A red fluorescent sensor for intensity-and lifetime imaging of cAMP in living cells

cAMP (cyclic adenosine monophosphate) is a crucial intracellular messenger involved in neuromodulation and plasticity, but more information on its spatiotemporal regulation is desirable. Here we constructed a red fluorescent indicator based on a truncated cAMP binding site derived from a regulatory PKA subunit of protozoan origin. It contains a single binding site for cAMP highly specific for cAMP over cGMP. chILI (cAMP highly-responsive Intensity and Lifetime Indicator) can be imaged as an intensity-based probe, but alternatively also offers options for fluorescence lifetime imaging. When expressed in the mouse brain using AAV-vector mediated gene transfer, it reports spontaneous and evoked cAMP transients from CA1 neurons in the hippocampus of awake mice. chILI will add valuable options for monitoring cAMP in vitro and in vivo.