Parathyroid hormone receptor in intact embryonic chicken bone: characterization and cellular localization.

Open Access
Publisher Website
Google Scholar
Abstract
The specific localization and characterization of the parathyroid hormone (PTH) receptor in bone were studied in 18-day embryonic chick calvariae and biologically active, electrolytically labeled [125I] bovine [b] PTH(1-34). Binding was initiated by adding [125I]-bPTH(1-34) to bisected calvariae at 30.degree. C. Steady-state binding was achieved at 90 min, at which time 10 mg dry wt of calvaria specifically bound 17% of the added [125I]bPTH(1-34). Nonspecific binding in the presence of 244 nM unlabeled bPTH(1-34) was < 2%. Insulin, glucagon and calcitonin (1 .mu.g/ml) did not compete for PTH binding sites. Half-maximal inhibition of binding was achieved at concentrations of unlabeled bPTH(1-34) or bPTH(1-84) of .apprx. 10 nM. The range of concentration (2-100 nM) over which bPTH(1-34) and bPTH(1-84) stimulated cAMP production was similar to that which inhibited the binding of [125I]bPTH(1-34). Light microscope autoradiograms showed that grains were concentrated over cells (osteoblasts and progenitor cells) at the external surface of the calvariae and in trabeculae. In the presence of excess unlabeled PTH, labeling of control autoradiograms was reduced to near background levels. No labeling of osteocytes or osteoclasts was observed. At the EM level, grains were localized primarily over cell membranes. A quantitative analysis of grain distribution suggested that cellular internalization of PTH occurred.