Signaling ER Store Depletion to Plasma Membrane Orai Channels

Excerpt

Cells maintain an inward Ca²⁺ gradient from the extracellular fluid to the cytosol, entrenched by the action of plasma membrane pumps/transporters that actively “pump out” Ca²⁺ and organellar pumps/transporters that mold the Ca²⁺ transients by storing it away in intracellular reservoirs [1,2]. External stimuli trigger Ca²⁺ influx driven by the electrochemical gradient between a plenteous extracellular reservoir of Ca²⁺ (millimolar ranges) and a Ca²⁺-free cytosol. This Ca²⁺ surge is indispensible for its role as a second messenger, controlling a wide range of cellular functions like exocytosis, mast cell degranulation, and immune cell proliferation.