Calcium modulation of the parathyroid hormone-sensitive adenylate cyclase in ROS 17/2.8 cells: effects of N-(6-aminohexyl-5-Cl-naphthalene sulfonamide) (W-7) and trifluoperazine (TFP).

The calcium modulation of the cyclic 3',5'-adenosine monophosphate (cAMP) response to parathyroid hormone (PTH) was studied in a clonal osteosarcoma cell line ROS 17/2.8. CaCl2 was found to stimulate the PTH-sensitive cAMP response of intact cells. At the maximal concentration of 1 mM CaCl2, the maximum response to PTH was increased, but the ED50 for PTH and the time course of maximal cAMP production were not affected. Verapamil blunted, while the cation ionophore A23187 enhanced, the stimulatory effect of CaCl2. Trifluoperazine (TFP) and N-(6-aminohexyl-5-Cl-naphthalene sulfonamide) (W-7) inhibited the stimulatory effect of CaCl2. In membranes prepared in the presence of 0.1 mM CaCl2, a biphasic effect of CaCl2 was demonstrated: stimulation at concentrations of 60-100 microM, and an inhibition above 200 microM, when adenylate cyclase was assayed in the presence of 200 microM EGTA. Addition of exogenous calmodulin to membranes prepared in the presence of EGTA did not have any effect on the PTH-sensitive adenylate cyclase activity, suggesting that endogenous calmodulin was not effectively stripped from the membranes by EGTA treatment. It is concluded that Ca2+ has both a stimulatory and an inhibitory role in modulating PTH-sensitive adenylate cyclase in ROS 17/2.8 cells by as yet unknown mechanisms, and that the involvement of endogenous calmodulin is implicated.