The effects of hydroxyethyl starches on intracellular calcium in platelets

Hydroxyethyl starch (HES) solutions impair platelet function. To determine whether this effect is achieved through interference of HES with intracellular activation processes, in which calcium is the key second messenger, we evaluated the agonist-induced increase of the cytoplasmic calcium concentration in the presence of HES of different molecular weights. Aliquots of citrated whole blood of 12 volunteers were incubated in vitro with saline, HES 450 (molecular weight in kilodalton), HES 130, and HES 70, resulting in 20% hemodilution. An undiluted sample served as control. The samples were stained with Fluo-3 as the calcium-sensitive fluorescent probe with subsequent flow cytometric analysis. After determination of a baseline, platelets were activated with thrombin receptor activator peptide 6. Platelet activation with thrombin receptor activator peptide 6 resulted in a fast increase in fluorescence (approximately eightfold), representing intracellular calcium mobilization. None of the tested HES solutions exerted a statistically significant effect on the cytoplasmic calcium concentration compared with samples that were incubated with saline or that remained undiluted. These results indicate that the known inhibiting effect of HES on platelets is not achieved through interference with intracellular activation processes.