Abstract
The effect of lysolecithin on the shape of human erythrocytes of varied cholesterol content was examined by scanning electron microscopy. Under the conditions of these experiments, all of the [14C]lysolecithin incubated with cells was shown to be located in the external membrane leaflet. The membrane lysolecithin required to induce echinocytosis (spiculation) in normal cells (0.8 mol cholesterol/mol phospholipid) was approximately 0.08-0.10 mumol/10(10) cells, which contributed 1.6-2.0 micrometer 2 or 1% of the cell surface area. This value is consistent with the premise that echinocytosis was caused by a slight differential expansion of the outer surface of the bilayer. The lysolecithin required for echinocytosis decreased as the membrane cholesterol content increased; from 0.14 mumol/10(10) cells at 0.5 mol cholesterol/mol phospholipid to 0.03 mumol/10(10) cells at 1.4 mol cholesterol/mol phospholipid. These data were interpreted in terms of a bilayer couple mechanism. Assuming that the two amphipaths acted additively, the amount of lysolecithin required to induce echinocytosis was used to estimate the partition of cholesterol between the two leaflets of the red cell membrane. A value of about 51:49% in favor of the outer leaflet was found at all cholesterol levels.
Highlights
T h e effect of lysolecithin on the shape of human erythrocytes of varied cholesterol content was examined by scanning electron microscopy
Supplementary key words echinocytosis scanning electron microscopy * membranes ported that these compounds are not incorporated into red cell membranes in measurable amounts, raising doubts as to the mechanism of their effect on cell shape
Preliminary to our study of the interplay between two blood lipids in affecting red cell shape, we examined the influence of red cell cholesterol on the uptake of added ['4C]lysolecithin
Summary
T h e effect of lysolecithin on the shape of human erythrocytes of varied cholesterol content was examined by scanning electron microscopy. The dramatic effect of intercalated amphipathic compounds on red cell shape [1] was rationalized by Sheetz and Singer [2] in terms of the asymmetric distribution of anionic phospholipids between the two sides of the bilayer [3, 4]. They proposed in their bilayer couple hypothesis that charged amphipaths will partition so as to minimize electrostatic free energy and that the preferential intercalation of a compound into one side of the bilayer will expand its area relative to that of the other side, altering membrane curvature and cell shape. Conrad and Singer [5] recently re-
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