Regulation of Arachidonic Acid-Dependent Ca++ Influx in Human Platelets

Abstract

SummaryQuin2 was used to study the rise in cytoplasmic free calcium ([Ca++]i) and the role of prostaglandin (PG) endoperoxides/thromboxane A2 (TxA2), reduced glutathione (GSH), ADP and the glycoprotein (GP) Ilb IIIa complex in mediating [Ca++]i rise during àiachidonic acid(AA)induced platelet aggregation. Ca++mobilization, mostly due to an influx across the plasma membrane, is completely inhibited by aspirin and persists after selective blockade of TxA2 synthase by dazoxiben. GSH total depletion causes a complete aggregation block and 90% inhibition of the transient: U-46619, a stable analog of cyclic endoperoxide PGH2, stimulates [Ca++]i transient in aspirintreated or in GSH depleted platelets. ADPscavengers, ATP (which competes for the ADP receptor), and monoclonal antibodies against the GP Ilb IIIa complex reduce AAinduced Ca++ influx. Therefore, PG endoperoxides alone or a PGH2/TxA2 mimetic stimulate Ca++ influx. Synthesis of PGH2 and TxA2 depends on the availability of GSH, which acts as the reducing cofactor for the PG peroxidase activity. ADP and GP II b ill a are regulating factors of AA mediated Ca++ influx during platelet activation.