Astrocytes can exocytotically release the gliotransmitter glutamate. Increased cytosolic Ca²⁺ concentration is necessary and sufficient in this process. The source of Ca²⁺ for the Ca²⁺-dependent exocytotic release of glutamate from astrocytes predominately comes from endoplasmic reticulum (ER) stores; both inositol trisphoshphate (IP3)- and ryanodine-sensitive receptors are involved. An additional source of Ca²⁺ in this process comes from the extracellular space; canonical transient receptor potential 1 protein, which forms channels that are activated by depletion of internal Ca²⁺ stores, allows Ca²⁺ entry from the extracellular space. Mitochondria can modulate cytosolic Ca²⁺ levels by affecting two aspects of the cytosolic Ca²⁺ kinetics in astrocytes. They play a role in immediate sequestration of Ca²⁺ during the cytosolic Ca²⁺ increase in stimulated astrocytes. As cytosolic Ca²⁺declines due to activity of pumps, such as the smooth ER Ca²⁺-ATPase, free Ca²⁺ is slowly released by mitochondria into cytosol. Furthermore, immunophilins, mitochondrial cyclophilin D and FK506-binding protein 12 of there ER, affect cytosolic Ca²⁺ dynamics and consequential exocytotic glutamate release from astrocytes. Taken together, ER, extracellular space and mitochondria, can vary concentration of cytosolic Ca²⁺ which in turn can regulate Ca²⁺- dependent vesicular glutamate release from astrocytes.