Life and Medical Sciences
Cell & Developmental Biology
Wiley InterScience Backfile Collection 1832-2000
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.
Type of Medium: