Loss of caveolar A1 adenosine receptor signalling blunts anti-adrenergic control in heart failure.

AIMS: Adenosine, acting through A1 adenosine receptors (A1ARs), exerts anti-adrenergic effects by inhibiting β1-adrenergic receptor (β1AR)-mediated cyclic adenosine monophosphate (cAMP) production and contractility in the heart. While the functional interaction between A1ARs and β1ARs is well established in both atrial and ventricular myocytes, the subcellular compartmentalization of this crosstalk and how it is disrupted in heart failure (HF) remains incompletely understood. This study investigates the spatial confinement of A1AR-β1AR signalling within atrial microdomains and assesses how structural remodelling in HF alters this regulatory axis.

METHODS AND RESULTS: Quantitative polymerase chain reaction (qPCR) analysis revealed that A1AR is the predominant adenosine receptor subtype in both rat and human atrial tissues. In healthy rat and mouse atrial myocytes, A1AR activation reduced β1AR-induced cAMP production and sarcomere shortening, with suppression of cAMP signals at sarcolemmal microdomains enriched in protein kinase A Type II. This was further supported by scanning ion conductance microscopy-guided scanning patch-clamp, which showed that A1AR suppressed β1AR-driven L-type Ca2+ channel activity at both T-tubule and crest membrane domains. In atrial myocytes isolated from failing rat and human hearts, A1AR-mediated inhibition of β1AR-induced cAMP production and contractility was impaired. Caveolar disruption by methyl-β-cyclodextrin in rat atrial myocytes or via cardiac-specific caveolin-3 (Cav3) knockout in mice abolished this A1AR-mediated inhibition. Notably, cholesterol repletion alone did not restore membrane cAMP regulation, whereas Cav3 overexpression rescued A1AR-dependent suppression, supporting a requirement for Cav3-dependent organization. In mouse atrial preparations isolated from failing hearts, high-resolution optical mapping showed that A1AR-mediated anti-adrenergic regulation of Ca2+ cycling was selectively lost in the intercaval region, correlating with the regional absence of T-tubule and downregulation of caveolae structures.

CONCLUSION: A1ARs provide anti-adrenergic restraint of β1AR signalling through Cav3-dependent membrane organization. In HF, regional caveolar disorganization uncouples this protective pathway, contributing to spatially heterogeneous Ca2+ dysregulation in the atrium.