Storage lesion of human platelets as revealed by ultrathin sections and freeze-fracture replicas.

We report the ultrastructural changes occurring in human platelets during eight days of storage. Extension of pseudopodia is frequently observed, but a concentration of organelles in the centre of the platelets is found only in a minor fraction (approximately 5%). Striking changes can be observed in both the granules and the open canalicular system. In fresh platelets, the latter often has the form of stacked membranes that have no lumen, but these membranes separate and spread with increasing storage time. However, the openings of this system on the outer surface of the platelet remain unchanged. Some of these features differ from the morphological description of platelets activated by thrombin or ADP, and suggest that the storage lesion is the result of a prolonged weak activation that leads to an incomplete release reaction within the first five days.