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 Ca(2+) concentration (Ca(2+)) changes in cultured rat cortical type-1 astrocytes were analyzed using fura-2-based Ca(2+) imaging microscopy. Upon prolonged ATP challenge (1-100 microM), astroglial cells displayed a biphasic Ca(2+) 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 Ca(2+) signal without affecting the transient phase. Finally, astrocyte challenge with the selective P2X7 agonist 3'-O-(4-benzoyl)benzoyl-ATP evoked a sustained Ca(2+) elevation, which occluded that induced by ATP. We can conclude that in cultured cortical astrocytes the ATP-mediated sustained Ca(2+) rise does not implicate capacitative Ca(2+) entry but involves Ca(2+) influx through P2X7-like receptors.