Loss of thrombin-induced Ca2+ mobilization in a subpopulation of platelets during storage.
Thrombin-induced changes in cytosolic free Ca2+ ([Ca2+]i) were studied in human platelets that had been stored for up to 6 days. Changes in [Ca2+]i were measured with Indo-1-loaded platelets and quantitated with two different methods: (i) measurement of the changes in total fluorescence; (ii) measurement of the [Ca2+]i changes in individual platelets in a flow cytometer, allowing the detection of non-responding platelets. The maximal concentration of [Ca2+]i after stimulation with 0.5 U of thrombin/ml decreased from 544 +/- 58 nM (mean +/- SEM, n = 6) on day 0, to 276 +/- 9 nM on day 3 and to 203 +/- 23 nM on day 6. The percentage of platelets responding to 0.5 U of thrombin/ml declined from 90 +/- 2% on day 0 to 72 +/- 4% on day 3, and to 47 +/- 8% on day 6. Nevertheless, also the responding platelets showed a decreased rise in [Ca2+]i. The study shows that during platelet storage a decrease in the rise in [Ca2+]i upon thrombin stimulation occurs. This decrease is partly due to the formation of a subpopulation of platelets that is completely unresponsive and partly due to a decreased responsiveness in the remainder of the platelets; it is not due to a gradual decline in [Ca2+]i rise in all platelets. This phenomenon provides new insight in the functional defect of stored platelets.
Fijnheer
R
R
Central Laboratory of the Netherlands Red Cross Blood Transfusion Service, Amsterdam.
Homburg
C H
CH
Hooibrink
B
B
Boomgaard
M N
MN
de Korte
D
D
Roos
D
D
D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D001793:Blood Preservation; D002118:Calcium / Q000097:blood*; D005434:Flow Cytometry; D006801:Humans; D066298:In Vitro Techniques; D013917:Thrombin / Q000494:pharmacology*
D013917:Thrombin; D002118:Calcium