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Biomedical subjects

G Benga

Publications and source records attributed to G Benga.

At least 37 records · Page 2Linked to original sources
PubMed1989

Studies of water permeability and proteins of erythrocyte membranes in patients with Duchenne muscular dystrophy.

The characteristics of water permeability of erythrocytes from 54 Duchenne muscular dystrophy (DMD) patients and age-matched controls have been determined by a pulse nuclear magnetic resonance (NMR) technique. A decreased permeability of erythrocyte membrane in DMD was definitely found at all temperatures between 15 and 42 degrees C, with normal values for the activation energy of water diffusion. No differences between DMD and control subjects in the pattern of erythrocyte membrane polypeptides separated by two-dimensional electrophoresis could be detected. The findings are discussed in relation to the molecular mechanisms of water diffusion across erythrocyte membrane and the problem of erythrocyte membrane abnormalities in DMD. A new interpretation of erythrocyte membrane alterations is proposed based on the recent findings regarding the molecular pathology of DMD.

Adolescent↗
PubMed1989

Water exchange through erythrocyte membranes: biochemical and nuclear magnetic resonance studies re-evaluating the effects of sulfhydryl reagents and of proteolytic enzymes on human membranes.

The water permeability of human red blood cell (RBC) membrane has been monitored by a doping nuclear magnetic resonance (NMR) technique on intact cells and resealed ghosts following exposure to various sulfhydryl-reacting (SH) reagents and proteolytic enzymes. The main conclusions are the following: (i) When appropriate conditions for exposure of erythrocytes or ghosts to mercury-containing SH reagents (concentration, temperature and duration of incubation) were found, the maximal inhibition of water diffusion could be obtained with all mercurials (including HgCl2 and mersalyl that failed to show their inhibitory action on RBC water permeability in some investigations). While previous studies claimed that long incubation times are required for the development of maximal inhibition of water diffusion by mercurials, the present results show that it can be induced in a much shorter time (5-15 min at 37 degrees C) if relatively high concentrations of PCMBS (2-4 mM) are used and no washings of the inhibitor are performed after incubation. Higher than optimal concentrations of mercurials and/or longer incubation times result in lower values of inhibition, sometimes a loss of inhibition, or can even lead to higher values of permeability compared to control RBCs. (ii) The conditions for inhibition by mercurials are drastically changed by preincubation of erythrocytes with noninhibitory SH reagents (such as NEM or IAM) or by exposure to proteolytic enzymes. If the cells are digested with papain, the duration of incubation with PCMBS should be decreased in order for inhibition to occur. This explains the lack of inhibition reported previously, when a relatively long duration of incubation with PCMBS was used subsequent to papain digestion.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1987

Effects of temperature on water diffusion in human erythrocytes and ghosts--nuclear magnetic resonance studies.

The temperature-dependence of water diffusion across human erythrocyte membrane was studied on isolated erythrocytes and resealed ghosts by a doping nuclear magnetic resonance technique. The conclusions are the following: (1) The storage of suspended erythrocytes at 2 degrees C up to 24 h or at 37 degrees C for 30 min did not change the water exchange time significantly, even if Mn2+ was present in the medium. This indicates that no significant penetration of Mn2+ is taking place under such conditions. (2) In case of cells previously incubated at 37 degrees C for longer than 30 min with concentrations of p-chloromercuribenzene sulfonate (PCMBS) greater than 0.5 mM, the water-exchange time gradually decreased if the cells were stored in the presence of Mn2+ for more than 10 min at 37 degrees C. (3) When the Arrhenius plot of the water-exchange time was calculated on the basis of measurements performed in such a way as to avoid a prolonged exposure of erythrocytes to Mn2+ no discontinuity occurred, regardless of the treatment with PCMBS. (4) No significant differences between erythrocytes and resealed ghosts regarding their permeability and the activation energy of water diffusion (Ea,d) were noticed. The mean value of Ea,d obtained on erythrocytes from 35 donors was 24.5 kJ/mol. (5) The value of Ea,d increased after treatment with PCMBS, in parallel with the percentage inhibition of water diffusion. A mean value of 41.3 kJ/mol was obtained for Ea,d of erythrocytes incubated with 1 mM PCMBS for 60 min at 37 degrees C and 28.3 kJ/mol for ghosts incubated with 0.1 mM PCMBS for 15 min, the values of inhibition being 46% and 21% respectively.

