Selective Membrane Permeability Research Articles

Advantages of expanded hemodialysis (HDx) over standard hemodialysis

Chronic kidney disease leads to the accumulation of a wide range of uremic toxins. Negative effects of uremic toxins are most likely due to the combined effects of many uremic solutes, including small molecules, middle molecules, and soluble protein-linked substances. Large and medium-sized molecules are directly associated with chronic inflammation and adverse effects, including major cardiovascular risks and consequently poor prognosis.
 Recent advances in chemical composition and new production techniques led to improved biocompatibility and selective permeability of dialysis membranes. Specifically, the creation of a new class of membranes provided the possibility to improve the clearance of medium to high molecular weight (MW) solutes (i.e. uremic toxins in the range of 5–50 kDa).
 The new HDx therapy (expanded HD) is the next evolution in hemodialysis, as it effectively targets the removal of large middle molecules. The HDx therapy is enabled by the THERANOVA dialyzer featuring an innovative membrane that combines a higher permeability than regular high-flux dialyzers with effective selectivity for large proteins.
 Expanded hemodialysis is an advanced therapy targeting large and medium-sized molecules that are currently not possible to remove by modern dialysis methods including traditional hemodialysis (HD) and hemodiafiltration (HDF). HDx became possible due to THERANOVA, a new dialyzer with an innovative membrane. The THERANOVA-based HDx provides a great new opportunity for dialysis patients, providing unique high-efficiency hemodialysis with the usage of already available infrastructure and standard HD workflows.

Survival of membrane-damaged Escherichia coli in a cytosol-mimicking solution

Selective permeability of cell membrane is critically important for cell survival. The damage caused to cell membrane by pore-forming antimicrobial peptides may result in the loss of selective permeability and leakage of intracellular molecules, eventually leading to cell death. Here, we examined whether the membrane-damaged Escherichia coli cells survive in a cytosol-mimicking solution (CMS), which compensates for the lethal leakage of intracellular molecules. We prepared a CMS comprising 34 low molecular weight compounds from the cytosol and found that the cells were able to grow in CMS even in the presence of a pore-forming peptide, melittin. We confirmed that the melittin-treated cells lost selective membrane permeability by staining with membrane-impermeable dyes, propidium iodide and SYTOX green. Some stained cells maintained the colony formation ability in CMS. These results provide an evidence that E.coli cells can at least partially survive in the CMS even after the temporary impairment of membrane selective permeability. This study demonstrates a technique that allows temporal loss of the selective permeability of the cell membrane while maintaining the viability of cells that may be useful for the introduction of membrane-impermeable molecules into E.coli cells.

Proanthocyanidin Interferes with Intrinsic Antibiotic Resistance Mechanisms of Gram-Negative Bacteria.

Antibiotic resistance is spreading at an alarming rate among pathogenic bacteria in both medicine and agriculture. Interfering with the intrinsic resistance mechanisms displayed by pathogenic bacteria has the potential to make antibiotics more effective and decrease the spread of acquired antibiotic resistance. Here, it is demonstrated that cranberry proanthocyanidin (cPAC) prevents the evolution of resistance to tetracycline in Escherichia coli and Pseudomonas aeruginosa, rescues antibiotic efficacy against antibiotic‐exposed cells, and represses biofilm formation. It is shown that cPAC has a potentiating effect, both in vitro and in vivo, on a broad range of antibiotic classes against pathogenic E. coli, Proteus mirabilis, and P. aeruginosa. Evidence that cPAC acts by repressing two antibiotic resistance mechanisms, selective membrane permeability and multidrug efflux pumps, is presented. Failure of cPAC to potentiate antibiotics against efflux pump‐defective mutants demonstrates that efflux interference is essential for potentiation. The use of cPAC to potentiate antibiotics and mitigate the development of resistance could improve treatment outcomes and help combat the growing threat of antibiotic resistance.

