Fluorescence Resonance Energy Transfer / Humans / cyclic AMP / Animals / FRET / PKA / Biological markers / Protein Conformation / In Vitro Studies / Signal to Noise Ratio / Conformational Change / Biosensing Techniques / Biochemistry and cell biology / Dynamic Range / PKA / Biological markers / Protein Conformation / In Vitro Studies / Signal to Noise Ratio / Conformational Change / Biosensing Techniques / Biochemistry and cell biology / Dynamic Range