Platelets gradually lose their disc shape during storage. The authors studied simultaneous changes in platelet cytosolic Ca2+ (Cai) and the polymerization state of actin as related to the shape. Platelet concentrates were stored under blood bank conditions for up to 10 days. Aliquots were removed and analyzed as follows: platelet Cai and increments in Cai induced by adenosine diphosphate (ADP) were determined by fluorescence of fura-2-loaded cells; loss of disc shape was determined by differences in light scattering intensity induced by stirring; and the ratio of globular and total actin (G/T) of platelets in plasma was determined by a modification of the DNase inhibition assay. Globular actin was found to be 86 +/- 3% of total actin in freshly drawn platelets suspended in plasma. The following changes occurred during storage: G/T in platelet concentrates increased from 63 +/- 5 (day 0) to 74 +/- 2% in the first 24 hours then fell to 33 +/- 6% by day 10. The percent discoid platelets also increased from day 0 to day 1 then fell in the ensuing days. There was an initial drop in Cai from day 0 to day 1, after which Cai increased on days 3 and 6. Globular actin polymerization during storage closely correlated with the change in percent discs (r = 0.95). During 6 days of storage Cai was highly correlated with shape change (r = 0.97) and to a lesser extent (r = 0.87) with the ratio of globular actin. The authors conclude that actin polymerization, shape, and Ca2+ change in a related fashion during storage.

Platelets gradually lose their disc shape during storage. The authors studied simultaneous changes in platelet cytosolic Ca2+ (Cai) and the polymerization state of actin as related to the shape. Platelet concentrates were stored under blood bank conditions for up to 10 days. Aliquots were removed and analyzed as follows: platelet Cai and increments in Cai induced by adenosine diphosphate (ADP) were determined by fluorescence of fura-2-loaded cells; loss of disc shape was determined by differences in light scattering intensity induced by stirring; and the ratio of globular and total actin (G/T) of platelets in plasma was determined by a modification of the DNase inhibition assay. Globular actin was found to be 86 +/- 3% of total actin in freshly drawn platelets suspended in plasma. The following changes occurred during storage: G/T in platelet concentrates increased from 63 +/- 5 (day 0) to 74 +/- 2% in the first 24 hours then fell to 33 +/- 6% by day 10. The percent discoid platelets also increased from day 0 to day 1 then fell in the ensuing days. There was an initial drop in Cai from day 0 to day 1, after which Cai increased on days 3 and 6. Globular actin polymerization during storage closely correlated with the change in percent discs (r = 0.95). During 6 days of storage Cai was highly correlated with shape change (r = 0.97) and to a lesser extent (r = 0.87) with the ratio of globular actin. The authors conclude that actin polymerization, shape, and Ca2+ change in a related fashion during storage.