Membrane proteins in human erythrocytes during cell fusion induced by oleoylglycerol

1. The fusion of human erythrocytes into multicellular bodies that is induced by microdroplets of oleoylglycerol was investigated by optical and electron microscopy, and by gel electrophoresis of membrane proteins. 2. At the highest concentrations of oleoylglycerol and Ca2+ used, at least 80% of the cells fused after 30min at 37°C and only about 5% of the cells had completely lysed; the shapes of fused multicellular bodies were usually retained in ‘ghosts’ prepared by hypo-osmotic lysis. 3. The rate of cell fusion was related to the concentration of Ca2+, although some cells fused when no exogenous Ca2+ was present. 4. Interactions of microdroplets of oleoylglycerol with the cells led to abnormalities in the structural appearance of the erythrocyte membrane; subsequent membrane fusion occurred, at least in some instances, at the sites of the microdroplets. 5. The intramembranous particles on the P-fracture face of the treated cells were more randomly distributed, but not significantly increased in number by comparison with the control cells. 6. Gel electrophoresis of the proteins of ‘ghosts’ prepared from fused human erythrocytes showed a production of material of very high molecular weight, the development of a new component in the band-3 region, an increased staining of bands 4.3 and 4.5, and a new component moving slightly faster than band 6. 7. Bands 2.1–2.3 were altered, band 3 was decreased and band 4.1 was lost. 8. Most, but not all, of the changes in the membrane proteins appeared to result from the entry of Ca2+ into the cell. 9. 1-Chloro-4-phenyl-3-l-toluene-p-sulphonamidobutan-2-one partially inhibited both cell fusion and the associated decrease in band-3 protein. 10. The possibility that proteolytic degradation of membrane proteins may be involved in cell fusion induced by oleoylglycerol is considered, and some implications of this possibility are discussed.