Polymersome nanoreactors with tumor pH-triggered selective membrane permeability for prodrug delivery, activation, and combined oxidation-chemotherapy

Therapeutic nanoreactors are currently emerging as promising nanoplatforms to in situ transform inert prodrugs into active drugs. Nevertheless, it is still challenging to engineer a nanoreactor with balanced key features of tunable selective membrane permeability and structural stability for prodrug delivery and activation in diseased tissues. Herein, we present a facile strategy to engineer a polymersome nanoreactor with tumor-specific tunable membrane permeability to load both hydrophobic phenylboronic ester-caged anticancer prodrugs (e.g., camptothecin or paclitaxel prodrug) and hydrophilic glucose oxidase (GOD) in the membranes and cavities, respectively. The nanoreactors maintain inactive during blood circulation and in normal tissues. Upon accumulation in tumors, the mild acidic microenvironment triggers selective membrane permeability to allow small molecules (glucose and O2) to diffuse across the membrane and react under the catalysis of GOD. The massively generated H2O2 triggers in situ transformation of innocuous prodrugs into toxic parental drugs through cleavage of the self-immolative degradable caging groups. The developed system showed significantly enhanced antitumor efficacy by H2O2 production and prodrug activation via combined oxidation-chemotherapy. The well-devised polymersome nanoreactors with tumor-pH-tunable membrane permeability to coload H2O2-responsive prodrug and GOD represent a novel strategy to realize prodrug delivery and activation for enhanced therapeutic efficacy with low side toxicity.

Chlorinated emodin as a natural antibacterial agent against drug-resistant bacteria through dual influence on bacterial cell membranes and DNA

The rise in infections caused by drug-resistant pathogens and a lack of effective medicines requires the discovery of new antibacterial agents. Naturally chlorinated emodin 1,3,8-trihydroxy-4-chloro-6-methyl-anthraquinone (CE) from fungi and lichens was found to markedly inhibit the growth of Gram-positive bacteria, especially common drug-resistant bacterial strains, including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecium (VRE). CE was confirmed to cause significant potassium leakage, cell membrane depolarization and damage to the selective permeability of cell membranes in bacterial cells, resulting in bacterial cell death. In addition, CE was shown to have a strong electrostatic interaction with bacterial DNA and induce DNA condensation. Thus, CE is a promising natural antibacterial pharmacophore against Gram-positive bacteria, especially common drug-resistant MRSA and VRE isolates, with a dual antibacterial mechanism that damages bacterial cell membranes and DNA.

A study of the mechanism for ultrafiltration isolation of sodium lignosulfonate from aqueous solutions with track membranes

Ultrafiltration of aqueous sodium lignosulfonate solutions through track membranes with 30-nm pores has been studied. Membrane selectivity has been investigated as depending on concentrations of sodium lignosulfonate (10, 20, 50, and 100 mg/dm3) and NaCl electrolyte (10–3, 10–2, and 10–1 M). Ultrafiltration of lignosulfonate solutions has been shown to be associated with the “charge-related” mechanism of membrane selective permeability. Membrane selectivity decreases with a rise in the concentrations of lignosulfonate and NaCl, as well as the degree of filtrate extraction.

In-situ crosslinking of anion exchange membrane bearing unsaturated moieties for electrodialysis

Abstract This study reports the preparation of the in-situ crosslinked anion exchange membrane that does not require the use of crosslinkers or catalysts. A polyelectrolyte bearing flexible unsaturated side chains was synthesized via the Menshutkin reaction with poly(2,6-dimethyl-1,4-phenylene oxide) and N,N-Dimethylvinylbenzylamine. The crosslinked derivatives were then prepared by the thermal crosslinking of the unsaturated side chains during the membrane formation process. This approach incorporates crosslinks, bearing quaternary ammonium cations, between the polymer chains in order to mitigate against excessive water swelling, and to enable the high ion contents to provide favorable low resistance of ion transport. Additionally, the resultant dense crosslinked network has the additional advantage of improving anion selective permeability of membrane. When being applied in ED application, the crosslinked membranes exhibit much higher desalination efficiency than commercial Neosepta AMX membrane, suggesting its potential application in ED.

