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  • 1
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Theoretical osmotic fragility curves were calculated and drawn by computer using the van't Hoff equation and the isotonic areas and volumes of 1000 individual erythrocytes. We studied the influence on the calculated curves of theoretically altering the fraction of the volume which was osmotically active from 50 to 70%, and of altering the permissible stretch before hemolysis from zero to 10%. With the two assumptions-that the membrane does not stretch before hemolysis, and that the osmotically active fraction of the cell volume is 0.58-it was possible to duplicate the general shape of the standard fragility curve; the exact NaCl concentration, however, at which there was 50% hemolysis was approximately 0.1 gm/100 ml higher than found in vitro. The calculated osmotic fragility curves can be made quantitatively similar to in vitro ones if the following statements are true: the osmotically active volume is 58%, the permissible stretch of the membrane without lysis is 6%, the cell membrane resists a slight osmotic pressure gradient of approximately 0.1 atmospheres, and hemolysis is an all or nothing phenomenon. This set of values for the relevant factors is sufficient but not unique in causing the superposition of the calculated and experimental curves. The frequency distribution of the cells according to the hemolytic salt concentrations (the sodium chloride concentration at which an individual cell just hemolyzes) was skewed positively and was leptokurtic for each of the seven normal subjects studied.
    Additional Material: 4 Ill.
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  • 2
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The sedimentation of individual cells was investigated in the context of the Stokes' equation for sedimenting spheres. Blood obtained from a finger prick was diluted 104 times by volume in Tris buffered Ringer solution (pH 7.4, 310 milliosmolar). A small sample of the suspension was put in a plastic, flat bottomed depression slide which was then closed with a coverslip. Thirty-six runs were done in which a cell was kept in focus on an inverted microscope. The 250 μm descent was monitored on a two channel chart recorder. The orientation, determined by the observer as edge, oblique, or flat, and the verticle displacement, indicated by a ten turn potentiometer connected to the fine focussing knob, were recorded simultaneously. The cells studied indicated that cells are more frequently in the edge-on orientation, that larger cells sediment faster than smaller cells despite the lower density for larger cells, and that cells wobble considerably. The biconcave cells made approximately three orientation changes per minute where one change in orientation was considered to be a rotation of 45° in any direction. Brownian motion is thought to be responsible for the wobble, or random rotations of the sedimenting cell. The edge-to-flat velocity ratio was 1.38 ± 0.30 S.D. which is significantly less than 1.5, the theoretical and experimental value for thin discs. There was a moderate dependence of sedimentation velocity on the square of the diameter (R = +0.5) in accordance with Stokes' Law. The variance in this relation can be accounted for by the known variation of cellular density within a normal population of red cells, and by the inherent errors of measurement.
    Additional Material: 7 Ill.
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  • 3
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The sedimentation behaviour of single human red blood cells fixed with glutaraldehyde at pH 7.4 and 6.4 was studied and compared to resiflts previously reported for normal fresh cells. The cells fixed at pH 7.4 were observed to have normal shapes while those fixed at pH 6.4 were more spherical and less disc-like. Fixation of glutaraldehyde removed “membrane flicker,” resulting in increased stability as indicated by a decrease in the number of orientation changes per minute from 2.93 ± 0.16 (SEM) to 1.74 ± 0.10 (SEM). An orientation change was defined as a change of 45° in any direction. Fixation also increased the edge-to-flat time preference ratio from 2.5 to 4.7, and increased the sedimentation velocities in all three orientations, despite a measured 2.5% decrease in mean cell density.Fixation of cells at pH 6.4 showed that the decrease in stability and preference for the on-edge orientation was associated with an increase in the sphericity of the cell.
    Additional Material: 1 Ill.
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