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PubMed2005

Ocular inflammation alters swelling and membrane characteristics of rat Müller glial cells.

Ocular inflammation is a common cause of retinal edema that may involve swelling of Müller glial cells. In order to investigate whether endotoxin-induced ocular inflammation in rats alters the swelling and membrane characteristics of Müller cells, lipopolysaccharide (LPS; 0.5%) was intravitreally injected. At 3 and 7 days after treatment, hypotonic challenge induced swelling of Müller cell somata that was not observed in non-treated control eyes. Müller cells of LPS-treated eyes displayed a downregulation of inward K(+) currents and upregulation of A-type K(+) currents that was associated with a decreased expression of Kir4.1 protein in retinal slices. The data suggest that ocular inflammation induces alterations of both the swelling characteristics and the K(+) channel expression of Müller cells.

Analysis of Variance↗
PubMed2005

Differential expression of matrix metalloproteinase-1 in vitro corresponds to tissue morphogenesis and quality assurance of cultured skin substitutes.

OBJECTIVE: To determine if matrix metalloproteinase-1 (MMP-1) was involved in the premature degradation of the dermal component in cultured skin substitutes (CSS) prepared with cells from burn patients. METHODS AND RESULTS: CSS 645 and 647 were prepared from clinical human fibroblasts (HF) and keratinocytes (HK) that demonstrated premature degradation of collagen-glycosaminoglycan sponges in vitro. The control CSS were prepared from clinical HF and HK, CSS 648, and a pre-clinical cell strain, CSS 644 that did not degrade the sponges. Surface electrical capacitance measures surface hydration and was significantly higher for CSS 647 from days 9 through 14. MTT (3-[4,5-dimethylthiazol-2-yl]- diphenyltetrazolium bromide) conversion, an indicator of cellular viability was significantly lower for the 6-mm punch biopsies from CSS 645 and 647 at day 15 as compared to control CSS. MMP-1 protein levels measured by ELISA were significantly higher in medium from HF 645 and 647 than controls on the day of CSS inoculation. At day 14 of incubation, the mean MMP-1 concentration was significantly elevated in the medium from CSS 645 and 647 versus the controls, CSS 644 and 648. Western blots, and casein zymography demonstrated the presence of the latent and active forms of MMP-1 in the HF and CSS media, respectively. CONCLUSION: MMP-1 was significantly higher in the media from two of the four HF strains and CSS after a 24 h incubation period. Elevated MMP-1 coincided with premature degradation of the dermal substitute in vitro, and reduced numbers of CSS that met quality assurance standards for clinical transplantation.

Burns↗
PubMed2005

An operator splitting method for solving the bidomain equations coupled to a volume conductor model for the torso.

In this paper we present a numerical method for the bidomain model, which describes the electrical activity in the heart. The model consists of two partial differential equations (PDEs), which are coupled to systems of ordinary differential equations (ODEs) describing electrochemical reactions in the cardiac cells. Many applications require coupling these equations to a third PDE, describing the electrical fields in the torso surrounding the heart. The resulting system is challenging to solve numerically, because of its complexity and very strict resolution requirements in time and space. We propose a method based on operator splitting and a fully coupled discretization of the three PDEs. Numerical experiments show that for simple simulation cases and fine discretizations, the algorithm is second-order accurate in space and time.

Algorithms↗
PubMed2005

The decrease in the presynaptic calcium current is a major cause of short-term depression at a calyx-type synapse.

Repetitive nerve firings cause short-term depression (STD) of release at many synapses. Its underlying mechanism is largely attributed to depletion of a readily releasable vesicle pool (RRP) and a decreased probability of releasing a readily releasable vesicle during an action potential. Which of these two mechanisms is dominant and the mechanism that decreases the release probability remain debated. Here, we report that a decreased release probability is caused by a calcium-induced inhibition of presynaptic calcium channels, particularly P/Q-type channels at the calyx of Held in rat brainstem. This mechanism was the dominant cause of STD in a wide range of stimulation conditions, such as during 2 to 20 action potential-equivalent stimuli (AP-e) at 0.2-30 Hz and after 2 to 20 AP-e at 0.2-100 Hz. Only during > or = 100 Hz AP-e was depletion the dominant mechanism.

