Erythrocyte and plasma Ca2+, Mg2+ and cell membrane adenosine triphosphatase activity in patients with essential hypertension.
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OBJECTIVE: To assess the relationships between plasma and intracellular Ca2+, Mg2+ and blood cell membrane adenosine triphosphatase (ATPase) activity in normotensive and hypertensive subjects. METHODS: Plasma and intracellular Ca2+, Mg2+ were measured with atomic absorption spectrophotometry, and red blood cell membrane Na(+)-K+ ATPase and Ca(2+)-ATPase activities were determined with colorimetric method in 55 patients with essential hypertension and 32 normotensive controls. RESULTS: The results showed that the hypertensive group consistently demonstrated a significant decreased activity of ATPase studied, with significantly lower plasma Ca2+ and higher cytosolic Ca2+ levels when compared with those in normotensive group (P < 0.01 or P < 0.05, respectively). No significant differences were found in either plasma Mg2+ or intracellular Mg2+ level between the two groups. CONCLUSIONS: This study suggests that patients with essential hypertension have widespread depression of cell membrane Na(+)-K(+)-ATPase and Ca(2+)-ATPase activities with plasma Ca2+ depletion and cytosolic Ca2+ overload, which may reflect an underlying membrane abnormality in essential hypertension. The cellular abnormalities may be related to the defective transport mechanisms that in turn may be aggravated by plasma Ca2+ depletion. (+info)
Effects of synthetic (-)-huperzine A on cholinesterase activities and mouse water maze performance.
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AIM: To compare the effects of synthetic and natural (-)-huperzine A (Hup A) on cholinesterase and mouse water maze performance. METHODS: Spectrophotometry was used to determine cholinesterase activity. Mouse water maze was used to evaluate nootropic effect. RESULTS: The IC50 of synthetic Hup A for acetylcholinesterase (AChE) of rat cortex and rat erythrocyte membrane determined in vitro were 64.7 (52.6-79.5) and 53.9 (43.6-66.6) nmol.L-1, respectively, and for butyrylcholinesterase of rat serum was 53.6 (44.9-63.8) mumol.L-1. Synthetic Hup A 0.12-0.48 mg.kg-1 ig produced a dose-dependent inhibition of brain AChE in mice. Synthetic Hup A 0.05 mg.kg-1 ig attenuated scopolamine-induced impairment of spatial memory. The efficacy of synthetic Hup A was the same as natural Hup A. CONCLUSION: Synthetic Hup A yielded an in vitro and in vivo pharmacological profile of activities similar to that of natural Hup A. (+info)
Iron-induced oxidative stress in erythrocyte membranes of non-insulin-dependent diabetic Nigerians.
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The presence of higher level of endogenous free radical reaction products in the erythrocyte ghost membrane (EGM) of Non-insulin-dependent diabetes mellitus (NIDDM) subjects compared with that of normal healthy controls has been demonstrated. The EGMs of NIDDM subjects were also shown to be more susceptible to exogenously generated oxidative stress than those of normal healthy individuals. The decreased level of reactive thiol groups in the EGM of NIDDM individuals supported this observation. We propose that the presence of significant levels of non-heme iron in the EGM of NIDDM subjects is an indication of the potential for iron-catalysed production of hydroxy and other toxic radicals which could cause continuous oxidative stress and tissue damage. Oxygen free radicals could therefore be responsible for most of the erythrocyte abnormalities associated with non-insulin-dependent diabetes and could indeed be intimately involved in the mechanism of tissue damage in diabetic complications. (+info)
Hereditary spherocytosis and elliptocytosis erythrocytes show a normal transbilayer phospholipid distribution.
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Phosphatidylserine (PS) asymmetry was determined in red blood cells from patients with hereditary spherocytosis and elliptocytosis. No PS-exposing subpopulations were detected using the very sensitive method with fluorescently labeled annexin V. Treatment with N-ethylmaleimide or adenosine triphosphate (ATP) depletion to inactivate the flipase did not lead to formation of PS-exposing subpopulations in these cells, but elevated intracellular calcium levels did lead to extensive scrambling of the PS asymmetry. Although interactions of the membrane skeleton with the phospholipid bilayer have been suggested to stabilize the asymmetric distribution of PS across the bilayer, our data show that red blood cells with a severely damaged membrane skeleton are able to preserve asymmetry, even under conditions in which restoration of the asymmetric distribution is excluded. Moreover, the loss of membrane asymmetry in these cells requires active scrambling involving high levels of intracellular calcium as in normal cells. Our data show that the severe disorder of the membrane skeleton found in these cells does not affect the activity of flipase or scramblase, indicating that these proteins are not regulated by, nor coupled to the membrane skeleton assembly, and that possible thrombotic events in spherocytosis patients are not likely associated with altered PS topology of the red blood cells. (+info)
Formation of the aldehydic choline glycerophospholipids in human red blood cell membrane peroxidized with an azo initiator.
