This is a mechanism module, not a specific disease. Do NOT create a "Cardiac cAMP/PKA Calcium Handling" Disease entry. Disorder entries reference individual nodes via conforms_to, for example "cardiac_camp_pka_calcium_handling#PKA Activation and Phosphorylation of the Calcium-Handling Apparatus". Conforming nodes substitute the specific cAMP-raising stimulus (exertion or emotional stress in the inherited catecholaminergic arrhythmia syndromes; a PDE3 or PDE4 inhibitor in the pharmacologic case) and the calcium-handling lesion the phosphorylation acts upon.
Scope. The module starts inside the cardiomyocyte. The systemic arm that produces the catecholamine surge (sympathoadrenal activation, plasma catecholamine rise) is left to the conforming disorder entry, which is why the two CPVT conformers declare conformance from an ORGANISM-scale stimulus node onto this module's MOLECULAR-scale trigger. The module also stops at spontaneous release and triggered activity: the organism-level chain from there (ventricular tachyarrhythmia, syncope, sudden cardiac death) already exists in `cardiac_ion_channel_repolarization` and is deliberately not duplicated. That module's new `Adrenergic and cAMP-Dependent Triggering` node conforms to this module's central effector, which is how the two are wired.
Ontology bindings. A CHEBI binding for cAMP itself is deliberately absent, and was declined during review of PR #11954: module nodes in this repository bind GO and CL terms only, per the `create-module` skill, so the cAMP pool is carried by the biosynthesis and catabolism processes on either side of it rather than by a chemical entity.
Deliberately out of scope, each for a stated reason. The direct, PKA-independent cyclic-nucleotide-gated arm (cAMP binding to HCN4 to set pacemaker rate, as in `Sick_Sinus_Syndrome_2_Autosomal_Dominant`'s "Loss of cAMP-Dependent Rate Modulation") is a different mechanism reaching a different endpoint, and folding it in would give the module two chains that never rejoin. Nodes describing a LOSS of the PKA arm rather than a gain (`Dilated_Cardiomyopathy_1P`'s "Protein Kinase A Sequestration by Mutant Phospholamban", `Hypertrophic_Cardiomyopathy_2`'s "Increased Myofilament Calcium Sensitivity and Loss of PKA-Mediated Desensitization") are not conformers: this module asserts a gain, and declaring conformance from a loss would be a contradiction rather than a consistency check. `Takotsubo_Cardiomyopathy` was examined and not wired: its beta2-adrenergic Gs-to-Gi switch is an attenuation of the cAMP arm, and its calcium-overload node runs to contraction-band necrosis rather than to triggered activity. `Long_QT_Syndrome`'s "Adrenergic Trigger Susceptibility" names the same arm but is curated as genotype-specific clinical trigger circumstances with no ontology bindings and no myocyte-level mechanism, so it is left for a later pass rather than conformed on the strength of its name.
Provenance and the AOP-Wiki caveat. This module was curated against AOP-Wiki Key Event 693 (Increased, cyclic adenosine monophosphate), issue #11949. None of the evidence here came from AOP-Wiki. In the 2026-09-16 XML snapshot KE 693 is an empty record (no description, no measurement method, no references) and every one of the four Key Event Relationships touching it sits at the 29.41% stub completion score with zero references; its cardiac parent pathway, AOP 558, has never been OECD reviewed and was last modified 2024-12-03. AOP 558 labels its own KER3446 (increased cAMP to RyR2 hyperphosphorylation) as "High" weight of evidence while the KER record behind that label holds nothing, and its bibliography cites a paper attributing RyR2 hyperphosphorylation to calpain rather than to the cAMP/PKA route the next edge asserts. The upstream edge KER3445 (phosphodiesterase inhibition to increased cAMP) was separately verified in issue #10454 and returned a do-not-curate-as-a-single-edge verdict, because the answer depends on PDE isoform, subcellular compartment, and disease state; that conditioning is recorded here as a discussion rather than flattened into a causal edge. Every reference in this module was found independently and each snippet verified against the cached paper.
Phospholamban Phosphorylation and Sarcoplasmic Reticulum Calcium Load Model
pka_phospholamban_sr_load_elevation
CANONICAL
Evidence: 2
Evidence balance
2 support
PKA phosphorylation of phospholamban relieves its inhibition of SERCA2a, accelerating calcium reuptake and raising the calcium content of the sarcoplasmic reticulum. Spontaneous release follows because the store is loaded past the threshold for it, not because the release channel has been made more sensitive. This is the route both camps in the RyR2 phosphorylation dispute accept, and it is the one this module treats as default.
