In situ detection of kinase activity with genetically encoded FRET reporter CKAR. (a) A schematic diagram of the CKAR activity reporter. (b) Live cell image of a mouse cardiomyocyte expressing the CKAR reporter . AKAP79 targets the associated CKAR in proximity to the KCNQ2 subunit of the M current. CKAR permits rapid and transient FRET changes in response to changes in intracellular Ca2+.