Phosphodiesterase Type 3A Regulates Basal Myocardial Contractility Through Interacting With Sarcoplasmic Reticulum Calcium ATPase Type 2a Signaling Complexes in Mouse Heart

Rationale: cAMP is an important regulator of myocardial function, and regulation of cAMP hydrolysis by cyclic nucleotide phosphodiesterases (PDEs) is a critical determinant of the amplitude, duration, and compartmentation of cAMP-mediated signaling. The role of different PDE isozymes, particularly PDE3A vs PDE3B, in the regulation of heart function remains unclear. Objective: To determine the relative contribution of PDE3A vs PDE3B isozymes in the regulation of heart function and to dissect the molecular basis for this regulation. Methods and Results: Compared with wild-type littermates, cardiac contractility and relaxation were enhanced in isolated hearts from PDE3A −/− , but not PDE3B −/− , mice. Furthermore, PDE3 inhibition had no effect on PDE3A −/− hearts but increased contractility in wild-type (as expected) and PDE3B −/− hearts to levels indistinguishable from PDE3A −/− . The enhanced contractility in PDE3A −/− hearts was associated with cAMP-dependent elevations in Ca 2+ transient amplitudes and increased sarcoplasmic reticulum (SR) Ca 2+ content, without changes in L-type Ca 2+ currents of cardiomyocytes, as well as with increased SR Ca 2+ -ATPase type 2a activity, SR Ca 2+ uptake rates, and phospholamban phosphorylation in SR fractions. Consistent with these observations, PDE3 activity was reduced ≈8-fold in SR fractions from PDE3A −/− hearts. Coimmunoprecipitation experiments further revealed that PDE3A associates with both SR calcium ATPase type 2a and phospholamban in a complex that also contains A-kinase anchoring protein-18, protein kinase type A-RII, and protein phosphatase type 2A. Conclusions: Our data support the conclusion that PDE3A is the primary PDE3 isozyme modulating basal contractility and SR Ca 2+ content by regulating cAMP in microdomains containing macromolecular complexes of SR calcium ATPase type 2a–phospholamban–PDE3A.