Abstract 209: A quantitative analysis of paclitaxel-induced mitotic catastrophe of MDA-MB-231 cells by high frequency ultrasound

Abstract In recent years, high-frequency ultrasound (HFUS) has shown promise of non-invasively detecting tumor death in response to chemotherapy. However, those studies have been limited to ultrasound B-mode and immunohistochemical image comparison over extended periods of time (≥24 hours). The purpose of this study was to evaluate the relationship of quantified HFUS spectral parameters to the dynamics of tumor cell death in MDA-MB-231 cell samples exposed to paclitaxel chemotherapy. Several ultrasound parameters were investigated, including the, attenuation, spectral slope, spectral y-intercept, midband fit, estimated scatterer diameter and estimated scatterer concentration. Changes in these spectral-based parameters were evaluated in their capacity to respond to various cell death events, including mitochondrial depolarization, caspase activation, phosphatidylserine exposition, and membrane selective permeability compromise, as determined by flow cytometry analysis. Standard histology and transmission electron microscopy (TEM) permitted further investigation of possible candidates responsible for the changes detected using ultrasound. Based on TEM, negative TUNEL staining, and cell cycle analysis it was found that paclitaxel at 1mM induces mitotic catastrophe as the main cell death modality. The spectral slope correlated strongly (r2 = 0.89) with the percentage of cells arrested at the G2/M checkpoint and exhibited an opposite trend to that of systems undergoing classical apoptosis, suggesting that it may be a prime biophysical marker for differentiating modalities of tumor cell death. Midband fit increases through time suggested an increase in the concentration of acoustic scatterers. The formation of condensed chromatin condensates of a 1 micron or greater diameter in the course of paclitaxel-induced mitotic catastrophe, as revealed by TEM, were hypothesized to act as large intracellular scatterers and correlated with the increase in ultrasound midband fit. Midband fit showed the strongest correlation of all parameters (r2 = 0.99) when plotted against the percentage of the cell population expected to possess these scattering structures, establishing the first quantitative correlation of ultrasound parameters to a cell death index. These findings support that HFUS spectral parameters may be used to quantify the degree of cell death and predict the efficacy of chemotherapeutic treatment within a short post-treatment timeframe. Citation Format: Maurice M. Pasternak, Gregory J. Czarnota. A quantitative analysis of paclitaxel-induced mitotic catastrophe of MDA-MB-231 cells by high frequency ultrasound. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 209. doi:10.1158/1538-7445.AM2015-209