4-Chloromercuribenzenesulfonate↗
PubMed1987

Freeze-fracture electron microscopic observations on the effects of sulphydryl group reagents on human erythrocyte membranes.

Freeze-fracture electron microscopy of human red blood cells at pH 7.4 and 5.5 reveals the presence of membrane elevations (50-100 nm diameter). These are also observed after incubation of the erythrocytes with N-ethylmaleimide but not after incubation with p-chloromercuribenzene sulphonate. Neither of the sulphydryl-group reagents affects the distribution or size of intramembrane particles. The findings are discussed in the light of the effects of mercurials on erythrocyte membrane proteins.

Erythrocyte Membrane↗
PubMed1986

p-(Chloromercuri)benzenesulfonate binding by membrane proteins and the inhibition of water transport in human erythrocytes.

The binding of [203Hg]-p-(chloromercuri)benzenesulfonate to the membrane proteins of human erythrocytes and erythrocyte ghosts was examined under conditions where binding to the bulk of membrane sulfhydryl groups was blocked by N-ethylmaleimide. Binding was essentially complete within 90 min when approximately 40 nmol was bound per milligram of membrane protein. This binding was correlated with the inhibition of water transport measured by an NMR technique. Maximal inhibition was observed with the binding of approximately 10 nmol of p-(chloromercuri)benzenesulfonate/mg of membrane protein. Under these conditions, both band 3 and band 4.5 bound 1 mol of inhibitor/mol of protein. In contrast to previous experiments, these results indicate that band 4.5 proteins as well as band 3 have to be considered as playing a role in water transport.

4-Chloromercuribenzenesulfonate↗
PubMed1986

Water exchange through erythrocyte membranes: nuclear magnetic resonance studies on resealed ghosts compared to human erythrocytes.

The water diffusion across human erythrocyte membrane has been studied on intact cells and resealed ghosts by a doping NMR technique. Although the water exchange time of ghosts was longer than that of erythrocytes, no significant differences in their diffusional permeability were noticed for temperatures in the range 2-43 degrees C. Contrary to what was previously noticed in erythrocytes, no significant increase in the water exchange time of ghosts in the acid range of pH occurred.

Adult↗
PubMed1986

Water permeability in human erythrocytes: identification of membrane proteins involved in water transport.

The water permeability of human erythrocytes has been monitored by nuclear magnetic resonance (NMR) before and after treatment of the cells with various sulfhydryl reagents. Preincubation of the cells with N-ethylmaleimide (NEM), a non-inhibitory sulfhydryl reagent, results in a faster and more sensitive inhibition of water exchange by mercurials. The inhibition of water exchange by p-chloromercuribenzene sulfonate (PCMBS) was maximal at a binding of approximately 10 nmol PCMBS per mg protein when non-specific sulfhydryl groups are blocked by NEM. Inhibition by PCMBS has been correlated with the binding of 203Hg to erythrocyte membrane proteins. A significant binding of label to band 3 and the polypeptides in band 4.5 occurs, with approximately 1 mol of mercurial bound per mol of protein. Inhibition of water transport by sulfhydryl reagents does not induce major morphological changes in the cells as assessed by freeze-fracture and scanning electron microscopy.

4-Chloromercuribenzenesulfonate↗
PubMed1985

Comparison of liposome entrapment parameters by optical and atomic absorption spectrophotometry.

