Abstract 18492: Cardiac-specific Ablation of Synapse-Associated Protein SAP97 in Mice Decreases Potassium Currents but Not Sodium Current
Introduction: Membrane-associated guanylate kinase (MAGUK) proteins are determinants of ion channel organization at the plasma membrane of various cell types. In the heart, the MAGUK protein SAP97 interacts with several ion channels via their PDZ-domain-binding motif and thus regulates their function and localization. SAP97 is considered as a susceptibility gene for inherited arrhythmias. In order to investigate the role of SAP97 in the mouse heart, we generated a genetically-modified mouse line where SAP97 was constitutively suppressed exclusively in cardiomyocytes.
Methods: SAP97fl/fl mice were generated by inserting LoxP sequences flanking exons 1 to 3 of the SAP97 gene. SAP97fl/fl mice were bred with αMHC-Cre mice to generate αMHC-Cre/SAP97fl/fl mice with a cardiomyocyte-specific deletion of SAP97. Whole hearts and isolated cardiomyocytes from 10-13 week old mice were used. SAP97 protein and mRNA expression levels were measured by Western-blot and quantitative RT-PCR. The patch-clamp technique was used to record ion currents and action potentials (AP). Echocardiography and surface ECGs were performed on anesthetized mice.
Results: Western blots showed a 71±4% decrease in SAP97 protein levels of αMHC-Cre/SAP97fl/fl hearts compared to SAP97fl/fl control hearts, while SAP97 mRNA transcript levels were decreased by 80±2% (n=4, p<0.05). AP maximal upstroke velocity was not modified, but AP duration (APD) was greatly prolonged in αMHC-Cre/SAP97fl/fl cardiomyocytes (respectively by 1.9±0.3, 2.3±0.4, and 2.1±0.2 -folds for APD30, APD50, and APD 90; n=10, p<0.05). This was consistent with the decreases observed in IK1, Ito, and IKur potassium currents, and the absence of effect on the sodium current INa. Echocardiography showed no difference in morphological and functional parameters, but surface ECG revealed an increased QTc interval in αMHC-Cre/SAP97fl/fl mice compared to controls (respectively 58.3±2.0 ms (n=6) vs. 49.1±1.2 ms (n=7); p<0.05).
Conclusions: These data suggest that constitutive ablation of SAP97 in the mouse heart mainly alters potassium channel function and/or localization. Additional experiments are needed to elucidate whether ion channel expression at the plasma membrane and/or unitary conductance is modified.
Author Disclosures: L. Gillet: None. J. Rougier: None. S. Sonntag: None. D. Shy: None. N. Mougenot: None. M. Essers: None. D. Shmerling: None. S. Hatem: None. E. Balse: None. H. Abriel: None.
- © 2014 by American Heart Association, Inc.