Abstract 17253: The Late Sodium Current Contributes to Electromechanical Defects Occurring With Aging

To establish the contribution of the late sodium current (I NaL ) on cardiovascular defects occurring with aging, mice with phosphomimetic mutation of Na + channel Nav1.5 at Ser571 (S571E), which causes I NaL enhancement in cardiomyocytes (I NaL gain-of-function), and mice with ablation of the Nav1.5 Ser571 (S571A), preventing CaMKII-mediated I NaL increase under stress condition (I NaL loss-of-function) were studied together with C57Bl/6 mice (wild-type, WT). Male mice at 2-6 (~4 m), 10-16 (~12 m), 17-20 (~18 m), and 20-27 (~24 m) months of age underwent electrocardiographic and echocardiographic evaluation. In WT mice, the QT interval duration of the ECG in the anesthetized state was similar at ~4 and ~12 months (56±5 ms and 58±5 ms, respectively) and was prolonged at ~18 and ~24 months (66±4 ms and 67±3 ms, respectively). In S571E mice, QT interval at ~4 months was prolonged with respect to WT animals (67±4 ms) and remained protracted at ~12, ~18, and ~24 months (65±3 ms, 68±6 ms, and 69±5 ms). S571A animals at ~4 months presented intermediate QT interval duration with respect to the other two strains (61±3 ms), and remained unchanged at ~12, ~18, and ~24 months (63±4 ms, 62±4 ms, and 64±4 ms). Ejection fraction was not altered with age and was comparable for the three mouse groups. In contrast, by transmitral flow Doppler echocardiography diastolic function, quantified here by the isovolumic relaxation time, was normal in WT mice at ~4 (17.4±1.6 ms) and ~12 months (16.8±1.6 ms) and became depressed at ~18 (21.5±2.5 ms) and ~24 months (21.4±1.7 ms). Defective diastolic function was apparent in S571E mice at ~4 months (19.7±2.9 ms) and persisted at ~12, ~18, and ~24 months (19.1±1.7 ms, 21.0±1.9 ms, and 22.1±2.2 ms, respectively). Interestingly, S571A mice at ~4 months had normal diastolic function (16.2±2.2 ms) and minor alterations were observed at ~12, ~18, and ~24 months (17.1±1.5 ms, 18.4±1.6 ms, and 19.3±3.3 ms, respectively). Overall, collected results suggest that I NaL enhancement in S571E mice is associated with premature appearance of prolonged electrical recovery and defective diastolic function, with respect to aging WT animals. In contrast, S571A mice, with inability to increase I NaL , are protected from electromechanical defects occurring with aging.