Coupling of hepatic prostaglandin receptors to adenylate cyclase through a pertussis toxin sensitive guanine nucleotide regulatory protein.

E-series prostaglandins (PGs) inhibit glucagon-stimulated cyclic AMP accumulation in hepatocytes as well as glucagon-stimulated glycogenolysis and fatty acid oxidation. The present study was designed to test the hypothesis that this inhibition occurs via interactions with a plasma membrane PGE2 receptor coupled to adenylate cyclase. PGE2 receptors in rat liver plasma membranes were examined using competitive binding studies [( 3H]PGE2 vs. PGE1). Binding data were analyzed to determine the number of apparent binding sites and the PGE dissociation constant (Kd) at each site. Rat liver plasma membranes contained two classes of binding sites with Kd values of 9.9 X 10(-10) and 8 X 10(-9) M. Addition of the GTP-analog guanyl-5'-6'-imidodiphosphate (0.1 mM) altered the PGE2 binding such that a single class of sites with low affinity (Kd = 4 X 10(-9) M) was observed. Similarly, liver plasma membranes isolated from rats pretreated with pertussis toxin contained only a single class of PGE2 binding sites in the absence of guanyl-5'-6'-imidodiphosphate (Kd = 3.4 X 10(-9) M). PGE2 (10(-10) M) inhibited liver membrane adenylate cyclase activity stimulated by forskolin (by 57%) and glucagon (by 24%). This inhibition was not observed in membranes isolated from rats treated with pertussis toxin. Thus, the present studies demonstrate that PGE binding to its hepatic receptors is regulated by a pertussis toxin sensitive guanine nucleotide binding protein coupled to inhibition of adenylate cyclase.