific flux is obtained at a lower pressure (<2 bar) than that required achieving the same flux for the untreated membrane (4-8 bar).

Physicochemical properties and membrane biofouling of extra-cellular polysaccharide produced by a Micrococcus luteus strain.

PubMed

Feng, Lei; Li, Xiufen; Song, Ping; Du, Guocheng; Chen, Jian

2014-07-01

The physicochemical properties of the extra-cellular polysaccharide (EPS) produced by a Micrococcus luteus strain, a dominating strain isolated from membrane biofouling layer, were determined in this study. The EPS isolated from this strain was measured to have an average molecular weight of 63,540 Da and some typical polysaccharide absorption peaks in Fourier transform infrared spectrum. Monosaccharide components of the EPS contained rhamnose, fucose, arabinose, xylose, mannose, galactose and glucose in a molar ratio of 0.2074:0.0454:0.0262:0.0446:1.7942:1.2086:0.4578. Pseudo plastic properties were also observed for the EPS through the rheological measurement. The EPS was further characterized for its behavior to cause membrane flux decline. The results showed that both flux declines for polyvinylidenefluoride (PVDF) and polypropylene membranes became more severe as EPS feed concentration increased. A higher irreversible fouling for the PVDF membrane suggested that the EPS had the larger fouling potential to this microfiltration membrane.

Effect of co-solvent on the structure and dielectric properties of porous polyimide membranes

NASA Astrophysics Data System (ADS)

Zhang, Panpan; Zhao, Jiupeng; Zhang, Ke; Wu, Yiyong; Li, Yao

2018-05-01

A series of porous polyimide (PI) membranes with 3,3‧,4,4‧-benzophenonetetracarboxylic dianhydride (BTDA) and 4,4‧-diaminodiphenyl ether (ODA) in the different ratio of co-solvent (N, N-dimethylacetamide (DMAC)/1, 4-butyrolactone (GBL)) were prepared by a novel wet phase inversion method. The influence of co-solvent on the structure and dielectric properties of membranes were investigated. PI membranes changed from finger-like structure to spongy-like structure with the increasing of the GBL content since the intermolecular interaction between PI induced by GBL. The proportion and size of finger-like structure gradually decreased with the increase of GBL content in DMAC/GBL co-solvent. Although PI membranes exhibited low dielectric permittivity ranges from 1.7–2.5, the dielectric breakdown strengths were also relatively low. In particular, the PI from pure GBL yielded the highest breakdown strength (260.05 kV mm‑1) since the low proportion of macrovoids and defects. Moreover, when the ratio of GBL/DAMC was 84/16, the resultant PI membrane possessed a low dielectric constant (1.99) as well as relatively high breakdown strength (100.53 kV mm‑1). Therefore, porous PI membraness may be potential in many applications of electronics and microelectronics.

APBSmem: A Graphical Interface for Electrostatic Calculations at the Membrane

PubMed Central

Callenberg, Keith M.; Choudhary, Om P.; de Forest, Gabriel L.; Gohara, David W.; Baker, Nathan A.; Grabe, Michael

2010-01-01

Electrostatic forces are one of the primary determinants of molecular interactions. They help guide the folding of proteins, increase the binding of one protein to another and facilitate protein-DNA and protein-ligand binding. A popular method for computing the electrostatic properties of biological systems is to numerically solve the Poisson-Boltzmann (PB) equation, and there are several easy-to-use software packages available that solve the PB equation for soluble proteins. Here we present a freely available program, called APBSmem, for carrying out these calculations in the presence of a membrane. The Adaptive Poisson-Boltzmann Solver (APBS) is used as a back-end for solving the PB equation, and a Java-based graphical user interface (GUI) coordinates a set of routines that introduce the influence of the membrane, determine its placement relative to the protein, and set the membrane potential. The software Jmol is embedded in the GUI to visualize the protein inserted in the membrane before the calculation and the electrostatic potential after completing the computation. We expect that the ease with which the GUI allows one to carry out these calculations will make this software a useful resource for experimenters and computational researchers alike. Three examples of membrane protein electrostatic calculations are carried out to illustrate how to use APBSmem and to highlight the different quantities of interest that can be calculated. PMID:20949122

APBSmem: a graphical interface for electrostatic calculations at the membrane.

PubMed

Callenberg, Keith M; Choudhary, Om P; de Forest, Gabriel L; Gohara, David W; Baker, Nathan A; Grabe, Michael

2010-09-29

Electrostatic forces are one of the primary determinants of molecular interactions. They help guide the folding of proteins, increase the binding of one protein to another and facilitate protein-DNA and protein-ligand binding. A popular method for computing the electrostatic properties of biological systems is to numerically solve the Poisson-Boltzmann (PB) equation, and there are several easy-to-use software packages available that solve the PB equation for soluble proteins. Here we present a freely available program, called APBSmem, for carrying out these calculations in the presence of a membrane. The Adaptive Poisson-Boltzmann Solver (APBS) is used as a back-end for solving the PB equation, and a Java-based graphical user interface (GUI) coordinates a set of routines that introduce the influence of the membrane, determine its placement relative to the protein, and set the membrane potential. The software Jmol is embedded in the GUI to visualize the protein inserted in the membrane before the calculation and the electrostatic potential after completing the computation. We expect that the ease with which the GUI allows one to carry out these calculations will make this software a useful resource for experimenters and computational researchers alike. Three examples of membrane protein electrostatic calculations are carried out to illustrate how to use APBSmem and to highlight the different quantities of interest that can be calculated.

Role of calcium stores and membrane voltage in the generation of slow wave action potentials in guinea-pig gastric pylorus

PubMed Central

Van Helden, D F; Imtiaz, M S; Nurgaliyeva, K; von der Weid, P-Y; Dosen, P J

2000-01-01

Intracellular recordings made in single bundle strips of a visceral smooth muscle revealed rhythmic spontaneous membrane depolarizations termed slow waves (SWs). These exhibited ‘pacemaker’ and ‘regenerative’ components composed of summations of more elementary events termed spontaneous transient depolarizations (STDs). STDs and SWs persisted in the presence of tetrodotoxin, nifedipine and ryanodine, and upon brief exposure to Ca2+-free Cd2+-containing solutions; they were enhanced by ACh and blocked by BAPTA AM, cyclopiazonic acid and caffeine. SWs were also inhibited in heparin-loaded strips. SWs were observed over a wide range of membrane potentials (e.g. −80 to −45 mV) with increased frequencies at more depolarized potentials. Regular spontaneous SW activity in this preparation began after 1–3 h superfusion of the tissue with physiological saline following the dissection procedure. Membrane depolarization applied before the onset of this activity induced bursts of STD-like events (termed the ‘initial’ response) which, when larger than threshold levels initiated regenerative responses. The combined initial-regenerative waveform was termed the SW-like action potential. Voltage-induced responses exhibited large variable latencies (typical range 0.3–4 s), refractory periods of ≈11 s and a pharmacology that was indistinguishable from those of STDs and spontaneous SWs. The data indicate that SWs arise through more elementary inositol 1,4,5-trisphosphate (IP3) receptor-induced Ca2+ release events which rhythmically synchronize to trigger regenerative Ca2+ release and induce inward current across the plasmalemma. The finding that action potentials, which were indistinguishable from SWs, could be evoked by depolarization suggests that membrane potential modulates IP3 production. Voltage feedback on intracellular IP3-sensitive Ca2+ release is likely to have a major influence on the generation and propagation of SWs. PMID:10747196

Potential Efficacy of Citicoline as Adjunct Therapy in Treatment of Cerebral Malaria

PubMed Central

El-Assaad, Fatima; Combes, Valery; Grau, Georges Emile Raymond

2014-01-01

Cerebral malaria (CM) is characterized by a dysregulated immune response that results in endothelial membrane destabilization and increased microparticle (MP) production. Citicoline (CTC) is a membrane stabilizer used for the treatment of neurological disorders. We evaluated the efficacy of CTC as adjunct therapy to aid recovery from experimental CM. We show that CTC reduces MP production in vitro; in combination with artesunate in vivo, confers partial protection against CM; and prolongs survival. PMID:24165175

Mechanical behavior of cells in microinjection: a minimum potential energy study.

PubMed

Liu, Fei; Wu, Dan; Chen, Ken

2013-08-01

Microinjection is a widely used technique to deliver foreign materials into biological cells. We propose a mathematical model to study the mechanical behavior of a cell in microinjection. Firstly, a cell is modeled by a hyperelastic membrane and interior cytoplasm. Then, based on the fact that the equilibrium configuration of a cell would minimize the potential energy, the energy function during microinjection is analyzed. With Lagrange multiplier and Rayleigh-Ritz technique, we successfully minimize the potential energy and obtain the equilibrium configuration. Upon this model, the injection force, the injection distance, the radius of the microinjector and the membrane stress are studied. The analysis demonstrates that the microinjector radius has a significant influence on the cell mechanical behavior: (1) the larger radius generates larger injection force and larger interior pressure at the same injection distance; (2) the radius determines the place where the membrane is most likely to rupture by governing the membrane stress distribution. For a fine microinjector with radius less than 20% of the cell radius, the most likely rupture point located at the edge of the contact area between the microinjector and the membrane; however, it may move to the middle of the equilibrium configuration as the radius increases. To verify our model, some experiments were conducted on zebrafish egg cells. The results show that the computational analysis agrees with the experimental data, which supports the findings from the theoretical model. Copyright © 2013 Elsevier Ltd. All rights reserved.

The effects of oxygen on the evolution of microbial membranes

NASA Technical Reports Server (NTRS)

Jahnke, L. L.

1991-01-01

One prokaryote, Methylococcus capsulatus, synthesizes both hopanoids and sterols and, thus, provides a unique opportunity to study the evolution of membrane function. When M. capsulatus was grown at different temperatures, lipid analysis of the whole cells showed that both sterol and unsaturated fatty acid levels decreased at higher growth temperatures; sterol concentrations were 0.116 micro mole/micro mole phospholipid at 30 C and 0.025 micro mole/mirco mole phospholipid at 45 C, while the saturated to unsaturated fatty acid ratio increased from 0.397 to 1.475. Hopane polyol levels were constant over this range; however, methylation of the A-ring decreased markedly in cells grown at 30 C. These results imply that sterol and hopane molecules are required for enhancement of some specific membrane function, potentially by modulating membrane fluidity.

mTORC1 Is a Local, Postsynaptic Voltage Sensor Regulated by Positive and Negative Feedback Pathways

PubMed Central

Niere, Farr; Raab-Graham, Kimberly F.

2017-01-01

The mammalian/mechanistic target of rapamycin complex 1 (mTORC1) serves as a regulator of mRNA translation. Recent studies suggest that mTORC1 may also serve as a local, voltage sensor in the postsynaptic region of neurons. Considering biochemical, bioinformatics and imaging data, we hypothesize that the activity state of mTORC1 dynamically regulates local membrane potential by promoting and repressing protein synthesis of select mRNAs. Our hypothesis suggests that mTORC1 uses positive and negative feedback pathways, in a branch-specific manner, to maintain neuronal excitability within an optimal range. In some dendritic branches, mTORC1 activity oscillates between the “On” and “Off” states. We define this as negative feedback. In contrast, positive feedback is defined as the pathway that leads to a prolonged depolarized or hyperpolarized resting membrane potential, whereby mTORC1 activity is constitutively on or off, respectively. We propose that inactivation of mTORC1 increases the expression of voltage-gated potassium alpha (Kv1.1 and 1.2) and beta (Kvβ2) subunits, ensuring that the membrane resets to its resting membrane potential after experiencing increased synaptic activity. In turn, reduced mTORC1 activity increases the protein expression of syntaxin-1A and promotes the surface expression of the ionotropic glutamate receptor N-methyl-D-aspartate (NMDA)-type subunit 1 (GluN1) that facilitates increased calcium entry to turn mTORC1 back on. Under conditions such as learning and memory, mTORC1 activity is required to be high for longer periods of time. Thus, the arm of the pathway that promotes syntaxin-1A and Kv1 protein synthesis will be repressed. Moreover, dendritic branches that have low mTORC1 activity with increased Kv expression would balance dendrites with constitutively high mTORC1 activity, allowing for the neuron to maintain its overall activity level within an ideal operating range. Finally, such a model suggests that recruitment of more positive feedback dendritic branches within a neuron is likely to lead to neurodegenerative disorders. PMID:28611595

A calcium channel blocker, benidipine, improves cell membrane fluidity in human subjects via a nitric oxide-dependent mechanism. An electron paramagnetic resonance investigation.

PubMed

Tsuda, Kazushi; Nishio, Ichiro

2004-12-01

Recent studies have revealed that benidipine, a long-acting dihydropyridine-type of calcium (Ca) channel blocker, may exert its protective effect against vascular disorders by increasing nitric oxide (NO) production. The purpose of the present study was to investigate the effects of benidipine and NO on the membrane function in human subjects. We measured the membrane fluidity of erythrocytes by using an electron paramagnetic resonance (EPR) and spin-labeling method. Benidipine decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (h(o)/h(-1)) for 16-NS obtained from EPR spectra of erythrocyte membranes in a dose-dependent manner in normotensive volunteers. The finding indicated that benidipine increased the membrane fluidity and improved the microviscosity of erythrocytes. The effect of benidipine was significantly potentiated by the NO donor, S-nitroso-n-acetylpenicillamine, and by the cyclic guanosine 3', 5'-monophosphate (cGMP) analog, 8-bromo-cGMP. In contrast, the change evoked by benidipine was counteracted by the NO synthase inhibitors, N(G)-nitro-L-arginine-methyl-ester and asymmetric dimethyl-L-arginine. These results demonstrated that benidipine increased the membrane fluidity of erythrocytes, at least in part, via the NO- and cGMP-dependent mechanism. Furthermore, the data strongly suggest that benidipine might have a beneficial effect on the rheologic behavior of erythrocytes and the improvement of the microcirculation in humans.

Release abilities of adenosine diphosphate from phospholipid vesicles with different membrane properties and their hemostatic effects as a platelet substitute.

PubMed

Okamura, Yosuke; Katsuno, Shunsuke; Suzuki, Hidenori; Maruyama, Hitomi; Handa, Makoto; Ikeda, Yasuo; Takeoka, Shinji

2010-12-20

We have constructed phospholipid vesicles with hemostatic activity as a platelet substitute. The vesicles were conjugated with a dodecapeptide (HHLGGAKQAGDV, H12), which is a fibrinogen γ-chain carboxy-terminal sequence (γ400-411). We have recently exploited these vesicles as a potential drug delivery system by encapsulation of adenosine 5'-diphosphate (ADP) (H12-(ADP)-vesicles). Here we explore the relationship between the ADP release from H12-(ADP)-vesicles with different membrane properties and their hemostatic effects. In total, we prepared five kinds of H12-(ADP)-vesicles with different lamellarities and membrane flexibilities. By radioisotope-labeling, we directly show that H12-(ADP)-vesicles were capable of augmenting platelet aggregation by releasing ADP in an aggregation-dependent manner. The amount of ADP released from the vesicles was dependent on their membrane properties. Specifically, the amount of ADP released increased with decreasing lamellarity and tended to increase with increasing membrane flexibility. Our in vivo results clearly demonstrated that H12-(ADP)-vesicles with the ability to release ADP exert considerable hemostatic action in terms of correcting prolonged bleeding time in a busulphan-induced thrombocytopenic rat model. We propose a recipe to control the hemostatic abilities of H12-(ADP)-vesicles by modulating ADP release based on membrane properties. We believe that this concept will be invaluable to the development of platelet substitutes and other drug carriers. Copyright © 2010 Elsevier B.V. All rights reserved.

Anion- or Cation-Exchange Membranes for NaBH4/H2O2 Fuel Cells?

PubMed

Sljukić, Biljana; Morais, Ana L; Santos, Diogo M F; Sequeira, César A C

2012-07-19

Direct borohydride fuel cells (DBFC), which operate on sodium borohydride (NaBH4) as the fuel, and hydrogen peroxide (H2O2) as the oxidant, are receiving increasing attention. This is due to their promising use as power sources for space and underwater applications, where air is not available and gas storage poses obvious problems. One key factor to improve the performance of DBFCs concerns the type of separator used. Both anion- and cation-exchange membranes may be considered as potential separators for DBFC. In the present paper, the effect of the membrane type on the performance of laboratory NaBH4/H2O2 fuel cells using Pt electrodes is studied at room temperature. Two commercial ion-exchange membranes from Membranes International Inc., an anion-exchange membrane (AMI-7001S) and a cation-exchange membrane (CMI-7000S), are tested as ionic separators for the DBFC. The membranes are compared directly by the observation and analysis of the corresponding DBFC's performance. Cell polarization, power density, stability, and durability tests are used in the membranes' evaluation. Energy densities and specific capacities are estimated. Most tests conducted, clearly indicate a superior performance of the cation-exchange membranes over the anion-exchange membrane. The two membranes are also compared with several other previously tested commercial membranes. For long term cell operation, these membranes seem to outperform the stability of the benchmark Nafion membranes but further studies are still required to improve their instantaneous power load.

Microbubble-Assisted Ultrasound-Induced Transient Phosphatidylserine Translocation.

PubMed

Escoffre, Jean-Michel; Derieppe, Marc; Lammertink, Bart; Bos, Clemens; Moonen, Chrit

2017-04-01

Microbubble-assisted ultrasound (sonopermeabilization) results in reversible permeabilization of the plasma membrane of cells. This method is increasingly used in vivo because of its potential to deliver therapeutic molecules with limited cell damage. Nevertheless, the effects of sonopermeabilization on the plasma membrane remain not fully understood. We investigated the influence of sonopermeabilization on the transverse mobility of phospholipids, especially on phosphatidylserine (PS) externalization. We performed studies using optical imaging with Annexin V and FM1-43 probes to monitor PS externalization of rat glioma C6 cells. Sonopermeabilization induced transient membrane permeabilization, which is positively correlated with reversible PS externalization. This membrane disorganization was temporary and not associated with loss of cell viability. Sonopermeabilization did not induce PS externalization via activation of the scramblase. We hypothesize that acoustically induced membrane pores may provide a new pathway for PS migration between both membrane leaflets. During the membrane-resealing phase, PS asymmetry may be re-established by amino-phospholipid flippase activity and/or endocytosis, along with exocytosis processes. Copyright © 2016 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Dramatic improvement in water retention and proton conductivity in electrically aligned functionalized CNT/SPEEK nanohybrid PEM.

PubMed

Gahlot, Swati; Kulshrestha, Vaibhav

2015-01-14

Nanohybrid membranes of electrically aligned functionalized carbon nanotube f CNT with sulfonated poly ether ether ketone (SPEEK) have been successfully prepared by solution casting. Functionalization of CNTs was done through a carboxylation and sulfonation route. Further, a constant electric field (500 V·cm(-2)) has been applied to align CNTs in the same direction during the membrane drying process. All the membranes are characterized chemically, thermally, and mechanically by the means of FTIR, DSC, DMA, UTM, SEM, TEM, and AFM techniques. Intermolecular interactions between the components in hybrid membranes are established by FTIR. Physicochemical measurements were done to analyze membrane stability. Membranes are evaluated for proton conductivity (30-90 °C) and methanol crossover resistance to reveal their potential for direct methanol fuel cell application. Incorporation of f CNT reasonably increases the ion-exchange capacity, water retention, and proton conductivity while it reduces the methanol permeability. The maximum proton conductivity has been found in the S-sCNT-5 nanohybrid PEM with higher methanol crossover resistance. The prepared membranes can be also used for electrode material for fuel cells and batteries.

Measuring peptide translocation into large unilamellar vesicles.

PubMed

Spinella, Sara A; Nelson, Rachel B; Elmore, Donald E

2012-01-27

There is an active interest in peptides that readily cross cell membranes without the assistance of cell membrane receptors(1). Many of these are referred to as cell-penetrating peptides, which are frequently noted for their potential as drug delivery vectors(1-3). Moreover, there is increasing interest in antimicrobial peptides that operate via non-membrane lytic mechanisms(4,5), particularly those that cross bacterial membranes without causing cell lysis and kill cells by interfering with intracellular processes(6,7). In fact, authors have increasingly pointed out the relationship between cell-penetrating and antimicrobial peptides(1,8). A firm understanding of the process of membrane translocation and the relationship between peptide structure and its ability to translocate requires effective, reproducible assays for translocation. Several groups have proposed methods to measure translocation into large unilamellar lipid vesicles (LUVs)(9-13). LUVs serve as useful models for bacterial and eukaryotic cell membranes and are frequently used in peptide fluorescent studies(14,15). Here, we describe our application of the method first developed by Matsuzaki and co-workers to consider antimicrobial peptides, such as magainin and buforin II(16,17). In addition to providing our protocol for this method, we also present a straightforward approach to data analysis that quantifies translocation ability using this assay. The advantages of this translocation assay compared to others are that it has the potential to provide information about the rate of membrane translocation and does not require the addition of a fluorescent label, which can alter peptide properties(18), to tryptophan-containing peptides. Briefly, translocation ability into lipid vesicles is measured as a function of the Foster Resonance Energy Transfer (FRET) between native tryptophan residues and dansyl phosphatidylethanolamine when proteins are associated with the external LUV membrane (Figure 1). Cell-penetrating peptides are cleaved as they encounter uninhibited trypsin encapsulated with the LUVs, leading to disassociation from the LUV membrane and a drop in FRET signal. The drop in FRET signal observed for a translocating peptide is significantly greater than that observed for the same peptide when the LUVs contain both trypsin and trypsin inhibitor, or when a peptide that does not spontaneously cross lipid membranes is exposed to trypsin-containing LUVs. This change in fluorescence provides a direct quantification of peptide translocation over time.

Physiological stimuli evoke two forms of endocytosis in bovine chromaffin cells.

