The binding of 6-oxo-prostaglandin E1 to platelet prostanoid receptors

6-oxo-PGE1 has been shown to cause a dose dependent stimulation of platelet adenylate cyclase (Km 1.6 X 10(-7)M). Since this compound also displaced specifically bound 9-3H-PGI2 from intact washed platelets (Ki 1.6 X 10(-6)M), the coupling to platelet PGI2 receptors has been suggested to account for the observed platelet cyclase stimulation. However, the Ki/Km-ratio of 6-oxo-PGE1 appears to be high (10.3) as compared to PGI2, ZK 36 374, and PGE1 (1.9, 2.4 and 3.1, resp.). Thus, one might expect that 6-oxo-PGE1 interacts with a heterogeneous population of platelet receptors mediating the same biological response, eg cyclase activation. In this study, we present evidence supporting this concept and report that 6-oxo-PGE1 also displaces specifically bound 3H-PGD2 from its platelet receptor (Ki 1.6 X 10(-5)M).