title: Potent and cooperative feedback inhibition of adenylate cyclase activity by calcium in pituitary-derived GH3 cells.
abstract: Calcium (Ca2+) ion concentrations that are achieved intracellularly upon membrane depolarization or activation of phospholipase C stimulate adenylate cyclase via calmodulin (CaM) in brain tissue. In the present study, this range of Ca2+ concentrations produced unanticipated inhibitory effects on the plasma membrane adenylate cyclase activity of GH3 cells. Ca2+ concentrations ranging from 0.1 to 0.8 microM exerted an increasing inhibition on enzyme activity, which reached a plateau (35-45% inhibition) at around 1 microM. This inhibitory effect was highly cooperative for Ca2+ ions, but was neither enhanced nor dependent upon the addition of CaM (1 microM) to EGTA-washed membranes. The inhibition was greatly enhanced upon stimulation of the enzyme by vasoactive intestinal peptide (VIP) and/or GTP. Prior exposure of cultured cells to pertussis toxin did not affect the inhibition of plasma membrane adenylate cyclase activity by Ca2+, although in these membranes, hormonal (somatostatin) inhibition was significantly attenuated. Maximally effective concentrations of Ca2+ and somatostatin produced additive inhibitory effects on adenylate cyclase. The addition of phosphodiesterase inhibitors demonstrated that inhibitory effects of Ca2+ were not mediated by Ca2(+)-dependent stimulation of a phosphodiesterase activity. These observations provide a mechanism for the feedback inhibition by elevated intracellular Ca2+ levels on cAMP-facilitated Ca2+ entry into GH3 cells, as well as inhibitory crosstalk between Ca2(+)-mobilizing signals and adenylate cyclase activity.
authors.affiliation: Department of Pharmacology, University of Colorado Health Sciences Center, Denver.
authors.forename: C L
authors.initials: CL
authors.lastname: Boyajian
authors.forename: D M
authors.initials: DM
authors.lastname: Cooper
mesh_terms: D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002147:Calmodulin / Q000494:pharmacology; D002460:Cell Line; D002462:Cell Membrane / Q000201:enzymology; D002531:Cerebellum / Q000648:ultrastructure; D005246:Feedback; D006160:Guanosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D008297:Male; D037342:Pertussis Toxin; D010903:Pituitary Gland, Anterior / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains; D013004:Somatostatin / Q000494:pharmacology; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D002147:Calmodulin; D010566:Virulence Factors, Bordetella; D014660:Vasoactive Intestinal Peptide; D013004:Somatostatin; D006160:Guanosine Triphosphate; D037342:Pertussis Toxin; D002118:Calcium