Different beta-adrenoceptor-effector coupling in human ventricular and atrial myocardium

Area of Science:

• Cardiology
• Molecular Cardiology
• Physiology

Background:

• Beta-adrenoceptor downregulation is a hallmark of heart failure.
• The functional consequences of beta-adrenoceptor changes in different heart chambers are not fully understood.

Purpose of the Study:

• To investigate the relationship between beta-adrenoceptor levels and their mediated effects in atrial and ventricular myocardium.
• To compare these effects in varying degrees of heart failure.

Main Methods:

• Isometric force of contraction measurements in atrial and papillary muscle strips.
• Radioligand binding assays to quantify beta-adrenoceptor density.
• Comparison of tissue from non-failing hearts and patients with moderate (NYHA II-III) and severe (NYHA IV) heart failure.

Main Results:

• Atrial muscle: Beta-adrenoceptor number decreased with heart failure severity, but isoprenaline's effect on contraction force (potency and efficacy) remained unchanged.
• Papillary muscle: Both isoprenaline-mediated contraction force and beta-adrenoceptor density progressively decreased with increasing heart failure severity.
• These findings indicate differential regulation and functional impact of beta-adrenoceptors in atrial versus ventricular tissues during heart failure.

Conclusions:

• Ventricular beta-adrenoceptor-mediated function is significantly impaired in heart failure, correlating with receptor downregulation.
• Atrial beta-adrenoceptor-mediated function is preserved despite receptor downregulation, suggesting compensatory mechanisms.
• These chamber-specific adaptations highlight the complexity of beta-adrenergic signaling in the failing heart.