The Experts below are selected from a list of 2127 Experts worldwide ranked by ideXlab platform
Wray H. Huestis - One of the best experts on this subject based on the ideXlab platform.
-
Membrane potential and human Erythrocyte Shape
Biophysical Journal, 1997Co-Authors: Margaret M. Gedde, Wray H. HuestisAbstract:Altered external pH transforms human Erythrocytes from discocytes to stomatocytes (low pH) or echinocytes (high pH). The process is fast and reversible at room temperature, so it seems to involve shifts in weak inter- or intramolecular bonds. This Shape change has been reported to depend on changes in membrane potential, but control experiments excluding roles for other simultaneously varying cell properties (cell pH, cell water, and cell chloride concentration) were not reported. The present study examined the effect of independent variation of membrane potential on red cell Shape. Red cells were equilibrated in a set of solutions with graduated chloride concentrations, producing in them a wide range of membrane potentials at normal cell pH and cell water. By using assays that were rapid and accurate, cell pH, cell water, cell chloride, and membrane potential were measured in each sample. Cells remained discoid over the entire range of membrane potentials examined (-45 to +45 mV). It was concluded that membrane potential has no independent effect on red cell Shape and does not mediate the membrane curvature changes known to occur in red cells equilibrated at altered pH.
-
cytoplasmic ph and human Erythrocyte Shape
Biophysical Journal, 1997Co-Authors: Margaret M. Gedde, D K Davis, Wray H. HuestisAbstract:Altered external pH transforms human Erythrocytes from discocytes to stomatocytes (low pH) or echinocytes (high pH). The mechanism of this transformation is unknown. The preceding companion study (Gedde and Huestis) demonstrated that these Shape changes are not mediated by changes in membrane potential, as has been reported. The aim of this study was to identify the physiological properties that mediate this Shape change. Red cells were placed in a wide range of physiological states by manipulation of buffer pH, chloride concentration, and osmolality. Morphology and four potential predictor properties (cell pH, membrane potential, cell water, and cell chloride concentration) were assayed. Analysis of the data set by stratification and nonlinear multivariate modeling showed that change in neither cell water nor cell chloride altered the morphology of normal pH cells. In contrast, change in cell pH caused Shape change in normal-range membrane potential and cell water cells. The results show that change in cytoplasmic pH is both necessary and sufficient for the Shape changes of human Erythrocytes equilibrated in altered pH environments.
-
wheat germ agglutinin stabilization of Erythrocyte Shape role of bilayer balance and the membrane skeleton
Biochimica et Biophysica Acta, 1995Co-Authors: Sansan Lin, Wray H. HuestisAbstract:The effects of wheat germ agglutinin (WGA), Limulus lectin, and concanavalin A on cell Shape changes were examined in human Erythrocytes. These agents inhibited echinocytosis in cells having elevated cytosolic Ca2+ or incorporated foreign phosphatidylcholine, but had no effect on cell stomatocytosis in response to incorporated phosphatidylserine. The role of the membrane skeleton in this selective membrane fixation was examined. WGA inhibited echinocytosis in cells previously depleted of polyphosphoinositides to reduce membrane skeleton binding to transmembrane proteins, treated with phorbol ester to enhance protein 4.1 phosphorylation, heat-treated to denature spectrin, alkylated with p-chloromercuribenzoate to dissociate glycophorin from the membrane skeleton, or subjected to elevated cell 2,3-diphosphoglycerate to alter organization of the spectrin-actin-protein 4.1 complex. Limulus lectin and increased concentrations of WGA also stabilized discoid Shape in pronase-digested cells containing no detectable intact glycophorin. In contrast, cell digestion with sialidase abolished the Shape-stabilizing effect of WGA. The results suggest that the membrane skeleton is not involved in WGA Shape stabilization. Rather, they suggest that glycoproteins and glycolipids interact with the lectin to stabilize cell surface molecular associations, forming a superficial calyx that inhibits outward, but not inward, membrane bending.
