Identification of two distinct adenosine diphosphate receptors in human platelets

(1) FSBA, an inhibitor of platelet shape change and aggregation, inhibits and reverses the binding of fibrinogen to washed platelets induced by ADP in the presence of calcium ion; (2) FSBA does not inhibit either aggregation of or fibrinogen binding to platelets treated with chymotrypsin; (3) additional evidence is provided that FSBA does not inhibit aggregation by stimulating cyclic AMP accumulation; (4) FSBA does not inhibit PGE1-induced cyclic AMP accumulation and has little ability to inhibit the action of ADP on cyclic AMP or the binding of the ADP analog [beta 32P] 2-MeSADP; and (5) these results provide additional support for the view that the effects of ADP on aggregation and on cyclic AMP are mediated by distinct receptors, one of which, designated "A", is labeled by FSBA; the second receptor designated "C", has selective affinity for 2-MeSADP.