Exchange Process in the Dielectric Loss of Molecular and Macromolecular Ionic Conductors in the Interfacial Layers Formed by Electrode Polarization Effects.

Here we report a first analytical approach to determine the spectral dependence of the complex permittivity function of molecular and macromolecular ionic conductors in the interfacial layers formed by electrode polarization effects. We show that a previous model of electrode polarization effects that was successfully applied for describing the dielectric behavior of ionic liquids ( Serghei, A.; Tress, M.; Sangoro, J. R.; Kremer, F. Electrode polarization and charge transport at solid interfaces. Phys. Rev. B 2009 , 80 , 184301 ) can be now generalized and applied for polymer/ionic liquid blends as well as for poly(ionic liquid)s. The determined dielectric function of the interfacial layers reveals a dramatic change in the charge transport process manifested by a large decrease in conductivity. Our approach brings the first evidence for a relaxation peak detected in the dielectric loss of the interfaces, which is attributed to an exchange process between the interface and the bulk. This study gives new insights into the mechanism of charge transport at interfaces and could thus contribute to a better correlation between the dielectric properties of ion conducting materials and their electrochemical behavior at interfaces.

Electrode polarization vs. Maxwell-Wagner-Sillars interfacial polarization in dielectric spectra of materials: Characteristic frequencies and scaling laws.

The characteristic frequencies of electrode polarization and of interfacial polarization effects in dielectric spectra of ionic liquids and of polymer bi-layers are determined and systematically analyzed, based on dielectric measurements by means of broadband dielectric spectroscopy, numerical simulations, and analytical calculations. It is shown that, to a large extent, identical scaling laws can be derived for these two dielectric phenomena taking place at external and internal interfaces. Surprisingly, a fundamentally different behavior concerning the interrelation between the characteristic frequencies is found. This brings direct evidence that different manifestations of the phenomenon of electrical polarization can be discriminated by examining the inter-relation governing their characteristic frequencies, which can be of significant importance in disseminating the nature of different contributions appearing in the dielectric spectra of complex materials. Based on our analysis, we derive a new formula, valid for both electrode polarization and interfacial polarization effects, that allows one to determine the conductivity value from the frequency position of the Maxwell-Wagner-Sillars peak. An excellent agreement between experiment and calculations is obtained. The formula can be used, furthermore, to estimate the thickness of the interfacial layers formed due to electrode polarization effects. Values in the order of several nanometers, increasing with decreasing temperature, are reported.

[Peripartum cardiomyopathy: incidence, pathogenesis, diagnosis, treatment and prognosis]. / Myocardiopathie du péripartum : incidence, physiopathologie, manifestations cliniques, prise en charge thérapeutique et pronostic.

INTRODUCTION: Peripartum cardiomyopathy (PPCM) is a rare and life-threatening disease of unknown aetiology. The primary objective of this review was to analysed aetiopathogeneses, clinical presentation and diagnosis, as well as pharmacological, perioperative and intensive care management and prognosis of this pathology. METHODS: We undertook a systematic review of the literature using Medline, Google Scholar and PubMed searches. RESULTS: Unlike other parts of the world in which cardiomyopathy are rare, dilated cardiomyopathy is a major cause of heart failure throughout Africa. Its aetiopathogenesis is still poorly understood, but recent evidence supports inflammation, viral infection and autoimmunity as the leading causative hypotheses. This diagnosis should be limited to previously healthy women who present with congestive heart failure (CHF) and decreased left ventricular systolic function in the last month of pregnancy or within 5 months after delivery. Recently, introduction of echocardiography has made diagnosis of PPCM easier and more accurate. Conventional treatment consists of diuretics, vasodilators, and sometimes digoxin and anticoagulants, usually in combination. Patients who fail to recover may require inotropic therapy. In resistant cases, newer therapeutic modalities such as immunomodulation, immunoglobulin and immunosuppression may be considered. Prognosis is highly related to reversal of ventricular dysfunction. Compared to historically higher mortality rates, recent reports describe better outcome, probably because of advances in medical care. Based on current information, future pregnancy is usually not recommended in patients who fail to recover normal heart function. CONCLUSION: PPCM is a rare but serious form of cardiac failure affecting women in the last months of pregnancy or early puerperium. Its aetiopathogenesis is still poorly understood. Introduction of echocardiography has made diagnosis of PPCM easier and more accurate. Prognosis is highly related to reversal of ventricular dysfunction.

