The effect of the fluorescent probe, 3,3′-dipropylthiodicarbocyanine iodide,on the membrane potential of Ehrlich ascites tumor cells

The effects of the potential-sensitive fluorescent dye, 3,3′dipropylthiodicarbocyanine iodide, on factors establishing the membrane potential of Ehrlich ascites tumor cells have been tested. The dye itself induces membrane hyperpolarization as monitored by electrophysiological methods. In addition, the dye inhibits active (Na⁺+K⁺-transport and increases cell membrane permeability to K⁺ by about 65% in these cells.     

Influence of cytosolic conditions on the reaction equilibrium and the reaction enthalpy of the enolase reaction accessed by calorimetry and van ‘t HOFF

BackgroundThermodynamic methods are finding more and more applications in systems biology, which attempts to understand cell functions mechanistically. Unfortunately, the state variables used (reaction enthalpy and Gibbs energy) do not take sufficient account of the conditions inside of cells, especially the crowding with macromolecules.MethodsFor this reason, the influence of crowding agents and various other parameters such as salt concentrations, pH and temperature on equilibrium position and reaction enthalpy of the glycolytic example reaction 9 (2-Phospoglycerate - > Phosphoenolpyruvate + H₂O) was investigated. The conditions were chosen to be as close as possible to the cytosolic conditions. Poly(ethylene glycol) MW = 20,000 g mol⁻¹ (PEG 20,000) was used to analyze the influence of crowding with macromolecules. The equation of state electrolyte Perturbed-Chain Statistical Associating Fluid Theory (ePC-SAFT) was applied to consider the influence of crowding agents on the reaction equilibria.Results and conclusionsFor the reaction enthalpies and for the equilibria, it was found that the influence of salts and temperature is not pronounced while that of pH and PEG 20,000 concentration is considerable. Furthermore, it could be shown that under identical measurement conditions there are no differences between the van ‘t Hoff and the calorimetrically determined reaction enthalpy.General significanceThe results show how important it is to consider the special cytosolic conditions when applying thermodynamic data in systems biology.     

Volume-induced increase of K+ and Cl− permeabilities in Ehrlich ascites tumor cells. Role of internal Ca2+

Summary Ehrlich ascites tumor cells resuspended in hypotonic medium initially swell as nearly perfect osmometers, but subsequently recover their volume within 5 to 10 min with an associated KCl loss. 1. The regulatory volume decrease was unaffected when nitrate was substituted for Cl^–, and was insensitive to bumetanide and DIDS. 2. Quinine, an inhibitor of the Ca²⁺-activated K⁺ pathway, blocked the volume recovery. 3. The hypotonic response was augmented by addition of the Ca²⁺ ionophore A23187 in the presence of external Ca²⁺, and also by a sudden increase in external Ca²⁺. The volume response was accelerated at alkaline pH. 4. The anti-calmodulin drugs trifluoperazine, pimozide, flupentixol, and chlorpromazine blocked the volume response. 5. Depletion of intracellular Ca²⁺ stores inhibited the regulatory volume decrease. 6. Consistent with the low conductive Cl^– permeability of the cell membrane there was no change in cell volume or Cl^– content when the K⁺ permeability was increased with valinomycin in isotonic medium. In contrast, addition of the Ca²⁺ ionophore A23187 in isotonic medium promoted Cl^– loss and cell shrinkage. During regulatory volume decrease valinomycin accelerated the net loss of KCl, indicating that the conductive Cl^– permeability was increased in parallel with and even more than the K⁺ permeability. It is proposed that separate conductive K⁺ and Cl^– channels are activated during regulatory volume decrease by release of Ca²⁺ from internal stores, and that the effect is mediated by calmodulin.     

Can a temporary bond between dye and redox mediator increase the efficiency of p-type dye-sensitized solar cells?

Efficient n-type dye-sensitized solar cells are known since the seminal work of O’Reagan and Grätzel in 1991. However, highly efficient p-type dye-sensitized solar cells have not been developed so far. This hinders the construction of tandem dye-sensitized solar cells, which can surpass the performance of n-type devices. Within this work, we investigate if a temporary coordination of transition metal-based redox mediators at a sensitizer can increase the efficiency of p-type dye-sensitized solar cells. Based on a computational screening, diverse Cu, Ni, and Co redox mediators were selected to construct p-type dye-sensitized solar cells. Unfortunately, the efficiency of the investigated devices does not surpass analogous cells with iodide-triiodide as redox mediator. While Ni and Cu complexes might be reduced to Ni(0) and Cu(0), respectively, the investigated Co-complex quenches the excited state efficiently. As a result, the necessary electron injection from the semiconductor is too slow, which hinders the construction of a highly efficient p-type dye-sensitized solar cell.

