P2X-GCaMPs as versatile tools for imaging extracellular ATP signaling

Abstract

Adenosine 5’ triphosphate (ATP) is an extracellular signaling molecule involved in numerous physiological and pathological processes. Yet, in situ characterization of the spatiotemporal dynamic of extracellular ATP is still challenging due to the lack of sensor with appropriate specificity, sensitivity and kinetics. Here we report the development of biosensors based on the fusion of cation permeable ATP receptors (P2X) to genetically encoded calcium sensors (GECI). By combining the features of P2X receptors with the high signal to noise ratio of GECIs, we generated ultrasensitive green and red fluorescent sniffers that detect nanomolar ATP concentrations in situ and also enable the tracking of P2X receptor activity. We provide the proof of concept that these sensors can dynamically track ATP release evoked by depolarization in mouse neurons or by extracellular hypotonicity. Targeting these P2X-based biosensors to diverse cell types should advance our knowledge of extracellular ATP dynamics in vivo.

Significance statement Purinergic signaling plays an important role in regulating neuro-glial communications and, as a consequence, in the modulation of network activities. Current ATP biosensors lack appropriate sensitivity and kinetics to precisely decipher the spatiotemporal dynamic of extracellular ATP in situ. We developed a series of ATP biosensors based on the fusion of calcium-permeant P2X receptors to the calcium indicator GCaMP6s. These sensors display fast kinetics and sensitivity allowing to dynamically detect sub-micromolar ATP concentration. We provide direct evidence that these sensors can dynamically detect ATP release evoked by KCl depolarization in neurons, or by osmotic-evoked cell swelling. These sensors can also be adapted in red-shifted versions, offering a toolbox to assess purinergic signaling in situ.