FIG. 7 .
7PTH-stimulated cAMP response in osteoblastic cells. Intracellular cAMP responses were measured by radioimmunoassay after 15-min exposures at 37°C to concentrations of rPTH(1-34) from 10 Ϫ7 to 10 Ϫ11 M. In A, cells were plated at 50,000 cells/cm 2 and grown for 60 h. PTH stimulated cAMP accumulation in a concentration-dependent manner in both ROS (thick solid line) and bG (thick dashed line). However, PTH-stimulated cAMP accumulation in RCx4 (thin solid line) and RCx16 (thin dashed line) was dramatically attenuated. The peak cAMP response to 10 Ϫ7 M rPTH(1-34) in RCx4 and RCx16 was only 26.2 and 21.9% of that of ROS, respectively. In B, the intracellular cAMP response of ROS (thin solid line) and bG (thin dashed line) plated at 5-10,000 cells/cm 2 and grown for 48 h are shown. An 80% reduction in functional coupling in these low density cultures resulted in the attenuation of PTH-stimulated cAMP by 50 and 55% in ROS and bG, respectively. Confluent cultures of ROS (thick solid line) and bG (thick dashed line) are shown for comparison and are the same values as those presented in A. The average basal cAMP response from all experiments was 8.1 Ϯ 1.7 pmol/million cells. All **data** represent means Ϯ S.E. of three to six experiments performed in duplicate. *, significantly different from either ROS or bG (p Ͻ 0.05). FIG. 8. Forskolin-stimulated cAMP accumulation in osteoblastic cells. Cells plated at 50,000 cells/cm 2 were exposed to 10 Ϫ7 , 10 Ϫ9 , or 10 Ϫ11 M forskolin for 15 min. Intracellular cAMP was quantified by radioimmunoassay. Forskolin stimulated cAMP accumulation in a concentration-dependent manner in ROS (thick solid line), bG (thick dashed line), RCx4 (thin solid line), and RCx16 (thin dashed line). There were no significant differences in cAMP responses among the cell lines examined. The average basal cAMP response from all experiments was 7.9 Ϯ 0.8 pmol/million cells. The **data** represent means Ϯ S.E. of four experiments performed in duplicate.