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Biomedical subjects

G Curatola

Publications and source records attributed to G Curatola.

140 records · Page 8Linked to original sources
PubMedDate not supplied

Plasma membrane fluidity in isolated rat hepatocytes: comparative study using DPH and TMA-DPH as fluorescent probes.

The study of membrane fluidity is a rapidly expanding field of research and its interest in hepatology has been stressed recently. The present study is the first report concerned with the determination of membrane fluidity of isolated rat hepatocytes. The data have been compared with those obtained in plasma membrane fractions and subfractions (basolateral or canalicular) derived from homogenates. The fluorescent probes used to measure the fluidity were diphenylhexatriene (DPH) a 'classical' probe, and its derivative trimethylammoniodiphenylhexatriene (TMA-DPH) at 25 degrees C and at 37 degrees C. The values obtained with DPH were lower than those with TMA-DPH, probably due to the localization of the probes in different regions of the phospholipid bilayer. In addition, DPH revealed significant differences in the fluorescence polarization values obtained in isolated hepatocytes compared with membrane fractions, which was in contrast to TMA-DPH, where the respective values were of the same order of magnitude. This behaviour is probably due to the mobility of DPH in the membrane core and its rapid internalization into the cell, whereas TMA-DPH remains anchored for a long time on the cell surface. These findings suggest that TMA-DPH is a better probe than DPH for measuring the fluorescence polarization of whole isolated hepatocytes and that the use of different probes might be of help in exploring different zones of the membrane bilayer.

Animals↗
PubMedDate not supplied

Properties of a phosphatidylcholine derivative of diphenyl hexatriene (DPH-PC) in lymphocyte membranes. A comparison with DPH and the cationic derivative TMA-DPH using static and dynamic fluorescence.

Using static and dynamic fluorescence we studied the fluorescence properties of a phosphatidylcholine analog of 1,6-diphenyl-1,3,5-hexatriene (DPH-PC) incorporated in lymphocyte plasma membranes with respect to DPH and its cationic derivative 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH), in order to study if phospholipid derivatives of DPH may be used to investigate structural and physicochemical properties of specific membrane lipid domains. DPH-PC and TMA-DPH showed similar fluorescence polarization values that were significantly higher with respect to DPH, suggesting a localization of the fluorescent portion of DPH-PC in a more ordered region of the membrane which was probably due to the elecrostatic interactions between phospholipid head-groups. The localization of the fluorescent moiety of DPH-PC near the membrane surface was also supported by the study of the fluorescence decay of the three probes using frequency-domain fluorometry. The main lifetime component of DPH-PC was rather similar to that of TMA-DPH (6.74 versus 6.24, ns) but considerably lower with respect to DPH (10.52 ns), in agreement with data obtained from exponential analysis. In lymphocyte membranes obtained from concanavalin A treated cells, a significant decrease of fluorescence polarization has been shown with DPH and its phosphatidylcholine derivative, but not with TMA-DPH. In liposomes obtained from total lipids extracted from lymphocyte membranes, a decrease of fluorescence polarization has been observed only with DPH. Our results suggest that DPH-PC localizes the fluorescent portion of its molecule in membrane microenvironments of different properties with respect to those probed by DPH and TMA-DPH. The use of DPH-phospholipid derivatives and other DPH-probes may represent an useful tool to study plasma membrane heterogeneity in biological membranes.

Animals↗
PubMedDate not supplied

[Bilateral hydronephrosis: a stringent diagnosis].

A forty-nine year old man was admitted to the Renal Unit of our Hospital because of renal failure, loin pain, low grade fever and loss of weight. It was done a complete work-up. The ultrasound and the computed tomography of the abdomen were very helpful to get the right diagnosis.

Humans↗
PubMedDate not supplied

[Large volume increase in a trastigian kidney].

With few exceptions renal volume is markedly reduced in patients with end-stage renal disease, a phenomenon which is almost always accompanied by a progressive loss of renal compliance secondary to renal structure fibrosis. We have observed a remarkable renal compliance during an episode of acute pyelonephritis in a patient on long-term dialysis.

Adult↗
PubMedDate not supplied

A conformational model of the action of general anesthetics at the membrane level. III. Anesthetics and the properties of membrane-bound enzymes: mitochondrial ATPase.

We have studied the effect of general anesthetics on the kinetic properties of the mitochondrial Mg2+-dependent ATPase. The enzyme is inhibited by anesthetics (alcohols, halotane, pentrane, ketamine) at concentrations of the order of those found to affect lipid-protein interactions. The inhibition appears usually uncompetitive with respect to the substrate, ATP, with a decrease of both Vmax and KM, indicating a possible stabilization of the enzyme-substrate complex. Arrhenius plots of ATPase activity show a striking increase in activation energy below 17-20 degrees C. Anesthetics affect the temperature dependence by increasing the activation energy above the break or abolishing the break whatsoever. An exception is diethyl ether, that induces a decrease in activation energy and a shift of the break to lower temperatures. Anesthetics make the ATPase insensitive to energy transfer inhibitor, oligomycin and dicyclohexyl carbodiimide. At low anesthetic concentration the oligomycin inhibition curve is changed from sigmoidal to hyperbolic, showing a loss of cooperativity in the inhibition.

Adenosine Triphosphatases↗
PubMedDate not supplied

[A "lump" in the throat].

This is a clinical case of a patient suspected to have a lymphoma. Later on, other diagnostic procedures and particularly a neck ultrasound, revealed an idiopathic hyperparathyroidism.

Aged↗
PubMedDate not supplied

Biophysical studies of erythrocyte membranes from patients with duchenne muscular dystrophy.

