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Purpose: The present study explored the potential of microwaves on membrane fluidity changes in diethylnitrosamine (DEN) induced hepatocellular carcinoma (HCC), in vivo., Methods: Rats were segregated into four groups: normal control, DEN-treated, microwave-treated, DEN+microwave-treated. Brush border membranes (BBM) were isolated from the rats and, using the membrane extrinsic fluorophore pyrene, we assessed the viscosities as well as fluidity parameters., Results: DEN treatment resulted in a significant rise in lipid peroxidation (LPO). Reduced glutathione levels (GSH) and the activities of glutathione reductase (GR), glutathione transferase (GST), superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) were found to be significantly decreased following DEN treatment. On the other hand, microwave treatment in DEN-treated rats resulted in a significant decrease in the levels of lipid peroxidation but caused a significant rise in the levels of GSH as well in the activities of GR, GST, SOD, CAT and GPx. The results further demonstrated a marked decrease in membrane microviscosity following DEN treatment. On the other hand, a significant increase was observed in the excimer/monomer ratio and fluidity parameter of DEN-treated rats when compared to normal control rats. However, the alterations in membrane microviscosity and the fluidity parameters were significantly restored after microwave treatment., Conclusion: The study, therefore, concludes that microwave proved quite useful in the modulation of membrane stability parameters following DEN-induced hepatic cancer.

Fullerenols (polyhydroxylated fullerene C 60 ) are nanomaterial with potentially broad applicability in biomedical sciences with high antioxidant ability, thus, we investigated the radioprotecting potential of fullerenol C 60 (OH) 36 on human erythrocytes irradiated by high-energy electrons of 6 MeV. The results demonstrate that C 60 (OH) 36 at concentration of 150 μg/mL protects the erythrocytes against the radiation-induced hemolysis (comparing to non-protected cells, we observed 30% and 39% protection for 0.65 and 1.3 kGy irradiation doses, respectively). The protecting effect was confirmed by 32% decreased release of potassium cations comparing to the cells irradiated without C 60 (OH) 36 . Measurements of the amount of lactate dehydrogenase (LDH) released from the irradiated erythrocytes showed that the size of the pores formed by irradiation was not sufficient to release LDH across the erythrocyte membranes. We also report a significant decrease of the affinity of acetylcholinesterase (AChE) for the substrate in the presence of fullerenol, indicating the relatively strong adsorption of C 60 (OH) 36 to components of plasma membrane. Changes in membrane fluidity detected by fluorescence spectroscopy and conformational changes in membrane proteins detected by spin labeling suggest the dose-dependent formation of disulfide groups as an effect of oxidation and this process was inhibited by C 60 (OH) 36. We suppose that scavenging the ROS as well as adsorption of fullerenol to membrane proteins and steric protection of -SH groups against oxidation are responsible for the observed effects., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Introduction: Authors of numerous publications have proved the therapeutic effect of laser irradiation on biological material, but the mechanisms at cellular and subcellular level are not yet well understood., Objective: The aim of this study was to assess the effect of laser radiation emitted by the MLS M1 system (Multiwave Locked System) at two wavelengths (808 nm continuous and 905 nm pulsed) on the stability and fluidity of liposomes with a lipid composition similar to that of human erythrocyte membrane or made of phosphatidylocholine., Material and Methods: Liposomes were exposed to low-energy laser radiation at surface densities 195 mW/cm 2 (frequency 1,000 Hz) and 230 mW/cm 2 (frequency 2,000 Hz). Different doses of radiation energy in the range 0-15 J were applied. The surface energy density was within the range 0.46 - 4.9 J/cm 2 ., Results: The fluidity and stability of liposomes subjected to such irradiation changed depending on the parameters of radiation used., Conclusions: Since MLS M1 laser radiation, depending on the parameters used, affects fluidity and stability of liposomes with the lipid content similar to erythrocyte membrane, it may also cause structural and functional changes in cell membranes.

Exposure of cells and nanoparticles to near-infrared nanosecond pulsed laser light can lead to efficient intracellular delivery of molecules while maintaining high cell viability by a photoacoustic phenomenon known as transient nanoparticle energy transduction (TNET). Here, we examined the influence of cytoskeletal mechanics and plasma membrane fluidity on intracellular uptake of molecules and loss of cell viability due to TNET. We found that destabilization of actin filaments using latrunculin A led to greater uptake of molecules and less viability loss caused by TNET. Stabilization of actin filaments using jasplakinolide had no significant effect on uptake or viability loss caused by TNET. To study the role of plasma membrane fluidity, we increased fluidity by depletion of membrane cholesterol using methyl-β-cyclodextrin and decreased fluidity by enrichment of the membrane with cholesterol using water-soluble cholesterol. Neither of these membrane fluidity changes significantly altered cellular uptake or viability loss caused by TNET. We conclude that weakening mechanical integrity of the cytoskeleton can increase intracellular uptake and decrease loss of cell viability, while plasma membrane fluidity does not appear to play a significant role in uptake or viability loss caused by TNET. The positive effects of cytoskeletal weakening may be due to an enhanced ability of the cell to recover from the effects of TNET and maintain viability. Biotechnol. Bioeng. 2017;114: 2390-2399. © 2017 Wiley Periodicals, Inc., (© 2017 Wiley Periodicals, Inc.)

We have been interested, in this work, to investigate the effect of the exposure to static magnetic field at 200 mT (SMF) on the fatty acid (FA) composition of Salmonella enterica subsp Enterica serovar Hadar isolate 287: effects on the proportion of saturated and unsaturated fatty acids (SFAs, UFAs), cyclopropane fatty acids (CFAs) and hydroxy fatty acids after exposure to the static magnetic field at 200 mT (SMF). Analysis with Gas Chromatography-Mass Spectrometry (GC-MS) of total lipid showed that the proportion of the most fatty acids was clearly affected. The comparison of UFAs/SFAs ratio in exposed bacteria and controls showed a diminution after 3 and 6 h of exposure. This ration reached a balance after 9 h of treatment with SMF. So we can conclude that S. Hadar tries to adapt to magnetic stress by changing the proportions of SFAs and UFAs over time to maintain an equilibrium after 9 h of exposure, thus to maintain the inner membranes fluidity. Also, a decrease in the proportion of hydroxy FAs was observed after 6 h but an increase of this proportion after 9 h of exposure. Concerning CFAs, its proportion raised after 6 h of exposure to the SMF but it decreased after 9 h of exposure. These results are strongly correlated with those of cfa (cyclopropane fatty acid synthase) gene expression which showed a decrease of its expression after 9 h of exposure., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Purpose: To investigate the effects of whole body ionizing radiation at a sublethal dose on rat brain homogenate membranes and the protective effects of amifostine on these systems at molecular level., Materials and Methods: Sprague-Dawley rats, in the absence and presence of amifostine, were whole-body irradiated at a single dose of 8 Gy and decapitated after 24 h. The brain homogenate membranes of these rats were analyzed using Fourier Transform Infrared (FTIR) spectroscopy., Results: Ionizing radiation caused a significant increase in the lipid to protein ratio and significant decreases in the ratios of olefinic = CH/lipid, CH 2 /lipid, carbonyl ester/lipid and CH 3 /lipid suggesting, respectively, a more excessive decrease in the protein content and the degradation of lipids as a result of lipid peroxidation. In addition, radiation changed the secondary structure of proteins and the status of packing of membrane lipid head groups. Furthermore, it caused a decrease in lipid order and an increase in membrane fluidity. The administration of amifostine before ionizing radiation inhibited all the radiation-induced alterations in brain homogenate membranes., Conclusions: The results revealed that whole body ionizing radiation at a sublethal dose causes significant alterations in the structure, composition and dynamics of brain homogenate membranes and amifostine has a protective effect on these membranes.

