Effects of feeding Spodoptera littoralis on lima bean leaves. III. Membrane depolarization and involvement of hydrogen peroxide

In response to herbivore (Spodoptera littoralis) attack, lima bean (Phaseolus lunatus) leaves produced hydrogen peroxide (H(2)O(2)) in concentrations that were higher when compared to mechanically damaged (MD) leaves. Cellular and subcellular localization analyses revealed that H(2)O(2) was mainly localized in MD and herbivore-wounded (HW) zones and spread throughout the veins and tissues. Preferentially, H(2)O(2) was found in cell walls of spongy and mesophyll cells facing intercellular spaces, even though confocal laser scanning microscopy analyses also revealed the presence of H(2)O(2) in mitochondria/peroxisomes. Increased gene and enzyme activations of superoxide dismutase after HW were in agreement with confocal laser scanning microscopy data. After MD, additional application of H(2)O(2) prompted a transient transmembrane potential (V(m)) depolarization, with a V(m) depolarization rate that was higher when compared to HW leaves. In transgenic soybean (Glycine max) suspension cells expressing the Ca(2+)-sensing aequorin system, increasing amounts of added H(2)O(2) correlated with a higher cytosolic calcium ([Ca(2+)](cyt)) concentration. In MD and HW leaves, H(2)O(2) also triggered the increase of [Ca(2+)](cyt), but MD-elicited [Ca(2+)](cyt) increase was more pronounced when compared to HW leaves after addition of exogenous H(2)O(2). The results clearly indicate that V(m) depolarization caused by HW makes the membrane potential more positive and reduces the ability of lima bean leaves to react to signaling molecules.     

Synthesis and properties of anionic cellulose ethers: influence of functional groups and molecular weight on flowability of concrete

The suitability of anionic cellulose ethers as superplasticizers and the effect of chemical structure on the fluidity of cement mixtures was investigated. To elucidate the influence of molecular weight and degree of cellulose backbone substitution, cellulose and hydroxyethyl cellulose with molecular weights <50,000 g/mol were synthesized by acid-catalyzed and oxidative degradation. Commercial as well as degraded samples were functionalized by carboxymethylation and sulfobutylation, controlling the degree of substitution (DS) by the molar ratio of reactants and by taking advantage of the high reactivity of sultones towards salts of carboxylic acids, even in aqueous solutions. The fluidizing effect of the cellulose ethers with anionic ‘cement-anchoring‘ groups was prescreened, measuring the static flow of cement pastes. The results indicated a high potential of sulfobutylated cellulose mixed ethers as dispersing agents for concrete. The fluidizing action increased with increasing DS and an optimum range of molecular weight between 100,000 and 150,000 g/mol was found.     

Double-barreled and Concentric Microelectrodes for Measurement of Extracellular Ion Signals in Brain Tissue

Electrical activity in the brain is accompanied by significant ion fluxes across membranes, resulting in complex changes in the extracellular concentration of all major ions. As these ion shifts bear significant functional consequences, their quantitative determination is often required to understand the function and dysfunction of neural networks under physiological and pathophysiological conditions. In the present study, we demonstrate the fabrication and calibration of double-barreled ion-selective microelectrodes, which have proven to be excellent tools for such measurements in brain tissue. Moreover, so-called “concentric” ion-selective microelectrodes are also described, which, based on their different design, offer a far better temporal resolution of fast ion changes. We then show how these electrodes can be employed in acute brain slice preparations of the mouse hippocampus. Using double-barreled, potassium-selective microelectrodes, changes in the extracellular potassium concentration ([K⁺]_o) in response to exogenous application of glutamate receptor agonists or during epileptiform activity are demonstrated. Furthermore, we illustrate the response characteristics of sodium-sensitive, double-barreled and concentric electrodes and compare their detection of changes in the extracellular sodium concentration ([Na⁺]_o) evoked by bath or pressure application of drugs. These measurements show that while response amplitudes are similar, the concentric sodium microelectrodes display a superior signal-to-noise ratio and response time as compared to the double-barreled design. Generally, the demonstrated procedures will be easily transferable to measurement of other ions species, including pH or calcium, and will also be applicable to other preparations.     

Micromere-specific cell surface proteins of 16-cell stage sea urchin embryos

Evidence is presented of cell-type specificity of surface proteins from the 16-cell stage sea urchin embryo. The protein composition of the micromere cell surface has been examined by 125I labelling of intact cells followed by SDS-PAGE. In Arbacia punctulata, four high molecular weight (HMW) proteins are detected on the surface of isolated micromeres--but not on mesomere-macromere fractions. In Strongylocentrotus droebachiensis, a micromere-specific protein of 133 K molecular weight (MW) was identified. This 133 K protein binds to wheat germ agglutinin (WGA) but not to concanavalin A (conA). Lectin binding was studied using a new technique. The procedure involves the separation, by SDS-PAGE, of iodinated cell-surface proteins followed by their electrophoretic transfer to lectin-coated nitrocellulose membranes. Using this procedure, cell-type-specific surface proteins which are also lectin-binding-specific, were detected.     

Apoptosis pathways and their therapeutic exploitation in pancreatic cancer

Resistance to apoptosis (programmed cell death) is a characteristic feature of human malignancies including pancreatic cancer, which is one of the leading causes of cancer deaths in the western world. Defects in this intrinsic cell death program can contribute to the multistep process of tumorigenesis, because too little cell death can disturb tissue homeostasis. Further, blockade of apoptosis pathways can cause treatment failure, because intact apoptosis signalling cascades largely mediate therapy-induced cytotoxicity. The elucidation of apoptosis pathways in pancreatic carcinoma over the last decade has resulted in the identification of various molecular defects. How apoptosis pathways can be exploited for the treatment of pancreatic cancer will be discussed in this review.