Ca2+ as an extracellular signal in bone.

Area of Science:

• Bone biology
• Calcium homeostasis
• Cellular physiology

Background:

• Bone serves as the primary reservoir for calcium, crucial for maintaining extracellular calcium concentration ([Ca2+]e) homeostasis.
• Bone cells, including osteoblasts and osteoclasts, regulate long-term calcium balance through bone turnover.
• Hormonal regulation, particularly parathyroid hormone (PTH) influenced by Ca2+-sensing receptor (CaR) in parathyroid glands, is key.

Purpose of the Study:

• To investigate the direct sensing and response of bone cells to local extracellular calcium ([Ca2+]e) changes.
• To explore the physiological impact of acute and long-term local [Ca2+]e fluctuations on bone cells.
• To elucidate the molecular mechanisms underlying calcium sensing in bone cells.

Main Methods:

• Review of existing tissue culture studies on bone cell responses to [Ca2+]e.
• Analysis of the role of the Ca2+-sensing receptor (CaR) in bone cells.
• Examination of hormonal regulation of calcium homeostasis.

Main Results:

• Bone cells exhibit direct responses to local extracellular calcium ([Ca2+]e) variations, independent of systemic factors.
• The Ca2+-sensing receptor (CaR) is expressed in bone cells, suggesting its involvement in sensing extracellular calcium.
• Accumulating evidence points to the CaR's role in mediating bone cell responses to environmental calcium.

Conclusions:

• Bone cells possess intrinsic mechanisms to sense and respond to local calcium concentrations.
• The Ca2+-sensing receptor (CaR) likely plays a significant role in mediating these bone cell responses.
• Further investigation is required to fully understand the molecular basis and physiological consequences of local calcium sensing in bone.