Compartmentalized signalling: Ca²⁺ compartments, microdomains and the many facets of Ca²⁺ signalling

Ca²⁺ regulates a multitude of cellular processes and does so by partitioning its actions in space and time. In this review, we discuss how Ca²⁺ responses are constructed from small quantal (elementary) events that have the potential to propagate to produce large pan-cellular responses. We review how Ca²⁺ is compartmentalized both physically and functionally, and describe how each organelle has its own distinct Ca²⁺-handling properties. We explain how coordination of the movement of Ca²⁺ between organelles is used to shape and hone Ca²⁺ signals. Finally, we provide a number of specific examples of where compartmentation and localization of Ca²⁺ are crucial to cell function.