Background
Chronic sympathetic stimulation drives desensitization and downregulation of β1 adrenergic receptor (β
1
AR) in heart failure. We aim to explore the differential downregulation subcellular pools of β
1
AR signaling in the heart.
Methods and Results
We applied chronic infusion of isoproterenol to induced cardiomyopathy in male C57BL/6J mice. We applied confocal and proximity ligation assay to examine β
1
AR association with L‐type calcium channel, ryanodine receptor 2, and SERCA2a ((Sarco)endoplasmic reticulum calcium ATPase 2a) and Förster resonance energy transfer‐based biosensors to probe subcellular β
1
AR‐PKA (protein kinase A) signaling in ventricular myocytes. Chronic infusion of isoproterenol led to reduced β
1
AR protein levels, receptor association with L‐type calcium channel and ryanodine receptor 2 measured by proximity ligation (puncta/cell, 29.65 saline versus 14.17 isoproterenol,
P
<0.05), and receptor‐induced PKA signaling at the plasma membrane (Förster resonance energy transfer, 28.9% saline versus 1.9% isoproterenol,
P
<0.05) and ryanodine receptor 2 complex (Förster resonance energy transfer, 30.2% saline versus 10.6% isoproterenol,
P
<0.05). However, the β
1
AR association with SERCA2a was enhanced (puncta/cell, 51.4 saline versus 87.5 isoproterenol,
P
<0.05), and the receptor signal was minimally affected. The isoproterenol‐infused hearts displayed decreased PDE4D (phosphodiesterase 4D) and PDE3A and increased PDE2A, PDE4A, and PDE4B protein levels. We observed a reduced role of PDE4 and enhanced roles of PDE2 and PDE3 on the β
1
AR‐PKA activity at the ryanodine receptor 2 complexes and myocyte shortening. Despite the enhanced β
1
AR association with SERCA2a, the endogenous norepinephrine‐induced signaling was reduced at the SERCA2a complexes. Inhibiting monoamine oxidase A rescued the norepinephrine‐induced PKA signaling at the SERCA2a and myocyte shortening.
Conclusions
This study reveals distinct mechanisms for the downregulation of subcellular β
1
AR signaling in the heart under chronic adrenergic stimulation.