Platelet annexin V: the ins and outs

One of the most important signals accompanying platelet activation is the increase in intracellular calcium, and it is known that calcium-binding proteins play an important role in linking this calcium signal to the final platelet responses. Annexins are highly conserved calcium-binding proteins, of which annexin V is the major annexin in human platelets. The last few years have seen an accumulation of information on and speculations about the roles of annexins in both intracellular and extracellular locations. Additionally, annexin V has proven very useful as a marker for apoptosis and platelet activation. It also has potential for the delivery of thrombolytic agents to thrombi and for imaging thrombi as they form in the human body. This review distinguishes between the potential intracellular role of annexin V in platelet activation, and the uses of annexin V in particular to detect apoptosis.