PubMed

Chan, S A; Smith, C

2001-12-15

1. Exocytosis and endocytosis were measured following single, or trains of, simulated action potentials (sAP) in bovine adrenal chromaffin cells. Catecholamine secretion was measured by oxidative amperometry and cell membrane turnover was measured by voltage clamp cell capacitance measurements. 2. The sAPs evoked inward Na(+) and Ca(2+) currents that were statistically identical to those evoked by native action potential waveforms. On average, a single secretory granule underwent fusion following sAP stimulation. An equivalent amount of membrane was then quickly internalised (tau = 560 ms). 3. Stimulation with sAP trains revealed a biphasic relationship between cell firing rate and endocytic activity. At basal stimulus frequencies (single to 0.5 Hz) cells exhibited a robust membrane internalisation that then diminished as firing increased to intermediate levels (1.9 and 6 Hz). However at the higher stimulation rates (10 and 16 Hz) endocytic activity rebounded and was again able to effectively maintain cell surface near pre-stimulus levels. 4. Treatment with cyclosporin A and FK506, inhibitors of the phosphatase calcineurin, left endocytosis characteristics unaltered at the lower basal stimulus levels, but blocked the resurgence in endocytosis seen in control cells at higher sAP frequencies. 5. Based on these findings we propose that, under physiological electrical stimulation, chromaffin cells internalise membrane via two distinct pathways that are separable. One is prevalent at basal stimulus frequencies, is lessened with increased firing, and is insensitive to cyclosporin A and FK506. A second endocytic form is activated by increased firing frequencies, and is selectively blocked by cyclosporin A and FK506.

Physiological stimuli evoke two forms of endocytosis in bovine chromaffin cells

PubMed Central

Chan, Shyue-An; Smith, Corey

2001-01-01

Exocytosis and endocytosis were measured following single, or trains of, simulated action potentials (sAP) in bovine adrenal chromaffin cells. Catecholamine secretion was measured by oxidative amperometry and cell membrane turnover was measured by voltage clamp cell capacitance measurements. The sAPs evoked inward Na+ and Ca2+ currents that were statistically identical to those evoked by native action potential waveforms. On average, a single secretory granule underwent fusion following sAP stimulation. An equivalent amount of membrane was then quickly internalised (τ = 560 ms). Stimulation with sAP trains revealed a biphasic relationship between cell firing rate and endocytic activity. At basal stimulus frequencies (single to 0.5 Hz) cells exhibited a robust membrane internalisation that then diminished as firing increased to intermediate levels (1.9 and 6 Hz). However at the higher stimulation rates (10 and 16 Hz) endocytic activity rebounded and was again able to effectively maintain cell surface near pre-stimulus levels. Treatment with cyclosporin A and FK506, inhibitors of the phosphatase calcineurin, left endocytosis characteristics unaltered at the lower basal stimulus levels, but blocked the resurgence in endocytosis seen in control cells at higher sAP frequencies. Based on these findings we propose that, under physiological electrical stimulation, chromaffin cells internalise membrane via two distinct pathways that are separable. One is prevalent at basal stimulus frequencies, is lessened with increased firing, and is insensitive to cyclosporin A and FK506. A second endocytic form is activated by increased firing frequencies, and is selectively blocked by cyclosporin A and FK506. PMID:11744761

Effects of O 2 and N 2/H 2 plasma treatments on the neuronal cell growth on single-walled carbon nanotube paper scaffolds

NASA Astrophysics Data System (ADS)

Yoon, Ok Ja; Lee, Hyun Jung; Jang, Yeong Mi; Kim, Hyun Woo; Lee, Won Bok; Kim, Sung Su; Lee, Nae-Eung

2011-08-01

The O 2 and N 2/H 2 plasma treatments of single-walled carbon nanotube (SWCNT) papers as scaffolds for enhanced neuronal cell growth were conducted to functionalize their surfaces with different functional groups and to roughen their surfaces. To evaluate the effects of the surface roughness and functionalization modifications of the SWCNT papers, we investigated the neuronal morphology, mitochondrial membrane potential, and acetylcholine/acetylcholinesterase levels of human neuroblastoma during SH-SY5Y cell growth on the treated SWCNT papers. Our results demonstrated that the plasma-chemical functionalization caused changes in the surface charge states with functional groups with negative and positive charges and then the increased surface roughness enhanced neuronal cell adhesion, mitochondrial membrane potential, and the level of neurotransmitter in vitro. The cell adhesion and mitochondrial membrane potential on the negatively charged SWCNT papers were improved more than on the positively charged SWCNT papers. Also, measurements of the neurotransmitter level showed an enhanced acetylcholine level on the negatively charged SWCNT papers compared to the positively charged SWCNT papers.

Ion pathways in the taste bud and their significance for transduction.

PubMed

DeSimone, J A; Ye, Q; Heck, G L

1993-01-01

Taste buds share a topology with ion-transporting epithelial and evidence now indicates that neural responses in rats to Na+ salts of differing anion are mediated by both transcellular and paracellular ion transport. Na+ exerts its effects mainly on the transcellular pathway. Neural responses to Na+ salts are enhanced by negative voltage clamp and suppressed by positive clamp in a manner indicating modulation of the apical membrane potential of receptor cells. Anion effects are mainly paracellular. Under zero current clamp increasing anion size reduces the neural response at constant Na+ concentration. Below about 50 mM this difference is entirely eliminated under voltage clamp. This suggests that paracellular transepithelial potentials normally create an anion difference. At higher concentrations the relatively high permeability of the paracellular shunt to Cl- permits sufficient electroneutral diffusion of NaCl below the tight junctions to stimulate cells that do not make direct contact with the oral cavity. In general, the sensitivity of a response to perturbations in the apical membrane potential indicates that some phase of Na+ salt taste transduction is accompanied by changes in an apical membrane channel conductance.

Leptin improves membrane fluidity of erythrocytes in humans via a nitric oxide-dependent mechanism--an electron paramagnetic resonance investigation.

PubMed

Tsuda, Kazushi; Kimura, Keizo; Nishio, Ichiro

2002-09-27

Abnormalities in physical properties of the cell membranes may underlie the defects that are strongly linked to hypertension, stroke, and other cardiovascular diseases. Recently, there has been an indication that leptin, the product of the human obesity gene, actively participates not only in the metabolic regulations but also in the control of cardiovascular functions. In the present study, to assess the role of leptin in the regulation of membrane properties, the effects of leptin on membrane fluidity of erythrocytes in humans are examined. The membrane fluidity of erythrocytes in healthy volunteers by means of an electron paramagnetic resonance (EPR) and spin-labeling method is determined. In an in vitro study, leptin decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (ho/h-1) for 16-NS obtained from EPR spectra of erythrocyte membranes in a dose-dependent manner in healthy volunteers. The finding indicated that leptin increased the membrane fluidity and improved the microviscosity of erythrocytes. The effect of leptin on the membrane fluidity was significantly potentiated by the nitric oxide (NO) donors, L-arginine and S-nitroso-N-acetylpenicillamine (SNAP), and a cyclic guanosine monophosphate (cGMP) analog, 8-bromo-cGMP. In contrast, the change evoked by leptin was significantly attenuated in the presence of the NO synthase inhibitors, N(G)-nitro-L-arginine-methyl-ester (L-NAME) and asymmetric dimethyl-L-arginine (ADMA). The results of the present study showed that leptin increased the membrane fluidity and improved the rigidity of cell membranes to some extent via an NO- and cGMP-dependent mechanism. Furthermore, the data also suggest that leptin might have a crucial role in the regulation of rheological behavior of erythrocytes and microcirculation in humans.

Nanocarbon-based membrane filtration integrated with electric field driving for effective membrane fouling mitigation.

PubMed

Fan, Xinfei; Zhao, Huimin; Quan, Xie; Liu, Yanming; Chen, Shuo

2016-01-01

Membrane filtration provides an effective solution for removing pollutants from water but is limited by serious membrane fouling. In this work, an effective approach was used to mitigate membrane fouling by integrating membrane filtration with electropolarization using an electroconductive nanocarbon-based membrane. The electropolarized membrane (EM) by alternating square-wave potentials between +1.0 V and -1.0 V with a pulse width of 60 s exhibited a permeate flux 8.1 times as high as that without electropolarization for filtering feed water containing bacteria, which confirms the ability of the EM to achieve biofouling mitigation. Moreover, the permeate flux of EM was 1.5 times as high as that without electropolarization when filtrating natural organic matter (NOM) from water, and demonstrated good performance in organic fouling mitigation with EM. Furthermore, the EM was also effective for complex fouling mitigation in filtering water containing coexisting bacteria and NOM, and presented an increased flux rate 1.9 times as high as that without electropolarization. The superior fouling mitigation performance of EM was attributed to the synergistic effects of electrostatic repulsion, electrochemical oxidation and electrokinetic behaviors. This work opens an effective avenue for membrane fouling mitigation of water-treatment membrane filtration systems. Copyright © 2015 Elsevier Ltd. All rights reserved.

An Integrated Framework Advancing Membrane Protein Modeling and Design

PubMed Central

Weitzner, Brian D.; Duran, Amanda M.; Tilley, Drew C.; Elazar, Assaf; Gray, Jeffrey J.

2015-01-01

Membrane proteins are critical functional molecules in the human body, constituting more than 30% of open reading frames in the human genome. Unfortunately, a myriad of difficulties in overexpression and reconstitution into membrane mimetics severely limit our ability to determine their structures. Computational tools are therefore instrumental to membrane protein structure prediction, consequently increasing our understanding of membrane protein function and their role in disease. Here, we describe a general framework facilitating membrane protein modeling and design that combines the scientific principles for membrane protein modeling with the flexible software architecture of Rosetta3. This new framework, called RosettaMP, provides a general membrane representation that interfaces with scoring, conformational sampling, and mutation routines that can be easily combined to create new protocols. To demonstrate the capabilities of this implementation, we developed four proof-of-concept applications for (1) prediction of free energy changes upon mutation; (2) high-resolution structural refinement; (3) protein-protein docking; and (4) assembly of symmetric protein complexes, all in the membrane environment. Preliminary data show that these algorithms can produce meaningful scores and structures. The data also suggest needed improvements to both sampling routines and score functions. Importantly, the applications collectively demonstrate the potential of combining the flexible nature of RosettaMP with the power of Rosetta algorithms to facilitate membrane protein modeling and design. PMID:26325167

Effect of Detergent on Electrical Properties of Squid Axon Membrane

PubMed Central

Kishimoto, Uichiro; Adelman, William J.

1964-01-01

The effects of detergents on squid giant axon action and resting potentials as well as membrane conductances in the voltage clamp have been studied. Anionic detergents (sodium lauryl sulfate, 0.1 to 1.0 mM; dimethyl benzene sulfonate, 1 to 20 mM, pH 7.6) cause a temporary increase and a later decrease of action potential height and the value of the resting potential. Cationic detergent (cetyl trimethyl ammonium chloride, 6 x 10-5 M or more, pH 7.6) generally brings about immediate and irreversible decreases in the action and resting potentials. Non-ionic detergent (tween 80, 0.1 M, pH 7.6) causes a slight reversible reduction of action potential height without affecting the value of the resting potential. Both anionic and cationic detergents generally decrease the sodium and potassium conductances irreversibly. The effect of non-ionic detergent is to decrease the sodium conductance reversibly, leaving the potassium conductance almost unchanged. PMID:14158665

Protein Kinase Cϵ (PKCϵ) Promotes Synaptogenesis through Membrane Accumulation of the Postsynaptic Density Protein PSD-95*

PubMed Central

Sen, Abhik; Hongpaisan, Jarin; Wang, Desheng; Nelson, Thomas J.; Alkon, Daniel L.

2016-01-01

Protein kinase Cϵ (PKCϵ) promotes synaptic maturation and synaptogenesis via activation of synaptic growth factors such as BDNF, NGF, and IGF. However, many of the detailed mechanisms by which PKCϵ induces synaptogenesis are not fully understood. Accumulation of PSD-95 to the postsynaptic density (PSD) is known to lead to synaptic maturation and strengthening of excitatory synapses. Here we investigated the relationship between PKCϵ and PSD-95. We show that the PKCϵ activators dicyclopropanated linoleic acid methyl ester and bryostatin 1 induce phosphorylation of PSD-95 at the serine 295 residue, increase the levels of PSD-95, and enhance its membrane localization. Elimination of the serine 295 residue in PSD-95 abolished PKCϵ-induced membrane accumulation. Knockdown of either PKCϵ or JNK1 prevented PKCϵ activator-mediated membrane accumulation of PSD-95. PKCϵ directly phosphorylated PSD-95 and JNK1 in vitro. Inhibiting PKCϵ, JNK, or calcium/calmodulin-dependent kinase II activity prevented the effects of PKCϵ activators on PSD-95 phosphorylation. Increase in membrane accumulation of PKCϵ and phosphorylated PSD-95 (p-PSD-95S295) coincided with an increased number of synapses and increased amplitudes of excitatory post-synaptic potentials (EPSPs) in adult rat hippocampal slices. Knockdown of PKCϵ also reduced the synthesis of PSD-95 and the presynaptic protein synaptophysin by 30 and 44%, respectively. Prolonged activation of PKCϵ increased synapse number by 2-fold, increased presynaptic vesicle density, and greatly increased PSD-95 clustering. These results indicate that PKCϵ promotes synaptogenesis by activating PSD-95 phosphorylation directly through JNK1 and calcium/calmodulin-dependent kinase II and also by inducing expression of PSD-95 and synaptophysin. PMID:27330081

Protein Kinase Cϵ (PKCϵ) Promotes Synaptogenesis through Membrane Accumulation of the Postsynaptic Density Protein PSD-95.

PubMed

Sen, Abhik; Hongpaisan, Jarin; Wang, Desheng; Nelson, Thomas J; Alkon, Daniel L

2016-08-05

Protein kinase Cϵ (PKCϵ) promotes synaptic maturation and synaptogenesis via activation of synaptic growth factors such as BDNF, NGF, and IGF. However, many of the detailed mechanisms by which PKCϵ induces synaptogenesis are not fully understood. Accumulation of PSD-95 to the postsynaptic density (PSD) is known to lead to synaptic maturation and strengthening of excitatory synapses. Here we investigated the relationship between PKCϵ and PSD-95. We show that the PKCϵ activators dicyclopropanated linoleic acid methyl ester and bryostatin 1 induce phosphorylation of PSD-95 at the serine 295 residue, increase the levels of PSD-95, and enhance its membrane localization. Elimination of the serine 295 residue in PSD-95 abolished PKCϵ-induced membrane accumulation. Knockdown of either PKCϵ or JNK1 prevented PKCϵ activator-mediated membrane accumulation of PSD-95. PKCϵ directly phosphorylated PSD-95 and JNK1 in vitro Inhibiting PKCϵ, JNK, or calcium/calmodulin-dependent kinase II activity prevented the effects of PKCϵ activators on PSD-95 phosphorylation. Increase in membrane accumulation of PKCϵ and phosphorylated PSD-95 (p-PSD-95(S295)) coincided with an increased number of synapses and increased amplitudes of excitatory post-synaptic potentials (EPSPs) in adult rat hippocampal slices. Knockdown of PKCϵ also reduced the synthesis of PSD-95 and the presynaptic protein synaptophysin by 30 and 44%, respectively. Prolonged activation of PKCϵ increased synapse number by 2-fold, increased presynaptic vesicle density, and greatly increased PSD-95 clustering. These results indicate that PKCϵ promotes synaptogenesis by activating PSD-95 phosphorylation directly through JNK1 and calcium/calmodulin-dependent kinase II and also by inducing expression of PSD-95 and synaptophysin. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

Probing lipid membrane electrostatics

NASA Astrophysics Data System (ADS)

Yang, Yi

The electrostatic properties of lipid bilayer membranes play a significant role in many biological processes. Atomic force microscopy (AFM) is highly sensitive to membrane surface potential in electrolyte solutions. With fully characterized probe tips, AFM can perform quantitative electrostatic analysis of lipid membranes. Electrostatic interactions between Silicon nitride probes and supported zwitterionic dioleoylphosphatidylcholine (DOPC) bilayer with a variable fraction of anionic dioleoylphosphatidylserine (DOPS) were measured by AFM. Classical Gouy-Chapman theory was used to model the membrane electrostatics. The nonlinear Poisson-Boltzmann equation was numerically solved with finite element method to provide the potential distribution around the AFM tips. Theoretical tip-sample electrostatic interactions were calculated with the surface integral of both Maxwell and osmotic stress tensors on tip surface. The measured forces were interpreted with theoretical forces and the resulting surface charge densities of the membrane surfaces were in quantitative agreement with the Gouy-Chapman-Stern model of membrane charge regulation. It was demonstrated that the AFM can quantitatively detect membrane surface potential at a separation of several screening lengths, and that the AFM probe only perturbs the membrane surface potential by <2%. One important application of this technique is to estimate the dipole density of lipid membrane. Electrostatic analysis of DOPC lipid bilayers with the AFM reveals a repulsive force between the negatively charged probe tips and the zwitterionic lipid bilayers. This unexpected interaction has been analyzed quantitatively to reveal that the repulsion is due to a weak external field created by the internai membrane dipole moment. The analysis yields a dipole moment of 1.5 Debye per lipid with a dipole potential of +275 mV for supported DOPC membranes. This new ability to quantitatively measure the membrane dipole density in a noninvasive manner will be useful in identifying the biological effects of the dipole potential. Finally, heterogeneous model membranes were studied with fluid electric force microscopy (FEFM). Electrostatic mapping was demonstrated with 50 nm resolution. The capabilities of quantitative electrostatic measurement and lateral charge density mapping make AFM a unique and powerful probe of membrane electrostatics.

Induced-Charge Enhancement of the Diffusion Potential in Membranes with Polarizable Nanopores

NASA Astrophysics Data System (ADS)

Ryzhkov, I. I.; Lebedev, D. V.; Solodovnichenko, V. S.; Shiverskiy, A. V.; Simunin, M. M.

2017-12-01

When a charged membrane separates two salt solutions of different concentrations, a potential difference appears due to interfacial Donnan equilibrium and the diffusion junction. Here, we report a new mechanism for the generation of a membrane potential in polarizable conductive membranes via an induced surface charge. It results from an electric field generated by the diffusion of ions with different mobilities. For uncharged membranes, this effect strongly enhances the diffusion potential and makes it highly sensitive to the ion mobilities ratio, electrolyte concentration, and pore size. Theoretical predictions on the basis of the space-charge model extended to polarizable nanopores fully agree with experimental measurements in KCl and NaCl aqueous solutions.

Long-term high-intensity sound stimulation inhibits h current (Ih ) in CA1 pyramidal neurons.

PubMed

Cunha, A O S; Ceballos, C C; de Deus, J L; Leão, R M

2018-05-19

Afferent neurotransmission to hippocampal pyramidal cells can lead to long-term changes to their intrinsic membrane properties and affect many ion currents. One of the most plastic neuronal currents is the hyperpolarization activated cationic current (I h ), which changes in CA1 pyramidal cells in response to many types of physiological and pathological processes, including auditory stimulation. Recently we demonstrated that long-term potentiation (LTP) in rat hippocampal Schaffer-CA1 synapses is depressed by high-intensity sound stimulation. Here we investigated if a long-term high-intensity sound stimulation could affect intrinsic membrane properties of rat CA1 pyramidal neurons. Our results showed that I h is depressed by long-term high intensity sound exposure (1 minute of 110 dB sound, applied two times per day for 10 days). This resulted in a decreased resting membrane potential, increased membrane input resistance and time constant, and decreased action potential threshold. In addition, CA1 pyramidal neurons from sound-exposed animals fired more action potentials than neurons from control animals; However, this effect was not caused by a decreased I h . Interestingly, a single episode (1 minute) of 110 dB sound stimulation which also inhibits hippocampal LTP did not affect I h and firing in pyramidal neurons, suggesting that effects on I h are long-term responses to high intensity sound exposure. Our results show that prolonged exposure to high-intensity sound affects intrinsic membrane properties of hippocampal pyramidal neurons, mainly by decreasing the amplitude of I h . This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Hysteresis in voltage-gated channels

PubMed Central

2017-01-01

ABSTRACT Ion channels constitute a superfamily of membrane proteins found in all living creatures. Their activity allows fast translocation of ions across the plasma membrane down the ion's transmembrane electrochemical gradient, resulting in a difference in electrical potential across the plasma membrane, known as the membrane potential. A group within this superfamily, namely voltage-gated channels, displays activity that is sensitive to the membrane potential. The activity of voltage-gated channels is controlled by the membrane potential, while the membrane potential is changed by these channels' activity. This interplay produces variations in the membrane potential that have evolved into electrical signals in many organisms. These signals are essential for numerous biological processes, including neuronal activity, insulin release, muscle contraction, fertilization and many others. In recent years, the activity of the voltage-gated channels has been observed not to follow a simple relationship with the membrane potential. Instead, it has been shown that the activity of voltage-gated channel displays hysteresis. In fact, a growing number of evidence have demonstrated that the voltage dependence of channel activity is dynamically modulated by activity itself. In spite of the great impact that this property can have on electrical signaling, hysteresis in voltage-gated channels is often overlooked. Addressing this issue, this review provides examples of voltage-gated ion channels displaying hysteretic behavior. Further, this review will discuss how Dynamic Voltage Dependence in voltage-gated channels can have a physiological role in electrical signaling. Furthermore, this review will elaborate on the current thoughts on the mechanism underlying hysteresis in voltage-gated channels. PMID:27689426

Chitosan-functionalized silk fibroin 3D scaffold for keratocyte culture.

PubMed

Guan, Linan; Tian, Pei; Ge, Hongyan; Tang, Xianling; Zhang, Hong; Du, Lingling; Liu, Ping

2013-10-01

The goal of this study was to evaluate the potential suitability of an artificial membrane composed of silk fibroin (SF) functionalized by different ratios of chitosan (CS) as a substrate for the stroma of the cornea. Keratocytes were cultured on translucent membranes made of SF and CS with different ratios. The biophysical properties of the silk fibroin and chitosan (SF/CS) membrane were examined. The SF/CS showed tensile strengths that increased as the CS concentration increased, but the physical and mechanical properties of chitosan-functionalized silk fibroin scaffolds weakened significantly compared with those of native corneas. The resulting cell scaffolds were evaluated using western blot in addition to light and electron microscopy. The cell attachment and proliferation on the scaffold were similar to those on a plastic plate. Keratocytes cultured in serum on SF/CS exhibited stellate morphology along with a marked increase in the expression of keratocan compared with identical cultures on tissue culture plastics. The biocompatibility was tested by transplanting the acellular membrane into rabbit corneal stromal pockets. There was no inflammatory complication detected at any time point on the macroscopic level. Taken together, these results indicate that SF/CS holds promise as a substrate for corneal reconstruction.

