Biomedical subjects

M Bitbol

Publications and source records attributed to M Bitbol.

10 recordsLinked to original sources

PubMed1990

Influence of altered phospholipid composition of the membrane outer layer on red blood cell aggregation: relation to shape changes and glycocalyx structure.

Reversible aggregation of erythrocytes was investigated after alteration of the phospholipid content in the membrane outer leaflet either by disturbance of endogenous transmembrane lipid asymmetry through changes in cellular free calcium, or by incorporation of exogenous lyso-derivatives. It was found that both calcium loading and lyso-phosphatidylcholine (LPC) addition induce a strong increase in red cell-red cell adhesive energy, whereas lyso-phosphatidylserine (LPS), added in the same amount as LPC, does not. Red cell morphological studies show differences in the shape change efficiency of LPS, LPC and calcium loading. However, it was further demonstrated that shape change is not directly responsible for the observed adhesive energy increase, since neuraminidase or trypsin treatment abolish this increase, even though the shape changes induced by alteration of phospholipid organization are not affected. The latter experiment strongly suggests that the red cell adhesive energy increase results from an alteration of the glycocalyx structure, which could be in turn a consequence of the shape change.

Calcium↗

PubMed1990

Biomembrane elastic response to intercalation of amphiphiles.

A model of the elastic behavior of a biomembrane in response to intercalation of amphiphiles into the bilayer is developed. This model takes into account the bilayer couple hypothesis (Sheetz and Singer 1974), and assumes that incorporation of amphiphiles into one layer of the membrane exerts mechanical work on the elastic biomembrane. The model accounts for an apparent experimental discordance noted by several authors: the variation in area observed upon incorporating amphiphiles is smaller by a factor of about 2 than the variation expected using previous models.

Elasticity↗

PubMed1990

Control of the transmembrane phospholipid distribution in eukaryotic cells by aminophospholipid translocase.

The aminophospholipid translocase is a plasma membrane Mg2(+)-ATPase which selectively pumps the aminophospholipids (phosphatidylserine and phosphatidylethanolamine) from the outer to the inner monolayer in eukaryotic cells and is predominantly responsible for the asymmetric phospholipid distribution of the plasma membrane. Similar ATP-dependent transport of phospholipid takes place in some organelles such as chromaffin granules. On the other hand, the phospholipid flippase of rat liver endoplasmic reticulum does not require ATP and has a low lipid specificity. The biological implications of these phospholipid flippases are discussed.

Carrier Proteins↗

PubMed1989

Weak interaction of spectrin with phosphatidylcholine-phosphatidylserine multilayers: a 2H and 31P NMR study.

Spectrin from human erythrocytes binds to bilayer dispersions of both DMPC and DMPS:DMPC (1:1, w/w). However, no effect of bound spectrin on the conformation of the lipid head groups, as measured from the deuterium quadrupolar splittings of DMPC or DMPS specifically deuterated in the polar head groups, was detected in 1:1 mixtures of the two lipids containing either deuterated DMPC or DMPS. Neither the phase transition of the DMPS:DMPC mixtures, nor the spin-lattice relaxation time (T1) of the deuterated DMPS head group, was affected by spectrin. These results argue against any strong interaction of spectrin with phosphatidylserine and rule out the possibility that spectrin is responsible for the maintenance of PS in the inner monolayer of the erythrocyte membrane during the whole life-span of this cell.

Deuterium↗

PubMed1988

Measurement of outward translocation of phospholipids across human erythrocyte membrane.

Spin-labeled phospholipids have been used to study the outside----inside and inside----outside transport of phospholipids across the human erythrocyte membrane at 37 degrees C. As already shown, inward transport is much faster for aminophospholipids than for phosphatidylcholine. In addition, we show here that outward transport of the phosphatidylserine and phosphatidylethanolamine analogues is three to four times faster than that of phosphatidylcholine. Magnesium depletion of the erythrocytes considerably decreases the outward rate of both aminophospholipids to values close to that of phosphatidylcholine. These results suggest that the outward aminophospholipid translocation is, at least partly, protein mediated. The protein involved could be identical to the inward Mg-ATP-dependent aminophospholipid carrier.