Action Potentials↗
PubMed2006

Postnatal development of carotid body glomus cell response to hypoxia.

This study examines developmental changes in CB glomus cell depolarization, intracellular calcium ([Ca(2+)](i)) and the magnitude of an O(2)-sensitive background ionic conductance that may play roles in the postnatal increase in oxygen sensitivity of glomus cells isolated from rats of 1-3 days and 11-14 days postnatal age. Using fura-2 and perforated patch whole cell recordings, we simultaneously measured [Ca(2+)](i) and membrane potential (E(m)) during normoxia and hypoxia. Resting E(m) in normoxia was similar at both ages. Hypoxia caused a larger E(m) depolarization and correspondingly larger [Ca(2+)](i) response in glomus cells from 11- to 14-day-old rats compared to 1-3-day-old rats. E(m) and [Ca(2+)](i) responses to 40mM K(+) were identical between the two age groups. Under normoxic conditions both age groups had similar background conductances. Under anoxic conditions (at resting membrane potential) background K(+) conductance decreased significantly more in cells from 11- to 14-day-old rats compared to cells from 1- to 3-day-old rats. Glomus cells from newborns therefore have less O(2)-sensitive background K(+) conductance. These results support the hypothesis that postnatal maturation of glomus cell O(2) sensitivity involves developmental regulation of the expression and/or O(2)-sensitivity of background ionic conductances.

4-Aminopyridine↗
PubMed2005

Determination of dipole moment in the ground and excited state by experimental and theoretical methods of N-nonyl acridine orange.

The absorption and fluorescence spectra of N-nonyl acridine orange are determined at room temperature (298 K) in cyclohexane, benzene, carbon tetrachloride, chloroform, chlorobenzene and dichloromethane. The ground state of dipole moment was obtained by impedance measurements using Guggenheim-Debeye's method. The experimental excited state dipole moment of N-nonyl acridine orange was determined using Bakhshiev's and Kawski-Chamma-Viallet's formulae and solvent polarity parameter proposed by Reichardt. These experimental results were completed with theoretical results using quantum chemical methods. The experimental (muexp=10.76 D) and theoretical (mucal=9.9 D) dipole moments in the ground and excited state (muexp*=14.56 D) were compared.

Acridine Orange↗
PubMed2003

Completion of trimeric hairpin formation of influenza virus hemagglutinin promotes fusion pore opening and enlargement.

For influenza virus hemagglutinin, an N-cap structure, created at low pH, interacts with membrane-proximal residues (173-178), bringing fusion peptides and membrane-spanning domains close together. Mutational analysis was used to define the role of these interactions in membrane fusion. For all N-cap mutants, both lipid and aqueous dye spread was greatly reduced. Mutation at residues that interact with the N-cap did not reduce levels of fusion, except for substitutions made at residue I173. For N-cap and I173 mutants, the addition of chlorpromazine greatly promoted transfer of aqueous dye. Electrical capacitance measurements confirmed that fusion pores usually did not form for the I173 mutants. Thus, neither N-cap formation nor interactions with segment 173-178 are needed for hemifusion, but are required for reliable formation and enlargement of the fusion pore. It is proposed that binding of I173 into a deep hydrophobic cavity within the coiled-coil promotes the transition from hemifusion to fusion.

Cell Line↗
PubMed1989

ATP-synthesis by proteoliposomes incorporating Rhodospirillum rubrum F0F1 as measured with firefly luciferase: dependence on delta psi and delta pH.

ATP-synthesis catalyzed by proteoliposomes incorporating Rhodospirillum rubrum F0F1 was driven by artificially applied electrochemical proton gradients. The time-course of ATP-synthesis was followed continuously by means of firefly luciferase. Correction methods were developed which allow one to calculate the initial rate of ATP-synthesis from the observed luminescence kinetics. The following results were obtained: (1) ATP-synthesis occurred above a threshold delta mu H+ of 90 mV; this threshold is not imposed by the activation requirement of the enzyme; (2) delta psi and delta pH appear to be equivalent as driving forces for ATP-synthesis if allowance is made for the effect of the electrical capacitance of the liposome membrane on the distribution of K+ at equilibrium; and (3) the highest rate observed so far is 200 mol ATP per mol F0F1 per s.

Adenosine Triphosphate↗
PubMed2003

Role of the dielectric constants of membrane proteins and channel water in ion permeation.

