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Biomedical subjects

R Fiorini

Publications and source records attributed to R Fiorini.

27 records · Page 2Linked to original sources
PubMed1989

Effect of cholesterol on membrane microheterogeneity: a study using 1,6-diphenyl-1,3,5-hexatriene fluorescence lifetime distributions.

The effect of cholesterol on microheterogeneity of liposomes obtained from saturated and unsaturated phospholipids was studied by measuring the fluorescence decay of 1,6-diphenyl-1,3,5-hexatriene (DPH). Data obtained by frequency domain fluorometry have been analyzed either by discrete exponential or continuous lifetime distribution approaches. In egg phosphatidylcholine liposomes, the addition of cholesterol increases the lifetime value or the centre of the lifetime distribution. At high cholesterol concentration, good fits are obtained using a monomodal distribution analysis or single exponential component. At low cholesterol concentration an additional short component of low fractional intensity must be included to obtain a good fit. In dipalmitoylphosphatidylcholine, the addition of cholesterol decreases the long lifetime component centre value both in the gel and in the liquid-crystalline state. The DPH lifetime value is sensitive to the dielectric constant of the probe microenvironment, and cholesterol has been shown to modify water penetration in the bilayer. Using this information our data indicate that cholesterol affects the polarity of the microenvironment in liposomes of unsaturated phosphatidylcholine and saturated phosphatidylcholine in different ways. Although the major conclusions of this paper are obtained using changes of the distribution centre upon cholesterol addition, there are also preliminary indications that the lifetime distribution width decreases as cholesterol is added. We have interpreted this observation as being due to the homogenizing effect of cholesterol.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1989

Modifications of erythrocyte membrane fluidity of in vivo functionally aged human erythrocytes.

The process of red blood cell senescence in the blood stream results in many changes in their physical and biochemical properties. In this work we have studied the physico-chemical state of erythrocyte membranes prepared from 5 subpopulations of erythrocytes of different age by using the fluorescence technique. Membrane fluidity has been evaluated by the fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) and a further study of the fluorescence decay of this probe has been performed by multifrequency phase and modulation fluorometry. DPH fluorescence polarization is significantly increased in the membranes prepared from the youngest fraction of erythrocytes, indicating a decreased fluidity without any significant change in DPH fluorescence decay.

Erythrocyte Aging↗
PubMed1988

Increased membrane heterogeneity in stimulated human granulocytes.

TMA-DPH fluorescence decay in human PMN before and after stimulation with FMLP was studied using frequency domain fluorometry. Membrane heterogeneity was assessed by the width of the continuous distributions of lifetime values of Lorentzian shape used to describe the fluorescence decay. In non-stimulated granulocytes TMA-DPH fluorescence decay is characterized by two distributions of lifetime values centered at 6.5 and 1.0 ns and full width at half maximum of 0.3 and 1.2 ns, respectively. Within 15 min after stimulation, the center values of the two distribution components were 5.1 and 0.8 ns and the distribution width was 0.8 and 0.6 ns, respectively. These results indicate changes of membrane domain organization which can be ascribed to compositional changes and redistribution of membrane components.

Cell Membrane↗
PubMed1988

Increased neutrophil leukocyte chemotaxis induced by release of a serum factor in toluene-diisocyanate (TDI) asthma.

The activation of blood neutrophil leukocytes has been proven in subjects with IgE-mediated and non-IgE-mediated asthma. This event appears to be modulated by the release of humoral factors. We submitted 12 toluene-diisocyanate (TDI) asthmatic workers to TDI provocation. During the late asthmatic reaction there was release of a serum chemoattracting factor for normal neutrophil leukocytes and activation of asthmatic neutrophil leukocytes. This appears to be the first demonstration of neutrophil chemotactic activity liberated during the late TDI reaction in humans. The results are explained by an acute inflammatory process occurring during the late asthmatic reaction induced by TDI.

Adult↗
PubMed1987

Fluorescence lifetime distributions of 1,6-diphenyl-1,3,5-hexatriene in phospholipid vesicles.