Algorithms↗

PubMed1987

Ion regulation of phosphatidylserine and phosphatidylethanolamine outside-inside translocation in human erythrocytes.

In previous publications, we have shown, by using spin-labeled derivatives, that the translocation of phosphatidylserine and phosphatidylethanolamine from the outer to the inner monolayer of human erythrocyte membrane is a protein-mediated phenomenon, which requires hydrolisable Mg2+-ATP. The inhibition by intracellular Ca2+ (0.2 microM) or by extracellularly added vanadate (50 microM) was reported (Seigneuret, M. and Devaux, P.F. (1984) Proc. Natl. Acad. Sci. USA 81, 3751-3755; Zachowski, A., Favre, E., Cribier, S., Hervé, P. and Devaux, P.F. (1986) Biochemistry 25, 2585-2590). The present article gives further insight into the effects of intracellular and extracellular ions on the aminophospholipid translocation in human erythrocytes. By measuring the cell ATP concentration, we now show that the inhibitory effect of intracellular calcium on spin-labeled aminophospholipid translocation is partly due to the ATP depletion, which follows the increased consumption by the calcium pump. However, a direct inhibitory effect of cytosolic Ca2+ on the aminophospholipid translocase can be demonstrated by measuring the initial rate of aminophospholipid translocation in the presence of variable amounts of intracellular calcium, at fixed ATP concentrations. Moreover, the transmembrane equilibrium distribution of phosphatidylserine and phosphatidylethanolamine are affected differently by Ca2+: when cytosolic Ca2+ concentration is increased, alteration of phosphatidylethanolamine distribution begins as soon as the inward translocation is affected by Ca2+ (approx. 50 nM), whereas phosphatidylserine distribution remains unchanged within a large inhibitory range of cytosolic Ca2+ concentrations and decreases above 0.2 microM of free Ca2+ within the cytosol. Decrease of the intracellular Mg2+ concentration below its physiological value (approx. 2 mM) results in the inhibition of aminophospholipid inward transport, whereas increase of Mg2+ concentration does not modify this transport. If Mn2+ is substituted for Mg2+, part of the aminophospholipid translocation is maintained, whereas if Co2+ is substituted for Mg2+, the rapid translocation is completely abolished. Concentrations as high as a millimolar of extracellular Ca2+, Mg2+ or Mn2+ have no effect on the aminophospholipid translocation. The less usual cations Cr3+, Fe2+, Cu2+, Sn2+ and Eu3+ are also uneffective. With extracellular Ni2+ or Co2+, some inhibition can be observed, half inhibition by Ni2+ corresponding to 500 microM. Vanadyl (VO2+), on the other hand, is a potent inhibitor of the aminophospholipid translocation when applied on the extracellular surface, half-inhibition being reached around 30 microM.(ABSTRACT TRUNCATED AT 400 WORDS)

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed1987

Cell disaggregation behavior in shear flow.

The disaggregation behavior of erythrocytes in dextran saline solution was investigated by a light reflectometry technique in a Couette flow and in a plane Poiseuille flow. Dextran concentration and mass average molecular weight of the polymer fraction strongly influence the shear stress dependence of the erythrocyte suspension reflectivity in shear flow and the critical hydrodynamic conditions (shear rate or shear stress) for near-complete cell dispersion. We investigated the influence of cell volume fraction and membrane deformability (heat treatment of the erythrocytes) on the reflectivity of the flowing suspension. This study indicates that the intercell adhesiveness and the shear stress are the only parameters that influence rouleau break-up in steady uniform shear flow, thus eliminating cell volume fraction and membrane deformability as possible factors. However, the critical cross-sectional average shear stress for near-complete cell dispersion through the flow cross-section is shown to depend on the flow pattern. The rotation of cells in a shear flow or the nonuniform shear field in Poiseuille flow indeed increases the flow resistance of cell aggregates. We give a theoretical description of the shear-induced cell disaggregation process in Couette flow and in plane Poiseuille flow. The quantitation of shear forces for cell dispersion provides a way for estimating the surface adhesive energy of the bridging membranes by fluid mechanical technique.

