Compartmentation Of Beta(2)-Adrenoceptor Stimulated Camp Responses By Phosphodiesterase Types 2 And 3 In Cardiac Ventricular Myocytes

Background and Purpose In cardiac myocytes, cyclic AMP (cAMP) produced by both beta(1)- and beta(2)-adrenoceptors increases L-type Ca2+ channel activity and myocyte contraction. However, only cAMP produced by beta(1)-adrenoceptors enhances myocyte relaxation through phospholamban-dependent regulation of the sarco/endoplasmic reticulum Ca2+ ATPase 2 (SERCA2). Here we have tested the hypothesis that stimulation of beta(2)-adrenoceptors produces a cAMP signal that is unable to reach SERCA2 and determine what role, if any, phosphodiesterase (PDE) activity plays in this compartmentation.Experimental Approach The cAMP responses produced by beta(1)-and beta(2)-adrenoceptor stimulation were studied in adult rat ventricular myocytes using two different fluorescence resonance energy transfer (FRET)-based biosensors, the Epac2-camps, which is expressed uniformly throughout the cytoplasm of the entire cell and the Epac2-alpha KAP, which is targeted to the SERCA2 signalling complex.Key Results Selective activation of beta(1)- or beta(2)-adrenoceptors produced cAMP responses detected by Epac2-camps. However, only stimulation of beta(1)-adrenoceptors produced a cAMP response detected by Epac2-alpha KAP. Yet, stimulation of beta(2)-adrenoceptors was able to produce a cAMP signal detected by Epac2-alpha KAP in the presence of selective inhibitors of PDE2 or PDE3, but not PDE4.Conclusion and Implications These results support the conclusion that cAMP produced by beta(2)-adrenoceptor stimulation was not able to reach subcellular locations where the SERCA2 pump is located. Furthermore, this compartmentalized response is due at least in part to PDE2 and PDE3 activity. This discovery could lead to novel PDE-based therapeutic treatments aimed at correcting cardiac relaxation defects associated with certain forms of heart failure.