Ser2808 Hyperphosphorylation and Calstabin-2 Dissociation Model
pka_ryr2_ser2808_calstabin_dissociation
ALTERNATIVE
Evidence: 3
Evidence balance
1 support
2 refute
Chronic adrenergic drive PKA-hyperphosphorylates RyR2 at Ser2808, which dissociates the stabilizing subunit calstabin-2 (FKBP12.6) from the channel and raises its open probability, producing a leaky release channel. This is the most cited account of how cAMP reaches the release channel and it is directly disputed: a knock-in mouse lacking the site is not protected, and a second group reports that Ser2808 is already largely phosphorylated at baseline and is not the site that responds to beta-adrenergic stimulation. Recorded as ALTERNATIVE rather than CANONICAL for that reason. The same model appears in `RYR2_CPVT` as the calstabin-2 dissociation hypothesis for the variant channel; here it is the pharmacologic and adrenergic entry into it.
Ser2030 Phosphorylation and Store-Overload-Induced Release Sensitization Model
pka_ryr2_ser2030_soicr_sensitization
ALTERNATIVE
Evidence: 2
Evidence balance
1 support
1 refute
PKA phosphorylates RyR2 at Ser2030, and the functional consequence is a heightened response of the channel to luminal calcium, lowering the store content at which spontaneous release occurs. This is the competing account from the group that disputes the Ser2808 model, and it makes a testable claim the Ser2808 model does not: that the effect is conditional on luminal calcium being present. It is itself contradicted by a direct measurement of the wave threshold in rabbit myocytes, where beta-adrenergic stimulation moved the threshold in the opposite direction.
Which serine on RyR2 carries the beta-adrenergic PKA signal, and does its phosphorylation change the channel's behaviour enough to cause arrhythmia on its own, or only by way of the store load that phospholamban phosphorylation produces?
CONTROVERSY
OPEN
controversy_pka_ryr2_phosphorylation_site_and_consequence
Attached to:
PKA Activation and Phosphorylation of the Calcium-Handling Apparatus
Spontaneous Diastolic Sarcoplasmic Reticulum Calcium Release
Three positions have been maintained in the primary literature for twenty-five years and none has displaced the others. The Ser2808 model holds that chronic adrenergic drive hyperphosphorylates that site and strips calstabin-2 from the channel. A knock-in mouse lacking the site shows an intact beta-adrenergic response and no protection from chronic stress, which is the result a sufficient mechanism should not produce. A second group reports that Ser2808 is already substantially phosphorylated before stimulation and that Ser2030 is the site that responds, and that RyR2 is not hyperphosphorylated in heart failure at all; that group's own functional work says PKA phosphorylation lowers the store threshold for spontaneous release. A direct measurement of intra-store calcium in rabbit myocytes then found acute beta-adrenergic stimulation raising the wave threshold rather than lowering it, attributing the waves to store load instead. The module therefore routes its default edge through store load, carries both channel-sensitization models as ALTERNATIVE hypothesis groups on a separate edge, and asserts neither as settled. Note that AOP-Wiki AOP 558 states this step as a plain causal relationship graded "High" weight of evidence, on a Key Event Relationship record carrying no references at all, and cites in its own bibliography a paper attributing RyR2 hyperphosphorylation to oxidative-stress-driven calpain activation rather than to PKA.
Proposed experiments:
Store-threshold measurement in site-specific RyR2 phosphomutant myocytes
Is the excess mortality seen when a phosphodiesterase-3 inhibitor is given long term in chronic heart failure caused by the arrhythmic arm this module models, or by something else?
KNOWLEDGE GAP
OPEN
gap_mechanism_of_pde3_inhibitor_mortality
Attached to:
Delayed Afterdepolarizations and Triggered Activity
The strongest human evidence that raising cardiomyocyte cAMP is harmful is the PROMISE trial, in which oral milrinone increased all-cause mortality by 28 percent in 1088 patients with severe chronic heart failure despite improving haemodynamics. It is tempting to read that result as the clinical endpoint of this module, and the trial itself refuses the reading: its abstract states that the mechanism of the harm is unknown. The module therefore cites PROMISE for the pharmacologic entry point, where the trial does state a mechanism, and not for the arrhythmic consequence. Closing this gap needs evidence connecting the drug to the mechanism in patients, not a plausible chain drawn between two things that are separately true.
