An ultrastructural basis for the shape changes induced in platelets by chilling.

B LOOD PLATELETS observed in vivo normally circulate in the form of flat discs. Vascular injury results in the loss of platelet disc shape and adherence of the cells to damaged tissue.4’5 In vitro, sequential morphologic alterations follow the addition of calcium, adenosine diphosphate (ADP) and other aggregating agents to citrated platelet-rich plasma ( PRP) #{149}69The discoid form is lost, platelets become swollen, and multiple pseudopods develop on the cell surfaces.’#{176}’1 Shape changes of this nature appear to be important steps in the development of platelet adhesiveness and lead to platelet aggregation.12 Many years ago Aynaudla14 observed that changes in platelet appearance similiar to those produced by the hemostatic or coagulation processes could be simulated by exposing platelets to low temperatures. The effect of cold on platelets has been studied extensively in recent years l)y Zucker and her col1eagues.1 18 Their work has shown that platelet changes caused by chilling closely resemble the sequential transformations which follow recalcification of PRP. Since conversion of discs to “spiny spheres” is closely related to platelet functional activity, we have examined the transformations caused by chilling in the electron microscope. Results of this study indicate that shape changes in platelets caused by cold are most likely secondary to alterations in the marginal bundle of microtubules.’9