Cell Aggregation↗

PubMed1986

Red blood cell orientation in orbit C = 0.

Two modes of behavior of single human red cells in a shear field have been described. It is known that in low viscosity media and at shear rates less than 20 s-1, the cells rotate with a periodically varying angular velocity, in accord with the theory of Jeffery (1922) for oblate spheroids. In media of viscosity greater than approximately 5 mPa s and sufficiently high shear rates, the cells align themselves at a constant angle to the direction of flow with the membrane undergoing tank-tread motion. Also, in low viscosity media, as the shear rate is increased, more and more cells lie in the plane of shear, undergoing spin with their axes of symmetry aligned with the vorticity axis of the shear field in an orbit "C = 0" (Goldsmith and Marlow, 1972). We have explored this latter phenomenon using two experimental methods. First, the erythrocytes were observed in the rheoscope and their diameters measured. Forward light scattering patterns were correlated with the red cell orientation mode. Light flux variations after flow onset or stop were measured, and the characteristic times of erythrocyte orientation and disorientation were assessed. The characteristic time of erythrocyte orientation in Orbit C = 0 is proportional to the inverse of the shear rate. The corresponding coefficient of proportionality depends on the suspending medium viscosity eta o. The disorientation time tau D, after flow has been stopped, is such that the ratio tau D/eta o is independent of the initial applied shear stress. However, tau D is much shorter than one would expect if pure Brownian motion were involved. The proportion of erythrocytes in orbit C = 0 was also measured. It was found that this proportion is a function of both the shear rate and eta o. At low values of eta o, the proportion increases with increasing shear rate and then reaches a plateau. For higher values of eta o (5 to 10 mPa s), the proportion of RBC in orbit C = 0 is a decreasing function of the shear stress. A critical transition between orbit C = 0 and parallel alignment was observed at high values of eta o, when the shear stress is on the order of 1 N/m2. Finally, the effect of altering membrane viscoelastic properties (by heat or diamide treatment) was tested. The proportion of oriented cells is a steep decreasing function of red cell rigidity.

Erythrocytes↗

PubMed1985

Measurement of erythrocyte orientation in flow by spin labeling II--phenomenological models for erythrocyte orientation rate.

We present two phenomenological models describing the flowing erythrocyte orientation rate. The first concerns the onset of a stable orientation in a very dilute erythrocyte suspension. It is based on a simple formula for erythrocyte elongation as a function of shear stress, and we assume that beyond a threshold of elongation, erythrocytes take on a stable orientation, while below this threshold, they have a flipping motion. We extend this model to high hematocrit values assuming that the effect of red cell collisions imposes a random moment to each erythrocyte, shifting it from its stable orientation. We obtain an approximate expression for erythrocyte orientation rate as a function of shear rate and then we compare these results to our experimental data in part III of this series.

Biomechanical Phenomena↗

PubMed1985

Measurement of erythrocyte orientation in flow by spin labeling III--erythrocyte orientation and rheological conditions.

The measurements of erythrocyte orientation, obtained through a spin labeling technique, are compared with a phenomenological model. Several rheological conditions are varied: hematocrit, suspending medium viscosity, blood age, artificial reversible aggregation. We found that the onset of orientation is very sensitive to any variation of these conditions, and that its measurement would be a good method to assess erythrocyte deformability. A critical shear rate for the orientation process is then determined and compared to the corresponding parameter obtained from viscosity measurements of identical suspensions. A close qualitative relationship is found between the two sets of values of the critical shear rate.

Biomechanical Phenomena↗