| Abstract: | The phospholipid composition and the distribution of phospholipids over the two leaflets of the membrane have been investigated for rabbit and horse erythrocyte membranes. Phosphatidylcholine (PC) comprises 39.4% and 41.3% of the total phospholipid complement of the rabbit and horse erythrocytes, respectively. In both membranes the distribution of this phospholipid is asymmetric: 70% of the PC is present in the outer layer of the rabbit membrane and 60% in that of the horse. The major species of this phospholipid class are the (1-palmitoyl-2-oleoyl)- and the (1-palmitoyl-2-linoleoyl)PC. The disaturated species, (1,2-dipalmitoyl)PC, is present in limited amounts only. Partial replacement of the native PC from intact erythrocytes was accomplished with a purified PC specific transfer protein from bovine liver. Replacement of the native PC species with (1-palmitoyl-2-oleoyl)PC up to 40% of the total PC complement had no effect on the osmotic fragility, the shape and the in vivo survival time of both erythrocyte species. Replacement of the native PC in both rabbit and horse erythrocytes with (1,2-dipalmitoyl)PC up to 20% gave rise to an increased osmotic fragility, a shape change from discocytic to echinocytic and a significant reduction in survival time measured after reinjection of the modified cells. At 30% replacement with (1,2-dipalmitoyl)PC the resulting spheroechinocytes appeared to be cleared from the circulation within 24 h after reinjection. The conclusion can be drawn that the repair mechanisms which may exist in vivo are insufficient to cope with the drastic changes in properties of the erythrocyte membrane which are induced by replacing more than 15% of the native PC by the dipalmitoyl species. |
