ATP stimulates both metabotropic receptors and entry of extracellular Ca²⁺ in striatal astrocytes.

<p>(a,b) Ca²⁺ transients were determined in astrocytes by real-time fluorescence imaging following stimulation with 1 µM ATP in the presence of the phospholipase C inhibitor, U73122 (10 µM), its inactive analog, U73343 (10 µM), or vehicle control (DMSO). Black arrows denote the time of addition of 1 µM ATP. (c–d) Removal of extracellular Ca²⁺ inhibited both the peak amplitude and sustained phase of the Ca²⁺ transient. The vertical bar (a,c) denotes 1 relative fluorescent unit; the horizontal bar denotes 10 sec. n = 500–700 cells analyzed per experiment over 2–3 independent experiments in separate cultures of striatal astrocytes; *<i>p</i><0.05 relative to control, ** <i>p</i><0.01 relative to control and treated groups.