Figure 3. Speculative model for SOC_CIF activation after calcium leak via the translocon. This activation occurs after passive ER depletion facilitated by thapsigargin or EGTA. On such depletion, CIF could be released from the ER and could stimulate membrane-bound Ca²⁺-independent phospholipase A₂ (iPLA₂), which in turn activates SOC_CIF after production of lysophospholipids. In contrast, IP₃R stimulation would directly activate SOC_CC (IP₃ROC) via protein–protein interaction. This latter pathway seems to be independent of Ca²⁺ leakage that occurs through the translocon. (ERM: ER membrane; PM: plasma membrane).