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

Area of Science:

• Endocrinology
• Bone Biology
• Cellular Biology

Background:

• Parathyroid hormone (PTH) plays a crucial role in calcium homeostasis and bone metabolism.
• Understanding the specific location and characteristics of the PTH receptor in bone is essential for elucidating PTH's mechanism of action.

Purpose of the Study:

• To determine the precise localization of the parathyroid hormone (PTH) receptor within embryonic chick bone.
• To characterize the binding properties and cellular distribution of the PTH receptor.

Main Methods:

• Utilized 18-day embryonic chick calvariae and radiolabeled [125I] bovine PTH(1-34) for binding studies.
• Performed light and electron microscopy with autoradiography to visualize receptor localization.
• Assessed competition binding with unlabeled PTH and other hormones, and measured cyclic AMP (cAMP) production.

Main Results:

• Steady-state binding of [125I]bPTH(1-34) was achieved, with minimal non-specific binding.
• Half-maximal inhibition of binding occurred at approximately 10 nM unlabeled PTH, correlating with cAMP stimulation.
• Autoradiography revealed PTH receptor concentration on osteoblasts and progenitor cells on the calvarial surface and trabeculae, with localization to cell membranes and evidence of internalization.

Conclusions:

• The parathyroid hormone (PTH) receptor is specifically localized to osteoblasts and progenitor cells in embryonic chick bone.
• These findings provide insights into the cellular targets of PTH action in bone development and remodeling.
• Evidence suggests that PTH undergoes cellular internalization after binding to its receptor.