1,721,061 research outputs found
Variations in the fatty acid composition of rat erythrocyte membrane lipids at different ages [Variazione della composizione in acidi grassi dei lipidi della membrana dell'eritrocita nel ratto a differente eta']
No full textThe fatty acid composition of the erythrocyte lipids was studied in newborn, growing and adult rats. The percentage of oleic acid progressively decreased from the birth up to the adult age, while that of linoleic acid markedly increased. A smaller increase was also seen in the arachidonic acid content. These changes do not seem to be accounted for by differences in the percentages of the major phospholipid fractions or to differences in the age of the erythrocyte. Rather, variations in the fatty acid pattern of the various fractions of plasma lipids seem to be responsible for the lipid changes in the erythrocyte membrane
Glucose 6-phosphate stimulation of MgATP-dependent Ca2+ uptake by rat kidney microsomes
No full text(1) The features of MgATP-dependent Ca2+ accumulation under stimulation with glucose 6-phosphate were studied in rat kidney microsomes. (2) ca2+ accumulated in the presence of MgATP alone does not exceed approx. 2 nmol/mg protein. (3) Glucose 6-phosphate markedly stimulates ca2+ accumulation, up to steady-state levels approx. 15-fold higher than in its absence. (4) The hydrolysis of glucose 6-phosphate by glucose-6-phosphate is essential for the stimulation, as shown by inhibiting the glucose 6-phosphate hydrolysis with adequate concentration of vanadate. Inorganic phospate is accumulated in microsomal vesicles during glucose 6-phosphate-stimulated ca2+ uptake in equimolar amounts with respects to ca2+. (5) Increasing concentrations of glucose 6-phosphate result in increasing stimulations of ca2+ uptake, until a maximal ca2+-loading capacity of approx. 27 nmol/mg microsomal protein is reached. It is suggested that the enlargement of the kidney microsomal ca2+ pool induced by glucose 6-phosphate (an important metabolite in kidney) might play a role in the regulation of ca2+ homeostatis in kidney tubular cells. © 1990
On the role of lipid peroxidation and protein-bound aldehydes in the haloalkane-induced inactivation of microsomal glucose 6 phosphatase
No full textThe inactivation of liver microsomal glucose 6 phosphatase induced either by Fe2+ or by haloalkanes (CCI4, CBrCl3) was investigated in NADPH-microsomes systems. In the case of haloalkanes, EDTA was included in the incubation mixtures, so to exclude participation of free Fe2+ in the ensuing lipid peroxidation. Microsomal glucose 6 phosphatase activity was measured along with the release of malonic dialdehyde and the appearance of carbonyl products bound to microsomal protein, taken as indices of the peroxidative process. Fe2+ was added to NADPH-microsomes at different concentrations, one (6 μM) resulting in an extent of lipid peroxidation comparable with that induced by haloalkanes, the other (60 μM) representing a situation of excess Fe2+, leading to massive lipid peroxidation. Inhibition of glucose 6 phosphatase caused by 6 μM Fe2+ was comparable to that induced by haloalkanes in EDTA-microsomes systems, which supports the view that lipid peroxidation - rather than covalent binding of free radical metabolites - represents the main event leading to the inactivation of glucose 6 phosphatase caused by haloalkanes. The production of 4-hydroxynonenal - the known toxic product of lipid peroxidation - was also studied. A remarkable accumulation of 4-hydroxynonenal was observed in the microsomal membranes after peroxidation induced by 6 μM Fe2+ or haloalkanes, as compared to the incubation medium. In addition, experiments carried out with CCl4 and CBrCl3 in vivo suggested the possible existence of a cytosolic detoxification system able to remove lipid-derived carbonyls bound to microsomal protein
Inhibition of store-dependent capacitative Ca2+ influx by unsaturated fatty acids
No full textThe effects of the unsaturated fatty acids, arachidonic and oleic acid, on the influx of Ca2+ activated by depletion of intracellular stores with thapsigargin were investigated in various cell types. By using a Ca2+ free/Ca2+ reintroduction protocol, we observed that arachidonic acid (2 to 5 microM) inhibited thapsigargin-induced rises in cytosolic free Ca2+ ([Ca2+]i) in Ehrlich tumor cells, Jurkat T lymphocytes, rat thymocytes, and Friend erythroleukemia and PC12 rat pheochromocytoma cells. This effect was attributed to the inhibition of Ca2+ entry, since arachidonate also inhibited thapsigargin-stimulated unidirectional entry of the Ca2+ surrogates Ba2+ and Mn2+. In Ehrlich cells, the IC50 for arachidonic and oleic acid was 1.2 and 1.8 microM, respectively. The inhibition appeared to depend on the ratio [fatty acid]/[cells] rather than on the absolute fatty acid concentration. Experiments with [3H]-oleic acid revealed that the inhibitory activity was not correlated with cell internalisation and metabolism of the fatty acid. The inhibition was reverted by removal of the fatty acid bound to cell membrane by fatty acid-free albumin treatment. The unsaturated fatty acids had no effect on ATP/ADP cell levels and plasma membrane potential. Pharmacological evidence indicated that cell phosphorylation/dephosphorylation events, and pertussis toxin-sensitive G proteins were not involved. Other amphipathic lipophilic compounds, i.e. 2-bromopalmitic acid, retinoic acid, sphingosine, and dihydrosphingosine, mimicked arachidonic/oleic acid as they inhibited thapsigargin-stimulated Ca2+ influx in an albumin-reversible fashion. These results suggest that physiologically relevant (unsaturated) fatty acids can inhibit capacitative Ca2+ influx possibly because they intercalate into the plasma membrane and directly affect the activity of the channels involved
