title: Differential regulation of receptor-stimulated cyclic adenosine monophosphate production by polyvalent cations in MC3T3-E1 osteoblasts.
abstract: Extracellular cations have paradoxical trophic and toxic effects on osteoblast function. In an effort to explain these divergent actions, we investigated in MC3T3-E1 osteoblasts if polyvalent cations differentially modulate the agonist-stimulated cyclic adenosine monophosphate (cAMP) pathway, an important regulator of osteoblastic function. We found that a panel of cations, including gadolinium, aluminum, calcium, and neomycin, inhibited prostaglandin E1 (PGE)-stimulated cAMP accumulation but paradoxically potentiated parathyroid hormone (PTH)-stimulated cAMP production. In contrast, these cations had no effect on forskolin- or cholera toxin-induced increases in cAMP, suggesting actions proximal to adenylate cyclase and possible modulation of receptor interactions with G proteins. Phorbol 12-myristate 13-acetated (PMA) mimicked the effects of cations on PGE1- and PTH-stimulated cAMP accumulation in MC3T3-E1 cells, respectively, diminishing and augmenting the responses. Moreover, down-regulation of protein kinase C (PKC) by overnight treatment with PMA prevented gadolinium (Gd3+) from attenuating PGE1- and enhancing PTH-stimulated cAMP production, indicating involvement of PKC-dependent pathways. Cations, however, activated signal transduction pathways not coupled to phosphatidylinositol-specific phospholipase C (PI-PLC), since there was no corresponding increase in inositol phosphate formation or intracellular calcium concentrations. In addition, pertussis toxin treatment failed to prevent Gd(3+)-mediated suppression of PGE1-stimulated cAMP, suggesting actions independent of Gm. Thus, polyvalent cations may either stimulate or inhibit hormone-mediated cAMP accumulation in osteoblasts. These differential actions provide a potential explanation for the paradoxical trophic and toxic effects of cations on osteoblast function that occur in vivo under different hormonal conditions.
authors.affiliation: Department of Medicine, Duke University Medical Center, Durham, North Carolina, USA.
authors.forename: J E
authors.initials: JE
authors.lastname: Hartle
authors.forename: V
authors.initials: V
authors.lastname: Prpic
authors.forename: S R
authors.initials: SR
authors.lastname: Siddhanti
authors.forename: R F
authors.initials: RF
authors.lastname: Spurney
authors.forename: L D
authors.initials: LD
authors.lastname: Quarles
mesh_terms: D037361:Adenylate Cyclase Toxin; D000527:Alprostadil / Q000037:antagonists & inhibitors; D000704:Analysis of Variance; D002412:Cations / Q000494:pharmacology*; D002478:Cells, Cultured; D002772:Cholera Toxin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D005576:Colforsin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis*; D005682:Gadolinium / Q000494:pharmacology; D009638:Norepinephrine / Q000037:antagonists & inhibitors; D010006:Osteoblasts / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000819:agonists; D037342:Pertussis Toxin; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D054801:Phosphoinositide Phospholipase C; D010727:Phosphoric Diester Hydrolases / Q000032:analysis / Q000187:drug effects; D011493:Protein Kinase C / Q000502:physiology; D010566:Virulence Factors, Bordetella / Q000037:antagonists & inhibitors / Q000494:pharmacology
chemical_list: D037361:Adenylate Cyclase Toxin; D002412:Cations; D010281:Parathyroid Hormone; D010566:Virulence Factors, Bordetella; D005576:Colforsin; D002772:Cholera Toxin; D005682:Gadolinium; D000242:Cyclic AMP; D037342:Pertussis Toxin; D011493:Protein Kinase C; D010727:Phosphoric Diester Hydrolases; D054801:Phosphoinositide Phospholipase C; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D000527:Alprostadil; D009638:Norepinephrine