β1- and β2-adrenergic receptor mediated spontaneous contractions and ryanodine receptor channel opening in human failing heart

In heart failure, β-adrenergic receptor (β-AR)-Gsα-cAMP-protein kinase A (PKA) signalling predisposes to delayed-afterdepolarisation-mediated arrhythmias. Phosphodiesterases (PDEs) hydrolyse cAMP, and PDE3 restrains β 1 -AR, β 2 -AR-mediated inotropic responses in failing hearts from β-blocker-treated patients. Whether these receptors provoke arrhythmias through ryanodine receptor (RyR2) dysregulation, and how PDE activity and prior β-blockade treatment modify this, is undefined. We sought to define how β 1 -AR and β 2 -AR activation provokes arrhythmias through RyR2 mechanisms in explanted human failing hearts, and how PDE activity and prior β-blocker therapy modulate this response. A diastolic model of ventricular arrhythmia using human right ventricular trabeculae with pacing stopped was used. Trabeculae were exposed to (-)-noradrenaline/(-)-adrenaline to activate β 1 -AR/β 2 -AR respectively with or without PDE inhibitors and monitored for spontaneous contractions. In parallel, sarcoplasmic reticulum vesicles from trabeculae were used to assess RyR2 channel function, phosphorylation and oxidation. Activation of β 1 -AR or β 2 -AR increased the frequency of spontaneous contractions, concomitant increases in diastolic RyR2 channel opening, phosphorylation and oxidation. Trabeculae from carvedilol-treated patients showed fewer β 2 -AR-mediated spontaneous contractions than those treated with β 1 -AR blockers. The PDE3 inhibitor cilostamide augmented β 2 -AR-mediated spontaneous contractions, RyR2 channel opening and Ser2808 phosphorylation. In human failing heart, β 1 -AR or β 2 -AR activation increased arrhythmic contractions associated with greater diastolic RyR2 channel opening, phosphorylation and oxidation. PDE3 attenuated β 2 -AR-mediated arrhythmic contractions, RyR2 channel opening and Ser2808 hyperphosphorylation. These findings suggest that combining β 1 - and β 2 -AR blockade with strategies that reduce RyR2 Ca 2+ leak and preserve RyR2-associated PDE3 activity may improve arrhythmia control in heart failure. Graphical abstract The arrhythmogenic human failing heart. Figure shows β 1 -AR, β 2 -AR mediated arrhythmia mechanisms in human HF. Activated β 1 -AR or β 2 -AR couple to the Gsα-protein-adenylyl cyclase signalling pathway to increase cyclic AMP, activation of PKA with consequent phosphorylation of RyR2. Other changes to RyR2 include oxidation and dissociation of FKBP12.6 (Walweel et al. 2017; Denniss et al. 2020). The changes contribute to Ca 2+ leak from the sarcoplasmic reticulum through RyR2 during diastole to cause outward transport of Ca 2+ /inward transport of Na + through the Na + /Ca 2+ exchanger resulting in DAD induced action potentials, depolarization of the myocyte and arrhythmic contractions (Walweel et al. 2017; Denniss et al. 2020). The β 2 -AR pathway that mediates arrhythmia generation is under the control of PDE3 (this paper).