Using both analytical solutions obtained from simplified systems and numerical results from more realistic cases, we investigate the role played by the dielectric constant of membrane proteins epsilon(p) and pore water epsilon(w) in permeation of ions across channels. We show that the boundary and its curvature are the crucial factors in determining how an ion's potential energy depends on the dielectric constants near an interface. The potential energy of an ion outside a globular protein has a dominant 1/epsilon(w) dependence, but this becomes 1/epsilon(p) for an ion inside a cavity. For channels, where the boundaries are in between these two extremes, the situation is more complex. In general, we find that variations in epsilon(w) have a much larger impact on the potential energy of an ion compared to those in epsilon(p). Therefore a better understanding of the effective epsilon(w) values employed in channel models is desirable. Although the precise value of epsilon(p) is not a crucial determinant of ion permeation properties, it still needs to be chosen carefully when quantitative comparisons with data are made.

Cell Membrane Permeability↗
PubMed2003

Proton transfer in gramicidin channels is modulated by the thickness of monoglyceride bilayers.

The thickness of monoglyceride planar bilayers has significant effects on the transfer of protons in both native gramicidin A (gA) and in covalently linked SS- and RR-dioxolane-linked gA proteins. Planar bilayers with various thicknesses were formed from an appropriate combination of monoglyceride with various fatty acid lengths and solvent. Bilayer thicknesses ranged from 25 A (monoolein in squalene) to 54 A (monoeicosenoin in decane). Single-channel conductances to protons (g(H)) were measured in the concentration range of 10-5000 mM HCl. In native gA as well as in RR channels, the shape of the log(g(H))-log([H(+)]) relationships was nonlinear and remained basically unaltered in monoglyceride bilayers with various thicknesses. For both native gA and RR channels, g(H) values were systematically and significantly larger in thin than in thick bilayers. By contrast, the shape of the log(g(H))-log([H(+)]) relationships in the SS channel was linear (with a slope considerably smaller than 1) in thick (>37 A) bilayers. However, in thin (<37 A) bilayers these plots became nonlinear and g(H) values approached those obtained in native gA channels. The linearization of the log-log plots in the SS channel in thick bilayers is a consequence of a dramatic increase (instead of a decrease as in native gA and RR channels) of g(H) in these bilayers in [H(+)] <1 M. The gating characteristics of the various gA channels as a function of bilayer thickness followed the same pattern as described previously. It was noticed, however, that in the thickest monoglyceride bilayer used in this study, both the SS- and RR-dioxolane-linked channels opened in a mode of bursting activity instead of remaining in the open state as in thin bilayers. It is proposed that the thickness of monoglyceride bilayers modulates proton transfer in native gA channels by a combination of factors including the access resistances of channels to H(+), and fluctuations in both the structure of the lipid bilayer and in the distance between gA monomers. The differential effects of relatively thick monoglyceride bilayers on proton transfer in both dioxolane-linked gA channels must relate to distinct interactions between the bilayers and the SS and RR dioxolanes.

Electric Capacitance↗
PubMed2003

A coded approach to system identification using a modified Golay FIR filter.

Several techniques are currently in use for system identification, each having its own level of performance. In this paper we present a coded interrogation approach for statistical system identification; it is based around a modified Golay sequence applied to an adaptive finite impulse response (AFIR) filter system. We show that this technique circumvents some of the shortfalls associated with other comparative approaches. The theory of the proposed technique is developed, and the operating principle of a prototype model to verify it is described. Analysis of the results obtained from experiments, performed on a simple first-order linear time invariant (LTI) system, gave an average deviation of +/- 2.94% from the ideal response.

Algorithms↗
PubMed2002

A three-dimensional multi-electrode array for multi-site stimulation and recording in acute brain slices.

