EXPRESSION OF THE PARATHYROID-HORMONE RECEPTOR AND CORRELATION WITH OTHER OSTEOBLASTIC PARAMETERS IN FETAL-RAT OSTEOBLASTS

Primary fetal rat calvarial cell cultures were examined for the expres sion of different osteoblastic parameters at the single cell level and in the whole population. The presence of the parathyroid hormone (PTH ) receptor was studied by employing receptor autoradiography. After 3 days of culture, 10% of the cells expressed the PTH receptor. Immunolo calization of osteocalcin in 3-day-old cell cultures was found to be s trongly correlated with the presence of the PTH receptor. Alkaline pho sphatase (APase) localization in 3-day-old cultures correlated with on ly 69% of the PTH receptor expressing cells. Our results show that in 3-day-old rat calvarial cell cultures, only about 10% of the cells sho w markers of osteoblastic differentiation. The presence of the PTH rec eptor is strongly correlated with the presence of osteocalcin, but les s with the presence of APase, indicating that it is the mature osteobl ast that expresses the PTH receptor. After 7 days of culture, most rec eptor labeling, APase, and osteocalcin expression was found in multila yered areas of cells (nodules).