Molecular basis for the transmural distribution of the transient outward current.

Regional differences in electrical properties of cardiac cells contribute to the normal function of the heart as well as to the inscription of the J wave and T wave of the ECG. Amplification of these electrical heterogeneities can lead to the development of life-threatening cardiac arrhythmias and sudden death. A number of ionic distinctions have been shown to contribute to the different action potential morphologies of epicardial, M and endocardial ventricular cells as well as to the distinctive responses of these three cell types to pharmacological agents and pathophysiological states (for reviews see Antzelevitch et al. 1999; Antzelevitch & Dumaine, 2000).