Cold temperatures reduce the sensitivity of stored platelets to disaggregating agents

In this study, we compared the effect of signal transduction inhibitors on fibrinogen binding, aggregation, the activation state of GPIIb-IIIa, and cytosolic calcium levels in cold and room temperature-stored platelets. Cold-stored platelets have a higher sensitivity to agonist-induced aggregation when compared to room temperature-stored platelets. We also found that cold-stored platelets had a significantly higher aggregation response to ADP and epinephrine, while platelets stored at room temperature responded poorly to these agonists (mean values of 61 vs. 18%, n = 14). Four inhibitors were selected to target various signaling pathways. Cold-stored platelets were more resistant to disaggregation by promethazine, prostaglandin D2, yohimbine, and echistatin. The effects of cold temperatures on stored platelets are targeted to activation pathways as there was no spontaneous aggregation or spontaneous fibrinogen binding as measured in this study. PAC-1 binding was not inhibited to the same degree as aggregation or fibrinogen binding responses, suggesting that the disaggregation was not caused by a change in the conformation of GPIIb-IIIa. Cytosolic calcium levels did not decrease in cold-stored platelets after inhibitor addition. The inhibitors are likely acting after the establishment of the GPIIb-IIIa activation state and may affect the post-occupancy signaling by the fibrinogen-occupied integrin. Differences between aggregation and disaggregation responses of cold- and room temperature-stored platelets suggest that cold-stored platelets may have different mechanisms to stabilize platelet aggregates during their formation.