PDE1 Inhibition Modulates Ca _v 1.2 Channel to Stimulate Cardiomyocyte Contraction

Abstract

Rationale: Cyclic adenosine monophosphate (cAMP) activation of protein kinase A (PKA) stimulates excitation-contraction coupling, increasing cardiac contractility. This is clinically achieved by beta-adrenergic receptor stimulation (b-ARs) or inhibition of phosphodiesterase type-3 (PDE3i), though both approaches are limited by arrhythmia and chronic myocardial toxicity. Phosphodiesterase type-1 inhibition (PDE1i) also augments cAMP and enhances contractility in intact dogs and rabbits. Unlike b-ARs or PDE3i, PDE1i-stimulated inotropy is unaltered by b-AR blockade and induces little whole-cell Ca 2+ ([Ca 2+ ]i) increase. Positive inotropy from PDE1i was recently reported in human heart failure. However, mechanisms for this effect remain unknown. Objective: Define the mechanism(s) whereby PDE1i increases myocyte contractility. Methods and Results: We studied primary guinea pig myocytes that express the PDE1C isoform found in larger mammals and humans. In quiescent cells, the potent, selective PDE1i (ITI-214) did not alter cell shortening or [Ca 2+ ]i whereas b-ARs or PDE3i increased both. When combined with low-dose adenylate cyclase stimulation, PDE1i enhanced shortening in a PKA-dependent manner but unlike PDE3i, induced little [Ca 2+ ]i rise nor augmented b-ARs. b-ARs or PDE3i reduced myofilament Ca 2+ sensitivity, and increased SR Ca 2+ content and phosphorylation of PKA-targeted serines on troponin-I, myosin binding protein C, and phospholamban. PDE1i did not significantly alter any of these. However, PDE1i increased Ca v 1.2 channel conductance similarly as PDE3i (both PKA-dependent), without altering NCX current density. Cell shortening and [Ca 2+ ]i augmented by PDE1i were more sensitive to Ca v 1.2 blockade and premature or irregular cell contractions and [Ca 2+ ]i transients less frequent than with PDE3i. Conclusions: PDE1i enhances contractility by a PKA-dependent increase in Ca v 1.2 conductance with less total [Ca 2+ ]i increase, and no significant changes in SR [Ca 2+ ], myofilament Ca 2+ -sensitivity, or phosphorylation of critical EC-coupling proteins as observed with b-ARs and/or PDE3i. PDE1i could provide a novel positive inotropic therapy for heart failure without the toxicities of b-ARs and PDE3i.

Cyclic nucleotide phosphodiesterases as therapeutic targets in cardiac hypertrophy and heart failure

“…Interestingly, in healthy dogs and rabbits and in those with HF, a newly developed PDE1 inhibitor, ITI-214, produces acute inotropic and lusitropic effects as well as arterial vasodilation by promoting a cAMP pool independent of β-AR signalling, specifically emanating from A2R 130 . In guinea pig cardiomyocytes, ITI-214 (with a low dose of the adenylate cyclase stimulator, forskolin) stimulated contractility, mainly by enhancing ICa,L, with little effect on Ca 2+ transients and myofilament protein phosphorylation, in contrast with β-AR stimulation or PDE3 inhibition 131 . These findings prompted the first clinical trial of ITI-214 in humans with HF 132 .…”

Phosphodiesterases and Compartmentation of cAMP and cGMP Signaling in Regulation of Cardiac Contractility in Normal and Failing Hearts

“…Recently, the group of David Kass has shown the role of PDE1C in rabbit and dog hearts, which, similar to human hearts, express predominantly this isoform and show positive inotropic and chronotropic effects after inhibiting PDE1. These effects are due to PDE1C activity over a soluble AC-cAMP nanodomain that regulates LTCC current via PKA, but does not involve modulation of SERCA current, phosphorylation of PLB, TnI, and myosin binding protein C, like in the β-AR-mediated contractility [119,121].…”

Compartmentalized cAMP signalling and control of cardiac rhythm

“…A possible explanation for the observed increased contractility was reported by Muller et al . [ 61 ], who demonstrated that the L-type calcium current, the trigger to calcium-sensitive calcium release, is potentiated by PDE1 inhibition. Interestingly, the study found only relatively small changes at PKA activity sites distal to L-type channels, such as PLB or the contractile machinery, indicating the importance of PDE1 in local control of cAMP.…”

“…At the same time, PDE3 inhibition was reported to lead to a substantial increase in L-type calcium current in human atrial cells [ 70 ]. In the ventricles of guinea pigs, PDE3A was shown to regulate the cAMP pool associated with the regulation of L-type calcium current [ 61 , 71 ], and this interaction was also suggested in one study using mouse cells [ 72 ], although this finding was not confirmed in another study [ 67 ]. The other type of PDE3, PDE3B, is localized preferentially in the t-tubules, close to dyads and mitochondria, and is thought to partly mediate the myocardial damage during ischaemia-reperfusion and probably contributes to the regulation of cellular metabolism [ 73 ].…”