Effects of storage conditions on platelet cytoskeletal proteins

The platelet cytoskeleton is a major determinant of platelet morphology and function. Changes in the protein composition of the cytoskeleton were studied during storage of platelets at 20 degrees to 24 degrees C under blood banking conditions. Cytoskeletons were prepared by extraction of washed platelets with the detergent Triton X-100 and then analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In addition to the three major proteins visible with Coomassie blue staining--actin, myosin, and actin-binding protein--silver staining revealed other proteins associated with the cytoskeletons of freshly collected and stored platelets. The resting platelet cytoskeleton contained 8% to 10% of the total platelet protein and approximately 50% of the total actin. During storage of platelet concentrates for up to five days in the PL 732 container, proteins of 50,000 to 55,000 and 90,000 mol wt were increasingly incorporated into the Triton-insoluble fraction, whereas the amounts of cytoskeleton-associated actin-binding protein, myosin, and actin were maintained at levels present in fresh platelets. Storage of platelets under conditions that allowed the reduction of platelet concentration pH to nearly 6.0 resulted in a marked decrease in the amounts of the major proteins of the cytoskeleton. The loss of specific proteins from platelets stored for extended periods with reduced pH, accompanied by the appearance of lower molecular weight proteins in the cytoskeleton, suggests that extensive proteolysis may occur under certain storage conditions. These data show that the conditions employed for storage of platelet concentrates influence the protein composition of the cytoskeleton and the total protein content of the platelet.