Tissue factor activity is increased in human endothelial cells cultured under elevated static pressure.

We tested the hypothesis that elevated blood pressure, a known stimulus for vascular remodeling and an independent risk factor for the development of atherosclerotic disease, can modulate basal and cytokine-induced tissue factor (TF; CD 142) expression in cultured human endothelial cells (EC). Using a chromogenic enzymatic assay, we measured basal and tumor necrosis factor-alpha (TNF-alpha; 10 ng/ml, 5 h)-induced TF activities in human aortic EC (HAEC) and vena cava EC (HVCEC) cultured at atmospheric pressure and at 170 mmHg imposed pressure for up to 48 h. Basal TF activities were 22 +/- 10 U/mg protein for HAEC and 14 +/- 9 U/mg protein for HVCEC and were upregulated in both cell types >10-fold by TNF-alpha. Exposure to pressure for 5 h induced additional elevation of basal TF activity by 47 +/- 16% (P < 0.05, n = 6) for HAEC and 17 +/- 5% (P < 0.05, n = 3) for HVCEC. Pressurization also enhanced TF activity in TNF-alpha-treated cells from 240 +/- 28 to 319 +/- 32 U/mg protein in HAEC (P < 0.05, n = 4) and from 148 +/- 25 to 179 +/- 0.8 U/mg protein (P < 0.05, n = 3) in HVCEC. Cytokine stimulation caused an approximately 100-fold increase in steady-state TF mRNA levels in HAEC, whereas pressurization did not alter either TF mRNA or cell surface antigen expression, as determined by quantitative RT-PCR methodology and ELISA. Elevated pressure, however, modulated the EC plasma membrane organization and/or permeability as inferred from the increased cellular uptake of the fluorescent amphipathic dye merocyanine 540 (33 +/- 7%, P < 0.05). Our data suggest that elevated static pressure modulates the hemostatic potential of vascular cells by modifying the molecular organization of the plasma membrane.

Launch conditions might affect the formation of blood vessels in the quail chorioallantoic membrane.

As a part of the first joint USA-Russian MIR/Shuttle program, fertilized quail eggs were flown on the MIR 18 mission. Post-flight examination indicated impaired survival of both the embryos in space and also of control embryo exposed to vibrational and g-forces simulating the condition experienced during the launch of Progress 227. We hypothesized that excess mechanical forces and/or other conditions during the launch might cause abnormal development or the blood supply in the chorioallantoic membrane (CAM) leading to the impaired survival of the embryos. The CAM, a highly vascularized extraembryonic organ, provides for the oxygen exchange across the egg shell and is thus pivotal for proper embryonic development. To test our hypothesis, we compared angiogenesis in CAMs of eggs which were either exposed to the vibration and g-force profile simulating the conditions at launch of Progress 227 (synchronous controls), or kept under routine conditions in a laboratory incubator (laboratory controls). At various time points during incubation, the eggs were fixed in paraformaldehyde for subsequent dissection. At the time of dissection, the CAM was carefully lifted from the egg shell and examined as whole mounts by bright-field and fluorescent microscopy. The development of the vasculature (angiogenesis) was assessed from the density of blood vessels per viewing field and evaluated by computer aided image analysis. We observed a significant decrease in blood-vessel density in the synchronous controls versus "normal" laboratory controls beginning from day 10 of incubation. The decrease in vascular density was restricted to the smallest vessels only, suggesting that conditions during the launch and/or during the subsequent incubation of the eggs may affect the normal progress of angiogenesis in the CAM. Abnormal angiogensis in the CAM might contribute to the impaired survival of the embryos observed in synchronous controls as well as in space.

In vitro testing of endothelial cell monolayers under dynamic conditions inside a beating ventricular prosthesis.

