WORTMANNIN INHIBITS STORE-MEDIATED CALCIUM-ENTRY AND PROTEIN-TYROSINEPHOSPHORYLATION IN HUMAN PLATELETS

The effects of the WT on store-mediated Ca2+ entry and protein tyrosin e phosphorylation were investigated in fura-2-loaded human platelets, Wortmannin (2 mu M) attenuated the rise in [Ca2+](i) caused by Ca2+ en try,while having no effect on the mobilisation of Ca2+ from internal s tores. It also reduced store-depletion-evoked protein tyrosine phospho rylation. These findings demonstrate that WT is an inhibitor of tyrosi ne phosphorylation and store-mediated calcium entry and provide furthe r evidence for the involvement of a tyrosine phosphorylation step in t he link between Ca2+ store depletion and Ca2+ influx in human platelet s.