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Graphical Abstract Comparison of the mode of action of p-type dye-sensitized solar cells. While top shows the traditional one, bottom shows the investigated devices where a temporary link between dye and redox mediator plays a crucial role.

     

A comparative study on the removal of cellular lipids from Landschütz ascites cells by human plasma apolipoproteins.

The effects of human plasma lipoprotein-proteins on the removal of cellular lipids from Landschütz ascites cells were studied. Cellular lipids were labeled by injecting mice previously injected with ascites with either [3H]cholesterol or [3H]choline. Apoproteins from very low density (apoC-I, C-II, and C-111) and high density (apoA-I and A-II) lipoproteins were used. Each of the apoproteins alone was ineffective in removing cellular [3H]cholesterol. However, when synthetic phosphatidylcholines of known composition were added to each apoprotein and the experiments were repeated using either apoprotein-lipid mixtures or ultracentrifugally isolated complexes, the removal of sterol was considerably enhanced. Complexes of saturated phosphatidylcholines with apoA-II, apoC-I, or apoC-III were the most effective in releasing cellular sterol. Apoprotein-phospholipid complexes were much less effective in removing cellular [3H]phosphatidylcholine than the free apoproteins; apoA-I and apoC-I were the best of the five apoproteins studied. When a comparison was made of the adsorption of iodinated apoproteins to ascites cells, 3 to 4 times more apoA-II and apoC-III were bound than apoA-I. The binding of apoproteins was time and temperature dependent. Approximately 50% of the radioactivity that remained in the washed cells was removed with trypsin. To determine if the counts remaining in the trypsin-treated cells were internalized, identical experiments were performed using human erythrocytes, cells that do not exhibit pinocytosis. Again, approximately 50% of the radioactivity of the iodinated apoproteins was not released by trypsin. Succinylation of apoA-II not only destroys its phospholipid-binding properties but also its adsorption to red cells. These results suggest that the plasma apoproteins differ in their ability to remove cellular lipids and bind to both ascites and red cell membranes, and possibly to specific phospholipids, in such a way that only a part of the apoprotein is degraded with proteases.     

Comparison of glutathione reductase activity and the intracellular glutathione reducing effects of 13 derivatives of 1′-acetoxychavicol acetate in Ehrlich ascites tumor cells

In a previous study, we showed that (1′S)-acetoxychavicol acetate ((S)-ACA) caused a rapid decrease in glutathione (GSH) levels less than 15 min after exposure. (S)-ACA-induced cell death was reversed by the addition of N-acetylcysteine. In the current study, we investigated the inhibitory activities of 13 derivatives of (S)-ACA on tumor cell viability, intracellular GSH level and GR activity. Correlations were found among a decrease in cell viability, intracellular GSH levels and the activity of GR in Ehrlich ascites tumor cells treated with the various ACA analogues. A test of the 13 derivatives revealed that the structural factors regulating activity were as follows: (1) the para or 1′-position of acetoxyl group (or other acyl group) was essential, (2) the presence of a C2′–C3′ double or triple bond was essential, and (3) the S configuration of the 1′-acetoxyl group was preferable.     

A Study on In-Line Tablet Coating—the Influence of Compaction and Coating on Tablet Dimensional Changes

Prior to coating, tablets are usually stored for a definite period to enable complete strain recovery and prevent subsequent volumetric expansion-related coating defects. In-line coating is defined as the coating of tablets immediately after compaction. In-line coating will be expected to improve manufacturing efficiencies. In this study, the possibility of in-line coating was studied by evaluating the influence of compaction and coating on tablet dimensional changes. The use of tapered dies for compaction was also evaluated. Two types of tablet coaters which presented different coating environments, namely the Supercell™ coater and pan coater, were employed for coating. The extent of tablet dimensional changes was studied in real time using optical laser sensors in a controlled environment. After compaction, tablet dimensional changes were found to be anisotropic. In contrast, coating resulted in isotropic volume expansion in both the axial and radial directions. Pan coating resulted in significantly greater tablet dimensional changes compared to Supercell™ coating. There was no significant difference in dimensional changes of tablets coated in line or after complete viscoelastic strain recovery for Supercell™ coating. However, significantly different dimensional changes were observed for pan coating. The use of tapered dies during compaction was found to result in more rapid viscoelastic strain recovery and also significantly reduced tablet dimensional changes when tablets were immediately coated after compaction using the pan coater. In conclusion, the Supercell™ coater appeared to be more suitable for in-line tablet coating, while tapered dies were beneficial in reducing tablet dimensional changes when the pan coater was employed for in-line coating.KEY WORDS: continuous manufacturing, in-line coating, tablet coating, tapered dies, viscoelastic strain recovery     

