NFATc3-dependent loss of I(to) gradient across the left ventricular wall during chronic beta adrenergic stimulation.

In heart, pore-forming Kv4 alpha channel subunits underlie the K(+) transient outward current (I(to)). Expression of Kv4 is greater in left ventricular epicardial (EPI) than in endocardial (ENDO) cells, resulting in larger I(to) in EPI than in ENDO cells. In adult ventricular myocytes, the transcription factor NFATc3 suppresses Kv4 expression.

Mechanisms underlying variations in excitation-contraction coupling across the mouse left ventricular free wall.

Ca(2+) release during excitation-contraction (EC) coupling varies across the left ventricular free wall. Here, we investigated the mechanisms underlying EC coupling differences between mouse left ventricular epicardial (Epi) and endocardial (Endo) myocytes. We found that diastolic and systolic [Ca(2+)](i) was higher in paced Endo than in Epi myocytes.