-
Human Erythrocyte Shape regulation : interaction of metabolic and redox status
Biochimica et Biophysica Acta, 1993Co-Authors: Hoai-thu N. Truong, David L. Daleke, Wray H. HuestisAbstract:Abstract The echinocyte-to-discocyte Shape recovery of metabolically depleted Erythrocytes is compromised by sulfhydryl reducing agents (Truong, H.-T.N., Ferrell, J.E., Jr. and Huestis, W.H. (1986) Blood 67, 214–221). In the presence of dithiothreitol (DTT) and sugars, crenated cells recover normal discoid Shape transiently, but then develop the invaginations and intracellular inclusions of stomatocytes. The stomatogenic effects of DTT were investigated in Erythrocytes recovering from crenation induced by several independent mechanisms. Cells crenated by direct manipulation of the membrane bilayer (lysophosphatidylcholine incorporation) recovered discoid Shape similarly in the presence and absence of the reducing agent. In contrast, rescaled ghosts and cells crenated by Mg 2+ depletion or Ca 2+ loading did not maintain stable discoid morphology in the presence of DTT, proceeding further to form stomatocytes. Thus cell crenation by expedients that involve cellular metabolic processes develop a redox-related morphological instability that is not found in amphipath-crenated cells.
Piotr Zielenkiewicz - One of the best experts on this subject based on the ideXlab platform.
-
theoretical model of thalassemic Erythrocyte Shape transformation
Journal of Theoretical Biology, 2008Co-Authors: P Pawlowski, Beata Burzynska, Piotr ZielenkiewiczAbstract:Abstract Our earlier model of reticulocyte Shape transformation [Pawlowski, P.H., Burzynska, B., Zielenkiewicz, P., 2006. Theoretical model of reticulocyte to Erythrocyte Shape transformation. J. Theor. Biol. 243, 24–38] was applied to explain the morphological properties of thalassemic Erythrocytes. Modification of the standard set of parameters of the model, describing minimal cell volume, membrane bending rigidity, and membrane tension, allowed for simulation of development of α - and β -thalassemic cells from splenectomized and nonsplenectomized individuals. This resulted in observation of thin rim discocytes, tailed Erythrocytes and oval forms, as well as in differentiation of time of the cell Shape metamorphosis. A comparative analysis of the susceptibility of thalassemic and normal Erythrocytes to undergo deformation as well of their stability was performed.
-
theoretical model of reticulocyte to Erythrocyte Shape transformation
Journal of Theoretical Biology, 2006Co-Authors: P Pawlowski, Beata Burzynska, Piotr ZielenkiewiczAbstract:Abstract A theoretical model describing the kinetics of reticulocyte Shape transformation was developed. The model considers the evolution of a simple cellular Shape under transmembrane pressure difference, and proposes a four-parameter axisymmetric approximation of the cell surface. The mathematical analysis considers plasma membrane tension in the plane of bilayer leaflets, membrane spontaneous curvature and transmembrane transport of water. Cytoskeleton dilatational and shear rigidity, and the energetic barrier preventing the decrease of cell volume below a certain minimum are also incorporated. The set of adequate physical assumptions allowed for formulation of the equation for free energy of the investigated system. Computer simulations of cell Shape changes, down to the state of free energy minimum, together with estimation of the time needed for the resulting transport of water, revealed a complex, three-phase picture of temporal alterations in cellular geometry with a wide spectrum of final results, and led to propose a standard model of reticulocyte–Erythrocyte transformation. According to the model, both cell volume and surface undergo changes, and the work of the pressure, initially accumulated in the cytoskeleton, is consumed for local bending of the cell membrane. Further simulations with modified initial Shape or parameters of the standard model show the trajectories of system evolution and help in better understanding the conditions for the erythro-, sphero-, ovalo-, stomato-, and leptoidal metamorphosis of maturing red blood cells. The stability of the final biconcave Shape was also verified. Spherogenic modifications were discussed in the context of spherocytosis. Future development of the model was proposed.
