Role of cytosolic calcium in the control of cAMP content by calcium in bovine parathyroid cells.
In the present studies we used the calcium (Ca2+)-sensitive dye Quin-2 to determine whether the cytosolic (Cyt) Ca2+ mediates the effects of extracellular (EC) Ca2+ on cAMP accumulation through changes in adenylate cyclase and phosphodiesterase activity in bovine parathyroid cells (bPTC). In dispersed (d) bPTC, increasing the EC Ca2+ from 0.5 to 2 mM produces a rise in the Cyt Ca2+ from 179 to 646 nM which is associated with a 52% inhibition of agonist-stimulated cAMP accumulation. Over this range of free Ca2+ adenylate cyclase activity decreased by approx. half (57%) and phosphodiesterase activity increases 2-fold (101%) suggesting that changes in the Cyt Ca2+ can account for the effects of EC Ca2+ on cAMP through changes in these enzymes. Unlike dbPTC, 4-day-old cultured bPTC show only a 23% suppression of cAMP by high EC Ca2+ and a reduced rise in the Cyt Ca2+ from 0.5 to 3 mM EC Ca2+. Although there is no reduction in the Ca2+ sensitivity of adenylate cyclase, phosphodiesterase activity shows no change at varied free Ca2+. Thus, this diminished Ca2+ sensitivity of phosphodiesterase activity, and the decreased rise in Cyt Ca2+ relative to EC Ca2+ may both contribute to the resistance to the effects of EC Ca2+ on cAMP content in cultured cells. Because in addition to Cyt Ca2+, protein kinase C may also mediate the effects of EC Ca2+ on PTH release, we studied the effects of TPA (12-alpha-tetradecanoylphorbol 13-acetate) on agonist-stimulated cAMP in dbPTC.(ABSTRACT TRUNCATED AT 250 WORDS)
D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000378:metabolism; D000262:Adenylyl Cyclases / Q000378:metabolism; D000634:Aminoquinolines; D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D002417:Cattle; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000096:biosynthesis*; D003600:Cytosol / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D005456:Fluorescent Dyes; D010280:Parathyroid Glands / Q000187:drug effects / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D000634:Aminoquinolines; D005456:Fluorescent Dyes; D004533:Egtazic Acid; D000242:Cyclic AMP; D011493:Protein Kinase C; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D000262:Adenylyl Cyclases; D013755:Tetradecanoylphorbol Acetate; C035739:Quin2; D002118:Calcium