Ultrastructure of sickling and unsickling in time-lapse studies.

The denser subpopulation of erythrocytes from patients with sickle cell anaemia was deoxygenated to a pO2 of 4.7 kPa or reoxygenated to a pO2 of 12 kPa with a continuous-flow apparatus. Samples were collected into modified Karnovsky's fixative at intervals between 0.5 and 15 S. .The earliest event after deoxygenation was aggreagation of haemoglobin followed by the formation of fibres of 160-200 A diameter. The polymers were always randomly distributed in a loose network. A highly ordered, close packing of fibres characteristic of the nematic liquid crystal was not achieved within 15 S. Depolymerization involved a shortening of fibres followed by aggregation similar to that observed early in the polymerization process and prior to the return to the unperturbed state. Irreversibly sickled cells were the first to demonstrate polymers following deoxygenation and that last to lose polymers after reoxygenation. Polymerization of the haemoglobin preceded the appearnce of the sickled deformity of reversibly sickled cells and, following reoxygenation, the return to the discoid shape lagged behind the disappearance of polymers. These studies, carried out under physiologic conditions, have demonstrated intracellular changes during time intervals that correspond to the normal venous and arterial circulation that may contribute to the pathophysiology of sickling disorders.