Thromboembolic complications remain a major problem associated with the long-term clinical use of cardiac prostheses. A promising approach toward resolving this predicament is lining the blood contacting surfaces with a functional monolayer of endothelial cells (EC). In developing an endothelialized cardiac prosthesis, the authors in the past focused on establishing a confluent EC monolayer on the luminal surface of ventricular blood sacs. In this study, the authors concentrated on exposing the post confluent monolayers to the dynamic conditions inside a beating ventricle. The cells, derived from either bovine aortae or jugular veins, were grown to post confluence inside fully assembled ventricles on fibronectin or plasma cryoprecipitate coated, textured surfaces. After 11 days of culturing under static conditions, the endothelialized ventricles were connected to a mock loop that was run for 6 and 24 hr at 60 bpm and mean flow rate of 3.2 L/min. The status of the monolayer was evaluated by Alamar Blue assay before and after each run, and the extent of surface coverage was determined visually using bright field microscopic study after cell staining with KMnO4 and toluidine blue. In addition, morphometric information on cells/polyurethane surface was obtained with a scanning electron microscope. After 6 hr of pumping, cell staining revealed signs of moderate cell loss in fibronectin coated blood sacs, whereas in cryoprecipitate coated bladders the signs of denudation were marginal. In seven ventricles operated for 24 hr, Alamar Blue measurements indicated 35 +/- 16% of cell loss from monolayers established on fibronectin coating, but only 4.8 +/- 6.25% on cryoprecipitate. Thus, the current study demonstrates the feasibility of maintaining an intact endothelial surface in a beating ventricular prosthesis and indicates that the integrity of the endothelial lining is dependent upon a proper choice of surface macrostructure and protein coating.

A new method for continual quantitation of viable cells on endothelialized polyurethanes.

Many of the segmented polyurethanes currently used in cardiovascular prostheses undergo either modification of their surface structure or are lined with a confluent monolayer of endothelial cells to improve their hemocompatibility. During the establishment of an endothelial cell lining on these biopolymers it is necessary to continually monitor the number of viable cells that are covering the substrate. Yet, not all of the conventional cell enumeration techniques are suitable for assessing the growth of endothelial cells on polyurethanes. Methods, such as direct cell counting, dye uptake, or DNA or protein staining require either a transparent scaffold or lead to termination of the culturing process prior to measurement. In addition, some of the spectroscopic assays are often hampered by interaction of the dyes and/or solubilizers with the various constituents (e.g., catalyzers, antioxidants) and/or functional groups in the polyurethane formulations. In addressing these problems, we adapted a novel, highly reproducible fluorescent assay which is based on reduction by viable cells of an electrochemically sensitive compound, Alamar Blue. The bioreduced product is soluble and stable in culture media and noncytotoxic. In addition, the assay is independent of the geometry or physicochemical properties of the polymeric surfaces. In the present study we focus on the implementation of this assay to monitoring attachment and growth of various endothelial cell types on segmented polyurethanes.

Regulation of the adenylyl cyclase signaling system in various types of cultured endothelial cells.

We studied the effects of modulators of the adenylyl cyclase pathway on the accumulation of cAMP in endothelial cells isolated from bovine aortas, pig pulmonary arteries, human umbilical veins, and human subcutaneous adipose microvessels. In addition to quantitative differences in the basal levels, cAMP stimulation in different endothelial cell types varied in sensitivity and magnitude in response to both the direct adenylyl cyclase activator forskolin and the beta-adrenergic receptor agonist isoproterenol. Furthermore, the ubiquitous phosphodiesterase inhibitor IBMX differentially enhanced both the basal and the stimulated cAMP levels in the various cell types. Histamine caused an elevation of cAMP only in bovine aortic endothelial cells and in human umbilical vein endothelial cells. Treatment of the cells with cholera and pertussis toxins, which uniquely affect G-protein subunits, resulted in divergent elevation of cAMP in the various cells. Thus, in each cell type, a distinct profile of regulation of the cAMP levels was found. Our results suggest that the adenylyl cyclase signaling system in various types of endothelial cells can be differentially regulated at the levels of receptors, G-proteins, adenylyl cyclase, and phosphodiesterase.

