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Biomedical subjects

S B Shohet

Publications and source records attributed to S B Shohet.

156 records · Page 9Linked to original sources
PubMed1968

Stages in the incorporation of fatty acids into red blood cells.

Mature human erythrocytes were incubated with (14)C-labeled palmitic acid bound to crystalline human albumin. Energy-dependent incorporation of the labeled palmitic acid into cell membrane phospholipids occurred, and various stages in this incorporation were defined. Initially the palmitic acid was rapidy transferred from the albumin to a "superficial" membrane pool of free fatty acid (F-1), which was removable when the cells were washed with defatted albumin. This process was independent of red cell metabolism. The labeled fatty acid then passed into a second "deeper" membrane pool of free fatty acids (F-2), which was not extractable with albumin. This process was energy-dependent and proceeded at a slower rate than the initial transfer from albumin to F-1. Ultimately the labeled fatty acid was incorporated into phosphatides (PL). This process also was dependent upon cellular metabolism. The kinetics of pulse label studies suggest that the processes observed were sequential and that precursor-product relationships exist between the F-1 and F-2 pools and the F-2 and PL pools. [Formula: see text] From the size and specific activities of these pools, calculations of the extent of phospholipid turnover were made. An approximate figure of 2% /hr or 30 nmoles/ml of packed red blood cells per hr was obtained. The figure was further calculated to represent an energy cost to the red blood cell of approximately 5% of the energy available from glycolysis.

Cell Membrane Permeability↗
PubMedDate not supplied

Deformability of stored red blood cells. Relationship to degree of packing.

An ektacytometer was used to measure red blood cell deformability during blood storage for 42 days at different degrees of cell packing in citrate-phosphate-dextrose preservative. Observed changes in deformability were studied in relationship to red blood cell adenosine triphosphate (ATP) levels, lipid content, osmotic fragility, and hematocrit during storage. Decrease in whole cell deformability as measured in isotonic medium did not occur until cellular ATP levels were reduced to less than 30 percent of initial values. The rate of deformability loss during storage increased with increased degrees of cell packing because of more rapid substrate depletion. The loss in isotonic deformability was further magnified when deformability measurements were carried out in hypotonic media, suggesting that a reduction in surface area-to-volume ratio was the dominant cause of the reduced deformability of stored red blood cells. Marked spherocytosis, decreased membrane lipid content and increased osmotic fragility confirmed loss of membrane surface area during storage. The significantly higher rate of deformability loss observed in packed red blood cells suggests that careful control of storage hematocrit may be necessary to avoid loss of cellular deformability and possibly posttransfusion viability.

Adenosine Triphosphate↗
PubMedDate not supplied

Rheological properties of antibody-coated red cells.

In vivo and in vitro antibody-coated nonspherocytic red cells have normal deformability in iso-osmolar media, and their isolated membranes have normal mechanical stability as measured in the ektacytometer, a laser visco-diffractometer. The deformability of red cells from patients with hemolytic anemia was proportionately reduced with the degree of spherocytosis irrespective of whether the direct antiglobulin test was positive. However, when antibody-sensitized nonspherocytic cells were suspended in hyperosmolar media and exposed to constant shear stress in the ektacytometer, they showed reduction of their deformability index in the presence of polyvinylpyrrolidone (PVP; 360,000 Daltons) but not dextran. This reduction was not due to alterations in cell water or cation content. Also, when incubated at 37 degrees C, sensitized red cells reacted specifically with PVP, and underwent a decrease in cell deformability. This appears to be the result of changes either in red cell membrane rigidity or membrane viscosity. The PVP effect was reproducible, time- and temperature-dependent, and predicted reliably the Rh phenotype. These observations were used to develop a novel approach to the antiglobulin test in the blood bank.

Anemia, Hemolytic, Autoimmune↗
PubMedDate not supplied

The effect of abnormal hemoglobins on the membrane regulation of cell hydration.

Several hemoglobinopathies are associated with abnormalities in the permeability of the red cell membrane, in some cases leading to permanent alterations of the intracellular milieu. Homozygous sickle cell disease is the most thoroughly studied example. Deoxygenation of sickle cells causes a transient increase in the permeability to monovalent cations and Ca; prolonged deoxygenation can lead to a permanent accumulation of Ca and loss of total cations and water. Although the mechanisms for the permeability changes are not yet defined, mechanical stress on the membrane, with subsequent damages by excess Ca or membrane-associated hemoglobin have been suggested to play a role. Loss of cell water and increase in mean cell hemoglobin concentration causes massive reduction of cell deformability in the oxygenated state and makes the hemoglobin more likely to undergo sickling because of the strong concentration dependence of the sickling process. Limited evidence suggests the occurrence of permeability defects in other hemoglobinopathies and the thalassemias. The suggested alterations range from a slight increase in K permeability of incubated thalassemia cells to substantial dehydration of cells from patients with homozygous hemoglobin C disease. Oxidative damage to the membrane, involving an abnormal hemoglobin-membrane association, may underly the permeability changes in these cells.

Adenosine Triphosphate↗
PubMedDate not supplied

Membrane-based, dry-reagent prothrombin time tests.

The authors describe a prototype membrane-based, dry-reagent prothrombin time assay for whole blood. This system uses an asymmetric polysulfone membrane to separate plasma from red blood cells, and works with samples as small as 10 microliters. The membrane contains calcium and thromboplastin, and permits the reactions of the complete extrinsic pathway to occur with minimal distortion from membrane surface interactions. Thrombin generation is monitored optically using a rhodamine-110-based fluorescent thrombin substrate. Fluorescence kinetics are analyzed to produce a prothrombin-time--equivalent parameter that can be converted to an international normalized ratio (INR) value. The system provides results that correlate well with conventional liquid phase prothrombin time assays (R2 = 0.96).

Anticoagulants↗