Polymerization of substrate-supported bilayers composed of dienoylphosphatidylcholine (PC) lipids is known to greatly enhance their chemical and mechanical stability; however, the effects of polymerization on membrane fluidity have not been investigated. Here planar supported lipid bilayers (PSLBs) composed of dienoyl PCs on glass substrates were examined to assess the degree to which UV-initiated polymerization affects lateral lipid mobility. Fluorescence recovery after photobleaching (FRAP) was used to measure the diffusion coefficients (D) and mobile fractions of rhodamine-DOPE in unpolymerized and polymerized PSLBs composed of bis-sorbyl phosphatidylcholine (bis-SorbPC), mono-sorbyl-phosphatidylcholine (mono-SorbPC), bis-dienoyl-phosphatidylcholine (bis-DenPC), and mono-dienoyl phosphatidylcholine (mono-DenPC). Polymerization was performed in both the Lα and Lβ phase for each lipid. In all cases, polymerization reduced membrane fluidity; however, measurable lateral diffusion was retained which is attributed to a low degree of polymerization. The D values for sorbyl lipids were less than those of the denoyl lipids; this may be a consequence of the distal location of polymerizable group in the sorbyl lipids which may facilitate interleaflet bonding. The D values measured after polymerization were 0.1-0.8 of those measured before polymerization, a range that corresponds to fluidity intermediate between that of a Lα phase and a Lβ phase. This D range is comparable to ratios of D values reported for liquid-disordered (Ld) and liquid-ordered (Lo) lipid phases and indicates that the effect of UV polymerization on lateral diffusion in a dienoyl PSLB is similar to the transition from a Ld phase to a Lo phase. The partial retention of fluidity in UV-polymerized PSLBs, their enhanced stability, and the activity of incorporated transmembrane proteins and peptides is discussed.

Purpose: 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., Materials and Methods: 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., Results: 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., Conclusion: These results show that ELF-EMF affects the crucial physicochemical processes in both Gram-positive and Gram-negative bacteria which need further research.

Vesicle and cell rupture caused by large viscous stresses in ultrasonication is central to biomedical and bioprocessing applications. The flow-induced opening of lipid membranes can be exploited to deliver drugs into cells, or to recover products from cells, provided that it can be obtained in a controlled fashion. Here we demonstrate that differences in lipid membrane and vesicle properties can enable selective flow-induced vesicle break-up. We obtained vesicle populations with different membrane properties by using different lipids (SOPC, DOPC, or POPC) and lipid:cholesterol mixtures (SOPC:chol and DOPC:chol). We subjected vesicles to large deformations in the acoustic microstreaming flow generated by ultrasound-driven microbubbles. By simultaneously deforming vesicles with different properties in the same flow, we determined the conditions in which rupture is selective with respect to the membrane stretching elasticity. We also investigated the effect of vesicle radius and excess area on the threshold for rupture, and identified conditions for robust selectivity based solely on the mechanical properties of the membrane. Our work should enable new sorting mechanisms based on the difference in membrane composition and mechanical properties between different vesicles, capsules, or cells.

Determinations of membrane fatty acid composition and fluidity were used together with acidification activity and viability measurements to characterize the physiological state after freezing of Lactobacillus buchneri R1102 and Bifidobacterium longum R0175 cells harvested in the exponential and stationary growth phases. For both strains, lower membrane fluidity was achieved in cells harvested in the stationary growth phase. This change was linked to a lower unsaturated-to-saturated fatty acid ratio for both strains and a higher cyclic-to-saturated fatty acid ratio for L. buchneri R1102 alone. These membrane properties were linked to survival and to maintenance of acidification activity of the cells after freezing, which differed according to the strain and the growth phase. Survival of B. longum R0175 was increased by 10% in cells with low membrane fluidity and high relative saturated fatty acid contents, without any change in acidification activity. Acidification activity was more degraded (70 min) in L. buchneri R1102 cells displaying low membrane fluidity and high saturated and cyclic fatty acid levels. Finally, this study showed that membrane modifications induced by the growth phase differed among bacterial strains in terms of composition. By lowering membrane fluidity, these modifications could be beneficial for survival of B. longum R0175 during the freezing process but detrimental for maintenance of acidification activity of L. buchneri R1102., (© 2014 The Authors. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology.)

The measurement of cell mechanics is crucial for a better understanding of cellular responses during the progression of certain diseases and for the identification of the cell's nature. Many techniques using optical tweezers, atomic force microscopy, and micro-pipettes have been developed to probe and manipulate cells in the spatial domain. In particular, we recently proposed a two-dimensional acoustic trapping method as an alternative technique for small particle manipulation. Although the proposed method may have advantages over optical tweezers, its applications to cellular mechanics have not yet been vigorously investigated. This study represents an initial attempt to use acoustic tweezers as a tool in the field of cellular mechanics in which cancer cell membrane deformability is studied. A press-focused 193-MHz single-element lithium niobate (LiNbO3) transducer was designed and fabricated to trap a 5-μm polystyrene microbead near the ultrasound beam focus. The microbeads were coated with fibronectin, and trapped before being attached to the surface of a human breast cancer cell (MCF-7). The cell membrane was then stretched by remotely pulling a cell-attached microbead with the acoustic trap. The maximum cell membrane stretched lengths were measured to be 0.15, 0.54, and 1.41 μm at input voltages to the transducer of 6.3, 9.5, and 12.6 Vpp, respectively. The stretched length was found to increase nonlinearly as a function of the voltage input. No significant cytotoxicity was observed to result from the bead or the trapping force on the cell during or after the deformation procedure. Hence, the results convincingly demonstrated the possible application of the acoustic trapping technique as a tool for cell manipulation.

