Acute acidosis-induced alteration in bone bicarbonate and phosphate

Area of Science:

• Biomineralization
• Skeletal Physiology
• Acid-Base Balance

Background:

• Metabolic acidosis causes a drop in systemic pH due to decreased serum bicarbonate.
• Bone acts as a buffer by taking up hydrogen ions, releasing sodium and potassium, and depleting mineral carbonate.
• Bone carbonate is distributed between the accessible hydration shell and less accessible interior regions.

Purpose of the Study:

• To hypothesize that bone's surface and interior respond differently to acidosis.
• To investigate preferential depletion of carbonate from the bone surface during acute metabolic acidosis.
• To localize changes in bone carbonate and phosphate using high-resolution imaging and mass spectrometry.

Main Methods:

• Utilized a high-resolution scanning ion microprobe with secondary ion mass spectroscopy.
• Localized changes in bone carbonate (HCO(3)(-)) and phosphate.
• Incubated neonatal mouse calvariae in control and acidified media simulating acute metabolic acidosis.

Main Results:

• Acute acidosis caused a significant decrease in surface bicarbonate (HCO(3)(-)) but no change in cross-sectional bicarbonate.
• Acidosis led to a substantial decrease in cross-sectional phosphate but no change in surface phosphate.
• Bone surface showed preferential depletion of HCO(3)(-) relative to phosphate, while the interior showed phosphate depletion relative to HCO(3)(-).

Conclusions:

• Acute buffering of hydrogen ions by bone involves preferential dissolution of surface bicarbonate.
• Cross-sectional phosphate also plays a role in buffering during acute metabolic acidosis.
• These findings highlight the differential response of bone's surface and interior to acid-base disturbances.