Enhanced asymmetric magnetization reversal in nanoscale Co/CoO arrays: competition between exchange bias and magnetostatic coupling.

Magnetization reversal was studied in square arrays of square Co/CoO dots with lateral size varying between 200 and 900 nm. While reference nonpatterned Co/CoO films show the typical shift and increased width of the hysteresis loop due to exchange bias, the patterned samples reveal a pronounced size dependence. In particular, an anomaly appears in the upper branch of the magnetization cycle and becomes stronger as the dot size decreases. This anomaly, which is absent at room temperature in the patterned samples, can be understood in terms of a competition between magnetostatic interdot interaction and exchange anisotropy during the magnetic switching process.

Intercellular Ca(2+)-transient propagation in normal and high glucose solutions in rat retinal epithelial (RPE-J) cells during mechanical stimulation.

We investigated the effect of high glucose and modulation of protein kinase C (PKC) on the intercellular propagation of Ca(2+)-waves in a rat retinal pigment epithelial cell line (RPE-J cells) in order to compare its properties with the properties previously investigated in primary LE-RPE cells. The intercellular propagation of the Ca(2+)-waves in RPE-J cells was analyzed by fluorescence imaging confocal microscopy and fluorescence recovery after photobleaching (FRAP). In control conditions the maximal normalized fluorescence in the mechanically stimulated (MS) cell and the propagation towards the neighboring RPE-J cells were similar to LE-RPE cells. As in LE-RPE cells, the propagation was reduced by the gap junction (GJ) blocker halothane, and FRAP experiments demonstrated the presence of functional GJ coupling. Similar to the effect in LE-RPE cells, the propagation of the Ca(2+)-transient was reduced by 25 mM glucose. However, unlike LE-RPE cells, the neighboring RPE-J cells presented a Ca(2+)-rise of amplitude similar to that in normal glucose levels. PKC activation with 1 microM PMA for 30 min resulted in inhibition of the Ca(2+)-wave propagation, which could be overcome by PKC downregulation as in LE-RPE cells. Cells grown for 72 h in a high glucose solution in which PKC activity was downregulated, did not develop the inhibitory effect on Ca(2+)-wave propagation that was induced by elevated glucose levels. However, the effects were not as pronounced as in LE-RPE cells. We concluded that despite marked similarities, the transduction and the modulation of intercellular propagation of the Ca(2+)-transients in RPE-J cells are not identical to the mechanisms in primary LE-RPE cells.

Effects of hyperglycemia and protein kinase C on connexin43 expression in cultured rat retinal pigment epithelial cells.

Previous results demonstrated that the intercellular communication mediated by gap junctions in retinal pigment epithelial (RPE) cells from the healthy Long Evans (LE) rat strain is higher than that from the dystrophic Royal College of Surgeons (RCS) rat strain. We examined connexin (Cx) expression in both cell types. At the mRNA level, a qualitatively similar expression pattern was found whereby Cx26, Cx32, Cx36, Cx43, Cx45 and Cx46 were all expressed. At the protein level, only Cx43 and Cx46 were detected. Expression of both isoforms was higher in LE-RPE as compared to RCS-RPE by a factor of 1.25 and 2 respectively. Phosphorylation of Cx43 was increased upon activation of protein kinase C (PKC) by 1 microM phorbol 12-myristate 13-acetate (PMA). The phosphorylation status was not changed in hyperglycemic conditions, but this treatment strongly decreased total Cx43 levels to about 75 and 40% (in LE-RPE and RCS-RPE cells respectively) of the control level in LE-RPE cells. This decrease could be overcome by PKC downregulation. These results demonstrate that PKC activation and hyperglycemic conditions have different effects on Cx43 and that PKC is involved in the metabolic pathway induced by hyperglycemic conditions.

Intra- and intercellular Ca2+ signaling in retinal pigment epithelial cells during mechanical stimulation.

