Abstract 18067: Phosphodiesterase 4B Controls a Subsarcolemmal Pool of Cyclic AMP
Rationale: Sympathetic regulation of the heart is mediated via β1- and β2-adrenergic receptors (βARs). Both receptors signal through cAMP, but produce distinct or even opposing effects on cardiac function. Localized or compartmentalized cAMP is thought to be the basis for these differential effects. Cyclic nucleotide phosphodiesterases (PDEs), the enzymes that degrade and inactivate cAMP, may contribute to compartmentalization and βAR signaling specificity.
Objective: To elucidate the role of the cardiac PDE4B in βAR signaling.
Methods and Results: Cyclic AMP accumulation was measured with FRET-based cAMP sensors in cytosolic and sarcolemmal compartments of cardiomyocytes from Wild Type and PDE4BKO mice. Ablation of PDE4B alters the cAMP transient induced by βAR stimulation at the sarcolemma but not in the cytosol. The effect of PDE4B ablation is further restricted to β1AR-induced cAMP transients, whereas β2AR or E prostanoid receptor (EPR) responses are not affected. In PDE4BKO cells, PKA-phosphorylation of proteins in the sarcolemmal compartment, including the vasodilator-stimulated phosphoprotein, the L-type Ca2+ channel (LTCC), the ryanodine receptor (RyR2) is increased. Conversely, phosphorylations of proteins distant from the cell membrane, including phospholamban or contractile proteins are not affected. β1AR but not β2AR ligation causes PKA-dependent activation of PDE4B. PKA inhibition produces a significant increase in subsarcolemmal cAMP in Wild Type cardiomyocytes, but has only a limited effect in PDE4BKO myocytes, confirming that this feedback regulation of PDE4B shapes the cAMP transient at the sarcolemma. Consistent with the augmented phosphorylation of LTCC and RyR2, contraction rate in PDE4BKO myocytes in response to βAR stimulation is increased compared to Wild Type.
Conclusions: PDE4B mediates a critical PKA-dependent feedback mechanism that controls β1AR-, but not β2AR- or EPR-induced cAMP signals. This regulation functions in a restricted subsarcolemmal compartment containing LTCC and RYR2.
- © 2013 by American Heart Association, Inc.