A GRAB sensor reveals activity-dependent non-vesicular somatodendritic adenosine release

The purinergic signaling molecule adenosine (Ado) modulates many physiological and pathological brain functions but its spatiotemporal release dynamics in the brain remains largely unknown. We developed a genetically encoded GPCR-Activation-Based Ado sensor (GRABAdo) in which Ado-induced changes in the human A2A receptor are reflected by fluorescence increases. This GRABAdo revealed that neuronal activity-induced extracellular Ado elevation was due to direct Ado release from somatodendritic regions of the neuron, requiring calcium influx through L-type calcium channels, rather than the degradation of extracellular ATP. The Ado release was slow (~30 s) and depended on equilibrative nucleoside transporters (ENTs) rather than conventional vesicular release mechanisms. Thus, GRABAdo reveals an activity-dependent slow Ado release from somatodendritic region of the neuron, potentially serving modulating functions as a retrograde signal.