Membrane permeability changes

The reported (14) mechanisms of action of allelochemlcals Include effects on root ultrastructure and subsequent Inhibition of Ion absorption and water uptake, effects on hormone-induced growth, alteration of membrane permeability, changes In lipid and organic acid metabolism, inhibition of protein synthesis and alteration of enzyme activity, and effects on stomatal opening and on photosynthesis. Reduced leaf water potential Is one result of treatment with ferulic and p-coumaric acids (15). Colton and Einhellig (16) found that aqueous extracts of velvetleaf (Abutllon theophrastl Medic.) Increased diffusive resistance In soybean fGlycine max. (L.) Merr.] leaves, probably as a result of stomatal closure. In addition, there was evidence of water stress and reduced quantities of chlorophyll In Inhibited plants. 

In addition to studies with whole cells and tissues, it has also been shown that the permeability of isolated organelles can be altered by ozone exposure. For example, Lee (11) showed that ozone altered the permeability of tobacco mitochondria, and Coulson and Heath (12) reported membrane permeability changes of isolated chloroplasts after ozone exposure. 

In the majority of patients with sickle cell disease, anemia is not the major problem the anemia is generally well compensated even though such individuals have a chronically low hematocrit (20-30%), a low serum hemoglobin level (7-10 g/dL), and an elevated reticulocyte count. Instead, the primary problem is that deoxygenated HbS chains form polymeric structures that dramatically change erythrocyte shape, reduce deformability, and elicit membrane permeability changes that further promote hemoglobin polymerization. Abnormal erythrocytes... 

In cortical cultures, AMPA receptor activation is also linked to chohne release and inhibition of PtdCho synthesis (Gasull et al., 2001). In contrast, the selective stimulation of KA receptors has no affect on the release of choline and does not reduce PtdCho synthesis. Sensitization of AMPA receptors plays an important role during this process. Thus in the presence of cyclothiazide (CTZ), an inhibitor of AMPA receptor desensitization (Bertolino et al., 1993), AMPA receptor over stimulation becomes neurotoxic after 24 h of treatment. However, significant neuronal death does not occur until the first hour of treatment. In contrast, stimulation of non-sensitized AMPA receptors causes a marked inhibition of PtdCho synthesis within 5 min of treatment. These observations suggest that AMPA-mediated inhibition of PtdCho synthesis precedes membrane permeability changes that may cause excitotoxic necrotic neuronal cell death (Gasull et al., 2001). 

The objective of this study was also to establish a link between an easily observable allelopathic effect (growth inhibition of roots) and a cellular-based explanation (membrane permeability changes). Several modes of action can explain these results, such as an increase in the lipid peroxidation, a disruption in the intrinsic membrane protein activities, or an alteration in plasma membrane ATPase activity. 

Fruit tissues respond to ethylene by exhibiting increases in the activities of enzymes that catalyze ripening reactions, and in some cases, the increases in enzyme activity probably are the result of de novo synthesis, rather than activation of preexisting enzymes. Other target tissues respond similarly to ethylene. But it is not known whether ethylene acts directly to evoke new enzyme production. Interpretation of results with inhibitors of RNA and protein synthesis is inconclusive, because it could be merely that RNA and protein synthesis are essential to maintain the cells in a state competent to respond to ethylene. Moreover, there are some responses to ethylene, besides fruit ripening, which occur under conditions which apparently do not directly involve RNA and protein synthesis (e.g., membrane permeability changes). It has been proposed that the in vivo ethylene receptor site contains a metal such as copper (34,35). 

Many factors are taken into consideration in the clinical interpretation of serum enzyme levels. Membrane permeability changes and cell destruction affect the release of... 

By means of suitable membrane-active additives, we have attempted to modify the structure of isolated thylakoids and thereby increase membrane permeability. Changes in resistance of the membranes to freezing were then determined. Figure 11 shows the effect of sodium caprylate on the permeability of thylakoids to protons. In the absence of the compound, illumination causes proton transfer across the thylakoids and acidification of the intrathylakoid space. A fluorescent weak amine was used to monitor formation of the proton gradient (86). When the light was turned off, protons moved slowly back across the thylakoid membrane. Transport followed first-order kinetics. In the presence of caprylate... 

Binding of acetylcholine triggers the opening of ion channels in the postsynaptic membrane (Figure 21.33d), initiating an action potential that can be passed on to the next axon (Figure 21.33e). The action potential involves a wave of membrane permeability changes that lead to sodium influx and potassium efflux. 

Hormone, drug, toxin, neurotransmitter Receptor Conformation change, membrane permeability change, production of secondary messenger Potentiometric or amperometric electrode or piezoelectric sensor with orientated receptor... 

In contrast to the well developed calixarene sensors of the potentiometric type, chemical sensors based on membrane permeability changes are still in its initial stage. In the present study the permeability of LB calix[4]resorcinarene was found to be controlled by the presence... 

In a recent study the same authors [92] investigated further the influence of cisplatin on the physiology of T24 cancer cells with their SECM technique. They employed FcMeOH redox mediator. Quantitative time-course images were made and the topography and membrane permeability changes were observed. It was found that acute addition of cisplatin to the outer environment of T24 cells immediately induced membrane permeability change. The loosening of the cell membrane permeability was a quick process. After the short period no more continuous increase of the permeability could be seen. It could be concluded that the increase of the cell membrane permeability is involved in the apoptotic process... 

Chemical Sensing Based on Membrane Permeability Changes... 

Chemical sensing based on membrane permeability changes is expected to be a most promising approach toward highly sensitive and selective sensing membranes, because... 

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