Cellular calcium homeostasis and regulation of its dynamic perturbation

Calcium ions (Ca²⁺) play pivotal roles in a host of cellular signalling processes. The requirement to maintain resting cytosolic Ca²⁺ levels in the 100-200 nM range provides a baseline for dynamic excursions from resting levels that determine the nature of many physiological responses to external stimuli and developmental processes. This review provides an overview of the key components of the Ca²⁺ homeostatic machinery, including known channel-mediated Ca²⁺ entry pathways along with transporters that act to shape the cytosolic Ca²⁺ signature. The relative roles of the vacuole and endoplasmic reticulum as sources or sinks for cytosolic Ca²⁺ are considered, highlighting significant gaps in our understanding. The components contributing to mitochondrial, chloroplast and nuclear Ca²⁺ homeostasis and organellar Ca²⁺ signals are also considered. Taken together, a complex picture of the cellular Ca²⁺ homeostatic machinery emerges with some clear differences from mechanisms operating in many animal cells.