The molecular control of cardiac ion channels.

The heart is composed of specialized cells ranging from sinoatrial nodal pacing cells with relatively few contractile elements to paced ventricular cells packed with contractile muscle protein. Arising in the sinoatrial node and transmitted throughout the atria, atrioventricular (AV) node, His-Purkinje system, and the ventricles, the cardiac action potential precisely activates distinct populations of ion channels. Most, if not all, ion channels are modulated by signal transduction mechanisms which shape the action potential. Six principal ion currents contribute to the nodal and pacemaking cell action potential and ten underlie the myocardial action potential. Other ion channels are specially designed for modulation of the action potential shape.