Figure 1.

Overview of ER Ca²⁺ handling. Schematic presentation of Ca²⁺ concentrations in the endoplasmic reticulum (ER, 0.6 mM) compared to the cytosol (CYT, 100 nM) and extracellular milieu (ECM, 1 mM). (A) Ca²⁺ flows down its electrochemical gradient from the ECM to CYT (through Orai) or (B) against its electrochemical gradient from the CYT to the ER (through SERCA). (C) Ca²⁺ flows from the ER to the CYT down its electrochemical gradient, either following the activation of IP₃R & RyR, or through ER Ca²⁺-leak channels TMBIM6 & TMCO1.