DISTRIBUTION OF PROSTAGLANDIN IP AND EP RECEPTOR SUBTYPES AND ISOFORMS IN PLATELETS AND HUMAN UMBILICAL ARTERY SMOOTH-MUSCLE CELLS

Prostaglandins act through specific receptors to stimulate cyclic AMP formation which inhibits platelet activation and relaxes vascular smoo th muscle. We have used RT-PCR combined with Southern blot analysis to determine the subtypes of prostaglandin receptor on platelets. Platel ets expressed the EP4 rather than the EP2 prostaglandin EP receptor su btype, whereas vascular smooth muscle cells predominantly expressed th e EP2 receptor. The IP receptor, which binds prostacyclin and couples to stimulation of adenylylcyclase, and three isoforms of the inhibitor y EP3 receptor were equally expressed in platelets, HEL cells and umbi lical artery smooth muscle cells. The EP3-II isoform showed variation in level of expression among the three cell types. As a positive contr ol for the presence of platelet RNA, PCR was performed using primers s pecific for the alpha chain of the platelet membrane glycoprotein Ib. As a negative control for the absence of T and B cell contamination in the platelet RNA, PCR was performed using primers specific for the ce ll specific cluster determinants CD2 (a T-cell marker) and CD20 (a B-c ell marker). The finding that platelets express both stimulatory and i nhibitory prostaglandin receptors provides confirmation of a homeostat ic model of regulation of platelet adenylyl cyclase previously propose d.