The 52nd Annual Meeting and Symposium of the Society of General Physiologists : Local Calcium Signaling in Cell Physiology

Several features, taken together, make Ca²⁺ stand out among the physiologically important cations: first, the concentration of “free” Ca²⁺ ([Ca²⁺]) in the cytoplasm is only ∼100 nM; second, Ca²⁺ binds with high affinity (dissociation constants from ∼100 nM to ∼10 μM) to many intracellular proteins that activate/control a wide variety of biochemical/cell physiological events; and third, the extracellular [Ca²⁺] is four orders of magnitude larger than the cytoplasmic [Ca²⁺] with similar concentration ratios for organellar vs. cytoplasmic [Ca²⁺], which means that transient increases in the plasma or organelle membrane permeability to Ca²⁺ may produce large relative changes in cytoplasmic [Ca²⁺]. The spatial and temporal evolution of these [Ca²⁺] transients is determined by the magnitude and time course of Ca²⁺ release, Ca²⁺ influx, and the kinetics of Ca²⁺ buffering by diffusible...