Vitamin D mediated changes in the calcium accumulation in rat osteogenic sarcoma cells

Rat osteogenic sarcoma cells (ROS 17/2) have long served as a model system for studying osteoblastic cell function and regulation. To delineate the action of 1,25(OH)2D3 on ROS cell function, 45Ca accumulation in response to the vitamin was studied. Cells were grown in the presence and absence of 1,25(OH)2D3 for 48 hours and then incubated for 4 min. in media containing 45Ca. In cultures at 100% confluency, 0.25-1.0 pg/ml of 1,25 (OH)2D3 stimulated 45Ca accumulation per mg of cell proteins, while 80 pg/ml or higher dosages inhibited accumulation. In cultures at 50% confluency, doses less than 80 pg/ml were without effect while 80-120 pg/ml dosages stimulated accumulation, and as much as 1000 pg/ml had no effect. These results indicate that the ROS cell response to 1,25(OH)2D3 is biphasic with low doses stimulating, higher doses inhibiting 45Ca accumulation. Furthermore, the sensitivity of the cells to 1,25(OH)2D3 increases as the cell population approaches confluence. Thus, in characterizing ROS cell function, it is important to carefully define the dose-response relationship and the cell culture density