ATP-induced, sustained calcium signalling in cultured rat cortical astrocytes: evidence for a non-capacitative, P2X7-like-mediated calcium entry

The receptor mechanisms regulating the ATP-induced free cytosolic Ca2+ concentration ([Ca2+](i)) changes in cultured rat cortical type-1 astrocytes were analyzed using fura-2-based Ca2+ imaging microscopy. Upon prolonged ATP challenge (1-100 muM), astroglial cells displayed a biphasic [Ca2+](i) response consisting of an initial peak followed by a sustained elevation. Suramin and pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid blocked both components, albeit to a different extent. By contrast, the selective P2X7 antagonist oxidized ATP irreversibly abrogated the sustained [Ca2+](i) signal without affecting the transient phase. Finally, astrocyte challenge with the selective P2X7 agonist 3'-O-(4-benzoyl)benzoyl-ATP evoked a sustained [Ca2+](i) elevation, which occluded that induced by ATP. We can conclude that in cultured cortical astrocytes the ATP-mediated sustained [Ca2+](i) rise does not implicate capacitative Ca2+ entry but involves Ca2+ influx through P2X7-like receptors. (C) 2003 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.