The impact of magnesium on isometric twitch parameters and resting membrane potential of the skeletal muscle in diabetic rats.

PubMed

Pelit, Aykut; Emre, Mustafa; Dağli, Kenan; Tuli, Abdullah

2013-04-01

To present the relationship between oral magnesium supplementation, blood glucose, and changes in isometric twitch parameters, resting membrane potential (RMP), in the gastrocnemius muscle in diabetic rats. Sixty rats were used in this study. The rats were divided into four groups: control (drinking tap water, Group I, n = 15), control with treated with magnesium sulfate (10 g/L) (Group II, n = 15), diabetic (Group III, n = 15), and diabetic with treated with magnesium sulfate (10 g/L) (Group IV, n = 15). In Group II and IV, the level of plasma magnesium was increased comparing to those of the control group (p < 0.05). Isometric twitch tensions were decreased significantly in the Group III, but Group IV isometric twitch tensions were increased significantly. Group IV RMP values were close to the Group I. Hyperglycemia decreases gastrocnemius muscle isometric twitch tension and increases RMP in diabetic rats. Magnesium treatment can prevent these diabetic complications.

The cluster [Re6Se8I6]3- penetrates biological membranes: drug-like properties for CNS tumor treatment and diagnosis.

PubMed

Estrada, Lisbell D; Duran, Elizabeth; Cisterna, Matias; Echeverria, Cesar; Zheng, Zhiping; Borgna, Vincenzo; Arancibia-Miranda, Nicolas; Ramírez-Tagle, Rodrigo

2018-03-24

Tumorigenic cell lines are more susceptible to [Re 6 Se 8 I 6 ] 3- cluster-induced death than normal cells, becoming a novel candidate for cancer treatment. Still, the feasibility of using this type of molecules in human patients remains unclear and further pharmacokinetics analysis is needed. Using coupled plasma optical emission spectroscopy, we determined the Re-cluster tissue content in injected mice, as a biodistribution measurement. Our results show that the Re-cluster successfully reaches different tissues, accumulating mainly in heart and liver. In order to dissect the mechanism underlying cluster biodistribution, we used three different experimental approaches. First, we evaluate the degree of lipophilicity by determining the octanol/water partition coefficient. The cluster mostly remained in the octanol fraction, with a coefficient of 1.86 ± 0.02, which indicates it could potentially cross cell membranes. Then, we measured the biological membrane penetration through a parallel artificial membrane permeability assays (PAMPA) assay. The Re-cluster crosses the artificial membrane, with a coefficient of 122 nm/s that is considered highly permeable. To evaluate a potential application of the Re-cluster in central nervous system (CNS) tumors, we analyzed the cluster's brain penetration by exposing cultured blood-brain-barrier (BBB) cells to increasing concentrations of the cluster. The Re-cluster effectively penetrates the BBB, reaching nearly 30% of the brain side after 24 h. Thus, our results indicate that the Re-cluster penetrates biological membranes reaching different target organs-most probably due to its lipophilic properties-becoming a promising anti-cancer drug with high potential for CNS cancer's diagnosis and treatment.

Synaptic hyperpolarization and inhibition of turtle cochlear hair cells.

PubMed

Art, J J; Fettiplace, R; Fuchs, P A

1984-11-01

Intracellular recordings were made from turtle cochlear hair cells in order to examine the properties of the post-synaptic potentials evoked by electrical stimulation of the efferent axons. Single shocks to the efferents generated a hair cell membrane hyperpolarization with an average amplitude generally less than 1 mV and lasting for about 100 ms. With short trains of shocks, the size of the post-synaptic potential grew markedly to a maximum of 20-30 mV. The interaction between pairs of shocks separated by a varying interval was studied. For an interval of 4 ms, the response to the second shock was increased on average by a factor of 3 and the conditioning effect of the first shock decayed with a time constant of about 100 ms. We suggest the augmentation in response to trains of shocks may be partly due to facilitation of efferent transmitter release. The efferent post-synaptic potentials could be reversibly abolished by perfusion with perilymphs containing 3 microM-curare or atropine, and infusion of acetylcholine gave a transient membrane hyperpolarization. These observations are consistent with efferent action being mediated via a cholinergic synapse onto the hair cells. The post-synaptic potentials could be reversed in polarity by injection of hyperpolarizing currents through the recording electrode. The reversal potential was estimated as about -80 mV, 30 mV negative to the resting potential. Near reversal, a small brief depolarization was evident and may constitute a minor component of the synaptic response. The value of the reversal potential was unaffected by substitution of the perilymphatic chloride, but was altered in a predictable manner by changes in extracellular potassium concentration indicating that the post-synaptic potentials arise mainly by an increase in the permeability of the hair cell membrane to potassium ions. Throughout the post-synaptic hyperpolarization there was a reduction in the sensitivity of the hair cell to tones at its characteristic frequency. The desensitization, maximal for low sound pressures, varied in different cells from a factor of 1.6 to 28. At the peak of the largest synaptic potentials, the receptor potential remained negative to the resting potential with all but the loudest characteristic frequency tone s. We suggest that there are two factors in efferent inhibition; one a r duction in the receptor potential at the hair cell's characteristic frequency and the other a hyperpolarization of its membrane potential which should reduce the release of excitatory transmitter onto the afferent terminals.

Influence of natural organic matter (NOM) coatings on nanoparticle adsorption onto supported lipid bilayers.

PubMed

Bo, Zhang; Avsar, Saziye Yorulmaz; Corliss, Michael K; Chung, Minsub; Cho, Nam-Joon

2017-10-05

As the worldwide usage of nanoparticles in commercial products continues to increase, there is growing concern about the environmental risks that nanoparticles pose to biological systems, including potential damage to cellular membranes. A detailed understanding of how different types of nanoparticles behave in environmentally relevant conditions is imperative for predicting and mitigating potential membrane-associated toxicities. Herein, we investigated the adsorption of two popular nanoparticles (silver and buckminsterfullerene) onto biomimetic supported lipid bilayers of varying membrane charge (positive and negative). The quartz crystal microbalance-dissipation (QCM-D) measurement technique was employed to track the adsorption kinetics. Particular attention was focused on understanding how natural organic matter (NOM) coatings affect nanoparticle-bilayer interactions. Both types of nanoparticles preferentially adsorbed onto the positively charged bilayers, although NOM coatings on the nanoparticle and lipid bilayer surfaces could either inhibit or promote adsorption in certain electrolyte conditions. While past findings showed that NOM coatings inhibit membrane adhesion, our findings demonstrate that the effects of NOM coatings are more nuanced depending on the type of nanoparticle and electrolyte condition. Taken together, the results demonstrate that NOM coatings can modulate the lipid membrane interactions of various nanoparticles, suggesting a possible way to improve the environmental safety of nanoparticles. Copyright © 2017 Elsevier B.V. All rights reserved.

Anion- or Cation-Exchange Membranes for NaBH4/H2O2 Fuel Cells?

PubMed Central

Šljukić, Biljana; Morais, Ana L.; Santos, Diogo M. F.; Sequeira, César A. C.

2012-01-01

Direct borohydride fuel cells (DBFC), which operate on sodium borohydride (NaBH4) as the fuel, and hydrogen peroxide (H2O2) as the oxidant, are receiving increasing attention. This is due to their promising use as power sources for space and underwater applications, where air is not available and gas storage poses obvious problems. One key factor to improve the performance of DBFCs concerns the type of separator used. Both anion- and cation-exchange membranes may be considered as potential separators for DBFC. In the present paper, the effect of the membrane type on the performance of laboratory NaBH4/H2O2 fuel cells using Pt electrodes is studied at room temperature. Two commercial ion-exchange membranes from Membranes International Inc., an anion-exchange membrane (AMI-7001S) and a cation-exchange membrane (CMI-7000S), are tested as ionic separators for the DBFC. The membranes are compared directly by the observation and analysis of the corresponding DBFC’s performance. Cell polarization, power density, stability, and durability tests are used in the membranes’ evaluation. Energy densities and specific capacities are estimated. Most tests conducted, clearly indicate a superior performance of the cation-exchange membranes over the anion-exchange membrane. The two membranes are also compared with several other previously tested commercial membranes. For long term cell operation, these membranes seem to outperform the stability of the benchmark Nafion membranes but further studies are still required to improve their instantaneous power load. PMID:24958292

Forward osmosis for application in wastewater treatment: a review.

PubMed

Lutchmiah, Kerusha; Verliefde, A R D; Roest, K; Rietveld, L C; Cornelissen, E R

2014-07-01

Research in the field of Forward Osmosis (FO) membrane technology has grown significantly over the last 10 years, but its application in the scope of wastewater treatment has been slower. Drinking water is becoming an increasingly marginal resource. Substituting drinking water for alternate water sources, specifically for use in industrial processes, may alleviate the global water stress. FO has the potential to sustainably treat wastewater sources and produce high quality water. FO relies on the osmotic pressure difference across the membrane to extract clean water from the feed, however the FO step is still mostly perceived as a "pre-treatment" process. To prompt FO-wastewater feasibility, the focus lies with new membrane developments, draw solutions to enhance wastewater treatment and energy recovery, and operating conditions. Optimisation of these parameters are essential to mitigate fouling, decrease concentration polarisation and increase FO performance; issues all closely related to one another. This review attempts to define the steps still required for FO to reach full-scale potential in wastewater treatment and water reclamation by discussing current novelties, bottlenecks and future perspectives of FO technology in the wastewater sector. Copyright © 2014 Elsevier Ltd. All rights reserved.

Osmoregulation in Lilium Pollen Grains Occurs via Modulation of the Plasma Membrane H+ ATPase Activity by 14-3-3 Proteins1[C][W][OA

PubMed Central

Pertl, Heidi; Pöckl, Magdalena; Blaschke, Christian; Obermeyer, Gerhard

2010-01-01

To allow successful germination and growth of a pollen tube, mature and dehydrated pollen grains (PGs) take up water and have to adjust their turgor pressure according to the water potential of the surrounding stigma surface. The turgor pressure of PGs of lily (Lilium longiflorum) was measured with a modified pressure probe for simultaneous recordings of turgor pressure and membrane potential to investigate the relation between water and electrogenic ion transport in osmoregulation. Upon hyperosmolar shock, the turgor pressure decreased, and the plasma membrane (PM) hyperpolarizes in parallel, whereas depolarization of the PM was observed with hypoosmolar treatment. An acidification and alkalinization of the external medium was monitored after hyper- and hypoosmotic treatments, respectively, and pH changes were blocked by vanadate, indicating a putative role of the PM H+ ATPase. Indeed, an increase in PM-associated 14-3-3 proteins and an increase in PM H+ ATPase activity were detected in PGs challenged by hyperosmolar medium. We therefore suggest that in PGs the PM H+ ATPase via modulation of its activity by 14-3-3 proteins is involved in the regulation of turgor pressure. PMID:20974894

Electrical properties of the costo-uterine muscle of the guinea-pig.

PubMed Central

Parkington, H C

1983-01-01

The spontaneous electrical and mechanical activity of the costo-uterine muscle of the guinea-pig are described. The spontaneous electrical activity, recorded intracellularly, is similar to that observed previously in longitudinal myometrium of rat (Marshall, 1959) and ionic substitution suggests that, though calcium may be the predominant ion carrying the current during the upstroke of the action potential, some influence of sodium cannot be ruled out. During dioestrus, when circulating progesterone levels are high, there is an increase in the resting membrane potential and a decrease in the frequency of electrical and mechanical activity. There is a two-fold decrease in the space constant (lambda) during dioestrus. At this time the membrane time constant (tau m) is also decreased. The diameter and length of the smooth muscle cells are smaller during dioestrus. However, the differences in cell diameter do not explain all of the differences observed in lambda at this time and it is suggested that there may be an increase in the resistance to current flow between cells. It is concluded that high circulating progesterone may bring about quiescence of target smooth muscle in two ways: by stabilizing the cell membrane and by restricting the spread of activity. PMID:6683758

Thrombopoietic status of patients on haemodialysis

PubMed Central

Bat, Taha; Bat, Betul Emine; El-Moghraby, Ahmed; Patel, Samir; Feng, Xingmin; Dunbar, Cynthia E.; Sarac, Erdal

2015-01-01

Thrombocytopenia is a potential dialysis-related treatment complication. Developments in bio-compatible dialyser membranes have decreased the occurrence of thrombocytopenia. We investigated whether thrombopoiesis is impaired in haemodialysis patients by measuring the thrombopoietin level and absolute immature platelet number (AIPN) in the blood of patients undergoing haemodialysis. Samples were collected from the dialysis tubing pre- and post- haemodialysis in a cohort of 45 well-characterized haemodialysis patients. Thrombopoietin levels and AIPN increased following haemodialysis, despite no change in platelet count. Observed increase in release of immature platelets from the bone marrow following haemodialysis indicates possible complement activation secondary to interaction between blood constituents and the dialysis membrane. PMID:26887628

Plasma membranes modified by plasma treatment or deposition as solid electrolytes for potential application in solid alkaline fuel cells.

PubMed

Reinholdt, Marc; Ilie, Alina; Roualdès, Stéphanie; Frugier, Jérémy; Schieda, Mauricio; Coutanceau, Christophe; Martemianov, Serguei; Flaud, Valérie; Beche, Eric; Durand, Jean

2012-07-30

In the highly competitive market of fuel cells, solid alkaline fuel cells using liquid fuel (such as cheap, non-toxic and non-valorized glycerol) and not requiring noble metal as catalyst seem quite promising. One of the main hurdles for emergence of such a technology is the development of a hydroxide-conducting membrane characterized by both high conductivity and low fuel permeability. Plasma treatments can enable to positively tune the main fuel cell membrane requirements. In this work, commercial ADP-Morgane® fluorinated polymer membranes and a new brand of cross-linked poly(aryl-ether) polymer membranes, named AMELI-32®, both containing quaternary ammonium functionalities, have been modified by argon plasma treatment or triallylamine-based plasma deposit. Under the concomitant etching/cross-linking/oxidation effects inherent to the plasma modification, transport properties (ionic exchange capacity, water uptake, ionic conductivity and fuel retention) of membranes have been improved. Consequently, using plasma modified ADP-Morgane® membrane as electrolyte in a solid alkaline fuel cell operating with glycerol as fuel has allowed increasing the maximum power density by a factor 3 when compared to the untreated membrane.

Plasma Membranes Modified by Plasma Treatment or Deposition as Solid Electrolytes for Potential Application in Solid Alkaline Fuel Cells

PubMed Central

Reinholdt, Marc; Ilie, Alina; Roualdès, Stéphanie; Frugier, Jérémy; Schieda, Mauricio; Coutanceau, Christophe; Martemianov, Serguei; Flaud, Valérie; Beche, Eric; Durand, Jean

2012-01-01

In the highly competitive market of fuel cells, solid alkaline fuel cells using liquid fuel (such as cheap, non-toxic and non-valorized glycerol) and not requiring noble metal as catalyst seem quite promising. One of the main hurdles for emergence of such a technology is the development of a hydroxide-conducting membrane characterized by both high conductivity and low fuel permeability. Plasma treatments can enable to positively tune the main fuel cell membrane requirements. In this work, commercial ADP-Morgane® fluorinated polymer membranes and a new brand of cross-linked poly(aryl-ether) polymer membranes, named AMELI-32®, both containing quaternary ammonium functionalities, have been modified by argon plasma treatment or triallylamine-based plasma deposit. Under the concomitant etching/cross-linking/oxidation effects inherent to the plasma modification, transport properties (ionic exchange capacity, water uptake, ionic conductivity and fuel retention) of membranes have been improved. Consequently, using plasma modified ADP-Morgane® membrane as electrolyte in a solid alkaline fuel cell operating with glycerol as fuel has allowed increasing the maximum power density by a factor 3 when compared to the untreated membrane. PMID:24958295

Evidence that electrostatic interactions between vesicle-associated membrane protein 2 and acidic phospholipids may modulate the fusion of transport vesicles with the plasma membrane.

PubMed

Williams, Dumaine; Vicôgne, Jérome; Zaitseva, Irina; McLaughlin, Stuart; Pessin, Jeffrey E

2009-12-01

The juxtamembrane domain of vesicle-associated membrane protein (VAMP) 2 (also known as synaptobrevin2) contains a conserved cluster of basic/hydrophobic residues that may play an important role in membrane fusion. Our measurements on peptides corresponding to this domain determine the electrostatic and hydrophobic energies by which this domain of VAMP2 could bind to the adjacent lipid bilayer in an insulin granule or other transport vesicle. Mutation of residues within the juxtamembrane domain that reduce the VAMP2 net positive charge, and thus its interaction with membranes, inhibits secretion of insulin granules in beta cells. Increasing salt concentration in permeabilized cells, which reduces electrostatic interactions, also results in an inhibition of insulin secretion. Similarly, amphipathic weak bases (e.g., sphingosine) that reverse the negative electrostatic surface potential of a bilayer reverse membrane binding of the positively charged juxtamembrane domain of a reconstituted VAMP2 protein and inhibit membrane fusion. We propose a model in which the positively charged VAMP and syntaxin juxtamembrane regions facilitate fusion by bridging the negatively charged vesicle and plasma membrane leaflets.

Membrane-Assisted Growth of DNA Origami Nanostructure Arrays

PubMed Central

2015-01-01

Biological membranes fulfill many important tasks within living organisms. In addition to separating cellular volumes, membranes confine the space available to membrane-associated proteins to two dimensions (2D), which greatly increases their probability to interact with each other and assemble into multiprotein complexes. We here employed two DNA origami structures functionalized with cholesterol moieties as membrane anchors—a three-layered rectangular block and a Y-shaped DNA structure—to mimic membrane-assisted assembly into hierarchical superstructures on supported lipid bilayers and small unilamellar vesicles. As designed, the DNA constructs adhered to the lipid bilayers mediated by the cholesterol anchors and diffused freely in 2D with diffusion coefficients depending on their size and number of cholesterol modifications. Different sets of multimerization oligonucleotides added to bilayer-bound origami block structures induced the growth of either linear polymers or two-dimensional lattices on the membrane. Y-shaped DNA origami structures associated into triskelion homotrimers and further assembled into weakly ordered arrays of hexagons and pentagons, which resembled the geometry of clathrin-coated pits. Our results demonstrate the potential to realize artificial self-assembling systems that mimic the hierarchical formation of polyhedral lattices on cytoplasmic membranes. PMID:25734977

Membrane-assisted growth of DNA origami nanostructure arrays.

PubMed

Kocabey, Samet; Kempter, Susanne; List, Jonathan; Xing, Yongzheng; Bae, Wooli; Schiffels, Daniel; Shih, William M; Simmel, Friedrich C; Liedl, Tim

2015-01-01

Biological membranes fulfill many important tasks within living organisms. In addition to separating cellular volumes, membranes confine the space available to membrane-associated proteins to two dimensions (2D), which greatly increases their probability to interact with each other and assemble into multiprotein complexes. We here employed two DNA origami structures functionalized with cholesterol moieties as membrane anchors--a three-layered rectangular block and a Y-shaped DNA structure--to mimic membrane-assisted assembly into hierarchical superstructures on supported lipid bilayers and small unilamellar vesicles. As designed, the DNA constructs adhered to the lipid bilayers mediated by the cholesterol anchors and diffused freely in 2D with diffusion coefficients depending on their size and number of cholesterol modifications. Different sets of multimerization oligonucleotides added to bilayer-bound origami block structures induced the growth of either linear polymers or two-dimensional lattices on the membrane. Y-shaped DNA origami structures associated into triskelion homotrimers and further assembled into weakly ordered arrays of hexagons and pentagons, which resembled the geometry of clathrin-coated pits. Our results demonstrate the potential to realize artificial self-assembling systems that mimic the hierarchical formation of polyhedral lattices on cytoplasmic membranes.

Membrane crystallinity and fuel crossover in direct ethanol fuel cells with Nafion composite membranes containing phosphotungstic acid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Hongjun; Lee, Sunghwan; Kim, Suran

2016-11-01

Interest has been growing in direct ethanol fuel cells (DEFCs) due to their non-toxicity, low cost and potential contribution to energy issues in third world countries. A reduction in fuel cross-over is of key importance to enhance the performance of DEFCs that operate at low temperatures (<100 °C). We report on the effect of the addition of phosphotungstic acid (PWA) in Nafion membrane on the ethanol-crossover for DEFC application. A set of PWANafion composite membranes (PWA 0, 5, 10, 15, 20 wt%) was prepared by solution casting and their microstructures, diffraction patterns and permeability were systematically characterized. The significant reductionmore » in ethanol-crossover was observed with increasing PWA concentration in PWA-Nafion membranes, which was mainly attributed to an improvement in crystallinity of the membrane. PWA provides additional nucleation sites during solidification leading to higher crystallinity, which is supported by the membrane permeability tests. These PWA-Nafion composites were implemented in proto-type DEFC devices as a membrane and the maximum power density achieved was 22% higher than that of commercial Nafion-117 device.« less

Betaine is a positive regulator of mitochondrial respiration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Icksoo, E-mail: icksoolee@dankook.ac.kr

2015-01-09

Highlights: • Betaine enhances cytochrome c oxidase activity and mitochondrial respiration. • Betaine increases mitochondrial membrane potential and cellular energy levels. • Betaine’s anti-tumorigenic effect might be due to a reversal of the Warburg effect. - Abstract: Betaine protects cells from environmental stress and serves as a methyl donor in several biochemical pathways. It reduces cardiovascular disease risk and protects liver cells from alcoholic liver damage and nonalcoholic steatohepatitis. Its pretreatment can rescue cells exposed to toxins such as rotenone, chloroform, and LiCl. Furthermore, it has been suggested that betaine can suppress cancer cell growth in vivo and in vitro.more » Mitochondrial electron transport chain (ETC) complexes generate the mitochondrial membrane potential, which is essential to produce cellular energy, ATP. Reduced mitochondrial respiration and energy status have been found in many human pathological conditions including aging, cancer, and neurodegenerative disease. In this study we investigated whether betaine directly targets mitochondria. We show that betaine treatment leads to an upregulation of mitochondrial respiration and cytochrome c oxidase activity in H2.35 cells, the proposed rate limiting enzyme of ETC in vivo. Following treatment, the mitochondrial membrane potential was increased and cellular energy levels were elevated. We propose that the anti-proliferative effects of betaine on cancer cells might be due to enhanced mitochondrial function contributing to a reversal of the Warburg effect.« less

Sodium-dependent nitrate transport at the plasma membrane of leaf cells of the marine higher plant Zostera marina L.