Proposed experiments:
Mode-of-death and continuous-rhythm analysis under phosphodiesterase-3 inhibition
Cardiomyocyte cAMP-Raising Stimulus
trigger
Something raises the rate at which cyclic AMP accumulates in the cardiomyocyte, by making more of it or by stopping its removal. The physiologic and pathophysiologic route is catecholamine occupancy of the beta-adrenergic receptor, which couples through Gs to adenylyl cyclase; the pharmacologic route is inhibition of the phosphodiesterases that hydrolyse cAMP, principally PDE3 and PDE4 in the myocyte. Conforming disorder entries substitute the particular stimulus: exertion or acute emotional stress in the inherited catecholaminergic arrhythmia syndromes, a PDE3 inhibitor such as milrinone or enoximone in the pharmacologic case. The systemic arm that generates the catecholamine surge sits upstream of this module.
Downstream
-
Increased Cardiomyocyte cAMP
Increased synthesis, decreased hydrolysis, or both, raise the concentration of cyclic AMP available to its effectors in the myocyte.
Show evidence (2 references)
"In cardiomyocytes, phosphodiesterases (PDEs) type 3 and 4 are the predominant enzymes that degrade cAMP generated by β-adrenergic receptors"
Names both entry points this node covers in one sentence: cAMP generated by beta-adrenergic receptors, and the PDE3 and PDE4 activity that removes it. Background framing in a study whose own measurements are FRET and patch clamp in isolated rat left ventricular myocytes.
"Milrinone, a phosphodiesterase inhibitor, enhances cardiac contractility by increasing intracellular levels of cyclic AMP"
The pharmacologic arm of this node stated by the randomised trial that tested the drug in patients. A PDE inhibitor is here precisely because it raises intracellular cAMP.
Increased Cardiomyocyte cAMP
amplifier
Cyclic AMP rises in the cardiomyocyte. The rise is not uniform across the cell: cAMP is confined into subcellular microdomains by the phosphodiesterases that degrade it, so which PDE is inhibited, which compartment is measured, and whether the heart is healthy or hypertrophied all change whether a rise is seen at all.
Downstream
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PKA Activation and Phosphorylation of the Calcium-Handling Apparatus
Cyclic AMP binds the regulatory subunits of protein kinase A and releases its catalytic subunits onto their substrates.
Show evidence (3 references)
"PDE4 inhibition with Ro 20-1724 (10 μM) markedly potentiated the amplitude and slowed the decline of the cAMP transient"
FRET-based cAMP biosensor in isolated rat left ventricular myocytes. The direct measurement that inhibiting a phosphodiesterase raises cardiomyocyte cAMP, which is the claim AOP-Wiki asserts for this step and supports with nothing.
"a short isoprenaline stimulation (Iso, 100 nM, 15 s) elicited a similar transient increase in cAMP"
The adrenergic route to the same node, measured with the same biosensor in the same cells. Beta-adrenergic agonist exposure produces a cAMP transient.
"Recent studies have identified cyclic nucleotide phosphodiesterases as key actors in limiting the spread of cAMP and cGMP, and in shaping and organizing intracellular signaling microdomains"
A review, cited for the qualification this node carries rather than for the rise itself. It supports treating "cAMP goes up" as a compartment-specific statement, which is why the node description refuses the cell-wide reading.
PKA Activation and Phosphorylation of the Calcium-Handling Apparatus
central effector
Protein kinase A is activated and phosphorylates the proteins that move calcium in the cardiomyocyte: phospholamban, which restrains SERCA2a; the L-type calcium channel, which admits the trigger calcium; troponin I, which sets myofilament calcium sensitivity; and the ryanodine receptor RyR2, which releases the store. Which RyR2 site carries the effect, and what that effect is, is disputed.
Downstream
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Increased Sarcoplasmic Reticulum Calcium Load
Phosphorylated phospholamban stops inhibiting SERCA2a, so more calcium is pumped into the store between beats and the store content rises.
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Spontaneous Diastolic Sarcoplasmic Reticulum Calcium Release
A second, disputed route in which phosphorylation of the release channel itself makes it likelier to open, independently of how much calcium the store holds. Both named models of this route are carried on this edge because both assert it and they disagree about the site and about the direction of the threshold change.
