Ventricular hypertrophy amplifies transmural dispersion of repolarization by preferentially increasing the late sodium current in endocardium

Background: The late sodium current (INa-L) contributes importantly to rate-dependent change in action potential duration (APD) and transmural dispersion of repolarization (TDR). However, little is known about the mechanisms of increased APD rate-dependence and amplified TDR in left ventricular hypertrophy (LVH) and failure. The purpose of this study was to investigate the role of INa-L in rate-adaptation of transmural APD heterogeneity. Methods: APD, its rate-dependence and INa-L, current were examined in myocytes isolated from the endocardium and epicardium of the control and LVH rabbits. AP was recorded using the standard microelectrode technique, and INa-L, was recorded using the whole-cell patch clamp technique. Results: Early afterdepolarizations (EADs) were frequently recorded in the isolated myocytes of the LVH rabbits but not in those of controls. LVH prolonged APD more significantly in the endocardial myocytes than in the epicardium (31.7 +/- 3.4 vs. 21.6 +/- 1.5% n = 6, p < 0.05), leading to a marked increase in TDR. LVH endocardial myocytes exhibited a greater rate-dependent change in APD compared to the epicardial myocytes. INa-L, densities were significantly increased in both LVH endocardium and epicardium. However, LVH increased the INa-L, density preferentially in the endocardial myocytes compared to the epicardial myocytes (54.5 +/- 4.8% vs. 39.2 +/- 3.3%, n = 6, p < 0.05). Conclusions: Our results demonstrate that LVH increased the INa-L, preferentially in the endocardium over the epicardium, which contributes importantly to the stronger rate-dependent change in repolarization and longer APD in the endocardium. This results in an amplified TDR capable of initiating EAT) and ventricular arrhythmias. (C) 2014 Elsevier Inc. All rights reserved.