Several multi-electrode array devices integrating planar metal electrodes were designed in the past 30 years for extracellular stimulation and recording from cultured neuronal cells and organotypic brain slices. However, these devices are not well suited for recordings from acute brain slice preparations due to a dead cell layer at the tissue slice border that appears during the cutting procedure. To overcome this problem, we propose the use of protruding 3D electrodes, i.e. tip-shaped electrodes, allowing tissue penetration in order to get closer to living neurons in the tissue slice. In this paper, we describe the design and fabrication of planar and 3D protruding multi-electrode arrays. The electrical differences between planar and 3D protruding electrode configuration were simulated and verified experimentally. Finally, a comparison between the planar and 3D protruding electrode configuration was realized by stimulation and recording from acute rat hippocampus slices. The results show that larger signal amplitudes in the millivolt range can be obtained with the 3D electrode devices. Spikes corresponding to single cell activity could be monitored in the hippocampus CA3 and CA1 region using 3D electrodes.

Action Potentials↗
PubMed1994

Surfactant-induced skin irritation and skin repair. Evaluation of the acute human irritation model by noninvasive techniques.

BACKGROUND: Although the induction of irritant dermatitis by surfactants has been extensively studied in recent years, our understanding of the repair phase of irritant dermatitis is limited. OBJECTIVE: We investigated qualitative and quantitative differences in surfactant-induced irritant skin reactions from short-term exposure to three structurally different surfactants. METHODS: Sodium lauryl sulfate (SLS), dodecyl trimethyl ammonium bromide (DTAB), and potassium soap were the model irritants. Surfactant solutions (0.5%) were applied for 24 hours to the volar aspect of the forearm of 11 volunteers. Irritant reactions were assessed until complete healing was indicated by visual assessment and by various aspects of skin function, that is, transepidermal water loss (TEWL), erythema (skin color reflectance), and stratum that is, transepidermal water loss (TEWL), erythema (skin color reflectance), and stratum corneum hydration (electrical capacitance). RESULTS: SLS and DTAB induced similar degrees of erythema, whereas SLS induced significantly higher TEWL increase. Although both erythema and TEWL were highest 1 hour after exposure to surfactants, skin dryness was a symptom with delayed onset, justifying the long observation period in this study. Minimum hydration values were measured as late as 7 days after surfactant exposure. Dryness was significantly more pronounced in areas exposed to SLS than in areas exposed to DTAB. Complete repair of the irritant reaction induced by either SLS or DTAB was achieved 17 days after surfactant exposure. Stratum corneum hydration was the last feature to return to baseline values. Potassium soap did not significantly influence any skin function. CONCLUSION: We emphasize the importance of extended periods needed before a patient with irritant contact dermatitis can be reexposed to irritant substances. The evaluation of the irritation potential of diverse surfactants depended significantly on the feature (erythema vs hydration and TEWL) measured.

Adult↗
PubMed2000

Electromigration of polyion homopolymers across biomembranes: a biophysical model.

The analysis of polyion transmembrane translocation was performed using membrane electrical equivalent circuit. The dependence of polyion flux across membranes on time, membrane electrical conductance, membrane electrical capacitance, degree of polymerization, water solution conductance and applied transmembrane potential is discussed. The changes in polyion flux were up to 88% after 1 ms. Both the increase of polyion chain length and the decrease of membrane conductance resulted in the diminution of this effect. Inversion of flux direction was observed as a result of external potential changes. Reversal curves, representing the values of considered parameters for zero-flux were also shown. The replacement of a polyanion by a polycation of the same chain length resulted in the same shape of the surface plot but with opposite orientation. The analysis describes the effect of transmembrane potential on the translocation rate of polyanionic polysialic acid and polynucleotides, and polycationic peptides across membranes.

Biological Transport, Active↗
PubMed2001

Fundamental new results in the energetics and thermodynamics of charged metal surfaces.

There should be close scientific relationships between the following: the bonding energy of an atom or molecule at a curved surface; the Laplace-Young equation (the 'equation for pressure difference across a curved surface'); the Kelvin equation (the 'equation for vapour pressure above a curved surface'); and the thermodynamics of surface diffusion. This paper briefly reports some surprising new theoretical results obtained by reviewing these relationships, and inserting 'atomic-type' surface electrostatic energy terms into the expression for system potential energy. The two main results are as follows. First, the field dependence of atomic bonding energy is shown to be associated with a change in the electrical capacitance between the specimen and its surroundings, when the atom is removed. Good agreement is found between old experiments and the new theory. Second, when atomic-type effects are taken into account, new terms appear in the formula for pressure difference across a charged curved surface. These describe a field-dependent correction to the 'surface tension' term and a curvature-dependent correction to the Maxwell field stress term. The main consequences are: the concepts of 'surface tension' and 'surface free energy' become no longer equivalent; a small correction is needed to the Raleigh criterion for the stability of charged droplets; and a mathematical Taylor cone is no longer a hydrodynamic equilibrium shape.