The goal of this study was to investigate the effect of the environmental conditions such as the temperature change, incubation time and surface type on the resistance of Staphylococcus aureus biofilms to disinfectants. The antibiofilm assays were performed against biofilms grown at 20 °C, 30 °C and 37 °C, on the stainless steel and polycarbonate, during 24 and 48 h. The involvement of the biofilm matrix and the bacterial membrane fluidity in the resistance of sessile cells were investigated. Our results show that the efficiency of disinfectants was dependent on the growth temperature, the surface type and the disinfectant product. The increase of growth temperature from 20 °C to 37 °C, with an incubation time of 24 h, increased the resistance of biofilms to cationic antimicrobials. This change of growth temperature did not affect the major content of the biofilm matrix, but it decreased the membrane fluidity of sessile cells through the increase of the anteiso-C19 relative amount. The increase of the biofilm resistance to disinfectants, with the rise of the incubation time, was dependent on both growth temperature and disinfectant product. The increase of the biofilm age also promoted increases in the matrix production and the membrane fluidity of sessile cells. The resistance of S. aureus biofilm seems to depend on the environment of the biofilm formation and involves both extracellular matrix and membrane fluidity of sessile cells. Our study represents the first report describing the impact of environmental conditions on the matrix production, sessile cells membrane fluidity and resistance of S. aureus biofilms to disinfectants.

The biostimulating activity of low level laser radiation of various wavelengths and energy doses is widely documented in the literature, but the mechanisms of the intracellular reactions involved are not precisely known. The aim of this paper is to evaluate the influence of low level laser radiation from an multiwave locked system (MLS) of two wavelengths (wavelength = 808 nm in continuous emission and 905 nm in pulsed emission) on the human erythrocyte membrane and on the secondary structure of human serum albumin (HSA). Human erythrocytes membranes and HSA were irradiated with laser light of low intensity with surface energy density ranging from 0.46 to 4.9 J cm(-2) and surface energy power density 195 mW cm(-2) (1,000 Hz) and 230 mW cm(-2) (2,000 Hz). Structural and functional changes in the erythrocyte membrane were characterized by its fluidity, while changes in the protein were monitored by its secondary structure. Dose-dependent changes in erythrocyte membrane fluidity were induced by near-infrared laser radiation. Slight changes in the secondary structure of HSA were also noted. MLS laser radiation influences the structure and function of the human erythrocyte membrane resulting in a change in fluidity.

Temperature is one of the key parameters that controlled the origin and evolution of life on earth and it continues to be a principal regulator of the functions of organisms. Some aspects of the response of simple and complex organisms to temperature variations are encoded in the physical properties of the cell components, with the all-important plasma membrane playing a principal role. Other responses to temperature are more specific and through evolution, specialized receptors with particular temperature sensitivities have appeared to mediate this signaling. While some of these receptors are ancient and can be found in very primitive organisms, it seems that the mechanisms used by prokaryotes and eukaryotes are very different, indicating that temperature sensitivity has evolved in more than one occasion during evolution.

In this paper, we established a theoretical model to investigate the local heating effect of magnetic nanoparticles (MNPs) aggregate on the support lipid bilayers (SLBs) under external alternating current (AC) magnetic field, which may be helpful to understand hyperthermia at single cell level. Using atomic force microscope (AFM), the transformation of the support phospholipid bilayers surrounding MNPs aggregate was observed in real-time. We found that the fluidity of lipid bilayers changed when the size of MNPs aggregate larger than 200 nm, as a result of magnetic heating in the AC magnetic field. These experimental data were consistent with the simulation results, which demonstrated the valid of our established model, as well as described more realistically the above phenomenon.

For sonoporation to be established as a drug/gene delivery paradigm, it is essential to account for the biological impact of this membrane permeation strategy on living cells. Here we provide new insight into the cellular impact of sonoporation by demonstrating in vitro that this way of permeating the plasma membrane may inadvertently induce repressive cellular features even while enhancing exogenous molecule uptake. Both suspension-type (HL-60) and monolayer (ZR-75-30) cells were considered in this investigation, and they were routinely exposed to 1-MHz pulsed ultrasound (pulse length, 100 cycles; pulse repetition frequency, 1 kHz; exposure period, 60 s) with calibrated field profile (spatial-averaged peak negative pressure, 0.45 MPa) and in the presence of microbubbles (cell:bubble ratio, 10:1). The post-exposure morphology of sonoporated cells (identified as those with calcein internalization) was examined using confocal microscopy, and their cell cycle progression kinetics were analyzed using flow cytometry. Results show that for both cell types investigated, sonoporated cells exhibited membrane shrinkage and intra-cellular lipid accumulation over a 2-h period. Also, as compared with normal cells, the deoxyribonucleic acid synthesis duration of sonoporated cells was significantly lengthened, indicative of a delay in cell cycle progression. These features are known to be characteristics of a cellular stress response, suggesting that sonoporation indeed constitutes as a stress to living cells. This issue may need to be addressed in optimizing sonoporation for drug/gene delivery purposes. On the other hand, it raises opportunities for developing other therapeutic applications via sonoporation., (Copyright © 2013 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.)

This study determined the membrane fluidity of clostridial endospores during treatment with heat and pressure with nisin or reutericyclin. Heating (90°C) reduced laurdan (6-dodecanoyl-2-dimethylaminonaphthalene) general polarization, corresponding to membrane fluidization. Pressure (200 MPa) stabilized membrane order. Reutericyclin and nisin exhibit divergent effects on heat- and pressure-induced spore inactivation and membrane fluidity.

Shape fluctuations of a planar lipid membrane in an ac electric field are investigated using a zero-thickness electromechanical model, which accounts for membrane conductivity and capacitance, and asymmetry in the properties of the fluids separated by the membrane. A linear stability analysis shows that unlike in the case of a dc electric field, a purely capacitive membrane can be destabilized in an ac electric field. The theory highlights that the instability originates from electric pressure exerted on the membrane.

Membrane flexoelectricity is an electromechanical coupling process that describes membrane electrical polarization due to bending and membrane bending under electric fields. In this paper we propose, formulate, and characterize a mechanical energy harvesting system consisting of a deformable soft flexoelectric thin membrane subjected to harmonic forcing from contacting bulk fluids. The key elements of the energy harvester are formulated and characterized, including (i) the mechanical-to-electrical energy conversion efficiency, (ii) the electromechanical shape equation connecting fluid forces with membrane curvature and electric displacement, and (iii) the electric power generation and efficiency. The energy conversion efficiency is cast as the ratio of flexoelectric coupling to the product of electric and bending elasticity. The device is described by a second-order curvature dynamics coupled to the electric displacement equation and as such results in mechanical power absorption with a resonant peak whose amplitude decreases with bending viscosity. The electric power generation is proportional to the conversion factor and the power efficiency decreases with frequency. Under high bending viscosity, the power efficiency increases with the conversion factor and under low viscosities it decreases with the conversion factor. The theoretical results presented contribute to the ongoing experimental efforts to develop mechanical energy harvesting from fluid flow energy through solid-fluid interactions and electromechanical transduction.