Lipid-soluble spin labels were used to probe the fluidity of membrane lipids in erythrocyte membranes from patients with Duchenne muscular dystrophy. A greater mobility of spin label motion was noticed at the surface of the Duchenne erythrocyte membranes in comparison with the similary labeled normal human erythrocytes. Changes in the protein conformation and/or protein-lipid organization, as a consequence of an altered membrane lipid fluidity, have been demonstrated by the use of a sulfhydryl group specific protein spin label. Strongly immobilized sulfhydryl groups appear to be located both at the membrane surface and deep within the lipid bilayer. The ratio of the spectral amplitude of the spin label attached to weakly immobilized sulfhydryl groups to that of strongly immobilized SH-groups is significantly greater in Duchenne membranes, compared to those of controls. These studies suggest alterations in lipid-protein organization at the surface of Duchenne erythrocytes, indicating that Duchenne muscular dystrophy may be a disease resulting from a membrane abnormality at the molecular level.

Electron Spin Resonance Spectroscopy↗
PubMedDate not supplied

Functional changes of endoplasmic reticulum membranes associated with liver regeneration.

The fluidity and lipid composition of microsomal membranes have been studied at the earliest stage of liver regeneration in the rat (16 h after partial hepatectomy). The physical properties of the membranes have been measured by electron paramagnetic resonance analysis of freedom of motion of lipid and protein analogue probes. The fluidity of the hydrophobic core and of the microenvironment surrounding membrane proteins appeared to be modified, while no modifications were detectable in the fluidity at the surface or in bulk biochemical composition. The kinetic parameters of two enzymes of the endoplasmic reticulum (3-hydroxy-3-methyl glutaryl coenzyme A reductase and glucose-6-phosphatase) which are differentially localized within the membrane bilayer, were also measured. The temperature dependence of both enzymes was modified in the proliferating system, but these modifications were not consistent with the changes detectable in their specific activity. A model to explain the changes that occur in this proliferating membrane system is presented.

Animals↗
PubMedDate not supplied

Duchenne muscular dystrophy. Morphological study of erythrocytes after treatment with L-alpha-lysophosphatidyl-choline in dystrophic patients and in the carrier state.

The percentage of echinocytes in the blood from patients affected by Duchenne muscular dystrophy, in mothers carriers of the dystrophic state, and in Steinert dystrophic patients, has been investigated after addition of low levels of lysolecithin. The echinocyte content was significantly higher in both Duchenne patients and in carriers, and lower in Steinert patients than in controls. The extents of the differences suggest the possibility to use this methodology as a diagnostic test in Duchenne muscular dystrophy.

Adolescent↗
PubMedDate not supplied

A conformational model for the action of general anesthetics at the membrane level. I. Theoretical considerations.

The first paper of this series describes a working hypothesis for the action of general anesthetics. According to such hypothesis, anesthetics, by inducing a labilisation of lipid-protein interactions in biomembranes, affect the conformation, and hence the activity of membrane-bound catalytic proteins. It is conceivable that such changes in ionic channels in neuronal membranes will abolish the transmission of nervous impulses and give rise to anesthesia. The hypothesis is discussed on the basis of previously known experimental data and of theoretical considerations. Thermodynamic considerations are in favour of the idea that a rupture of lipid-protein interactions will expose protein groups to water destabilising helical structures. A large decrease of alpha-helical content after lipid removal had been previously found. Furthermore lipids affect the kinetics of membrane-bound enzymes, suggesting that conformational changes occur in the catalytic site after lipid removal or perturbation.

Anesthesia, General↗
PubMedDate not supplied

A conformational model for the action of general anesthetics at the membrane level. II. Experimental observations on the effects of anesthetics on lipid fluidity and lipid protein interactions.

We have investigated the effect of general anesthetics (the normal alcohol series up to pentanol, halothane, pentrane, ether, chloroform, and ketamine) on lipid fluidity of phospholipid vesicles and mitochondrial and erythrocyte membranes by using spin labels and fluorescent probes. The spin labels used (5- and 16-doxyl stearic acids) show that all anesthetics tested have a slight fluidizing effect on lipid vesicles but induce a very strong increase in mobility of spin labels in mitochondria and lower in erythrocyte ghosts. These results are interpreted as a labilization of lipid protein interactions at all depths in the bilayer. The fluorescent molecules ANS and NPN, which probe the glycerol region and the core of the bilayer respectively, show a decrease of fluorescence induced by alcohols, halothane, ether, chloroform in both lipid vesicles and membranes. The decrease of fluorescence is due to decreased quantum yield as shown by double reciprocal plots of probe fluorescence against membrane concentration. The fluorescence decrease is interpreted mainly as an increase in fluidity of the lipid bilayer and not as an increase of polarity of the probe environment. The effect of ketamine is that of fluidization in the bilayer core (NPN) but of increased rigidity in the glycerol region (ANS) perhaps due to the amphipathic character of this anesthetic, that is supposed to bind in the polar region of the bilayer. Pentrane also induces fluidization in the bilayer core (NPN) but has a peculiar effect near the surface (ANS): in lipid vesicles it induces a fluorescence decrease, whereas an increase is seen in mitochondrial membranes. These complex effects are considered as the result of some specific change in the lipid protein interactions in the region probed by ANS. The effects of anesthetics on maximal NPN fluorescence (Fo) have been usually found to be stronger in mitochondrial membranes than in lipid vesicles, thus confirming the results of the spin label studies, showing a labilization of lipid protein interactions induced by anesthetics. The effects on Fo of ANS, however, appear to be stronger in lipid vesicles than in membranes. These findings indicate that the presence of the proteins counteracts the perturbation induced by anesthetics at the level of the membrane surface, in contrast with the disruption of lipid protein interactions observed in the membrane hydrophobic areas.

Anesthesia, General↗