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Updated: Jun 23, 2026
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Mitochondrial Ca2+ Retention Capacity Assay and Ca2+-triggered Mitochondrial Swelling Assay
Published on: May 1, 2018
Store-operated Ca2+ influx and subplasmalemmal mitochondria
Marek K Korzeniowski1, Gergö Szanda, Tamas Balla
1Section on Molecular Signal Transduction, Program on Developmental Neuroscience, NICHD, NIH, Bethesda, MD, USA.
Cell Calcium
|May 12, 2009
Summary
Subplasmalemmal mitochondria are not directly within high-calcium microdomains formed during store-operated calcium influx (SOC). Mitochondria sense calcium diffused from these domains, influencing cellular calcium regulation.
Area of Science:
- Cellular Biology
- Calcium Signaling
Background:
- Calcium depletion of the endoplasmic reticulum (ER) triggers STIM proteins to activate Orai channels in the plasma membrane, initiating store-operated calcium influx (SOC).
- Subplasmalemmal mitochondria can mitigate the negative feedback of calcium on SOC by sequestering calcium ions.
Purpose of the Study:
- To investigate the spatial relationship between subplasmalemmal mitochondria and high-calcium microdomains (HCMDs) formed during SOC.
- To determine if mitochondria are positioned to directly sense the elevated calcium within these HCMDs.
Main Methods:
- COS-7 cells were co-transfected with Orai1, STIM1 (fluorescently tagged), and a mitochondrially targeted calcium sensor.
- Total internal reflection fluorescence (TIRF) microscopy was used to visualize STIM1 puncta and mitochondrial localization.
- ER calcium was depleted using ATP and thapsigargin in a calcium-free medium, followed by calcium addition.
Main Results:
- STIM1 puncta formed within 100 nm of the plasma membrane upon ER calcium depletion.
- Mitochondria were observed in gaps between STIM1 puncta or in STIM1-free regions, indicating they were not consistently within the HCMDs.
- Mitochondrial calcium levels increased upon calcium addition, regardless of proximity to STIM1 puncta.
Conclusions:
- Subplasmalemmal mitochondria are not typically located within the immediate high-calcium microdomains adjacent to Orai channels.
- Mitochondria are exposed to calcium that diffuses laterally from these microdomains, suggesting an indirect role in regulating SOC feedback.
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