Magnetic fluid hyperthermia as a cancer treatment method is an attractive alternative to other forms of hyperthermia. It is based on the heat released by magnetic nanoparticles subjected to an alternating magnetic field. Recent studies have shown that magnetic fluid hyperthermia-treated cells respond significantly better to chemotherapeutic treatment compared with cells treated with hot water hyperthermia under the same temperature conditions. We hypothesized that this synergistic effect is due to an additional stress on the cellular membrane, independent of the thermal heat dose effect that is induced by nanoparticles exposed to an alternating magnetic field. This would result in an increase in Cis-diammine-dichloroplatinum (II) (cDDP, cisplatin) uptake via passive transport. To test this hypothesis, we exposed cDDP-treated cells to extracellular copper in order to hinder the human cell copper transporter (hCTR1)-mediated active transport of cDDP. This, in turn, can increase the passive transport of the drug through the cell membrane. Our results did not show statistically significant differences in surviving fractions for cells treated concomitantly with magnetic fluid hyperthermia and cDDP, in the presence or absence of copper. Nonetheless, significant copper-dependent variations in cell survival were observed for samples treated with combined cDDP and hot water hyperthermia. These results correlated with platinum uptake studies, which showed that cells treated with magnetic fluid hyperthermia had higher platinum uptake than cells treated with hot water hyperthermia. Changes in membrane fluidity were tested through fluorescence anisotropy measurements using trimethylamine-diphenylhexatriene. Additional uptake studies were conducted with acridine orange and measured by flow cytometry. These studies indicated that magnetic fluid hyperthermia significantly increases cell membrane fluidity relative to hot water hyperthermia and untreated cells, and hence this could be a factor contributing to the increase of cDDP uptake in magnetic fluid hyperthermia-treated cells. Overall, our data provide convincing evidence that cell membrane permeability induced by magnetic fluid hyperthermia is significantly greater than that induced by hot water hyperthermia under similar temperature conditions, and is at least one of the mechanisms responsible for potentiation of cDDP by magnetic fluid hyperthermia in Caco-2 cells.

Cell sonoporation enables the delivery of various exogenous molecules into the cells. To maximize the percentage of reversibly sonoporated cells and to increase cell viability we propose a model for implicit dosimetry for adjustment of ultrasound (US) exposure duration. The Chinese hamster ovary cell suspension was supplemented with microbubbles (MB) and exposed to US, operating at the frequency of 880kHz, with a 100% duty cycle and with an output peak negative pressure (PNP) of 500kPa for durations ranging from 0.5 to 30s. Using diagnostic B-scan imaging we showed that the majority of the MB at 500kPa US peak negative pressure undergo sonodestruction in less than a second. During this time maximal number of reversibly sonoporated cells was achieved. Increase of US exposure duration did not increase sonoporated cell number, however it induced additional cell viability decrease. Therefore aiming to achieve the highest level of reversibly sonoporated cells and also to preserve the highest level of cell viability, the duration of US exposure should not exceed the duration needed for complete MB sonodestruction.

Observations of enhanced growth of melanized fungi under low-dose ionizing radiation in the laboratory and in the damaged Chernobyl nuclear reactor suggest they have adapted the ability to survive or even benefit from exposure to ionizing radiation. However, the cellular and molecular mechanism of fungal responses to such radiation remains poorly understood. Using the black yeast Wangiella dermatitidis as a model, we confirmed that ionizing radiation enhanced cell growth by increasing cell division and cell size. Using RNA-seq technology, we compared the transcriptomic profiles of the wild type and the melanin-deficient wdpks1 mutant under irradiation and non-irradiation conditions. It was found that more than 3000 genes were differentially expressed when these two strains were constantly exposed to a low dose of ionizing radiation and that half were regulated at least two fold in either direction. Functional analysis indicated that many genes for amino acid and carbohydrate metabolism and cell cycle progression were down-regulated and that a number of antioxidant genes and genes affecting membrane fluidity were up-regulated in both irradiated strains. However, the expression of ribosomal biogenesis genes was significantly up-regulated in the irradiated wild-type strain but not in the irradiated wdpks1 mutant, implying that melanin might help to contribute radiation energy for protein translation. Furthermore, we demonstrated that long-term exposure to low doses of radiation significantly increased survivability of both the wild-type and the wdpks1 mutant, which was correlated with reduced levels of reactive oxygen species (ROS), increased production of carotenoid and induced expression of genes encoding translesion DNA synthesis. Our results represent the first functional genomic study of how melanized fungal cells respond to low dose ionizing radiation and provide clues for the identification of biological processes, molecular pathways and individual genes regulated by radiation.

Freeze-drying is commonly used to preserve probiotics, but it could cause cell damage and loss of viability. The cryoprotectants play an important role in the conservation of viability during freeze-drying. In this study, we investigated the survival rates of Lactobacillus reuteri CICC6226 in the presence of cryoprotectants such as sucrose, trehalose, and reconstituted skim milk (RSM). In addition, we determined the activities of hexokinase (HK), pyruvate kinase (PK), lactate dehydrogenase (LDH), and ATPases immediately following the freeze-drying. The results showed that the differences in HK and PK activities with and without the cryoprotectants during freeze-drying were not significant, but cell viability and activities of LDH and ATPase were significantly different (P<0.01) prior to and after freeze-drying. Meanwhile, the results showed that the maintenance of the membrane integrity and fluidity was improved in the presence of the 10% trehalose or 10% RSM than other treatments during freeze-drying. These results have provided direct biochemical and metabolic evidence of injured cell during freeze-drying. Freeze-drying damaged membrane structure and function of cell and inactivated enzymes (LDH and ATPases). The results imply that LDH and ATPases are key markers and could be used to evaluate the effect of cryoprotectants on viability and metabolic activities of L. reuteri CICC6226 during freeze-drying.

