Endoplasmic reticulum calcium signaling in nerve cells.

The endoplasmic reticulum (ER) is an important organelle involved in various types of signaling in nerve cells. The ER serves as a dynamic Ca2+ pool being thus involved in rapid signaling events associated with cell stimulation by either electrical (action potential) or chemical (neurotransmitters) signals. This function is supported by Ca2+ release channels (InsP3 and ryanodine receptors) and SERCA Ca2+ pumps residing in the endomembrane. In addition the ER provides a specific environment for the posttranslational protein processing and transport of various molecules towards their final destination. In parallel, the ER acts as a "calcium tunnel," which facilitates Ca2+ movements within the cell by avoiding cytoplasmic routes. Finally the ER appears as a source of numerous signals aimed at the nucleus and involved in long-lasting adaptive cellular responses. All these important functions are controlled by intra-ER free Ca2+ which integrates various signaling events and establishes a link between fast signaling, associated with ER Ca2+ release/uptake, and long-lasting adaptive responses relying primarily on the regulation of protein synthesis. Disruption of ER Ca2+ homeostasis triggers several forms of cellular stress response and is intimately involved in neurodegeneration and neuronal cell death.