Calcium oscillations and waves in cells.

From beginning of the life to final moment of the life, Ca(2+) functions as an important signaling messenger. The intracellular Ca(2+) concentration, [Ca(2+)](i), in resting cells is normally maintained at around 100 nM with a very steep ∼20,000 times concentration gradient of Ca(2+) between extracellular and intracellular compartments. Ca(2+) signals in the form of time-dependent changes in [Ca(2+)](i) appear as brief spikes that are organized into regenerative Ca(2+) waves. The release of Ca(2+) from internal stores plays a key role in regulating such Ca(2+) signals. Since global Ca(2+) oscillations arise from Ca(2+) waves initiated locally, it results in generation of stochastic Ca(2+) oscillations. In addition, the hierarchical organization of signaling structures translate the molecular fluctuations of single channels to the whole cell leading to formation of stochastic media. Several recent observations indicate that [Ca(2+)](i) changes are fluctuation driven as opposed to a typical deterministic intracellular reaction-diffusion system model. Elucidation of this signaling mechanism can provide detailed knowledge of relationship between cell signaling and cell physiology of living systems.