Figure 8. Effect of β‐adrenergic receptor (β‐AR) stimulation on repolarization, protein expression, and protein phosphorylation .

A, AP signals illustrate that the difference between APD_baseline − APD_{β‐stimulation} is ΔAPD. B, statistical analysis of ΔAPD shows desensitization of β₁‐AR at the sub‐EPI, MID, and sub‐ENDO. C, statistical analysis of ΔAPD shows sensitization of β₂‐AR at the sub‐EPI and MID but not at the sub‐ENDO. B and C, negative values indicate a reduction in APD. D, Western blot reveals a reversal of the sub‐EPI to sub‐ENDO gradient of β₂‐AR protein expression (β₂‐AR‐epi/β₂‐AR‐endo) in HF. E, phosphorylation of β₂‐AR is reduced in HF. D, donor hearts; F, failing hearts. Adapted from Lang et al. (2015).