Regional adaptation of Müller cells in the chick retina. A Golgi and electron microscopical study

We report the morphological differences of Müller cells in relation to their topography, using the Golgi method. Müller cells in the central retina are long and slender, with numerous inner prolongations. In the peripheral retina, the morphology of the Müller cells adapts to the reduced thickness of the retinal layers. In this zone, they are short and have thick inner prolongations which end in a large foot in the internal limiting membrane. In the optic disc margin, Müller cells have a particular morphology characterized by thick, arched prolongations that in general form a glial network between the retina and optic nerve. The ultrastructure of these cells is also described. The results are discussed with respect to the nature of Müller cells.     

Studies on ethylene production by a subcellular fraction from ripening tomatoes—I. : Effects of several substrates,cofactors and cations

Studies were made of the effects of several substrates, cofactors and cations on the production of ethylene by a subcellular fraction from ripening tomatoes. Compounds found to be effective were ethanol, aspartic acid, glutamic acid, serine, γ-aminobutyric acid, propionic acid and galactose. Those found to exert little influence on ethylene evolution were β-alanine, α-ketoglutaric acid and xylose. Inhibitory to ethylene production were glycolaldehyde, pyruvate, acrylic acid, and glyoxylate. None of the added cations stimulated ethylene evolution, and copper, zinc and cobalt reduced it. Cofactors found to be stimulatory were: reduced α-lipoate, nicotinamide adenine dinucleotide phosphate, and thiamine pyrophosphate. Coenzyme A, reduced glutathione, nicotinamide adenine dinucleotide, bovine serum albumin, flavin adenine dinucleotide, flavin mononucleotide and pyridoxal phosphate, were either inhibitory or had little effect on ethylene production.     

Influence of pH and ionic strength on the viscoelastic properties of starch gels — A comparison of potato and cassava starches

The influence of pH, and of electrolytes, on the viscoelastic properties of potato and cassava starch gels was investigated, using a cone-and-plate rheometer run in the oscillatory mode. The gel strength of the potato starch gels had a maximum around pH 8·5, and was markedly lowered by the addition of even small amounts of electrolytes. This may be due to an electrostatic interaction between potato starch phosphate groups and added cations which blocks the normal phosphate-to-phosphate cross-linking. Neither pH nor electrolytes affected the viscoelastic properties of cassava starch gels. The gelatinization temperature and the gelatinization enthalpy of potato starch, as measured by differential scanning calorimetry, were insensitive to pH and to low electrolyte concentrations.     

Influence of the position of the double bond in steroid substrates on the efficiency of the proton-transfer reaction by Pseudomonas testosteroni 3-oxo steroid Δ4–Δ5-isomerase

Studies of the proton-transfer reaction by Pseudomonas testosteroni 3-oxo steroid Delta(4)-Delta(5)-isomerase with Delta(5(6))- and Delta(5(10))-steroid substrates demonstrate the importance of the position of the double bond for the efficiency of the isomerization process. Thus 3-oxo-Delta(5(6))-substrates have markedly high k(cat.) values, whereas those of 3-oxo-Delta(5(10))-substrates are very low and their apparent K(m) values approach equilibrium dissociation constants. The first step in the isomerization process is: [Formula: see text] which is governed by the k(-1)/k(+1) ratio and is shown to be very similar for the two classes of substrates (3-oxo-Delta(5(6))- and -Delta(5(10))-steroids). They therefore differ in the steps distal to the initial formation of the Michaelis-Menten complex. The use of the deuterated androst-5(6)-ene-3,17-dione substrate enabled us to calculate individual rate constants k(+1) and k(-1) as well as to determine the apparent rate-limiting step in the isomerization process. With the deuterated oestr-5(10)-ene-3,17-dione substrate, no significant isotope effect was observed suggesting that a different rate-limiting step may be operative in this isomerization process. Data are presented that indicate that under optimal concentrations of the efficient androst-5(6)-ene-3,17-dione substrate, the forward reaction for ES complex formation (as defined by k(+1)) is limited only by diffusion and the apparent K(m) does not approach the equilibrium constant, suggesting that the evolution of this enzyme has proceeded close to ;catalytic perfection'.     

