Figure 1.

Schematic representation of Ca²⁺ mobilization in the ER. Upon activation of the cell surface GPCRs, PLC action results in the formation of InsP3. The binding of InsP3 to the InsP3 receptor triggers Ca²⁺ release from the ER to the cytoplasm. Following Ca²⁺ release, the dissociation of Ca²⁺ from the STIM proteins leads to STIM oligomerization and interaction with the plasma membrane Ca²⁺ channel Orai, allowing Ca²⁺ to enter the cell from the extracellular space. Conversely, cytoplasmic Ca²⁺ is withdrawn to the ER via SERCA activity. Abbreviations: GPCR, G-protein-coupled receptor; PLC, phospholipase C; InsP3, inositol-1,4,5-trisphosphate; STIM, stromal interaction molecules; SERCA, sarco/endoplasmic reticulum calcium ATPase.