Philip W. Kuchel - One of the best experts on this subject based on the ideXlab platform.
-
Erythrocyte Shape reversion from echinocytes to discocytes kinetics via fast measurement nmr diffusion diffraction
Magnetic Resonance in Medicine, 2010Co-Authors: Guilhem Pages, Tsz W Yau, Philip W. KuchelAbstract:Pulsed field-gradient spin-echo (PGSE) NMR spectroscopy via q-space plots can characterize Erythrocyte Shapes and their evolution. The present study employed PGSE NMR to investigate Shape reversion from advanced echinocytic to normal discocytic Shapes due to depletion and then readdition of Mg(2+). In q-space plots of the data, the diffusion-diffraction minima disappeared for Mg(2+)-depleted Erythrocytes and reappeared during the Shape recovery process, but with lower definition than for control cells. Shape estimates from PGSE NMR spectra and light microscopy were in excellent agreement after application of a scaling/correction factor. (31)P NMR was used to probe the biochemical processes activated in Erythrocytes after depletion or addition of Mg(2+); it showed the activation of the nonoxidative part of the pentose phosphate pathway. Experimental conditions were optimized to bypass this pathway without any influence on the q-space plots. The release of choline from phosphatidylcholine in the outer leaflet of the plasma membrane of the cells, observed using (1)H spin-echo NMR, showed a higher rate for Shape-recovered than for control cells. This points to a change in phospholipid asymmetry in the plasma membrane. This variation in asymmetry affected the mean cell Shape and hence influenced the average alignment of the Erythrocytes with the static magnetic field and so affected the Shapes of the q-space plots.
-
Erythrocyte Shape evolution recorded with fast measurement nmr diffusion diffraction
Journal of Magnetic Resonance Imaging, 2008Co-Authors: Guilhem Pages, David Szekely, Philip W. KuchelAbstract:Purpose To monitor red blood cell (RBC) Shape evolution by 1H2O diffusion–diffraction NMR in time steps comparable to those required for the acquisition of a 31P NMR spectrum; thus, to correlate RBC mean diameter with ATP concentration after poisoning with NaF. Materials and Methods Pulsed-field gradient-stimulated echo (PFGSTE) diffusion experiments were recorded on 1H2O in RBC suspensions. Under conditions of restricted diffusion, q-space experiments report on mean RBC diameter. To decrease experiment time, the phase cycling of radiofrequency (RF) pulses was cut to two transients by using unbalanced pairs of gradient pulses. Data processing used a recent digital filter. Differential interference contrast (DIC) light microscopy also recorded Shape changes. 31P NMR spectroscopy gave estimates of mean ATP concentration. Results NaF caused RBC-Shape evolution from discocytes, through various forms of echinocytes, to spherocytes, over ∼6 h and ∼10 h at 37°C and 25°C, respectively. ATP declined to ∼0.5 its normal concentration before the first stage of discocyte transformation; the concentration was 0.0 after ∼1.5 h and 3.0 h, respectively, at the two temperatures. Conclusion RBC Shape was readily monitored by NMR with a temporal resolution that was useful for correlations with both DIC microscopy and 31P NMR spectra. J. Magn. Reson. Imaging 2008;28:1409–1416. © 2008 Wiley-Liss, Inc.
