title: Cell-free lutropin-dependent desensitization of the lutropin-sensitive adenylate cyclase of pig ovarian follicles is dependent on ATP.
abstract: Experiments were conducted to clarify the nucleotide requirements for lutropin (LH)-dependent adenylate cyclase desensitization in a cell-free membrane preparation derived from a thecal-cell-enriched component of preovulatory pig ovarian follicles. The follicular membranes were extensively washed in 2M-urea to remove endogenously bound GTP, and ATP devoid of GTP was utilized. Results conducted in the presence of 60 microM-GTP and various concentrations of ATP confirm the dependence of LH-stimulated adenylate cyclase activation and desensitization on millimolar concentrations of ATP. In experiments in which adenylate cyclase activation was supported by Mg2+, LH and adenosine 5'-[beta, gamma-imido]triphosphate, GTP did not support the desensitization response. Moreover, although GTP increased both basal and LH-stimulable adenylate cyclase activities in a concentration-dependent manner, the percentage desensitization was not significantly modified by the presence of 10nM-10mM-GTP. These results demonstrate that, even in the presence of exogenous GTP and Mg2+, activation of adenylate cyclase by saturating concentrations of LH in the presence of adenosine 5'-[beta, gamma-imido]triphosphate is not sufficient to initiate desensitization; millimolar concentrations of ATP are also required for the adenylate cyclase desensitization response.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000266:Adenylyl Imidodiphosphate / Q000494:pharmacology; D000818:Animals; D002474:Cell-Free System / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D006160:Guanosine Triphosphate / Q000494:pharmacology; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D066298:In Vitro Techniques; D007986:Luteinizing Hormone / Q000494:pharmacology*; D006080:Ovarian Follicle / Q000187:drug effects / Q000201:enzymology*; D013552:Swine
chemical_list: D000266:Adenylyl Imidodiphosphate; D006165:Guanylyl Imidodiphosphate; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D007986:Luteinizing Hormone; D000262:Adenylyl Cyclases