Regulation of mitochondrial metabolism by ER Ca2+ release: an intimate connection

New live-cell imaging techniques indicate that mitochondria exist in the li ving cell as a continuous interconnected mitochondrial reticulum, or 'MR', closely associated with the endoplasmic reticulum (ER). Ca2+ ions released from the ER in response to hormonal stimulation might thus be preferentiall y transferred into the mitochondrial matrix causing the local activation of ATP synthesis. Ca2+ uptake into the MR might also subtly modify the activi ty of ER Ca2+ release channels and thus the dynamics of cytosolic Ca2+ osci llations and waves.