The Dangers of Dental Amalgam

researched mercury poisoning and identified through his research that silver amalgam fillings in the mouth were a source of mercury vapor. More recently, many studies reported that amalgam may constitute potential toxic hazards to patients through mercury release and absorption, surface corrosion, and the reaction of released mercury with residual alloy particles to form additional inter metallic compounds. Furthermore, mercury may migrate gradually from an amalgam restoration into the enamel, dentin, pulp tissues, and adjacent gingival tissue where it accumulates [1]. Increased mercury levels in the gingiva adjacent to sub gingival amalgam restorations have been reported. In addition, fine amalgam particles may become accidentally embedded in the soft tissues of the mouth, most commonly the gingiva, when they are abraded by high speed rotary instruments, during the removal of the amalgam fillings and preparation of crowns over amalgam cores. Moreover, this can occur when amalgam is used as a retrograde root filling material, and produces tattoo [2]. Examinations of tissue biopsies from both human and experimental animal lesions by light, electron microscopy and energy dispersive x-ray micro-analysis have shown that the small particles of amalgam undergo progressive degradation within phagocytic cells, with a subsequent redistribution of their constituted elements. Fine secondary particles containing silver become widely distributed in tissues, producing the characteristic tattooing, thereafter, mercury is released into surrounding soft tissues [3]. Amalgam debris is able to activate immunologic adaptive reaction where tissue reaction to amalgam tattoo depends on amalgam particles size and composition. While copper and zinc are rapidly lost from the area of the tattoo, mercury and tin are lost more slowly and finally silver remains permanent in the tissues. The residual elements of amalgam tattoo develop a noxious effect within soft tissues, where mercury passes from the tissue fluid into the blood stream and accumulates in the kidneys [4]. Exposure to large amounts of metallic mercury vapor, compared to small amounts released from amalgam fillings, causes certain symptoms that may include cough, fever, skin rashes, tremors, difficulty in muscle coordination and walking, renal abnormalities, and memory loss [5]. Patients allergic to mercury used in dental clinics may experience itching, hives, local soreness, burning, and dryness of throat and mouth. Several studies reported a strong relationship between the total surface areas of amalgam restorations and blood or urine mercury levels [6]. Heintze et al. [7] reported in vitro formation of methyl mercury from a conventional and mixed amalgam by the action of streptococcus sanguis, mutans and mitior in pure cultures, suggesting the possibility of methyl mercury formation in the mouth if amalgam is present. Mercury compounds have high affinity to proteins, amino acids, purine, pyrimidine and nucleic acid [8]. Mercury toxicity was explained by its interaction with these molecules through sulfhydryl groups, and disulfide bonds on cell membrane; thus, mercury compounds alter the selective permeability of cell membranes for ions and nutrients and possibly block more specific membrane transport processes. Fetal exposure may follow previous mercury uptake by a pregnant mother where mercury compounds, as most other substances, may pass through the placenta to the fetal circulation [9]. Fetal toxicity occurs following certain degrees of mercury compounds accumulation within the central nervous system. Although studies shown that little mercury compounds penetrate to fetal tissues, embryopathic effects of these compounds have been demonstrated as growth retardation, subcutaneous edema, exencephaly, anophthalmia, and teratogenic effects, such as cleft lip and palate, ribs fusion and syndactylia and embryopathic death. Therefore, the safety of dental amalgam-released-mercury during pregnancy became questionable. Data from Soussa E [10] study shows a positive correlation between blood mercury levels in mothers and their oral tissue response; however, the negative impact of mercury on oral tissues is regarded to have taken place during pregnancy in relation to elevated blood mercury levels of mothers. Monitoring the blood mercury following dental amalgam restorations during pregnancy is recommended to avoid its harmful effect on the fetus. The World Health Organization (WHO) has stated that there is no safe level of mercury. That means that no amount of mercury is safe, not even one atom. Even if enough mercury hasn’t accumulated to manifest a symptom directly or indirectly related to chronic mercury poisoning, The World Health Organization, O.S.H.A., N.I.O.S.H., etc, all agree that mercury is an environmental poison and have established specific occupational exposure limits. The Environment Protection Agency has declared amalgam removed from teeth to be a toxic waste. Even the American Dental Association warns that amalgam filling material is hazardous to dental office personnel, Editorial

Selective membrane permeability and peroxidase activity response of lettuce and arugula irrigated with cyanobacterial-contaminated water

Irrigation with microcystins-contaminated water has been shown to cause oxidative stress and negatively affect the development of vegetables. However, the effect of non-microcystins producing cyanobacteria on vegetables is yet to be investigated. In this study, the effects of microcystin-producing (MC+) and non-microcystin-producing (MC−) cyanobacterial (Microcystis aeruginosa) extracts on lettuce (Lactuca sativa L.) and arugula (Erucasativa Mill.) were investigated. Chlorophyll production, peroxidase (POD) activity and selective membrane permeability of the vegetables were monitored after exposure to 0.6–12.5 µg L−1 MC+ for 15 days. For MC− extracts, an equivalent biomass of each MC+ extract concentration per total MCs concentration was also applied to the vegetables for 15 days. In arugula, exposure to both toxic and non-toxic cyanobacterial extracts resulted in higher POD activity than the control. However, in lettuce plants, significantly lower POD activities were recorded in the presence of MC+ and MC− extracts. Although both crude (MC+ and MC−) extracts increased plasma membrane electrical conductivity of the vegetables, the effect of MC+ extract was higher. Chlorophyll content of both vegetables was not significantly influenced by MC+ and MC− extracts. The results of the present study show that vegetables have variable responses to MC+ and MC− extracts of M. aeruginosa. Therefore, care must be taken to avoid the excessive use of M. aeruginosa contaminated water to irrigate vegetables, regardless of their MCs production potential.