PubMed

García-Sánchez, M J; Jaime, M P; Ramos, A; Sanders, D; Fernández, J A

2000-03-01

NO(3)(-) is present at micromolar concentrations in seawater and must be absorbed by marine plants against a steep electrochemical potential difference across the plasma membrane. We studied NO(3)(-) transport in the marine angiosperm Zostera marina L. to address the question of how NO(3)(-) uptake is energized. Electrophysiological studies demonstrated that micromolar concentrations of NO(3)(-) induced depolarizations of the plasma membrane of leaf cells. Depolarizations showed saturation kinetics (K(m) = 2.31 +/- 0.78 microM NO(3)(-)) and were enhanced in alkaline conditions. The addition of NO(3)(-) did not affect the membrane potential in the absence of Na(+), but depolarizations were restored when Na(+) was resupplied. NO(3)(-)-induced depolarizations at increasing Na(+) concentrations showed saturation kinetics (K(m) = 0.72 +/- 0.18 mM Na(+)). Monensin, an ionophore that dissipates the Na(+) electrochemical potential, inhibited NO(3)(-)-evoked depolarizations by 85%, and NO(3)(-) uptake (measured by depletion from the external medium) was stimulated by Na(+) ions and by light. Our results strongly suggest that NO(3)(-) uptake in Z. marina is mediated by a high-affinity Na(+)-symport system, which is described here (for the first time to our knowledge) in an angiosperm. Coupling the uptake of NO(3)(-) to that of Na(+) enables the steep inwardly-directed electrochemical potential for Na(+) to drive net accumulation of NO(3)(-) within leaf cells.

Increased Isoprenoid Quinone Concentration Modulates Membrane Fluidity in Listeria monocytogenes at Low Growth Temperatures.

PubMed

Seel, Waldemar; Flegler, Alexander; Zunabovic-Pichler, Marija; Lipski, André

2018-07-01

Listeria monocytogenes is a food pathogen capable of growing at a broad temperature range from 50°C to refrigerator temperatures. A key requirement for bacterial activity and growth at low temperatures is the ability to adjust the membrane lipid composition to maintain cytoplasmic membrane fluidity. In this study, we confirmed earlier findings that the extents of fatty acid profile adaptation differed between L. monocytogenes strains. We were able to demonstrate for isolates from food that growth rates at low temperatures and resistance to freeze-thaw stress were not impaired by a lower adaptive response of the fatty acid composition. This indicated the presence of a second adaptation mechanism besides temperature-regulated fatty acid synthesis. For strains that showed weaker adaptive responses in their fatty acid profiles to low growth temperature, we could demonstrate a significantly higher concentration of isoprenoid quinones. Three strains even showed a higher quinone concentration after growth at 6°C than at 37°C, which is contradictory to the reduced respiratory activity at lower growth temperatures. Analyses of the membrane fluidity in vivo by measuring generalized polarization and anisotropy revealed modulation of the transition phase. Strains with increased quinone concentrations showed an expanded membrane transition phase in contrast to strains with pronounced adaptations of fatty acid profiles. The correlation between quinone concentration and membrane transition phase expansion was confirmed by suppression of quinone synthesis. A reduced quinone concentration resulted in a narrower transition phase. Expansion of the phase transition zone by increasing the concentration of non-fatty acid membrane lipids is discussed as an additional mechanism improving adaptation to temperature shifts for L. monocytogenes strains. IMPORTANCE Listeria monocytogenes is a foodborne pathogen with an outstanding temperature range for growth. The ability for growth at temperatures close to the freezing point constitutes a serious contamination potential for cold stored food. The only known mechanism of the species for adaptation of membrane fluidity is modification of the membrane fatty acid composition. We were able to demonstrate that, at least for some strains, this adaptation mechanism is supported by regulation of the menaquinone concentration. The increase of this neutral membrane lipid is correlated with fluidization of the membrane under low-temperature conditions and therefore represents a fatty acid-independent mechanism for adaptation to low temperatures. Copyright © 2018 American Society for Microbiology.

Pseudorabies Virus Infection Alters Neuronal Activity and Connectivity In Vitro

PubMed Central

McCarthy, Kelly M.; Tank, David W.; Enquist, Lynn W.

2009-01-01

Alpha-herpesviruses, including human herpes simplex virus 1 & 2, varicella zoster virus and the swine pseudorabies virus (PRV), infect the peripheral nervous system of their hosts. Symptoms of infection often include itching, numbness, or pain indicative of altered neurological function. To determine if there is an in vitro electrophysiological correlate to these characteristic in vivo symptoms, we infected cultured rat sympathetic neurons with well-characterized strains of PRV known to produce virulent or attenuated symptoms in animals. Whole-cell patch clamp recordings were made at various times after infection. By 8 hours of infection with virulent PRV, action potential (AP) firing rates increased substantially and were accompanied by hyperpolarized resting membrane potentials and spikelet-like events. Coincident with the increase in AP firing rate, adjacent neurons exhibited coupled firing events, first with AP-spikelets and later with near identical resting membrane potentials and AP firing. Small fusion pores between adjacent cell bodies formed early after infection as demonstrated by transfer of the low molecular weight dye, Lucifer Yellow. Later, larger pores formed as demonstrated by transfer of high molecular weight Texas red-dextran conjugates between infected cells. Further evidence for viral-induced fusion pores was obtained by infecting neurons with a viral mutant defective for glycoprotein B, a component of the viral membrane fusion complex. These infected neurons were essentially identical to mock infected neurons: no increased AP firing, no spikelet-like events, and no electrical or dye transfer. Infection with PRV Bartha, an attenuated circuit-tracing strain delayed, but did not eliminate the increased neuronal activity and coupling events. We suggest that formation of fusion pores between infected neurons results in electrical coupling and elevated firing rates, and that these processes may contribute to the altered neural function seen in PRV-infected animals. PMID:19876391

[Functional organization and structure of the serotonergic neuronal network of terrestrial snail].

PubMed

Nikitin, E S; Balaban, P M

2011-01-01

The extension of knowledge how the brain works requires permanent improvement of methods of recording of neuronal activity and increase in the number of neurons recorded simultaneously to better understand the collective work of neuronal networks and assemblies. Conventional methods allow simultaneous intracellular recording up to 2-5 neurons and their membrane potentials, currents or monosynaptic connections or observation of spiking of neuronal groups with subsequent discrimination of individual spikes with loss of details of the dynamics of membrane potential. We recorded activity of a compact group of serotonergic neurons (up to 56 simultaneously) in the ganglion of a terrestrial mollusk using the method of optical recording of membrane potential that allowed to record individual action potentials in details with action potential parameters and to reveal morphology of the neurons rcorded. We demonstrated clear clustering in the group in relation with the dynamics of action potentials and phasic or tonic components in the neuronal responses to external electrophysiological and tactile stimuli. Also, we showed that identified neuron Pd2 could induce activation of a significant number of neurons in the group whereas neuron Pd4 did not induce any activation. However, its activation is delayed with regard to activation of the reacting group of neurons. Our data strongly support the concept of possible delegation of the integrative function by the network to a single neuron.

NaCl regulation of plasma membrane H(+)-ATPase gene expression in a glycophyte and a halophyte.

PubMed

Niu, X; Narasimhan, M L; Salzman, R A; Bressan, R A; Hasegawa, P M

1993-11-01

NaCl regulation of plasma membrane H(+)-ATPase gene expression in the glycophyte tobacco (Nicotiana tabacum L. var Wisconsin 38) and the halophyte Atriplex nummularia L. was evaluated by comparison of organ-specific mRNA abundance using homologous cDNA probes encoding the ATPases of the respective plants. Accumulation of mRNA was induced by NaCl in fully expanded leaves and in roots but not in expanding leaves or stems. The NaCl responsiveness of the halophyte to accumulate plasma membrane H(+)-ATPase mRNA in roots was substantially greater than that of the glycophyte. Salt-induced transcript accumulation in A. nummularia roots was localized by in situ hybridization predominantly to the elongation zone, but mRNA levels also increased in the zone of differentiation. Increased message accumulation in A. nummularia roots could be detected within 8 h after NaCl (400 mM) treatment, and maximal levels were severalfold greater than in roots of untreated control plants. NaCl-induced plasma membrane H(+)-ATPase gene expression in expanded leaves and roots presumably indicates that these organs require increased H(+)-electrochemical potential gradients for the maintenance of plant ion homeostasis for salt adaptation. The greater capacity of the halophyte to induce plasma membrane H(+)-ATPase gene expression in response to NaCl may be a salt-tolerance determinant.

NaCl regulation of plasma membrane H(+)-ATPase gene expression in a glycophyte and a halophyte.

PubMed Central

Niu, X; Narasimhan, M L; Salzman, R A; Bressan, R A; Hasegawa, P M

1993-01-01

NaCl regulation of plasma membrane H(+)-ATPase gene expression in the glycophyte tobacco (Nicotiana tabacum L. var Wisconsin 38) and the halophyte Atriplex nummularia L. was evaluated by comparison of organ-specific mRNA abundance using homologous cDNA probes encoding the ATPases of the respective plants. Accumulation of mRNA was induced by NaCl in fully expanded leaves and in roots but not in expanding leaves or stems. The NaCl responsiveness of the halophyte to accumulate plasma membrane H(+)-ATPase mRNA in roots was substantially greater than that of the glycophyte. Salt-induced transcript accumulation in A. nummularia roots was localized by in situ hybridization predominantly to the elongation zone, but mRNA levels also increased in the zone of differentiation. Increased message accumulation in A. nummularia roots could be detected within 8 h after NaCl (400 mM) treatment, and maximal levels were severalfold greater than in roots of untreated control plants. NaCl-induced plasma membrane H(+)-ATPase gene expression in expanded leaves and roots presumably indicates that these organs require increased H(+)-electrochemical potential gradients for the maintenance of plant ion homeostasis for salt adaptation. The greater capacity of the halophyte to induce plasma membrane H(+)-ATPase gene expression in response to NaCl may be a salt-tolerance determinant. PMID:8022933

Quantitative method of measuring cancer cell urokinase and metastatic potential

NASA Technical Reports Server (NTRS)

Morrison, Dennis R. (Inventor)

1993-01-01

The metastatic potential of tumors can be evaluated by the quantitative detection of urokinase and DNA. The cell sample selected for examination is analyzed for the presence of high levels of urokinase and abnormal DNA using analytical flow cytometry and digital image analysis. Other factors such as membrane associated urokinase, increased DNA synthesis rates and certain receptors can be used in the method for detection of potentially invasive tumors.

Bone conditioned media (BCM) improves osteoblast adhesion and differentiation on collagen barrier membranes.

PubMed

Fujioka-Kobayashi, Masako; Caballé-Serrano, Jordi; Bosshardt, Dieter D; Gruber, Reinhard; Buser, Daniel; Miron, Richard J

2016-07-04

The use of autogenous bone chips during guided bone regeneration procedures has remained the gold standard for bone grafting due to its excellent combination of osteoconduction, osteoinduction and osteogenesis. Recent protocols established by our group have characterized specific growth factors and cytokines released from autogenous bone that have the potential to be harvested and isolated into bone conditioned media (BCM). Due to the advantageous osteo-promotive properties of BCM, the aims of the present study was to pre-coat collagen barrier membranes with BCM and investigate its effect on osteoblast adhesion, proliferation and differentiation for possible future clinical use. Scanning electron microscopy (SEM) was first used to qualitative assess BCM protein accumulation on the surface of collagen membranes. Thereafter, undifferentiated mouse ST2 stromal bone marrow cells were seeded onto BioGide porcine derived collagen barrier membranes (control) or barrier membranes pre-coated with BCM (test group). Control and BCM samples were compared for cell adhesion at 8 h, cell proliferation at 1, 3 and 5 days and real-time PCR at 5 days for osteoblast differentiation markers including Runx2, alkaline phosphatase (ALP), osteocalcin (OCN) and bone sialoprotein (BSP). Mineralization was further assessed with alizarin red staining at 14 days post seeding. SEM images demonstrated evidence of accumulated proteins found on the surface of collagen membranes following coating with BCM. Analysis of total cell numbers revealed that the additional pre-coating with BCM markedly increased cell attachment over 4 fold when compared to cells seeded on barrier membranes alone. No significant difference could be observed for cell proliferation at all time points. BCM significantly increased mRNA levels of osteoblast differentiation markers including ALP, OCN and BSP at 5 days post seeding. Furthermore, barrier membranes pre-coated with BCM demonstrated a 5-fold increase in alizarin red staining at 14 days. The results from the present study suggest that the osteoconductive properties of porcine-derived barrier membranes could be further improved by BCM by significantly increasing cell attachment, differentiation and mineralization of osteoblasts in vitro. Future animal testing is required to fully characterize the additional benefits of BCM for guided bone regeneration.

A process efficiency assessment of serum protein removal from milk using ceramic graded permeability microfiltration membrane.

PubMed

Tremblay-Marchand, D; Doyen, A; Britten, M; Pouliot, Y

2016-07-01

Microfiltration (MF) is a well-known process that can be used in the dairy industry to separate caseins from serum proteins (SP) in skim milk using membranes with a pore diameter of 0.1μm. Graded permeability ceramic membranes have been studied widely as means of improving milk fractionation by overcoming problems encountered with other MF membranes. The ideal operating parameters for process efficiency in terms of membrane selectivity, permeate flux, casein loss, SP transmission, energy consumption, and dilution with water remain to be determined for this membrane. Our objective was to evaluate the effects of transmembrane pressure (TMP), volumetric concentration factor (VCF), and diafiltration on overall process efficiency. Skim milk was processed using a pilot-scale MF system equipped with 0.72-m(2) graded permeability membranes with a pore size of 0.1μm. In the first experiment, in full recycle mode, TMP was set at 124, 152, 179, or 207 kPa by adjusting the permeate pressure at the outlet. Whereas TMP had no significant effect on permeate and retentate composition, 152 kPa was found to be optimal for SP removal during concentration and concentration or diafiltration experiments. When VCF was increased to 3×, SP rejection coefficient increased along with energy consumption and total casein loss, whereas SP removal rate decreased. Diafiltering twice allowed an increase in total SP removal but resulted in a substantial increase in energy consumption and casein loss. It also reduced the SP removal rate by diluting permeate. The membrane surface area required for producing cheese milk by blending whole milk, cream, and MF retentate (at different VCF) was estimated for different cheese milk casein concentrations. For a given casein concentration, the same quantity of permeate and SP would be produced, but less membrane surface area would be needed at a lower retentate VCF. Microfiltration has great potential as a process of adding value to conventional cheesemaking processes, but its cost-effectiveness at a large scale remains to be demonstrated. Copyright © 2016 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Minimal models of electric potential oscillations in non-excitable membranes.

PubMed

Perdomo, Guillermo; Hernández, Julio A

2010-01-01

Sustained oscillations in the membrane potential have been observed in a variety of cellular and subcellular systems, including several types of non-excitable cells and mitochondria. For the plasma membrane, these electrical oscillations have frequently been related to oscillations in intracellular calcium. For the inner mitochondrial membrane, in several cases the electrical oscillations have been attributed to modifications in calcium dynamics. As an alternative, some authors have suggested that the sustained oscillations in the mitochondrial membrane potential induced by some metabolic intermediates depends on the direct effect of internal protons on proton conductance. Most theoretical models developed to interpret oscillations in the membrane potential integrate several transport and biochemical processes. Here we evaluate whether three simple dynamic models may constitute plausible representations of electric oscillations in non-excitable membranes. The basic mechanism considered in the derivation of the models is based upon evidence obtained by Hattori et al. for mitochondria and assumes that an ionic species (i.e., the proton) is transported via passive and active transport systems between an external and an internal compartment and that the ion affects the kinetic properties of transport by feedback regulation. The membrane potential is incorporated via its effects on kinetic properties. The dynamic properties of two of the models enable us to conclude that they may represent alternatives enabling description of the generation of electrical oscillations in membranes that depend on the transport of a single ionic species.

The role of counterions in the membrane-disruptive properties of pH-sensitive lysine-based surfactants.

PubMed

Nogueira, D R; Mitjans, M; Infante, M R; Vinardell, M P

2011-07-01

Surfactants are among the most versatile and widely used excipients in pharmaceuticals. This versatility, together with their pH-responsive membrane-disruptive activity and low toxicity, could also enable their potential application in drug delivery systems. Five anionic lysine-based surfactants which differ in the nature of their counterion were studied. Their capacity to disrupt the cell membrane was examined under a range of pH values, concentrations and incubation times, using a standard hemolysis assay as a model for endosomal membranes. The surfactants showed pH-sensitive hemolytic activity and improved kinetics at the endosomal pH range. Low concentrations resulted in negligible hemolysis at physiological pH and high membrane lytic activity at pH 5.4, which is in the range characteristic of late endosomes. With increasing concentration, the surfactants showed an enhanced capacity to lyse cell membranes, and also caused significant membrane disruption at physiological pH. This observation indicates that, at high concentrations, surfactant behavior is independent of pH. The mechanism of surfactant-mediated membrane destabilization was addressed, and scanning electron microscopy studies were also performed to evaluate the effects of the compounds on erythrocyte morphology as a function of pH. The in vitro cytotoxicity of the surfactants was assessed by MTT and NRU assays with the 3T3 cell line. The influence of different types of counterion on hemolytic activity and the potential applications of these surfactants in drug delivery are discussed. The possibility of using pH-sensitive surfactants for endosome disruption could hold great promise for intracellular drug delivery systems in future therapeutic applications. Copyright © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Nanophotonics-enabled solar membrane distillation for off-grid water purification.

PubMed

Dongare, Pratiksha D; Alabastri, Alessandro; Pedersen, Seth; Zodrow, Katherine R; Hogan, Nathaniel J; Neumann, Oara; Wu, Jinjian; Wang, Tianxiao; Deshmukh, Akshay; Elimelech, Menachem; Li, Qilin; Nordlander, Peter; Halas, Naomi J

2017-07-03

With more than a billion people lacking accessible drinking water, there is a critical need to convert nonpotable sources such as seawater to water suitable for human use. However, energy requirements of desalination plants account for half their operating costs, so alternative, lower energy approaches are equally critical. Membrane distillation (MD) has shown potential due to its low operating temperature and pressure requirements, but the requirement of heating the input water makes it energy intensive. Here, we demonstrate nanophotonics-enabled solar membrane distillation (NESMD), where highly localized photothermal heating induced by solar illumination alone drives the distillation process, entirely eliminating the requirement of heating the input water. Unlike MD, NESMD can be scaled to larger systems and shows increased efficiencies with decreased input flow velocities. Along with its increased efficiency at higher ambient temperatures, these properties all point to NESMD as a promising solution for household- or community-scale desalination.

A reversible component of mitochondrial respiratory dysfunction in apoptosis can be rescued by exogenous cytochrome c

PubMed Central

Mootha, Vamsi K.; Wei, Michael C.; Buttle, Karolyn F.; Scorrano, Luca; Panoutsakopoulou, Vily; Mannella, Carmen A.; Korsmeyer, Stanley J.

2001-01-01

Multiple apoptotic pathways release cytochrome c from the mitochondrial intermembrane space, resulting in the activation of downstream caspases. In vivo activation of Fas (CD95) resulted in increased permeability of the mitochondrial outer membrane and depletion of cytochrome c stores. Serial measurements of oxygen consumption, NADH redox state and membrane potential revealed a loss of respiratory state transitions. This tBID-induced respiratory failure did not require any caspase activity. At early time points, re-addition of exogenous cytochrome c markedly restored respiratory functions. Over time, however, mitochondria showed increasing irreversible respiratory dysfunction as well as diminished calcium buffering. Electron microscopy and tomographic reconstruction revealed asymmetric mitochondria with blebs of herniated matrix, distended inner membrane and partial loss of cristae structure. Thus, apoptogenic redistribution of cytochrome c is responsible for a distinct program of mitochondrial respiratory dysfunction, in addition to the activation of downstream caspases. PMID:11179211

Nanophotonics-enabled solar membrane distillation for off-grid water purification

PubMed Central

Dongare, Pratiksha D.; Alabastri, Alessandro; Pedersen, Seth; Zodrow, Katherine R.; Hogan, Nathaniel J.; Neumann, Oara; Wu, Jinjian; Wang, Tianxiao; Deshmukh, Akshay; Elimelech, Menachem; Li, Qilin; Nordlander, Peter; Halas, Naomi J.

