Discocyte-Echinocyte Transformation in Human Platelets: Geometries of Echinocytes Prepared with Osmotic Stress and Aggregating Agents

Abstract

Many agents cause platelets in the disc-form (discocytes) to change into spherical forms from which many pseudopods project (echinocytes). It is not known whether echinocytes prepared with different stimuli are the same. Here we investigate the geometries of echinocytes prepared with aggregating agents and osmotic stress. Geometric parameters were estimated from a cinematographic analysis of freely-rotating platelets in citrated platelet-rich plasma (PRP) under a phase contrast microscope. Echinocytes were prepared by the addition of adenosine diphosphate, thrombin or 35-50% by volume of distilled water to PRP. Under conditions of osmotic stress, 75-90% of the discocytes convert to echinocytes within five minutes followed by a slow reversion to discocytes complete within 1 - 2 hours. Main body diameters for the echinocytes, excluding consideration of the pseudopods, were in all cases 2.1 ± 0.4 um. Comparisons of the mean volume and mean surface area of the main body of the echinocyte with that of the original discocyte show that in each case echinocyte formation is accompanied by: 1) ~15% reduction in main body platelet volume, and 2) ~25% decrease in main body platelet surface area.These results indicate that the main body geometries of echinocytes are essentially independent of the stimuli used and suggest a common pathway for echinocyte formation with of the original discocyte surface area available for pseudopod formation.