Endothelial cell seeding with rotation of a ventricular blood sac.

Successful establishment of a durable endothelial cell (EC) monolayer inside a ventricular blood sac requires homogeneous coverage of the entire luminal surface with attached cells. For this purpose, a new device was developed that slowly rotates a fully assembled cardiac prosthesis with three degrees of freedom. We seeded ECs derived from human adipose tissue at a density of approximately 3.5 x 10(4) cells/cm2 onto the surfaces of polyurethane-made blood sacs and "ersatz" bladders (consisting of T-25 tissue culture flasks). The kinetics of cell attachment, spreading, and proliferation were determined using video microscopy combined with image analysis and cell viability assays. After 60 min of seeding at 5-10 rotations/hr, the plating efficiency inside the blood sacs was 35.7 +/- 11%, with cell viability remaining approximately 90 +/- 5%. After 3 hr, when the plating efficiency reached a plateau (approximately 70%), the rotation was stopped and the ECs were allowed to spread and proliferate under static conditions. Within 48 hr, the entire luminal surface was evenly covered by a confluent EC monolayer. Our long-term studies show that with a proper feeding schedule, such an EC monolayer can be maintained intact in vitro for more than 2 weeks.

A new, cryoprecipitate based coating for improved endothelial cell attachment and growth on medical grade artificial surfaces.

Monoprotein coatings of biomaterials with either natural adhesion molecules or genetically designed analogs have been used to facilitate attachment and spreading of endothelial cells. However, such treatments were found insufficient to maintain the integrity of the endothelial surface under turbulent flow conditions. In addition, when brought into contact with blood, these coatings were susceptible to plasma and cell proteinases that could readily destroy their structure and weaken cell adherence to the surface. In addressing these problems, we developed a cryoprecipitate-based coating that can firmly bind to any nonporous, prosthetic surface and interact with endothelial cells. The primary structure of the coating consisted of an autologous fibrin meshwork. It was refined by various compositions of the fibrinogen containing mixture and secured to polystyrene or polyurethane surfaces by dry-heat treatment. Further modulation of the coating was achieved by physically immobilizing various doses of heparin and insulin into the three dimensional matrix of the meshwork. Endothelial cells attached and grew much better on polyurethanes coated with this autologous protein complex than on a polystyrene tissue culture surface. With proper use of its capacity to mimic the properties of basal membrane, and absence of immunologic complications, the resulting coating may become an ideal multifunctional interface between cells and prosthetic materials.

Flow patterns and endothelial cell morphology in a simplified model of an artificial ventricle.

The aim of this study was to delineate the flow patterns in a non-unidirectional flow field inside a ventricle-shaped cell culture chamber, and examine the resulting morphology and integrity of the endothelium in select regions of the monolayer. The chamber was perfused by pulsatile flow, and the coherent motion of the fluid was studied using flow visualization aided by image analysis. Four distinct flow patterns were discerned and examined: central jet, flow impingement, flow separation, and recirculating eddies. The influence of these patterns on endothelial cell morphology was assessed after 20 h of exposure to flow. There were no signs of damage to the endothelium in the jet region nor was there evidence of cell alignment with the flow. Yet, there were changes in cell morphology and cytoskeletal architecture as compared to control. By contrast, within the eddies where the flow was highly disturbed, there was apparent damage to the endothelium. Thus, exposure of cells to random velocity fluctuations in regions of quasi-static flow compromises the integrity of the monolayer. Identification of such sites and acquisition of the knowledge necessary to protect the cells from denudation will be valuable for the endothelialization efforts of cardiac prostheses.

Morphology and integrity of endothelial cell monolayers inside a ventricle shaped perfusion chamber.

The long-term maintenance of patients with failing hearts on cardiac prostheses requires prevention of device related thromboembolic events. This challenge is being addressed by endothelialization of the blood sacs. However, the practice of establishing and maintaining a durable endothelial cell monolayer inside a beating prosthesis has not been fully realized. Thus, before exposing endothelial cell monolayers to the hemodynamics inside an artificial heart, the authors studied the effect of various flow patterns in a ventricle shaped chamber on the integrity and morphology of the endothelium. After 20 hours of superfusion by pulsatile flow, there were no denudation signs in the jet, where shear stress was 1.5 dynes/cm2. However, there was measurable damage to the monolayer close to the periphery of the eddies (turbulent flow) at 0.15 dynes/cm2. In either case, there were no signs of cell alignment with the flow, but there were changes in cell morphology compared with that of static control. These findings suggest that adjustment of endothelial cells in response to frictional forces occurs even at low shear stresses and that random velocity fluctuations might jeopardize the integrity of endothelial cell monolayers.

Experimental studies of pulsatile flow and endothelial cell adaptation in ventricle shaped cell culture chambers.

The authors' long-term research goal is to minimize the risk of thromboembolic complications in cardiac prostheses by lining blood contacting surfaces with a functional monolayer of autologous endothelial cells. These cells recognize changes in hemodynamics and can adapt effectively to experimentally manipulated flow conditions. By implication, the morphology of endothelial cells, in conjunction with their function, might serve as an indicator of the flow patterns in a particular location. It was hypothesized that, by understanding flow patterns at a given site, the local morphology and function of the endothelial cells in such a region could be predicted. To test this hypothesis, a series of ventricle shaped flow chambers were designed and perfused with pulsatile flow. The flow field in the chambers was studied by computer aided dye visualization and nuclear scintigraphy. The results showed that the large scale motion of the fluid in the cavity was highly coherent and consisted of distinct flow patterns. The temporal and spatial characteristics of the flow patterns, and their implications with respect to endothelial cell endurance in this in vitro environment, were examined in detail.

Endothelialization of the luminal sac in artificial cardiac prostheses: a challenge for both biologists and engineers.

Thromboembolic complications are a major obstacle for the permanent use of artificial cardiac prostheses. Many of these complications are caused by the intrinsic thrombogenicity of the biomaterials, which are used to cast the luminal blood sac. Numerous attempts have been made to improve the hemocompatibility of the new generation of totally implantable blood pumps, mainly by physico-chemical modifications of the biopolymeric materials and the blood contacting surfaces. We, on the other hand, believe that the most promising and challenging approach, from both the biologists' and engineers' point of view, is to coat the luminal surfaces of cardiac prostheses with a functional monolayer of autologous endothelial cells (ECs) and thus reproduce "nature's biocompatible blood container." The key to lining an artificial heart with a nonthrombogenic monolayer of endothelial cells is to explore the molecular and cellular mechanisms which render the EC lining inside the beating ventricle nonthrombogenic and resistant to flow-induced shear stresses and cyclic, tensional deformations. This knowledge has then to be translated into biotechnological know-how, in order to maintain an intact EC monolayer inside the blood sac of an artificial device. In this paper we emphasize some of the bioengineering issues associated with the endothelialization of the luminal sac, and also discuss some aspects related to the blood sac itself.

Evidence against functional adenosine receptors on murine lymphocytes.

The effects of adenosine, 2-chloroadenosine (2Cl Ado) and N6-phenylisopropyladenosine (PIA) were examined on peripheral blood and splenic lymphocytes from mice. Lectin-stimulated DNA synthesis was antagonized by adenosine and 2Cl Ado at high concentrations. Lower concentrations of all three nucleosides produced an enhancement of lectin-stimulated thymidine uptake in splenic lymphocytes. Peripheral blood lymphocytes were found to exhibit only inhibitions of mitogenic stimulation suggesting a difference in response to nucleoside exposure between spleen and peripherally circulating cells. The synthesis of antibody to sheep red blood cells was inhibited in a non-cytotoxic manner by 2Cl Ado and PIA while adenosine was without effects. The receptor antagonist 8-phenyltheophylline was found to block nucleoside increases in thymidine uptake and low concentrations of 2Cl Ado with regard to antibody production. The effects of high concentrations of 2Cl Ado or PIA on humoral responses were not antagonized by receptor blockade. The data suggest that functional alterations of lymphocyte responses to nucleoside exposure are not a consequence of surface receptors for adenosine nucleosides in murine cells.

