Key result
Platelet dense and alpha granules contain high calcium concentrations, possess Ca2+-ATPase on their membranes, and release calcium upon activation, indicating they function as intracellular calcium stores.
Platelet dense and alpha granules contain high calcium concentrations, possess Ca2+-ATPase, and release calcium upon activation, suggesting they function as intracellular calcium stores.
Animal data on platelet Ca2+ stores warrant no clinical practice change; leaves open their role in human thrombosis or HF.
The atrial specific granule has been described as an intracellular Ca store (ICaS). It is reasonably proposed that other polypeptidesecretory granules could also play the function of ICaS. In the present work, high Ca concentration in the dense granule (dG) and α granule (αG) of platelets was confirmed by using x-ray microanalysis in both ultrathin cryosections and ethanolic phosphotungstic acid staining sections, and Ca2+-ATPase activities were found on the membrane of both the granules. Furthermore, when platelets were activated by A 23187 1 mM, thrombin 2 U/ml or ADP 200μM, both the Ca content and number of the granules decreased, which means that the Ca2+ was released and secretion of the granules increased. It is suggested that the release Ca2+ raise the cytosolic Ca2+ level and, thus, the secretion of the granules is promoted. In addition, it was described that the ultrastructure of the platelet granules in ultrathin cryosections was somewhat different from that in routine sections.
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Zhong et al. (1997) studied Healthy (platelet granule function) (n=5). Platelet activation by agonists (A23187, thrombin, ADP) vs. Non-activated platelets was evaluated on Calcium content and numerical density of platelet granules. Platelet dense and alpha granules contain high calcium concentrations, possess Ca2+-ATPase on their membranes, and release calcium upon activation, indicating they function as intracellular calcium stores.
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