High-affinity prostaglandin E receptors attenuate adenylyl cyclase activity in isolated bovine myometrial membrane.

Purified bovine myometrial plasma membranes were used to characterize prostaglandin (PG) E2 binding. Two binding sites were found: a high-affinity site with a dissociation constant (KD) of 0.27 +/- 0.08 nM and maximum binding (Bmax) of 102.46 +/- 8.6 fmol/mg membrane protein, and a lower affinity site with a KD = 6.13 +/- 0.50 nM and Bmax = 467.93 +/- 51.63 fmol/mg membrane protein. Membrane characterization demonstrated that [3H]PGE2 binding was localized in the plasma membrane. In binding competition experiments, unlabelled PGE1 displaced [3H]PGE2 from its receptor at the same concentrations as did PGE2. Neither PGF2 alpha nor PGD2 effectively competed for [3H]PGE2 binding. Adenylyl cyclase activity was inhibited at concentrations of PGE2 that occupy the high-affinity receptor. These data demonstrate that two receptor sites, or states of binding within a single receptor, are present for PGE2 in purified myometrial membranes. PGE2 inhibition of adenylyl cyclase activity support the view that cAMP has a physiological role in the regulation of myometrial contractility by PGE2.