Inhibition of antibody production by 2-chloroadenosine.

The ability of 2-chloroadenosine (2Cl Ado) to modulate lymphocyte function was examined in culture and in vivo. Mitogenic stimulation of B cell DNA synthesis was antagonized by 2Cl Ado while adenosine produced both stimulations and inhibitions. In culture, 2Cl Ado was found to suppress antibody production to sheep erythrocytes (SRBC) regardless of whether the nucleoside was added at the initiation of culture or 48 hours after sensitization. Inhibiting adenosine deaminase (ADA) did not affect the response to 2Cl Ado, and 1-homocysteine thiolactone was found to potentiate the inhibition suggesting formation of S-adenosylhomocysteine. Similar responses were found with adenosine provided ADA was inhibited. When 2Cl Ado was administered to mice 3-4 days after SRBC, a concentration-dependent decrease in antibody producing cells was observed. These data suggest that nucleosides can inhibit antibody production by inhibiting transmethylation reactions. 2Cl Ado appears to be an effective immunosuppressant without concomitant cytotoxicity both in culture and in vivo.

Antagonism of the positive chronotropic effect of norepinephrine by purine nucleosides in rat atria.

Adenosine has been shown previously to antagonize the positive chronotropic effects of beta adrenoceptor agonists. In the present study, the effects of adenosine and related compounds were observed on the concentration-effect curve for the positive chronotropic effect of norepinephrine in isolated spontaneously beating rat atria. Adenosine produced both a decrease in the potency of norepinephrine and a decrease in the maximal effect. The decrease in the potency was postulated to be mediated by an action on an external membrane receptor because it was also produced by the potent A1 receptor agonist N6-phenylisopropyladenosine. The effect of N6-phenylisopropyladenosine was antagonized by 8-phenyltheophylline which is known to block external adenosine receptors. When adenosine deaminase was inhibited with erythro-9-(2-hydroxy-3-nonyl)adenine, both effects of adenosine were enhanced markedly suggesting considerable metabolism of exogenous adenosine to inosine under the conditions of this study. Inosine increased rather than decreased the potency of norepinephrine while decreasing its maximal effect. The decrease in the maximal effect of norepinephrine was also produced by 2',5' dideoxyadenosine, 2' deoxyadenosine and S-adenosylhomocysteine but not by N6-phenylisopropyladenosine. This suggests that the decrease in the maximal effect of norepinephrine by adenosine analogs is related to an interaction with an internal site. Adenine had no effect on the concentration-effect curve for norepinephrine. It is suggested that adenosine may regulate cardiac function by antagonizing the chronotropic effect of norepinephrine released upon nerve stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlations between phospholipid methylation and neuronal catecholamine transport.

A change in the fluidity of biological membranes can be produced by methylation reactions which sequentially transfer methyl groups from phosphatidylethanolamine to phosphatidylcholine. Since the physical properties of membranes may affect the function of membrane-localized transport proteins, the accumulation of norepinephrine (NE) by rat cortical synaptosomes was examined in the presence of S-adenosylhomocysteine (AdoHcy) which inhibits the methylation of phospholipids. A concentration-related decrease in the uptake of [3H]NE was produced by AdoHcy with coincident decreases in the S-adenosylmethionine (AdoMet)-dependent transmethylation of phospholipids in neuronal membranes. A kinetic analysis for the effects of AdoHcy on the neuronal uptake of NE revealed a significant decrease in both the apparent Km and Vmax. Treatment of synaptosomes with adenosine, L-homocysteine thiolactone (HTL), and erythro-9(2-hydroxy-3-nonyl)adenine (EHNA) which leads to the synthesis of intracellular AdoHcy resulted in a decrease in the Vmax with no significant change in the Km. Adenosine or EHNA alone had no effect on NE uptake, but HTL alone significantly inhibited NE uptake. The data suggest that the processes of enzymatic methylation of membrane phospholipids and the transport of norepinephrine may be associated within neuronal membranes. Inhibiting phospholipid methylation reactions can reduce the efficiency of neurotransmitter removal and perhaps indirectly alter synaptic function.