Cryocapacitation and Fertility of Cryopreserved Semen

Cryopreservation of semen is the most widely applied reproductive biotechnological tool used for rapid genetic improvement of livestock through artificial insemination, but the process of cryopreservation and thawing inflicts certain damage to spermatozoa plasma membrane and acrosome. This damage includes swelling and breakage of plasma membrane, loss of membrane selective permeability, change in membrane fluidity, leakage and aggregation of phospholipids and protein, reduction in motility and enzyme activity and viability. These spermatozoa exhibit elevated metabolic rates, increased membrane fluidity and permeability and they do not achieve fertilization, they undergo spontaneous acrosome reaction due to an uncontrolled influx of Ca2+. Hence, the fertilizing lifespan of these spermatozoa is limited. Further investigation regarding mechanism involved thereof and the prevention of premature membrane modifications will hopefully lead to the improvement of the fertility of cryopreserved semen.

Introduction of impermeable actin-staining molecules to mammalian cells by optoporation.

The selective insertion of foreign materials, such as fluorescent markers or plasmids, into living cells has been a challenging problem in cell biology due to the cell membrane's selective permeability. However, it is often necessary that researchers insert such materials into cells for various dynamical and/or drug delivery studies. This problem becomes even more challenging if the study is to be limited to specific cells within a larger population, since other transfection methods, such as viral transfection and lipofection, are not realizable with a high degree of spatial selectivity. Here, we have used a focused femtosecond laser beam to create a small transient hole in the cellular membrane (optoporation) in order to inject nanomolar concentrations of rhodamine phalloidin (an impermeable dye molecule for staining filamentous actin) into targeted living mammalian cells (both HEK and primary cortical neurons). Following optoporation, the dye bound to the intracellular actin network and rise in fluorescence intensity was observed. Theoretical dynamics of the dye's diffusion is discussed, and numerical simulations of diffusion time constants are found to match well with experimental values.

Nature of the charged headgroup determines the fusogenic potential and membrane properties of lithocholic acid phospholipids.

Phospholipids play a crucial role in many cellular processes ranging from selective membrane permeability, to membrane fission and fusion, to cellular signaling. Headgroups of phospholipids determine the membrane properties and fusogenicity of these lipids with target cell membranes. We studied the fusogenic and membrane properties of phospholipids possessing unnatural charged headgroups with model membranes using laurdan based membrane hydration studies, DPH based membrane fluidity, and differential scanning calorimetry. We unravel that fusogenicity, membrane hydration, and fluidity of membranes are strongly contingent on the nature of the phospholipid charged headgroup. Our studies unraveled that introduction of bulky headgroups like dimethylamino pyridine induces maximum membrane hydration and perturbations with high fusogenicity as compared to small headgroup based phospholipids. These phospholipids also have the capability of high retention in DPPC membranes. Hydration and fluidity of these phospholipid-doped DPPC membranes are contingent on the nature of the charged headgroup. This study would help in future design of phospholipid based nanomaterials for effective drug delivery.

Low-frequency dielectric dispersion of bacterial cell suspensions

Dielectric spectra of Escherichia coli cells suspended in 0.1–10mM NaCl were measured over a frequency range of 10Hz to 10MHz. Low-frequency dielectric dispersion, so-called the α-dispersion, was found below 10kHz in addition to the β-dispersion, due to interfacial polarization, appearing above 100kHz. When the cells were killed by heating at 60°C for 30min, the β-dispersion disappeared completely, whereas the α-dispersion was little influenced. This suggests that the plasma (or inner) membranes of the dead cells are no longer the permeability barrier to small ions, and that the α-dispersion is not related to the membrane potential due to selective membrane permeability of ions. The intensity of the α-dispersion depended on both of the pH and ionic strength of the external medium, supporting the model that the α-dispersion results from the deformation of the ion clouds formed outside and inside the cell wall containing charged residues.

