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Acid and base effects on avian osteoclast activity
A Carano1, P H Schlesinger, N A Athanasou
1Department of Pathology, Jewish Hospital, Washington University Medical Center, St. Louis, Missouri.
The American Journal of Physiology
|March 1, 1993
Summary
Bone resorption by osteoclasts is influenced by extracellular pH, but bicarbonate concentration is not a limiting factor under physiological conditions. Acid secretion requires bicarbonate, but its levels don't significantly alter bone degradation rates.
Area of Science:
- Biochemistry
- Cell Biology
- Physiology
Background:
- Osteoclasts are crucial for bone resorption, mobilizing calcium via acid secretion.
- Acidification is mediated by vacuolar-type H(+)-ATPase, balanced by HCO3-(-)Cl- exchange.
- The impact of extracellular pH, PCO2, and HCO3- on bone resorption is not well understood.
Purpose of the Study:
- To investigate the effects of extracellular pH, PCO2, and bicarbonate concentration ([HCO3-]) on osteoclast bone resorption.
- To determine if these parameters or their gradients influence bone matrix dissolution.
- To elucidate the regulatory feedback mechanisms in bone resorption.
Main Methods:
- Isolated avian osteoclasts were used to measure bone resorption.
- Extracellular pH, PCO2, and [HCO3-] were varied across physiological ranges.
- Bone degradation was quantified under different ionic and gaseous conditions.
Main Results:
- Bone degradation increased significantly (50%) as extracellular pH decreased from 7.3 to 6.7.
- Changes in PCO2 and [HCO3-] at constant pH did not affect bone resorption within physiological limits.
- Complete removal of HCO3- substantially reduced bone degradation, confirming its necessity for acid secretion.
Conclusions:
- Osteoclastic bone resorption is coupled to proton and HCO3- transport.
- Bicarbonate concentration is not rate-limiting for bone resorption under physiological conditions.
- Extracellular pH affects osteoclastic bone resorption, but not dramatically, at physiological HCO3- levels.