6-keto-prostaglandin E1-sensitive adenylate cyclase and binding sites in membranes from platelets and cultured smooth muscle cells

6-keto-PGE₁ elicits the same biological effects as PGI₂ in human platelets and in rabbit aorta and mesenteric artery, being, however, less potent. We report here that 6-keto-PGE₁ dose-dependently stimulates adenylate cyclase activity in membranes of human platelets and cultured myocytes from rabbit aorta and mesenteric artery. The extent of stimulation of the enzyme by 6-keto-PGE₁ is the same as elicited by PGI₂ while the apparent affinity is lower than that of prostacyclin, both in platelets and in vascular smooth muscle cells. At the level of platelet membranes, 6-keto-PGE₁ interacts with the binding sites labelled by PGI₂. However, in platelets as well as in mesenteric artery myocytes, 6-keto-PGE₁ interacts with only one class of sites as demonstrated either by binding or by adenylate cyclase studies, whereas PGI₂ in the same conditions recognizes two different classes.