Methods for the complete characterization of liposomes prepared by ether-injection are described in detail. The validity of atomic absorption spectrophotometry for measuring markers of trapped volume was checked by comparative determinations of markers with established optical spectrophotometrical methods. The favorable results using atomic absorption spectrophotometry to quantitate the marker Mn2+ are of particular relevance as manganese ion is also the paramagnetic probe in n.m.r. measurements of water permeability of liposomes; our results indicate that in such measurements no other marker need be incorporated.

Liposomes↗
PubMed1985

Water exchange through erythrocyte membranes: p-chloromercuribenzene sulfonate inhibition of water diffusion in ghosts studied by a nuclear magnetic resonance technique.

A comparison of water diffusion in human erythrocytes and ghosts revealed a longer relaxation time in ghosts, corresponding to a decreased exchange rate. However, the diffusional permeability of ghosts was not significantly different from that of erythrocytes. The changes in water diffusion following exposure to p-chloromercuribenzene sulfonate (PCMBS) have been studied on ghosts suspended in isotonic solutions. It was found that a significant inhibitory effect of PCMBS on water diffusion occurred only after several minutes of incubation at 37 degrees C. No inhibition was noticed after short incubation at 0 degree C, as previously used in some labelling experiments. This indicates the location in the membrane interior of the SH groups involved in water diffusion across human erythrocyte membranes. The nuclear magnetic resonance (n.m.r.) method appears as a useful tool for studying changes in water diffusion in erythrocyte ghosts with the aim of locating the water channel.

4-Chloromercuribenzenesulfonate↗
PubMed1985

Plasma and cerebrospinal fluid concentrations of magnesium in epileptic children.

In order to discriminate between conflicting reports in the literature, plasma and cerebrospinal fluid magnesium levels from epileptic children were compared with those of control children. To exclude the possibility of methodological artifacts, two methods for Mg determination were used: atomic absorption spectrophotometry and a colorimetric procedure. By both methods a significantly decreased concentration of Mg in plasma was found in epileptics. A positive correlation of the hypomagnesemia with the severity of epilepsy was found: the more severe the epilepsy, the lower was the plasma Mg. A significant increase of Mg concentration in CSF of epileptics was found. The most likely origin of Mg in CSF in epilepsy is the CNS tissue from which Mg is released. It is suggested that these alterations of Mg concentrations in plasma and CSF originate from a functional impairment of the cell membranes which might occur in epilepsy.

Adolescent↗
PubMed1984

The effect of the saturation and isomerization of dietary fatty acids on the osmotic fragility and water diffusional permeability of rat erythrocytes.

Weanling rats were fed semi-purified diets containing 15% by weight of either corn oil, a high oleic acid safflower oil, lard or hydrogenated soybean oil. Significant changes in the fatty acid composition of erythrocytes were induced by these dietary fats. The compositional changes did not effect water diffusional permeability, but did affect their osmotic fragility. An increased fragility appeared to be associated with an increased octadecenoate content of the membranes.

Animals↗
PubMed1983

Comparison of human and rat liver microsomes by spin label and biochemical analyses.

Detailed lipid analyses of human and rat liver microsomes revealed interesting differences. It was found that human liver microsomes contain twice as much lipid as those from the rat. This increased lipid content is not associated with an increase in content of a particular lipid class; human liver microsomes contain higher amounts of each of the lipid classes. Human and rat liver microsomes differ especially in the essential fatty acid composition of total lipids and phospholipids: human liver microsomes contain more linoleic acid and less arachidonic acid than those of the rat. Such a pattern of distribution of fatty acids is similar to that previously reported for human liver mitochondria and has not been reported for other species. Although the previously reported for human liver mitochondria and has not been reported for other species. Although the unsaturation of lipids is lower in human than in rat liver microsomes, spin label studies revealed a higher fluidity in human membranes. It is suggested that this might arise from a lesser immobilization of lipids by proteins in human liver subcellular membranes.

Animals↗