The intercellular communication (IC) was investigated between cultured rat retinal pigment epithelial (RPE) cells isolated from Long-Evans (LE) or dystrophic Royal College of Surgeons (RCS) rats and grown in solutions containing normal and high glucose concentrations, or after modulation of protein kinase C (PKC). This was performed by studying the conduction of the free Ca2+-concentration ([Ca2+]i) wave elicited by mechanical stimulation and by analyzing the fluorescence recovery after photobleaching (FRAP). Mechanical stimulation of LE-RPE cells triggers Ca2+ influx, mediated by stretch-sensitive cation channels followed by intracellular Ca2+ release. A regenerative [Ca2+]i wave was found with a lower propagation rate in RCS-RPE cells. This rate could be increased by PKC down-regulation. Mechanical stimulation caused a [Ca2+]i increase in the mechanically stimulated (MS) cell followed after a delay by a [Ca2+]i rise in the adjacent cell layers. The intercellular [Ca2+]i wave propagation could be blocked by gap junction blockers such as halothane or PKC activation. An inhibition of the [Ca2+]i-wave propagation similar to that induced by halothane could be observed in cells grown in solutions containing 14 mM or higher concentrations of glucose. PKC down-regulated cells grown in glucose-rich medium did not develop this inhibitory effect on gap junction communication (GJC). FRAP experiments confirmed that the observed changes were consistent with a PKC-mediated inhibitory effect of high glucose concentrations on GJC.

ATP-induced Ca2+ signals in bronchial epithelial cells.

Ca2+-dependent Cl- secretion in the respiratory tract occurs physiologically or under pathophysiological conditions when inflammatory mediators are released. The mechanism of intracellular Ca2+ release was investigated in the immortalized bronchial epithelial cell line 16HBE14o-. Experiments on both intact and permeabilized cells revealed that only inositol 1,4,5-trisphosphate (InsP3) receptors and not ryanodine receptors are involved in intracellular Ca2+ release. The expression pattern of the three InsP3 receptor isoforms was assessed both at the mRNA and at the protein level. The level of expression at the mRNA level was type 3 (92.5%) >> type 2 (5.4%) > type 1 (2.1%) and this rank order was also observed at the protein level. The ATP-induced Ca2+ signals in the intact cell, consisting of abortive Ca2+ spikes or fully developed [Ca2+] rises and intracellular Ca2+ waves, were indicative of positive feedback of Ca2+ on the InsP3 receptors. Low Ca2+ concentrations stimulated and high Ca2+ concentrations inhibited InsP3-induced Ca2+ release in permeabilized 16HBE14o- cells. We localized a cytosolic Ca2+-binding site between amino acid residues 2077 and 2101 in the type-2 InsP3 receptor and between amino acids 2030 and 2050 in the type-3 InsP3 receptor by expressing the respective parts of these receptors as glutathione S-transferase fusion proteins in bacteria. We conclude that the InsP3 receptor isoforms expressed in 16HBE14o- cells (mainly type-3 and type-2) are stimulated by Ca2+ and that this phenomenon contributes to the ATP-induced Ca2+ signals in intact 16HBE14o- cells.

Wavelet-based image denoising using a Markov random field a priori model.

This paper describes a new method for the suppression of noise in images via the wavelet transform. The method relies on two measures. The first is a classic measure of smoothness of the image and is based on an approximation of the local Holder exponent via the wavelet coefficients. The second, novel measure takes into account geometrical constraints, which are generally valid for natural images. The smoothness measure and the constraints are combined in a Bayesian probabilistic formulation, and are implemented as a Markov random field (MRF) image model. The manipulation of the wavelet coefficients is consequently based on the obtained probabilities. A comparison of quantitative and qualitative results for test images demonstrates the improved noise suppression performance with respect to previous wavelet-based image denoising methods.

[Growth of lignocellulolytic microorganisms on activated sludge: potential application]. / La croissance de microorganismes lignocellulolytiques sur les boues activées: application potentielle.

A culture medium containing activated sludge and sawdust supports the growth of numerous lignocellulolytic microorganisms. One of them, Phanerochaete chrysosporium could be used in a composite feed for ruminants.

Growth and cellulase production of Micromonospora chalcae and Pseudonocardia thermophila.

Beta(1,4)glucosidases and carboxymethylcellulases were demonstrated in both strains when using carboxymethylcellulose as a carbon source for growth. Beta(1,4)Glucosidases appeared mainly as cell-bound activities, whereas carboxymethylcellulases were evenly distributed between the incubation fluids and the cellular fractions. In both microorganisms, glucose appeared to repress biosynthesis of the enzymes, and cellobiose and carboxymethylcellulose acted as inducers of the cellulase complex.