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Intracellular calcium puffs in osteoclasts
W Radding1, S E Jordan, R B Hester
1Keck Center for Computational Biology, Rice University, Houston, Texas, USA.
Experimental Cell Research
|December 10, 1999
Summary
Calcium puffs, localized intracellular calcium ([Ca(2+)](i)) transients, are increased in acid-secreting osteoclasts and occur near the acid-transporting membrane, suggesting an indirect role in maintaining bone resorption.
Area of Science:
- Cell Biology
- Biochemistry
- Physiology
Background:
- Osteoclasts are crucial for bone remodeling, involving acid secretion to resorb bone mineral.
- Intracellular calcium ([Ca(2+)](i)) dynamics are vital for cellular functions, including signaling and transport.
- Understanding calcium regulation in osteoclasts is key to deciphering bone resorption mechanisms.
Purpose of the Study:
- To investigate the characteristics and localization of intracellular calcium ([Ca(2+)](i)) transients in acid-secreting osteoclasts.
- To determine the relationship between calcium puffs and acid secretion activity in osteoclasts.
- To explore the potential role of calcium puffs in regulating osteoclast function.
Main Methods:
- Utilized H(+)-restricted dyes, fura-2, and fluo-3 for real-time monitoring of [Ca(2+)](i).
- Employed confocal microscopy and spot measurements to analyze calcium transient kinetics and spatial distribution.
- Used lysotracker red DND99 to identify acid-secreting regions of osteoclasts.
- Applied pharmacological agents to probe the involvement of calcium signaling pathways and transport mechanisms.
Main Results:
- Acid-secreting osteoclasts exhibit localized [Ca(2+)](i) transients (calcium puffs) to 500-1000 nM, distinct from whole-cell levels (~100 nM).
- Calcium puffs predominantly occurred over acid-secreting regions and at irregular intervals (5-15 s) in these cells.
- Puff activity was largely unaffected by inhibitors of calmodulin, calcium transport, or endoplasmic reticulum ATPase, suggesting an independent mechanism.
- Calcium puffs were rare in non-acid-secreting osteoclasts.
Conclusions:
- [Ca(2+)](i) transients, or calcium puffs, are significantly increased in acid-secreting osteoclasts.
- These calcium puffs are spatially associated with the acid-transporting membrane.
- While cell membrane acid transport requires calcium, the H(+)-ATPase activity was insensitive to the observed calcium levels, indicating an indirect role for calcium puffs in regulating acid secretion.