Ramlibacter tataouinensis TTB310(T) (strain TTB310), a betaproteobacterium isolated from a semi-arid region of South Tunisia (Tataouine), is characterized by the presence of both spherical and rod-shaped cells in pure culture. Cell division of strain TTB310 occurs by the binary fission of spherical "cyst-like" cells ("cyst-cyst" division). The rod-shaped cells formed at the periphery of a colony (consisting mainly of cysts) are highly motile and colonize a new environment, where they form a new colony by reversion to cyst-like cells. This unique cell cycle of strain TTB310, with desiccation tolerant cyst-like cells capable of division and desiccation sensitive motile rods capable of dissemination, appears to be a novel adaptation for life in a hot and dry desert environment. In order to gain insights into strain TTB310's underlying genetic repertoire and possible mechanisms responsible for its unusual lifestyle, the genome of strain TTB310 was completely sequenced and subsequently annotated. The complete genome consists of a single circular chromosome of 4,070,194 bp with an average G+C content of 70.0%, the highest among the Betaproteobacteria sequenced to date, with total of 3,899 predicted coding sequences covering 92% of the genome. We found that strain TTB310 has developed a highly complex network of two-component systems, which may utilize responses to light and perhaps a rudimentary circadian hourglass to anticipate water availability at the dew time in the middle/end of the desert winter nights and thus direct the growth window to cyclic water availability times. Other interesting features of the strain TTB310 genome that appear to be important for desiccation tolerance, including intermediary metabolism compounds such as trehalose or polyhydroxyalkanoate, and signal transduction pathways, are presented and discussed.

From an electrical point of view a planar lipid bilayer can be considered as a non-perfect capacitor; it can be presented as an ideal capacitor in parallel with resistor. In this study the whole measuring system including planar lipid bilayer was modeled by an equivalent electric circuit in Spiceopus software. Such a model gives additional information of experimentally obtained results. In this way we analyze measurements of transmembrane voltage that appears on planar lipid bilayer as consequence of linear rising current. Small voltage drops were obtained before the planar lipid bilayer breakdown. The model showed that effective current on planar lipid bilayer is actually much smaller than the current applied with current generator and should be used in calculations of a conductance related to voltage drops.

The biological consequences of exposure to TiO2, UV light, and their combined effect were studied on the Escherichia coli (E. coli) cells. The damage of outer membrane was observed for the cells after treatment of TiO2 or UV light. TiO2 alone can break down lipopolysacchride (LPS), the outermost layer of the E. coli cells, but was not able to destroy peptidoglycan underneath. The same phenomenon was observed for E. coli under 500 W UV light treatment alone. However, the outer membrane of E. coli could be removed completely in the presence of both TiO2 and UV light, and the cells became elliptical or round without a mechanically strong network. From the analysis of the concentrations for Ca2+ and Mg2+, a large amount of Ca2+ and Mg2+ were detected in the solution of the treated cells by photo-catalysis, and this was attributed to the damage of LPS dispatches. After TiO2 or UV light treatment, a significant decrease in membrane fluidity of E. coli was found from an increase in fluorescence polarization by a fluorescence probe. The permeability of the treated cells increased to some degree that can be confirmed by quantum dots labeling technique., (2010 Elsevier B.V. All rights reserved.)

The behavior of a conductive membrane in a static (dc) electric field is investigated theoretically. An effective zero-thickness model is constructed based on a Robin-type boundary condition for the electric potential at the membrane, originally developed for electrochemical systems. Within such a framework, corrections to the elastic moduli of the membrane are obtained, which arise from charge accumulation in the Debye layers due to capacitive effects and electric currents through the membrane and can lead to an undulation instability of the membrane. The fluid flow surrounding the membrane is also calculated, which clarifies issues regarding these flows sharing many similarities with flows produced by induced charge electro-osmosis (ICEO). Nonequilibrium steady states of the membrane and of the fluid can be effectively described by this method. It is both simpler, due to the zero thickness approximation which is widely used in the literature on fluid membranes, and more general than previous approaches. The predictions of this model are compared to recent experiments on supported membranes in an electric field.

The electrical properties of the cellular membrane are important for ion transport across cells and electrophysiology. Plasma membranes also resist bending and stretching, and mechanical properties of the membrane influence cell shape and forces in membrane tethers pulled from cells. There exists a coupling between the electrical and mechanical properties of the membrane. Previous work has shown that applied voltages can induce forces and movements in the lipid bilayer. We present a theory that computes membrane bending deformations and forces as the applied voltage is changed. We discover that electromechanical coupling in lipid bilayers depends on the voltage-dependent adsorption of ions into the region occupied by the phospholipid head groups. A simple model of counter-ion absorption is investigated. We show that electromechanical coupling can be measured using membrane tethers and we use our model to predict the membrane tether tension as a function of applied voltage. We also discuss how electromechanical coupling in membranes may influence transmembrane protein function.

A system for studying biological effect of radio frequency electromagnetic field was developed. The system can form an area where electromagnetic wave with large frequency range is well distributed. The strength of electromagnetic wave was measured easily. Electromagnetic wave in the system did not have effect on environment. The sensitivity of spinach chloroplast membrane to low intensity electromagnetic radiation of 300 MHz under power density of 5 mW x cm(-2) was studied by the spectral analysis method of fluorescence of 8-anilino-1-naphthalene-sulfonic acid (ANS) and the changes in chlorophyll a (Chla) fluorescence parameters of spinach chloroplast membrane. The result showed that the position of spectrum of ANS fluorescence of spinach chloroplast membrane did not change, but the intensity of ANS fluorescence was obviously increased under the action of electromagnetic radiation with power density of 1-5 mW x cm(-2). There was an increase in the intensity of ANS fluorescence with the increase in electromagnetic radiation. The increase of ANS fluorescence of spinach chloroplast membrane showed that low level electromagnetic field induced the decrease in fluidity of chloroplast membrane compared with control experiment. The cause of the change in the fluidity could be related to the polarization of chloroplast membrane under the electromagnetic field. The analysis of Chla fluorescence parameters of spinach chloroplast membrane indicated that low level electromagnetic field of 300 MHz made the fluorescence parameters F0 and F(VI/)F(V) decrease, and F(V)/Fo, Fv/F(m) and deltaF(V)/T increase. It was showed that low level electromagnetic field caused the change of non-active center of photosystem II of spinach chloroplast membrane to active center and the increase in potential active and photochemical efficiency of PSII, and promoted the transmit process of electron in photosynthesis of chloroplast membrane of photosynthesis cell in spinach leaf. The study confirmed that low level electromagnetic field has non--thermal effects on photosynthesis system of spinach chloroplast membrane. The cell in spinach leaf can keep the photosynthesis through the change in heterogeneity of photosystem II and adapt to the environment of electromagnetic radiation increase.

Electric-field induced changes in structure and conductivity of supported bilayer lipid membranes (SLM) have been studied at submicroscopic resolution using atomic force microscopy and electrochemical impedance spectroscopy. The SLMs are formed on gold surfaces modified with mixed self-assembled monolayers of a cholesterol-tether and 6-mercaptohexanol. At applied potentials of < or =-0.25 V versus standard hydrogen electrode, the conductance of the SLM increases and membrane areas of <150 nm in size are found to elevate from the surface up to 15 nm in height. To estimate the electric field experienced by the lipid membrane, electrowetting has been used to determine the point of zero charge of a 6-mercaptohexanol-modified surface (0.19 +/- 0.13 V versus standard hydrogen electrode). The effects of electric fields on the structure and conductance of supported membranes are discussed.

