Figure 47

Types of sickle cells and released membrane structures. Franck and coworkers [10] reported that the normal membrane phospholipid organization is altered in sickled erythrocytes. These authors presented evidence of enhanced trans-bilayer movement of phosphatidyl-choline in deoxygenated reversibly sickled cells and put forward the hypothesis that these abnormalities in phospholipid organization are confined to the characteristic protrusions of these cells. Scanning electron micrographs of various types of sickle cells and released membrane structures are shown. A, Deoxygenated despicular red sickle cells (RSC). B, Deoxygenated native RSC. C, Oxygenated irreversibly sickled cell. D, Spicules. E, Purified microvesicles. The free spicules released from RSC by repeated sickling and unsickling as well as the remnant despicular cells were studied by following the fate of 14C-labeled phosphatidylcholine. The results are shown in Figure 4-8. The free spicules have the same lipid composition as do the native cell but are deficient in spectrin. These spicules markedly enhance the rate of thrombin and prothrombin formation, explaining the prethrombotic state of the patient with sickle cell disease and the tendency toward the occurrence of crises. The prethrombotic state, also present in the renal circulation, stimulates sickle cell formation occurring in the inner renal medulla and papillae where hyperosmosis also contributes to sickling and microthrombi formation in the vasa recta. (From Franck and coworkers. [10]; with permission.)

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