Production of bone resorbing activity in the co-cultures of 5TGM1 myeloma cells and ST2 mouse bone marrow stromal cells.

Conditioned media (48-hour culture) obtained from ST2 alone, 5TGM1 alone, and co-cultures of ST2 (viable or fixed) and 5TGM1 were assayed for bone resorbing activity in organ cultures of⁴⁵Ca-labeled fetal rat long bones. ⁴⁵Ca-labeled fetal rat long bones were cultured in the presence of conditioned media 40%, (v/v) or control medium for 120 hours. Percent ⁴⁵Ca release was determined as ⁴⁵Ca in the medium/⁴⁵Ca in the medium plus bone × 100.⁴⁵Ca release in control culture medium was 18 ± 2%. Percent increase over control was calculated as ⁴⁵Ca release in test medium / ⁴⁵Ca release in control medium −1 × 100. Data are expressed as mean ± SE (n = 4). *Significantly different from control (P < .05). **Significantly different from 5TGM1 alone (P < .05).