Gradient of sodium current across the left ventricular wall of adult rat hearts

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Abstract
1. Gradients of ion channels across the left ventricular (LV) wall have been well characterized and it has been shown that disruption of such gradients leads to altered rates of repolarization across the wall, which is associated with the generation of arrhythmias. 2. We have hypothesized that a transmural gradient of I(Na) is present and have directly measured this current in adult rat myocytes isolated from both the epicardial and endocardial layers of the left ventricle. Currents were also recorded in right ventricular (RV) myocytes for comparison. 3. Peak inward I(Na) currents, at -30 mV, were -49.7 +/- 2.5 pA pF(-1) (n = 22), -32.9 +/- 3.2 pA pF(-1) (n = 16) and -49.7 +/- 3.7 pA pF(-1) (n = 24) for RV, LV epicardial and LV endocardial myocytes, respectively. No differences in the voltage dependence of inactivation, the voltage dependence of steady-state inactivation, or reactivation were reported. 4. Our results demonstrate that a gradient of sodium current density is present across the LV wall of adult rat hearts.