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Biomedical subjects

R Grebe

Publications and source records attributed to R Grebe.

10 recordsLinked to original sources
PubMed1991

Choroidal blood flow in diabetic retinopathy.

The ocular hemodynamics in diabetic patients with increasingly severe retinopathy have been evaluated using a non-invasive computerized methodology. In a group of 19 healthy volunteers the mean ophthalmic arterial pressure and the ocular pulsatile blood flow were 83 +/- 2.4 mmHg and 648 +/- 42 microliters min-1 respectively. Nine diabetics with no apparent retinopathy had ophthalmic pressures and pulsatile blood flows similar to those in the control subjects. In 11 diabetic patients with background retinopathy the mean pulsatile blood flow was 471 +/- 70 microliters min-1. Thirteen diabetics with proliferative retinopathy had a pulsatile blood flow of 210 +/- 37 microliters min-1 and abnormally low ophthalmic arterial pressures. The results provide evidence that the choroidal blood flow decreases with the severity of the retinopathy in diabetes due to increased vascular resistance and a decreased ocular perfusion pressure.

Adult↗
PubMed1991

Treatment of experimental murine Coxsackie B3 myocarditis.

Using the murine model of coxsackievirus B3-induced myocarditis we studied the effects of various immunosuppressive agents on the course and outcome of the disease in genetically different strains of mice. The response to drug treatment varied greatly among the strains of inbred mice, which suggests different immune pathomechanisms operative in mediating myocarditis.

Animals↗
PubMed1990

Erythrocyte shape simulation by numerical optimization.

In a recent paper we examined the morphology of erythrocytes in terms of the mean mean curvature (MMC) of their cell membranes. A computer simulation of these shapes based on the different geometries showed that the MMC increased from the sphero-stomatocyte to the spheroechinocyte via the discocyte. In this work we extend this analysis by using a numerical optimization method based on importance sampling and the principle of adiabatic cooling. The erythrocyte membrane is treated as a single closed fluid lamina exhibiting viscoelastic characteristics. The energy function of the lamina includes the following terms: (i) Curvature-elastic energy terms which depend on both local and global curvature. (ii) A term describing the compression elasticity of the lamina. (iii) A term which depends on the volume of the cell and which is related to the osmotic pressure across the membrane. In the simulation the cell is assumed to have axial symmetry and it can therefore be described by a finite set of conic sections. So far we have been able to obtain an energy minimum corresponding to a discocyte shape using a sphere as the initial configuration. Our results therefore imply that the well-known sequence of erythrocyte shapes could solely be governed by the above mentioned properties of an ideal fluid forming a closed singly connected lamina.

Blood Viscosity↗
PubMed1989

Automatic shape quantification of freely suspended red blood cells by isodensity contour tracing and tangent counting.

In several blood diseases, the resting red blood cells show deviations from the normal discoidal shape. This is of great diagnostic importance. Similar shape changes occur if cells are subjected to various physical and chemical treatments. An automatic on-line method is introduced which can quantify the mean shape of such cells, freely suspended and unaltered by the method. With the cells inside a special flow chamber, pictures are taken in the form of optical sections using a CCD camera. The image processing includes digitization, cumulation of regions of interest (ROI), contour determination by two-dimensional histogram and isodensity contour tracing, chain coding and tangent counting. The method determines the mean of the absolute number of tangents per section Ts, a quantitative unique shape factor, which allows quantification of pathological red blood cell shapes and follow-up shape changes in experiments, and makes different experiments quantitatively comparable.

Erythrocyte Count↗
PubMed1988

Influence of red cell surface charge on red cell membrane curvature.

The wellknown biconcave shape of resting RBC reflects an intrinsic overall negative spontaneous membrane curvature. It depends to a high degree on the integrity of the spectrin-actin-ankyrin-Band-3 hetero-complex. Alterations of this complex have previously been shown to be associated with shape transitions, which have been abolished by treatment with enzymes reducing the surface charge of the RBC. In this report we show that treatment of erythrocytes with enzymes reducing the surface charge (e.g. neuraminidase, trypsin, chymotrypsin and pronase), consistently exerts a "stomatocytogenic" effect, i.e. it reduces mean mean curvature. Also the time dependency for the charge reduction and for the correlated decrease of mean mean curvature is shown. So-called stomatocytogenic agents (e.g. clorpromazine, tetracain and triton X100) and so-called echinocytogenic agents (e.g. dinitrophenol and Na-salicylate) are known to change membrane curvature in a dose dependent manner. It is further shown that by prior reduction of surface charge by various enzymes the dose response curves of all stomatocytogenic and echinocytogenic agents tested is shifted towards higher degrees of stomatocytosis or lesser degrees of echinocytosis. The data show, that in RBC pronounced curvature influences are produced by the surface charge located on the sialic acid residues in the glycocalix.

Electrophysiology↗
PubMed1988

Influence of moxaverine hydrochloride on membrane curvature and microsieve filterability of red cells after exposure to hyperosmolarity and lactacidosis.

