title: Calcium dependence of hormone-stimulated cAMP accumulation in intact glial tumor cells.
abstract: The Ca2+ content of glial tumor (C6) cells was reduced approximately 5-fold by repeated treatment with media containing ethylene glycol bis(beta-aminoethyl ether) N,N'-tetraacetic acid (EGTA) without loss of cellular viability. The ability of the cells to accumulate cAMP in response to beta-adrenergic agonists was reduced 60 to 70% following Ca2+ depletion. Ca2+ did not affect the apparent KACT for norepinephrine, nor did it change the concentration of propranolol required to produce 50% inhibition of the maximal norepinephrine response. Phentolamine did not alter the Ca2+ dependence of the response. The binding of dihydroalprenolol by intact C6 cells was not influenced by Ca2+. Furthermore, pretreatment with norepinephrine did not affect the Ca2+ dependence of cAMP accumulation. The effects of Ca2+, therefore, appeared to be exerted on components of the adenylate cyclase system other than the catecholamine receptor. Micromolar free Ca2+ concentration in the extracellular medium were sufficient to restore a maximal norepinephrine response to Ca2+-depeleted cells. The effect of Ca2+ on cAMP accumulation in response to hormone was immediate and was rapidly reversible upon the addition of EGTA in excess of the cation. Cells in media containing Ca2+ exhibited a characteristic biphasic time course of cAMP accumulation; with Ca2+-depleted cells cAMP was accumulated more slowly and the subsequent decline in cAMP content was also reduced. Verapamil, an inhibitor of plasmalemmal Ca2+ influx, decreased the Ca2+-dependent component of the cAMP accumulation when added prior to the cation. The effect of Ca2+ on cAMP accumulation was reduced more extensively by pretreatment of cells at 45 degrees C under Ca2+-depleted (80% loss) than under Ca2+-restored (30% loss) conditions. Trifluoperazine at micromolar concentrations decreased the Ca2+-dependent increment in accumulation of cAMP in Ca2+-restored cells. This inhibition was not overcome by increasing concentrations of norepinephrine or of extracellular Ca2+.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism*; D004298:Dopamine / Q000494:pharmacology; D006632:Histamine / Q000494:pharmacology; D007700:Kinetics; D009457:Neuroglia; D009638:Norepinephrine / Q000494:pharmacology*; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism; D012701:Serotonin / Q000494:pharmacology; D014268:Trifluoperazine / Q000494:pharmacology
chemical_list: D011943:Receptors, Adrenergic, beta; D014268:Trifluoperazine; D012701:Serotonin; D006632:Histamine; D000242:Cyclic AMP; D002118:Calcium; D004298:Dopamine; D009638:Norepinephrine