title: Forskolin-stimulated cyclic AMP accumulation mediates protein synthesis-dependent refractoriness in C6-2B rat glioma cells.
abstract: We have examined the roles that cyclic AMP and protein synthesis play in the development of refractoriness in C6-2B rat glioma cells using the diterpene, forskolin, a general activator of cyclic AMP-generating systems. Forskolin-stimulated cyclic AMP accumulation peaked at 30 min and declined thereafter to 10% of peak levels by 3 hr despite the continued presence of sufficient forskolin to produce 98% of the control response when the incubation medium was transferred to naive cells. C6-2B cells treated for 3 hr with forskolin were refractory to a subsequent challenge with forskolin or isoproterenol. The phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) increased the degree of refractoriness developed after forskolin treatment. In the presence of IBMX, the induction of refractoriness by forskolin and forskolin-stimulated cyclic AMP accumulation were similarly dependent on forskolin concentration. Pre-treatment with isoproterenol or the cyclic AMP analogue, dibutyryl cyclic AMP, induced refractoriness to forskolin. When C6-2B cells were pre-treated with forskolin plus the protein synthesis inhibitor, cycloheximide, the development of refractoriness to forskolin or isoproterenol was attenuated. Cycloheximide prevented isoproterenol- or dibutyryl cyclic AMP-induced refractoriness to forskolin. These data provide further evidence that the onset of the refractory state in C6-2B cells is mediated by cyclic AMP and is a protein synthesis-requiring process.
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002478:Cells, Cultured; D005576:Colforsin; D000242:Cyclic AMP / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D004224:Diterpenes / Q000494:pharmacology*; D005910:Glioma / Q000378:metabolism*; D007545:Isoproterenol / Q000494:pharmacology; D009363:Neoplasm Proteins / Q000096:biosynthesis*; D014176:Protein Biosynthesis; D051381:Rats
chemical_list: D004224:Diterpenes; D009363:Neoplasm Proteins; D005576:Colforsin; D003994:Bucladesine; D003513:Cycloheximide; D000242:Cyclic AMP; D007545:Isoproterenol; D015056:1-Methyl-3-isobutylxanthine