Calcium-Handling Abnormalities Underlying Atrial Arrhythmogenesis and Contractile Dysfunction in Dogs With Congestive Heart Failure
Why this work is in the frame
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Bibliographic record
Abstract
BACKGROUND: Congestive heart failure (CHF) is a common cause of atrial fibrillation. Focal sources of unknown mechanism have been described in CHF-related atrial fibrillation. The authors hypothesized that abnormal calcium (Ca(2+)) handling contributes to the CHF-related atrial arrhythmogenic substrate. METHODS AND RESULTS: CHF was induced in dogs by ventricular tachypacing (240 bpm x2 weeks). Cellular Ca(2+)-handling properties and expression/phosphorylation status of key Ca(2+) handling and myofilament proteins were assessed in control and CHF atria. CHF decreased cell shortening but increased left atrial diastolic intracellular Ca(2+) concentration ([Ca(2+)](i)), [Ca(2+)](i) transient amplitude, and sarcoplasmic reticulum (SR) Ca(2+) load (caffeine-induced [Ca(2+)](i) release). SR Ca(2+) overload was associated with spontaneous Ca(2+) transient events and triggered ectopic activity, which was suppressed by the inhibition of SR Ca(2+) release (ryanodine) or Na(+)/Ca(2+) exchange. Mechanisms underlying abnormal SR Ca(2+) handling were then studied. CHF increased atrial action potential duration and action potential voltage clamp showed that CHF-like action potentials enhance Ca(2+)(i) loading. CHF increased calmodulin-dependent protein kinase II phosphorylation of phospholamban by 120%, potentially enhancing SR Ca(2+) uptake by reducing phospholamban inhibition of SR Ca(2+) ATPase, but it did not affect phosphorylation of SR Ca(2+)-release channels (RyR2). Total RyR2 and calsequestrin (main SR Ca(2+)-binding protein) expression were significantly reduced, by 65% and 15%, potentially contributing to SR dysfunction. CHF decreased expression of total and protein kinase A-phosphorylated myosin-binding protein C (a key contractile filament regulator) by 27% and 74%, potentially accounting for decreased contractility despite increased Ca(2+) transients. Complex phosphorylation changes were explained by enhanced calmodulin-dependent protein kinase IIdelta expression and function and type-1 protein-phosphatase activity but downregulated regulatory protein kinase A subunits. CONCLUSIONS: CHF causes profound changes in Ca(2+)-handling and -regulatory proteins that produce atrial fibrillation-promoting atrial cardiomyocyte Ca(2+)-handling abnormalities, arrhythmogenic triggered activity, and contractile dysfunction.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it