Before revision: Ca^{2+} signaling is crucial for feedback of a URLanism to external stimulation. In intracellular space, Ca^{2+ the signal may become a global signal fast, and die away in the propagation.
After revision: Ca^{2+} plays important role in cell signal transduction. Its intracellular propagation is the most basic process of Ca^{2+ the signal may become a global signal fast, and die away in the propagation.