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Analysis of Minerals Produced by hFOB 1.19 and Saos-2 Cells Using Transmission Electron Microscopy with Energy Dispersive X-ray Microanalysis
Published on: June 24, 2018
High capacity Na+/H+ exchange activity in mineralizing osteoblasts
Li Liu1, Paul H Schlesinger, Nicole M Slack
1Department of Pathology and Physiology, Pittsburgh Veteran's Affairs Medical Center, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA.
Journal of Cellular Physiology
|March 18, 2011
Summary
Osteoblasts manage acid buildup during bone formation using sodium-hydrogen exchangers (NHE1 and NHE6). These transporters maintain intracellular pH and dissipate external acid loads, crucial for bone mineralization.
Area of Science:
- Cell Biology
- Biochemistry
- Physiology
Background:
- Osteoblasts synthesize bone matrix, a process involving significant acid production.
- Maintaining intracellular pH is critical for osteoblast function and bone mineralization.
- The mechanisms by which osteoblasts handle acid loads are not fully understood.
Purpose of the Study:
- To investigate the mechanisms osteoblasts use to manage acid loads during bone mineralization.
- To identify the specific transporters involved in regulating intracellular pH in osteoblasts.
- To elucidate the roles of sodium-hydrogen exchangers (NHEs) and chloride-bicarbonate exchangers in osteoblast physiology.
Main Methods:
- Measurement of intracellular pH (pHi) in osteoblasts under various loading conditions (weak acid, bicarbonate, Na+-free solutions).
- Assessment of transporter activity using pharmacological inhibitors (amiloride) and ion substitutions.
- Analysis of transporter expression (NHE1, NHE6, AE2) via Western blotting and immunohistochemistry.
- Functional validation using gene manipulation (overexpression, knockdown) in osteosarcoma cells.
Main Results:
- Osteoblasts maintain a basal pHi of ~7.3, with significant acidification in Na+-free conditions.
- Na+-dependent pHi recovery from acid load indicates active sodium-hydrogen exchanger (NHE) activity.
- NHE1 and NHE6 are strongly expressed and upregulated during mineralization, localized to basolateral surfaces.
- Na+-independent Cl-/HCO3- exchange activity, mediated by AE2, was observed for eliminating metabolic carbonate.
Conclusions:
- Mineralizing osteoblasts utilize high-capacity Na+/H+ exchange via NHE1 and NHE6 to maintain a slightly basic pHi.
- These NHEs are crucial for dissipating external acid loads generated during bone formation.
- AE2 contributes to pH regulation through Cl-/HCO3- exchange, facilitating the removal of metabolic byproducts.
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