Prostaglandin E receptors in cardiac sarcolemma: Identification and coupling to adenylate cyclase

Abstract

Purified cardiac sarcolemmal membrane vesicles were used to determine if specific prostaglandin (PG) receptors are present on the myocyte. Two binding sites for PGE2 were identified in isolated bovine sarcolemmal membranes: a high-affinity site with a dissociation constant (K(d)) of 0.32 nM and a maximum binding (B(max)) of 376 fmol/mg of protein and a lower-affinity site with a K(d) of 3.41 nM and a B(max) of 2,112 fmol/mg of protein. In competition experiments, unlabeled PGE1 displaced [3H]PGE2 from its membrane receptor at concentrations similar to those of unlabeled PGE2. Both PGF(2α) and PGD2 displaced [3H]PGE2 from the membrane, but only at high concentrations (> 10-6 M and > 10-5 M, respectively). Digestion of sarcolemmal membrane with trypsin resulted in a threefold decrease in specific [3H]PGE2 binding. Phosphorylation of the membrane with protein kinase A also decreased specific [3H]PGE2 binding. At concentrations of PGE2 that occupy the high-affinity site, sarcolemmal adenylate cyclase activity was inhibited in the presence of 5'-guanylylimidodiphosphate [Gpp(NH)p]. We conclude that the isolated cardiac sarcolemmal membrane contains a high-affinity binding site for PGE2 that is functionally coupled to adenylate cyclase. The binding site is stereospecific and probably recognizes the 9-keto,11-hydroxyl portion of the ring structure of these prostaglandins.