Journal Article↗
PubMed1999

The combined use of moisturizers and occlusive gloves: an experimental study.

BACKGROUND: Protective gloves are used in the workplace to protect the hands from occupational hazards, but side effects from glove use are frequently reported. Among these side effects, irritant skin reactions are common. OBJECTIVE: The present study was undertaken to investigate whether applying a moisturizer to compromised skin before wearing an occlusive glove could reduce skin irritation. METHODS: Healthy volunteers had both hands immersed in a sodium lauryl sulfate solution twice daily for 2 days. After each immersion, one hand had a moisturizer applied and both hands were put in occlusive gloves for 2 hours. Skin barrier function was evaluated by transepidermal water loss, skin hydration was measured by electrical capacitance and inflammation was evaluated by colorimetry. RESULTS: The moisturizer had a statistically significant positive effect on both the water barrier function and the hydration level of the skin. Although not statistically significant, less inflammation was observed on the moisturizer-treated hand. CONCLUSION: The findings suggest that use of a moisturizer under an occlusive glove may diminish irritation from exposure to a detergent followed by glove wearing.

Adult↗
PubMed2005

Effect of sample and substrate electric properties on the electric field enhancement at the apex of SPM nanotips.

Finite element (FE) models were built to define the optimal experimental conditions for tip-enhanced Raman spectroscopy (TERS) of thin samples. TERS experimental conditions were mimicked by including in the FE models dielectric or metallic substrates with thin dielectric samples and by considering the wavelength dependence of the dielectric properties for the metallic materials. Electromagnetic coupling between the substrate/sample and the SPM tips led to dramatic changes of both the spatial distribution and magnitude of the scattered electric field which depended on the substrate dielectric permittivity and excitation wavelength. Raman scattering as high as 10(8) with a spatial resolution of approximately 8 nm was estimated for gold SPM tips and gold substrate when excitation is performed at 532 nm (near-resonance wavelength). For dielectric samples (approximately 4 nm thick), the enhancement of Raman scattering intensity is estimated at approximately 10(5); this does not depend significantly on the sample dielectric permittivity for dielectric samples. These results suggest that TERS experimental conditions should be estimated and optimized for every individual application considering the geometric factors and electric properties of the materials involved. Such optimizations could enlarge the range of applications for TERS to samples eliciting weaker intrinsic Raman scattering, such as biological samples.

Algorithms↗
PubMed2000

Seasonal variability in the biophysical properties of stratum corneum from different anatomical sites.

BACKGROUND/PURPOSE: A 10-month-long study on a panel of 24 young female subjects was carried out to determine whether various biophysical aspects of the stratum corneum (SC) varied with season. METHODS: Three different anatomical sites (calf, inner forearm and crow's foot wrinkle area of the face) were assessed in February, April, July and December of the same year. The assessments made were skin surface hydration using an electrical capacitance technique, transepidermal water loss by evaporimetry, number of corneocytes released using a turbine stimulation method, and skin surface topography using optical profilometry. RESULTS: The results showed significant anatomical differences: with the crow's foot site > forearm > calf, for skin surface hydration and corneocyte numbers; and the crow's foot site > forearm and calf, with no difference between the latter two sites, for TEWL measurements. With these techniques, seasonal differences were observed mainly in the calf, to a lesser extent in the forearm, but not in the crow's foot area. These mainly involved increases in these three parameters in July, as opposed to the other time-points. Parameters of skin surface topography however, showed no consistent seasonal pattern, but markedly higher values were observed for the forearm in comparison to the calf and crow's foot sites, which were similar. From meteorological data obtained, the average daily maximum temperature and hours of sunshine increased to peak values in July, as did the absolute humidity derived from relative humidity data. CONCLUSION: We conclude that the results are most likely to represent changes in the SC due to climatic factors, with the calf and forearm sites being most affected in comparison to the face (crow's foot wrinkle area), which seems unaffected. The reasons for this latter site remaining unchanged may be due to its greater UV exposure, sebum content, and that the use of facial cosmetics was allowed.

Journal Article↗