Initial responses of a clonal osteoblast-like cell line, MOB 3-4, to phosphatidic acid in vitro.
A number of studies have shown membrane phospholipid metabolism to have an important role in biological mineralization. We considered the effects of exogenously applied phosphatidic acid (PA), a minor component of membrane phospholipids, on an osteoblast-like cell line, MOB 3-4. Exogenous PA (10-40 micrograms/ml) raised the level of cytoplasmic free Ca2+ [( Ca2+]i), independent of the level of extracellular Ca2+, in a dose-dependent fashion, and this Ca2+ response to PA gradually fell on serial application of PA. In a dose-dependent manner, exogenous PA also increased inositol 1,4,5-trisphosphate (IP3) accumulation and cytoplasmic pH, but decreased basal cAMP level. This cytoplasmic alkalinization was inhibited by pretreatment with nonspecific protein kinase C (PKC) inhibitors, such as sphingosine or H-7. A long-term incubation with PA increased alkaline phosphatase (ALP) activity and cell proliferation. Exogenous PA thus appeared to increase IP3 accumulation by activating phospholipase C, raise [Ca2+] by releasing Ca2+ from intracellular stores, induce cytoplasmic alkalinization via a PKC-dependent mechanism, and simultaneously decrease basal cAMP level. We suggest that these initial responses may be responsible for the increase in ALP activity and the proliferation of PA-treated MOB 3-4 cells.
Kawase
T
T
Department of Pharmacology, Niigata University School of Dentistry, Japan.
Suzuki
A
A
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006863:Hydrogen-Ion Concentration; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D051379:Mice; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D010712:Phosphatidic Acids / Q000008:administration & dosage / Q000494:pharmacology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors
D010712:Phosphatidic Acids; D015544:Inositol 1,4,5-Trisphosphate; D000242:Cyclic AMP; D011493:Protein Kinase C; D000469:Alkaline Phosphatase; D002118:Calcium