Studies on the altered membrane characteristics of sickle cells.

It has been shown that sickle cell anaemia causes abnormalities of the red cell membrane which are reflected in altered red cell deformability, permeability, surface area [l], elevated calcium content [2], altered protein patterns and reduced membrane sialic acid content [3 1, potassium loss and cellular dehydration [4]. The major feature of this disease is the tendency of erythrocytes to sickle when exposed to decreased oxygen tensions and to unsickle when reoxygenated. The sickle cell membrane is deformed by polymerised tibres of deoxygenated Hb-SS which adhere to the internal surface of the membrane [5]. This polymerisation is essentially reversible with oxygenation, although some of the cells do maintain their original sickle shape. These irreversibly sickled cells constitute 4-44% of cells in oxygenated capillary blood of individuals with sickle cell disease [6-81. In this communication we have investigated alterations in the fluidity of the hydrophobic lipid region and changes at the surface of the sickle cell membranes compared with those of normal erythrocytes. The results indicate that, in comparison with normal erythrocyte membranes: (i) The hydrophobic lipid region of sickle cell membrane is less fluid. (ii) This is not a consequence of alterations in the cholesterol/phospholipid ratio or fatty acid content. (iii) The negative potential at the surface of the sickle cell membrane is decreased. 2. Experimental