Using a combination of novel techniques to assess quantitatively the shape and the filterability of red blood cells (RBC) after exposure to stress conditions (400 mosmol/l, lactacidosis, pH 6.8), the effects of 1-benzyl-3-ethyl-6,7-dimethoxy-isoquinoline hydrochloride (moxaverine-HCl, Kollateral) were tested. The shape of freely suspended RBC was quantified using the tangent count procedure. The filterability (microrheological performance) of leukocyte-free RBC suspensions was determined by computer-assisted conductometry using novel precision metal microsieves with uniform pore diameter of 4.2 micron. Moxaverine, when present in doses between 10(-5) und 10(-2) mol/l while the RBC are stressed, restored both the normal discoid red cell configuration and the microrheological performance when tested under low shear stresses. The data show that moxaverine, a papaverine derivative, hitherto considered as a classical vasodilator exerts protective effects on RBC membrane curvature and whole cell microrheological behavior (performance). The protective effects manifest themselves when the RBC's are exposed to abnormal biochemical conditions such as they might occur in poststenotic areas, where hypoxic ischemia is known to lead to a combination of hyperosmolarity and lactacidosis which modify the RBCs.

Acidosis, Lactic↗
PubMed1986

Spectrin, red cell shape and deformability. I. Membrane curvature in genetic spectrin deficiency.

Using novel microscopic techniques for observing individual cells in suspension, the shape and deformability of the erythrocytes of a spectrin-deficient strain of mouse were investigated in vitro (fresh and after fixation) and in vivo (intravital microscopy of the mesenteric capillaries). The animals were identical to those studied by Greenquist et al. [14]; however, in contrast to the descriptions by these authors, in the present study, spherical cells were seen only exceptionally. Instead, sphero-echinocytes, spherules with tethered microvesicles, myelin figures and occasional stomato-spherocytes were observed. This pleomorphy, also seen in scanning electron micrographs, can be explained by the fact that in the majority of these cells the membrane assumes an extremely positive outward curvature. After osmotic dehydration, all cells responded by developing progressive membrane protrusions with a positive curvature. Osmotic inflation led to reincorporation of the membrane tethers. After hypoosmolar lysis, the ghosts of the spectrum-deficient mouse cells also showed a pronounced tendency to assume shapes characterized by a progressively positive outward curvature. In vivo observation of the mouse erythrocytes using high magnification interference contrast optics confirmed this in vitro observation. Thus, it is concluded that spectrin deficiency does not primarily lead to spherocytosis: instead, the equilibrium shapes assumed are associated with membrane evaginations which are easily torn off from the main cell body by mechanical forces.

Animals↗
PubMed1986

Spectrin, red cell shape and deformability. II. The antagonistic action of spectrin and sialic acid residues in determining membrane curvature in genetic spectrin deficiency in mice.

In a companion paper, the shapes of spectrin deficient mouse erythrocytes were described; in contrast to previous assumptions, spherules with tethered microvesicles rather than true "spherocytes" were found. Thence, spectrin deficient mouse erythrocytes are endowed with an excess of surface area for the given volume but the membrane is assuming a highly positive curvature. Observations during and after the action of enzymes cleaving the red cell surface charge (Neuraminidase, Trypsin, Chymotrypsin) showed that the previously positive membrane curvature, as well as the tendency of the membrane to flow into fingerlike protrusions was completely abolished. The erythrocytes of the spectrin deficient, desialylated mouse erythrocytes assumed a variety of shapes, often discocytic or even stomatocytic, i.e. their membrane presented with negative curvature. However, while these desialylated membranes could be easily deformed (elongated) by shear flow they did not recoil elastically into any definitive configuration after removal of the deforming forces. It is concluded from these observations that spectrin (acting on the inner interface between membrane and cytoplasm) and sialic acid residues (acting on the outer interface between membrane and plasma) exert antagonizing effects on membrane curvature and membrane bending elasticity. Sialic acid residues, strongly charged and situated on the outer side of the cell, produce positive membrane curvature; this observation can most readily be explained by assuming that this mechanical effect is caused by repulsive coulombic forces expanding the outer half of the bilayer. To explain the effect of the spectrin-complex in counteracting positive or in producing negative membrane curvature, a similar expansive coulombic force acting between the highly charged residues has been postulated. Thence, a model for explaining the overall elastic behaviour of the normal mammalian red cell is developed which is based on the assumption of elastic interactions of proteinacous membrane components coupled to the lipid bilayer of the membrane.

Animals↗
PubMed1985

Tangent counting for objective assessment of erythrocyte shape changes.

The resting shape of the human erythrocyte is maintained mainly by the elastic properties of its membrane. There is evidence that negative spontaneous membrane curvature is the cause of the biconcave shape; also negative membrane curvature is thought to be enhanced under "stomatocytogenic" influences and reduced under "echinocytogenic" influences. Experimental tests of these hypotheses are difficult in the absence of objective methods to quantify cell shape and/or membrane curvature. A new method is introduced to estimate the changes in convex and concave curvatures of the cell outlines in larger populations of RBC. It is based on the so-called "tangent count" procedure, carried out on microphotographs of freely suspended, randomly oriented RBCs in isotonic solutions. The method was validated by subjective shape assessment according to BESSIS' classification. It proved to be most sensitive in the range of moderate shape changes (classified subjectively as echinocyte II and stomatocyte II).

Elasticity↗