Interaction of terbium with human platelets

Abstract The effect of terbium on platelets has been studied by aggregation experiments and by fluorescence measurements. TbCl 3 does not substitute for CaCl 2 in the aggregation of platelets induced by ADP, but it may even inhibit, probably by a competition mechanism. It was impossible to observe a sensitized emission of Tb 3+ in the presence of platelets. Instead the lanthanide, like Ca 2+ , significantly increases the aggregation of platelets induced by A23187. The fluorescence yield of this compound is greater in the presence of platelets than in buffer alone. Energy transfer appears to take place from the aromatic amino acids of the platelet membrane to the bound ionophore.