Factors controlling phosphate-calcium-induced fusion for erythrocytes of several species.

Fusion of normal human, goat, bovine and chicken erythrocytes was investigated using the phosphate-calcium protocol. The relative effects on fusion efficiency of cell shape, membrane deformability, and composition and orientation of phospholipids in the lipid bilayer were ascertained. Exposure of red blood cells to phosphate ions followed by calcium led to cell agglutination at room temperature for all species. Incubation at 37 degrees C for periods up to 2 hours caused hemolysis and membrane-associated protein aggregation followed by fusion in human and chicken erythrocytes but not in bovine or goat red cells. Cell shape may not be a determinant in fusion since bovine, like human erythrocytes, are biconcave but do not fuse with the above protocol. Bovine and goat red blood cells lack phosphatidylcholine in their membranes. Incorporation of phosphatidylcholine into bovine red blood cells, mediated by a specific transfer protein, promoted their fusion. Our results indicate the important role played by phospholipid composition and orientation in red cell membranes for fusion by phosphate and calcium.