ADRB2 and hydrops fetalis: Typical traces of FRET ratios recorded following local β2AR stimulation on the T-tubules or on the crests are presented in Figure 5A. As we reported previously in,13 we observed that in control cardiomyocytes, the β2AR-dependent cAMP response is five-fold greater in the T-tubule openings than at the crests (Figure 5A,B,C), whereas in cardiomyocytes isolated from rat hearts at end stage HF (16-week post-MI), the β2AR-cAMP response was found to be equally present in T-tubules and in the crests (Figure 5A,B,C).