Figure 2.

Propagating intercellular Ca²⁺ waves are unlikely to occur between astrocytes in acute hippocampal slices from healthy brain. Astrocytes in stratum radiatum of hippocampal slices from MrgA1 G_q GPCR transgenic mice were bulk-loaded with Ca²⁺ Green 1-AM indicator dye as described previously (Fiacco et al., 2007; left panel). Boxed regions of interest over individual astrocyte somata match numbered Ca²⁺ traces (right panel). Stimulation with either 10 μM FMRF or 50 μM DHPG evoked Ca²⁺ elevations in 56/75 (75%) or 67/75 (89%) of astrocytes, respectively, through activation of MrgA1Rs or group I mGluRs (n = 9 slices). In total, 50/75 (67%) of astrocytes responded to both agonists. However, 24/75 (32%) of astrocytes responded to one, but not the other, agonist. These results suggest that despite strong Ca²⁺ elevations in many astrocytes, the gliotransmitter ATP is not released in sufficient quantity to stimulate purinergic P2Y G_q GPCRs on adjacent astrocytes.