Oxygen-glucose deprivation-induced enhancement of extracellular ATP-P2Y purinoceptors signaling for the propagation of astrocytic calcium waves

Waves of elevated intracellular free Ca2+ that propagate between neighboring astrocytes (Ca2+ waves) are important for the communication among astrocytes. We have previously revealed that focal photolysis of a caged calcium ionophore results in an increase in the concentration of intracellular Ca2+ in the target astrocytes, then the increase propagates to neighboring astrocytes through gap junctions. The extracellular ATP-purinoceptors signaling pathways are not primarily responsible for the propagation of the photolytic flash-induced Ca2+ waves. Here we examined whether and if so how the dynamics of Ca2+ waves changed after treatment with sublethal simulated ischemia; oxygen-glucose deprivation (OGD). OGD treatment increased the astrocytic expression of P2Y1 and P2Y2 receptors early during reperfusion, resulting in an increase in the propagating waves speed. In contrast, the expression of a gap junction protein was not changed significantly by the OGD suggesting that the extracellular ATP-P2Y receptors signaling pathways were preferentially enhanced after OGD. The present method to induce Ca2+ waves by focal photolysis of a caged calcium ionophore may provide a valuable tool with which to analyze glial Ca2+ waves under not only normal but also pathologic conditions.