Structural correlates of platelet functional damage by physical forces

Human platelets, which were selectively damaged either in a device designed to impose surface injury or one in which damage is primarily limited to shear forces in the fluid bulk, were examined with the electron microscope in an effort to correlate functional and ultrastructural evidence of injury. Surface injury results in more severe inhibition of platelet adhesion and aggregation, as well as PF-3 and PF-4 activity. These functional effects are accompanied by profound and widespread ultrastructural changes, including membrane defects, enlargement of the open cannicular system, alterations in dense bodies and alpha granules, and the development of globular shapes. Very little serotonin is lost, but there is an increase in the number of abnormal dense bodies. In contrast, the shear injured cells demonstrate few functional defects, despite a lesser but still substantial number of structural changes, at forces up to 10(5) dynes/cm2. At higher shears, both functional and structural evidence of severe injury is present, along with apparently normal platelet aggregation.