2017-01-01

With more than a billion people lacking accessible drinking water, there is a critical need to convert nonpotable sources such as seawater to water suitable for human use. However, energy requirements of desalination plants account for half their operating costs, so alternative, lower energy approaches are equally critical. Membrane distillation (MD) has shown potential due to its low operating temperature and pressure requirements, but the requirement of heating the input water makes it energy intensive. Here, we demonstrate nanophotonics-enabled solar membrane distillation (NESMD), where highly localized photothermal heating induced by solar illumination alone drives the distillation process, entirely eliminating the requirement of heating the input water. Unlike MD, NESMD can be scaled to larger systems and shows increased efficiencies with decreased input flow velocities. Along with its increased efficiency at higher ambient temperatures, these properties all point to NESMD as a promising solution for household- or community-scale desalination. PMID:28630307

Reconciling Differences between Lipid Transfer in Free-Standing and Solid Supported Membranes: A Time-Resolved Small-Angle Neutron Scattering Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wah, Benny; Breidigan, Jeffrey M.; Adams, Joseph

Maintaining compositional lipid gradients across membranes in animal cells is essential to biological function, but what is the energetic cost to maintain these differences? It has long been recognized that studying the passive movement of lipids in membranes can provide insight into this toll. Confusingly the reported values of inter- and, particularly, intra-lipid transport rates of lipids in membranes show significant differences. To overcome this difficulty, biases introduced by experimental approaches have to be identified. The present study addresses the difference in the reported intramembrane transport rates of dimyristoylphosphatidylcholine (DMPC) on flat solid supports (fast flipping) and in curved free-standingmore » membranes (slow flipping). Two possible scenarios are potentially at play: one is the difference in curvature of the membranes studied and the other the presence (or not) of the support. Using DMPC vesides and DMPC supported membranes on silica nanoparticles of different radii, we found that an increase in curvature (from a diameter of 30 nm to a diameter of 100 nm) does not change the rates significantly, differing only by factors of order I. Additionally, we found that the exchange rates of DMPC in supported membranes are similar to the ones in vesicles. And as previously reported, we found that the activation energies for exchange on free-standing and supported membranes are similar (84 and 78 kJ/mol, respectively). However, DMPC's flip-flop rates increase significantly when in a supported membrane, surpassing the exchange rates and no longer limiting the exchange process. Although the presence of holes or cracks in supported membranes explains the occurrence of fast lipid flip-flop in many studies, in defect-free supported membranes we find that fast flip-flop is driven by the surface's induced disorder of the bilayer's acyl chain packing as evidenced from their broad melting temperature behavior.« less

Reconciling Differences between Lipid Transfer in Free-Standing and Solid Supported Membranes: A Time-Resolved Small-Angle Neutron Scattering Study.

PubMed

Wah, Benny; Breidigan, Jeffrey M; Adams, Joseph; Horbal, Piotr; Garg, Sumit; Porcar, Lionel; Perez-Salas, Ursula

2017-04-11

Maintaining compositional lipid gradients across membranes in animal cells is essential to biological function, but what is the energetic cost to maintain these differences? It has long been recognized that studying the passive movement of lipids in membranes can provide insight into this toll. Confusingly the reported values of inter- and, particularly, intra-lipid transport rates of lipids in membranes show significant differences. To overcome this difficulty, biases introduced by experimental approaches have to be identified. The present study addresses the difference in the reported intramembrane transport rates of dimyristoylphosphatidylcholine (DMPC) on flat solid supports (fast flipping) and in curved free-standing membranes (slow flipping). Two possible scenarios are potentially at play: one is the difference in curvature of the membranes studied and the other the presence (or not) of the support. Using DMPC vesicles and DMPC supported membranes on silica nanoparticles of different radii, we found that an increase in curvature (from a diameter of 30 nm to a diameter of 100 nm) does not change the rates significantly, differing only by factors of order ∼1. Additionally, we found that the exchange rates of DMPC in supported membranes are similar to the ones in vesicles. And as previously reported, we found that the activation energies for exchange on free-standing and supported membranes are similar (84 and 78 kJ/mol, respectively). However, DMPC's flip-flop rates increase significantly when in a supported membrane, surpassing the exchange rates and no longer limiting the exchange process. Although the presence of holes or cracks in supported membranes explains the occurrence of fast lipid flip-flop in many studies, in defect-free supported membranes we find that fast flip-flop is driven by the surface's induced disorder of the bilayer's acyl chain packing as evidenced from their broad melting temperature behavior.

Metal stress consequences on frost hardiness of plants at northern high latitudes: a review and hypothesis.

PubMed

Taulavuori, Kari; Prasad, M N V; Taulavuori, Erja; Laine, Kari

2005-05-01

This paper reviews the potential of trace/heavy metal-induced stress to reduce plant frost hardiness at northern high latitudes. The scientific questions are first outlined prior to a brief summary of heavy metal tolerance. The concepts of plant capacity and survival adaptation were used to formulate a hypothesis, according to which heavy metal stress may reduce plant frost hardiness for the following reasons: (1) Heavy metals change membrane properties through impaired resource acquisition and subsequent diminution of the cryoprotectant pool. (2) Heavy metals change membrane properties directly through oxidative stress, i.e. an increase of active oxygen species. (3) The involved co-stress may further increase oxidative stress. (4) The risk of frost injury increases due to membrane alterations. An opposite perspective was also discussed: could metal stress result in enhanced plant frost hardiness? This phenomenon could be based on the metabolism (i.e. glutathione, polyamines, proline, heat shock proteins) underlying a possible general adaptation syndrome of stress (GAS). As a result of the review it was suggested that metal-induced stress seems to reduce rather than increase plant frost hardiness.

Optomechanical characterization of proton-exchange membrane fuel cells

NASA Astrophysics Data System (ADS)

Jalani, Nikhil H.; Mizar, Shivananda P.; Choi, Pyoungho; Furlong, Cosme; Datta, Ravindra

2004-08-01

Nafion is widely used as the polymer electrolyte in proton exchange membrane (PEM) fuel cells. The properties that make the Nafion membrane indispensable are the combination of good water uptake, ion-exchange capacity, proton conductivity, gas permeability, and excellent electrochemical stability. The amount of water sorbed in the Nafion membrane is critical as the proton conductivity depends directly on the water content of the membrane which determines the fuel cell performance. The factors which affect the extent of the solvent uptake by Nafion are temperature, ion-exchange capacity, pretreatment of membrane, and the physical state of absorbing water, whether it is in liquid or vapor phase. The water sorption in the membrane is explained in terms of thermodynamic equilibrium of water in the vapor and absorption phases. As the membrane imbibes more water, the membrane matrix expands and exerts a pressure on the pore liquid which affects its chemical potential and limits extent of swelling. The extent of matrix expansion of the membranes depends on the elastic modulus, E, of the membrane, which directly affects the sorption. Hence, it is important to understand the variation of E for Nafion membrane with relative humidity (RH) and temperature. Optoelectronic holography (OEH) techniques are applied to perform quantitative, noninvasive, full field of view investigations to determine temperature and water activity dependence of E. The results obtained confirm that with the increase in temperature, E decreases and the membranes imbibes more water. Such results will allow optimization and realization of fuel cells with improved efficiency and performance.

Nitric Oxide Treatment for the Control of Reverse Osmosis Membrane Biofouling

PubMed Central

Barnes, Robert J.; Low, Jiun Hui; Bandi, Ratnaharika R.; Tay, Martin; Chua, Felicia; Aung, Theingi; Fane, Anthony G.; Kjelleberg, Staffan

2015-01-01

Biofouling remains a key challenge for membrane-based water treatment systems. This study investigated the dispersal potential of the nitric oxide (NO) donor compound, PROLI NONOate, on single- and mixed-species biofilms formed by bacteria isolated from industrial membrane bioreactor and reverse osmosis (RO) membranes. The potential of PROLI NONOate to control RO membrane biofouling was also examined. Confocal microscopy revealed that PROLI NONOate exposure induced biofilm dispersal in all but two of the bacteria tested and successfully dispersed mixed-species biofilms. The addition of 40 μM PROLI NONOate at 24-h intervals to a laboratory-scale RO system led to a 92% reduction in the rate of biofouling (pressure rise over a given period) by a bacterial community cultured from an industrial RO membrane. Confocal microscopy and extracellular polymeric substances (EPS) extraction revealed that PROLI NONOate treatment led to a 48% reduction in polysaccharides, a 66% reduction in proteins, and a 29% reduction in microbial cells compared to the untreated control. A reduction in biofilm surface coverage (59% compared to 98%, treated compared to control) and average thickness (20 μm compared to 26 μm, treated compared to control) was also observed. The addition of PROLI NONOate led to a 22% increase in the time required for the RO module to reach its maximum transmembrane pressure (TMP), further indicating that NO treatment delayed fouling. Pyrosequencing analysis revealed that the NO treatment did not significantly alter the microbial community composition of the membrane biofilm. These results present strong evidence for the application of PROLI NONOate for prevention of RO biofouling. PMID:25636842

Acid Gradient across Plasma Membrane Can Drive Phosphate Bond Synthesis in Cancer Cells: Acidic Tumor Milieu as a Potential Energy Source

PubMed Central

Dhar, Gautam; Sen, Suvajit; Chaudhuri, Gautam

2015-01-01

Aggressive cancers exhibit an efficient conversion of high amounts of glucose to lactate accompanied by acid secretion, a phenomenon popularly known as the Warburg effect. The acidic microenvironment and the alkaline cytosol create a proton-gradient (acid gradient) across the plasma membrane that represents proton-motive energy. Increasing experimental data from physiological relevant models suggest that acid gradient stimulates tumor proliferation, and can also support its energy needs. However, direct biochemical evidence linking extracellular acid gradient to generation of intracellular ATP are missing. In this work, we demonstrate that cancer cells can synthesize significant amounts of phosphate-bonds from phosphate in response to acid gradient across plasma membrane. The noted phenomenon exists in absence of glycolysis and mitochondrial ATP synthesis, and is unique to cancer. Biochemical assays using viable cancer cells, and purified plasma membrane vesicles utilizing radioactive phosphate, confirmed phosphate-bond synthesis from free phosphate (Pi), and also localization of this activity to the plasma membrane. In addition to ATP, predominant formation of pyrophosphate (PPi) from Pi was also observed when plasma membrane vesicles from cancer cells were subjected to trans-membrane acid gradient. Cancer cytosols were found capable of converting PPi to ATP, and also stimulate ATP synthesis from Pi from the vesicles. Acid gradient created through glucose metabolism by cancer cells, as observed in tumors, also proved critical for phosphate-bond synthesis. In brief, these observations reveal a role of acidic tumor milieu as a potential energy source and may offer a novel therapeutic target. PMID:25874623

Membrane potential bistability in nonexcitable cells as described by inward and outward voltage-gated ion channels.

PubMed

Cervera, Javier; Alcaraz, Antonio; Mafe, Salvador

2014-10-30

The membrane potential of nonexcitable cells, defined as the electrical potential difference between the cell cytoplasm and the extracellular environment when the current is zero, is controlled by the individual electrical conductance of different ion channels. In particular, inward- and outward-rectifying voltage-gated channels are crucial for cell hyperpolarization/depolarization processes, being amenable to direct physical study. High (in absolute value) negative membrane potentials are characteristic of terminally differentiated cells, while low membrane potentials are found in relatively depolarized, more plastic cells (e.g., stem, embryonic, and cancer cells). We study theoretically the hyperpolarized and depolarized values of the membrane potential, as well as the possibility to obtain a bistability behavior, using simplified models for the ion channels that regulate this potential. The bistability regions, which are defined in the multidimensional state space determining the cell state, can be relevant for the understanding of the different model cell states and the transitions between them, which are triggered by changes in the external environment.

Monitoring sperm mitochondrial respiration response in a laser trap using ratiometric fluorescence

NASA Astrophysics Data System (ADS)

Mei, Adrian; Botvinick, Elliot; Berns, Michael

2005-08-01

Sperm motility is an important area in understanding male infertility. Various techniques, such as the Computer Assisted Sperm Analysis (CASA), have been used to understand sperm motility. Sperm motility is related to the energy (ATP) production of sperm. ATP is produced by the depolarization of the membrane potential of the inner membrane of the mitochondria. In this study, a mitochondrial dye, JC-1, has been used to monitor the energetics of the mitochondria. This fluorescent dye can emit at two different wavelengths, depending on the membrane potential of the mitochondria. It can fluoresce green at low membrane potential and red at high membrane potential. The ratio of the two colors (red/green) allows for an accurate measurement of the change of membrane potential. Various experiments were conducted to quantify the behavior of the dye within the sperm and the reaction of the sperm to trap. Sperm were trapped using laser tweezers. Results have shown that the ratio drops dramatically when sperm are trapped, indicating a depolarization of the membrane. The physiological response to this depolarization is yet to be determined, but the studies indicate that the sperm could have been slightly damaged by the laser. However, knowing that sperm depolarizes their membrane when trapped can help understand how sperm react to their environment and consequently help treat male infertility.

Programmable carbon nanotube membrane-based transdermal nicotine delivery with microdialysis validation assay.

PubMed

Gulati, Gaurav Kumar; Chen, Tao; Hinds, Bruce Jackson

2017-01-01

To evaluate the performance of switchable carbon nanotubes (CNT) membrane devices for transdermal nicotine delivery, we have developed an in-vitro microdialysis method that allow us to detect variable transdermal fluxes of nicotine through CNT devices and can be applied directly to in-vivo studies. Microdialysis membranes were placed beneath the porcine skin and its nicotine levels increased 6-8 times when the CNT membrane on skin was turned from OFF to ON state by application of bias. Fluxes in the ON state were approximately 3 times that of commercial nicotine patches and switching times were less than two hours, thus suggesting the improved therapeutic potential of our device. Blue tooth enabled CNT devices that can be programmed by smartphone and coupled with remote counseling application for enhanced smoking cessation treatments. Copyright © 2016. Published by Elsevier Inc.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fauzi, Iqbal, E-mail: arcana@chem.itb.ac.id; Arcana, I Made, E-mail: arcana@chem.itb.ac.id

Recently, the need of secondary battery application continues to increase. The secondary battery which using a liquid electrolyte was indicated had some weakness. A solid polymer electrolyte is an alternative electrolytes membrane which developed in order to replace the liquid electrolyte type. In the present study, the effect of phosphorylation on to polymer electrolyte membrane which synthesized from chitosan and lithium perchlorate salts was investigated. The effect of the component’s composition respectively on the properties of polymer electrolyte, was carried out by analyzed of it’s characterization such as functional groups, ion conductivity, and thermal properties. The mechanical properties i.e tensilemore » resistance and the morphology structure of membrane surface were determined. The phosphorylation processing of polymer electrolyte membrane of chitosan and lithium perchlorate was conducted by immersing with phosphoric acid for 2 hours, and then irradiated on a microwave for 60 seconds. The degree of deacetylation of chitosan derived from shrimp shells was obtained around 75.4%. Relative molecular mass of chitosan was obtained by viscometry method is 796,792 g/mol. The ionic conductivity of chitosan membrane was increase from 6.33 × 10{sup −6} S/cm up to 6.01 × 10{sup −4} S/cm after adding by 15 % solution of lithium perchlorate. After phosphorylation, the ionic conductivity of phosphorylated lithium chitosan membrane was observed 1.37 × 10{sup −3} S/cm, while the tensile resistance of 40.2 MPa with a better thermal resistance. On the strength of electrolyte membrane properties, this polymer electrolyte membrane was suggested had one potential used for polymer electrolyte in field of lithium battery applications.« less

Sustainable operation of submerged Anammox membrane bioreactor with recycling biogas sparging for alleviating membrane fouling.

PubMed

Li, Ziyin; Xu, Xindi; Xu, Xiaochen; Yang, FengLin; Zhang, ShuShen

2015-12-01

A submerged anaerobic ammonium oxidizing (Anammox) membrane bioreactor with recycling biogas sparging for alleviating membrane fouling has been successfully operated for 100d. Based on the batch tests, a recycling biogas sparging rate at 0.2m(3)h(-1) was fixed as an ultimate value for the sustainable operation. The mixed liquor volatile suspended solid (VSS) of the inoculum for the long operation was around 3000mgL(-1). With recycling biogas sparging rate increasing stepwise from 0 to 0.2m(3)h(-1), the reactor reached an influent total nitrogen (TN) up to 1.7gL(-1), a stable TN removal efficiency of 83% and a maximum specific Anammox activity (SAA) of 0.56kg TNkg(-1) VSSd(-1). With recycling biogas sparging rate at 0.2 m(3) h(-1) (corresponding to an aeration intensity of 118m(3)m(-2)h(-1)), the membrane operation circle could prolong by around 20 times compared to that without gas sparging. Furthermore, mechanism of membrane fouling was proposed. And with recycling biogas sparging, the VSS and EPS content increasing rate in cake layer were far less than the ones without biogas sparging. The TN removal performance and sustainable membrane operation of this system showed the appealing potential of the submerged Anammox MBR with recycling biogas sparging in treating high-strength nitrogen-containing wastewaters. Copyright © 2014 Elsevier Ltd. All rights reserved.

Origin and voltage dependence of asparagine-induced depolarization in intestinal cells of Xenopus embryo.

PubMed Central

Bergman, C; Bergman, J

1985-01-01

The kinetics and voltage dependence of asparagine (Asn)-induced depolarization in endoderm cells from Xenopus laevis embryos were analysed using current-clamp techniques. The depolarization is assumed to reflect the activation of an amino acid membrane carrier; it is accompanied by a slight increase in membrane resistance and cannot be explained by only the electrogenic character of the Asn carrier. It is proposed that the Asn depolarization arises, at least in part, from the decrease of the permeability ratio PK/PNa indirectly associated with the Na-coupled amino acid uptake. At room temperature (20-23 degrees C) the Asn response develops according to a single exponential function whose time constant is correlated with the final level of depolarization. Both amplitude and rise time of the depolarization are sensitive to variations of membrane potential and changes in Asn or Na external concentrations. Lowering the temperature decreases the amplitude of the Asn depolarization and increases its rise time with a Q10 factor of two; the kinetics remain of the Michaelis-Menten type, with a marked decrease in delta Emax and no change in Km. When the holding potential is altered by depolarizing and hyperpolarizing currents, the Asn response varies according to a bell-shaped characteristic presenting an optimum near the normal resting level. Membrane depolarizations induced by Na/K-pump inhibitors or high external K concentrations reduce the size of the Asn response; repolarizing the cell by current injection does not reverse the inhibitory effect of external K ions. Hyperpolarizing the membrane with a K-free Ringer solution increases the amplitude of the Asn response. In all these cases a decrease in delta Emax accounts for the apparent voltage sensitivity of the carrier mechanism. When induced by alterations of [K]o, an additional change in Km is observed, suggesting a K/Na-competitive inhibition of the Asn carrier. The results are discussed in terms of the amino acid carrier and passive membrane properties. It is suggested that the outward K-electrochemical gradient contributes an additional source of energy to the Na-dependent Asn uptake. PMID:4057089

Effects of dithiothreitol on end-plate currents.

PubMed Central

Terrar, D A

1978-01-01

1. End-plate currents have been studied in frog cutaneus pectoris nerve-muscle preparations mounted in continuously flowing solution, using the voltage clamp technique. 2. Exposure of the muscle to 1 mM-dithiothreitol reduced the amplitude of end-plate currents by a factor of 2.7 (mean; range 1.6-3.4; twelve fibres). 3. 1 mM-dithiothreitol also caused a 2.7-fold (2.3-3.1) increase in the rate of decay, and a 1.4-fold (1.3-1.6) decrease in the time to peak of end-plate currents. During the onset of action of dithiothreitol, there was little or no indication of departure of end-plate current decay from a simple exponential. 4. Dithiothreitol actions on amplitude and decay of end-plate currents developed with similar time courses and both effects were slower in onset at pH 7.2 than at pH 8.5. 5. The actions of dithiothreitol were reversed by exposure of the muscle to 1 mM-5,5'-dithio-bis-(2-nitrobenzoic acid). 6. Following dithiothreitol treatment, the rates of decay of end-plate currents continued to depend on membrane potential; there was little or no change in the slope of the relation between in (rate of decay) and membrane potential, consistent with little or no change in the dipole moment of a gating molecule for ion channels. 7. Dithiothreitol changed the relation between peak end-plate current and membrane potential, so that peak conductance increased at more negative membrane potentials; this finding could be accounted for in terms of the closure of ion-channel gates becoming faster though remaining voltage-sensitive after exposure to dithiothreitol. 8. It is concluded that dithiothreitol causes changes in the kinetics of gating of ion channels associated with receptors and that these changes accompany changes in the binding of ACh to receptors. PMID:25960

Barbiturates Block Sodium and Potassium Conductance Increases in Voltage-Clamped Lobster Axons

PubMed Central

Blaustein, M. P.

1968-01-01

Sodium pentobarbital and sodium thiopental decrease both the peak initial (Na) and late steady-state (K) currents and reduce the maximum sodium and potassium conductance increases in voltage-clamped lobster giant axons. These barbiturates also slow the rate at which the sodium conductance turns on, and shift the normalized sodium conductance vs. voltage curves in the direction of depolarization along the voltage axis. Since pentobarbital (pKa = 8.0) blocks the action potential more effectively at pH 8.5 than at pH 6.7, the anionic form of the drug appears to be active. The data suggest that these drugs affect the axon membrane directly, rather than secondarily through effects on intermediary metabolism. It is suggested that penetration of the lipid layer of the membrane by the nonpolar portion of the barbiturate molecules may cause the decrease in membrane conductances, while electrostatic interactions involving the anionic group on the barbiturate, divalent cations, and "fixed charges" in the membrane could account for the slowing of the rate of sodium conductance turn-on and the shift of the normalized conductance curves along the voltage axis. PMID:5648829

Enhanced chemotherapeutic efficacy of apigenin liposomes in colorectal cancer based on flavone-membrane interactions.

PubMed

Banerjee, Kacoli; Banerjee, Shubhadeep; Mandal, Mahitosh

2017-04-01

Recent endeavors in exploiting vast array of natural phytochemicals to ameliorate colorectal cancer led us to investigate apigenin, a naturally occurring dietary flavone as a potential chemo-therapeutic agent. The present study focuses on establishing apigenin as a potential chemotherapeutic agent for alleviating colorectal cancer and reports the development of a stable liposomal nanocarrier with high encapsulation of the hydrophobic flavone apigenin for enhanced chemotherapeutic effects. The enhanced pharmacological activity of apigenin has been assigned to its ability to interact and subsequently influence membrane properties which also resulted in optimal yield of a stable, rigidified, non-leaky nano-carrier with ideal release kinetics. Extensive testing of drug and its liposomal counterpart for potential clinical chemotherapeutic applications yielded hemocompatibility and cytocompatibility with normal fibroblast cells while enhanced antineoplastic activity was observed in tumor xenograft model. The increased chemotherapeutic potential of liposomal apigenin highlights the clinical potential of apigenin-based vesicles. Copyright © 2016 Elsevier Inc. All rights reserved.