Show evidence (3 references)
"This second messenger produces many of its effects by activating protein kinase A (PKA), which phosphorylates key proteins involved in excitation and contraction of cardiac myocytes, including L-type Ca2+ channels (LTCCs) and phospholamban (PLN)"
States the node: cAMP acts by activating PKA, and PKA's cardiac substrates are the excitation-contraction proteins. Background framing in a study whose own measurements are FRET biosensors in adult rat ventricular myocytes.
"Activation of cAMP-dependent protein kinase A (PKA) in ventricular myocytes by isoproterenol (Iso) causes phosphorylation of both phospholamban (PLB) and troponin I (TnI) and accelerates relaxation by up to twofold"
Names two of the substrates and the functional consequence, in ventricular myocytes under a beta-adrenergic agonist. The paper's own contribution is the phospholamban-knockout comparison that apportions the effect between them.
"Carvedilol, but not VK-II-86, abolished the Iso-induced PKA phosphorylation of RyR2"
Immunoblot in mice given isoproterenol, with a beta-blocking and a minimally beta-blocking compound compared. Establishes that RyR2 is a PKA substrate under adrenergic drive and that blocking the receptor removes the phosphorylation, without committing to which site or what the phosphorylation does.
Increased Sarcoplasmic Reticulum Calcium Load
effector
The calcium content of the sarcoplasmic reticulum rises. Phospholamban, once phosphorylated, releases its grip on SERCA2a, which then pumps calcium back into the store faster; combined with greater calcium entry through the phosphorylated L-type channel, the store ends each beat holding more than it did. This is the step that makes beta-adrenergic stimulation both inotropic and arrhythmogenic by the same action.
Downstream
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Spontaneous Diastolic Sarcoplasmic Reticulum Calcium Release
Past a critical store content the release channels open of their own accord between beats, and the store empties in a wave.
Show evidence (3 references)
"PKA-dependent phosphorylation of PLN diminishes the inhibitory effect that PLN has on SERCA2, resulting in an increase in the amount of Ca2+ taken up into the SR and available for subsequent release"
The mechanism of this node stated in full, including the consequence that matters for the next one: the extra calcium is available for subsequent release.
"PLB phosphorylation increases sarcoplasmic reticulum (SR) Ca pumping"
The pumping half of the claim, in a study of ventricular myocytes and muscle from wild-type and phospholamban-knockout mice.
"excessive beta-adrenergic receptor (AR) stimulation can result in sarcoplasmic recticulum (SR) Ca2+ overload that can trigger spontaneous Ca2+ waves"
Names the consequence of this node and the reason it matters, connecting the adrenergic route to store overload. Graded OTHER because the sentence restates established physiology the paper did not itself measure.
Spontaneous Diastolic Sarcoplasmic Reticulum Calcium Release
effector
Past a critical store content the release channels open of their own accord between beats, and calcium leaves the sarcoplasmic reticulum as a propagating wave rather than as the synchronized release that follows excitation. RyR2 carries much of it, though not all.
Downstream
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Delayed Afterdepolarizations and Triggered Activity
The released calcium is extruded by the sodium-calcium exchanger, which carries a net inward current and depolarizes the cell between beats.
Show evidence (2 references)
"when the sarcoplasmic reticulum store Ca2+ content reaches a critical level, spontaneous Ca2+ release occurs, a process we refer to as store-overload-induced Ca2+ release (SOICR)"
Defines the node and names the quantity that governs it. The paper's own measurements are HEK293 cells expressing RyR2 and single-channel recordings.
"Much, but not all, of the SR Ca leak occurs via ryanodine receptors and can be exacerbated in pathological states such as heart failure"
A review, cited for the channel identity and for the qualification that RyR2 is not the only route by which the store leaks. The review also assigns the leak systolic and diastolic consequences this module does not model; those belong to the contractile arm tracked in issue #11951.
Delayed Afterdepolarizations and Triggered Activity
consequence
The inward exchanger current raised by the diastolic calcium wave depolarizes the cardiomyocyte between beats. If the depolarization reaches threshold it fires a beat that no pacemaker asked for. That triggered beat is the module's endpoint.
Show evidence (1 reference)
"This SOICR can evoke delayed afterdepolarizations (DADs) that can lead to triggered arrhythmias and sudden death"
The step this node stands for, from a spontaneous release event to a triggered beat. Graded OTHER because the sentence restates established electrophysiology that this paper did not itself measure.