Endoplasmic reticulum-mitochondria coupling: Local Ca 2+ signalling with functional consequences

Plasma membrane store-operated Ca 2+ release-activated Ca 2+ (CRAC) channels are a widespread and conserved Ca 2+ influx pathway, driving activation of a range of spatially and temporally distinct cellular responses. Although CRAC channels are activated by the loss of Ca 2+ from the endoplasmic reticulum, their gating is regulated by mitochondria. Through their ability to buffer cytoplasmic Ca 2+, mitochondria take up Ca 2+ released from the endoplasmic reticulum by InsP 3 receptors, leading to more extensive store depletion and stronger activation of CRAC channels. Mitochondria also buffer Ca 2+ that enters through CRAC channels, reducing Ca 2+-dependent slow inactivation of the channels. In addition, depolarised mitochondria impair movement of the CRAC channel activating protein STIM1 across the endoplasmic reticulum membrane. Because they regulate CRAC channel activity, particularly Ca 2+-dependent slow inactivation, mitochondria influence CRAC channel-driven enzyme activation, secretion and gene expression. Mitochondrial regulation of CRAC channels therefore provides an important control element to the regulation of intracellular Ca 2+ signalling. © 2012 Springer-Verlag.