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Updated: Apr 20, 2026
Fluorescence-based Measurement of Store-operated Calcium Entry in Live Cells: from Cultured Cancer Cell to Skeletal Muscle Fiber
Published on: February 13, 2012
Sodium entry through endothelial store-operated calcium entry channels: regulation by Orai1
Ningyong Xu1, Donna L Cioffi2, Mikhail Alexeyev3
1Department of Pharmacology, University of South Alabama, Mobile, Alabama; Center for Lung Biology, University of South Alabama, Mobile, Alabama.
Abstract:
Orai1 interacts with transient receptor potential protein of the canonical subfamily (TRPC4) and contributes to calcium selectivity of the endothelial cell store-operated calcium entry current (ISOC). Orai1 silencing increases sodium permeability and decreases membrane-associated calcium, although it is not known whether Orai1 is an important determinant of cytosolic sodium transitions. We test the hypothesis that, upon activation of store-operated calcium entry channels, Orai1 is a critical determinant of cytosolic sodium transitions. Activation of store-operated calcium entry channels transiently increased cytosolic calcium and sodium, characteristic of release from an intracellular store. The sodium response occurred more abruptly and returned to baseline more rapidly than did the transient calcium rise. Extracellular choline substitution for sodium did not inhibit the response, although 2-aminoethoxydiphenyl borate and YM-58483 reduced it by ∼50%. After this transient response, cytosolic sodium continued to increase due to influx through activated store-operated calcium entry channels. The magnitude of this sustained increase in cytosolic sodium was greater when experiments were conducted in low extracellular calcium and when Orai1 expression was silenced; these two interventions were not additive, suggesting a common mechanism. 2-Aminoethoxydiphenyl borate and YM-58483 inhibited the sustained increase in cytosolic sodium, only in the presence of Orai1. These studies demonstrate that sodium permeates activated store-operated calcium entry channels, resulting in an increase in cytosolic sodium; the magnitude of this response is determined by Orai1.
Insights
Orai1 channels regulate cytosolic sodium levels by controlling influx through store-operated calcium entry (SOCE) channels. Orai1 expression significantly impacts the magnitude of sodium increase during SOCE.
Area of Science:
- Cell Biology
- Ion Channel Physiology
- Molecular Medicine
Background:
- Orai1 and TRPC4 proteins influence calcium selectivity in endothelial cells.
- Orai1 silencing affects sodium permeability and membrane calcium levels.
- The role of Orai1 in cytosolic sodium dynamics during store-operated calcium entry (SOCE) remains unclear.
Purpose of the Study:
- To investigate whether Orai1 is a critical determinant of cytosolic sodium transitions upon activation of SOCE channels.
- To elucidate the mechanism by which Orai1 influences sodium influx during SOCE.
Main Methods:
- Activation of store-operated calcium entry (SOCE) channels.
- Measurement of cytosolic calcium and sodium levels.
- Manipulation of extracellular sodium concentration using choline substitution.
- Inhibition of SOCE using 2-aminoethoxydiphenyl borate and YM-58483.
- Orai1 gene silencing.
Main Results:
- SOCE activation caused transient increases in both cytosolic calcium and sodium.
- The sodium response was faster and shorter than the calcium response.
- Extracellular choline substitution did not inhibit the transient sodium response.
- 2-aminoethoxydiphenyl borate and YM-58483 reduced the transient response by approximately 50%.
- A sustained increase in cytosolic sodium occurred due to influx through activated SOCE channels.
- This sustained sodium increase was amplified in low extracellular calcium and upon Orai1 silencing, suggesting a common regulatory pathway.
- Inhibitors of SOCE blocked the sustained sodium increase only when Orai1 was present.
Conclusions:
- Sodium ions permeate activated store-operated calcium entry channels.
- Orai1 plays a crucial role in determining the magnitude of cytosolic sodium increase during SOCE.
- These findings highlight Orai1's function beyond calcium regulation, extending to sodium homeostasis during SOCE.
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