Coptis chinensis Franch. exhibits neuroprotective properties against oxidative stress in human neuroblastoma cells.

PubMed

Friedemann, Thomas; Otto, Benjamin; Klätschke, Kristin; Schumacher, Udo; Tao, Yi; Leung, Alexander Kai-Man; Efferth, Thomas; Schröder, Sven

2014-08-08

The dried rhizome of Coptis chinensis Franch. (family Ranunculaceae) is traditionally used in Chinese medicine for the treatment of inflammatory diseases and diabetes. Recent studies showed a variety of activities of Coptis chinensis Franch. alkaloids, including neuroprotective, neuroregenerative, anti-diabetic, anti-oxidative and anti-inflammatory effects. However, there is no report on the neuroprotective effect of Coptis chinensis Franch. watery extract against tert-butylhydroperoxide (t-BOOH) induced oxidative damage. The aim of the study is to investigate neuroprotective properties of Coptis chinensis Franch. rhizome watery extract (CRE) and to evaluate its potential mechanism of action. Neuroprotective properties on t-BOOH induced oxidative stress were investigated in SH-SY5Y human neuroblastoma cells. Cells were pretreated with CRE for 2 h or 24 h followed by 2 h of treatment with t-BOOH. To evaluate the neuroprotective effect of CRE, cell viability, cellular reactive oxygen species (ROS), mitochondrial membrane potential (MMP) and the apoptotic rate were determined and microarray analyses, as well as qRT-PCR analyses were conducted. Two hours of exposure to 100 µM t-BOOH resulted in a significant reduction of cell viability, increased apoptotic rate, declined mitochondrial membrane potential (MMP) and increased ROS production. Reduction of cell viability, increased apoptotic rate and declined mitochondrial membrane potential (MMP) could be significantly reduced in cells pretreated with CRE (100 µg/ml) for 2h or 24h ahead of t-BOOH exposure with the greatest effect after 24h of pretreatment; however ROS production was not changed significantly. Furthermore, microarray analyses revealed that the expressions of 2 genes; thioredoxin-interacting protein (TXNIP) and mitochondrially encoded NADH dehydrogenase 1, were significantly regulated. Down regulation of TXNIP was confirmed by qRT-PCR. Due to its neuroprotective properties CRE might be a potential therapeutic agent for the prevention or amelioration of diseases like diabetic neuropathy and neurodegenerative disorders like Alzheimer and Parkinsons disease. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

Activation of the Ca2+-sensing receptors increases currents through inward rectifier K+ channels via activation of phosphatidylinositol 4-kinase.

PubMed

Liu, Chung-Hung; Chang, Hsueh-Kai; Lee, Sue-Ping; Shieh, Ru-Chi

2016-11-01

Inward rectifier K + channels are important for maintaining normal electrical function in many cell types. The proper function of these channels requires the presence of membrane phosphoinositide 4,5-bisphosphate (PIP 2 ). Stimulation of the Ca 2+ -sensing receptor CaR, a pleiotropic G protein-coupled receptor, activates both G q/11 , which decreases PIP 2 , and phosphatidylinositol 4-kinase (PI-4-K), which, conversely, increases PIP 2 . How membrane PIP 2 levels are regulated by CaR activation and whether these changes modulate inward rectifier K + are unknown. In this study, we found that activation of CaR by the allosteric agonist, NPSR568, increased inward rectifier K + current (I K1 ) in guinea pig ventricular myocytes and currents mediated by Kir2.1 channels exogenously expressed in HEK293T cells with a similar sensitivity. Moreover, using the fluorescent PIP 2 reporter tubby-R332H-cYFP to monitor PIP 2 levels, we found that CaR activation in HEK293T cells increased membrane PIP 2 concentrations. Pharmacological studies showed that both phospholipase C (PLC) and PI-4-K are activated by CaR stimulation with the latter played a dominant role in regulating membrane PIP 2 and, thus, Kir currents. These results provide the first direct evidence that CaR activation upregulates currents through inward rectifier K + channels by accelerating PIP 2 synthesis. The regulation of I K1 plays a critical role in the stability of the electrical properties of many excitable cells, including cardiac myocytes and neurons. Further, synthetic allosteric modulators that increase CaR activity have been used to treat hyperparathyroidism, and negative CaR modulators are of potential importance in the treatment of osteoporosis. Thus, our results provide further insight into the roles played by CaR in the cardiovascular system and are potentially valuable for heart disease treatment and drug safety.

Vitamin K3 induces antiproliferative effect in cervical epithelial cells transformed by HPV 16 (SiHa cells) through the increase in reactive oxygen species production.

PubMed

de Carvalho Scharf Santana, Natália; Lima, Natália Alves; Desoti, Vânia Cristina; Bidóia, Danielle Lazarin; de Souza Bonfim Mendonça, Patrícia; Ratti, Bianca Altrão; Nakamura, Tânia Ueda; Nakamura, Celso Vataru; Consolaro, Marcia Edilaine Lopes; Ximenes, Valdecir Farias; de Oliveira Silva, Sueli

2016-10-01

Cervical cancer is characterized as an important public health problem. According to latest estimates, cancer of the cervix is the fourth most common cancer among women. Due to its high prevalence, the search for new and efficient drugs to treat this infection is continuous. The progression of HPV-associated cervical cancer involves the expression of two viral proteins, E6 and E7, which are rapidly degraded by the ubiquitin-proteasome system through the increase in reactive oxygen species generation. Vitamins are essential to human substances, participate in the regulation of metabolism, and facilitate the process of energy transfer. Some early studies have indicated that vitamin K3 exerts antitumor activity by inducing cell death by apoptosis through an increase in the generation of reactive oxygen species. Thus, we evaluated the antiproliferative effect and a likely mechanism of action of vitamin K3 against cervical epithelial cells transformed by HPV 16 (SiHa cells) assessing the production of total ROS, the mitochondrial membrane potential, the cell morphology, the cell volume, and the cell membrane integrity. Our results show that vitamin K3 induces an increase in ROS production in SiHa cells, triggering biochemical and morphological events, such as depolarization of mitochondrial membrane potential and decreasing cell volume. Our data showed that vitamin K3 generates an oxidative imbalance in SiHa cells, leading to mechanisms that induce cell death by apoptosis.

Spatial distribution of mechanical forces and ionic flux in electro-kinetic instability near a permselective membrane

NASA Astrophysics Data System (ADS)

Magnico, Pierre

2018-01-01

This paper is devoted to the numerical investigation of electro-kinetic instability in a polarization layer next to a cation-exchange membrane. An analysis of some properties of the electro-kinetic instability is followed by a detailed description of the fluid flow structure and of the spatial distribution of the ionic flux. In this aim, the Stokes-Poisson-Nernst-Planck equation set is solved until the Debye length scale. The results show that the potential threshold of the marginal instability and the current density depend on the logarithm of the concentration at the membrane surface. The size of the stable vortices seems to be an increasing function of the potential drop. The fluid motion is induced by the electric force along the maximum concentration in the extended space charge (ESC) region and by the pressure force in the region around the inner edge of the ESC layer. Two spots of kinetic energy are located in the ESC region and between the vortices. The cationic motion, controlled by the electric field and the convection, presents counter-rotating vortices in the stagnation zone located in the fluid ejection region. The anion transport is also characterized by two independent layers which contain counter-rotating vortices. The first one is in contact with the stationary reservoir. In the second layer against the membrane, the convection, and the electric field control, the transversal motion, the Fickian diffusion, and the convection are dominant in the longitudinal direction. Finally, the longitudinal disequilibrium of potential and pressure along the membrane is analyzed.

Lipido-sterolic extract of Serenoa repens (LSESr, Permixon) treatment affects human prostate cancer cell membrane organization.

PubMed

Petrangeli, E; Lenti, L; Buchetti, B; Chinzari, P; Sale, P; Salvatori, L; Ravenna, L; Lococo, E; Morgante, E; Russo, A; Frati, L; Di Silverio, F; Russo, M A

2009-04-01

The molecular mechanism by which the lipido-sterolic extract of Serenoa repens (LSESr, Permixon) affects prostate cells remains to be fully elucidated. In androgen-independent PC3 prostate cancer cells, the LSESr-induced effects on proliferation and apoptosis were evaluated by counting cells and using a FACScan cytofluorimeter. PC3 cells were stained with JC-1 dye to detect mitochondrial membrane potential. Cell membrane lipid composition was evaluated by thin layer chromatography and gas chromatographic analysis. Akt phosphorylation was analyzed by Western blotting and cellular ultrastructure through electron microscopy. LSESr (12.5 and 25 microg/ml) administration exerted a biphasic action by both inhibiting proliferation and stimulating apoptosis. After 1 h, it caused a marked reduction in the mitochondrial potential, decreased cholesterol content and modified phospholipid composition. A decrease in phosphatidylinositol-4,5-bisphosphate (PIP2) level was coupled with reduced Akt phosphorylation. After 24 h, all of these effects were restored to pre-treatment conditions; however, the saturated (SFA)/unsaturated fatty acid (UFA) ratio increased, mainly due to a significant decrease in omega 6 content. The reduction in cholesterol content could be responsible for both membrane raft disruption and redistribution of signaling complexes, allowing for a decrease of PIP2 levels, reduction of Akt phosphorylation and apoptosis induction. The decrease in omega 6 content appears to be responsible for the prolonged and more consistent increase in the apoptosis rate and inhibition of proliferation observed after 2-3 days of LSESr treatment. In conclusion, LSESr administration results in complex changes in cell membrane organization and fluidity of prostate cancer cells that have progressed to hormone-independent status. (c) 2008 Wiley-Liss, Inc.

Investigation on the reaction of phenolic pollutions to mono-rhamnolipid micelles using MEUF.

PubMed

Liu, Zhifeng; Yu, Mingda; Zeng, Guangming; Li, Min; Zhang, Jiachao; Zhong, Hua; Liu, Yang; Shao, Binbin; Li, Zhigang; Wang, Zhiquan; Liu, Guansheng; Yang, Xin

2017-01-01

Micellar-enhanced ultrafiltration (MEUF) processes of resorcinol, phenol, and 1-Naphthol with rhamnolipid as an anionic biosurfactant were investigated using polysulfone membrane. The effects of retentate/permeate concentration of phenolic pollutants (C R /C P ), distribution coefficient of phenolic pollutions (D), concentration ratios of phenolic pollutions (α P ) and rhamnolipids (α R ) and adsorption capacity of the membrane (N m ) were studied by operating pressure, pH condition, feed surfactant, and phenolic pollution concentrations. Results showed that C R (with pH) increased and ranked in the following order: resorcinol > phenol > 1-Naphthol, which is same with C R (with pressure), C R (with surfactant), C R /C P (with pollution), α, P and D, while C P (with pH), C P (with pressure), and C P (with surfactant) ranked in the reverse order. The operating pressure increased the solubility of phenolic from 0 to 0.1 MPa and then decreased slowly above 0.1 MPa. The concentration ratio of rhamnolipid was nearly at 2.0 and that of phenolic pollution was slightly above 1.0. D of phenolic pollutants reached the maximum at phenolic pollution concentration of 0.1 mM and the feed rhamnolipid concentration at 1 CMC. Moreover, zeta potential in feed stream and retentate stream and membrane adsorption of phenolic pollutions were firstly investigated in this article; the magnitudes of zeta potential with the feed stream of three phenolic pollutions were nearly the same and slightly lower than those with the retentate stream. The adsorption capacity of the membrane (N m ) was calculated and compared to the former research, which showed that rhamnolipid significantly decreases the membrane adsorption of phenolic pollutions at a relatively lower concentration. It was implied that rhamnolipid can be substituted for chemical surfactants.

Chloride Fluxes in Isolated Dialyzed Barnacle Muscle Fibers

PubMed Central

DiPolo, R.

1972-01-01

Chloride outflux and influx has been studied in single isolated muscle fibers from the giant barnacle under constant internal composition by means of a dialysis perfusion technique. Membrane potential was continually recorded. The chloride outfluxes and influxes were 143 and 144 pmoles/cm2-sec (mean resting potential: 58 mv, temperature: 22°–24°C) with internal and external chloride concentrations of 30 and 541 mM, respectively. The chloride conductance calculated from tracer measurements using constant field assumptions is about fourfold greater than that calculated from published electrical data. Replacing 97% of the external chloride ions by propionate reduces the chloride efflux by 51%. Nitrate ions applied either to the internal or external surface of the membrane slows the chloride efflux. The external pH dependence of the chloride efflux follows the external pH dependence of the membrane conductance, in the range pH 3.9–4.7, increasing with decreasing pH. In the range pH 5–9, the chloride efflux increased with increasing pH, in a manner similar to that observed in frog muscle fibers. The titration curve for internal pH changes in the range 4.0–7.0 was quantitatively much different from that for external pH change, indicating significant asymmetry in the internal and external pH dependence of the chloride efflux. PMID:5074810

Transport of K+ and other cations across phospholipid membranes by nonesterified fatty acids.

PubMed

Sharpe, M A; Cooper, C E; Wrigglesworth, J M

1994-07-01

The rate of change of internal pH and transmembrane potential has been monitored in liposomes following the external addition of various cation salts. Oleic acid increases the transmembrane movement of H+ following the imposition of a K+ gradient. An initial fast change in internal pH is seen followed by a slower rate of alkalinization. High concentrations of the fatty acid enhance the rate comparable to that seen in the presence of nigericin in contrast to the effect of FCCP (carbonyl cyanide p-(tri-fluoromethoxy)phenyl hydrazone) which saturates at an intermediate value. The ability of nonesterified fatty acids to catalyze the movement of cations across the liposome membrane increases with the degree of unsaturation and decreases with increasing chain length. Li and Na salts cause a similar initial fast pH change but have less effect on the subsequent slower rate. Similarly, the main effect of divalent cation salts is on the initial fast change. The membrane potential can enhance or inhibit cation transport depending on its polarity with respect to the cation gradient. It is concluded that nonesterified fatty acids have the capability to complex with, and transport, a variety of cations across phospholipid bilayers. However, they do not act simply as proton/cation exchangers analogous to nigericin nor as protonophores analogous to FCCP. The full cycle of ionophoric action involves a combination of both functions.

Hydrogen production by reforming of liquid hydrocarbons in a membrane reactor for portable power generation-Experimental studies

NASA Astrophysics Data System (ADS)

Damle, Ashok S.

One of the most promising technologies for lightweight, compact, portable power generation is proton exchange membrane (PEM) fuel cells. PEM fuel cells, however, require a source of pure hydrogen. Steam reforming of hydrocarbons in an integrated membrane reactor has potential to provide pure hydrogen in a compact system. Continuous separation of product hydrogen from the reforming gas mixture is expected to increase the yield of hydrogen significantly as predicted by model simulations. In the laboratory-scale experimental studies reported here steam reforming of liquid hydrocarbon fuels, butane, methanol and Clearlite ® was conducted to produce pure hydrogen in a single step membrane reformer using commercially available Pd-Ag foil membranes and reforming/WGS catalysts. All of the experimental results demonstrated increase in hydrocarbon conversion due to hydrogen separation when compared with the hydrocarbon conversion without any hydrogen separation. Increase in hydrogen recovery was also shown to result in corresponding increase in hydrocarbon conversion in these studies demonstrating the basic concept. The experiments also provided insight into the effect of individual variables such as pressure, temperature, gas space velocity, and steam to carbon ratio. Steam reforming of butane was found to be limited by reaction kinetics for the experimental conditions used: catalysts used, average gas space velocity, and the reactor characteristics of surface area to volume ratio. Steam reforming of methanol in the presence of only WGS catalyst on the other hand indicated that the membrane reactor performance was limited by membrane permeation, especially at lower temperatures and lower feed pressures due to slower reconstitution of CO and H 2 into methane thus maintaining high hydrogen partial pressures in the reacting gas mixture. The limited amount of data collected with steam reforming of Clearlite ® indicated very good match between theoretical predictions and experimental results indicating that the underlying assumption of the simple model of conversion of hydrocarbons to CO and H 2 followed by equilibrium reconstitution to methane appears to be reasonable one.

Deciphering membrane-associated molecular processes in target tissue of autoimmune uveitis by label-free quantitative mass spectrometry.

PubMed

Hauck, Stefanie M; Dietter, Johannes; Kramer, Roxane L; Hofmaier, Florian; Zipplies, Johanna K; Amann, Barbara; Feuchtinger, Annette; Deeg, Cornelia A; Ueffing, Marius

2010-10-01

Autoimmune uveitis is a blinding disease presenting with autoantibodies against eye-specific proteins as well as autoagressive T cells invading and attacking the immune-privileged target tissue retina. The molecular events enabling T cells to invade and attack the tissue have remained elusive. Changes in membrane protein expression patterns between diseased and healthy stages are especially interesting because initiating events of disease will most likely occur at membranes. Since disease progression is accompanied with a break-down of the blood-retinal barrier, serum-derived proteins mask the potential target tissue-related changes. To overcome this limitation, we used membrane-enriched fractions derived from retinas of the only available spontaneous animal model for the disease equine recurrent uveitis, and compared expression levels by a label-free LC-MSMS-based strategy to healthy control samples. We could readily identify a total of 893 equine proteins with 57% attributed to the Gene Ontology project term "membrane." Of these, 179 proteins were found differentially expressed in equine recurrent uveitis tissue. Pathway enrichment analyses indicated an increase in proteins related to antigen processing and presentation, TNF receptor signaling, integrin cell surface interactions and focal adhesions. Additionally, loss of retina-specific proteins reflecting decrease of vision was observed as well as an increase in Müller glial cell-specific proteins indicating glial reactivity. Selected protein candidates (caveolin 1, integrin alpha 1 and focal adhesion kinase) were validated by immunohistochemistry and tissue staining pattern pointed to a significant increase of these proteins at the level of the outer limiting membrane which is part of the outer blood-retinal barrier. Taken together, the membrane enrichment in combination with LC-MSMS-based label-free quantification greatly increased the sensitivity of the comparative tissue profiling and resulted in detection of novel molecular pathways related to equine recurrent uveitis.

Action potentials recorded from bundles of very thin, gray matter axons in rat cerebellar slices using a grease-gap method.

PubMed

Palani, Damodharan; Pekala, Dobromila; Baginskas, Armantas; Szkudlarek, Hanna; Raastad, Morten

2012-07-15

We investigated the ability of a grease-gap method to record fast and slow changes of the membrane potential from bundles of gray matter axons. Their membrane potentials are of particular interest because these axons are different from most axons that have been investigated using intra-axonal or gap techniques. One of the main differences is that gray matter axons typically have closely spaced presynaptic specializations, called boutons or varicosities, distributed along their entire paths. In response to electrical activation of bundles of parallel fiber axons we were able to record small (128-416μV) but stable signals that we show most likely represented a fraction of the trans-membrane action potentials. A less-than 100% fraction prevents measurements of absolute values for membrane potentials, but the good signal-to-noise ratio (typically 10-16) allows detection of changes in resting membrane potential, action potentials and their after-potentials. Because very little is known about the shape of action potentials and after-potentials in these axons we used several independent methods to make it likely that the grease-gap signal was of intra-axonal origin. We demonstrate the utility of the method by showing that the action potentials in cerebellar parallel fibers and hippocampal Schaffer collaterals had a slowly decaying, depolarized after-potential. The method is ideal for pharmacological tests, which we demonstrate by showing that the slow after-potential was sensitive to 4-AP, and that the membrane potential was reduced by 200μM Ba(2+). Copyright © 2012 Elsevier B.V. All rights reserved.

The membrane properties and firing characteristics of rat jaw-elevator motoneurones.

PubMed Central

Moore, J; Appenteng, K

1990-01-01

1. We have determined the membrane and firing properties of fifty-six jaw-elevator motoneurones in rats that were anaesthetized with pentobarbitone, paralysed and artificially ventilated. 2. Forty-two neurones were identified as masseter motoneurones and fourteen as masseter synergist motoneurones. The membrane potentials for the sample ranged from -60 to -86 (mean = -68; S.D. = 7.3; n = 56), and spike amplitudes from 50 to 95 mV. The duration of the after-hyperpolarization following antidromic spikes in masseter motoneurones ranged from 15 to 50 ms (mean = 30; S.D. = 12.8) and their amplitudes from 1.0 to 4.5 mV (mean = 2.7; S.D. = 2.2; n = 42). 3. The mean input resistance for the total sample was 2.3 M omega (S.D. = 0.9; n = 56), membrane time constant 3.9 ms (S.D. = 0.9; n = 48) and rheobase 4.2 nA (S.D. = 2.6; n = 56). The distribution of these parameters was independent of membrane potential. We found no significant interrelationships between the membrane properties and one interpretation of this is that our sample may be drawn from a homogenous population of motoneurones. We also suggest that elevator motoneurones may have a lower Rm (specific membrane resistivity) value than cat hindlimb motoneurones because they have a similar range of input resistance values but only half the total surface area. 4. Forty-six out of forty-nine neurones fired repetitively to a depolarizing current pulse at a mean threshold of 1.6 x rheobase. Current-frequency plots were constructed for thirteen neurones and all but one showed a primary and secondary range in the firing of the first interspike interval. The mean slope in the primary range was 31 impulses s-1 nA-1 and 77 impulses s-1 nA-1 for the secondary range. The mean minimal firing frequency for steady firing was 26 impulses s-1 and, in response to an increase of stimulation, the rate increased monotonically with a slope of 11 impulses s-1 nA-1. 5. The dynamic sensitivity of twelve neurones was assessed from their response to ramp waveforms of current of constant amplitude but varying frequencies (0.2-2 Hz). Firing initially increased along a steep slope up to a frequency of between 40 and 60 impulses s-1 and then increased along a much shallower slope. Both the threshold for eliciting firing and the firing at the transition point of the two slopes remained constant with changes in ramp frequency.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:2388148

Significance of dissolved methane in effluents of anaerobically treated low strength wastewater and potential for recovery as an energy product: A review.

