Calcium signalling in astroglia

Astroglia possess excitability based on movements of Ca2+ ions between intracellular compartments and plasmalemmal Ca2+ fluxes. This Ca2+ excitability is controlled by several families of proteins located in the plasma membrane, within the cytosol and in the intracellular organelles, most notably in the endoplasmic reticulum (ER) and mitochondria. Accumulation of cytosolic Ca2+ can be caused by the entry of Ca2+ from the extracellular space through ionotropic receptors and store-operated channels expressed in astrocytes. Plasmalemmal Ca2+ ATP-ase and sodium-calcium exchanger extrude cytosolic Ca2+ to the extracellular space; the exchanger can also operate in reverse, depending of the intercellular Na+ concentration, to deliver Ca2+ to the cytosol. The ER internal store possesses inositol 1,4,5-trisphosphate receptors which can be activated upon stimulation of astrocytes through a multiple plasma membrane metabotropic G-protein coupled receptors. This leads to release of Ca2+ from the ER and its elevation in the cytosol, the level of which can be modulated by mitochondria. The mitochondrial uniporter takes up Ca2+ into the matrix, while free Ca2+ exits the matrix through the mitochondrial Na+/Ca2+ exchanger as well as via transient openings of the mitochondrial permeability transition pore. One of the prominent consequences of astroglial Ca2+ excitability is gliotransmission, a release of transmitters from astroglia which can lead to signalling to adjacent neurones. (C) 2011 Elsevier Ireland Ltd. All rights reserved.