Linoleic acid hydroperoxide favours hypochlorite- and myeloperoxidase-induced lipid peroxidation

Liposomes composed of soybean phosphatidylcholine were peroxidized using the reagent sodium hypochlorite or the myeloperoxidase-hydrogen peroxide-Cl^- system. Linoleic acid hydroperoxide previously prepared from linoleic acid by means of lipoxidase was incorporated into liposomes. The yield of thiobarbituric acid reactive substances (TBARS) continuously increased with higher amounts of hydroperoxide groups after the initiation of lipid peroxidation by hypochlorous acid producing systems. The accumulation of TBARS was inhibited by scavengers of free radicals such as butylated hydroxytoluene and by the scavengers of hypochlorous acid, taurine and methionine. Lipid peroxidation was also prevented by sodium azide or chloride free medium in the myeloperoxidase-hydrogen peroxide-Cl^- system. Here we show for the first time that the reaction of hypochlorous acid with a biologically relevant hydroperoxide yields free radicals able to cause further oxidation of lipid molecules.     

Subtle re-location of dendritic spine branches containing membrane with fast spiking mechanisms can alter synaptic efficacy

The potential physiological impact of morphological changes in the active dendritic spines, which are believed to be associated with altered synaptic efficacy, was investigated in a computer simulation study using the NEURON package [1]. A compartmental model of a simplified neuron was built, which included 30 complex spines (neck, head, and active zone) and accommodating AMPA-type synaptic inputs with alpha-function conductances. Hodgkin-Huxley type excitable membranes were inserted into the spine heads. It was shown that arranging spines in dense clusters, as opposed to a uniformly random spine distribution, has a negligible effect on the synaptic signal transfer (other model conditions, including synaptic input and spine density, remained unchanged). However, if a proportion (e.g., 3–20%) of the spines partly fuse with their neighbors forming branched spines, this could increase dramatically the cell response to the unchanged synaptic input. Results of this pilot study provide the basis for a more detailed investigation of the relationship between the spine arrangement and synaptic function, considering dual-component synaptic currents and mechanisms controlling ion fluxes in the dendritic compartments.     

Activation of superoxide production and differential exocytosis in polymorphonuclear leukocytes by cytochalasins A,B, C,D and E: Effects of various ions

All of the common cytochalasins activate superoxide anion release and exocytosis of β-N-acetylglucosaminidase and lysozyme from guinea-pig polymorphonuclear leukocytes (neutrophils) incubated in a buffered sucrose medium. Half-maximal activation of both processes is produced by approx. 2 μM cytochalasin A, C >μM cytochalasin B ? 4–5 μM cytochalasin D, E. While maximal rates of O₂^? release and extents of exocytosis require extracellular calcium (1–2 mM), replacing sucrose with monovalent cation chlorides is inhibitory to neutrophil activation by cytochalasins. Na⁺, K⁺ or choline inhibited either cytochalasin B- or E-stimulated O₂^? production with IC₅₀ values of 5–10 mM and inhibition occurs whether Cl^?, NO₃^? or SCN^? is the anion added with Na⁺ or K⁺. Release of β-N-acetylglucosaminidase in control or cytochalasin B-stimulated cells is inhibited by NaCl (IC₅₀ ≈ 10 mM), while cytochalasin E-stimulated exocytosis is reduced less and K⁺ or choline chloride are ineffective in inhibiting either cytochalasin B- or E-stimulated exocytosis. Release of β-glucuronidase, myeloperoxidase or acid phosphatase from neutrophils incubated in buffered sucrose is not stimulated by cytochalasin B. Stimulation of either O₂^? or β-N-acetylglucosaminidase release by low concentrations of cytochalasin A is followed by inhibition of each at higher concentrations. It appears that all cytochalasins can activate both NAD(P)H oxidase and selective degranulation of neutrophils incubated in salt-restricted media and that differential inhibition of these two processes by monovalent cations and/or anions is produced at some step(s) subsequent to cytochalasin interaction with the cell.     

Effect of water-soluble antioxidants on the permeability of lysosomal membranes and on the structure of the liver in rats with thermal burns

Experiments on rats were made to study the effect of water-soluble antioxidants on the permeability of lysosomal membranes of liver cells and liver structure under burn. Antioxidants were injected intraperitoneally shortly after burn, whereas examination was performed after one day. It has been discovered that one day after burn there takes place an appreciable destabilization of lysosomal membranes with the release of a lysosomal matrix enzyme, cathepsin D to the cytoplasm. Liver structure had undergone substantial changes by that time. After administration of water-soluble antioxidants lysosomal membranes got stabilized while liver structure manifested but insignificant disorders.     

Interaction of the organic anion 1-aniline 8-naphthalene sulfonate (ANS) with isolated rat hepatocytes

The interaction of ANS with rat hepatocytes in time was studied by fluorescence spectroscopy. The intercept of the first linear portion of the time curve of interaction showed a positive value over all the ANS concentration range employed. This value was maintained after cellular disruption by homogenization. It was affected by ionic strength, pH, and divalent cation in the incubation medium, all conditions affecting the cellular surface. These data suggest that this phenomenon might be a binding of the compound to the hepatocytes surface. Due to the time constant and its disappearance after cellular disruption the other slower component of the curve seems to correspond to a process of translocation across the membrane.     

Deoxyuridine triphosphatase: A potential site of interaction with pyrimidine nucleotide analogues

Deoxyuridine triphosphatase has been purified from cultured human lymphoid cells in high yield and stable form by a relatively simple procedure. The properties differed somewhat from those reported previously, e.g. apparent K_m, molecular weight, and effects of divalent metals. No other naturally occurring dNTP or NTP serves as substrate, however, the enzyme may be an important site of interaction with intracellular derivatives of analogues of dUrd. It is shown here that deoxyuridine triphosphatase acts on araUTP, 6-azadUTP, 2′-FdUTP, and 2′,3′-dideoxyUTP, but the enzyme has no effect on 5-C1dUTP, 5-BrdUTP, 5-HgdUTP and dUrd-5′[α-thio]triphosphate. For the preparation of one of the analogues, the enzyme, trans-N-deoxyribosylase, from Lactobacillus, was used to prepare the deoxynucleoside from the base, a procedure that may have general usefulness.