PDE4 is critical in controlling cAMP levels and thereby Ca(2+) influx and release in human atrial muscle, hence limiting the susceptibility to arrhythmias.

(PDEs) regulate local cAMP concentration in cardiomyocytes, with PDE4 being predominant for the control of β-AR-dependent cAMP signals. Three genes encoding PDE4 are expressed in mouse heart: Pde4a, Pde4b, and Pde4d. Here we show that both PDE4B and PDE4D are tethered to the LTCC in the mouse heart but that β-AR stimulation of the L-type Ca 2+ current (I Ca,L ) is increased only in Pde4b -/-mice. A fraction of PDE4B colocalized with the LTCC along T-tubules in the mouse heart. Under β-AR stimulation, Ca 2+ transients, cell contraction, and spontaneous Ca 2+ release events were increased in Pde4b -/-and Pde4d -/-myocytes compared with those in WT myocytes. In vivo, after intraperitoneal injection of isoprenaline, catheter-mediated burst pacing triggered ventricular tachycardia in Pde4b -/-mice but not in WT mice. These results identify PDE4B in the Ca V 1.2 complex as a critical regulator of I Ca,L during β-AR stimulation and suggest that distinct PDE4 subtypes are important for normal regulation of Ca 2+ -induced Ca 2+ release in cardiomyocytes. IntroductionDuring the cardiac action potential, Ca 2+ influx through sarcolemmal L-type Ca 2+ channels (LTCCs) triggers Ca 2+ release from juxtaposed ryanodine receptor 2 (RyR2) located in the sarcoplasmic reticulum (SR). This allows a rapid and synchronous Ca 2+ elevation throughout the cell, which activates contraction. During cardiac relaxation, Ca 2+ is rapidly extruded by the Na + /Ca 2+ exchanger and re-sequestered into the SR by the Ca 2+ -ATPase, SERCA2 (1). This process is highly regulated, in particular, by the sympathetic nervous system. β-Adrenergic receptors (β-ARs) exert strong inotropic and lusitropic effects by increasing intracellular cAMP levels and activating cAMP-dependent PKA. PKA then phosphorylates the key proteins of the excitation-contraction coupling (ECC) process, including LTCC and RyR2 but also phospholamban (PLB), which controls Ca 2+ reuptake by SERCA2, as well as the myofilament proteins troponin I and myosin binding protein C (1).The cardiac LTCC consists of the central pore-forming subunit α 1C (Ca V 1.2) and auxiliary β and α 2 -δ subunits that modulate its function (2). Upon β-AR stimulation, phosphorylation of Ca V 1.2, the auxiliary β 2 subunit, or the closely associated protein AHNAK by PKA increases channel activity, thus enhancing the L-type Ca 2+ current (I Ca,L ) (3-5). This regulation involves physical

PDE4 isoenzymes are critical in the control of cAMP signaling in rodent cardiac myocytes. Ablation of PDE4 affects multiple key players in excitation–contraction coupling and predisposes mice to the development of heart failure. As little is known about PDE4 in human heart, we explored to what extent cardiac expression and functions of PDE4 are conserved between rodents and humans. We find considerable similarities including comparable amounts of PDE4 activity expressed, expression of the same PDE4 subtypes and splicing variants, anchoring of PDE4 to the same subcellular compartments and macromolecular signaling complexes, and downregulation of PDE4 activity and protein in heart failure. The major difference between the species is a fivefold higher amount of non-PDE4 activity in human hearts compared to rodents. As a consequence, the effect of PDE4 inactivation is different in rodents and humans. PDE4 inhibition leads to increased phosphorylation of virtually all PKA substrates in mouse cardiomyocytes, but increased phosphorylation of only a restricted number of proteins in human cardiomyocytes. Our findings suggest that PDE4s have a similar role in the local regulation of cAMP signaling in rodent and human heart. However, inhibition of PDE4 has ‘global’ effects on cAMP signaling only in rodent hearts, as PDE4 comprises a large fraction of the total cardiac PDE activity in rodents but not in humans. These differences may explain the distinct pharmacological effects of PDE4 inhibition in rodent and human hearts.Electronic supplementary materialThe online version of this article (doi:10.1007/s00395-010-0138-8) contains supplementary material, which is available to authorized users.

Cystic fibrosis (CF) is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) that impair its expression and/or chloride channel function. Here, we provide evidence that type 4 cyclic nucleotide phosphodiesterases (PDE4s) are critical regulators of the cAMP/PKA-dependent activation of CFTR in primary human bronchial epithelial cells. In non-CF cells, PDE4 inhibition increased CFTR activity under basal conditions (ΔISC 7.1 μA/cm(2)) and after isoproterenol stimulation (increased ΔISC from 13.9 to 21.0 μA/cm(2)) and slowed the return of stimulated CFTR activity to basal levels by >3-fold. In cells homozygous for ΔF508-CFTR, the most common mutation found in CF, PDE4 inhibition alone produced minimal channel activation. However, PDE4 inhibition strongly amplified the effects of CFTR correctors, drugs that increase expression and membrane localization of CFTR, and/or CFTR potentiators, drugs that increase channel gating, to reach ∼ 25% of the chloride conductance observed in non-CF cells. Biochemical studies indicate that PDE4s are anchored to CFTR and mediate a local regulation of channel function. Taken together, our results implicate PDE4 as an important determinant of CFTR activity in airway epithelia, and support the use of PDE4 inhibitors to potentiate the therapeutic benefits of CFTR correctors and potentiators.