ATP as a messenger in astrocyte-neuronal communication

Astrocytes are activated during both excitatory and inhibitory synaptic transmission and respond with intracellular Ca(2+)i elevations. Ca(2+)i oscillations and waves in astrocytes now appear to represent the glial arm of a dynamic neuronal-glial signaling process. Advances within the last year have shown that stimuli that elevate Ca(2+)i in astrocytes have the potential to modulate synaptic function. Recent studies have shown that astrocytic calcium waves, initially believed to depend on the integrity of functional gap junction channels for the passage of intercellular signals, are actually mediated by release of ATP and subsequent activation of purinergic receptors on neighboring cells. ATP release is in turn regulated by the expression of gap junction proteins, establishing a novel dimension between gap junctions and extracellular-mediated signaling events. The role of ATP and its breakdown product, adenosine, on synaptic transmission are discussed.