Cardiac-Restricted Overexpression of the A2A-Adenosine Receptor in FVB Mice Transiently Increases Contractile Performance and Rescues the Heart Failure Phenotype in Mice Overexpressing the A1-Adenosine Receptor

In the heart, adenosine binds to pharmacologically distinct G-protein-coupled receptors (A(1)-R, A(2A)-R, and A(3)-R). While the role of A(1)- and A(3)-Rs in the heart has been clarified, the effect of genetically manipulating the A(2A)-R has not been defined. Thus, we created mice overexpressing a cardiac-restricted A(2A)-R transgene. Mice with both low (Lo) and high (Hi) levels of A(2A)-R overexpression demonstrated an increase in cardiac contractility at 12 weeks. These changes were associated with a significantly higher systolic but not diastolic [Ca2+](i), higher maximal contraction amplitudes, and a significantly enhanced sarcoplasmic reticulum Ca2+ uptake activity. At 20 weeks, the effects of A(2A)-R overexpression on cardiac contractility diminished. The positive effects elicited by A(2A)-R overexpression differ from the heart failure phenotype we observed with A(1)-R overexpresson. Interestingly, coexpression of A(2A)-R TG(Hi), but not A(2A)-R TGLo, enhanced survival, prevented the development of left ventricular dysfunction and heart failure, and improved Ca2+ handling in mice overexpressing the A(1)-R. These results suggest that adenosine-mediated signaling in the heart requires a balance between A(1)- and A(2A)-Rs-a finding that may have important implications for the ongoing clinical evaluation of adenosine receptor subtype-specific agonists and antagonists for the treatment of cardiovascular diseases.