Funzionamento accoppiato delle pompe del calcio e dell'attività glucoso-6 fosfatasica nei microsomi epatici: risultati preliminari [Functional coupling of the calcium pump and glucose 6-phosphatase activity in liver microsomes: preliminary results]
No full textThe addition of G-6-Pi to the incubation system for MgATP-dependent calcium transport in liver microsomes results in a marked stimulation of Ca2+ uptake. At physiological pH values (7.2-7.4), the G-6-Pi stimulated calcium uptake is maximal and equals that obtained with oxalate at pH 6.8. In the system for the G-6-Pi-stimulated calcium uptake, G-6-Pi is actively hydrolyzed by the glucose 6-phosphatase activity of liver microsomes. Such an activity is not influenced by the concomitant calcium uptake. After the incubation of the system for the MgATP-dependent microsomal calcium transport in the presence of G-6-Pi, Pi and calcium are found in equal concentrations, on a molar base, in the recovered microsomal fraction. These results are interpreted in the light of a possible cooperative activity between the energy-dependent calcium pump of liver microsomes and the glucose 6-phosphatase multicomponent system
Inibizione dell'attività calcio sequestrante dei microsomi epatici nella intossicazione da monobromotriclorometano: studi preliminari sui possibili meccanismi [Inhibition of the calcium-sequestering activity of liver microsomes in monobromotrichloromethane poisoning: preliminary studies on possible mechanisms]
No full textThe mechanisms by which the in vivo intoxication with BrCCl3 inhibits the calcium sequestration activity of liver microsomes were studied. The initial rate of Ca2+ transport is inhibited by nearly 50% in the intoxicated rats as compared to the controls; this indicates that the active transport of Ca2+ is markedly affected by the intoxication. The microsomal ATPases activities both in the presence and in the absence of Ca2+ were not decreased at all in the intoxicated animals. However, the Ca2+-dependent extra ATP hydrolysis shows a different kinetics in the BrCCl3-poisoned rats with respect to the controls. The release of Ca2+ from Ca2+ loaded liver microsomes is higher in the intoxicated animals. It seems therefore that the increased permeability of the membrane to Ca2+ contributes to some extent to the haloalkane-induced inhibition of the calcium sequestration activity of liver microsomes
On the mechanisms of the inhibition of calcium sequestering activity of liver microsomes in bromotrichloromethane intoxication
No full textThe mechanisms by which the in vivo intoxication with BrCCl3 inhibits the calcium sequestration activity of liver microsomes were studied. The initial rate of Ca2+ transport is inhibited by nearly 50% in the intoxicated rats as compared to the controls; this indicates that the active transport of Ca2+ is markedly affected by the intoxication. The microsomal ATPase activities both in the presence and in the absence of Ca2+ were not decreased at all in the intoxicated animals. However, the Ca2+-dependent extra ATP-hydrolysis shows a different kinetics in the BrCCl3-Ca2+-loaded liver microsomes is higher in the intoxicated animals. It seems therefore that the increased permeability of the membrane to Ca2+ contributes to some extent to the haloalkane-induced inhibition of the calcium sequestration activity of liver microsomes
Calcium sequestration activity in rat liver microsomes. Evidence for a cooperation of calcium transport with glucose-6-phosphatase
No full textDetection of 4-hydroxynonenal and other lipid peroxidation products in the liver of bromobenzene-poisoned mice
No full textLipid peroxidation in cellular membranes leads to the formation of toxic aldehydes. One product provided with particular reactivity has been identified as 4-hydroxynonenal and thoroughly studied as one of the possible mediators of the cellular injury induced by pro-oxidants. In the present study we have searched for the presence of 4-hydroxynonenal and other lipid peroxidation products in the liver of bromobenzene-poisoned mice, since under this experimental condition the level of lipid peroxidation is much greater than in the case of CCl4 or BrCCl3 hepatotoxicity. 4-Hydroxynonenal was looked for in liver extracts as either free aldehyde or its 2,4-dinitrophenylhydrazone derivative. In both cases, by means of thin-layer chromatography (TLC) and high-pressure liquid chromatography, a well resolved peak corresponding to the respective standards (free aldehyde or 2,4-dinitrophenylhydrazone derivative) was obtained. Total carbonyls present in the liver of intoxicated animals were detected as 2,4-dinitrophenylhydrazone derivatives. The hydrazones were pre-separated by TLC into three fractions according to different polarity (polar, non-polar, fraction I, and non-polar, fraction II). The amounts of carbonyls present in each fraction were determined by ultraviolet-visible spectroscopy. 'Non-polar carbonyls, fraction II' were further fractionated by TLC. The fraction containing alkanals and alk-2-enals was analyzed by high-pressure liquid chromatrography and several aldehydes were identified. In addition, protein bound carbonyls were determined in the liver of bromobenzene-treated mice. The biological implications of the finding of 4-hydroxynonenal and other carbonyls in vivo in an experimental model of hepatotoxicity are discussed. © 1986
Liver glucose-6-phosphatase activity is not modulated by physiological intracellular Ca2+ concentrations
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