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The production of phospholipid hydroperoxide and aldehydic phospholipid was examined in human red blood cell (RBC) membranes after peroxidation with 2,2-azobis(2-amidinopropane)dihydrochloride (AAPH) or xanthine/xanthine oxidase (XO/XOD/Fe3+). Both radical-generation systems caused a profound decrease in the amount of polyunsaturated fatty acid (PUFA) in choline glycerophospholipid (CGP) and induced formation of peroxidized CGP in RBC membranes to different extents. No consistent generation of peroxidized lipids from CGP was evident after peroxidation with XO/XOD/Fe3+, which caused the apparent decomposition of phospholipids and the formation of large amounts of thiobarbituric acid-reactive substance (TBARS). On the other hand, CGP hydroperoxide was formed as a primary product of peroxidation with AAPH. Aldehydic CGP was also detected as a secondary product of hydroperoxide decomposition in AAPH-peroxidized RBC membranes. Aldehydic CGP was preferentially generated from arachidonoyl CGP rather than from linoleoyl CGP in AAPH-peroxidized membranes. AAPH mainly oxidized CGP to hydroperoxide and aldehydic phospholipids. The sum of hydroperoxide and aldehyde of CGP corresponded to the loss of CGP due to peroxidation by AAPH. This result indicates that CGP was mainly converted into these two oxidized phospholipids in AAPH-peroxidized RBC membranes. (+info)
Fingerprinting of large oligosaccharides linked to ceramide by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry: highly heterogeneous polyglycosylceramides of human erythrocytes with receptor activity for Helicobacter pylori.
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Highly microheterogeneous polyglycosylceramides (PGCs) of human erythrocytes with an average composition of about 25 monosaccharides linked to ceramide were analyzed by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS). The human gastric pathogen Helicobacter pylori was earlier shown to bind this glycosphingolipid mixture by thin-layer chromatogram binding assay. The receptor activity was present along the whole nonresolved chromatographic interval. Mass spectra of intact PGCs were compared with corresponding spectra of oligosaccharides enzymatically released from the ceramides. Two subfractions of PGCs containing less than one and more than one sialic acid residue per molecule were used. MALDI-MS spectra were recorded in both linear and reflectron mode with the accuracies of +info)
Nine-year longitudinal study of antibodies to variant antigens on the surface of Plasmodium falciparum-infected erythrocytes.
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PfEMP1 is an antigenically variable molecule which mediates the adhesion of parasitized erythrocytes to a variety of cell types and which is believed to constitute an important target for naturally acquired protective immune responses in malaria. For 9 years we have monitored individuals living in an area of low-intensity, seasonal, and unstable malaria transmission in eastern Sudan, and we have used this database to study the acquisition, specificity, and duration of the antibody response to variant parasitized erythrocyte surface antigens. Both the levels and the spectrum of reactivity of these antibodies varied considerably among individuals, ranging from low levels of antibodies recognizing only few parasitized erythrocyte surface antigens to high levels of broad-specificity antibodies. In general, episodes of clinical malaria were associated with increases in the levels of parasitized erythrocyte surface-specific antibodies that subsided within months of the attack. This response was often, but not always, specific for the antigenic variants expressed by the parasite isolate causing disease. Our study provides evidence that Palciparum falciparum malaria is associated with a short-lived, variant-specific antibody response to PfEMP1-like antigens exposed on the surface of parasitized erythrocytes. Furthermore, our data suggest that the antigenic repertoires of variant antigens expressed by different parasite isolates show considerable overlapping, at least under Sahelian conditions of low-intensity, seasonal, and unstable malaria transmission. Finally, we demonstrate the existence of persistent differences among individuals in the capacity to mount antibody responses to variant surface antigens. (+info)
Protein kinase C-promoted inhibition of Galpha(11)-stimulated phospholipase C-beta activity.
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The effects of protein kinase C (PKC) activation on inositol lipid signaling were examined. Using the turkey erythrocyte model of receptor-regulated phosphoinositide hydrolysis, we developed a membrane reconstitution assay to study directly the effects of activation of PKC on the activities of Galpha(11), independent of potential effects on the receptor or on PLC-beta. Membranes isolated from erythrocytes pretreated with 4beta-phorbol-12beta-myristate-13alpha-acetate (PMA) exhibited a decreased capacity for Galpha(11)-mediated activation of purified, reconstituted PLC-beta1. This inhibitory effect was dependent on both the time and concentration of PMA incubation and occurred as a decrease in the efficacy of GTPgammaS for activation of PLC-beta1, both in the presence and absence of agonist; no change in the apparent affinity for the guanine nucleotide occurred. Similar inhibitory effects were observed after treatment with the PKC activator phorbol-12,13-dibutyrate but not after treatment with an inactive phorbol ester. The inhibitory effects of PMA were prevented by coaddition of the PKC inhibitor bisindolylmaleimide. Although the effects of PKC could be localized to the membrane, no phosphorylation of Galpha(11) occurred either in vitro in the presence of purified PKC or in intact erythrocytes after PMA treatment. These results support the hypothesis that a signaling protein other than Galpha(11) is the target for PKC and that PKC-promoted phosphorylation of this protein results in a phosphorylation-dependent suppression of Galpha(11)-mediated PLC-beta1 activation. (+info)