PubMed

Crone, Brian C; Garland, Jay L; Sorial, George A; Vane, Leland M

2016-11-01

The need for energy efficient Domestic Wastewater (DWW) treatment is increasing annually with population growth and expanding global energy demand. Anaerobic treatment of low strength DWW produces methane which can be used to as an energy product. Temperature sensitivity, low removal efficiencies (Chemical Oxygen Demand (COD), Suspended Solids (SS), and Nutrients), alkalinity demand, and potential greenhouse gas (GHG) emissions have limited its application to warmer climates. Although well designed anaerobic Membrane Bioreactors (AnMBRs) are able to effectively treat DWW at psychrophilic temperatures (10-30 °C), lower temperatures increase methane solubility leading to increased energy losses in the form of dissolved methane in the effluent. Estimates of dissolved methane losses are typically based on concentrations calculated using Henry's Law but advection limitations can lead to supersaturation of methane between 1.34 and 6.9 times equilibrium concentrations and 11-100% of generated methane being lost in the effluent. In well mixed systems such as AnMBRs which use biogas sparging to control membrane fouling, actual concentrations approach equilibrium values. Non-porous membranes have been used to recover up to 92.6% of dissolved methane and well suited for degassing effluents of Upflow Anaerobic Sludge Blanket (UASB) reactors which have considerable solids and organic contents and can cause pore wetting and clogging in microporous membrane modules. Microporous membranes can recover up to 98.9% of dissolved methane in AnMBR effluents which have low COD and SS concentrations. Sequential Down-flow Hanging Sponge (DHS) reactors have been used to recover between 57 and 88% of dissolved methane from Upflow Anaerobic Sludge Blanket (UASB) reactor effluent at concentrations of greater than 30% and oxidize the rest for a 99% removal of total dissolved methane. They can also remove 90% of suspended solids and COD in UASB effluents and produce a high quality effluent. In situ degassing can increase process stability, COD removal, biomass retention, and headspace methane concentrations. A model for estimating energy consumption associated with membrane-based dissolved methane recovery predicts that recovered dissolved and headspace methane may provide all the energy required for operation of an anaerobic system treating DWW at psychrophilic temperatures. Copyright © 2016 Elsevier Ltd. All rights reserved.

Improved antifouling performance of ultrafiltration membrane via preparing novel zwitterionic polyimide

NASA Astrophysics Data System (ADS)

Huang, Haitao; Yu, Jiayu; Guo, Hanxiang; Shen, Yibo; Yang, Fan; Wang, Han; Liu, Rong; Liu, Yang

2018-01-01

On the basis of the outstanding fouling resistance of zwitterionic polymers, an antifouling ultrafiltration membrane was fabricated through phase inversion induced by immersion precipitation method, directly using the novel zwitterionic polyimide (Z-PI), which was synthesized via a two-step procedure including polycondensation and quaternary amination reaction, as membrane material. The chemical structure and composition of the obtained polymer were confirmed by using FTIR, 1H NMR and XPS analysis, and its thermal stability was thoroughly characterized by TGA measurement, respectively. The introduction of zwitterionic groups into polyimide could effectively increase membrane pore size, porosity and wettability, and convert the membrane surface from hydrophobic to highly hydrophilic. As a result, Z-PI membrane displayed significantly improved water permeability compared with that of the reference polyimide (R-PI) membrane without having an obvious compromise in protein rejection. According to the static adsorption and dynamic cycle ultrafiltration experiments of bovine serum albumin (BSA) solution, Z-PI membrane exhibited better fouling resistant ability, especially irreversible fouling resistant ability, suggesting superior antifouling property and long-term performance stability. Moreover, Z-PI membrane had a water flux recovery ratio of 93.7% after three cycle of BSA solution filtration, whereas only about 68.5% was obtained for the control R-PI membrane. These findings demonstrated the advantages of Z-PI membrane material and aimed to provide a facile and scalable method for the large-scale preparation of low fouling ultrafiltration membranes for potential applications.

Neuroprotective effects of seaweeds against 6-hydroxidopamine-induced cell death on an in vitro human neuroblastoma model.

PubMed

Silva, Joana; Alves, Celso; Pinteus, Susete; Mendes, Susana; Pedrosa, Rui

2018-02-14

Parkinson's disease (PD) is a progressive neurodegenerative disorder of the central nervous system. Although the causes of PD pathogenesis remain incomplete, some evidences has suggested that oxidative stress is an important mediator in its pathogenesis. The aim of this study was to evaluate the protective effects of seaweeds with high antioxidant activity on 6-hydroxydopamine (6-OHDA)-induced neurotoxicity in the human neuroblastoma cell line SH-SY5Y, as well as the associated intracellular signaling pathways. Cell viability studies were assessed by 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium (MTT) bromide assay and the intracellular signaling pathways analyzed were: hydrogen peroxide (H 2 O 2 ) production, changes in the mitochondrial membrane potential and Caspase-3 activity. Exposure of SH-SY5Y cells to 6-OHDA (10-1000 μM) reduced cell's viability in a concentration and time-dependent manner. The data suggest that the cell death induced by 6-OHDA was mediated by an increase of H 2 O 2 production, the depolarization of mitochondrial membrane potential and the increase of Caspase-3 activity. Extracts from S. polyshides, P. pavonica, S. muticum, C. tomentosum and U. compressa revealed to efficiently protect cell's viability in the presence of 6-OHDA (100 μM; 24 h). These effects appear to be associated with the reduction of H 2 O 2 cell's production, the protection of mitochondrial membrane's potential and the reduction of Caspase-3 activity. These results suggest that seaweeds can be a promising source of new compounds with neuroprotective potential.

Interaction of thrombocytes with poly(ether imide): The influence of processing.

PubMed

Braune, S; Lange, M; Richau, K; Lützow, K; Weigel, T; Jung, F; Lendlein, A

2010-01-01

The processing of polymers for blood contacting devices can have a major influence on surface properties. In this study, we fabricated poly(ether imide) (PEI) membranes and films to investigate the effects of the processing on physicochemical surface properties by atomic force microscopy (AFM), scanning electron microscopy, contact angle as well as zeta potential measurements. A static platelet adhesion test was performed to analyze the thrombogenicity of both devices. While contact angle measurements showed similar levels of hydrophobicity and zeta potential values were equivalent, mean surface roughness as well as surface energies in the dispersive part were found to be increased for the PEI membrane. The static platelet adhesion test showed a significantly decreased number of adherent platelets per surface area on the PEI film (178.98 ± 102.70/45000 μm2) compared to the PEI membrane (504 ± 314.27/45000μm2) and, consequently, revealed evidence for higher thrombogenicity of the PEI membrane. This study shows that processing can have a significant effect on platelet adhesion to biomaterials, even though, molar weight was identical. Thrombogenicity of polymer-based cardiovascular devices, therefore, have to be evaluated at the final product level, following the entire processing procedure.

Ion selectivity of the Vibrio alginolyticus flagellar motor.

PubMed Central

Liu, J Z; Dapice, M; Khan, S

1990-01-01

The marine bacterium, Vibrio alginolyticus, normally requires sodium for motility. We found that lithium will substitute for sodium. In neutral pH buffers, the membrane potential and swimming speed of glycolyzing bacteria reached maximal values as sodium or lithium concentration was increased. While the maximal potentials obtained in the two cations were comparable, the maximal swimming speed was substantially lower in lithium. Over a wide range of sodium concentration, the bacteria maintained an invariant sodium electrochemical potential as determined by membrane potential and intracellular sodium measurements. Over this range the increase of swimming speed took Michaelis-Menten form. Artificial energization of swimming motility required imposition of a voltage difference in concert with a sodium pulse. The cation selectivity and concentration dependence exhibited by the motile apparatus depended on the viscosity of the medium. In high-viscosity media, swimming speeds were relatively independent of either ion type or concentration. These facts parallel and extend observations of the swimming behavior of bacteria propelled by proton-powered flagella. In particular, they show that ion transfers limit unloaded motor speed in this bacterium and imply that the coupling between ion transfers and force generation must be fairly tight. PMID:2394685

Interaction of proteins with weak amphoteric charged membrane surfaces: effect of pH.

PubMed

Matsumoto, Hidetoshi; Koyama, Yoshiyuki; Tanioka, Akihiko

2003-08-01

Weak amphoteric charged membranes were prepared by the graft copolymerization of poly(ethylene glycol) (PEG) derivatives with pendant ionizable groups onto polyethylene (PE) porous membranes. Two types of weak amphoteric charged membranes and two types of weak single charged membranes were prepared. The pH dependence of the protein (fluorescein isothiocyanate-labeled bovine serum albumin, FITC-BSA) adsorption onto the membranes was investigated by fluorescence spectroscopy. The interfacial charge properties of the membranes and protein were also characterized at different pH values by streaming potential and electrophoretic light scattering (ELS) measurements, respectively. The adsorbed amount onto each ionic PEG chain grafted membrane showed a uniform maximum value near the isoelectric point (IEP) of the protein (pH 4.1). On both sides of the IEP (pHs 3.3 and 7.2), the adsorption experiments and zeta (zeta) potential measurements were well correlated: the contribution of electrostatic interaction was dominant for the protein adsorption behavior. In the alkaline condition (pH 10.2), the adsorption experiments contradict the zeta potential measurements. It suggested that the conformational change of protein molecule influenced the adsorption behavior. Finally, these results indicated the potential of controlling the protein-ionic PEG chain interaction on the membrane surfaces by the pH adjustment of the outer solution.

Membrane technology for the future treatment of paper mill effluents: chances and challenges of further system closure.

PubMed

Simstich, B; Oeller, H-J

2010-01-01

The pressure on the European paper industry to further close its water circuits has increased significantly during the past decade. Since the technologies of the past can no longer meet the requirements of the future, new water treatment methods have become necessary. A constant rise in the interest in membrane technology expressed by the European paper industry confirms that in the future this method will evolve into a key technology for continued water savings. The publication provides an overview of current and future applications of membrane plants in the European paper industry. A range of technologies is briefly presented together with their advantages and drawbacks, and the economic potential of membrane use is discussed. Among other topics, the authors take a look at the utilization of membrane filtration for treating internal circulation water, partial flows containing coating colours, and biologically treated effluents. The technologies addressed include ultrafiltration, nanofiltration and membrane bioreactor technology. Possible recovery and treatment routes for the concentrates produced by the nanofiltration of biologically treated effluents are examined and evaluated.

Receptor clustering affects signal transduction at the membrane level in the reaction-limited regime

NASA Astrophysics Data System (ADS)

Caré, Bertrand R.; Soula, Hédi A.

2013-01-01

Many types of membrane receptors are found to be organized as clusters on the cell surface. We investigate the potential effect of such receptor clustering on the intracellular signal transduction stage. We consider a canonical pathway with a membrane receptor (R) activating a membrane-bound intracellular relay protein (G). We use Monte Carlo simulations to recreate biochemical reactions using different receptor spatial distributions and explore the dynamics of the signal transduction. Results show that activation of G by R is severely impaired by R clustering, leading to an apparent blunted biological effect compared to control. Paradoxically, this clustering decreases the half maximal effective dose (ED50) of the transduction stage, increasing the apparent affinity. We study an example of inter-receptor interaction in order to account for possible compensatory effects of clustering and observe the parameter range in which such interactions slightly counterbalance the loss of activation of G. The membrane receptors’ spatial distribution affects the internal stages of signal amplification, suggesting a functional role for membrane domains and receptor clustering independently of proximity-induced receptor-receptor interactions.

Review of 1,000 consecutive extracorporeal membrane oxygenation runs as a quality initiative.

PubMed

Lovvorn, Harold N; Hardison, Daphne C; Chen, Heidi; Westrick, Ashly C; Danko, Melissa E; Bridges, Brian C; Walsh, William F; Pietsch, John B

2017-08-01

Extracorporeal membrane oxygenation is a resource-intensive mode of life-support potentially applicable when conventional therapies fail. Given the initial success of extracorporeal membrane oxygenation to support neonates and infants in the 1980s, indications have expanded to include adolescents, adults, and selected moribund patients during cardiopulmonary resuscitation. This single-institution analysis was conducted to evaluate programmatic growth, outcomes, and risk for death despite extracorporeal membrane oxygenation across all ages and diseases. Beginning in 1989, we registered prospectively all extracorporeal membrane oxygenation patient data with the Extracorporeal Life Support Organization. We queried this registry for our institution-specific data to compare the parameter of "discharge alive" between age groups (neonatal, pediatric, adult), disease groups (respiratory, cardiac, cardiopulmonary resuscitation), and modes of extracorporeal membrane oxygenation (veno-venous; veno-arterial). Extracorporeal membrane oxygenation-specific complications (mechanical, hemorrhagic, neurologic, renal, cardiovascular, pulmonary, infectious, metabolic) were analyzed similarly. Descriptive statistics, Kaplan-Meier, and linear regression analyses were conducted. After 1,052 extracorporeal membrane oxygenation runs, indications have expanded to include adults, to supplement cardiopulmonary resuscitation, to support hemodialysis in neonates and plasmapheresis in children, and to bridge all age patients to heart and lung transplant. Overall survival to discharge was 52% and was better for respiratory diseases (P < .001). Probability of individual survival decreased to <50% if pre-extracorporeal membrane oxygenation mechanical ventilation exceeded respectively 123 hours for cardiac, 166 hours for cardiopulmonary resuscitation, and 183 hours for respiratory diseases (P = .013). Complications occurred most commonly among cardiac and cardiopulmonary resuscitation runs (P < .001), the veno-arterial mode (P < .001), and in adults (P = .044). Our extracorporeal membrane oxygenation program, an Extracorporeal Life Support Organization-designated Center of Excellence, has experienced substantial growth in volume and indications, including increasing age and disease severity. Considering the entire cohort, pre-extracorporeal membrane oxygenation ventilation exceeding 7 days was associated with an increased probability of death. Copyright © 2017 Elsevier Inc. All rights reserved.

Highly branched penta-saccharide-bearing amphiphiles for membrane protein studies

PubMed Central

Ehsan, Muhammad; Du, Yang; Scull, Nicola J.; Tikhonova, Elena; Tarrasch, Jeffrey; Mortensen, Jonas S.; Loland, Claus J.; Skiniotis, Georgios; Guan, Lan; Byrne, Bernadette; Kobilka, Brian K.; Chae, Pil Seok

2016-01-01

Detergents are essential tools for membrane protein manipulation. Micelles formed by detergent molecules have the ability to encapsulate the hydrophobic domains of membrane proteins. The resulting protein-detergent complexes (PDCs) are compatible with the polar environments of aqueous media, making structural and functional analysis feasible. Although a number of novel agents have been developed to overcome the limitations of conventional detergents, most of them have traditional head groups such as glucoside or maltoside. In this study, we introduce a class of amphiphiles, the PSA’Es with a novel highly branched penta-saccharide hydrophilic group. The PSA’Es conferred markedly increased stability to a diverse range of membrane proteins compared to conventional detergents, indicating a positive role for the new hydrophilic group in maintaining the native protein integrity. In addition, PDCs formed by PSA’Es were smaller and more suitable for electron microscopic analysis than those formed by DDM, indicating that the new agents have significant potential for the structure-function studies of membrane proteins. PMID:26966956

High-Flux Carbon Molecular Sieve Membranes for Gas Separation.

PubMed

Richter, Hannes; Voss, Hartwig; Kaltenborn, Nadine; Kämnitz, Susanne; Wollbrink, Alexander; Feldhoff, Armin; Caro, Jürgen; Roitsch, Stefan; Voigt, Ingolf

2017-06-26

Carbon membranes have great potential for highly selective and cost-efficient gas separation. Carbon is chemically stable and it is relative cheap. The controlled carbonization of a polymer coating on a porous ceramic support provides a 3D carbon material with molecular sieving permeation performance. The carbonization of the polymer blend gives turbostratic carbon domains of randomly stacked together sp 2 hybridized carbon sheets as well as sp 3 hybridized amorphous carbon. In the evaluation of the carbon molecular sieve membrane, hydrogen could be separated from propane with a selectivity of 10 000 with a hydrogen permeance of 5 m 3 (STP)/(m 2 hbar). Furthermore, by a post-synthesis oxidative treatment, the permeation fluxes are increased by widening the pores, and the molecular sieve carbon membrane is transformed from a molecular sieve carbon into a selective surface flow carbon membrane with adsorption controlled performance and becomes selective for carbon dioxide. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ultem((R))/ZIF-8 mixed matrix hollow fiber membranes for CO2/N-2 separations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dai, Y; Johnson, JR; Karvan, O

2012-05-15

Organic-inorganic hybrid (mixed matrix) membranes can potentially extend the separation performance of traditional polymeric materials while maintaining processing convenience. Although many dense films studies have been reported, there have been few reported cases of these materials being successfully extended to asymmetric hollow fibers. In this work we report the first successful production of mixed matrix asymmetric hollow fiber membranes containing metal-organic-framework (MOF) ZIF-8 fillers. Specifically, we have incorporated ZIF-8 into a polyetherimide (Ultem((R)) 1000) matrix and produced dual-layer asymmetric hollow fiber membranes via the dry jet-wet quench method. The outer separating layer of these composite fibers contains 13 wt% (17more » vol%) of ZIF-8 filler. These membranes have been tested over a range of temperatures and pressures for a variety of gas pairs. An increase in separation performance for the CO2/N-2 gas pairs was observed for both pure gas and mixed gas feeds. (C) 2012 Elsevier B.V. All rights reserved.« less

Influence of fermentation liquid from waste activated sludge on anoxic/oxic- membrane bioreactor performance: Nitrogen removal, membrane fouling and microbial community.

PubMed

Han, Xiaomeng; Zhou, Zhen; Mei, Xiaojie; Ma, Yan; Xie, Zhenfang

2018-02-01

In order to investigate effects of waste activated sludge (WAS) fermentation liquid on anoxic/oxic- membrane bioreactor (A/O-MBR), two A/O-MBRs with and without WAS fermentation liquid addition were operated in parallel. Results show that addition of WAS fermentation liquid clearly improved denitrification efficiency without deterioration of nitrification, while severe membrane fouling occurred. WAS fermentation liquid resulted in an elevated production of proteins and humic acids in bound extracellular polymeric substance (EPS) and release of organic matter with high MW fractions in soluble microbial product (SMP) and loosely bound EPS (LB-EPS). Measurement of deposition rate and fluid structure confirmed increased fouling potential of SMP and LB-EPS. γ-Proteobacteria and Ferruginibacter, which can secrete and export EPS, were also found to be abundant in the MBR with WAS fermentation liquid. It is implied that when WAS fermentation liquid was applied, some operational steps to control membrane fouling should be employed. Copyright © 2017 Elsevier Ltd. All rights reserved.

A FRET sensor enables quantitative measurements of membrane charges in live cells.

PubMed

Ma, Yuanqing; Yamamoto, Yui; Nicovich, Philip R; Goyette, Jesse; Rossy, Jérémie; Gooding, J Justin; Gaus, Katharina

2017-04-01

Membrane charge has a critical role in protein trafficking and signaling. However, quantification of the effective electrostatic potential of cellular membranes has remained challenging. We developed a fluorescence membrane charge sensor (MCS) that reports changes in the membrane charge of live cells via Förster resonance energy transfer (FRET). MCS is permanently attached to the inner leaflet of the plasma membrane and shows a linear, reversible and fast response to changes of the electrostatic potential. The sensor can monitor a wide range of cellular treatments that alter the electrostatic potential, such as incorporation and redistribution of charged lipids and alterations in cytosolic ion concentration. Applying the sensor to T cell biology, we used it to identify charged membrane domains in the immunological synapse. Further, we found that electrostatic interactions prevented spontaneous phosphorylation of the T cell receptor and contributed to the formation of signaling clusters in T cells.

Membrane permeabilization of mammalian cells using bursts of high magnetic field pulses

PubMed Central

Grainys, Audrius; Kranjc, Matej; Miklavčič, Damijan

2017-01-01

Background Cell membrane permeabilization by pulsed electromagnetic fields (PEMF) is a novel contactless method which results in effects similar to conventional electroporation. The non-invasiveness of the methodology, independence from the biological object homogeneity and electrical conductance introduce high flexibility and potential applicability of the PEMF in biomedicine, food processing, and biotechnology. The inferior effectiveness of the PEMF permeabilization compared to standard electroporation and the lack of clear description of the induced transmembrane transport are currently of major concern. Methods The PEMF permeabilization experiments have been performed using a 5.5 T, 1.2 J pulse generator with a multilayer inductor as an applicator. We investigated the feasibility to increase membrane permeability of Chinese Hamster Ovary (CHO) cells using short microsecond (15 µs) pulse bursts (100 or 200 pulses) at low frequency (1 Hz) and high dB/dt (>106 T/s). The effectiveness of the treatment was evaluated by fluorescence microscopy and flow cytometry using two different fluorescent dyes: propidium iodide (PI) and YO-PRO®-1 (YP). The results were compared to conventional electroporation (single pulse, 1.2 kV/cm, 100 µs), i.e., positive control. Results The proposed PEMF protocols (both for 100 and 200 pulses) resulted in increased number of permeable cells (70 ± 11% for PI and 67 ± 9% for YP). Both cell permeabilization assays also showed a significant (8 ± 2% for PI and 35 ± 14% for YP) increase in fluorescence intensity indicating membrane permeabilization. The survival was not affected. Discussion The obtained results demonstrate the potential of PEMF as a contactless treatment for achieving reversible permeabilization of biological cells. Similar to electroporation, the PEMF permeabilization efficacy is influenced by pulse parameters in a dose-dependent manner. PMID:28462057

A potential link between insulin signaling and GLUT4 translocation: Association of Rab10-GTP with the exocyst subunit Exoc6/6b

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sano, Hiroyuki; Peck, Grantley R.; Blachon, Stephanie

Insulin increases glucose transport in fat and muscle cells by stimulating the exocytosis of specialized vesicles containing the glucose transporter GLUT4. This process, which is referred to as GLUT4 translocation, increases the amount of GLUT4 at the cell surface. Previous studies have provided evidence that insulin signaling increases the amount of Rab10-GTP in the GLUT4 vesicles and that GLUT4 translocation requires the exocyst, a complex that functions in the tethering of vesicles to the plasma membrane, leading to exocytosis. In the present study we show that Rab10 in its GTP form binds to Exoc6 and Exoc6b, which are the twomore » highly homologous isotypes of an exocyst subunit, that both isotypes are found in 3T3-L1 adipocytes, and that knockdown of Exoc6, Exoc6b, or both inhibits GLUT4 translocation in 3T3-L1 adipocytes. These results suggest that the association of Rab10-GTP with Exoc6/6b is a molecular link between insulin signaling and the exocytic machinery in GLUT4 translocation. - Highlights: • Insulin stimulates the fusion of vesicles containing GLUT4 with the plasma membrane. • This requires vesicular Rab10-GTP and the exocyst plasma membrane tethering complex. • We find that Rab10-GTP associates with the Exoc6 subunit of the exocyst. • We find that knockdown of Exoc6 inhibits fusion of GLUT4 vesicles with the membrane. • The interaction of Rab10-GTP with Exoc6 potentially links signaling to exocytosis.« less

Transient Receptor Potential Vanilloid 1 Expression Mediates Capsaicin-Induced Cell Death.