Modular organization of cardiac energy metabolism: energy conversion, transfer and feedback regulation

To meet high cellular demands, the energy metabolism of cardiac muscles is organized by precise and coordinated functioning of intracellular energetic units (ICEUs). ICEUs represent structural and functional modules integrating multiple fluxes at sites of ATP generation in mitochondria and ATP utilization by myofibrillar, sarcoplasmic reticulum and sarcolemma ion-pump ATPases. The role of ICEUs is to enhance the efficiency of vectorial intracellular energy transfer and fine tuning of oxidative ATP synthesis maintaining stable metabolite levels to adjust to intracellular energy needs through the dynamic system of compartmentalized phosphoryl transfer networks. One of the key elements in regulation of energy flux distribution and feedback communication is the selective permeability of mitochondrial outer membrane (MOM) which represents a bottleneck in adenine nucleotide and other energy metabolite transfer and microcompartmentalization. Based on the experimental and theoretical (mathematical modelling) arguments, we describe regulation of mitochondrial ATP synthesis within ICEUs allowing heart workload to be linearly correlated with oxygen consumption ensuring conditions of metabolic stability, signal communication and synchronization. Particular attention was paid to the structure-function relationship in the development of ICEU, and the role of mitochondria interaction with cytoskeletal proteins, like tubulin, in the regulation of MOM permeability in response to energy metabolic signals providing regulation of mitochondrial respiration. Emphasis was given to the importance of creatine metabolism for the cardiac energy homoeostasis.

Regulation of Mitochondrial Respiration by Different Tubulin Isoforms in Vivo

Studies of regulation of mitochondrial outer membrane selective permeability of cardiac and brain cells in vitro (isolated mitochondria) and in situ (permeabilized cells) condition has revealed remarkable differences between kinetic parameters of respiration activation. This is probably a result of the specific control of voltage dependent anion channel (VDAC) permeability by some cytoskeleton proteins, among them may be some isoforms of tubulin. Our recent results with immunofluorescence and Western blot analysis have shown that possible candidates could be β-tubulin isoforms 2c (IVb) or 4 (IVa). The aim of this study was to construct, express and purify different β-tubulin isoforms and their C-terminal tail truncated recombinants and to investigate their effect on regulation of mitochondrial respiration.Therefore we have designed a GST-tagged β-tubulin isoform constructs to express the recombinant proteins in BL21(DE3)pLys cell line. The proteins were purified in native conditions and utilized to study the kinetics of mitochondrial respiration regulation. The reconstitution experiments with isolated brain mitochondria and GST-TUBB2c or with GST-TUBB4 were carried out. The preliminary results showed that using GST-TUBB2c there were two populations of mitochondria with different properties; the Km value for ADP of the second population of mitochondria was significantly higher, compared to the first population. Therefore, it's possible to conclude that β2c-tubulin is one possible candidate of factor X, which is able to restore the low permeability of VDAC. As the β-tubulin C-terminal tail has been shown to be responsible for selective regulation of VDAC permeability, we have also produced truncated β-tubulin isoforms which lack the C-terminal tail and investigated their effect on mitochondrial respiration. Our results show that β-tubulin 2c isoform is able to restore the diffusion restrictions for ADP which is common for permeabilized cells with oxidative metabolism.

Encapsulation studies and selective membrane permeability properties of self-assembly hollow nanospheres

This paper presents a kind of self-assembled hollow nanosphere for enzyme encapsulation. The enzyme molecules were encapsulated in hollow spheres directly in aqueous solution through the self-assembly of rod-coil Alg-g-PEG and α-CDs complexes. These Alg-g-PEG/α-CD hollow spheres showed semi-permeability which could prevent big enzyme molecules from leaving while allowing small substrates and products to pass through to maintain the enzyme activity. The permeability properties of Alg-g-PEG/α-CD hollow nanospheres were investigated by encapsulating different probes. The results showed that the molar mass cutoff (MMCO) of these hollow nanospheres was between 20 and 40 kDa. The encapsulation capability of Alg-g-PEG/α-CD hollow nanospheres was also investigated, the results indicated a maximal values for L-asparaginase encapsulation. Furthermore, the encapsulation behavior for L-asparaginase showed PEG graft density (GD) dependence.

