Ouabain increases the calcium concentration in intracellular stores involved in stimulus-response coupling in human platelets.
The effect of ouabain on Ca2+ homeostasis in human platelets was studied using both quin 2 and chlorotetracycline to monitor changes in cytosolic Ca2+ as well as changes in the amount of Ca2+ accumulated in intracellular storage sites. In resting platelets, ouabain induces a concentration- and time-dependent increase in cytosolic Ca2+ concentration and a marked elevation of Ca2+ in the intracellular stores. The amount of Ca2+ mobilized from these stores upon stimulation with thrombin, as well as thrombin-induced secretion of platelet 5-hydroxytryptamine, was increased after preincubation with the glycoside (3 x 10(-6) M). These data show that ouabain induces an elevation of intracellular Ca2+ levels, most likely mediated via Na(+)-Ca2+ exchange, and that this incremental amount of Ca2+ is accumulated in an intracellular store involved in stimulus-response coupling. This may explain the enhanced functional responses of platelets to agonists in the presence of ouabain and suggests a role for Na(+)-Ca2+ exchange in Ca2+ homeostasis of the human platelet.
Roevens
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Department of Biochemistry II, Janssen Research Foundation, Beerse, Belgium.
de Chaffoy de Courcelles
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D000634:Aminoquinolines; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000097:blood* / Q000378:metabolism; D002751:Chlortetracycline; D004789:Enzyme Activation; D005456:Fluorescent Dyes; D006706:Homeostasis; D006801:Humans; D010042:Ouabain / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism; D013268:Stimulation, Chemical; D013917:Thrombin / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism
D000634:Aminoquinolines; D005456:Fluorescent Dyes; D010042:Ouabain; D012964:Sodium; D010738:Type C Phospholipases; D013917:Thrombin; C035739:Quin2; D002118:Calcium; D002751:Chlortetracycline