title: Guanine nucleotide effects on catecholamine secretion from digitonin-permeabilized adrenal chromaffin cells.
abstract: The nonhydrolyzable GTP analogue guanosine 5'-(beta, gamma-imido)triphosphate (GMP-PNP) produced an ATP-dependent but Ca2+-independent stimulation of [3H]norepinephrine release from permeabilized chromaffin cells. This stimulation of secretion was 25-35% of the secretion induced by 10 microM Ca2+. A similar Ca2+-independent stimulation was produced by other non-hydrolyzable GTP analogues. No effect was seen with a variety of other nucleotides, including GTP. The GMP-PNP effect was specifically inhibited by low concentrations of guanine nucleotides. Addition of cAMP did not mimic the Ca2+-independent GMP-PNP effect, but did slightly enhance Ca2+-dependent secretion. Pretreatment with pertussis toxin had no effect on Ca2+-dependent secretion or on the GMP-PNP effect. There was no detectable diglyceride or inositol phosphate produced during GMP-PNP treatment, and addition of diglyceride and inositol trisphosphate did not induce secretion. Guanosine 5'-(beta-thio)diphosphate (GDP-beta-S), in addition to its ability to inhibit the GMP-PNP effect, partially inhibited Ca2+-dependent secretion. At 10 microM free Ca2+, the effects of GMP-PNP and Ca2+ were nonadditive. In fact, secretion in the presence of both GMP-PNP and 10 microM Ca2+ was slightly less than secretion due to Ca2+ alone. These data suggest that a guanine nucleotide-dependent process interacts in some way with one or more components of the normal Ca2+-dependent secretory pathway. However, it may not be an intrinsic part of the mechanism underlying Ca2+-dependent secretion.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000313:Adrenal Medulla / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002417:Cattle; D002463:Cell Membrane Permeability / Q000187:drug effects; D002478:Cells, Cultured; D002838:Chromaffin System / Q000187:drug effects / Q000378:metabolism*; D000242:Cyclic AMP / Q000494:pharmacology; D004072:Digitonin / Q000494:pharmacology; D006150:Guanine Nucleotides / Q000494:pharmacology*; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D007700:Kinetics; D009638:Norepinephrine / Q000378:metabolism*; D013873:Thionucleotides / Q000494:pharmacology
chemical_list: D006150:Guanine Nucleotides; D013873:Thionucleotides; D006153:Guanosine Diphosphate; D006165:Guanylyl Imidodiphosphate; C023427:guanosine 5'-O-(2-thiodiphosphate); D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D004072:Digitonin; D002118:Calcium; D009638:Norepinephrine