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Biomedical subjects

T M Fischer

Publications and source records attributed to T M Fischer.

42 records · Page 3Linked to original sources
PubMed1981

The stress-free shape of the red blood cell membrane.

The two main proposals found in the literature for the stress-free shape of the red cell membrane are (a) the bioconcave shape and (b) the sphere of the same surface area. These possibilities are evaluated in this paper using theoretical modeling of equilibrium membrane shapes according to Zarda et al. (1977. J. Biomech. 10:211-221) and by comparison to experiments on red cells whose membrane shear modulus has been increased by treatment with diamide. Neither proposal is found to be compatible with all the experimental behaviour of native red cells. Neither proposal is found to be compatible with all the experimental behaviour of native red cells. To account for this discrepancy we propose that either the shear modulus of the native membrane is dependent on the membrane strain or that the bending stiffness is higher than estimated by Evans (1980. Biophys. J. 30:265-286). These studies suggest that the bioconcave disk is the more likely possibility for the stress-free shape.

Diamide↗
PubMed1980

Is "deformability" a parameter for the rate of elimination of erythrocytes from the circulation?

The "deformability" of rat erythrocytes can be gradually decreased by an in vitro treatment with the SH-oxidizing agent diamide. Despite of this reduced deformability the cells are retained in the circulation for many hours when reinfused into the rat. Cells rigidified with glutaraldehyde are even less deformable than diamide treated cells, but also survive for many hours. In contrast to rigidified cells of normal volumes swollen rigidified cells obtained by a heat treatment of erythrocytes are rapidly eliminated. The results support the notion that the "recognition" preceding the elimination of senescent and damaged cells of normal volumes by the reticulo-endothelial system is not solely based on their diminished deformability.

Animals↗
PubMed1980

On the energy dissipation in a tank-treading human red blood cell.

The energy dissipation in the membrane (ED mem) and in the cytoplasm (ED cyt) of tank-treading human red blood cells is estimated. The tank-tread motion of the membrane occurs when the cells in a sheared suspension assume a steady-state of orientation (Fischer et al., 1978, Science [Wash. D. C.], 202:894). The kinematic data used are from red cells suspended either in a dextran-saline solution at a low hematocrit, or in plasma at a hematocrit of 45%. The viscosities of the cytoplasm and the membrane are taken from the literature. The cell in dextran was subjected to seven different shear rates. Both ED mem and ED cyt showed a strong increase with shear rate. Their ratio, however, was always of the order of 1. From this value and the value which was given by Hochmuth et al. (1979, Biophys. J., 26:101) for a shape recovery of a red cell, it is concluded that the range of ED mem/ED cyt for all possible geometries is 1-100.

Energy Transfer↗
PubMed1980

Stabilization of erythrocyte shape by a chemical increase in membrane shear stiffness.

Treatment of human erythrocytes with the SH oxidant, diamide, suppresses shape transformations of biconcave erythrocytes into echinocytes or stomatocytes by shape-transforming agents assumed to exert their action via the lipid phase as well as via membrane proteins. The effect of diamide on shape changes is due to a formation of inter- and intramolecular disulfide bonds in membrane proteins, and can be reversed by reduction of these disulfide bonds. A monofunctional SH reagent, N-ethylmaleimide, also stabilizes the shape of the cell. Moreover, echinocytes produced by salicylate, and stomatocytes produced by Triton X-100, can be stabilized by diamide and do not return to the biconcave shape upon removal of the shape-transforming agents. The stabilizing effect of the SH reagents is paralleled by a loss of shear-induced deformability of the erythrocytes. A model is discussed that describes the possible mechanism by which SH reagents may stabilize the shape of the cell due to an increase of membrane shear stiffness.

Diamide↗
PubMed1978

Selective alteration of erythrocyte deformabiliby by SH-reagents: evidence for an involvement of spectrin in membrane shear elasticity.

In order to elucidate the molecular basis of membrane shear elasticity, the effect of membrane protein modification by SH-reaents on the deformability of human erythrocytes was studied. Deformability was quuantified by measuring the elongation of erythrocytes subjected to viscometric flow in a transparent cone plate viscometer. Impermeable SH-reagents proved to have no mechanical effect. Many, but not all, permeable SH-reagents markedly decreased the elongation. Among these, bifunctional SH-reagents (e.g. diamide, tetrathionate and N, N' -p-phenylenedimaleimide) able to cross-link membrane SH-groups were more effective than monofunctional SH-reagents (e.g. N-ethylmaleimide and ethacrynic acid). The bifunctional SH-reagents produced a 50% decrease of elongation after modification of less than 5% of the membrane SH-groups. In contrast, for a comparable effect, more than 20% of the SH-groups had to be modified by the monofunctional reagents. The effect of SH-oxidizing agents was fully reversible after treatment with disulfide-reducing agents. All bifunctional SH-reagents induced a dimerization of a small fraction of spectrin. Anaalysis of the distribution of the diamide-induced disulfide bonds among the various membrane protein fractions showed that this agent preferentially acts on the spectrin polypeptides. The results provide direct experimental evidence that the native arrangement of spectrin is essential for the shear resistance of the erythrocyte membrane and that introduction of small numbers of intermolecular cross-links as well as modification within the molecule lead to a rapid loss of this function.

Diamide↗