Interactions between sarco-endoplasmic reticulum and mitochondria in cardiac and skeletal muscle - pivotal roles in Ca²⁺ and reactive oxygen species signaling.

Mitochondria are strategically and dynamically positioned in the cell to spatially coordinate ATP production with energy needs and to allow the local exchange of material with other organelles. Interactions of mitochondria with the sarco-endoplasmic reticulum (SR/ER) have been receiving much attention owing to emerging evidence on the role these sites have in cell signaling, dynamics and biosynthetic pathways. One of the most important physiological and pathophysiological paradigms for SR/ER-mitochondria interactions is in cardiac and skeletal muscle. The contractile activity of these tissues has to be matched by mitochondrial ATP generation that is achieved, at least in part, by propagation of Ca(2+) signals from SR to mitochondria. However, the muscle has a highly ordered structure, providing only limited opportunity for mitochondrial dynamics and interorganellar interactions. This Commentary focuses on the latest advances in the structure, function and disease relevance of the communication between SR/ER and mitochondria in muscle. In particular, we discuss the recent demonstration of SR/ER-mitochondria tethers that are formed by multiple proteins, and local Ca(2+) transfer between SR/ER and mitochondria.