Abstract 19102: Cardiac Specific Ablation of SAP97 Alters Normal Excitability of the Murine Heart
Synapse-associated protein 97 (SAP97) is a scaffolding protein and is the archetypical MAGUK. In vitro studies suggest that SAP97 regulates expression of cardiac Na and K channels, and may be important for cardiac excitation.
OBJECTIVES: To generate a model for inducible, targeted SAP97 ablation, and to investigate arrhythmia susceptibility and the underlying cellular/molecular mechanisms.
Methods: SAP97 targeted deletion was generated using the Cre-Lox system. Animals were subjected to biochemistry, electrophysiology, echo- and electrocardiographic analyses.
Results: Western blot analyses demonstrated SAP97 ablation was specific to the myocardium. Test animals showed several ECG abnormalities; including changes in P waves, premature atrial contractions, and prolongations in ST and QT intervals. ST interval averaged (ms) 22.3±2.53 (heterozygote) compared to 15.9±0.98 (control; p=0.03). ST prolongation was more pronounced (34.8±2.22 ms) in homozygote than in heterozygote mice; p< 0.001. Similarly, QT interval was much longer in homozygote than in heterozygote animals, both of which were longer than control values (p<0.001; n=13-15 in each group). In isolated ventricular cells, action potential duration at 80% repolarization; (APD80) were significantly longer in test animals compared to controls. Thus, control APD80 (ms) was 11.6±2.38 versus 47.19±11.27 in heterozygote animals (p=0.012). APD prolongation was more severe in homozygote animals. Early after depolarizations were more prevalent in test mice, compared to control. Data in cells isolated from control and homozygote mouse hearts showed significant changes in INa, ITO and IK1 current densities following SAP97 ablation. Control densities of ITO and IK1 were (pA/pF) 43.68±3.91 (+60mV) and -18.13±0.95 (-120mV) and were 19.96±2.48 and -12.38±0.64 after SAP97 ablation. In contrast, INa density was upregulated, averaging (pA/pF) -32.52±4.60 (-50mV) in control and -47.53±4.47 after SAP97 ablation.
Conclusion: SAP97 is important for normal functionality of cardiac ion channels in the murine myocardium, and its ablation predisposes to arrhythmogenicity. Our model of targeted SAP97 ablation is important for understanding the role of SAP97 in cardiac excitation.
- © 2013 by American Heart Association, Inc.