Pannexin 1 channels mediate ‘find-me’ signal release and membrane permeability during apoptosis

Apoptotic cells release 'find-me' signals at the earliest stages of death to recruit phagocytes. The nucleotides ATP and UTP represent one class of find-me signals, but their mechanism of release is not known. Here, we identify the plasma membrane channel pannexin 1 (PANX1) as a mediator of find-me signal/nucleotide release from apoptotic cells. Pharmacological inhibition and siRNA-mediated knockdown of PANX1 led to decreased nucleotide release and monocyte recruitment by apoptotic cells. Conversely, PANX1 overexpression enhanced nucleotide release from apoptotic cells and phagocyte recruitment. Patch-clamp recordings showed that PANX1 was basally inactive, and that induction of PANX1 currents occurred only during apoptosis. Mechanistically, PANX1 itself was a target of effector caspases (caspases 3 and 7), and a specific caspase-cleavage site within PANX1 was essential for PANX1 function during apoptosis. Expression of truncated PANX1 (at the putative caspase cleavage site) resulted in a constitutively open channel. PANX1 was also important for the 'selective' plasma membrane permeability of early apoptotic cells to specific dyes. Collectively, these data identify PANX1 as a plasma membrane channel mediating the regulated release of find-me signals and selective plasma membrane permeability during apoptosis, and a new mechanism of PANX1 activation by caspases.

Physical–chemical properties of plasma membrane and function of erythrocytes of cosmonauts after long-term space flight

We studied microfluidity and selective ion permeability of plasma membranes and O 2-binding properties of erythrocytes of cosmonauts during early rehabilitation after a long-term space flight (LTSF). Microfluidity of plasma membranes in surface regions was found to undergo a reversible decrease during 13–15 days following LTSF, which was accompanied by a reversible increase in relative cholesterol content. Cosmonauts’ erythrocytes revealed an increased activity of Na/H-exchanger and K Ca -channel as well as a decrease in number of discocytes and increase in number of echinocytes, stomatocytes and knizocytes. Total hemoglobin content as well as oxyhemoglobin content were lowered after the LTSF, while the affinity of hemoglobin to O 2 was advanced. It is suggested that the changes in Hb properties, microfluidity and selective permeability of plasma membranes following the elevated cholesterol content in the membranes can decrease tissue supply with O 2.

A Microfluidic Device For Concentrating High Molecular Weight DNA

Direct Linear Analysis (DLA) technology obtains high content sequence information by optically mapping sequence specific fluorescent tags bound to elongated genomic DNA molecules in shear flows.[1] To facilitate sensitivity and throughput, we have implemented a high molecular weight DNA concentrating system by photopatterning a semi-permeable membrane inside the microfluidic device. This minimizes the fluid volume in which the DNA molecules reside prior to optical mapping leading to decreased read times. The membrane is selectively permeable to buffer ions but not high molecular weight DNA molecules allowing enhanced sample concentration at the membrane surface during electrokinetic transfer. In addition, the semi-permeable membrane allows electrophoretic sample transfer into and throughout the microfluidic device avoiding hydrodynamic induced shear forces that can degrade the integrity of large DNA molecules. The device employs novel microfluidic channel geometries to limit the electric field strength to appropriate levels near the membrane surface to minimize both sample and membrane degradation while maintaining a sufficiently high electric field for rapid sample transfer. Additionally, ion polarization across the membrane due to selective membrane permeability is addressed by active buffer replenishment through devoted channels behind the membrane. This architecture is amenable to integration into electrophoretic systems requiring rapid sample concentration, positioning, and transfer between microfluidic components. This research was supported by the Department of Homeland Security Science and Directorate Technology. [1] Chan et al., Genome Research, 2004, 14:1137.