Calcium SignalingAbout This Hardback Calcium signaling is a step in signal transduction that makes use of calcium ions to communicate and drive intracellular processes. Calcium ions play an important role in cellular signaling because when they enter the cytosol of the cell, they exert allosteric effects on many enzymes and proteins. The resting concentration of calcium ions in the cytoplasm is 100 nM and this is much lower than the extracellular concentration.