PubMed

Ramírez-Barrantes, Ricardo; Córdova, Claudio; Gatica, Sebastian; Rodriguez, Belén; Lozano, Carlo; Marchant, Ivanny; Echeverria, Cesar; Simon, Felipe; Olivero, Pablo

2018-01-01

The transient receptor potential (TRP) ion channel family consists of a broad variety of non-selective cation channels that integrate environmental physicochemical signals for dynamic homeostatic control. Involved in a variety of cellular physiological processes, TRP channels are fundamental to the control of the cell life cycle. TRP channels from the vanilloid (TRPV) family have been directly implicated in cell death. TRPV1 is activated by pain-inducing stimuli, including inflammatory endovanilloids and pungent exovanilloids, such as capsaicin (CAP). TRPV1 activation by high doses of CAP (>10 μM) leads to necrosis, but also exhibits apoptotic characteristics. However, CAP dose-response studies are lacking in order to determine whether CAP-induced cell death occurs preferentially via necrosis or apoptosis. In addition, it is not known whether cytosolic Ca 2+ and mitochondrial dysfunction participates in CAP-induced TRPV1-mediated cell death. By using TRPV1-transfected HeLa cells, we investigated the underlying mechanisms involved in CAP-induced TRPV1-mediated cell death, the dependence of CAP dose, and the participation of mitochondrial dysfunction and cytosolic Ca 2+ increase. Together, our results contribute to elucidate the pathophysiological steps that follow after TRPV1 stimulation with CAP. Low concentrations of CAP (1 μM) induce cell death by a mechanism involving a TRPV1-mediated rapid and transient intracellular Ca 2+ increase that stimulates plasma membrane depolarization, thereby compromising plasma membrane integrity and ultimately leading to cell death. Meanwhile, higher doses of CAP induce cell death via a TRPV1-independent mechanism, involving a slow and persistent intracellular Ca 2+ increase that induces mitochondrial dysfunction, plasma membrane depolarization, plasma membrane loss of integrity, and ultimately, cell death.

Docosahexaenoic acid attenuates oxidative stress and protects human gingival fibroblasts against cytotoxicity induced by hydrogen peroxide and butyric acid.

PubMed

Zgorzynska, Emilia; Wierzbicka-Ferszt, Anita; Dziedzic, Barbara; Witusik-Perkowska, Monika; Zwolinska, Anna; Janas, Anna; Walczewska, Anna

2015-01-01

The oxidative burst of the host cells associated with bacterial pathogen infection contributes to the destruction of periodontal tissue. The present study investigates the effect of docosahexaenoic acid (DHA) on human gingival fibroblast (HGF) viability and ROS generation. The cell viability by MTT assay, ROS level using H2DCF-DA probe, and protein thiol content were measured in HGFs after 24h preincubation with different concentrations of DHA followed by treatment with H2O2. The cell death rate was determined by Annexin V/propidium iodide staining, and mitochondrial membrane potential (ΔΨm) was examined by MitoTracker Red probe in H2O2- and butyric acid-treated HGFs. The fatty acid composition of plasma membranes after incubation with DHA was determined by gas chromatography mass spectrometry. DHA preincubation in a dose-dependent manner increased the viability of HGFs exposed to H2O2 and decreased ROS generation compared to the control cells. In HGFs preincubated with 30μM DHA, the ΔΨm significantly increased in both H2O2- and butyric acid-treated cells. Moreover, incubation with DHA preserved the protein thiol level as effectively as N-acetylcysteine. Application of 50μM DHA increased the quantity of viable cells, decreased the number of necrotic cells after H2O2 treatment, and protected HGFs from apoptosis induced by butyric acid. DHA in the plasma membranes of these HGFs represented about 6% of the total amount of fatty acids. These results demonstrate that enrichment of HGFs with DHA reduces ROS generation and enhances the mitochondrial membrane potential protecting the fibroblasts against cytotoxic factors. Copyright © 2014 Elsevier Ltd. All rights reserved.

Role of an inward rectifier K+ current and of hyperpolarization in human myoblast fusion

PubMed Central

Liu, J-H; Bijlenga, P; Fischer-Lougheed, J; Occhiodoro, T; Kaelin, A; Bader, C R; Bernheim, L

1998-01-01

The role of K+ channels and membrane potential in myoblast fusion was evaluated by examining resting membrane potential and timing of expression of K+ currents at three stages of differentiation of human myogenic cells: undifferentiated myoblasts, fusion-competent myoblasts (FCMBs), and freshly formed myotubes. Two K+ currents contribute to a hyperpolarization of myoblasts prior to fusion: IK(NI), a non-inactivating delayed rectifier, and IK(IR), an inward rectifier. IK(NI) density is low in undifferentiated myoblasts, increases in FCMBs and declines in myotubes. On the other hand, IK(IR) is expressed in 28 % of the FCMBs and in all myotubes. IK(IR) is reversibly blocked by Ba2+ or Cs+. Cells expressing IK(IR) have resting membrane potentials of −65 mV. A block by Ba2+ or Cs+ induces a depolarization to a voltage determined by IK(NI) (−32 mV). Cs+ and Ba2+ ions reduce myoblast fusion. It is hypothesized that the IK(IR)-mediated hyperpolarization allows FCMBs to recruit Na+, K+ and T-type Ca2+ channels which are present in these cells and would otherwise be inactivated. FCMBs, rendered thereby capable of firing action potentials, could amplify depolarizing signals and may accelerate fusion. PMID:9705997

Membrane development for vanadium redox flow batteries.

PubMed

Schwenzer, Birgit; Zhang, Jianlu; Kim, Soowhan; Li, Liyu; Liu, Jun; Yang, Zhenguo

2011-10-17

Large-scale energy storage has become the main bottleneck for increasing the percentage of renewable energy in our electricity grids. Redox flow batteries are considered to be among the best options for electricity storage in the megawatt range and large demonstration systems have already been installed. Although the full technological potential of these systems has not been reached yet, currently the main problem hindering more widespread commercialization is the high cost of redox flow batteries. Nafion, as the preferred membrane material, is responsible for about 11% of the overall cost of a 1 MW/8 MWh system. Therefore, in recent years two main membrane related research threads have emerged: 1) chemical and physical modification of Nafion membranes to optimize their properties with regard to vanadium redox flow battery (VRFB) application; and 2) replacement of the Nafion membranes with different, less expensive materials. This review summarizes the underlying basic scientific issues associated with membrane use in VRFBs and presents an overview of membrane-related research approaches aimed at improving the efficiency of VRFBs and making the technology cost-competitive. Promising research strategies and materials are identified and suggestions are provided on how materials issues could be overcome.

Review on the fate of organic micropollutants in wastewater treatment and water reuse with membranes.

PubMed

Siegrist, H; Joss, A

2012-01-01

A brief review of the fate of micropollutants in membrane-based wastewater treatment due to sorption, stripping, biological degradation/transformation and membrane separation is discussed, to give an overview of these technologies due to the growing importance for water reuse purposes. Compared with conventional activated sludge treatment (CAS) micropollutant removal in membrane bioreactor (MBR) is slightly improved due to complete suspended solids removal and increased sludge age. For discharge to sensitive receiving waters advanced treatment, such as post-ozonation or activated carbon adsorption, is recommended. In water reuse plants nanofiltration (NF) and reverse osmosis (RO) efficiently reject micropollutants due to size exclusions as well as electrostatic and hydrophobic effects reaching potable quality. To remove micropollutants fully, additionally post-ozone or the addition of powdered activated carbon (PAC) have to be applied, which in parallel also reduce NDMA precursors. The concentrate has to be treated if disposed to sensitive receiving waters due to its high micropollutant concentration and ecotoxicity potential. The present review summarizes principles and capabilities for the most important membrane-based applications for wastewater treatment, i.e. porous membranes in MBRs (micro- or ultrafiltration) and dense membrane applications (NF and RO) for water reuse.

Zeta potential response of human erythrocyte membranes to the modulators of Gardos channel activity under low rate β-radiation.

PubMed

Zhirnov, V V; Iakovenko, I N; Voitsitskiy, V M; Khyzhnyak, S V; Zubrikova-Chugainova, O G; Gorobetz, V A

2015-12-01

Study of human erythrocyte DP response under modification by activators and blockers of the functional state of Ca2+-dependent K+ channels under low rate β-radiation. Erythrocytes were isolated from the donor blood. The zeta potential was computed from the value of the cell electrophoretic mobility. The investigated drugs preliminary introduced in cellular suspensions, and then aliquote of 90Sr(NO3)2 solution to get the final activity concentration of 44,4kBq⋅l-1. The radioisotope radiation of 90Sr/90Y (RR, 15 μGy⋅h-1) increases an absolute value of erythrocyte membranes DP (DPab), and its action is reversible. It specifies the effect is mediated by non-ionizing part of the RR. Dibutyril-cAMP dose-independent increases DPab of erythrocyte membranes in the concentration range of 1-100 мкМ, but RR does not amplify this effect. Anaprilin increases dose-independent DPab in concentrations 10 and 100 μМ. The effect of maximal concentration of anaprilin (100 μМ) decreases by RR. Clotrimazol increases DPab of erythrocyte membranes in the concentration range of 0,1-10 μМ relatively control, while its maximal concentration - decreases, and the minimal level does not reliably influence on this index The action of сlotrimazol on DP in concentrations of 10-100 μМ is abolished by RR, and is not changed in the range of 0,1-1,0 μМ. Nitrendipine raises DPab of erythrocyte membranes in all of range of concentrations, and RR amplifies the effect of the drug. 1. There is a threshold of the biological action on cells for the ionizing component of radioisotope radiation determined by efficiency of operation their antioxidant system.2. At dose rates below a threshold, the action of ionizing radiation is mediated by its non-ionizing component, and is reversible, and therefore is determined only in the field of radiation. V. V. Zhirnov, I. N. Iakovenko, V.M. Voitsitskiy, S. V. Khyzhnyak, О. G. Zubrikova-Chugainova, V.A. Gorobetz.

Na+/Ca2+ exchange in cardiac myocytes. Effect of ouabain on voltage dependence.

PubMed

Lee, H C; Clusin, W T

1987-02-01

Sarcolemmal sodium/calcium exchange activity was examined in individual chick embryonic myocardial cell aggregates that were loaded with quin 2. The baseline [Ca2+]i was 68 +/- 4 nM (n = 29). Abrupt superfusion with sodium-free lithium solution produced a fourfold increase in steady-state [Ca2+]i to 290 +/- 19 nM, which was reversible upon sodium restitution. Other methods of increasing [Ca2+]i such as KCl-depolarization or caffeine produced a dose-dependent increase in quin 2 fluorescence, accompanied by sustained contracture. The [Ca2+]i increase in zero sodium was linear, and its half-time (t1/2) of 15.1 +/- 0.1 s was similar to that of the sodium-free contracture (t1/2 = 14.4 +/- 0.5 s) under the same conditions. The sodium-dependent [Ca2+]i increase was not significantly greater when potassium served as the sodium substitute instead of lithium. This suggests that sodium/calcium exchange has little voltage dependence in this situation. However, in aggregates pretreated with ouabain (2.5 microM), the [Ca2+]i increase was almost threefold greater with potassium than with lithium (P less than 0.007). Ouabain therefore potentiated the effect of membrane potential on calcium influx. We propose that elevation of [Na2+]i is a prerequisite for voltage dependence of the sodium/calcium exchange under the conditions studied. Sodium loading will then drastically increase calcium influx during the action potential while inducing an outward membrane current that could accelerate repolarization.

Sodium influxes in internally perfused squid giant axon during voltage clamp.

PubMed

Atwater, I; Bezanilla, F; Rojas, E

1969-05-01

1. An experimental method for measuring ionic influxes during voltage clamp in the giant axon of Dosidicus is described; the technique combines intracellular perfusion with a method for controlling membrane potential.2. Sodium influx determinations were carried out while applying rectangular pulses of membrane depolarization. The ratio ;measured sodium influx/computed ionic flux during the early current' is 0.92 +/- 0.12.3. Plots of measured sodium influx and computed ionic flux during the early current against membrane potential are very similar. There was evidence that the membrane potential at which the sodium influx vanishes is the potential at which the early current reverses.

Bergmann glia modulate cerebellar Purkinje cell bistability via Ca2+-dependent K+ uptake

PubMed Central

Wang, Fushun; Xu, Qiwu; Wang, Weishan; Takano, Takahiro; Nedergaard, Maiken

2012-01-01

Recent studies have shown that cerebellar Bergmann glia display coordinated Ca2+ transients in live mice. However, the functional significance of Bergmann glial Ca2+ signaling remains poorly understood. Using transgenic mice that allow selective stimulation of glial cells, we report here that cytosolic Ca2+ regulates uptake of K+ by Bergmann glia, thus providing a powerful mechanism for control of Purkinje cell-membrane potential. The decline in extracellular K+ evoked by agonist-induced Ca2+ in Bergmann glia transiently increased spike activity of Purkinje cells in cerebellar slices as well as in live anesthetized mice. Thus, Bergmann glia play a previously unappreciated role in controlling the membrane potential and thereby the activity of adjacent Purkinje cells. PMID:22547829

Transmembrane voltage: Potential to induce lateral microdomains.

PubMed

Malinsky, Jan; Tanner, Widmar; Opekarova, Miroslava

2016-08-01

Lateral segregation of plasma membrane lipids is a generally accepted phenomenon. Lateral lipid microdomains of specific composition, structure and biological functions are established as a result of simultaneous action of several competing mechanisms which contribute to membrane organization. Various lines of evidence support the conclusion that among those mechanisms, the membrane potential plays significant and to some extent unique role. Above all, clear differences in the microdomain structure as revealed by fluorescence microscopy could be recognized between polarized and depolarized membranes. In addition, recent fluorescence spectroscopy experiments reported depolarization-induced changes in a membrane lipid order. In the context of earlier findings showing that plasma membranes of depolarized cells are less susceptible to detergents and the cells less sensitive to antibiotics or antimycotics treatment we discuss a model, in which membrane potential-driven re-organization of the microdomain structure contributes to maintaining membrane integrity during response to stress, pathogen attack and other challenges involving partial depolarization of the plasma membrane. This article is part of a Special Issue entitled: The cellular lipid landscape edited by Tim P. Levine and Anant K. Menon. Copyright © 2016 Elsevier B.V. All rights reserved.

In situ observation of the growth of biofouling layer in osmotic membrane bioreactors by multiple fluorescence labeling and confocal laser scanning microscopy.

PubMed

Yuan, Bo; Wang, Xinhua; Tang, Chuyang; Li, Xiufen; Yu, Guanghui

2015-05-15

Since the concept of the osmotic membrane bioreactor (OMBR) was introduced in 2008, it has attracted growing interests for its potential applications in wastewater treatment and reclamation; however, the fouling mechanisms of forward osmosis (FO) membrane especially the development of biofouling layer in the OMBR are not yet clear. Here, the fouled FO membranes were obtained from the OMBRs on days 3, 8 and 25 in sequence, and then the structure and growing rule of the biofouling layer formed on the FO membrane samples were in-situ characterized by multiple fluorescence labeling and confocal laser scanning microscopy (CLSM). CLSM images indicated that the variations in abundance and distribution of polysaccharides, proteins and microorganisms in the biofouling layer during the operation of OMBRs were significantly different. Before the 8th day, their biovolume dramatically increased. Subsequently, the biovolumes of β-d-glucopyranose polysaccharides and proteins continued increasing and leveled off after 8 days, respectively, while the biovolumes of α-d-glucopyranose polysaccharides and microorganisms decreased. Extracellular polymeric substances (EPS) played a significant role in the formation and growth of biofouling layer, while the microorganisms were seldom detected on the upper fouling layer after 3 days. Based on the results obtained in this study, the growth of biofouling layer on the FO membrane surface in the OMBR could be divided into three stages. Initially, EPS was firstly deposited on the FO membrane surface, and then microorganisms associated with EPS located in the initial depositing layer to form clusters. After that, the dramatic increase of the clusters of EPS and microorganisms resulted in the quick growth of biofouling layer during the flux decline of the OMBR. However, when the water flux became stable in the OMBR, some microorganisms and EPS would be detached from the FO membrane surface. Copyright © 2015 Elsevier Ltd. All rights reserved.

Basolateral membrane chloride permeability of A6 cells: implication in cell volume regulation.

PubMed

Brochiero, E; Banderali, U; Lindenthal, S; Raschi, C; Ehrenfeld, J

1995-11-01

The permeability to Cl- of the basolateral membrane (blm) was investigated in renal (A6) epithelial cells, assessing their role in transepithelial ion transport under steady-state conditions (isoosmotic) and following a hypoosmotic shock (i.e. in a regulatory volume decrease, RVD). Three different complementary studies were made by measuring: (1) the Cl- transport rates (delta F/Fo s-1 (x10(-3))), where F is the fluorescence of N-(6-methoxyquinoyl) acetoethyl ester, MQAE, and Fo the maximal fluorescence (x10(-3)) of both membranes by following the intracellular Cl- activities (ai Cl-, measured with MQAE) after extracellular Cl- substitution (2) the blm 86Rb and 36Cl uptakes and (3) the cellular potential and Cl- current using the whole-cell patch-clamp technique to differentiate between the different Cl- transport mechanisms. The permeability of the blm to Cl- was found to be much greater than that of the apical membranes under resting conditions: aiCl- changes were 5.3 +/- 0.7 mM and 25.5 +/- 1.05 mM (n = 79) when Cl- was substituted by NO3(-) in the media bathing apical and basolateral membranes. The Cl- transport rate of the blm was blocked by bumetanide (100 microM) and 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB, 50 microM) but not by N-phenylanthranilic acid (DPC, 100 microM). 86Rb and 36Cl uptake experiments confirmed the presence of a bumetanide- and a NPPB-sensitive Cl- pathway, the latter being approximately three times more important than the former (Na/K/2Cl cotransporter). Appli-cation of a hypoosmotic medium to the serosal side of the cell increased delta F/Fo s-1 (x10(-3)) after extracellular Cl- substitution (1.03 +/- 0.10 and 2.45 +/- 0.17 arbitrary fluorescent units s-1 for isoosmotic and hypoosmotic conditions respectively, n = 11); this delta F/Fo s-1 (x10(-3)) increase was totally blocked by serosal NPPB application; on the other hand, cotransporter activity was decreased by the hypoosmotic shock. Cellular Ca2+ depletion had no effect on delta F/Fo s-1 (x10(-3)) under isoosmotic conditions, but blocked the delta F/Fo s-1 (x10(-3)) increase induced by a hypoosmotic stress. Under isotonic conditions the measured cellular potential at rest was -37.2 +/- 4.0 mV but reached a maximal and transient depolarization of -25.1 +/- 3.7 mV (n = 9) under hypoosmotic conditions. The cellular current at a patch-clamping cellular potential of -85 mV (close to the Nernst equilibrium potential for K+) was blocked by NPPB and transiently increased by hypoosmotic shock (≈50% maximum increase). This study demonstrates that the major component of Cl- transport through the blm of the A6 monolayer is a conductive pathway (NPPB-sensitive Cl- channels) and not a Na/K/2Cl cotransporter. These channels could play a role in transepithelial Cl- absorption and cell volume regulation. The increase in the blm Cl- conductance, inducing a depolarization of these membranes, is proposed as one of the early events responsible for the stimulation of the 86Rb efflux involved in cell volume regulation.

Cell water balance of white button mushrooms (Agaricus bisporus) during its post-harvest lifetime studied by quantitative magnetic resonance imaging.

PubMed

Donker, H C; Van As, H

1999-04-19

A combination of quantitative water density and T2 MRI and changes therein observed after infiltration with 'invisible' Gd-DTPA solution was used to study cell water balances, cell water potentials and cell integrity. This method was applied to reveal the evolution and mechanism of redistribution of water in harvested mushrooms. Even when mushrooms did not lose water during the storage period, a redistribution of water was observed from stipe to cap and gills. When the storage condition resulted in a net loss of water, the stipe lost more water than the cap. The water density in the gill increased, probably due to development of spores. Deterioration effects (i.e. leakage of cells, decrease in osmotic water potential) were found in the outer stipe. They were not found in the cap, even at prolonged storage at 293 K and R.H.=70%. The changes in osmotic potential were partly accounted for by changes in the mannitol concentration. Changes in membrane permeability were also indicated. Cells in the cap had a constant low membrane (water) permeability. They developed a decreasing osmotic potential (more negative), whereas the osmotic potential in the outer stipe increased, together with the permeability of cells.