Parathyroid hormone stimulation of alkaline phosphatase activity in cultured neonatal mouse calvarial bone cells: involvement of cyclic AMP and calcium.

The involvement of cAMP and calcium in the rise in alkaline phosphatase (AP) activity observed when confluent, serum-free primary cultures of neonatal mouse calvarial cells are treated with parathyroid hormone (PTH) has been studied. Synthetic bovine PTH [bPTH-(1-34)] increased cellular cAMP at concentrations (10(-9) to 10(-7) M) previously found to elevate AP activity. Other substances that increase cAMP in these cells (forskolin, prostaglandin E2, 8-bromoadenosine cAMP and 3-isobutyl-1-methylxanthine) also increased enzyme activity. By comparison, increasing the concentration of calcium in the culture medium from 1.8 to 3.8 or 5.8 mM lowered the magnitude of the maximal AP response. In addition, treatment of cultures with the divalent cation ionophore A23187 caused a significant decrease in AP activity. These results suggest that: 1) cAMP mediates the rise in the specific activity of AP in cultured neonatal mouse calvarial cells treated with bPTH-(1-34) and 2) the concentration of calcium in the environment significantly influences the responsivity of bone cells to the hormone.