Loss of Thrombin-Induced Ca2+ Mobilization in a Subpopulation of Platelets during Storage

Hemostatic and signaling functions of transfused platelets

Metabolic studies have revealed a gradual impairment in platelet integrity during storage, a process termed the platelet storage lesion. Recent evidence shows that stored platelets also lose signaling responses to physiological agonists with impaired integrin activation, secretion, and aggregation of the cells. On the other hand, storage leads to a gain in platelet activation properties, such as release of microparticles and appearance of surface epitopes for their clearance by macrophages. New techniques for measuring flow-induced thrombus formation and platelet-dependent coagulation provide evidence that the hemostatic activity of platelets decreases during storage. Besides pharmacological inhibition, novel storage strategies, like metabolic suppression, should be considered to better preserve platelet functionality while limiting the expression of clearance markers. Understanding the changes that occur in association with the platelet storage lesion and the use of updated storage methods will help to generate platelets for transfusion with optimal hemostatic function and a long circulation time after transfusion.

The mitochondrial membrane potential in human platelets: a sensitive parameter for platelet quality

BACKGROUND

Deterioration of platelet (PLT) quality during storage is accompanied by an increase in lactate production, indicating a decrease in mitochondrial function. In this study, the optimal conditions under which the fluorescent dye JC-1 can be used to detect changes in mitochondrial function in PLTs were established.

STUDY DESIGN AND METHODS

PLTs were incubated at 37 degrees C in synthetic medium under various conditions of JC-1 loading. In the presence of a high membrane potential, this dye accumulates in the mitochondria with a concomitant increase in red fluorescence. After JC-1 loading, the ratio of red (FL2) to green (FL1) fluorescence was determined by flow cytometry.

RESULTS

The FL2-to-FL1 ratio of PLTs (3 x 10(7)/mL, loaded with 0.5 micromol/L JC-1) amounted to about 5 in 1-day-old PLTs. At higher dye concentrations, the FL2-to-FL1 ratio was significantly lower, suggesting uncoupling by the dye itself. Plasma concentrations above 3 percent significantly affected the JC-1 signal. The FL2-to-FL1 ratio showed a dose-dependent decrease to an uncoupler of oxidative phosphorylation or to inhibition of the respiratory chain. JC-1-loaded PLTs showed a clear decrease in FL2-to-FL1 ratio after prolonged storage or upon ultraviolet (UV) illumination. Only after UV treatment did changes in JC-1 signal correlate with changes in CD62P expression.

CONCLUSION

The FL2-to-F1 ratio of PLTs loaded with JC-1 is a reliable and sensitive indicator of the mitochondrial membrane potential, provided that the proper experimental conditions have been applied.