Influence of altered phospholipid composition of the membrane outer layer on red blood cell aggregation: relation to shape changes and glycocalyx structure.

Reversible aggregation of erythrocytes was investigated after alteration of the phospholipid content in the membrane outer leaflet either by disturbance of endogenous transmembrane lipid asymmetry through changes in cellular free calcium, or by incorporation of exogenous lyso-derivatives. It was found that both calcium loading and lyso-phosphatidylcholine (LPC) addition induce a strong increase in red cell-red cell adhesive energy, whereas lyso-phosphatidylserine (LPS), added in the same amount as LPC, does not. Red cell morphological studies show differences in the shape change efficiency of LPS, LPC and calcium loading. However, it was further demonstrated that shape change is not directly responsible for the observed adhesive energy increase, since neuraminidase or trypsin treatment abolish this increase, even though the shape changes induced by alteration of phospholipid organization are not affected. The latter experiment strongly suggests that the red cell adhesive energy increase results from an alteration of the glycocalyx structure, which could be in turn a consequence of the shape change.