Studies on the role of calcium in the control of thromboxane B2 production

5-hydroxytryptamine (5-ht) secretion and thromboxane B2 (TxB2) production by platelet-rich plasma in response to the Ionophore A23187 or the sulphydryl group reagent N-ethyl maleimide (NEM) were potentiated in the presence of EDTA. No such potentiation by EDTA was observed using aspirin-treated platelets. The addition of Ca2+ and also Mg2+ to suspensions of washed human platelets reduced the rate and extent of TxB2 formation in response to thrombin, A23187, collagen or NEM. In contrast, Sr2+ resulted in spontaneous TxB2 production and 5-HT secretion.