EVIDENCE THAT EXTRACELLULAR CALCIUM-IONS INHIBIT THROMBOXANE-B2 BIOSYNTHESIS BY HUMAN-PLATELETS

The ionophore A23187 induced aggregation, 5-hydroxytryptamine secretion and thromboxane B2 (TxB2) production in human platelet-rich plasma. In the presence of 1 mM EDTA or 0.5 mM EGTA, each of the above responses to A23187 was potentiated. With higher concentrations of EDTA, aggregation, secretion and TxB2 production were progressively inhibited. The increased activity of A23187 in the presence of 1 mM EDTA was not observed in aspirin-treated platelets, suggesting that the effect was dependent upon thromboxane biosynthesis. In addition, the effects of N-ethyl maleimide, a compound which induces secretion and thromboxane biosynthesis in the absence of aggregation, were enhanced in the presence of 1 mM EDTA. These results suggest that the chelation of extracellular ionised calcium by EDTA or EGTA resulted in enhanced thromboxane B2 biosynthesis. © 1979.