Liposome size is a vital parameter of many quantitative biophysical studies. Sonication, or exposure to ultrasound, is used widely to manufacture artificial liposomes, yet little is known about the mechanism by which liposomes are affected by ultrasound. Cavitation, or the oscillation of small gas bubbles in a pressure-varying field, has been shown to be responsible for many biophysical effects of ultrasound on cells. In this study, we correlate the presence and type of cavitation with a decrease in liposome size. Aqueous lipid suspensions surrounding a hydrophone were exposed to various intensities of ultrasound and hydrostatic pressures before measuring their size distribution with dynamic light scattering. As expected, increasing ultrasound intensity at atmospheric pressure decreased the average liposome diameter. The presence of collapse cavitation was manifested in the acoustic spectrum at high ultrasonic intensities. Increasing hydrostatic pressure was shown to inhibit the presence of collapse cavitation. Collapse cavitation, however, did not correlate with decreases in liposome size, as changes in size still occurred when collapse cavitation was inhibited either by lowering ultrasound intensity or by increasing static pressure. We propose a mechanism whereby stable cavitation, another type of cavitation present in sound fields, causes fluid shearing of liposomes and reduction of liposome size. A mathematical model was developed based on the Rayleigh-Plesset equation of bubble dynamics and principles of acoustic microstreaming to estimate the shear field magnitude around an oscillating bubble. This model predicts the ultrasound intensities and pressures needed to create shear fields sufficient to cause liposome size change, and correlates well with our experimental data.

ABM (3-aminobenzanthrrone derivative) developed at the Riga Technical University, Riga, Latvia) has been previously shown as a potential probe for determination of the immune state of patients with different pathologies . The fist study (using probe ABM) of peripheral blood mononuclear cells (PBMC) membranes of 97 Chernobyl clean-up workers from Latvia was conducted in 1997. Now we repeatedly examine the same (n = 54) individuals in dynamics. ABM spectral parameters in PBMC suspension, fluorescence anisotropy and blood plasma albumin characteristics were recorded. In 1997 screening showed 5 different patterns of fluorescence spectra, from which in 2007 we obtained only two. These patterns of spectra had never been previously seen in healthy individuals or patients with tuberculosis, multiple sclerosis, rheumatoid arthritis, etc., examined by us. Patterns of ABM fluorescence spectra are associated with membrane anisotropy and conformational changes of blood plasma albumin. We observed that in dynamics 1997-2007 the lipid compartment of the membrane became more fluid while the lipid-protein interface became more rigid. The use of probe ANS and albumin auto-fluorescence allowed show conformational alterations in Chernobyl clean-up workers blood plasma. It is necessary to note that all investigated parameters significantly differ in observed groups of patients. These findings reinforce our understanding that that the cell membrane is a significant biological target of radiation. The role of the membrane in the expression and course of cell damage after radiation exposure must be considered. So ten years dynamic of PBMC membrane characteristics by ABM (spectral shift and anisotropy indexes) in Chernobyl clean-up workers reveal progressive trend toward certain resemblance with those of chronic B-cell lymphoid leukemia.

Liposomes are lipid bilayer-bound micron scale structures critical to therapeutic treatments, biophysical studies, cosmetics, food, constrained volume experiments, and gene transfer. Applying an electric field to separate mixtures of liposomes played a role in their discovery and is still presently used for a variety of processes. Our group has found agreement between models of electric field-induced transport and capillary electrophoresis measurements where the liposomes are described as slightly elongated with the charged lipids migrating to form a local dipole. Here we show much more diverse structures that cannot be accounted for in these models. A variety of morphologies emerge, from individual liposomes being stretched into nanotubules several microns in length to long-range organized assemblies of liposomes over tens of microns. Based in this result, existing theories for electromigration of soft particles need to be re-addressed. Also, the formation of nanoscale lipid tubules suggests that unique structures for bionanoengineering can be fabricated. Much higher intrinsic fields than those applied here are observed in biology that suggests mechanical electrostatic interaction may play role in shape and function of individual biological membranes and networks of membrane-bound structures.

We investigate the effect on biomembrane mechanical properties due to the presence an external potential for a nonconductive incompressible membrane surrounded by different electrolytes. By solving the Debye-Hückel and Laplace equations for the electrostatic potential and using the relevant stress-tensor we find (1) in the small screening length limit, where the Debye screening length is smaller than the distance between the electrodes, the screening certifies that all electrostatic interactions are short range and the major effect of the applied potential is to decrease the membrane tension and increase the bending rigidity; explicit expressions for electrostatic contribution to the tension and bending rigidity are derived as a function of the applied potential, the Debye screening lengths, and the dielectric constants of the membrane and the solvents. For sufficiently large voltages the negative contribution to the tension is expected to cause a membrane stretching instability. (2) For the dielectric limit, i.e., no salt (and small wave vectors compared to the distance between the electrodes), when the dielectric constant on the two sides are different the applied potential induces an effective (unscreened) membrane charge density, whose long-range interaction is expected to lead to a membrane undulation instability.

Electroporation uses electric pulses to promote delivery of DNA and drugs into cells. This study presents a model of electroporation in a spherical cell exposed to an electric field. The model determines transmembrane potential, number of pores, and distribution of pore radii as functions of time and position on the cell surface. For a 1-ms, 40 kV/m pulse, electroporation consists of three stages: charging of the cell membrane (0-0.51 micros), creation of pores (0.51-1.43 micros), and evolution of pore radii (1.43 micros to 1 ms). This pulse creates approximately 341,000 pores, of which 97.8% are small ( approximately 1 nm radius) and 2.2% are large. The average radius of large pores is 22.8 +/- 18.7 nm, although some pores grow to 419 nm. The highest pore density occurs on the depolarized and hyperpolarized poles but the largest pores are on the border of the electroporated regions of the cell. Despite their much smaller number, large pores comprise 95.3% of the total pore area and contribute 66% to the increased cell conductance. For stronger pulses, pore area and cell conductance increase, but these increases are due to the creation of small pores; the number and size of large pores do not increase.

Oxidation decomposition of unsaturated fatty acids with singlet oxygen generated from a photosensitizing agent was investigated in liposome bilayer membranes under a light irradiation condition. The liposome of which the bilayer membrane was composed of L-alpha-dipalmitoylphosphatidylcholine (DPPC), protoporphyrin IX (PpIX), and an unsaturated fatty acid (oleic acid, linoleic acid, alpha-linolenic acid, or arachidonic acid) were prepared with Bangham's method. In irradiating the liposome dispersion with light ranged from 550 to 750 nm, the unsaturated fatty acid was decomposed through an oxidation reaction with singlet oxygen. The decomposition rate constant was obeyed as the following order: arachidonic acid > oleic acid > alpha-linolenic acid > linoleic acid. This result indicates that oleic acid is readily degraded despite its lower unsaturated degree. In addition, micropolarity and microfluidity of the hydrocarbon region in the liposome bilayer membrane including the unsaturated fatty acid and PpIX decreased with an increase in light irradiation time. These findings suggest that interaction among the hydrocarbon chains of DPPC in the liposome bilayer membrane is promoted by migration of the oxidized unsaturated fatty acid from the hydrocarbon region, leading to form close-packed and well-ordered orientation of the hydrocarbon chains.