-
Parametric-equation representation of biconcave Erythrocytes
Bulletin of Mathematical Biology, 1999Co-Authors: Philip W. Kuchel, Edward D. FackerellAbstract:The representation of the Shape of a biconcave Erythrocyte by a set of three parametric equations was achieved by using the expressions that transform the curvilinear coordinates from the disc-cyclide coordinate system [denoted J2R; Moon and Spencer (1988), Field Theory Handbook , Springer-Verlag, Berlin] to Cartesian coordinates. The equations are products of elliptic functions, so the challenge was to relate the three major ’Shape-defining’ measurements of the human Erythrocyte in Cartesian coordinates to three parameters in the new curvilinear coordinates, to give a realistic representation of the Shape of the membrane-surface. The relationships between the coefficients of the Cartesian degree-4 surface that describes the discocyte and the coordinate transformation equations were derived with the aid of Mathematica ; and the membrane-surface of the cell was drawn using the ParametricPlot3D function in this ‘package’. By having the Erythrocyte Shape expressed in its new form it is readily amenable to further transformations that might be used to model those changes in Shape that are seen when the cells are immersed in media of various osmolalities, or when they change metabolic ’states’. On the other hand, the relationship between the coefficients of the Cartesian expression for the disc-cyclide surface is relevant to image analysis of Erythrocytes, as determined by physical methods that rely on Cartesian imaging ’slices’. These methods include confocal microscopy and various nuclear magnetic resonance microimaging procedures.
Patrick G. Gallagher - One of the best experts on this subject based on the ideXlab platform.
-
the common hereditary elliptocytosis associated α spectrin l260p mutation perturbs Erythrocyte membranes by stabilizing spectrin in the closed dimer conformation
Blood, 2013Co-Authors: Sandra L Harper, Patrick G. Gallagher, Sira Sriswasdi, Hsinyao Tang, Massimiliano Gaetani, David W SpeicherAbstract:Hereditary elliptocytosis (HE) and hereditary pyropoikilocytosis (HPP) are common disorders of Erythrocyte Shape primarily because of mutations in spectrin. The most common HE/HPP mutations are located distant from the critical αβ-spectrin tetramerization site, yet still interfere with formation of spectrin tetramers and destabilize the membrane by unknown mechanisms. To address this question, we studied the common HE-associated mutation, αL260P, in the context of a fully functional mini-spectrin. The mutation exhibited wild-type tetramer binding in univalent binding assays, but reduced binding affinity in bivalent-binding assays. Biophysical analyses demonstrated the mutation-containing domain was only modestly structurally destabilized and helical content was not significantly changed. Gel filtration analysis of the αL260P mini-spectrin indicated more compact structures for dimers and tetramers compared with wild-type. Chemical crosslinking showed structural changes in the mutant mini-spectrin dimer were primarily restricted to the vicinity of the αL260P mutation and indicated large conformational rearrangements of this region. These data indicate the mutation increased the stability of the closed dimer state, thereby reducing tetramer assembly and resulting in membrane destabilization. These results reveal a novel mechanism of Erythrocyte membrane destabilization that could contribute to development of therapeutic interventions for mutations in membrane proteins containing spectrin-type domains associated with inherited disease.
-
Hereditary elliptocytosis: spectrin and protein 4.1R
Seminars in hematology, 2004Co-Authors: Patrick G. GallagherAbstract:Abstract Hereditary elliptocytosis (HE) is a common disorder of Erythrocyte Shape, occurring especially in individuals of African and Mediterranean ancestry, presumably because elliptocytes confer some resistance to malaria. The principle lesion in HE is mechanical weakness or fragility of the Erythrocyte membrane skeleton due to defects in α-spectrin, β-spectrin, or protein 4.1. Numerous mutations have been described in the genes encoding these proteins, including point mutations, gene deletions and insertions, and mRNA processing defects. Several mutations have been identified in a number of individuals on the same genetic background, suggesting a “founder effect.” The majority of HE patients are asymptomatic, but some may experience hemolytic anemia, splenomegaly, and intermittent jaundice.
