PDE3A Regulates Basal Myocardial Contractility Through Interacting with SERCA2a-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 versus PDE3B, in the regulation of heart function remains unclear. Objective: To determine the relative contribution of PDE3A versus PDE3B isozymes in the regulation of heart function and to dissect the molecular basis for this regulation. Methods and Results: Compared to wild-type (WT) 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 WT (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 SR Ca 2+ content, without changes in L-type Ca 2+ currents (I CaL ) of cardiomyocytes, as well as with increased SR Ca 2+ -ATPase (SERCA2a) activity, SR Ca 2+ uptake rates, and phospholamban (PLN) phosphorylation in SR fractions. Consistent with these observations, PDE3 activity was reduced ~8-fold in SR fractions from PDE3A -/- hearts. Co-immunoprecipitation experiments further revealed that PDE3A associates with both SERCA2a and PLN in a complex which also contains AKAP-18, PKA-RII and PP2A. 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 SERCA2a-PLN-PDE3A.