The 52nd Annual Meeting and Symposium of the Society of General Physiologists

Several features, taken together, make Ca 2 1 stand out among the physiologically important cations: first, the concentration of “free” Ca 2 1 ([Ca 2 1 ]) in the cytoplasm is only z 100 nM; second, Ca 2 1 binds with high affinity (dissociation constants from z 100 nM to z 10 m M) to many intracellular proteins that activate/control a wide variety of biochemical/cell physiological events; and third, the extracellular [Ca 2 1 ] is four orders of magnitude larger than the cytoplasmic [Ca 2 1 ] with similar concentration ratios for organellar vs. cytoplasmic [Ca 2 1 ], which means that transient increases in the plasma or organelle membrane permeability to Ca 2 1 may produce large relative changes in cytoplasmic [Ca 2 1 ]. The spatial and temporal evolution of these [Ca 2 1 ] transients is determined by the magnitude and time course of Ca 2 1 release, Ca 2 1 influx, and the kinetics of Ca 2 1