title: Coupling of opiate receptors to adenylate cyclase: requirement for Na+ and GTP.
abstract: Inhibition of the adenylate cyclase activity in homogenates of mouse neuroblastoma-glioma hybrid cells (NG108-15) by the opioid peptide [D-Ala2,Met5]enkephalin amide (AMEA) requires the presence of Na+ and GTP. In this process, the selectivity for monovalent cations is Na+ greater than or equal Li+ greater than K+ greater than choline+; ITP will replace GTP but ATP, UTP, or CTP will not. The apparent Km for Na+ is 20 mM and for GTP it is 1 microM. Under saturating Na+ and GTP conditions, the apparent Ki for AMEA-directed inhibition is 20 nM for basal and 100 nM for prostaglandin E1-activated adenylate cyclase activity. For both cyclase activities, maximal inhibition is only partial (i.e., approximately 55% of control in each case). In intact viable NG108-15 cells, the decrease in basal and prostaglandin E1-stimulated intracellular cyclic AMP concentrations by AMEA is also dependent upon extracellular Na+. The enkephalin-directed reductions in cyclic AMP concentrations are at least 75%. The specificity of the monovalent cation requirement for enkephalin action on intact cells is the same as for enkephalin regulation of homogenate adenylate cyclase activity. Based on these data, a model is presented in which the transfer of information from opiate receptors to adenylate cyclase requires active separate membrane components, which correspond to the sites of action of Na+ and GTP in this process.
mesh_terms: D000067956:Adenylyl Cyclase Inhibitors; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D002413:Cations, Divalent / Q000494:pharmacology; D002414:Cations, Monovalent / Q000494:pharmacology; D002460:Cell Line; D004745:Enkephalins / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology*; D008566:Membranes / Q000201:enzymology; D051379:Mice; D009474:Neurons / Q000201:enzymology; D011458:Prostaglandins E / Q000494:pharmacology; D011957:Receptors, Opioid / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology*
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D002413:Cations, Divalent; D002414:Cations, Monovalent; D004745:Enkephalins; D011458:Prostaglandins E; D011957:Receptors, Opioid; D006160:Guanosine Triphosphate; D012964:Sodium; D000262:Adenylyl Cyclases