Influence of electrical and thermal properties on RF ablation of breast cancer: is the tumour preferentially heated?

Background  

Techniques based on radio frequency (RF) energy have many applications in medicine, in particular tumour ablation. Today, mammography screening detects many breast cancers at an early stage, facilitating treatment by minimally invasive techniques such as radio frequency ablation (RFA). The breast cancer is mostly surrounded by fat, which during RFA-treatment could result in preferential heating of the tumour due to the substantial differences in electrical parameters. The object of this study was to investigate if this preferential heating existed during experimental in vitro protocols and during computer simulations.     

Electron-paramagnetic-resonance measurements of the electron-transfer components of the reaction centre of Rhodopseudomonas viridis. Oxidation–reduction potentials and interactions of the electron acceptors

Oxidation-reduction potentiometry was carried out on Rhodopseudomonas viridis chromatophores. Measurements of e.p.r. signals of the semiquinone-iron type at g=1.82 have revealed a more complex situation than previously reported. The presence of three different components is indicated. The midpoint potential (E(m)) of the primary acceptor quinone/semiquinone couple was found to be approx. -165mV at pH10, with a pK being reached at around pH7.5. The primary acceptor also accepts a second electron with an E(m) of -525mV, but this redox transition exhibits a hysteresis effect. Interaction effects indicate the presence of another component with E(m) values at pH10 of approx. -165mV (pK reached at around pH7.5) for single reduction and -350mV (pK at pH10 or greater) for double reduction. It is suggested that this component is the secondary acceptor. Another semiquinone-iron-type component which gives a g=1.82 signal is also present. This component is distinguishable from the primary acceptor by its e.p.r. spectrum, which shows a double peak at g=1.82 and a g(x) line at g=1.76. This component has E(m) values at pH10 for single and double reduction of -15mV and approx. -150mV respectively. Both of these E(m) values are pH-dependent. The presence of an interaction between this component and the photoreduced primary acceptor indicates the close proximity of these components. However, the midpoint potential of this component indicates a function as a secondary electron-transport component rather than an electron acceptor in the reaction centre. The dependence of the bacteriopheophytin intermediate (I) doublet e.p.r. signal on the presence of the semiquinone-iron form of the primary acceptor is demonstrated. The midpoint potential of the I/I(-) couple is estimated to be lower than -600mV.     

The influence of electrostatic interactions and intramolecular dynamics on electron transfer from the cytochrome subunit to the cation —radical of the bacteriochlorophyll dimer in reaction centers from Rps. viridis

Interheme electrostatic interaction can explain the acceleration of the electron transfer (ET) rate from the highest potential heme (C38o) to the photooxidized bacteriochlorophyll dimer (P⁺) which takes place after the reduction of neighbouring heme(s) of the cytochrome subunit in the reaction center of Rps. viridis. The electrostatic interaction energies calculated for neighbouring hemes, 7.0 Å apart (edge-to-edge), and for two high potential hemes, 21.5 Å apart are found to be 0.110 eV and 0.040 eV respectively. The reorganisation energy of the C₃₈₀-P⁺ transition of about 0.290±0.030 eV is calculated using the Marcus theory of electron tunneling. An empirical relation for the rate of ET is given. The low temperature restriction of the C₃₈₀-⁺ transition is caused by an energetic inhibition which originates from an opposite shifting of the energy levels of C₃₈₀ and P⁺ due to the freezing of protein dynamics and protein-bound water mobility. The freezing of the protein dynamics is revealed by the Mössbauer effect and correlates with the efficiency of the ET.Abbreviations RC reaction center - P⁺ cation-radical of bacteriochlorophyll dimer - C₃₈₀, C20, C310, C_–60, hemes indexed by the values of their individual redox potentials (in mV) - ET electron transfer     

Chloromycetin in the nutrition of the silkworm Bombyx mori L.—II. Influence on digestion and utilization of protein,fat, and minerals

The nature and extent of the influence of chloromycetin on larval digestion and utilization of the principal dietary constituents—the proteins, fats, and minerals—was studied. The antibiotic was shown to influence favourably the utilization of all the constituents studied. The results have been discussed in the light of these and other findings.