Interest in using ultrasound energy in wound management and intracellular drug delivery has been growing rapidly. Development and treatment optimization of such non-diagnostic applications requires a fundamental understanding of interactions between the acoustic wave and phospholipid membranes, be they cell membranes or liposome bilayers. This work investigates the changes in membrane permeation (leakage mimicking drug release) in vitro during exposure to ultrasound applied in two frequency ranges: "conventional" (1 MHz and 1.6 MHz) therapeutic ultrasound range and low (20 kHz) frequency range. Phospholipids vesicles were used as controllable biological membrane models. The membrane properties were modified by changes in vesicle dimensions and incorporation of poly(ethylene glycol) i.e. PEGylated lipids. Egg phosphatidylcholine vesicles with 5 mol% PEG were prepared with sizes ranging from 100 nm to 1 microm. Leakage was quantified in terms of temporal fluorescence intensity changes observed during carefully controlled ultrasound ON/OFF time intervals. Custom-built transducers operating at frequencies of 1.6 MHz (focused) and 1.0 MHz (unfocused) were used, the I(spta) of which were 46.9 W/cm2 and 3.0 W/cm2, respectively. A commercial 20 kHz, point-source, continuous wave transducer with an I(spta) of 0.13 W/cm2 was also used for comparative purposes. Whereas complete leakage was obtained for all vesicle sizes at 20 kHz, no leakage was observed for vesicles smaller than 100 nm in diameter at 1.6 or 1.0 MHz. However, introducing leakage at the higher frequencies became feasible when larger (greater than 300 nm) vesicles were used, and the extent of leakage correlated well with vesicle sizes between 100 nm and 1 microm. This observation suggests that physico-chemical membrane properties play a crucial role in ultrasound mediated membrane permeation and that low frequency (tens of kilohertz) ultrasound exposure is more effective in introducing permeability change than the "conventional" (1 MHz) therapeutic one. The experimental data also indicate that the leakage level is controlled by the exposure time. The results of this work might be helpful to optimize acoustic field and membrane parameters for gene or drug delivery. The outcome of this work might also be useful in wound management.

In this article, we report for the first time unusual shape changes of vesicles subjected to strong electric pulses in salt solutions of low concentration. The electric field is created by two parallel electrodes between which the vesicle solution is located. Surprisingly, the vesicles assume cylindrical shapes during the pulse. These deformations are short-lived (their lifetime is approximately 1 ms) and occur only in the presence of salt outside the vesicles, irrespective of their content. When the solution conductivities inside and outside are the same, vesicles with square cross section are observed. Using a fast digital camera, we were able to record these deformations and study the vesicle shape dynamics. The aims of this article are to report the new vesicle morphologies and their dynamics and to provoke theoretical work in this direction.

The recent applications of nanosecond, megavolt-per-meter electric field pulses to biological systems show striking cellular and subcellular electric field induced effects and revive the interest in the biophysical mechanism of electroporation. We first show that the absolute rate theory, with experimentally based parameter input, is consistent with membrane pore creation on a nanosecond time scale. Secondly we use a Smoluchowski equation-based model to formulate a self-consistent theoretical approach. The analysis is carried out for a planar cell membrane patch exposed to a 10 ns trapezoidal pulse with 1.5 ns rise and fall times. Results demonstrate reversible supraelectroporation behavior in terms of transmembrane voltage, pore density, membrane conductance, fractional aqueous area, pore distribution, and average pore radius. We further motivate and justify the use of Krassowska's asymptotic electroporation model for analyzing nanosecond pulses, showing that pore creation dominates the electrical response and that pore expansion is a negligible effect on this time scale.

Much attention has recently been paid to the study of positively charged polypeptides as a possible carrier for therapeutic protein or DNA delivery to cells. In this study, we have investigated the translocation of positively charged copoly(Lys/Tyr) (MW=72000, DP=385) across lipid membranes constituted from egg-phosphatidylcholine (EPC), dioleoyl-phosphatidylethanolamine (DOPE), as well as soybean phospholipids (SBPL) using zeta potential method, circular dichroism spectroscopy (CD), electrophysiology technique, fluorescence spectroscopy, and confocal laser scanning microscopy. Results of zeta potentials show that copoly(Lys/Tyr) associate with lipid membranes and become gradually saturated on the membranes either hydrophobically or electrostatically or both. CD studies demonstrate that the copoly(Lys/Tyr) takes and remains beta-sheet conformation during its interaction with liposome membranes, indicating that the translocation process should be carpet-mode like. Data from the electrophysiology technique reveal that positively charged copoly(Lys/Tyr) can cause transmembrane currents under an applied voltage, confirming its transfer across lipid membranes. Fluorescence spectroscopy results display a three-step mechanism of translocation across membrane: adsorption, transportation, and desorption, which has been verified by results from confocal laser scanning microscopy. We provided the first direct observation that the positively charged polypeptides, copoly(Lys/Tyr), can translocate through SBPL and EPC/DOPE lipid bilayer membranes. In addition, we found that the translocation efficiency of copoly(Lys/Tyr) was higher on the EPC/DOPE lipid membrane than on the SBPL lipid membrane.

We studied by X-ray reflectivity the behaviour of fully hydrated solid-supported lipid multilayers under the influence of a transverse electric field, under conditions routinely used in the electroformation process. The kinetics of sample loss (unbinding) was measured as a function of the amplitude and frequency of the applied field by monitoring the integrated intensity of the Bragg peaks. We also performed a time-resolved analysis of the intensity of the first Bragg peak and characterized the final state of the sample.

While conformational flexibility of proteins is widely recognized as one of their functionally crucial features and enjoys proper attention for this reason, their elastic properties are rarely discussed. In ion channel studies, where the voltage-induced or ligand-induced conformational transitions, gating, are the leading topic of research, the elastic structural deformation by the applied electric field has never been addressed at all. Here we examine elasticity using a model channel of known crystal structure-Staphylococcus aureus alpha-hemolysin. Working with single channels reconstituted into planar lipid bilayers, we first show that their ionic conductance is asymmetric with voltage even at the highest salt concentration used where the static charges in the channel interior are maximally shielded. Second, choosing 18-crown-6 as a molecular probe whose size is close to the size of the narrowest part of the alpha-hemolysin pore, we analyze the blockage of the channel by the crown/K(+) complex. Analysis of the blockage within the framework of the Woodhull model in its generalized form demonstrates that the model is able to correctly describe the crown effect only if the parameters of the model are considered to be voltage-dependent. Specifically, one has to include either a voltage-dependent barrier for crown release to the cis side of the channel or voltage-dependent interactions between the binding site and the crown. We suggest that the voltage sensitivity of both the ionic conductance of the channel seen at the highest salt concentration and its blockage by the crown reflects a field-induced deformation of the pore.