The fluorescence emission properties of 1,6-diphenyl-1,3,5-hexatriene (DPH) in 1,2-dipalmitoyl-3-sn-phosphatidylcholine and 1,2-dimyristoyl-3-sn-phosphatidylcholine multilamellar vesicles have been measured by using multifrequency phase fluorometry. The fluorescence decay of DPH in the phospholipid vesicles has been analyzed by assuming either that the decay is made up of a discrete sum of exponential components or that the decay is made up of one or more continuous distributions of lifetime components. The fit of the decay curve using exponentials required at least two terms, and the reduced X2 was relatively large. The fit using a continuous distribution of lifetime values used two continuous components. Several symmetric distribution functions were used: uniform, Gaussian, and Lorentzian. The distribution function that best described the decay was the Lorentzian. The full width at half-maximum of the Lorentzian distribution was about 0.6 ns at temperatures below the phase transition temperature. At the phospholipid phase transition and at higher temperatures, the distribution became quite narrow, with a width of about 0.1 ns. It is proposed that the lifetime distribution is generated by a continuum of different environments of the DPH molecule characterized by different dielectric constants. Below the transition temperature in the gel phase, the dielectric constant gradient along the membrane normal determines the distribution of decay rates. Above the transition, in the liquid-crystalline phase, the translational and rotational mobility of the DPH molecule increases, and the DPH experiences an average environment during the excited-state lifetime. Consequently, the distribution becomes narrower.(ABSTRACT TRUNCATED AT 250 WORDS)

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1986

Changes of membrane fluidity in chemotactic peptide-stimulated polymorphonuclear leukocytes.

Although the phenomenon of stimulus-response coupling in polymorphonuclear leukocytes involves a series of membrane events the influence of stimulation on membrane fluidity is to clarify. In our experiments we have used 1-(4-trimethylaminophenyl) 6-phenyl-1,3,5-hexatriene and 1,6-diphenyl-1,3,5-hexatriene fluorescence polarization technique to evaluate membrane fluidity in living polymorphonuclear leukocytes after stimulation with N-formyl-methyonil-leucyl-phenylalanine peptide which has a well defined membrane receptor on the plasma membrane. We report that polymorphonuclear leukocytes stimulation increases 1-(4-trimethylaminophenyl)-6-phenyl-1,3,5-hexatriene polarization, only when colcemid, a microtubule disrupting drug, is added to polymorphonuclear leukocytes. This can be viewed as an indirect evidence that microtubules are involved in the control of polymorphonuclear leukocytes membrane fluidity. On the contrary no changes have been observed with 1,6-diphenyl-1,3,5-hexatriene. This study indicates the potential use of 1-(4-trimethylaminophenyl)-6-phenyl-1,3,5-hexatriene to evaluate the involvement of plasma membrane physical state during intact cell activity.

Cell Membrane↗
PubMedDate not supplied

Interaction of trout hemoglobin with H2O2: a chemiluminescence study.

Erythrocytes from trout Salmo irideus are characterized by four different hemoglobin components (HbI, HbII, HbIII and HbIV), HbI and HbIV being predominant. In this study we describe the interaction between trout hemoglobin (HbI and HbIV) and H2O2 using a chemiluminescence assay. Our data show that the reaction of hemoglobins with H2O2 produces a time-limited and significant increase of chemiluminescence signal. The half-life of the decay of this chemiluminescence signal was characteristic for each type of hemoglobin used. These results indicate the formation of excited molecules related to the interaction between trout hemoglobin and H2O2.

Animals↗
PubMedDate not supplied

Plasma membrane fluidity and polarity of polymorphonuclear leukocytes from children with type I diabetes mellitus.

Polymorphonuclear leukocytes (PMN) from diabetic subjects have been found to be abnormal in various functional activities. These activities are mediated by the plasma membrane. This study was designed to evaluate plasma membrane fluidity and polarity in children with type I diabetes mellitus using fluorescence spectroscopy. PMN membrane fluidity and polarity were assessed in a group of 32 diabetic children. Membrane fluidity was investigated by measuring steady-state fluorescence anisotropy and fluorescence decay of 1-[4-trimethylammonium-phenyl]-6-phenyl- 1,3,5-hexatriene (TMA-DPH), whereas membrane polarity was studied by measuring the steady-state fluorescence emission and excitation spectra of 2-dimethylamino[6-lauroyl]-naphthalene (Laurdan). TMA-DPH and Laurdan are known to be incorporated at the hydrophobic-hydrophilic interface of the bilayer. Our data show a significant increase in steady-state fluorescence anisotropy in diabetic PMN that reflects a decrease in membrane fluidity, and a decrease in TMA-DPH lifetime distribution indicating a decrease in membrane heterogeneity. Laurdan shows a blue shift of the fluorescence emission and a red shift of the excitation spectra in diabetic PMN with respect to the control group, indicating a decrease in membrane polarity. The results demonstrate a decrease in the phospholipid order at the membrane surface and a decrease in membrane polarity in diabetic PMN. These alterations in the physico-chemical properties of the plasma membrane could be the basis of the modifications in functional activities of PMN. The changes in the plasma membrane of PMN could be the result of metabolic and chemical modification associated with type I diabetes.

Adolescent↗