-
molecular basis and haplotyping of the alphaii domain polymorphisms of spectrin application to the study of hereditary elliptocytosis and pyropoikilocytosis
American Journal of Human Genetics, 1996Co-Authors: Patrick G. Gallagher, David W Speicher, Leszek Kotula, Y Wang, Sally L Marchesi, Peter J Curtis, Bernard G ForgetAbstract:Hereditary elliptocytosis (HE) and hereditary pyropoikilocytosis (HPP) are inherited disorders of Erythrocyte Shape that are frequently associated with abnormalities in alpha-spectrin, one of the principal structural proteins of the Erythrocyte membrane skeleton. Five polymorphisms of the alpha-spectrin gene, located in a 6-kb interval of genomic DNA, were identified and analyzed in normal and mutant alpha-spectrin alleles. Three of these polymorphisms are due to single nucleotide substitutions in the alpha-spectrin gene coding region that lead to changes in the amino acid sequence. In combination, these three polymorphisms are responsible for the different peptide phenotypes of the alphaII domain previously observed following limited tryptic digestion of spectrin protein. The most common haplotype, type 1, was found predominantly in Caucasians and was the only haplotype identified in Asians. Haplotypes 2, 3, and 4 were identified predominantly in individuals of African ancestry and were commonly found in patients with HE or HPP. Analysis of coinheritance of alphaII domain polymorphisms with alpha-spectrin gene mutations causing HE or HPP in African-American patients with HE and HPP suggests that, with one exception, a given HE/HPP mutation is present in an alpha-spectrin gene of only one haplotype, indicating a founder effect. The other two polymorphisms located in this region of the alpha-spectrin gene do not change the amino acid sequence of the encoded alpha-spectrin chain and are not in linkage disequilibrium with three of the four alphaII domain haplotypes. A model is proposed for the evolutionary origin of the different haplotypes.
Margaret M. Gedde - One of the best experts on this subject based on the ideXlab platform.
-
Membrane potential and human Erythrocyte Shape
Biophysical Journal, 1997Co-Authors: Margaret M. Gedde, Wray H. HuestisAbstract:Altered external pH transforms human Erythrocytes from discocytes to stomatocytes (low pH) or echinocytes (high pH). The process is fast and reversible at room temperature, so it seems to involve shifts in weak inter- or intramolecular bonds. This Shape change has been reported to depend on changes in membrane potential, but control experiments excluding roles for other simultaneously varying cell properties (cell pH, cell water, and cell chloride concentration) were not reported. The present study examined the effect of independent variation of membrane potential on red cell Shape. Red cells were equilibrated in a set of solutions with graduated chloride concentrations, producing in them a wide range of membrane potentials at normal cell pH and cell water. By using assays that were rapid and accurate, cell pH, cell water, cell chloride, and membrane potential were measured in each sample. Cells remained discoid over the entire range of membrane potentials examined (-45 to +45 mV). It was concluded that membrane potential has no independent effect on red cell Shape and does not mediate the membrane curvature changes known to occur in red cells equilibrated at altered pH.
-
cytoplasmic ph and human Erythrocyte Shape
Biophysical Journal, 1997Co-Authors: Margaret M. Gedde, D K Davis, Wray H. HuestisAbstract:Altered external pH transforms human Erythrocytes from discocytes to stomatocytes (low pH) or echinocytes (high pH). The mechanism of this transformation is unknown. The preceding companion study (Gedde and Huestis) demonstrated that these Shape changes are not mediated by changes in membrane potential, as has been reported. The aim of this study was to identify the physiological properties that mediate this Shape change. Red cells were placed in a wide range of physiological states by manipulation of buffer pH, chloride concentration, and osmolality. Morphology and four potential predictor properties (cell pH, membrane potential, cell water, and cell chloride concentration) were assayed. Analysis of the data set by stratification and nonlinear multivariate modeling showed that change in neither cell water nor cell chloride altered the morphology of normal pH cells. In contrast, change in cell pH caused Shape change in normal-range membrane potential and cell water cells. The results show that change in cytoplasmic pH is both necessary and sufficient for the Shape changes of human Erythrocytes equilibrated in altered pH environments.