The surface stress on the real shape (biconcave disklike) of an erythrocyte under laser irradiation is theoretically studied according to the finite-difference time-domain (FDTD) method. The distribution of the surface stresses depends on the orientation of erythrocytes in the laser beam. Typically when the erythrocyte was irradiated from the side direction (the laser beam was perpendicular to the normal of the erythrocyte plane), the surface stresses were so asymmetrical and nonuniform that the magnitude of the surface stress on the back surface was three times higher than that on the front surface, and the highest-to-lowest ratio of the stress reached 16 times. For comparison, the surface stress was also calculated according to the ray optics (RO) method. The tendency of the stress distribution from the RO calculation was roughly similar to that of the FDTD method. However the RO calculation produced some unphysical results, such as the infinite stress on some surface region and the zero stress on the most parts of the erythrocyte surface, which is due to the neglecting of light diffraction. The results obtained from the FDTD calculation are believed quantitatively reliable, because the FDTD method automatically takes into account of the diffraction and interference effects of the light wave. Thus, the FDTD method is more suitable than the RO method for the stress study of erythrocytes.

We determine the equations governing the equilibrium shape of an axially symmetric charged fluid membrane under the action of an external field. We consider that the charges are free to diffuse along the membrane, and we neglect the effect of screening counterions. By numerically integrating these equations for a membrane spread across a hole by a constant tension, we show that there exists a threshold electric field above which an infinitely long tube can be pulled. The threshold field for pulling a tube decreases as the surface charge density of the membrane increases, reaching zero at a finite critical value. Above this critical density of charge, the membrane spontaneously buds, in the absence of externally applied fields, because of the electrostatic repulsion of its charges.

The material properties of biomembranes can be measured by forming a tether, a thin bilayer tube that extends from the membrane surface. Recent experiments have demonstrated that the force required to maintain a tether is sensitive to the transmembrane potential. As a first approach towards understanding this phenomenon, a thermodynamic analysis of the influence of electrical fields on tether formation from an aspirated lipid vesicle is developed. The analysis considers contributions from Maxwell stresses as well as two forms of electromechanical coupling: coupling between the electric field and curvature strain (flexoelectric coupling) and between the electric field and areal strain (piezoelectric coupling). Predictions of equilibrium tether conformations are obtained numerically. For expected values of the dimensionless coupling parameters, flexoelectric coupling alters the force required to form a tether of a given length, while piezoelectric coupling and Maxwell forces do not greatly change the force versus tether length behavior. The results of this analysis indicate that tether experiments have the potential to characterize electromechanical coupling in both synthetic and cellular membranes.

The anti-malarial drug chloroquine (CQ) is also thought to be a potential radiation sensitizer. To gain a better understanding of how the lysomotropic CQ can potentiate the effects of ionizing radiation, we investigated the effects of CQ on lysosomal and mitochondrial membrane stability, the subcellular localization of ceramide, plasma membrane permeability, and the mode of cell death in response to irradiation. We found that CQ accumulated in the lysosomes and thus lysosomal volumes increased. As a result, both the lysosomal and plasma membranes were destabilized. After 7 Gy irradiation, most ceramide was associated with the lysosomes in the cells treated with CQ but not in the CQ-untreated control. The elevated levels of ceramide in the lysosomes of the CQ-treated cells appeared to further destabilize the lysosomal and plasma membranes of the cell. Both CQ-treated and -untreated cells had approximately the same rate of cell death by apoptosis after 7 Gy irradiation (P > 0.05, ns). However, in contrast to the CQ-untreated control, the CQ-treated cells underwent massive cell death by necrosis at 24-48 h after irradiation (P < 0.05). Taken together, our data support the idea that the increase in cytotoxic effects by the combination of CQ and radiation is due to radiation-mediated apoptosis and CQ-mediated necrosis.

A combined MD simulator and time dependent Laplace solver are used to analyze the electrically driven phosphatidylserine externalization process in cells. Time dependent details of nanopore formation at cell membranes in response to a high-intensity (100 kV/cm), ultrashort (10 ns) electric pulse are also probed. Our results show that nanosized pores could typically be formed within about 5 ns. These predictions are in very good agreement with recent experimental data. It is also demonstrated that defect formation and PS externalization in membranes should begin on the anode side. Finally, the simulations confirm that PS externalization is a nanopore facilitated event, rather than the result of molecular translocation across the trans-membrane energy barrier.

The combination of inorganic semiconductor nanocrystals, also called quantum dots (QDs), with biological materials has recently attracted considerable interest since the QDs can be used as superior fluorescent labels. Here, we report on CdSe QD initiated current bursts in lipid bilayer membranes on application of a bias voltage. The current bursts observed resemble those produced by the peptaibol class of antibiotics such as alamethicin and trichorzins. The current fluctuations are dependent on the bias voltage and on the concentration of the QD applied to the membrane. Our data suggest that QDs with intrinsic dipole moments similar to alamethicin can be controlled by an external electric field, which creates a torque resulting in the insertion into the lipid membrane.

Steadily growing use of electromagnetic fields, especially in conjunction with wireless communication systems, has led to increasing public concern about possible health effects of electromagnetic radiation. However, besides the well-known thermal effect of electromagnetic fields on biological tissue, there is no clear evidence of further athermal interaction mechanisms with biological systems. The present study was designed to determine the changes in bilayer permeability in egg lecithin multilamellar vesicles after exposure to 900 MHz microwave radiation for a period of 5 h. Specific absorption rate (SAR) of the radiation for the investigated liposome sample was found to be 12 +/- 1 W/kg. Liposomal changes in permeability were monitored using a light scattering technique. Optical anisotropy of the liposome sample decreased dramatically upon exposure to microwave radiation, indicating structural changes in acyl chain packing. IR and NMR ((1)H NMR) studies, which have been employed to reveal structural alterations in microwave, exposed vesicles showed an increased damage upon exposure to microwave. The changes observed in the (1)H NMR spectrum of the microwave exposed sample indicated hydrolysis of carboxylic and phosphoric esters. IR study showed conformational changes in the acyl chains of the lipids upon microwave exposure. However, both IR and (31)P NMR did not show any appreciable changes in the head group part of the lipids.